Viral particles with fusogen display and related compositions and methods

Abstract

Provided herein are lipid particles containing a viral envelope attachment protein, such as derived from paramyxovirus or baboon endogenous virus (BaEV). In some embodiments, the lipid particles also contain a codisplay protein, such as a transduction adjuvant or an immune stimulating protein. Also provided are such lipid particles that are viral vectors, such as lentiviral vectors or lentiviral-like particles. Also provided are producer cells and compositions containing such lipid particles and methods of making and using the lipid particles.

Description

186152009940 VIRAL PARTICLES WITH FUSOGEN DISPLAY AND RELATED COMPOSITIONS AND METHODS Cross-reference to related applications

[0001] This application claims priority to U.S. Provisional Patent Application No.63 / 560,612 filed on March 01, 2024, entitled “VIRAL PARTICLES WITH FUSOGEN DISPLAY AND RELATED COMPOSITIONS AND METHODS”, and U.S. Provisional Patent Application No.63 / 635,585 filed on April 17, 2024, entitled “VIRAL PARTICLES WITH FUSOGEN DISPLAY AND RELATED COMPOSITIONS AND METHODS”, each of which are hereby incorporated by reference in its entirety. Reference to an electronic sequence listing

[0002] The present application is being filed along with a Sequence Listing in electronic format. The Sequence Listing is provided as a file entitled 186152009940_Seq created February 27, 2025 which is 1,164,085 bytes in size. The information in the electronic format of the Sequence Listing is incorporated by reference in its entirety. Field

[0003] The present disclosure relates to lipid particles containing certain viral envelope attachment protein, such as derived from paramyxovirus or baboon endogenous virus (BaEV). In some embodiments, the lipid particles also contain a codisplay protein, such as a transduction adjuvant or an immune stimulating protein. Also provided are such lipid particles that are viral vectors, such as lentiviral vectors or lentiviral-like particles. Also provided are producer cells and compositions containing such lipid particles and methods of making and using the lipid particles. Background

[0004] Lipid particles, including viral-based particles like virus-like particles and viral vectors such as lentiviral particles, are commonly used for delivery of exogenous agents to cells. For various particles, such as lentiviral vector particles, the host range can be altered by pseudotyping with at least one retargeted attachment protein that is or comprises a heterologous envelope protein or modified envelope protein. The efficient preparation and production of particles with certain retargeted pseudotyped envelope proteins to produce a higher titer and with efficient transduction efficiency of target cells are needed. The provided disclosure addresses this need. 1 sf-5667634186152009940 Summary

[0005] Provided herein is a lipid particle, comprising (a) a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, (b) a co-display protein; and (c) at least one paramyxovirus fusion (F) protein; and wherein the co-display protein increases the potency and / or specificity of the lipid particle as compared to a lipid particle not comprising the co-display protein, wherein the protein in (a), (b) and (c) are exposed on the outside of the lipid bilayer / embedded in the lipid bilayer.

[0006] Provided herein is a lipid particle, comprising (a) a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, (b) a co-display protein for increasing the potency and / or specificity of the lipid particle as compared to a lipid particle not comprising the co-display protein; and (c) at least one paramyxovirus fusion (F) protein; and wherein the protein in (a), (b) and (c) are exposed on the outside of the lipid bilayer / embedded in the lipid bilayer.

[0007] Provided herein is a lipid particle, comprising: (a) a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a first target molecule expressed on the surface of a target cell, (b) a co-display protein comprising a binding means for specifically interacting with a second target molecule expressed on the surface of the target cell; and (c) at least one paramyxovirus fusion (F) protein; and wherein the protein in (a), (b) and (c) are exposed on the outside of the lipid bilayer / embedded in the lipid bilayer.

[0008] Provided herein is a lipid particle, comprising: (a) a Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof, and (b) a co-display protein comprising a binding means for specifically interacting with a target molecule expressed on the surface of the target cell; and wherein the protein in (a) and (b) are exposed on the outside of the lipid bilayer / embedded in the lipid bilayer.

[0009] In some of any of the provided embodiments, the co-display protein is an immune stimulating protein and / or is a transduction adjuvant.

[0010] Provided herein is a lipid particle, comprising (a) a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, (b) a co-display protein selected from an immune stimulating protein and a transduction adjuvant; and (c) at least one paramyxovirus fusion (F) protein; and wherein the protein in (a), (b) and (c) are embedded in the lipid bilayer.

[0011] In some of any of the provided embodiments, the co-display protein is selected from the group comprising of a glycoprotein, transmembrane protein, receptor, integrin, antibody or antigen- binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide. In some 2 sf-5667634186152009940 of any of the provided embodiments, the co-display protein increases specificity to the target cell. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell.

[0012] In some of any of the provided embodiments, the co-display protein increases specificity to a target cell that is a hematopoietic stem cell. In some of any of the provided embodiments, the cell surface molecule is selected from CD34, CD105, or CD117. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell that is a T cell. In some of any of the provided embodiments, the cell surface molecule is selected from CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell that is a hepatocyte. In some of any of the provided embodiments, the cell surface molecule is selected from ASGR1, ASGR2 and TM4SF5.

[0013] In some of any of the provided embodiments, the co-display protein binds to a different protein than the targeting moiety of the retargeted attachment protein. In some of any of the provided embodiments, the co-display protein does not include a paramyxovirus envelope attachment protein or a fragment thereof. In some of any of the provided embodiments, the co-display protein is an immune stimulating protein and the immune stimulating protein stimulates a T cell activity or function. In some of any of the provided embodiments, the immune stimulating protein comprises (i) an extracellular domain, (ii) a linker, and (iii) an anchor. In some of any of the provided embodiments, the extracellular domain of the immune stimulating protein binds to a T cell stimulatory receptor. In some of any of the provided embodiments, the T cell stimulatory receptor is selected from CD3, CD2, CD28, CD27. In some of any of the provided embodiments, the extracellular domain of the immune stimulating protein binds to CD3. In some of any of the provided embodiments, the extracellular domain is selected from the group comprising an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide. In some of any of the provided embodiments, the extracellular domain of the immune stimulating protein is an anti-CD3 antibody or single chain fragment thereof. 3 sf-5667634186152009940

[0014] In some of any of the provided embodiments, the co-display protein is a transduction adjuvant that increases transduction efficiency of the lipid particle as compared to a lipid particle that does not have a co-display protein comprising a transduction adjuvant. In some of any of the provided embodiments, the co-display protein is a transduction adjuvant that binds to a surface molecule on target cells to enhance transduction. In some of any of the provided embodiments, the transduction adjuvant comprises (i) an extracellular domain, (ii) a linker, and (iii) an anchor. In some of any of the provided embodiments, the extracellular domain of the transduction adjuvant binds an integrin binding domain. In some of any of the provided embodiments, the extracellular domain of the transduction adjuvant comprises the extracellular domain of fibronectin, retronectin, or a functional variant thereof.

[0015] In some of any of the provided embodiments, the linker is derived from a human protein. In some of any of the provided embodiments, the linker is a derived from human CD8α, IgG3 hinge, IgG1 hinge, IgG4 heavy chain, IgG4, or CD28. In some of any of the provided embodiments, the linker is modified to remove a cysteine residue. In some of any of the provided embodiments, the linker is rigid or wherein the linker is flexible.

[0016] In some of any of the provided embodiments, the anchor is a peptide anchor that is a transmembrane domain. In some of any of the provided embodiments, the anchor is a transmembrane domain that is a transmembrane domain of a protein selected from PDGFR, VSV-G, CD8α, ICAM1, HLA-DRB, CD49d, or Transferrin. In some of any of the provided embodiments, the anchor is a GPI lipid anchor.

[0017] In some of any of the provided embodiments, the targeting moiety is selected from the group consisting of an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide. In some of any of the provided embodiments, the targeting moiety binds to a cell surface molecule present on a target cell. In some of any of the provided embodiments, the cell surface molecule is a protein, glycan, or lipid. In some of any of the provided embodiments, the target cell is selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells. In some of any of the provided embodiments, the target cells is selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell. In some of any of the provided embodiments, the target is a hematopoietic stem cell. In some of any of the provided embodiments, the cell surface molecule is selected from CD34, 4 sf-5667634186152009940 CD105, or CD117. In some of any of the provided embodiments, the target cell is a T cell. In some of any of the provided embodiments, the cell surface molecule is selected from the group consisting of CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3. In some of any of the provided embodiments, the target cell is a hepatocyte. In some of any of the provided embodiments, the cell surface molecule is selected from the group consisting of ASGR1, ASGR2 and TM4SF5. In some of any of the provided embodiments, the targeting moiety is selected from the group consisting of a single domain antibody or a single chain variable fragment (scFv). In some of any of the provided embodiments, the single domain antibody is a VHH.

[0018] In some of any of the provided embodiments, the retargeted attachment protein is linked to a (i) first targeting moiety directed to a first target molecule expressed on the surface of a target cell, and a (ii) second targeting moiety directed to a second target molecule expressed on the surface of a target cell. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein of the retargeted attachment protein is a first paramyxovirus envelope attachment protein and the lipid particle further comprises a second paramyxovirus envelope attachment protein. In some of any of the provided embodiments, the second paramyxovirus envelope attachment protein is linked to the first paramyxovirus envelope attachment protein in tandem. In some of any of the provided embodiments, the retargeted attachment protein comprising the first paramyxovirus envelope attachment protein and the second paramyxovirus envelope attachment protein are each separately exposed the outside of the lipid bilayer / embedded in the lipid bilayer. In some of any of the provided embodiments, the second paramyxovirus attachment protein is a retargeted attachment protein. In some of any of the provided embodiments, the second retargeted attachment protein comprises (i) a second paramyxovirus envelope attachment protein; and (ii) a second targeting moiety directed to a target molecule expressed on the surface of a target cell. In some of any of the provided embodiments, the targeting moiety is selected from the group consisting of an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide. In some of any of the provided embodiments, the target cell is selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells. In some of any of the provided embodiments, the target cells is selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell. In some of any of the provided embodiments, the target is a hematopoietic 5 sf-5667634186152009940 stem cell. In some of any of the provided embodiments, the cell surface molecule is selected from CD34, CD105, or CD117. In some of any of the provided embodiments, the target cell is a T cell. In some of any of the provided embodiments, the cell surface molecule is selected from the group consisting of CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3. In some of any of the provided embodiments, the target cell is a hepatocyte. In some of any of the provided embodiments, the cell surface molecule is selected from the group consisting of ASGR1, ASGR2 and TM4SF5. In some of any of the provided embodiments, the targeting moiety is selected from the group consisting of a single domain antibody or a single chain variable fragment (scFv). In some of any of the provided embodiments, the single domain antibody is a VHH.

[0019] In some of any of the provided embodiments, the BaEV envelope glycoprotein is a truncated BaEV envelope glycoprotein comprising a cytoplasmic tail with a partial fusion inhibitory R peptide relative to the inhibitory R peptide of a wild-type BaEV envelope glycoprotein, wherein the partial fusion inhibitory R peptide comprises at least one amino-terminal amino acid but less than the full length of the inhibitory R peptide of the wild-type BaEV envelope glycoprotein. In some of any of the provided embodiments, the BaEV envelope glycoprotein is a truncated BaEV envelope glycoprotein comprising a cytoplasmic tail with a partial fusion inhibitory R peptide relative to a wild-type BaEV envelope glycoprotein, wherein the cytoplasmic tail is 25 amino acids in length and contains 8 contiguous amino- terminal acids of the inhibitory R peptide (R+8) of the full length inhibitory R peptide of wild-type BaEV envelope glycoprotein. In some of any of the provided embodiments, the truncated BaEV glycoprotein comprises: (i) a glycoprotein 70 (g70) subunit or a biologically active portion thereof, and (ii) a portion of the glycoprotein p20E (p20E) subunit comprising the cytoplasmic tail with the partial inhibitory R peptide. In some of any of the provided embodiments, the BaEV envelope glycoprotein binds an ASCT-2 or ASCT-1 receptor. In some of any of the provided embodiments, the truncated BaEV envelope glycoprotein is truncated relative to SEQ ID NO: 622 and lacks up to 16 contiguous amino acids from the C-terminal cytoplasmic tail of SEQ ID NO: 622. In some of any of the provided embodiments, the partial fusion inhibitory R peptide is set forth as amino acids 1 to 8 of SEQ ID NO: 623, optionally wherein the cytoplasmic tail is set forth in SEQ ID NO: 624 (R+8). In some of any of the provided embodiments, the truncated BaEV envelope glycoprotein is set forth in SEQ ID NO: 625.

[0020] Provided herein is a lipid particle, comprising a variant Baboon Endogenous Virus (BaEV) fusogen wherein the fusogen is exposed on the outside of the lipid bilayer / embedded in the lipid bilayer. In some of any of the provided embodiments, the variant BaEV envelope glycoprotein has the amino acid sequence set forth in SEQ ID NO: 795 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at 6 sf-5667634186152009940 least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:795. In some of any of the provided embodiments, the variant BaEV envelope glycoprotein has the amino acid sequence set forth in SEQ ID NO: 796 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:796. In some of any of the provided embodiments, the variant BaEV envelope glycoprotein has the amino acid sequence set forth in SEQ ID NO: 797 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:797.

[0021] In some embodiments, the BaEV Baboon Endogenous Virus (BaEV) is a BaEVTR fusogen. In some embodiments, the BaEV Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof comprises a protease site modification. In some embodiments, the protease site modification comprises modifying a MLV-A cleavage site to a MA / CA cleavage site.

[0022] In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is an envelope attachment protein from a Nipah virus, Hendra virus, or Measles virus, or is a variant or biologically active portion thereof of any of the foregoing. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is a wild-type paramyxovirus G protein, H protein or HN protein or is a variant or biologically active portion of any of the foregoing. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is a wild-type Nipah virus G (NiV-G) protein or is a variant or biologically active portion of a NiV-G. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is a variant paramyxovirus envelope attachment protein. In some of any of the provided embodiments, the variant paramyxovirus envelope attachment protein comprises one or more mutations that reduces native tropism relative to the wild-type paramyxovirus envelope attachment protein not comprising the one or more mutations. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is a variant NiV-G that is a variant or a biologically active portion of a wild-type NiV-G. In some of any of the provided embodiments, the variant is a variant NiV-G that is a variant of a wild-type Nipah virus G (NiV-G) protein or a biologically active portion thereof. In some of any of the provided embodiments, 7 sf-5667634186152009940 the variant NiV-G is truncated by up to 40 contiguous amino acids at or near the N-terminus of the wild- type NiV-G set forth in SEQ ID NO:1. In some of any of the provided embodiments, the variant NiV-G has a truncation of amino acids 2-34 of the wild-type NiV-G set forth in SEQ ID NO:1. In some of any of the provided embodiments, the variant NiV-G exhibits reduced binding to Ephrin B2 or Ephrin B3. In some of any of the provided embodiments, the variant NiV-G comprises: one or more amino acid substitutions corresponding to amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:1. In some of any of the provided embodiments, the variant NiV-G comprises amino acid substitutions E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:1. In some of any of the provided embodiments, the variant NiV-G has the amino acid sequence set forth in SEQ ID NO: 228 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:228. In some of any of the provided embodiments, the variant NiV-G has the amino acid sequence set forth in SEQ ID NO:228.

[0023] In some of any of the provided embodiments, the particle further comprises an additional attachment protein that is a paramyxovirus envelope attachment protein that is a variant NiV-G that is a variant or a biologically active portion of a wild-type NiV-G. In some of any of the provided embodiments, the variant NiV-G exhibits reduced binding to Ephrin B2 or Ephrin B3. In some of any of the provided embodiments, the variant NiV-G comprises: one or more amino acid substitutions corresponding to amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:1.

[0024] In some of any of the provided embodiments, the at least one paramyxovirus fusion (F) protein is an F protein from a henipavirus or is a biologically active portion thereof or variant thereof. In some of any of the provided embodiments, the henipavirus is a Hendra virus. In some of any of the provided embodiments, the henipavirus is a Nipah virus. In some of any of the provided embodiments, the paramyxovirus F protein is a wild-type NiV-F protein or a variant or a biologically active portion thereof. In some of any of the provided embodiments, the paramyxovirus F protein is a variant NiV-F that is a variant or a biologically active portion of a wild-type NiV-F protein. In some of any of the provided embodiments, the variant NiV-F is truncated by up to 22 contiguous amino acids the at the C- terminus of the wild-type NiV-F set forth in SEQ ID NO:235, optionally not include the initial methionine. In some of any of the provided embodiments, the variant NiV-F protein is a truncated NiV-F that lacks amino acids 525-546 of SEQ ID NO:235. In some of any of the provided embodiments, the 8 sf-5667634186152009940 variant NiV-F has the amino acid sequence set forth in SEQ ID NO: 227 or an amino acid sequence having at or about 80%, at least at or about 81%, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91%, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:227. In some of any of the provided embodiments, the variant NiV-F has the amino acid sequence set forth in SEQ ID NO:227. In some of any of the provided embodiments, the paramyxovirus F protein is an F0 precursor or is a proteolytically cleaved form thereof comprising F1 and F2 subunits. In some of any of the provided embodiments, the proteolytically cleaved form is a cathepsin L cleavage product.

[0025] In some of any of the provided embodiments, the targeting moiety and the paramyxovirus envelope attachment protein or biologically active portion thereof is attached via a linker. In some of any of the provided embodiments, the linker is a peptide linker. In some of any of the provided embodiments, the peptide linker is 2 to 65 amino acids in length. In some of any of the provided embodiments, the peptide linker is a flexible linker that comprises GS, GGS, GGGGS, GGGGGS or combinations thereof. In some of any of the provided embodiments, the peptide linker is selected from: (GGS)n, wherein n is 1 to 10; (GGGGS)n, wherein n is 1 to 10; or (GGGGGS)n, wherein n is 1 to 6. In some of any of the provided embodiments, the paramyxovirus fusion (F) protein exhibits fusogenic activity with a target cell upon binding of at least one paramyxovirus envelope attachment protein o to the target molecule on the target cell.

[0026] In some of any of the provided embodiments, the lipid particle comprises a viral nucleic acid. In some of any of the provided embodiments, the viral nucleic acid comprises one or more of (e.g., all of) the following nucleic acid sequences: 5’ LTR (e.g., comprising U5 and lacking a functional U3 domain), Psi packaging element (Psi), Central polypurine tract (cPPT) / central termination sequence (CTS) (e.g. DNA flap), Poly A tail sequence, a posttranscriptional regulatory element (e.g. WPRE), a Rev response element (RRE), and 3’ LTR (e.g., comprising U5 and lacking a functional U3). In some of any of the provided embodiments, the lipid particle is a viral vector. In some of any of the provided embodiments, the lipid particle is a retroviral vector. In some of any of the provided embodiments, the lipid particle is a lentiviral vector. In some of any of the provided embodiments, the lipid particle is devoid of viral genomic DNA. In some of any of the provided embodiments, the lipid particle is a viral-like particle. In some of any of the provided embodiments, the lipid particle is a retroviral -like particle. In some of any of the provided embodiments, the lipid particle is a lentiviral -like particle. In some of any of the provided embodiments, the lentiviral vector or lentiviral-like particle is derived from HIV. In some of any of the provided embodiments, the Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof is a BaEVTR fusogen. In some of any of the provided embodiments, the BaEV Baboon 9 sf-5667634186152009940 Endogenous Virus (BaEV) fusogen or functional variant thereof comprises a protease site modification. In some of any of the provided embodiments, the protease site modification comprises modifying a MLV-A cleavage site to a MA / CA cleavage site.

[0027] In some of any of the provided embodiments, the lipid particle is produced as a preparation with increased titer compared to a reference lipid particle preparation that is similarly produced but with only the first retargeted attachment protein. In some of any of the provided embodiments, the titer is increased by at or greater than 1.2-fold, 1.3-fold, 1.4-fold, 1.5-fold, 1.6-fold, 1.7-fold, 1.8-fold, 2-fold, 2.5-fold, 3-fold, 4-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, 10-fold, or more.

[0028] In some of any of the provided embodiments, the particle further comprises an exogenous agent for delivery to a target cell. In some of any of the provided embodiments, the exogenous agent is present in the lumen. In some of any of the provided embodiments, the exogenous agent is a protein or a nucleic acid, optionally wherein the nucleic acid is a DNA or RNA. In some of any of the provided embodiments, the exogenous agent is a nucleic acid encoding a cargo for delivery to the target cell. In some of any of the provided embodiments, the exogenous agent is or encodes a therapeutic agent, a diagnostic agent or a genome-modifying enzyme. In some of any of the provided embodiments, the exogenous agent encodes a membrane protein, optionally wherein the membrane protein is an antigen receptor for targeting cells expressed by or associated with a disease or condition. In some of any of the provided embodiments, the membrane protein is a chimeric antigen receptor (CAR). In some of any of the provided embodiments, the exogenous agent is a nucleic acid comprising a payload gene for correcting a genetic deficiency, optionally a genetic deficiency in the target cell, optionally wherein the genetic deficiency is associated with a liver cell or a hepatocyte. In some of any of the provided embodiments, binding of the paramyxovirus envelope attachment protein or biologically active portion thereof to a target molecule expressed on the surface of a target cell mediates fusion of the particle with the target cell and delivery of the exogenous agent to the target cell. In some of any of the provided embodiments, at or greater than 10%, 20%, 30%, 40%, 50%, 60% of the target cells are delivered the exogenous agent. In some of any of the provided embodiments, delivery of the exogenous cell to the target cell is increased compared to a reference particle preparation that is similarly produced but with only a retargeted attachment protein (e.g., no co-display protein). In some of any of the provided embodiments, the delivery to the target cell is increased by at or greater than 1.2-fold, 1.3-fold, 1.4-fold, 1.5-fold, 1.6-fold, 1.7-fold, 1.8-fold, 2-fold, 2.5-fold, 3-fold, 4-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, 10-fold, or more.

[0029] Provided herein is a producer cell comprising (a) a nucleic acid encoding a retargeted attachment protein comprising a paramyxovirus envelope attachment protein; and (i) a targeting moiety directed to a target molecule expressed on the surface of a target cell, (b) a nucleic acid encoding a co- display protein, and (c) a nucleic acid encoding at least one paramyxovirus F protein. 10 sf-5667634186152009940

[0030] Provided herein is a producer cell comprising (a) a nucleic acid encoding a retargeted attachment protein comprising a Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof expressed on the surface of a target cell, and (b) a nucleic acid encoding a co-display protein.

[0031] In some of any of the provided embodiments, the cell further comprises a viral nucleic acid(s). In some of any of the provided embodiments, the viral nucleic acid(s) are lentiviral nucleic acids. In some of any of the provided embodiments, the cell is a mammalian cell. In some of any of the provided embodiments, the producer cell is selected from the group consisting of CHO cells, BHK cells, MDCK cells, C3H 10T1 / 2 cells, FLY cells, Psi-2 cells, BOSC 23 cells, PA317 cells, WEHI cells, COS cells, BSC 1 cells, BSC 40 cells, BMT 10 cells, VERO cells, W138 cells, MRC5 cells, A549 cells, HT1080 cells, 293 cells, 293T cells, B-50 cells, 3T3 cells, NIH3T3 cells, HepG2 cells, Saos-2 cells, Huh7 cells, HeLa cells, W163 cells, 211 cells, and 211A cells. In some of any of the provided embodiments, the producer cell comprises 293T cells.

[0032] In some of any of the provided embodiments, the viral nucleic acid(s) lacks one or more genes involved in viral replication. In some of any of the provided embodiments, the viral nucleic acid comprises a nucleic acid encoding a viral packaging protein selected from one or more of Gag, Pol, Rev and Tat. In some of any of the provided embodiments, the viral nucleic acid comprises: one or more of (e.g., all of) the following nucleic acid sequences: 5’ LTR (e.g., comprising U5 and lacking a functional U3 domain), Psi packaging element (Psi), Central polypurine tract (cPPT) / central termination sequence (CTS) (e.g. DNA flap), Poly A tail sequence, a posttranscriptional regulatory element (e.g. WPRE), a Rev response element (RRE), and 3’ LTR (e.g., comprising U5 and lacking a functional U3). In some of any of the provided embodiments, the co-display protein increases specificity to the target cell. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus- infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell that is a hematopoietic stem cell. In some of any of the provided embodiments, the cell surface molecule is selected from CD34, CD105, or CD117. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell that is a T cell. In some of any of the provided embodiments, the cell surface molecule is selected from CD3, CD4, 11 sf-5667634186152009940 CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3. In some of any of the provided embodiments, the co-display protein increases specificity to a target cell that is a hepatocyte. In some of any of the provided embodiments, the cell surface molecule is selected from ASGR1, ASGR2 and TM4SF5. In some of any of the provided embodiments, the co-display protein binds to a different protein than the targeting moiety of the retargeted attachment protein. In some of any of the provided embodiments, the co-display protein does not include a paramyxovirus envelope attachment protein or a fragment thereof.

[0033] In some of any of the provided embodiments, the co-display protein is an immune stimulating protein and the immune stimulating protein stimulates a T cell activity or function. In some of any of the provided embodiments, the immune stimulating protein comprises (i) an extracellular domain (ii)a linker and (iii) an anchor. In some of any of the provided embodiments, the extracellular domain of the immune stimulating protein binds to a T cell stimulatory receptor. In some of any of the provided embodiments, the T cell stimulatory receptor is selected from CD3, CD2, CD28, CD27. In some of any of the provided embodiments, the extracellular domain of the immune stimulating protein binds to CD3. In some of any of the provided embodiments, the extracellular domain is selected from the group comprising an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide. In some of any of the provided embodiments, the extracellular domain of the immune stimulating protein is an anti-CD3 antibody or single chain fragment thereof. In some of any of the provided embodiments, the co-display protein is a transduction adjuvant that increases transduction efficiency of the lipid particle as compared to a lipid particle that does not have a co-display protein comprising a transduction adjuvant. In some of any of the provided embodiments, the co-display protein is a transduction adjuvant that binds to a surface molecule on target cells to enhance transduction.

[0034] In some of any of the provided embodiments, the transduction adjuvant comprises (i) an extracellular domain (ii)a linker and (iii) an anchor. In some of any of the provided embodiments, the extracellular domain of the transduction adjuvant binds an integrin binding domain. In some of any of the provided embodiments, the extracellular domain of the transduction adjuvant comprises the extracellular domain of fibronectin, retronectin, or a functional variant thereof. In some of any of the provided embodiments, the linker is derived from a human protein. In some of any of the provided embodiments, the linker is a derived from human CD8α, IgG3 hinge, IgG1 hinge, IgG4 heavy chain, IgG4, or CD28. In some of any of the provided embodiments, the linker is modified to remove a cysteine residue. In some of any of the provided embodiments, the linker is rigid or wherein the linker is flexible. In some of any of the provided embodiments, the anchor is a peptide anchor that is a transmembrane domain. In some of any of the provided embodiments, the anchor is a transmembrane domain that is a transmembrane 12 sf-5667634186152009940 domain of a protein selected from PDGFR, VSV-G, CD8α, ICAM1, HLA-DRB, CD49d, or Transferrin. In some of any of the provided embodiments, the anchor is a GPI lipid anchor.

[0035] In some of any of the provided embodiments, the targeting moiety is selected from the group consisting of an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide. In some of any of the provided embodiments, the targeting moiety binds to a cell surface molecule present on a target cell. In some of any of the provided embodiments, the cell surface molecule is a protein, glycan, or lipid. In some of any of the provided embodiments, the target cell is selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells. In some of any of the provided embodiments, the target cells is selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell . In some of any of the provided embodiments, the target is a hematopoietic stem cell. In some of any of the provided embodiments, the cell surface molecule is selected from CD34, CD105, or CD117. In some of any of the provided embodiments, the target cell is a T cell. In some of any of the provided embodiments, the cell surface molecule is selected from the group consisting of CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3. In some of any of the provided embodiments, the target cell is a hepatocyte. In some of any of the provided embodiments, the cell surface molecule is selected from the group consisting of ASGR1, ASGR2 and TM4SF5. In some of any of the provided embodiments, the targeting moiety is selected from the group consisting of a single domain antibody or a single chain variable fragment (scFv). In some of any of the provided embodiments, the single domain antibody is a VHH. In some of any of the provided embodiments, the retargeted attachment protein is a first attachment protein and the lipid particle further comprises a second retargeted attachment protein. In some of any of the provided embodiments, the second retargeted attachment protein comprises (i) a second paramyxovirus envelope attachment protein; and (ii) a second targeting moiety directed to a target molecule expressed on the surface of a target cell. In some of any of the provided embodiments, the second targeting moiety is selected from the group consisting of an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide. In some of any of the provided embodiments, the target cell is selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus- 13 sf-5667634186152009940 infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells. In some of any of the provided embodiments, the target cells is selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell. In some of any of the provided embodiments, the target is a hematopoietic stem cell. In some of any of the provided embodiments, the cell surface molecule is selected from CD34, CD105, or CD117. In some of any of the provided embodiments, the target cell is a T cell. In some of any of the provided embodiments, the cell surface molecule is selected from the group consisting of CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3. In some of any of the provided embodiments, the target cell is a hepatocyte. In some of any of the provided embodiments, the cell surface molecule is selected from the group consisting of ASGR1, ASGR2 and TM4SF5.

[0036] In some of any of the provided embodiments, the targeting moiety is selected from the group consisting of a single domain antibody or a single chain variable fragment (scFv). In some of any of the provided embodiments, the single domain antibody is a VHH. In some of any of the provided embodiments, the BaEV envelope glycoprotein is a truncated BaEV envelope glycoprotein comprising a cytoplasmic tail with a partial fusion inhibitory R peptide relative to the inhibitory R peptide of a wild- type BaEV envelope glycoprotein, wherein the partial fusion inhibitory R peptide comprises at least one amino-terminal amino acid but less than the full length of the inhibitory R peptide of the wild-type BaEV envelope glycoprotein. In some of any of the provided embodiments, the BaEV envelope glycoprotein is a truncated BaEV envelope glycoprotein comprising a cytoplasmic tail with a partial fusion inhibitory R peptide relative to a wild-type BaEV envelope glycoprotein, wherein the cytoplasmic tail is 25 amino acids in length and contains 8 contiguous amino-terminal acids of the inhibitory R peptide (R+8) of the full length inhibitory R peptide of wild-type BaEV envelope glycoprotein. In some of any of the provided embodiments, the truncated BaEV glycoprotein comprises: (i) a glycoprotein 70 (g70) subunit or a biologically active portion thereof, and (ii) a portion of the glycoprotein p20E (p20E) subunit comprising the cytoplasmic tail with the partial inhibitory R peptide. In some of any of the provided embodiments, the BaEV envelope glycoprotein binds an ASCT-2 or ASCT-1 receptor. In some of any of the provided embodiments, the truncated BaEV envelope glycoprotein is truncated relative to SEQ ID NO: 622 and lacks up to 16 contiguous amino acids from the C-terminal cytoplasmic tail of SEQ ID NO: 622. In some of any of the provided embodiments, the partial fusion inhibitory R peptide is set forth as amino acids 1 to 8 of SEQ ID NO: 623, optionally wherein the cytoplasmic tail is set forth in SEQ ID NO: 624 (R+8). 14 sf-5667634186152009940 In some of any of the provided embodiments, the truncated BaEV envelope glycoprotein is set forth in SEQ ID NO: 625.

[0037] In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is an envelope attachment protein from a Nipah virus, Hendra virus, or Measles virus, or is a variant or biologically active portion thereof of any of the foregoing. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is a wild-type paramyxovirus G protein, H protein or HN protein or is a variant or biologically active portion of any of the foregoing. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is a wild-type Nipah virus G (NiV-G) protein or is a variant or biologically active portion of a NiV-G. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is a variant paramyxovirus envelope attachment protein. In some of any of the provided embodiments, the variant paramyxovirus envelope attachment protein comprises one or more mutations that reduces native tropism relative to the wild-type paramyxovirus envelope attachment protein not comprising the one or more mutations. In some of any of the provided embodiments, the paramyxovirus envelope attachment protein is a variant NiV-G that is a variant or a biologically active portion of a wild-type NiV-G. In some of any of the provided embodiments, the variant is a variant NiV-G that is a variant of a wild-type Nipah virus G (NiV-G) protein or a biologically active portion thereof. In some of any of the provided embodiments, the variant NiV-G is truncated by up to 40 contiguous amino acids at or near the N-terminus of the wild- type NiV-G set forth in SEQ ID NO:1. In some of any of the provided embodiments, the variant NiV-G has a truncation of amino acids 2-34 of the wild-type NiV-G set forth in SEQ ID NO:1. In some of any of the provided embodiments, the variant NiV-G exhibits reduced binding to Ephrin B2 or Ephrin B3. In some of any of the provided embodiments, the variant NiV-G comprises: one or more amino acid substitutions corresponding to amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:1. In some of any of the provided embodiments, the variant NiV-G comprises amino acid substitutions E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:1. In some of any of the provided embodiments, the variant NiV-G has the amino acid sequence set forth in SEQ ID NO: 228 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:228. In some of any of the provided embodiments, the variant NiV-G has the amino acid sequence set forth in SEQ ID NO:228. 15 sf-5667634186152009940

[0038] In some of any of the provided embodiments, the particle further comprises an additional attachment protein that is a paramyxovirus envelope attachment protein that is a variant NiV-G that is a variant or a biologically active portion of a wild-type NiV-G. In some of any of the provided embodiments, the variant NiV-G exhibits reduced binding to Ephrin B2 or Ephrin B3. In some of any of the provided embodiments, the variant NiV-G comprises: one or more amino acid substitutions corresponding to amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:1.

[0039] In some of any of the provided embodiments, the at least one paramyxovirus fusion (F) protein is an F protein from a henipavirus or is a biologically active portion thereof or variant thereof. In some of any of the provided embodiments, the henipavirus is a Hendra virus. In some of any of the provided embodiments, the henipavirus is a Nipah virus. In some of any of the provided embodiments, the paramyxovirus F protein is a wild-type NiV-F protein or a variant or a biologically active portion thereof. In some of any of the provided embodiments, the paramyxovirus F protein is a variant NiV-F that is a variant or a biologically active portion of a wild-type NiV-F protein. In some of any of the provided embodiments, the variant NiV-F is truncated by up to 22 contiguous amino acids the at the C- terminus of the wild-type NiV-F set forth in SEQ ID NO:235, optionally not include the initial methionine. In some of any of the provided embodiments, the variant NiV-F protein is a truncated NiV-F that lacks amino acids 525-546 of SEQ ID NO:235. In some of any of the provided embodiments, the variant NiV-F has the amino acid sequence set forth in SEQ ID NO: 227 or an amino acid sequence having at or about 80%, at least at or about 81%, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91%, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:227. In some of any of the provided embodiments, the variant NiV-F has the amino acid sequence set forth in SEQ ID NO:227.

[0040] In some of any of the provided embodiments, the paramyxovirus F protein is an F0 precursor or is a proteolytically cleaved form thereof comprising F1 and F2 subunits. In some of any of the provided embodiments, the proteolytically cleaved form is a cathepsin L cleavage product. In some of any of the provided embodiments, the targeting moiety and the paramyxovirus envelope attachment protein or biologically active portion thereof is attached via a linker. In some of any of the provided embodiments, the linker is a peptide linker. In some of any of the provided embodiments, the peptide linker is 2 to 65 amino acids in length. In some of any of the provided embodiments, the peptide linker is a flexible linker that comprises GS, GGS, GGGGS, GGGGGS or combinations thereof. In some of any of the provided embodiments, the peptide linker is selected from: (GGS)n, wherein n is 1 to 10; 16 sf-5667634186152009940 (GGGGS)n, wherein n is 1 to 10; or (GGGGGS)n, wherein n is 1 to 6. In some of any of the provided embodiments, the paramyxovirus fusion (F) protein exhibits fusogenic activity with a target cell upon binding of at least one paramyxovirus envelope attachment protein o to the target molecule on the target cell.

[0041] In some of any of the provided embodiments, the lipid particle comprises a viral nucleic acid. In some of any of the provided embodiments, the viral nucleic acid comprises one or more of (e.g., all of) the following nucleic acid sequences: 5’ LTR (e.g., comprising U5 and lacking a functional U3 domain), Psi packaging element (Psi), Central polypurine tract (cPPT) / central termination sequence (CTS) (e.g. DNA flap), Poly A tail sequence, a posttranscriptional regulatory element (e.g. WPRE), a Rev response element (RRE), and 3’ LTR (e.g., comprising U5 and lacking a functional U3). In some of any of the provided embodiments, the lipid particle is a viral vector. In some of any of the provided embodiments, the lipid particle is a retroviral vector. In some of any of the provided embodiments, the lipid particle is a lentiviral vector.

[0042] In some of any of the provided embodiments, the lipid particle is devoid of viral genomic DNA. In some of any of the provided embodiments, the particle is a viral-like particle. In some of any of the provided embodiments, the particle is a retroviral-like particle. In some of any of the provided embodiments, the particle is a lentiviral-like particle. In some embodiments, the lentiviral vector or the lentiviral-like particle is derived from HIV. In some embodiments, the BaEV Baboon Endogenous Virus (BaEV) is a BaEVTR fusogen. In some embodiments, the BaEV Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof comprises a protease site modification. In some embodiments, the protease site modification comprises modifying a MLV-A cleavage site to a MA / CA cleavage site. In some of any of the provided embodiments, the lipid particle is produced as a preparation with increased titer compared to a reference lipid particle preparation that is similarly produced but with only the first retargeted attachment protein. In some of any of the provided embodiments, the titer is increased by at or greater than 1.2-fold, 1.3-fold, 1.4-fold, 1.5-fold, 1.6-fold, 1.7-fold, 1.8-fold, 2-fold, 2.5-fold, 3-fold, 4- fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, 10-fold, or more.

[0043] In some of any of the provided embodiments, the particle further comprises an exogenous agent for delivery to a target cell. In some of any of the provided embodiments, the exogenous agent is present in the lumen. In some of any of the provided embodiments, the exogenous agent is a protein or a nucleic acid, optionally wherein the nucleic acid is a DNA or RNA. In some of any of the provided embodiments, the exogenous agent is a nucleic acid encoding a cargo for delivery to the target cell. In some of any of the provided embodiments, the exogenous agent is or encodes a therapeutic agent, a diagnostic agent or a genome-modifying enzyme. In some of any of the provided embodiments, the exogenous agent encodes a membrane protein, optionally wherein the membrane protein is an antigen 17 sf-5667634186152009940 receptor for targeting cells expressed by or associated with a disease or condition. In some of any of the provided embodiments, the membrane protein is a chimeric antigen receptor (CAR).

[0044] In some of any of the provided embodiments, the exogenous agent is a nucleic acid comprising a payload gene for correcting a genetic deficiency, optionally a genetic deficiency in the target cell, optionally wherein the genetic deficiency is associated with a liver cell or a hepatocyte. In some of any of the provided embodiments, binding of the paramyxovirus envelope attachment protein or biologically active portion thereof to a target molecule expressed on the surface of a target cell mediates fusion of the particle with the target cell and delivery of the exogenous agent to the target cell. In some of any of the provided embodiments, at or greater than 10%, 20%, 30%, 40%, 50%, 60% of the target cells are delivered the exogenous agent. In some of any of the provided embodiments, delivery of the exogenous cell to the target cell is increased compared to a reference particle preparation that is similarly produced but with only a retargeted attachment protein (e.g., no co-display protein). In some of any of the provided embodiments, the delivery to the target cell is increased by at or greater than 1.2-fold, 1.3- fold, 1.4-fold, 1.5-fold, 1.6-fold, 1.7-fold, 1.8-fold, 2-fold, 2.5-fold, 3-fold, 4-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, 10-fold, or more.

[0045] Provided herein is a method of making a lipid particle, comprising a) providing a producer cell as any of those provided herein, b) culturing the cell under conditions that allow for production of the lipid particle, and c) separating, enriching, or purifying the lipid particle from the cell, thereby making the lipid particle. In some of any of the provided embodiments, the lipid particle is a pseudotyped lentiviral vector.

[0046] Provided herein is a lipid particle produced by any of the provided claims. Provided herein is a composition comprising a plurality of any of the provided lipid particles. In some of any of the provided embodiments, the composition further comprises a pharmaceutically acceptable carrier.

[0047] Provided herein is a method of transducing a cell comprising contacting a cell with any of the provided lipid particles or compositions. Provided herein is a method of delivering an exogenous agent into a target cell, the method comprising contacting a lipid particle provided herein or a composition provided herein with a target cell.

[0048] In some of any of the provided embodiments, the contacting is in vitro or ex vivo. In some of any of the provided embodiments, the contacting is in vivo in a subject.

[0049] Provided herein is a method of delivering an exogenous agent to a cell in a subject, the method comprising administering to the subject any of the provided lipid particles or compositions. In some of any of the provided embodiments, the exogenous agent is or encodes a therapeutic agent for treating a disease or condition in the subject.

[0050] Provided herein is a method of treatment, the method comprising administering to the subject any of the provided lipid particles or compositions. In some of any of the provided embodiments, the 18 sf-5667634186152009940 exogenous agent is or encodes a membrane protein, optionally a chimeric antigen receptor, for targeting an antigen associated with a disease or condition in the subject. In some of any of the provided embodiments, the exogenous agent is for use in gene therapy to correct a genetic deficiency or replaces a deficient or missing gene in the subject. In some of any of the provided embodiments, the subject is a human subject.

[0051] Provided herein is a co-display polypeptide, comprising one or more of: a leader domain; one or more fibronectin fragments; a hinge domain; an anchor domain; and a intracellular domain.

[0052] In some embodiments, the co-display polypeptide is partially derived or derived from one or more recombinant fibronectin fragments. In some embodiments, the one or more recombinant fibronectin fragments are selected from: CH296-A, CH296-B, CH296-C, CH296-D, CH296-E, and CH296-F.

[0053] Provided herein is a co-display polypeptide, comprising one or more of: a leader domain; a CS-1 domain; a linker; a C-domain; a hinge domain; an anchor domain; and a intracellular domain. Brief Description of the Drawings

[0054] An exemplary pseudotyped vector is shown with an exemplary co-display protein in FIG.1.

[0055] FIG.2A depicts titer as sorted by co-display protein anchor domain. FIG.2B depicts titer as sorted by co-display protein anchor domain.

[0056] Transduction of PanT cells is shown in FIG.3A. Comparative activation of CD3 co-display in vector which also expresses a CD8 retargeted fusogen is shown in FIG.3B. PanT transduction and activation for exemplary co-display constructs is shown in FIG.3C.

[0057] FIG.4A depicts GFP expression as a percentage of total cells as sorted by co-display protein anchor domain. FIG.4B depicts GFP expression as sorted by co-display protein linker domain. Expression of CD8 retargeted NiV-G and CD3 co-display protein is shown in FIG.4C.

[0058] FIG.5A depicts GFP positive T cells following transduction with an exemplary co-display construct. Off-target transduction for the exemplary co-display construct is shown in FIG.5B.

[0059] FIG.6 depicts tumor cell (Nalm6) killing following transduction of a vector comprising a co-display construct, CD8 retargeted fusogen, as well as CAR transgene.

[0060] FIG.7A depicts transduction with a retronectin co-display on BaEVTR LV particles. Transduction efficiency as a function of plasmid ratios is shown in FIG.7B. Transduction efficiency across transduction dilutions is depicted in FIG.7C. FIG.7D shows BaEVTR fusogen and retronectin co-display assessed via infectivity on mobilized peripheral blood (mPB) CD34+ cells. CD34+ editing titers are shown in FIG.7E. FIG.7F shows a schematic of a retronectin co-display protein.

[0061] FIG.8A shows a schematic of the modification introduced in the BaEVTR protease cleavage site. 19 sf-5667634186152009940

[0062] FIG.8B shows a schematic of a VLP comprising a BaEVTR (-MACA) protein and a RetroNectin Co-Display.

[0063] FIG.8C shows percentage of GFP+ cells for a titration curves of BaEVTR with (+) or without (-) MACA and with (+) or without (-) Co-Display (CoD).

[0064] FIG.8D shows experimental details used to test the indicated VLP in a short-term humanization model for 16 weeks.

[0065] In vivo transduction efficiency of a BaEVTR co-display LV is shown in FIGs.8E-8K. FIG. 8E shows percentage of GFP+ cells in bone marrow (BM) huCD45+ cells at week 16 for the indicated conditions. FIG.8E shows percentage of GFP+ cells in BM HSPC over time for the indicated conditions. FIG.8F shows percentage of GFP+ cells in BM fractions over time for the indicated conditions. M - myeloid, LP – lymphoid progenitor, L – lymphoid, and P - primitive. FIG.8G shows flow plots for huCD45+ BM fractions in the short-term humanization model described in FIG.8D. M - myeloid, LP – lymphoid progenitor. and L – lymphoid. FIG.8H shows percentage GFP+ cells (log10) in peripheral blood (PB) huCD45+ cells over time (left panel), PB huCD13+CD33+ cells over time (middle panel), and PB huCD19+ cells over time (right panel). FIG.8I shows viral copy number (VCN) in total peripheral blood (PB) over time for the indicated conditions. FIG.8J shows percentage GFP+ cells in spleen HSPC at week 16 for the indicated conditions. FIG.8K shows histology performed on sternums collected from treated animals at different timepoints after infusion.

[0066] Assessment of NiV LV-CD133, with or without retronectin co-display, for transduction of resting CD34+ cells is shown in FIG.9A. Left panel shows a schematic of an exemplary VLP. Right panel shows titration curves for the indicated VLPs in resting CD34+ cells.

[0067] FIG.9B shows CD117 and CD133 expression in CD34 negative (-) and CD34 positive (+) cells. FIG.9B shows transduction efficiency in resting and stimulated CD34+ cells.

[0068] FIG.9C depicts a full titration curve with exemplary target cell titer heat map.

[0069] FIG.9D shows titers as a heatmap for the various combinations of VLP and cell type.

[0070] FIG.9E shows titers as heatmaps for the various combinations of VLP and cell type (left panel, flow cytometry plots of percentage GFP+ cells for the indicated VLPs (right panel), and plots of VCNs for the indicated VLPs (9F continued).

[0071] FIG.9F shows heatmaps of expression levels for the targets in the various cell types.

[0072] Transduction of human hepatocytes in vivo is shown in FIG.9G.

[0073] FIG.10A. shows comparative titer of BaEV fusogen pseudotyped VLP on recipient 293LX cells. FIG.10B. shows comparative titer of BaEV fusogen pseudotyped VLP on recipient CD34+ cells.

[0074] FIG.11A shows experimental details for the D7 post-humanization model used to test the indicated VLP (or LV). 20 sf-5667634186152009940

[0075] FIG.11B shows CD133 expression in the infused human CD34+ cells (day 0) and CD133 expression over time.

[0076] FIG.11C percentage of HPSC cells that are CD133 negative (-) or CD133 positive (+) over time.

[0077] FIG.11D-G shows transduction of human CD45+ cells using pseudotyped lentiviral vector. FIG.11D shows percentage of GFP positive (GFP+) cells in bone marrow (BM) huCD45+ cells at day 12 (D12) for the indicated VLPs. FIG.11E shows percentage of GFP positive (GFP+) cells in bone marrow (BM) HSPC at day 12 (D12) for the indicated VLPs. FIG.11F shows percentage of GFP positive (GFP+) cells in bone marrow (BM) CD133+ cells at day 12 (D12) for the indicated VLPs. FIG. 11G shows the percentage of cells that are BM CD133+ cells for each of the indicated subpopulations.

[0078] FIG.11H shows experimental details for co-infusion model used to test the indicated VLP (or LV).

[0079] FIG.11I shows percentage of huCD45+ cells (log10) in peripheral blood (PB) over time.

[0080] FIG.11J shows percentage of huCD45+ cells for each of the indicated groups.

[0081] FIG.11K shows percentage of huCD45+ cells that are GFP+ for each of the indicated groups.

[0082] BaEVTR LV and NiV-CD133-CoD-LV transduction efficiency in the presence of off-target cellular sinks is shown in FIG.11L-Q. FIG.11L shows percentage of GFP+ cells in bone marrow (BM) HSPC at day 12 (D12) for the indicated group. FIG.11M and FIG.11N shows percentage of cells of each BM fraction in the BM composition at day 12 (D12) for the indicated groups. FIG.11O shows percentage of GFP+ cells in BM CD133+ cells at D12. FIG.11P shows percentage of cells in BM CD133+ fraction at day 12. FIG.11Q shows percentage of GFP+ cells in peripheral blood (PB) huCD45+ cells at D12.

[0083] FIG.11R shows experimental details for a model used to test the VLP (or LV).

[0084] FIG.11S shows a heatmap summarizing the transduction for each of the reagents in human hepatocytes or mouse non-parenchymal cells (NPC).

[0085] FIG.11T shows histology of liver for livers isolated from mice having received the indicated treatment.

[0086] FIG.11U shows a heatmap of RNA-seq data comparing freshly thawed PHH, PHH cultured in vitro for 24h (time of vector dosing for the in vitro titration experiments) and human hepatocytes freshly isolated from FRG mice prior to vector dosing.

[0087] FIG.11V left panel shows hierarchical clustering of the RNA-seq data from FIG.11U. FIG. 11V right panel shows a heatmap of RNA-seq data for a selection of genes from FIG.11U. 21 sf-5667634186152009940

[0088] FIG.12A shows a schematic of a VLP having a BaEVTR envelope and carrying a Beta 2 Microglobulin (B2M) guide RNA and a CRISPR-Cas9 editor covalently fused with a MLV capsid.

[0089] FIG.12B shows a representative flow strategy for readout of gene editing of the B2M locus.

[0090] FIG.12C (left panel) shows an experimental strategy for in vitro testing of gene editing efficiency of a BaEVTR VLP. FIG.12C (right panel) shows titration curves as measured by OTA and flow for BaEVTR tested using the strategy shown in the left panel.

[0091] FIG.12D shows gene editing efficiency in 5 HSPC FACS-sorted fractions. Upper left panel shows gene editing efficiency in 5 HSPC FACS-sorted fractions following transduction with BaEVTR VLP at an MOI of 16. Upper right panel shows gene editing efficiency in 5 HSPC FACS-sorted fractions following transduction with BaEVTR VLP at an MOI of 83. Lower panel shows the relative proportion of editing variants in each HSPC subtype as well as in the bulk HSPC population following transduction with BaEVTR VLP at an MOI 16 or 83.

[0092] FIG.12E shows an experimental strategy for in vivo testing using a D7 post-humanization model.

[0093] FIG.12F shows results of gene editing efficiency as measured by flow cytometry for the indications conditions in BM huCD45+ at day 12 (D12).

[0094] FIG.12G shows editing efficiency as measured by flow cytometry for individual HSPC subtypes in BM at day 12 (D12).

[0095] FIG.12H shows editing efficiency as measured by flow cytometry and OTA for BM huCD45+ at day 12 (D12).

[0096] FIG.12I shows a schematic of a long-term follow up study was conducted, similarly to what done for testing the LV constructs, with interim BM takedowns at week 4 and week 8 and terminal readout at week 16 after 3 VLP dosing at D7-D9 post humanization.

[0097] FIG.12J shows percentage of BM2 negative cells as measured by flow cytometry in BM huCD45+ cells at week 16.

[0098] FIG.12K shows percentage of B2M negative cells as measured by flow cytometry in BM HSPC over time.

[0099] FIG.12L shows percentage of B2M negative cells as measured by flow cytometry in BM HSCP subpopulations at week 16.

[0100] FIG.12M shows percentage of B2M negative cells in four human BM factions over time.

[0101] FIG.12N shows percentage of B2M negative cells in huCD45+, huCD13+CD33+, and huCD19+ populations over time.

[0102] FIG.12O shows percentage of B2M edited cells in spleen HSPC at week 16. 22 sf-5667634186152009940

[0103] FIG.12P shows percentage of B2M edited cells over time as measured by flow cytometry and OTA.

[0104] FIG.12Q shows percentage of B2M edited cells over time as measured by flow cytometry and OTA.

[0105] FIG.12R shows percentage of B2M edited cells as in multipotent P fraction as measured by flow cytometry and OTA.

[0106] FIG.12S shows percentage of editing variants (no edits, insertions, and deletions) in PB over time.

[0107] FIG.12T shows the relative proportion of editing variants for BM huCD45+ at day 12 (D12) for the indicated conditions.

[0108] FIG.12U shows an experimental strategy for testing VLP in a limiting scenario with a high number of human target cells inject at 9 weeks post-humanization.

[0109] FIG.12V shows percentage of huCD45+ cells at week 9 in the experimental model described in FIG.12U.

[0110] FIG.12W shows percentage of B2M edited cells in huCD45+ bone marrow (BM) or peripheral blood (PB) at week 11.

[0111] FIG.12X shows relative percentage of editing variants in BM fractions over time: primitive, myeloid, lymphoid progenitors, and on lymphoid.

[0112] FIG.13A shows percentage of B2M edited cells in resting CD34+ cells for the indicated VLPs at each of the indicated dilution series.

[0113] FIG.13B shows an experimental strategy for testing VLPs in a co-infusion model.

[0114] FIG.13C shows percentage of B2M edited cells (log10) in PB huCD45+ cells over time up to week 8 after cell and vector infusion.

[0115] FIG.13D shows percentage of B2M edited cells in peripheral blood (PB), bone marrow (BM) and huCD133+ BM cells at week 8 for the indicated VLPs.

[0116] FIG.13E shows percentage of B2M edited cells for the indicated VLPs when gated on huCD133+ cells.

[0117] FIG.13F shows percentage of B2M edited cells (log10) in peripheral blood (PB) huCD45+ over time after being treated with BaEVTR VLP (left panel) or NiV-CD133-CoD (right panel).

[0118] FIG.13G shows percentage of B2M edited cells using OTA and flow cytometry in bone marrow (BM) huCD45+ cells for the indicated VLPs at week 8.

[0119] FIG.13H left panel shows an exemplary VLP. FIG.13H right panel shows titers (TU / mL (B2M- cells) in resting CD34+ cells for BaEVTR with (+) or without (-) MACA and with (+) or without (-) CoDisplay (CoD). 23 sf-5667634186152009940

[0120] FIG.13I shows percentage of B2M edited cells in resting CD34+ cells at the indicated titrations for BaEVTR VLP and BaEVTR-CoD VLP.

[0121] FIG.13J shows an experimental strategy for testing VLPs in D7 post-humanization model with PB collections at weeks 4-8 and takedown (TD) at week 8.

[0122] FIG.13K shows in vivo editing variants in huCD45+ cells at week 8. FIG.13L shows an experimental strategy for testing VLPs in D7 post-humanization model and takedown (TD) at day 12.

[0123] FIG.13M shows % of colony forming units (CFU) for each of the indicated treatment conditions.

[0124] FIG.14A shows a schematic of a VLP having a BaEVTR envelope, a RetroNectin Co- Display and carrying a Beta 2 Microglobulin (B2M) guide RNA and a CRISPR-Cas9 editor covalently fused with a MLV capsid.

[0125] FIG.14B shows percentage of B2M negative cells in bone marrow (BM) huCD45+ cells at week 8 for BaEVTR without (-) and with (+) Codisplay (CoD).

[0126] FIG.14C shows percentage of B2M negative cells in bone marrow (BM) HSPC cells at week 8 for BaEVTR without (-) and with (+) Codisplay (CoD).

[0127] FIG.14D shows percentage of B2M negative cells in bone marrow (BM) fractions: P – primitive; M – myeloid; LP – lymphoid progenitors; and L – lymphoid.

[0128] FIG.14E shows percentage of B2M negative cells over time in PB huCD45+ (left panel), PB huCD13+CD33+ (middle panel); PB huCD19+ cells (right panel) for the indicated VLPs.

[0129] FIG.14F shows percentage of B2M negative cells in Spleen huCD45+ cells at week 8 for the indicated VLPs.

[0130] FIG.14G shows percentage of B2M edited cells (log10) in peripheral blood (PB) huCD45+ cells over time as measured by OTA and flow for BaEVTR without CoDisplay (VLP) and with CoDisplay (VLP-CoD).

[0131] FIG.14H shows percentage of B2M edited cells (log10) in bone marrow (BM) huCD45+ cells at week 8 as measured by OTA and flow for BaEVTR without CoDisplay (VLP) and with CoDisplay (VLP-CoD).

[0132] FIG.14I shows percentage of B2M edited cells (log10) in bone marrow (BM) fractions at week 8 as measured by OTA and flow for BaEVTR without CoDisplay (VLP) and with CoDisplay (VLP-CoD).

[0133] FIG.14J shows relative percentage of editing variants in the B2M locus with respect to what observed with the BaEVTR VLP design. 24 sf-5667634186152009940

[0134] FIG.15A shows a schematic of a VLP having a BaEVTR envelope, a RetroNectin Co- Display and carrying a Beta 2 Microglobulin (B2M) guide RNA and a CRISPR-Cas9 editor or a Adenine Base Editor (ABE) covalently fused with a MLV capsid.

[0135] FIG.15B shows a schematic for guide RNA targeting an enhancer region of Bcl11a or a HBG1 / 2 promoter region.

[0136] FIG.15C shows experimental details for testing for the indicated VLPs.

[0137] FIG.15D shows percentage of editing at the Bcl11a locus or a HBG1 / 2 locus in bone marrow (BM) huCD45+ cell at day 12 (D12).

[0138] FIG.15E shows relative percentage of editing variants at the Bcll1 locus edited with the ABE or at the HBG1 / 2 locus with Cas9.

[0139] FIG.15F show number of CFU-GM and BFU-E colonies for each condition tested.

[0140] FIG.15G shows flow cytometry plots of HbF expression following editing with the indicated conditions.

[0141] FIG.15H shows percentage of HbF positive cells (left panel) and HbF MFI on live cells for the indicated conditions.

[0142] FIG.16 shows a model study design for non-human primates. I. DETAILED DESCRIPTION

[0143] Provided herein is a lipid particle, such as a lentiviral vector or viral vector particle, that contains at least one viral envelope attachment protein, such as derived from paramyxovirus or baboon endogenous virus (BaEV). The viral envelope attachment proteins are designed to provide for targeted delivery of the lipid particles to a target cells. In some embodiments, the lipid particles also contain a codisplay protein, sch as a transduction adjuvant or immune stimulating protein.

[0144] Among provided lipid particles are those in which the viral attachment protein is derived from a paramyxovirus and is a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell. In such embodiments, the lipid particles also contain a fusion (F) protein that mediates fusion of the lipid particle with the target cell. In some embodiments, the paramyxovirus attachment protein, fusion protein, and codisplay protein are exposed on the outside surface of the lipid bilayer. In some embodiments, the paramyxovirus attachment protein, fusion protein, and codisplay protein are embedded in the lipid bilayer.

[0145] Also among provided lipid particles are those in which the viral attachment protein is derived from baboon endogenous virus (BaEV). In some embodiments, the BaEV is a variant of wild-type BaEV that contains one or more mutations that promote cleavage of a region of the protein to remove the inhibitory domain, thereby improving expression and function and targeted delivery of lipid particles 25 sf-5667634186152009940 containing the variant BaEV. In some embodiments, the BaEV protein, such as a variant BaEV protein, and codisplay protein are exposed on the outside surface of the lipid bilayer. In some embodiments, the BaEV protein, such as a variant BaEV protein, and codisplay protein are embedded in the lipid bilayer.

[0146] In some embodiments, the lipid particles can be a virus-like particle, a virus, or a viral vector, such as a lentiviral vector.

[0147] The provided lipid particles, such as lentiviral vectors, exhibit advantages over available envelope-pseudotyped particles. For instance, VSV-G is the most common envelope glycoprotein used for pseudotyping but its broad tropism is often not ideal or desirable for specific target cell delivery, such as is desired for gene therapy or exogenous protein delivery. Further, although alternative envelope proteins may exhibit reduced tropism or may be amenable to linkage to a binding domain for redirected targeting to a desired target cell, the titer of a preparation of lentiviral vectors containing such envelope proteins may be too low to allow for efficient transduction. Thus, alternative approaches are needed. It is found herein that certain duplicate proteins when pseudotyped on a lentiviral vector exhibit high titers.

[0148] The provided lipid particles, such as lentiviral vectors, exhibit advantages over available envelope-pseudotyped particles produced without a co-display protein. For instance, delivery efficiency and potency of viral vectors are often not ideal or desirable for specific target cell delivery, such as is desired for gene therapy or exogenous protein delivery. Further, titer of a preparation of lentiviral vectors containing such co-display protein may be significantly increased with respect to efficient transduction. Thus, alternative approaches are needed. It is found herein that certain co-display proteins when expressed with a fusogen pseudotyped on a lentiviral vector exhibit high titers.

[0149] Also provided are lipid particles, such as targeted lipid particles, additionally containing one or more exogenous agents, such as for delivery of a diagnostic or therapeutic agent to cells, including following in vivo administration to a subject. Also provided herein are methods and uses of the lipid particles, such in diagnostic and therapeutic methods. Also provided are polynucleotides, methods for engineering, preparing, and producing the lipid non-cell particles, compositions containing the particles, and kits and devices containing and for using, producing and administering the particles.

[0150] All publications, including patent documents, scientific articles and databases, referred to in this application are incorporated by reference in their entirety for all purposes to the same extent as if each individual publication were individually incorporated by reference. If a definition set forth herein is contrary to or otherwise inconsistent with a definition set forth in the patents, applications, published applications and other publications that are herein incorporated by reference, the definition set forth herein prevails over the definition that is incorporated herein by reference.

[0151] The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. 26 sf-5667634186152009940 II. DEFINITIONS

[0152] Unless defined otherwise, all terms of art, notations and other technical and scientific terms or terminology used herein are intended to have the same meaning as is commonly understood by one of ordinary skill in the art to which the claimed subject matter pertains. In some cases, terms with commonly understood meanings are defined herein for clarity and / or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over what is generally understood in the art. Unless indicated otherwise, abbreviations and symbols for chemical and biochemical names is per IUPAC-IUB nomenclature. Unless indicated otherwise, all numerical ranges are inclusive of the values defining the range as well as all integer values in-between.

[0153] As used herein, the articles “a” and “an” refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

[0154] As used herein, the term “about” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which it is used. As used herein, “about” when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20% or ±10%, more preferably ±5%, even more preferably ±1%, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.

[0155] As used herein, “lipid particle” refers to any biological or synthetic particle that contains a bilayer of amphipathic lipids enclosing a lumen or cavity. Typically a lipid particle does not contain a nucleus. Such lipid particles include, but are not limited to, viral particles (e.g. lentiviral particles), virus- like particles, viral vectors (e.g., lentiviral vectors) exosomes, enucleated cells, various vesicles, such as a microvesicle, a membrane vesicle, an extracellular membrane vesicle, a plasma membrane vesicle, a giant plasma membrane vesicle, an apoptotic body, a mitoparticle, a pyrenocyte, or a lysosome. In some embodiments, a lipid particle can be a fusosome. In some embodiments, the lipid particle is not a platelet. In some embodiments, the fusosome is derived from a source cell. A lipid particle also may include an exogenous agent or a nucleic acid encoding an exogenous agent, which may be present in the lumen of the lipid particle.

[0156] The terms “viral vector particle” and “viral vector” are used interchangeably herein and refer to a vector for transfer of an exogenous agent (e.g. non-viral or exogenous nucleic acid) into a recipient or target cell and that contains one or more viral structural proteins in addition to at least one non- structural viral genomic component or functional fragment thereof (i.e., a polymerase, an integrase, a protease or other non-structural component). The viral vector thus contains the exogenous agent, such as 27 sf-5667634186152009940 heterologous nucleic acid that includes non-viral coding sequences, to be transferred into a cell. Examples of viral vectors are retroviral vectors, such as lentiviral vectors.

[0157] The term “retroviral vector” refers to a viral vector that contains retroviral nucleic acid or is derived from a retrovirus. A retroviral vector particle includes the following components: a vector genome (retrovirus nucleic acid), a nucleocapsid encapsidating the nucleic acid, and a membrane envelope surrounding the nucleocapsid. Typically, a retroviral vector contains sufficient retroviral genetic information to allow packaging of an RNA genome, in the presence of packaging components, into a viral particle capable of infecting a target cell. Infection of the target cell may include reverse transcription and integration into the target cell genome. A retroviral vector may be a recombinant retroviral vector that is replication defective and lacks genes essential for replication, such as a functional gag-pol and / or env gene and / or other genes essential for replication. A retroviral vector also may be a self-inactivating (SIN) vector.

[0158] As used herein, a “lentiviral vector” or LV refers to a viral vector that contains lentiviral nucleic acid or is derived from a lentivirus. A lentiviral vector particle includes the following components: a vector genome (lentivirus nucleic acid), a nucleocapsid encapsidating the nucleic acid, and a membrane surrounding the nucleocapsid. Typically, a lentiviral vector contains sufficient lentiviral genetic information to allow packaging of an RNA genome, in the presence of packaging components, into a viral particle capable of infecting a target cell. Infection of the target cell may include reverse transcription and integration into the target cell genome. A lentiviral vector may be a recombinant lentiviral vector that is replication defective and lacks genes essential for replication, such as a functional gag-pol and / or env gene and / or other genes essential for replication. A lentiviral vector also may be a self-inactivating (SIN) vector.

[0159] As used herein, a “retroviral nucleic acid,” refers to a nucleic acid containing at least the minimal sequence requirements for packaging into a retroviral vector, alone or in combination with a helper cell, helper virus, or helper plasmid. In the case of “lentiviral nucleic acid” the nucleic acid refers to at least the minimal sequence requirements for packaging into a lentiviral vector, alone or in combination with a helper cell, helper virus, or helper plasmid. In some embodiments, the viral nucleic acid comprises one or more of (e.g., all of) a 5’ LTR (e.g., to promote integration), U3 (e.g., to activate viral genomic RNA transcription), R (e.g., a Tat-binding region), U5, a 3’ LTR (e.g., to promote integration), a packaging site (e.g., psi (Ψ)), RRE (e.g., to bind to Rev and promote nuclear export). The viral nucleic acid can comprise RNA (e.g., when part of a virion) or DNA (e.g., when being introduced into a source cell or after reverse transcription in a recipient cell). In some embodiments, the viral nucleic acid is packaged using a helper cell, helper virus, or helper plasmid which comprises one or more of (e.g., all of) gag, pol, and env. 28 sf-5667634186152009940

[0160] As used herein, “fusosome” refers to a lipid particle containing a bilayer of amphipathic lipids enclosing a lumen or cavity and a fusogen that interacts with the amphipathic lipid bilayer. In some embodiments, the fusosome is a membrane enclosed preparation. In some embodiments, the fusosome is derived from a source cell. A fusosome also may include an exogenous agent or a nucleic acid encoding an exogenous agent, which may be present in the lumen of the fusosome.

[0161] As used herein, “fusosome composition” refers to a composition comprising one or more fusosomes.

[0162] As used herein, “fusogen” refers to an agent or molecule that creates an interaction between two membrane enclosed lumens. In embodiments, the fusogen facilitates fusion of the membranes. In other embodiments, the fusogen creates a connection, e.g., a pore, between two lumens (e.g., a lumen of a retroviral vector and a cytoplasm of a target cell). In some embodiments, the fusogen comprises a complex of two or more proteins, e.g., wherein neither protein has fusogenic activity alone. In some embodiments, the fusogen comprises a targeting domain. Examples of fusogens include paramyxovirus F and G proteins such as those from Nipah Virus (NiV) and biologically active portions or variants thereof including any as described.

[0163] As used herein, a “re-targeted fusogen,” such as a re-targeted G protein, refers to a fusogen that comprises a targeting moiety having a sequence that is not part of the naturally-occurring form of the fusogen in which the targeting moiety targets or binds a molecule on a desired cell type. In embodiments, the fusogen comprises a different targeting moiety relative to the targeting moiety in the naturally-occurring form of the fusogen. In embodiments, the naturally-occurring form of the fusogen lacks a targeting domain, and the re-targeted fusogen comprises a targeting moiety that is absent from the naturally-occurring form of the fusogen. In embodiments, the fusogen is modified to comprise a targeting moiety. In some such embodiments, the attachment of the targeting moiety to a fusogen (e.g. G protein) may be directly or indirectly via a linker, such as a peptide linker. In embodiments, the fusogen comprises one or more sequence alterations outside of the targeting moiety relative to the naturally- occurring form of the fusogen, e.g., in a transmembrane domain, fusogenically active domain, or cytoplasmic domain.

[0164] As used herein, a “target cell” refers to a cell of a type to which it is desired that a lipid particle, such as a targeted lipid particle, delivers an exogenous agent. In embodiments, a target cell is a cell of a specific tissue type or class, e.g., an immune effector cell, e.g., a T cell. In some embodiments, a target cell is a diseased cell, e.g., a cancer cell. In some embodiments, the fusogen, e.g., re-targeted fusogen leads to preferential delivery of the exogenous agent to a target cell compared to a non-target cell.

[0165] As used herein a “non-target cell” refers to a cell of a type to which it is not desired that a lipid particle delivers an exogenous agent. In some embodiments, a non-target cell is a cell of a specific 29 sf-5667634186152009940 tissue type or class. In some embodiments, a non-target cell is a non-diseased cell, e.g., a non-cancerous cell. In some embodiments, the fusogen, e.g., re-targeted fusogen leads to lower delivery of the exogenous agent to a non-target cell compared to a target cell.

[0166] As used herein a “biologically active portion,” such as with reference to a protein such as a G protein or an F protein, refers to a portion of the protein that exhibits or retains an activity or property of the full-length of the protein. For example, a biologically active portion of an F protein retains fusogenic activity in conjunction with the G protein when each are embedded in a lipid bilayer. A biologically active portion of the G protein retains fusogenic activity in conjunction with an F protein when each is embedded in a lipid bilayer. The retained activity can include 10%-150% or more of the activity of a full-length or wild-type F protein or G protein. Examples of biologically active portions of F and G proteins include proteins with truncations of the cytoplasmic domain, such as any of the described variant NiV-F with a truncated cytoplasmic tail.

[0167] As used herein, “percent (%) amino acid sequence identity” and “homology” with respect to a peptide, polypeptide or antibody sequence are defined as the percentage of amino acid residues in a candidate sequence that are identical with the amino acid residues in the specific peptide or polypeptide sequence, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent sequence identity, and not considering any conservative substitutions as part of the sequence identity. Alignment for purposes of determining percent amino acid sequence identity can be achieved in various ways that are within the skill in the art, for instance, using publicly available computer software such as BLAST, BLAST-2, ALIGN or MEGALIGN (DNASTAR) software. Those skilled in the art can determine appropriate parameters for measuring alignment, including any algorithms needed to achieve maximal alignment over the full length of the sequences being compared.

[0168] An amino acid substitution may include but are not limited to the replacement of one amino acid in a polypeptide with another amino acid. Exemplary substitutions are shown in Table 1. Amino acid substitutions may be introduced into an antibody of interest and the products screened for a desired activity, for example, retained / improved binding. 30 sf-5667634186152009940

[0169] Amino acids may be grouped according to common side-chain properties: (1) hydrophobic: Norleucine, Met, Ala, Val, Leu, Ile; (2) neutral hydrophilic: Cys, Ser, Thr, Asn, Gln; (3) acidic: Asp, Glu; (4) basic: His, Lys, Arg; (5) residues that influence chain orientation: Gly, Pro; (6) aromatic: Trp, Tyr, Phe.

[0170] Non-conservative substitutions will entail exchanging a member of one of these classes for another class.

[0171] The term, “corresponding to” with reference to positions of a protein, such as recitation that nucleotides or amino acid positions “correspond to” nucleotides or amino acid positions in a disclosed sequence, such as set forth in the Sequence listing, refers to nucleotides or amino acid positions identified upon alignment with the disclosed sequence based on structural sequence alignment or using a standard alignment algorithm, such as the GAP algorithm. For example, corresponding residues of a similar sequence (e.g. fragment or species variant) can be determined by alignment to a reference sequence by structural alignment methods. By aligning the sequences, one skilled in the art can identify corresponding residues, for example, using conserved and identical amino acid residues as guides. 31 sf-5667634186152009940

[0172] The term “isolated” as used herein refers to a molecule that has been separated from at least some of the components with which it is typically found in nature or produced. For example, a polypeptide is referred to as “isolated” when it is separated from at least some of the components of the cell in which it was produced. Where a polypeptide is secreted by a cell after expression, physically separating the supernatant containing the polypeptide from the cell that produced it is considered to be “isolating” the polypeptide. Similarly, a polynucleotide is referred to as “isolated” when it is not part of the larger polynucleotide (such as, for example, genomic DNA or mitochondrial DNA, in the case of a DNA polynucleotide) in which it is typically found in nature, or is separated from at least some of the components of the cell in which it was produced, for example, in the case of an RNA polynucleotide. Thus, a DNA polynucleotide that is contained in a vector inside a host cell may be referred to as “isolated”.

[0173] The term “effective amount” as used herein means an amount of a pharmaceutical composition which is sufficient to significantly and positively modify the symptoms and / or conditions to be treated (e.g., provide a positive clinical response). The effective amount of an active ingredient for use in a pharmaceutical composition will vary with the particular condition being treated, the severity of the condition, the duration of treatment, the nature of concurrent therapy, the particular active ingredient(s) being employed, the particular pharmaceutically-acceptable excipient(s) and / or carrier(s) utilized, and like factors with the knowledge and expertise of the attending physician.

[0174] An “exogenous agent” as used herein with reference to a lipid particle, such as a viral vector, refers to an agent that is neither comprised by nor encoded in the corresponding wild-type virus or fusosome made from a corresponding wild-type source cell. In some embodiments, the exogenous agent does not naturally exist, such as a protein or nucleic acid that has a sequence that is altered (e.g., by insertion, deletion, or substitution) relative to a naturally occurring protein. In some embodiments, the exogenous agent does not naturally exist in the source cell. In some embodiments, the exogenous agent exists naturally in the source cell but is exogenous to the virus. In some embodiments, the exogenous agent does not naturally exist in the recipient cell. In some embodiments, the exogenous agent exists naturally in the recipient cell, but is not present at a desired level or at a desired time. In some embodiments, the exogenous agent comprises RNA or protein.

[0175] As used herein, a “promoter” refers to a cis- regulatory DNA sequence that, when operably linked to a gene coding sequence, drives transcription of the gene. The promoter may comprise a transcription factor binding sites. In some embodiments, a promoter works in concert with one or more enhancers which are distal to the gene.

[0176] As used herein, a composition refers to any mixture of two or more products, substances, or compounds, including cells. It may be a solution, a suspension, liquid, powder, a paste, aqueous, non- aqueous or any combination thereof. 32 sf-5667634186152009940

[0177] As used herein, the term “pharmaceutically acceptable” refers to a material, such as a carrier or diluent, which does not abrogate the biological activity or properties of the compound, and is relatively nontoxic, i.e., the material may be administered to an individual without causing undesirable biological effects or interacting in a deleterious manner with any of the components of the composition in which it is contained.

[0178] As used herein, the term “pharmaceutical composition” refers to a mixture of at least one compound of the invention with other chemical components, such as carriers, stabilizers, diluents, dispersing agents, suspending agents, thickening agents, and / or excipients. The pharmaceutical composition facilitates administration of the compound to an organism. Multiple techniques of administering a compound exist in the art including, but not limited to, intravenous, oral, aerosol, parenteral, ophthalmic, pulmonary and topical administration.

[0179] A “disease” or “disorder” as used herein refers to a condition where treatment is needed and / or desired.

[0180] As used herein, the terms “treat,” “treating,” or “treatment” refer to ameliorating a disease or disorder, e.g., slowing or arresting or reducing the development of the disease or disorder or reducing at least one of the clinical symptoms thereof. For purposes of this disclosure, ameliorating a disease or disorder can include obtaining a beneficial or desired clinical result that includes, but is not limited to, any one or more of: alleviation of one or more symptoms, diminishment of extent of disease, preventing or delaying spread (for example, metastasis, for example metastasis to the lung or to the lymph node) of disease, preventing or delaying recurrence of disease, delay or slowing of disease progression, amelioration of the disease state, inhibiting the disease or progression of the disease, inhibiting or slowing the disease or its progression, arresting its development, and remission (whether partial or total).

[0181] The terms “individual” and “subject” are used interchangeably herein to refer to an animal; for example a mammal. The term patient includes human and veterinary subjects. In some embodiments, methods of treating mammals, including, but not limited to, humans, rodents, simians, felines, canines, equines, bovines, porcines, ovines, caprines, mammalian laboratory animals, mammalian farm animals, mammalian sport animals, and mammalian pets, are provided. The subject can be male or female and can be any suitable age, including infant, juvenile, adolescent, adult, and geriatric subjects. In some examples, an “individual” or “subject” refers to an individual or subject in need of treatment for a disease or disorder. In some embodiments, the subject to receive the treatment can be a patient, designating the fact that the subject has been identified as having a disorder of relevance to the treatment, or being at adequate risk of contracting the disorder. In particular embodiments, the subject is a human, such as a human patient. 33 sf-5667634186152009940 III. LIPID PARTICLES COMPRISING FUSOGEN

[0182] In some embodiments, the lipid particles contain one or more fusogens. In some embodiments, the lipid particle contains an exogenous or overexpressed fusogen. In some embodiments, the fusogen is disposed in the lipid bilayer. In some embodiments, the fusogen facilitates the fusion of the lipid particle (e.g., viral vector) to a membrane. In some embodiments, the membrane is a plasma cell membrane of a target cell. In some embodiments, the lipid particle (e.g., viral vector) comprising the fusogen integrates into the membrane into a lipid bilayer of a target cell. In some embodiments, the fusogen results in mixing between lipids in the lipid particle (e.g., viral vector) and lipids in the target cell. In some embodiments, the fusogen results in formation of one or more pores between the interior of the non-cell particle and the cytosol of the target cell.

[0183] In some embodiments, fusogens are protein based, lipid based, and chemical based fusogens. In some embodiments, the lipid particle (e.g., viral vector), contain a first fusogen that is a protein fusogen and a second fusogen that is a lipid fusogen or chemical fusogen. In some embodiments, the fusogen binds a fusogen binding partner on a target cell surface. In some embodiments, the lipid particle (e.g., viral vector) is pseudotyped with the fusogen. In some examples, a virus of viral-like particle has a modification to one or more of its envelope proteins, e.g., an envelope protein is substituted with an envelope protein from another virus. In some embodiments, retroviral envelope proteins, e.g. lentiviral envelope proteins, are pseudotyped with a fusogen.

[0184] In some embodiments, the fusogen is a protein fusogen, e.g., a mammalian protein or a homologue of a mammalian protein (e.g., having 50%, 60%, 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or greater identity), a non-mammalian protein such as a viral protein or a homologue of a viral protein (e.g., having 50%, 60%, 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or greater identity), a native protein or a derivative of a native protein, a synthetic protein, a fragment thereof, a variant thereof, a protein fusion comprising one or more of the fusogens or fragments, and any combination thereof.

[0185] In some embodiments, the fusogen may include a mammalian protein. Examples of mammalian fusogens may include, but are not limited to, a SNARE family protein such as vSNAREs and tSNAREs, a syncytin protein such as Syncytin-1 (DOI: 10.1128 / JVI.76.13.6442–6452.2002), and Syncytin-2, myomaker (biorxiv.org / content / early / 2017 / 04 / 02 / 123158, doi.org / 10.1101 / 123158, doi: 10.1096 / fj.201600945R, doi:10.1038 / nature12343), myomixer (www.nature.com / nature / journal / v499 / n7458 / full / nature12343.html, doi:10.1038 / nature12343), myomerger (science.sciencemag.org / content / early / 2017 / 04 / 05 / science.aam9361, DOI: 10.1126 / science.aam9361), FGFRL1 (fibroblast growth factor receptor-like 1), Minion (doi.org / 10.1101 / 122697), an isoform of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (e.g., as 34 sf-5667634186152009940 disclosed in US 6,099,857A), a gap junction protein such as connexin 43, connexin 40, connexin 45, connexin 32 or connexin 37 (e.g., as disclosed in US 2007 / 0224176, Hap2, any protein capable of inducing syncytium formation between heterologous cells, any protein with fusogen properties, a homologue thereof, a fragment thereof, a variant thereof, and a protein fusion comprising one or more proteins or fragments thereof. In some embodiments, the fusogen is encoded by a human endogenous retroviral element (hERV) found in the human genome. Additional exemplary fusogens are disclosed in US 6,099,857A and US 2007 / 0224176, the entire contents of which are hereby incorporated by reference.

[0186] In some embodiments, the fusogen may include a non-mammalian protein, e.g., a viral protein. In some embodiments, a viral fusogen is a Class I viral membrane fusion protein, a Class II viral membrane protein, a Class III viral membrane fusion protein, a viral membrane glycoprotein, or other viral fusion proteins, or a homologue thereof, a fragment thereof, a variant thereof, or a protein fusion comprising one or more proteins or fragments thereof.

[0187] In some embodiments, Class I viral membrane fusion proteins include, but are not limited to, Baculovirus F protein, e.g., F proteins of the nucleopolyhedrovirus (NPV) genera, e.g., Spodoptera exigua MNPV (SeMNPV) F protein and Lymantria dispar MNPV (LdMNPV), and paramyxovirus F proteins.

[0188] In some embodiments, Class II viral membrane proteins include, but are not limited to, tick bone encephalitis E (TBEV E), Semliki Forest Virus E1 / E2.

[0189] In some embodiments, Class III viral membrane fusion proteins include, but are not limited to, rhabdovirus G (e.g., fusogenic protein G of the Vesicular Stomatitis Virus (VSV-G)), herpesvirus glycoprotein B (e.g., Herpes Simplex virus 1 (HSV-1) gB)), Epstein Barr Virus glycoprotein B (EBV gB), thogotovirus G, baculovirus gp64 (e.g., Autographa California multiple NPV (AcMNPV) gp64), Baboon endogenous retrovirus envelope glycoprotein (BaEV), and Borna disease virus (BDV) glycoprotein (BDV G). In some embodiments, the fusogen is Baboon endogenous retrovirus envelope glycoprotein (BaEV) or a variant thereof.

[0190] Examples of other viral fusogens, e.g., membrane glycoproteins and viral fusion proteins, include, but are not limited to: viral syncytia proteins such as influenza hemagglutinin (HA) or mutants, or fusion proteins thereof; human immunodeficiency virus type 1 envelope protein (HIV-1 ENV), gp120 from HIV binding LFA-1 to form lymphocyte syncytium, HIV gp41, HIV gp160, or HIV Trans- Activator of Transcription (TAT); viral glycoprotein VSV-G, viral glycoprotein from vesicular stomatitis virus of the Rhabdoviridae family; glycoproteins gB and gH-gL of the varicella-zoster virus (VZV); murine leukemia virus (MLV)-10A1; Gibbon Ape Leukemia Virus glycoprotein (GaLV); type G glycoproteins in Rabies, Mokola, vesicular stomatitis virus and Togaviruses; murine hepatitis virus JHM surface projection protein; porcine respiratory coronavirus spike- and membrane glycoproteins; avian infectious bronchitis spike glycoprotein and its precursor; bovine enteric coronavirus spike protein; the F 35 sf-5667634186152009940 and H, HN or G genes of Measles virus; canine distemper virus, Newcastle disease virus, human parainfluenza virus 3, simian virus 41, Sendai virus and human respiratory syncytial virus; gH of human herpesvirus 1 and simian varicella virus, with the chaperone protein gL; human, bovine and cercopithicine herpesvirus gB; envelope glycoproteins of Friend murine leukemia virus and Mason Pfizer monkey virus; mumps virus hemagglutinin neuraminidase, and glycoproteins F1 and F2; membrane glycoproteins from Venezuelan equine encephalomyelitis; paramyxovirus F protein; SIV gp160 protein; Ebola virus G protein; or Sendai virus fusion protein, or a homologue thereof, a fragment thereof, a variant thereof, and a protein fusion comprising one or more proteins or fragments thereof.

[0191] Non-mammalian fusogens include viral fusogens, homologues thereof, fragments thereof, and fusion proteins comprising one or more proteins or fragments thereof. Viral fusogens include class I fusogens, class II fusogens, class III fusogens, and class IV fusogens. In embodiments, class I fusogens such as human immunodeficiency virus (HIV) gp41, have a characteristic post fusion conformation with a signature trimer of α-helical hairpins with a central coiled-coil structure. Class I viral fusion proteins include proteins having a central post fusion six-helix bundle. Class I viral fusion proteins include influenza HA, parainfluenza F, HIV Env, Ebola GP, hemagglutinins from orthomyxoviruses, F proteins from paramyxoviruses (e.g. Measles, (Katoh et al. BMC Biotechnology 2010, 10:37)), ENV proteins from retroviruses, and fusogens of filoviruses and coronaviruses. In embodiments, class II viral fusogens such as dengue E glycoprotein, have a structural signature of β- sheets forming an elongated ectodomain that refolds to result in a trimer of hairpins. In embodiments, the class II viral fusogen lacks the central coiled coil. Class II viral fusogen can be found in alphaviruses (e.g., E1 protein) and flaviviruses (e.g., E glycoproteins). Class II viral fusogens include fusogens from Semliki Forest virus, Sinbis, rubella virus, and dengue virus. In embodiments, class III viral fusogens such as the vesicular stomatitis virus G glycoprotein, combine structural signatures found in classes I and II. In embodiments, a class III viral fusogen comprises α helices (e.g., forming a six-helix bundle to fold back the protein as with class I viral fusogens), and β sheets with an amphiphilic fusion peptide at its end, reminiscent of class II viral fusogens. Class III viral fusogens can be found in rhabdoviruses and herpesviruses. In embodiments, class IV viral fusogens are fusion-associated small transmembrane (FAST) proteins (doi:10.1038 / sj.emboj.7600767, Nesbitt, Rae L., "Targeted Intracellular Therapeutic Delivery Using Liposomes Formulated with Multifunctional FAST proteins" (2012). Electronic Thesis and Dissertation Repository. Paper 388), which are encoded by nonenveloped reoviruses. In embodiments, the class IV viral fusogens are sufficiently small that they do not form hairpins (doi: 10.1146 / annurev-cellbio- 101512-122422, doi:10.1016 / j.devcel.2007.12.008).

[0192] Additional exemplary fusogens are disclosed in US 9,695,446, US 2004 / 0028687, US 6,416,997, US 7,329,807, US 2017 / 0112773, US 2009 / 0202622, WO 2006 / 027202, and US 2004 / 0009604, the entire contents of all of which are hereby incorporated by reference. 36 sf-5667634186152009940

[0193] In some embodiments, the fusogen is a poxviridae fusogen.

[0194] In some embodiments, the lipid particle comprises a fusogen that is a paramyxovirus envelope attachment proteins. In some embodiments, the lipid particle comprises a paramyxovirus envelope attachment protein exposed on the surface of the targeted lipid particle. In some embodiments, the lipid particle comprises a fusogen that is a retargeted attachment protein exposed on the surface of the targeted lipid particle.

[0195] In some embodiments, the paramyxovirus envelope attachment protein and / or retargeted attachment protein provided herein exhibit fusogenic activity to a target cell, such as to deliver an exogenous agent or nucleic acid exogenous agent to the target cell.

[0196] In some embodiments, the paramyxovirus attachment protein is or comprises a hemagglutinin-neuraminidase (HN) from a respiratory paramyxovirus. In some embodiments, the respiratory paramyxovirus is a Sendai virus. The HN glycoproteins of Sendai viruses function to attach to sialic acids via the HN protein, and to mediate cell fusion for entry to cells via the F (fusion) protein. In some embodiments, the paramyxovirus attachment protein is or comprises a HN protein from the murine parainfluenza virus type 1 (See e.g., US Patent No.10704061).

[0197] In some embodiments, the paramyxovirus attachment protein is or comprises a Nipah virus protein G, a measles protein H, a tupaia paramyxovirus H protein, a paramyxovirus G protein, a paramyxovirus H protein, a paramyxovirus HN protein, a Morbillivirus H protein, a respirovirus HN protein, a Sendai HN protein, a rubulavirus HN protein, an avulavirus HN protein, or a derivative thereof. In some embodiments, the paramyxovirus attachment protein is or comprises a sequence chosen from Nipah virus G proteins, measles virus H proteins, tupaia paramyxovirus H proteins, paramyxovirus G proteins and H proteins and HN proteins, Hendra virus G proteins, Henipavirus G proteins, Morbillivirus H proteins, respirovirus HN protein, a Sendai virus HN protein, rubulavirus HN proteins, or avulavirus HN proteins, or a derivative thereof, or any combination thereof.

[0198] In some embodiments, the lipid particles, such as viral vectors or viral-like particles, contain one or more attachment proteins (e.g., fusogens). In some embodiments, the lipid particle, e.g. viral vector or viral-like particle, contains one or more exogenous or overexpressed attachment protein (e.g., fusogen). In some embodiments, the one or more fusogen is disposed in the lipid bilayer. In some embodiments, the one or more fusogen facilitates the fusion of the lipid particle to a membrane. In some embodiments, the lipid particle comprises one or more attachment proteins that are retargeted, such as an attachment protein that is linked to at least two targeting moieties, such as a first and second targeting moiety.

[0199] In some embodiments, the lipid particle comprises an attachment protein that is a first fusogen (e.g., paramyxovirus attachment protein) that is retargeted, such as a fusogen (e.g., paramyxovirus envelope attachment protein) that is linked to at least two targeting moieties, such as a 37 sf-5667634186152009940 first and second targeting moiety. In some embodiments, the lipid particle further comprises at least one fusion protein.

[0200] In some embodiments, the lipid particle comprises at least two fusogens (co-fusogens). In some embodiments, the lipid particle comprises at least two fusogens (e.g., paramyxovirus envelope attachment proteins as described below) exposed on the surface of the targeted lipid particle. In some embodiments, the lipid particle comprises at least two retargeted fusogens (e.g., attachment proteins) exposed on the surface of the targeted lipid particle. In some embodiments, the lipid particle further comprises at least one fusion protein.

[0201] In some embodiments, the fusogens (e.g., paramyxovirus envelope attachment proteins) and / or retargeted fusogens (e.g., attachment proteins provided herein) exhibit fusogenic activity to a target cell, such as to deliver an exogenous agent or nucleic acid exogenous agent to the target cell. A. Paramyxovirus Fusogen

[0202] In some embodiments, the lipid particle comprises a fusogen that is a paramyxovirus fusogen. In some embodiments, the lipid particle comprises a paramyxovirus fusogen exposed on the surface of the targeted lipid particle. In some embodiments, the lipid particle comprises a paramyxovirus fusogen that is a retargeted attachment protein exposed on the surface of the targeted lipid particle.

[0203] In some embodiments, the paramyxovirus fusogen and / or retargeted paramyxovirus fusogen provided herein exhibit fusogenic activity to a target cell, such as to deliver an exogenous agent or nucleic acid exogenous agent to the target cell.

[0204] In some embodiments, the paramyxovirus fusogen is or comprises a hemagglutinin- neuraminidase (HN) from a respiratory paramyxovirus. In some embodiments, the respiratory paramyxovirus is a Sendai virus. The HN glycoproteins of Sendai viruses function to attach to sialic acids via the HN protein, and to mediate cell fusion for entry to cells via the F (fusion) protein. In some embodiments, the paramyxovirus attachment protein is or comprises a HN protein from the murine parainfluenza virus type 1 (See e.g., US Patent No.10704061).

[0205] In some embodiments, the paramyxovirus fusogen is or comprises a Nipah virus protein G, a measles protein H, a tupaia paramyxovirus H protein, a paramyxovirus G protein, a paramyxovirus H protein, a paramyxovirus HN protein, a Morbillivirus H protein, a respirovirus HN protein, a Sendai HN protein, a rubulavirus HN protein, an avulavirus HN protein, or a derivative thereof. In some embodiments, the paramyxovirus attachment protein is or comprises a sequence chosen from Nipah virus G proteins, measles virus H proteins, tupaia paramyxovirus H proteins, paramyxovirus G proteins and H proteins and HN proteins, Hendra virus G proteins, Henipavirus G proteins, Morbillivirus H proteins, respirovirus HN protein, a Sendai virus HN protein, rubulavirus HN proteins, or avulavirus HN proteins, or a derivative thereof, or any combination thereof. 38 sf-5667634186152009940

[0206] In some embodiments, the fusogens may be derived from a paramyxovirus. In some embodiments, the fusogen includes a fusogen derived from a paramyxovirus envelope attachment protein, such as a G, H or HN protein, and at least one fusion (F) protein. In some embodiments, the attachment protein is a retargeted attachment protein that is fused to a targeting moiety directed against a target molecule on the surface of a cell. In some embodiments, an attachment protein can include a protein that is variant attachment protein containing one or more mutations (e.g. amino acid substitutions) to reduce or ablate the native tropism relative to the wild-type paramyxovirus envelope attachment protein not comprising the one or more mutations.

[0207] In other aspects, provided herein is a lipid particle in which a retargeted attachment protein includes a targeting moiety directed to a target molecule on the surface of the cells and the lipid particle, in some embodiments the attachment protein is a variant attachment protein that comprises one or more mutations to reduce native tropism relative to the wild-type paramyxovirus envelope attachment protein not comprising the one or more mutations. In some embodiments, the retargeted attachment protein comprises a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule on a T cell, such as CD4 or CD8.

[0208] In some embodiments, the targeting moiety, such as each of the first targeting moiety and the second targeting moiety, are independently selected from the group consisting of an antibody or antigen- binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide.

[0209] In some embodiments, any of the provided lipid particles also contains at least one paramyxovirus fusion (F) protein or a biologically active portion thereof embedded in the lipid bilayer. In some embodiments, the F protein is from a Paramyxovirus, a Henipavirus (e.g., Hendra (HeV), Nipah (NiV) virus, Cedar henipavirus (CedV), Kumasi virus (KV), Mòjiāng virus (MojV), or Langya virus), or is a biologically active portion thereof or is a variant or mutant thereof. In particular embodiments, the F protein is from a Nipah (NiV) virus.

[0210] In naturally occurring paramyxoviruses, the fusion (F) and attachment (G, H, or HN) glycoproteins mediate cellular entry of paramyxovirus, such as Nipah virus. In some embodiments, the combination of an F protein, such as a NiV-F protein, and variant NiV-G protein as provided herein is able to mediate cellular entry of a provided lipid particle (e.g. lentiviral vector).

[0211] The F protein, such as Nipah Virus F protein, also known as NiV-F, is a class I fusion protein that has structural and functional features in common with fusion proteins of many families (e.g., HIV-1 gp41 or influenza virus hemagglutinin [HA]), such as an ectodomain with a hydrophobic fusion peptide and two heptad repeat regions (White JM et al.2008. Crit Rev Biochem Mol Biol 43:189–219). F proteins are synthesized as inactive precursors F0and are activated by proteolytic cleavage into the two disulfide-linked subunits F1and F2(Moll M. et al.2004. J. Virol.78(18): 9705-9712). 39 sf-5667634186152009940

[0212] In some embodiments, the lipid particle comprises a paramyxovirus envelope attachment protein comprising a G protein. G proteins are attachment proteins of henipavirus (e.g. Nipah virus or Hendra virus) that are type II transmembrane glycoproteins containing an N-terminal cytoplasmic tail, a transmembrane domain, an extracellular stalk, and a globular head (Liu, Q. et al.2015. Journal of Virology, 89(3):1838-1850). The Nipah virus attachment protein, NiV-G, recognizes the receptors EphrinB2 and EphrinB3. Binding of the receptor to NiV-G triggers a series of conformational changes that eventually lead to the triggering of NiV-F, which exposes the fusion peptide of NiV-F, allowing another series of conformational changes that lead to virus-cell membrane fusion (Stone J.A. et al.2016. J Virol.90(23): 10762-10773). EphrinB2 was previously identified as the primary NiV receptor (Negrete et al., 2005), as well as ephrinB3 as an alternate receptor (Negrete et al., 2006). In fact, wild-type NiV-G has a high affinity for ephrinB2 and B3, with affinity binding constants (Kd) in the picomolar range (Negrete et al., 2006) (Kd=0.06 nM and 0.58 nM for cell surface expressed ephrinB2 and B3, respectively). In some embodiments, the G protein is from a Paramyxovirus, a Henipavirus (e.g., Hendra (HeV), Nipah (NiV) virus, Cedar henipavirus (CedV), Kumasi virus (KV), Mòjiāng virus (MojV), or Langya virus), or is a biologically active portion thereof or is a variant or mutant thereof. In particular embodiments, the G protein is from a Nipah (NiV) virus.

[0213] In some embodiments, the paramyxovirus envelope attachment protein comprising a G protein may be further linked to a targeting moiety as a retargeted attachment protein to facilitate specific targeting of the lipid particle to a target molecule for fusion with a desired target cell. Thus, the provided embodiments, the paramyxovirus envelope attachment protein comprising a G protein may be re-targeted as retargeted attachment proteins to any desired cell type for specific targeting of a lipid particle (e.g. lentiviral vector) and, in some cases, specific delivery to a target cell of a transgene or heterologous protein contained therein.

[0214] Thus, also provided herein are lipid particles containing a lipid bilayer enclosing a lumen or cavity and a paramyxovirus envelope attachment protein (e.g., G protein) containing an antigen binding domain or a biologically active portion thereof, such as a single domain antibody (sdAb) variable domain, in which the retargeted G glycoprotein is embedded in the lipid bilayer of the lipid particles. In particular embodiments, the binding domain is an antibody with the ability to bind, such as specifically bind, to a desired target molecule. Exemplary binding domains are described in Section III.A.1.B.

[0215] The efficiency of transduction of lipid particles can be improved by engineering mutations in one or both of NiV-F and NiV-G. Several such mutations have been previously described (see, e.g., Lee at al., 2011, Trends in Microbiology). This is useful, for example, for maintaining the specificity and picomolar affinity of NiV-G for ephrinB2 and / or B3. Additionally, mutations in NiV-G that completely abrogate ephrinB2 and B3 binding, but that do not impact the association of this NiV-G with NiV-F, have been identified (Aguilar, et al. J Biol Chem.2009;284(3):1628-1635.; Weise et al. J Virol. 40 sf-5667634186152009940 2010;84(15):7634-764; Negrete et al.. J Virol.2007;81(19):10804-10814; Negrete et al. PLoS Pathog. 2006; Guillaume et al., J. Virol 2006, 80 (15) 7546-7554 In some cases, methods to improve targeting of lipid particles can be achieved by fusion of a binding molecule with a G protein (e.g. NiV-G, including a NiV-G with mutations to abrogate Ephrin B2 and Ephrin B3 binding). This does allow for altered G protein tropism allowing for targeting of other desired cell types that are not ephrinB2+ through the addition of the binding molecule directed against a different cell surface molecule. Thus, in provided aspects, a paramyxovirus envelope attachment protein is a variant NiV-G protein that may further contain a mutation to reduce or abrogate binding to Ephrin B2 and / B3. In some embodiments, the mutations can include one or more of mutations E501A, W504A, Q530A and E533A, with reference to numbering of wild-type NiV-G set forth in SEQ ID NO:1.

[0216] It has been reported that the henipavirus F proteins from various species exhibit compatibility with G proteins from other species to trigger fusion (Brandel-Tretheway et al. Journal of Virology.2019.93(13):e00577-19). In some aspects of the provided lipid particles (e.g. lentiviral vector), the F protein is heterologous to the G protein, i.e. the F and G protein or biologically active portions are from different henipavirus species. For example, the G protein is from Hendra virus and the F protein is a NiV-F as described. In other aspects, the F and / or G protein can be retargeted F and / or G protein containing regions of F and / or G proteins from different species of Henipavirus. In some embodiments, switching a region of amino acid residues of the F protein from one species of Henipavirus to another can result in fusion to the G protein of the species comprising the amino acid insertion. (Brandel-Tretheway et al.2019). In some cases, the chimeric F and / or G protein contains an extracellular domain from one henipavirus species and a transmembrane and / or cytoplasmic domain from a different henipavirus species. For example, the F protein contains an extracellular domain of Hendra virus and a transmembrane / cytoplasmic domain of Nipah virus. 1. Paramyxovirus Attachment Proteins

[0217] In some embodiments, the lipid particles provided herein comprise a paramyxovirus envelope attachment protein. In some embodiments, the paramyxovirus envelope attachment protein may be derived from an envelope glycoprotein G, H and / or HN of the Paramyxoviridae family. In some embodiments, the paramyxovirus attachment protein may be a variant paramyxovirus attachment protein that contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus attachment protein. In some embodiments, the paramyxovirus attachment protein, such as a variant paramyxovirus attachment protein, is retargeted.

[0218] In some embodiments, the lipid particles provided herein comprise more than one paramyxovirus envelope attachment protein, such as 1, 2 or 3 paramyxovirus envelope attachment protein. In some embodiments, the lipid particles provided herein comprise a first paramyxovirus 41 sf-5667634186152009940 envelope attachment protein, and a second paramyxovirus envelope attachment protein. In some embodiments, at least one of the paramyxovirus attachment protein is retargeted, such as by fusion with a targeting moiety. In some embodiments, such a retargeted paramyxovirus attachment protein also typically contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus attachment protein. In some embodiments, at least one of the paramyxovirus attachment protein is modified not to exhibit target tropism, in which the protein contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus attachment protein and in which such protein also is not fused with a targeting moiety. In some embodiments, the first and second paramyxovirus envelope attachment protein are displayed on the surface of the lipid particle, such as embedded in the lipid bilayer, as separate proteins. In some embodiments, the first and second paramyxovirus envelope attachment protein are a fusion protein in which the first and second paramyxovirus envelope attachment protein are linked in tandem, in some cases via a linker. In some embodiments, the paramyxovirus envelope attachment protein may be derived from an envelope glycoprotein G, H and / or HN of the Paramyxoviridae family.

[0219] In some embodiments, the lipid particles provided herein comprise a first paramyxovirus envelope attachment protein, a second paramyxovirus envelope attachment protein, and a third paramyxovirus envelope attachment protein. In some embodiments, at least two of the paramyxovirus attachment protein is retargeted, such as by fusion with a targeting moiety. In some embodiments, such a retargeted paramyxovirus attachment protein also typically contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus attachment protein. In some embodiments, at least one of the paramyxovirus attachment protein is modified not to exhibit target tropism, in which the protein contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus attachment protein and in which such protein also is not fused with a targeting moiety. In some embodiments, the first, second, and third paramyxovirus envelope attachment protein are each displayed on the surface of the lipid particle, such as embedded in the lipid bilayer, as separate proteins. In some embodiments, at least two of the paramyxovirus envelope attachment proteins are a fusion protein in which the two paramyxovirus envelope attachment protein are linked in tandem, in some cases via a linker. In some embodiments, each of the first, second, and third paramyxovirus envelope attachment protein may independently be derived from an envelope glycoprotein G, H and / or HN of the Paramyxoviridae family.

[0220] In some embodiments, the lipid particles provided herein comprise a first paramyxovirus envelope attachment protein, a second paramyxovirus envelope attachment protein, a third paramyxovirus envelope attachment protein, and one or more additional paramyxovirus envelope attachment proteins, such as a fourth paramyxovirus envelope attachment protein, or a fourth and fifth paramyxovirus envelope attachment protein, or a fourth, fifth, and sixth paramyxovirus envelope 42 sf-5667634186152009940 attachment protein, or beyond. In some embodiments, each of the paramyxovirus envelope attachment proteins may independently be an envelope glycoprotein G, H and / or HN of the Paramyxoviridae family. A) G Proteins

[0221] In some embodiments, the paramyxovirus envelope attachment protein is an attachment glycoprotein G (G protein) or biologically active portion thereof. In some embodiments, the paramyxovirus G protein may be a variant paramyxovirus G protein that contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus G protein. In some embodiments, the paramyxovirus G protein is retargeted.

[0222] In some embodiments, the lipid particle comprises a retargeted attachment protein, exposed on the surface of the targeted lipid particle. In some embodiments, the retargeted attachment protein is or comprises a paramyxovirus attachment protein, wherein the paramyxovirus attachment protein is an attachment glycoprotein G (G protein) or biologically active portion thereof. In some embodiments, the retargeted attachment protein is or comprises a paramyxovirus attachment protein, wherein the paramyxovirus attachment protein is an attachment glycoprotein G (G protein) or biologically active portion thereof, and comprises a targeting moiety directed to a target molecule, e.g., a binding domain or a binding agent, expressed on the surface of a target cell.

[0223] In some embodiments, the paramyxovirus envelope attachment protein, first paramyxovirus envelope attachment protein, and / or second paramyxovirus envelope attachment protein and / or the third paramyxovirus envelope attachment protein and / or the fourth paramyxovirus envelope attachment protein and / or the fifth paramyxovirus envelope attachment protein and / or the sixth paramyxovirus envelope attachment protein, and / or any additional paramyxovirus envelope attachment protein is an attachment glycoprotein G (G protein) or biologically active portion thereof. In some embodiment, the retargeted attachment protein comprises a first paramyxovirus envelope attachment protein G.

[0224] In some embodiments, the lipid particle comprises a retargeted attachment protein, a first retargeted attachment protein, and / or second retargeted attachment protein exposed on the surface of the targeted lipid particle. In some embodiments, the lipid particle further comprises a third retargeted attachment protein exposed on the surface of the targeted lipid particle. In some embodiments, the lipid particle further comprises a third retargeted attachment protein and a fourth retargeted attachment protein exposed on the surface of the targeted lipid particle. In some embodiments, the lipid particle further comprises a third retargeted attachment protein, a fourth retargeted attachment protein, and a fifth retargeted attachment protein exposed on the surface of the targeted lipid particle. In some embodiments, the lipid particle further comprises a third retargeted attachment protein, a fourth retargeted attachment protein, a fifth retargeted attachment protein, and one or more additional retargeted attachment proteins, exposed on the surface of the targeted lipid particle. In some embodiments, the retargeted attachment 43 sf-5667634186152009940 protein is or comprises a paramyxovirus attachment protein, wherein the paramyxovirus attachment protein is an attachment glycoprotein G (G protein) or biologically active portion thereof. In some embodiments, the retargeted attachment protein is or comprises a paramyxovirus attachment protein, wherein the paramyxovirus attachment protein is an attachment glycoprotein G (G protein) or biologically active portion thereof, and comprises a targeting moiety directed to a target molecule, e.g., a binding domain or a binding agent, expressed on the surface of a target cell.

[0225] In some embodiments, the lipid particles provided herein comprise a first paramyxovirus envelope G protein, and a second paramyxovirus envelope G protein. In some embodiments, the paramyxovirus attachment protein is retargeted, such as by fusion with a targeting moiety. In some embodiments, such a retargeted paramyxovirus G protein also typically contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus G protein. In some embodiments, at least one of the paramyxovirus G protein is modified not to exhibit target tropism, in which the protein contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus G protein and in which such protein also is not fused with a targeting moiety. In some embodiments, the first and second paramyxovirus envelope G protein are displayed on the surface of the lipid particle, such as embedded in the lipid bilayer, as separate proteins. In some embodiments, the first and second paramyxovirus envelope G protein are a fusion protein in which the first and second paramyxovirus envelope G protein are linked in tandem, in some cases via a linker.

[0226] In some embodiments, the lipid particles provided herein comprise a first paramyxovirus envelope G protein, a second paramyxovirus envelope G protein, and a third paramyxovirus envelope G protein. In some embodiments, at least two of the paramyxovirus G protein is retargeted, such as by fusion with a targeting moiety. In some embodiments, such a retargeted paramyxovirus G protein also typically contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus G protein. In some embodiments, at least one of the paramyxovirus G protein is modified not to exhibit target tropism, in which the protein contains one or more mutations to ablate natural tropism of the wildtype paramyxovirus G protein and in which such protein also is not fused with a targeting moiety. In some embodiments, the first, second, and third paramyxovirus envelope G protein are each displayed on the surface of the lipid particle, such as embedded in the lipid bilayer, as separate proteins. In some embodiments, at least two of the paramyxovirus envelope G proteins are a fusion protein in which the two paramyxovirus envelope G protein are linked in tandem, in some cases via a linker.

[0227] The envelope attachment G proteins are type II transmembrane glycoproteins containing an N-terminal cytoplasmic tail (e.g. corresponding to amino acids 1-49 of SEQ ID NO:1), a transmembrane domain (e.g. corresponding to amino acids 50-70 of SEQ ID NO:1), and an extracellular domain containing an extracellular stalk (e.g. corresponding to amino acids 71-187 of SEQ ID NO:1), and a globular head (corresponding to amino acids 188-602 of SEQ ID NO:1). The N-terminal cytoplasmic 44 sf-5667634186152009940 domain is within the inner lumen of the lipid bilayer and the C-terminal portion is the extracellular domain that is exposed on the outside of the lipid bilayer. Regions of the stalk in the C-terminal region (e.g. corresponding to amino acids 71-187 of SEQ ID NO: 1) have been shown to be involved in interactions with F protein and triggering of F protein fusion (Liu et al.2015 J of Virology 89:1838). In wild-type G protein, the globular head mediates receptor binding to henipavirus entry receptors Ephrin B2 and Ephrin B3, but is dispensable for membrane fusion (Brandel-Tretheway et al. Journal of Virology.2019.93(13)e00577-19).

[0228] In some embodiments herein, tropism of the G protein is altered by linkage of the G protein or biologically active fragment thereof (e.g. cytoplasmic truncation) to a sdAb variable domain. Binding of the G protein to a binding partner can trigger fusion mediated by a compatible paramyxovirus fusion protein (e.g., F protein) or biologically active portion thereof (such as any of the F proteins described in II.B below). G protein sequences disclosed herein are predominantly disclosed as expressed sequences including an N-terminal methionine required for start of translation. As such N-terminal methionines are commonly cleaved co- or post-translationally, the mature protein sequences for all G protein sequences disclosed herein are also contemplated as lacking the N-terminal methionine.

[0229] G glycoproteins are highly conserved between henipavirus species. For example, the G protein of NiV and HeV viruses share 79% amino acid identity. Studies have shown a high degree of compatibility among G proteins with F proteins of different species as demonstrated by heterotypic fusion activation (Brandel-Tretheway et al. Journal of Virology.2019). As described, a lipid particle can contain at least two envelope attachment proteins (e.g., co-fusogens). In particular embodiments, the F protein or the functionally active variant or biologically active portion thereof retains fusogenic activity in conjunction with the at least two envelope attachment proteins (e.g., co-fusogens that are paramyxovirus attachment protein Gs) as provided, such as any set forth below. Fusogenic activity includes the activity of the paramyxovirus fusion protein (e.g., F protein) in conjunction with a G protein to promote or facilitate fusion of two membrane lumens, such as the lumen of the lipid particle provided herein (e.g. having embedded in its lipid bilayer, such as exposed on its surface, at least two G proteins and a F protein), and a cytoplasm of a target cell, e.g. a cell that contains a surface receptor or molecule that is recognized or bound by the G protein.

[0230] Exemplary Henipavirus protein G sequences are provided in Table 2 Table 2. Henipavirus protein G sequence clusters. Column 1, Genbank ID includes the Genbank ID of the whole genome sequence of the virus that is the centroid sequence of the cluster. Column 2, nucleotides of CDS provides the nucleotides corresponding to the CDS of the gene in the whole genome. Column 3, Full Gene Name, provides the full name of the gene including Genbank ID, virus species, strain, and protein name. Column 4, Sequence, provides the amino acid sequence of the 45 sf-5667634186152009940 gene. Column 5, #Sequences / Cluster, provides the number of sequences that cluster with this centroid sequence. Column 6 provides the SEQ ID numbers for the described sequences.46 sf-566763418615200994047 sf-5667634186152009940

[0231] In some embodiments, at least one G protein has a sequence set forth in any of SEQ ID NOS: 1, 561, 562, 563, or 564 or is a functionally active variant or biologically active portion thereof that has a sequence that is at least at or about 80%, at least at or about 81%, at least at or about 82%, at least at or about 83%, at least at or about 84%, at least at or about 85%, at least at or about 86%, at least at or about 87%, at least at or about 88%, at least at or about 89%, at least at or about 90%, at least at or about 91%, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at least at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% identical to any one of SEQ ID NOS: 1, 561, 562, 563, or 564.

[0232] In particular embodiments, the paramyxovirus envelope attachment protein (e.g., G protein) or functionally active variant or biologically active portion is a protein that retains fusogenic activity in conjunction with a paramyxovirus fusion protein (e.g., F protein), such as a NiV-F protein described herein. Fusogenic activity includes the activity of the paramyxovirus envelope attachment protein (e.g., G protein) in conjunction with a paramyxovirus fusion protein (e.g., F protein) to promote or facilitate fusion of two membrane lumens, such as the lumen of the targeted lipid particle having embedded in its lipid bilayer a paramyxovirus fusion protein (e.g., F protein) and paramyxovirus envelope attachment protein (e.g., G protein), and a cytoplasm of a target cell, e.g. a cell that contains a surface receptor or molecule that is recognized or bound by the targeted envelope protein. In some embodiments, the paramyxovirus fusion protein (e.g., F protein) and the paramyxovirus envelope attachment protein (e.g., G protein) are from the same paramyxovirus species (e.g. the same Henipavirus species such as NiV-G and NiV-F).

[0233] In some embodiments, the NiV-G is a variant NiV-G proteins that contain an altered cytoplasmic tail compared to native NiV-G (e.g. SEQ ID NO:5) that are or can be incorporated into a lipid particle, such as a viral particle, including a lentiviral particle or lentiviral-like particle. The cytoplasmic tail of NiV-G corresponds to amino acids 1-45 of SEQ ID NO:5. In some cases, it is understood that the N-terminal methionine of NiV-G, or a variant NiV-G, as described herein can be cleaved and the cytoplasmic tail lacks an initial N-terminal methionine. For instance, in some embodiments, the cytoplasmic tail of wild-type NiV-G may correspond to amino acids 2-45 of SEQ ID NO:5, and the variant NiV-G protein contains a cytoplasmic tail that is altered compared to amino acids 2-45 of SEQ ID NO:5. In some embodiments, the variant NiV-G contains a modified cytoplasmic tail in which the native cytoplasmic tail is truncated or is replaced by a heterologous cytoplasmic tail.

[0234] Non-limiting examples of variant NiV-G proteins, including truncated NiV-G or NiV-G with a altered or modified cytoplasmic tail, are described in WO2013148327, WO2017182585, or 48 sf-5667634186152009940 PCT / US2022 / 081872. Further exemplary variant NiV-G proteins are described in Bender et al.2016 PLoS Pathol 12(6):e1005641.

[0235] In some embodiments, at least one G protein is a variant G protein that is a functionally active variant or biologically active portion containing one or more amino acid mutations, such as one or more amino acid insertions, deletions, substitutions or truncations. In some embodiments, the mutations described herein relate to amino acid insertions, deletions, substitutions or truncations of amino acids compared to a reference G protein sequence. In some embodiments, the reference G protein sequence is the wild-type sequence of a G protein or a biologically active portion thereof. In some embodiments, at least one functionally active variant or the biologically active portion thereof is a variant of a wild-type Hendra (HeV) virus G protein, a wild-type Nipah (NiV) virus G-protein (NiV- G), a wild-type Cedar (CedPV) virus G-protein, a wild-type Mojiang virus G-protein, a wild-type bat Paramyxovirus G-protein or biologically active portion thereof. In some embodiments, the wild-type G protein has the sequence set forth in any one of SEQ ID NOS: 1, 561, 562, 563, or 564.

[0236] In some embodiments, at least one G protein is a variant G protein that is a biologically active portion that is an N-terminally and / or C-terminally truncated fragment of a wild-type Hendra (HeV) virus G protein, a wild-type Nipah (NiV) virus G-protein (NiV-G), a wild-type Cedar (CedPV) virus G-protein, a wild-type Mojiang virus G-protein, a wild-type bat Paramyxovirus G-protein. In particular embodiments, the truncation is an N-terminal truncation of all or a portion of the cytoplasmic domain. In some embodiments, at least one variant G protein is a biologically active portion that is truncated and lacks up to 49 contiguous amino acid residues at or near the N-terminus of the wild-type G protein, such as a wild-type G protein set forth in any one of SEQ ID NOS: 1, 561, 562, 563, or 564. In some embodiments, at least one variant G protein is truncated and lacks up to 49 contiguous amino acids, such as up to 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 30, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1 contiguous amino acids at the N-terminus of the wild-type G protein.

[0237] In some embodiments, at least one G protein is a wild-type Nipah virus G (NiV-G) protein or a Hendra virus G protein, or is a functionally active variant or biologically active portion thereof. In some embodiments, at least one G protein is a NiV-G protein that has the sequence set forth in SEQ ID NO:1, or is a functional variant or a biologically active portion thereof that has an amino acid sequence having at least at or about 80%, at least at or about 81%, at least at or about 82%, at least at or about 83%, at least at or about 84%, at least at or about 85%, at least at or about 86%, at least at or about 87%, at least at or about 88%, at least at or about 89%, at least at or about 90%, at least at or about 91%, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, at least at or about 99% sequence identity to SEQ ID NO:1. 49 sf-5667634186152009940

[0238] In some embodiments, at least one G protein is a variant NiV-G that comprises a modified cytoplasmic tail which comprises a truncated cytoplasmic tail from a glycoprotein from the same Nipah virus. In some embodiments, the variant NiV-G contains a modified cytoplasmic tail in which at least a part of the native cytoplasmic tail (e.g. corresponding to amino acids 1-45 of SEQ ID NO:5) is a truncated portion thereof from a glycoprotein from Nipah Virus. In some embodiments, the cytoplasmic tail is a truncated portion thereof that is at least 5 amino acids in length. from or from about 5-44, from or from about 5-40, from or from about 5-30, from or from about 5-20, from or from about 5-10, from or from about 10-44, from or from about 10-40, from or from about 10-30, from or from about 10-20, from or from about 20-44, from or from about 20-40, from or from about 20-30, from or from about 30-44, from or from about 30-40, from or from about 40-44amino acids in length. In some embodiments, the truncated portion thereof is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43 or 44 amino acids in length. In some embodiments, the variant NiV-G has a cytoplasmic tail that is a truncated NiV-G cytoplasmic tail. In some embodiments, the truncated NiV-G cytoplasmic tail has a deletion of up to 40, up to 35, up to 30, up to 29, up to 28, up to 27, up to 26, up to 25, up to 24, up to 23, up to 22, up to 21, up to 20, up to 19, up to 18, up to 17, up to 16, up to 15, or up to 14 contiguous amino acid residues at or near the N- terminus of the wild-type NiV-G cytoplasmic tail set forth in SEQ ID NO: 28. In some embodiments, the variant NiV-G has a deletion of between 5 and 41 contiguous amino acid residues at or near the N- terminus of the wild-type NiV-G protein cytoplasmic tail set forth in SEQ ID NO: 4. In some embodiments, the variant NiV-G has a deletion of between 26 and 40 contiguous amino acid residues at or near the N-terminus of the wild-type NiV-G protein cytoplasmic tail set forth in SEQ ID NO: 4.

[0239] In some embodiments, at least one G protein is a variant NiV-G protein that is a biologically active portion of a wild-type NiV-G. In some embodiments, the biologically active portion is an N-terminally truncated fragment. In some embodiments, the variant NiV-G protein is truncated and lacks up to 5 contiguous amino acid residues at or near the N-terminus of the wild- type NiV-G protein, such as compared to wild-type NiV-G set forth in SEQ ID NO: 1. In some embodiments, the variant NiV-G protein is truncated and lacks up to 10 contiguous amino acid residues at or near the N-terminus of the wild-type NiV-G protein, such as compared to wild-type NiV-G set forth in SEQ ID NO: 1. In some embodiments, the variant NiV-G protein is truncated and lacks up to 15 contiguous amino acid residues at or near the N-terminus of the wild-type NiV-G protein, such as compared to wild-type NiV-G set forth in SEQ ID NO: 1. n some embodiments, the variant NiV-G protein is truncated and lacks up to 20 contiguous amino acid residues at or near the N-terminus of the wild-type NiV-G protein, such as compared to wild-type NiV-G set forth in SEQ ID NO: 1. In some embodiments, the variant NiV-G protein is truncated and lacks up to 25 contiguous amino acid residues at or near the N-terminus of the wild-type NiV-G protein, such as 50 sf-5667634186152009940 compared to wild-type NiV-G set forth in SEQ ID NO: 1. In some embodiments, the variant NiV-G protein is truncated and lacks up to 30 contiguous amino acid residues at or near the N-terminus of the wild-type NiV-G protein, such as compared to wild-type NiV-G set forth in SEQ ID NO: 1. In some embodiments, the variant NiV-G protein is truncated and lacks up to 35 contiguous amino acid residues at or near the N-terminus of the wild-type NiV-G protein, such as compared to wild-type NiV-G set forth in SEQ ID NO: 1. In some embodiments, the variant NiV-G protein (also called variant NiV-G) contains an N-terminal methionine.

[0240] In some embodiments, the variant NiV-G has a cytoplasmic tail deletion of amino acid residues 2-41, 2-40, 2-39, 2-38, 2-37, 2-36, 2-34, 2-35, 2-33, 2-32, 2-31, 2-30, 2-29, 2-28, 2-27, 2-26, 2- 25, 2-22, 2-21, 2-16, 2-11, or 2-5 of SEQ ID NO:4. In some embodiments, the cytoplasmic tail is a truncated portion of the Nipah virus cytoplasmic tail set forth in any one of SEQ ID NOS: 6-28. In some embodiments, the cytoplasmic tail is a truncated portion of the Nipah virus cytoplasmic tail set forth in any one of SEQ ID NOS: 6-28 that lacks the N-terminal methionine. In some embodiments, the variant NiV-G has a sequence in which the cytoplasmic tail, such as set forth in any one of SEQ ID NOS: 6-28, is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the variant NiV-G has a sequence in which the cytoplasmic tail set forth in any one of SEQ ID NOS: 6- 28 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3. In some of any such embodiments, the cytoplasmic tail is set forth in SEQ ID NO:7, 13, or 19.

[0241] In some embodiments, the truncated NiV-G comprises the sequence of amino acids set forth in SEQ ID NO: 211, 220 or 221, or a sequence of amino acids that exhibits at least 85% sequence identity, at least 86% sequence identity, at least 87% sequence identity, at least 88% sequence identity, at least 89% sequence identity, at least 90% sequence identity, at least 91% sequence identity, at least 92% sequence identity, at least 93% sequence identity, at least 94% sequence identity, at least 95% sequence identity, at least 96% sequence identity, at least 97% sequence identity, at least 98% sequence identity, or at least 99% sequence identity to any one of SEQ ID NOs: 211, 220 or 221. In some embodiments, the variant NiV-G is the sequence of amino acids set forth in SEQ ID NO: 211, 220 or 221.

[0242] In some embodiments, the variant NiV-G comprises a modified cytoplasmic tail which comprises a heterologous cytoplasmic tail or a truncated portion thereof from a glycoprotein from another virus. In some embodiments, the other virus is a member of the Kingdom Orthornavirae. In some embodiments, the other virus is a member of the family Paramyxoviridae, Rhabdoviridae, Arenaviridae, or Retroviridae. In some embodiments, the other virus is a member of the family Paramyxoviridae.

[0243] In some embodiments, the variant NiV-G contains a modified cytoplasmic tail in which at least a part of the native cytoplasmic tail (e.g. corresponding to amino acids 1-45 of SEQ ID NO:5) is replaced by a heterologous cytoplasmic tail or a truncated portion thereof from a glycoprotein from another virus from another virus or viral-associated protein. In some embodiments, the replaced 51 sf-5667634186152009940 cytoplasmic tail is a heterologous cytoplasmic tail or a truncated portion thereof that is at least 5 amino acids in length. In some embodiments, the replaced heterologous cytoplasmic tail or a truncated portion thereof is from or from about 5-180 amino acids in length, such as from or from about 5-150, from or from about 5-100, from or from about 5-75, from or from about 5-50, from or from about 5-40, from or from about 5-30, from or from about 5-20, from or from about 5-10, from or from about 10-150, from or from about 10-100, from or from about 10-75, from or from about 10-50, from or from about 10-40, from or from about 10-30, from or from about 10-20, from or from about 20-150, from or from about 20-100, from or from about 20-75, from or from about 20-50, from or from about 20-40, from or from about 20- 30, from or from about 30-150, from or from about 30-100, from or from about 30-75, from or from about 30-50, from or from about 30-40, from or from about 40-150, from or from about 40-100, from or from about 40-75, from or from about 40-50, from or from about 50-150, from or from about 50-100, from or from about 50-75, from or from about 75-150, from or from about 75-100 or from or from about 100-150 amino acids in length. In some embodiments, the replaced heterologous cytoplasmic tail or a truncated portion thereof is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40 amino acids in length. In some embodiments, the heterologous cytoplasmic tail or the truncated portion thereof is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the heterologous cytoplasmic tail or the truncated portion thereof is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3.

[0244] In some embodiments, the heterologous cytoplasmic tail is a cytoplasmic tail or a truncated portion thereof from a glycoprotein from another virus, such as a paramyxovirus, a retrovirus, a filovirus, a rhabdovirus or an arenavirus. In some embodiments, the virus is a paramyxovirus other than a Nipah virus. For instance, the virus is a measles virus, Bat paramyxovirus, Cedar Virus, Canine Distemper Virus, Sendai virus, Hendra virus, Human Parainfluenza virus, or Newcastle Disease virus. In some embodiments, the replaced heterologous cytoplasmic tail is the native cytoplasmic tail or a truncated portion of the native cytoplasmic tail of another virus, such as a truncated portion of the cytoplasmic tail set forth in any one of SEQ ID NOS: 40-166. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in any one of SEQ ID NOS: 40-166 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the variant NiV-G contains mutations in the extracellular domain that reduce or abrogate binding to an Ephrin B2 or B3 corresponding to one or more of E501A, W504A, Q530A and E533A, with numbering of residues as set forth SEQ ID NO:1. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in any one of SEQ ID NOS: 40-166 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3. In some embodiments, it is understood that the heterologous cytoplasmic tail or the truncated portion 52 sf-5667634186152009940 thereof may include any sequence set forth in any one of SEQ ID NOS: 40-166 that lacks the N-terminal methionine.

[0245] In some embodiments, the virus is a retrovirus. For instance, the virus may be a baboon endogenous virus (BaEV), Gibbon Ape Leukemia virus (GaLV), murine leukemia virus, or human immunodeficiency virus 1 (HIV-1). In some embodiments, the replaced heterologous cytoplasmic tail is the native cytoplasmic tail or a truncated portion of the native cytoplasmic tail of another virus, such as set forth in any one of SEQ ID NOS: 167-168, 174-177, 179-182, or 185-199. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in any one of SEQ ID NOS: 167-168, 174-177, 179-182, or 185-199 is directly linked to the N- terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the variant NiV-G contains mutations in the extracellular domain that reduce or abrogate binding to an Ephrin B2 or B3 corresponding to one or more of E501A, W504A, Q530A and E533A, with numbering of residues as set forth SEQ ID NO:1. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in any one of SEQ ID NOS: 167-168, 174-177, 179-182, or 185-199 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3. In some embodiments, it is understood that the heterologous cytoplasmic tail or the truncated portion thereof may include any sequence set forth in any one of SEQ ID NOS: 167-168, 174-177, 179-182, or 185-199 that lacks the N-terminal methionine.

[0246] In some embodiments, the virus is a filovirus. For instance, the virus may be an Ebola virus (EboV). In some embodiments, the replaced heterologous cytoplasmic tail is the native cytoplasmic tail or a truncated portion of the native cytoplasmic tail of another virus, such as set forth in any one of SEQ ID NOS: 172 or 173. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in any one of SEQ ID NOS: 172 or 173 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the variant NiV-G contains mutations in the extracellular domain that reduce or abrogate binding to an Ephrin B2 or B3 corresponding to one or more of E501A, W504A, Q530A and E533A, with numbering of residues as set forth SEQ ID NO:1. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in any one of SEQ ID NOS: 172 or 173 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3. In some embodiments, it is understood that the heterologous cytoplasmic tail or the truncated portion thereof may include any sequence set forth in any one of SEQ ID NOS: 172 or 173 that lacks the N-terminal methionine.

[0247] In some embodiments, the virus is a rhabdovirus. For instance, the virus may be Cocal vesiculovirus (Cocal) or vesicular stomatitis virus (VSV). In some embodiments, the replaced heterologous cytoplasmic tail is the native cytoplasmic tail or a truncated portion of the native 53 sf-5667634186152009940 cytoplasmic tail of another virus, such as set forth in any one of SEQ ID NOS: 170, 171, 183, or 184. In some embodiments, the variant NiV-G has a cytoplasmic tail in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in any one of SEQ ID NOS: 70, 171, 183, or 184 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the variant NiV-G contains mutations in the extracellular domain that reduce or abrogate binding to an Ephrin B2 or B3 corresponding to one or more of E501A, W504A, Q530A and E533A, with numbering of residues as set forth SEQ ID NO:1. In some embodiments, variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in any one of SEQ ID NOS: 70, 171, 183, or 184 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3. In some embodiments, it is understood that the heterologous cytoplasmic tail or the truncated portion thereof may include any sequence set forth in any one of SEQ ID NOS: 70, 171, 183 or 184 that lacks the N-terminal methionine.

[0248] In some embodiments, the virus is an arenavirus. For instance, the virus may be Lymphocytic choriomeningitis virus (LCMV). In some embodiments, the replaced heterologous cytoplasmic tail is the native cytoplasmic tail or a truncated portion of the native cytoplasmic tail of another virus, such as set forth in SEQ ID NOS: 178. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in SEQ ID NOS: 178 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the variant NiV-G contains mutations in the extracellular domain that reduce or abrogate binding to an Ephrin B2 or B3 corresponding to one or more of E501A, W504A, Q530A and E533A, with numbering of residues as set forth SEQ ID NO:1. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail or the truncated portion thereof set forth in SEQ ID NOS: 178 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3. In some embodiments, it is understood that the heterologous cytoplasmic tail or the truncated portion thereof may include any sequence set forth in any one of SEQ ID NOS: 178 that lacks the N-terminal methionine.

[0249] In some embodiments, at least one variant NiV-G protein is truncated and lacks up to amino acid 34 at or near the N-terminus of the wild-type NiV-G protein, such as compared to wild- type NiV-G set forth in SEQ ID NO: 1. In some embodiments, the variant NiV-G protein (also called variant NiV-G) contains an N-terminal methionine. In some embodiments, the variant NiV-G protein lacks amino acids 2-34 as compared to wild-type NiV-G set forth in SEQ ID NO:1. In some embodiments, the NiV-G has the sequence set forth in SEQ ID NO:228.

[0250] In some embodiments, the variant NiV-G contains a heterologous cytoplasmic tail that is a cytoplasmic tail or a truncated portion thereof from a glycoprotein from CD63. In some embodiments, the heterologous cytoplasmic tail replaces at least a part of the native cytoplasmic tail of NiV-G (e.g. corresponding to amino acids 1-45 of SEQ ID NO:5). In some embodiments, the heterologous tail is a 54 sf-5667634186152009940 contiguous sequence of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 N- terminal amino acids of the native cytoplasmic tail of CD63. In some embodiments, the native cytoplasmic tail of CD63 is set forth in SEQ ID NOs: 200, 201, or 202. In some embodiments, the heterologous cytoplasmic tail is a truncated portion of the CD63 cytoplasmic tail set forth in any one of SEQ ID NOS: 200-205. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail set forth in any one of SEQ ID NOS: 200-205 is directly linked to the N- terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the variant NiV-G has a sequence in which the heterologous cytoplasmic tail set forth in any one of SEQ ID NOS: 200-205 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3.In some embodiments, the variant NiV-G comprises a modified cytoplasmic tail which comprises a mutated cytoplasmic tail from a glycoprotein from the same Nipah virus. In some embodiments, the variant NiV-G contains a modified cytoplasmic tail in which at least a part of the native cytoplasmic tail (e.g. corresponding to amino acids 1-45 of SEQ ID NO:5) is a mutated portion thereof from a glycoprotein from Nipah Virus. In some embodiments, the cytoplasmic tail is a mutated portion of the Nipah virus cytoplasmic tail set forth in any one of SEQ ID NOS: 29-38. In some embodiments, it is understood that the truncated NiV-G cytoplasmic tail may include the sequence set forth in any one of SEQ ID NOS: 29-38 that lacks the N- terminal methionine. In some embodiments, the variant NiV-G has a sequence in which the cytoplasmic tail set forth in any one of SEQ ID NOS: 29-38 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 2. In some embodiments, the variant NiV-G has a sequence in which the cytoplasmic tail set forth in any one of SEQ ID NOS: 29-38 is directly linked to the N-terminus of the sequence set forth in SEQ ID NO: 3.

[0251] In some embodiments, at least one G protein or the functionally active variant or biologically active portion thereof binds to Ephrin B2 or Ephrin B3. In some embodiments, the G protein is a variant G protein, such as a truncated G protein as described and retains binding to Ephrin B2 or B3. Reference to retaining binding to Ephrin B2 or B3 includes binding that is similar to the level or degree of binding of the corresponding wild-type G protein, such as set forth in SEQ ID NO: 1, 561, 562, 563, or 564, such as at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the binding of the wild-type G protein.

[0252] In some embodiments, also provided are any of the provided variant NiV-G proteins that are re-targeted compared to the native tropism of NiV-G. For instance, mutations in NiV-G that completely abrogate ephrinB2 and B3 binding, but that do not impact the association of this NiV-G with NiV-F, have been identified (Aguilar, et al. J Biol Chem.2009;284(3):1628-1635.; Weise et al. J Virol. 2010;84(15):7634-764; Negrete et al.. J Virol.2007;81(19):10804-10814; Negrete et al. PLoS Pathog. 2006; Guillaume et al., J. Virol 2006, 80 (15) 7546-7554). Thus, in provided aspects, a variant NiV-G protein provided herein may further contain a mutation in its extracellular domain to reduce or abrogate 55 sf-5667634186152009940 binding to Ephrin B2 and / B3. In some embodiments, the mutations can include one or more of mutations E501A, W504A, Q530A and E533A, with reference to numbering of wild-type NiV-G set forth in SEQ ID NO:5. In some embodiments, any of the provided variant NiV-G proteins may also be linked or fused to a binding molecule for targeted binding to a target molecule of interest. In some embodiments, the variant G protein is a fusion of a binding molecule with variant NiV-G, including a NiV-G with mutations to abrogate Ephrin B2 and / or Ephrin B3 binding. This could allow for altered G protein tropism allowing for targeting of other desired cell types that are not ephrinB2+ through the addition of the binding molecule directed against a different cell surface molecule.

[0253] In some embodiments, the paramyxovirus envelope attachment protein is a variant G protein that exhibits reduced binding for the native binding partner of a wild-type G protein. In some embodiments, the variant G protein or the biologically active portion thereof is a variant of wild-type NiV-G and exhibits reduced binding to one or both of the native binding partners Ephrin B2 or Ephrin B3. In some embodiments, the variant G-protein or the biologically active portion, such as a variant NiV-G protein, exhibits reduced binding to the native binding partner. In some embodiments, the reduced binding to Ephrin B2 or Ephrin B3 is reduced by greater than at or about 5%, at or about 10%, at or about 15%, at or about 20%, at or about 25%, at or about 30%, at or about 40%, at or about 50%, at or about 60%, at or about 70%, at or about 80%, at or about 90%, or at or about 100%.

[0254] In some embodiments, the mutations can improve transduction efficiency. In some embodiments, the mutations allow for specific targeting of other desired cell types that are not Ephrin B2 or Ephrin B3. In some embodiments, the mutations result in at least the partial inability to bind at least one natural receptor, such has reduced the binding to at least one of Ephrin B2 or Ephrin B3. In some embodiments, the mutations described herein interfere with natural receptor recognition.

[0255] In some embodiments, at least one G protein contains one or more amino acid substitutions in a residue that is involved in the interaction with one or both of Ephrin B2 and Ephrin B3. In some embodiments, the amino acid substitutions correspond to mutations E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:1. In some embodiments, at least one G protein is a variant G protein containing one or more amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:1. In some embodiments, at least one G protein is a variant G protein that contains one or more amino acid substitutions elected from the group consisting of E501A, W504A, Q530A and E533A with reference to SEQ ID NO:1 and is a biologically active portion thereof containing an N-terminal truncation. 56 sf-5667634186152009940

[0256] In particular embodiments, at least one G protein has the sequence of amino acids set forth in SEQ ID NO: 228, or is a functionally active variant thereof or a biologically active portion thereof that retains binding and / or fusogenic activity. In some embodiments, the functionally active variant comprises an amino acid sequence having at least at or about 80%, at least at or about 85%, at least at or about 90%, at least at or about 91%, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO: 228 and retains fusogenic activity in conjunction with a variant NiV-F protein as described. In some embodiments, at least one G protein is a variant G protein that comprises the amino acid sequence of SEQ ID NO: 228.

[0257] In some embodiments, any of the provided lipid particles (lentiviral vectors) may also contain an F protein, such as a NiV-F protein, such as a full-length NiV-F protein or a biologically active portion thereof or a variant thereof. For instance, also provided herein are viral particles or viral-like particles, such as lentiviral particles or lentiviral-like particles, that are pseudotyped with any of the provided variant NiV-G proteins and a NiV-F protein, such as a full-length NiV-F protein or a biologically active portion or a variant thereof. Exemplary NiV-F proteins are further described in Section III.A.2.

[0258] Reference to retaining fusogenic activity includes activity of a lipid particle (e.g. lentiviral vector) containing at least two paramyxovirus envelope attachment protein and paramyxovirus fusion protein (e.g., F and G proteins) that is between at or about 10% and at or about 150% or more of the level or degree of binding of a reference lipid particle (e.g. lentiviral vector) that is similar, such as contains the same variant NiV-F, but that contains the corresponding wild-type G protein, such as set forth in SEQ ID NO: 1. For instance, a lipid particle (e.g. lentiviral vector) that retains fusogenic activity has at least or at least about 10% of the level or degree of fusogenic activity of the reference lipid particle that is similar (such as contains the same variant NiV-F) but that contains the corresponding wild-type G protein, such as at least or at least about 15% of the level or degree of fusogenic activity, at least or at least about 20% of the level or degree of fusogenic activity, at least or at least about 25% of the level or degree of fusogenic activity, at least or at least about 30% of the level or degree of fusogenic activity, at least or at least about 35% of the level or degree of fusogenic activity, at least or at least about 40% of the level or degree of fusogenic activity, at least or at least about 45% of the level or degree of fusogenic activity, at least or at least about 50% of the level or degree of fusogenic activity, at least or at least about 55% of the level or degree of fusogenic activity, at least or at least about 60% of the level or degree of fusogenic activity, at least or at least about 65% of the level or degree of fusogenic activity, at least or at least about 70% of the level or degree of fusogenic activity, at least or at least about 75% of the level or degree of fusogenic activity, at least or at least about 80% of the level or degree of fusogenic activity, at least or at least about 85% of the level or degree of fusogenic activity, at least or at least about 90% of the 57 sf-5667634186152009940 level or degree of fusogenic activity, at least or at least about 95% of the level or degree of fusogenic activity, at least or at least about 100% of the level or degree of fusogenic activity, or at least or at least about 120% of the level or degree of fusogenic activity.

[0259] Reference to retaining fusogenic activity includes activity of a lipid particle (e.g. lentiviral vector) containing at least two paramyxovirus envelope attachment protein and paramyxovirus fusion protein (e.g., F and G proteins) that is between at or about 10% and at or about 150% or more of the level or degree of binding of a reference lipid particle (e.g. lentiviral vector) that is similar, such as contains the same variant NiV-F, but that contains only one of the provided paramyxovirus envelope attachment proteins (e.g., G proteins). For instance, a lipid particle (e.g. lentiviral vector) that retains fusogenic activity has at least or at least about 10% of the level or degree of fusogenic activity of the reference lipid particle that is similar (such as contains the same variant NiV-F) but that contains only one of the provided paramyxovirus envelope attachment proteins, such as at least or at least about 15% of the level or degree of fusogenic activity, at least or at least about 20% of the level or degree of fusogenic activity, at least or at least about 25% of the level or degree of fusogenic activity, at least or at least about 30% of the level or degree of fusogenic activity, at least or at least about 35% of the level or degree of fusogenic activity, at least or at least about 40% of the level or degree of fusogenic activity, at least or at least about 45% of the level or degree of fusogenic activity, at least or at least about 50% of the level or degree of fusogenic activity, at least or at least about 55% of the level or degree of fusogenic activity, at least or at least about 60% of the level or degree of fusogenic activity, at least or at least about 65% of the level or degree of fusogenic activity, at least or at least about 70% of the level or degree of fusogenic activity, at least or at least about 75% of the level or degree of fusogenic activity, at least or at least about 80% of the level or degree of fusogenic activity, at least or at least about 85% of the level or degree of fusogenic activity, at least or at least about 90% of the level or degree of fusogenic activity, at least or at least about 95% of the level or degree of fusogenic activity, at least or at least about 100% of the level or degree of fusogenic activity, or at least or at least about 120% of the level or degree of fusogenic activity. B) Retargeted Attachment Proteins

[0260] In some embodiments, a paramyxovirus envelope attachment protein, such as a G protein (e.g., NiV-G), is further attached or linked to a binding domain that binds to a target molecule to comprise a retargeted attachment protein. For instance, provided in some aspects is a lipid particle that includes a targeted paramyxovirus envelope attachment proteins (e.g., a chimeric attachment G protein) containing any of the provided G proteins described above that is attached to a binding domain, in which the retargeted attachment protein (e.g., re-targeted G protein) is exposed on the surface of the targeted lipid particle (e.g. lentiviral vector). In some of any of the provided embodiments, the lipid particle 58 sf-5667634186152009940 comprises a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a first target molecule expressed on the surface of a target cell.

[0261] In some embodiments, the paramyxovirus envelope attachment protein, such as a G protein (e.g., NiV-G), is further attached or linked to targeting moiety, e.g., a binding domain or a binding agent, directed to a target molecule expressed on the surface of a target cell. The binding domain or binding agent can be any binding domain or binding agent described herein, e.g., in Section III.A.1.B. Accordingly, in some embodiments, the lipid particle comprises one or more retargeted attachment proteins, wherein each of the one or more retargeted attachment proteins independently comprise: (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell. The targeting moiety can be a binding domain or binding agent, such as any binding domain or any binding agent described herein, e.g., in Section III.A.1.B.

[0262] In some embodiments, a paramyxovirus envelope attachment protein, such as a G protein (e.g., NiV-G), is further attached or linked in tandem with at least two binding domains that bind to a first and second target molecule respectively to comprise a retargeted attachment protein. For instance, provided in some aspects is a lipid particle that includes a targeted paramyxovirus envelope attachment proteins (e.g., a chimeric attachment G protein) containing any of the provided G proteins described above that is attached (e.g., operably fused in tandem) to a first and second binding domain, in which the retargeted attachment protein (e.g., re-targeted G protein) is exposed on the surface of the targeted lipid particle (e.g. lentiviral vector). In some of any of the provided embodiments, the lipid particle comprises a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a first targeting moiety directed to a first target molecule expressed on the surface of a target cell, and (iii) a second targeting moiety directed to a second target molecule expressed on the surface of a target cell.

[0263] In some embodiments, each of the one or more of the paramyxovirus envelope attachment proteins, such as a G protein (e.g., NiV-G), is further attached or linked in tandem to a first and a second targeting moiety, e.g., a first and second binding domain or a binding agent, directed to a first and second target molecule expressed on the surface of a target cell. The binding domains or binding agents can be individually selected from any binding domain or binding agent described herein, e.g., in Section III.A.1.B. Accordingly, in some embodiments, the lipid particle comprises one or more retargeted attachment proteins, wherein each of the one or more retargeted attachment proteins independently comprise: (i) a paramyxovirus envelope attachment protein; and (ii) a first targeting moiety directed to a first target molecule expressed on the surface of a target cell, and (iii) a second targeting moiety directed to a second target molecule expressed on the surface of a target cell. The targeting moieties can be a binding domain or binding agent, such as any binding domain or any binding agent described herein, e.g., in Section III.A.1.B. 59 sf-5667634186152009940

[0264] In some embodiments, the envelope attachment protein is a retargeted attachment protein containing a henipavirus G protein or a biologically active portion thereof. In some embodiments, the envelope attachment proteins (e.g., G protein) may be retargeted by linkage to a targeting moiety, such as a binding molecule (e.g. antibody or antigen-binding fragment, e.g. sdAb or scFv) that binds to a target cell, such as a retargeted attachment protein. In some embodiments, the retargeted attachment protein and paramyxovirus fusion protein (e.g., G protein and a NiV-F protein provided herein) together exhibit fusogenic activity to a target cell, such as to deliver an exogenous agent or nucleic acid exogenous agent to the target cell.

[0265] In some embodiments, the targeting the target molecule does not activate or inhibit, induce a phenotype change (for example maturation and / or differentiation), induce proliferation, and / or induce apoptosis of said target cell.

[0266] In some embodiments, the paramyxovirus retargeted attachment protein is a targeted envelope protein containing a G protein provided herein. In some embodiments the paramyxovirus retargeted attachment protein comprises at least one envelope attachment proteins (e.g., G protein) that is any of those provided in Section III.A.1.A, including NiV-G proteins with cytoplasmic domain modifications, truncated NiV-G cytoplasmic tails, or modified NiV-G cytoplasmic tails.

[0267] In some of any embodiments, the retargeted attachment protein comprises (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a first target molecule expressed on the surface of a target cell. In some of any embodiments, the retargeted attachment protein, comprises (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell. In some embodiments, the targeting moiety is a binding domain, such as any of the binding domains or binding agents described herein in Section III.A.1.B, e.g., a T cell binding domain or an HSC binding domain. In some embodiments, the binding domain can be any agent that binds to a cell surface molecule on a target cells. In some embodiments, the binding domain can be an antibody or an antibody portion or fragment. In some embodiments, the binding domain is a single domain antibody (sdAb). In some embodiments, the binding domain is a single chain variable fragment (scFv). The binding domain can be linked directly or indirectly to the G protein. In particular embodiments, the binding domain is linked to the C-terminus (C-terminal amino acid) of the G protein or the biologically active portion thereof. The linkage can be via a peptide linker, such as a flexible peptide linker.

[0268] The retargeted attachment protein comprising a binding domain linked to a paramyxovirus envelope attachment protein may be modulated to have different binding strengths. For example, scFvs and antibodies with various binding strengths may be used to alter the fusion activity of the retargeted attachment proteins towards cells that display high or low amounts of the target antigen. For example DARPins with different affinities may be used to alter the fusion 60 sf-5667634186152009940 activity towards cells that display high or low amounts of the target antigen. Binding domains may also be modulated to target different regions on the target ligand, which will affect the fusion rate with cells displaying the target.

[0269] The binding domain may comprise a humanized antibody molecule, intact IgA, IgG, IgE or IgM antibody; bi- or multi- specific antibody (e.g., Zybodies®, etc.); antibody fragments such as Fab fragments, Fab’ fragments, F(ab’)2 fragments, Fd’ fragments, Fd fragments, and isolated CDRs or sets thereof; single chain Fvs; polypeptide-Fc fusions; single domain antibodies (e.g., shark single domain antibodies such as IgNAR or fragments thereof); cameloid antibodies; masked antibodies (e.g., Probodies®); Small Modular ImmunoPharmaceuticals (“SMIPsTM”); single chain or Tandem diabodies (TandAb®); VHHs; Anticalins®; Nanobodies®; minibodies; BiTE®s; ankyrin repeat proteins or DARPINs®; Avimers®; DARTs; TCR-like antibodies;, Adnectins®; Affilins®; Trans- bodies®; Affibodies®; TrimerX®; MicroProteins; Fynomers®, Centyrins®; and KALBITOR®s. A targeting moiety can also include an antibody or an antigen-binding fragment thereof (e.g., Fab, Fab', F(ab')2, Fv fragments, scFv antibody fragments, disulfide-linked Fvs (sdFv), a Fd fragment consisting of the VH and CH1 domains, linear antibodies, single domain antibodies such as sdAb (either VL or VH), nanobodies, or camelid VHH domains), an antigen-binding fibronectin type III (Fn3) scaffold such as a fibronectin polypeptide minibody, a ligand, a cytokine, a chemokine, or a T cell receptor (TCRs).

[0270] The binding domain may comprise a humanized antibody molecule, intact IgA, IgG, IgE or IgM antibody; bi- or multi- specific antibody (e.g., Zybodies®, etc.); antibody fragments such as Fab fragments, Fab’ fragments, F(ab’)2 fragments, Fd’ fragments, Fd fragments, and isolated CDRs or sets thereof; single chain Fvs; polypeptide-Fc fusions; single domain antibodies (e.g., shark single domain antibodies such as IgNAR or fragments thereof); cameloid antibodies; masked antibodies (e.g., Probodies®); Small Modular ImmunoPharmaceuticals (“SMIPsTM”); single chain or Tandem diabodies (TandAb®); VHHs; Anticalins®; Nanobodies®; minibodies; BiTE®s; ankyrin repeat proteins or DARPINs®; Avimers®; DARTs; TCR-like antibodies;, Adnectins®; Affilins®; Trans- bodies®; Affibodies®; TrimerX®; MicroProteins; Fynomers®, Centyrins®; and KALBITOR®s. A targeting moiety can also include an antibody or an antigen-binding fragment thereof (e.g., Fab, Fab', F(ab')2, Fv fragments, scFv antibody fragments, disulfide-linked Fvs (sdFv), a Fd fragment consisting of the VH and CH1 domains, linear antibodies, single domain antibodies such as sdAb (either VL or VH), nanobodies, or camelid VHH domains), an antigen-binding fibronectin type III (Fn3) scaffold such as a fibronectin polypeptide minibody or a T cell receptor (TCRs). In some embodiments, the binding domain does not comprise a ligand, a cytokine, or a chemokine,

[0271] In some embodiments, the binding domain is a single chain molecule. In some embodiments, the binding domain is a single domain antibody. In some embodiments, the binding 61 sf-5667634186152009940 domain is a single chain variable fragment. In particular embodiments, the binding domain contains an antibody variable sequence (s) that is human or humanized.

[0272] In some embodiments, the binding domain is a single domain antibody. In some embodiments, the single domain antibody can be human or humanized. In some embodiments, the single domain antibody or portion thereof is naturally occurring. In some embodiments, the single domain antibody or portion thereof is synthetic.

[0273] In some embodiments, the single domain antibodies are antibodies whose complementary determining regions are part of a single domain polypeptide. In some embodiments, the single domain antibody is a heavy chain only antibody variable domain. In some embodiments, the single domain antibody does not include light chains.

[0274] In some embodiments, the heavy chain antibody devoid of light chains is referred to as VHH. In some embodiments, the single domain antibody antibodies have a molecular weight of 12-15 kDa. In some embodiments, the single domain antibody antibodies include camelid antibodies or shark antibodies. In some embodiments, the single domain antibody molecule is derived from antibodies raised in Camelidae species, for example in camel, llama, dromedary, alpaca, vicuna and guanaco. In some embodiments, the single domain antibody is referred to as immunoglobulin new antigen receptors (IgNARs) and is derived from cartilaginous fishes. In some embodiments, the single domain antibody is generated by splitting dimeric variable domains of human or mouse IgG into monomers and camelizing critical residues.

[0275] In some embodiments, the single domain antibody can be generated from display libraries, e.g., phage display libraries. In some embodiments, the display libraries are generated from a VHH repertoire of camelids immunized with various antigens, as described in Arbabi et al., FEBS Letters, 414, 521-526 (1997); Lauwereys et al., EMBO J., 17, 3512-3520 (1998); Decanniere et al., Structure, 7, 361- 370 (1999). In some embodiments, the display library is generated comprising antibody fragments of a non-immunized camelid. In some embodiments, single domain antibodies a library of human single domain antibodies is synthetically generated by introducing diversity into one or more scaffolds.

[0276] In some embodiments, the binding domain is a single domain antibody (sdAb). In some embodiments, the binding domain is a single chain variable fragment (scFv). The binding domain can be linked directly or indirectly to the paramyxovirus envelope attachment protein, first paramyxovirus envelope attachment protein, and / or second paramyxovirus envelope attachment protein (e.g., G protein). In particular embodiments, the binding domain is linked to the C-terminus (C-terminal amino acid) of the G protein or the biologically active portion thereof. The linkage can be via a peptide linker, such as a flexible peptide linker.

[0277] In some embodiments, the C-terminus of the binding domain is attached to the C-terminus of the G protein or biologically active portion thereof. In some embodiments, the N-terminus of the binding 62 sf-5667634186152009940 domain is exposed on the exterior surface of the lipid bilayer. In some embodiments, the N-terminus of the binding domain binds to a cell surface molecule of a target cell. In some embodiments, the binding domain specifically binds to a cell surface molecule present on a target cell. In some embodiments, the cell surface molecule is a protein, glycan, lipid or low molecular weight molecule. In some embodiments, the binding domain is one of any binding domains as described above.

[0278] In some embodiments, a binding domain (e.g. sdAb or one of any binding domains as described herein) binds to a cell surface antigen of a cell. In some embodiments, a cell surface antigen is characteristic of one type of cell. In some embodiments, a cell surface antigen is characteristic of more than one type of cell.

[0279] In some embodiments, the cell surface molecule of a target cell is an antigen or portion thereof. In some embodiments, the single domain antibody or portion thereof is an antibody having a single monomeric domain antigen binding / recognition domain that is able to bind selectively to a specific antigen. In some embodiments, the single domain antibody binds an antigen present on a target cell.

[0280] Exemplary cells include polymorphonuclear cells (also known as PMN, PML, PMNL, or granulocytes), stem cells, embryonic stem cells, neural stem cells, mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), human myogenic stem cells, muscle-derived stem cells (MuStem), embryonic stem cells (ES or ESCs), limbal epithelial stem cells, cardio-myogenic stem cells, cardiomyocytes, progenitor cells, immune effector cells, lymphocytes, macrophages, dendritic cells, natural killer cells, T cells, cytotoxic T lymphocytes, allogenic cells, resident cardiac cells, induced pluripotent stem cells (iPS), adipose-derived or phenotypic modified stem or progenitor cells, CD133+ cells, aldehyde dehydrogenase-positive cells (ALDH+), umbilical cord blood (UCB) cells, peripheral blood stem cells (PBSCs), neurons, neural progenitor cells, pancreatic beta cells, glial cells, or hepatocytes.

[0281] In some embodiments, the target cell is a cell of a target tissue. The target tissue can include liver, lungs, heart, spleen, pancreas, gastrointestinal tract, kidney, testes, ovaries, brain, reproductive organs, central nervous system, peripheral nervous system, skeletal muscle, endothelium, inner ear, or eye.

[0282] In some embodiments, the target cell is a muscle cell (e.g., skeletal muscle cell), kidney cell, liver cell (e.g. hepatocyte), or a cardiac cell (e.g. cardiomyocyte). In some embodiments, the target cell is a cardiac cell, e.g., a cardiomyocyte (e.g., a quiescent cardiomyocyte), a hepatoblast (e.g., a bile duct hepatoblast), an epithelial cell, a T cell (e.g. a naive T cell), a macrophage (e.g., a tumor infiltrating macrophage), or a fibroblast (e.g., a cardiac fibroblast).

[0283] In some embodiments, the target cell is a tumor-infiltrating lymphocyte, a T cell, a neoplastic or tumor cell, a virus-infected cell, a stem cell, a central nervous system (CNS) cell, a hematopoietic stem cell (HSC), a liver cell or a fully differentiated cell. In some embodiments, the 63 sf-5667634186152009940 target cell is a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell.

[0284] In some embodiments, the target cell is an antigen presenting cell, an MHC class II+ cell, a professional antigen presenting cell, an atypical antigen presenting cell, a macrophage, a dendritic cell, a myeloid dendritic cell, a plasmacyteoid dendritic cell, a CD11c+ cell, a CD11b+ cell, a splenocyte, a B cell, a hepatocyte, a endothelial cell, or a non-cancerous cell). In some embodiments, the first and second target molecules are present on the same target cell. In some embodiments, the first and second target molecules are present on different cells.

[0285] In some embodiments, the binding domain (e.g. sdAb) variable domain binds a cell surface molecule or antigen. In some embodiments, the cell surface molecule is ASGR1, ASGR2, TM4SF5, CD8, CD4, or low density lipoprotein receptor (LDL-R). In some embodiments, the cell surface molecule is ASGR1. In some embodiments, the cell surface molecule is ASGR2. In some embodiments, the cell surface molecule is TM4SF5. In some embodiments, the cell surface molecule is CD8. In some embodiments, the cell surface molecule is CD4. In some embodiments, the cell surface molecule is LDL- R.

[0286] In some embodiments, the target cell is a hematopoietic lineage cell. Reference to a "hematopoietic cell" includes blood cells, both from the myeloid and the lymphoid lineage. In particular, the term "hematopoietic cell" includes both undifferentiated or poorly differentiated cells, such as hematopoietic stem cells and progenitor cells, and differentiated cells such as T lymphocytes, B lymphocytes, or dendritic cells. In some embodiments, the hematopoietic cells are hematopoietic stem cells (HSCs), CD34+ progenitor cells, in particular peripheral blood CD34+ cells, very early progenitor CD34+ cells, B-cell CD19+ progenitors, myeloid progenitor CD13+ cells, T lymphocytes, B lymphocytes, monocytes, dendritic cells, cancer B cells in particular B-cell chronic lymphocytic leukemia (BCLL) cells and marginal zone lymphoma (MZL) B cells, or thymocytes.

[0287] As known from the skilled person, many hematopoietic cells are produced from bone marrow hematopoietic stem cells.

[0288] In some embodiments, a hematopoietic cell is a hematopoietic stem cell (HSC), which are cells able to replenish all blood cell types and to self-renew. Hematopoietic stem cells may be in particular defined as cells that keep the levels of myeloid, T cells, and B cells at robustly detectable levels (typically more than 1 % of peripheral blood cells) for 16 weeks when injected into the circulation of a recipient mouse with a depleted hematopoietic system (Schroeder (2010) Cell Stem Cell 6:203-207). 64 sf-5667634186152009940

[0289] In some embodiments, the hematopoietic cell is a "CD34+ progenitor cell,” which is a heterogeneous cell population that includes a subpopulation of HSCs, pluripotent stem cells and cells in the early stages of lineage commitment. CD34+ progenitor cells continuously migrate to and from the bone marrow in normal adult animals. They can differentiate to produce all hematopoietic cell lineages found in the circulation. In some embodiments, the hematopoietic cell is a very early progenitor CD34+ cell which is a subgroup of CD34+ progenitor cells enriched from HSCs.

[0290] In some embodiments, the hematopoietic cell is a "peripheral blood CD34+ cell”, which is a CD34+ cell present in the blood.

[0291] In some embodiments, the hematopoietic cell is a B cell CD19+ progenitor, which is a population of B-lineage cells that express cell surface CD10, CD34, and CD19.

[0292] In some embodiments, the hematopoietic cell is a myeloid progenitor CD13+ cells, which is a population of myeloid lineage cells that express cell surface CD34 and CD13, and in some cases, also CD33.

[0293] In some embodiments, the target cell is selected from the group consisting of myeloid- lymphoid balanced hematopoietic lineage cells, myeloid-biased hematopoietic lineage cells, lymphoid- biased hematopoietic lineage cells, a platelet-biased hematopoietic lineage cells, a platelet-myeloid- biased hematopoietic lineage cells, a long-term repopulating hematopoietic lineage cells, an intermediate- term repopulating hematopoietic lineage cells, or a short-term repopulating hematopoietic lineage cells. In some embodiments, the target cell is selected from monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, megakaryocytes and platelets. In some embodiments, the target cell is selected from T cells, B cells, natural killer (NK) cells and innate lymphoid cells.

[0294] In some embodiments the target cell is an effector cell, e.g., a cell of the immune system that expresses one or more Fc receptors and mediates one or more effector functions. In some embodiments, a target cell may include one or more of a monocyte, macrophage, neutrophil, dendritic cell, eosinophil, mast cell, platelet, large granular lymphocyte, Langerhans' cell, natural killer (NK) cell, T lymphocyte (e.g., T cell), a Gamma delta T cell, B lymphocyte (e.g., B cell) and may be from any organism including humans, mice, rats, rabbits, and monkeys.

[0295] In some embodiment, the hematopoietic cell is a T cell. In some embodiments, the T cell is a naïve T cell. In some embodiments, the T cell is a memory T cell.

[0296] In some embodiments, the hematopoietic cell is a B cell. In some embodiments, the target cell is a resting B cell, such as a naive or a memory B cell. In some embodiments, the target cell is a cancer B cell, such as a B-cell chronic lymphocytic leukemia (BCLL) cell or a marginal zone lymphoma (MZL) B cell.

[0297] In some embodiments, the target cell is a thymocyte. In some embodiments, the target cell is a natural killer (NK) cell. In some embodiments, the thymocyte expresses CD4 or CD8. In some 65 sf-5667634186152009940 embodiments, the thymocyte does not express CD4 or CD8. In some embodiments, the natural killer (NK) cell is a cell that expresses CD56.

[0298] In some embodiments, the target cell is a CD3+ T cell, a CD4+ T cell, or a CD8+ T cell.

[0299] In some embodiments, the target cell is an antigen presenting cell, an MHC class II+ cell, a professional antigen presenting cell, an atypical antigen presenting cell, a macrophage, a dendritic cell, a myeloid dendritic cell, a plasmacyteoid dendritic cell, a CD11c+ cell, a CD11b+ cell, or a B cell.

[0300] In some embodiments, the binding domain (e.g. sdAb) variable domain binds a cell surface molecule or antigen. In some embodiments, the cell surface molecule is ASGR1, ASGR2, TM4SF5, CD3, CD8, CD4, CD7, or low density lipoprotein receptor (LDL-R). In some embodiments, the cell surface molecule is ASGR1. In some embodiments, the cell surface molecule is ASGR2. In some embodiments, the cell surface molecule is TM4SF5. In some embodiments, the cell surface molecule is CD3. In some embodiments, the cell surface molecule is CD8. In some embodiments, the cell surface molecule is CD4. In some embodiments, the cell surface molecule is LDL-R. In some embodiments, the cell surface molecule is ASCT2, CD105, CD110, CD117, CD133, CD146, CD164, CD34, CD46, CD49f, CD90, EPCR, or ITGA3.

[0301] In some embodiments, the retargeted attachment protein comprises the paramyxovirus envelope attachment protein (e.g., G protein or functionally active variant or biologically active portion thereof) linked directly to the binding domain and / or variable domain thereof. In some embodiments, the targeted envelope protein is a fusion protein that has the following structure: (N’-single domain antibody- C’)-(C’-G protein-N’).

[0302] In some embodiments, the retargeted attachment protein comprises the paramyxovirus envelope attachment protein (e.g., G protein or functionally active variant or biologically active portion thereof) linked indirectly via a linker to the binding domain and / or variable domain thereof. In some embodiments, the linker is a peptide linker. In some embodiments, the linker is a chemical linker.

[0303] In some embodiments, the linker is a peptide linker and the targeted envelope protein is a fusion protein containing the paramyxovirus envelope attachment protein (e.g., G protein or functionally active variant or biologically active portion thereof) linked via a peptide linker to the binding molecule variable domain (e.g. antibody or antigen-binding fragment, e.g. sdAb or scFv variable domain). In some embodiments, the targeted envelope protein is a fusion protein that has the following structure: (N’-single domain antibody-C’)-Linker-(C’-G protein-N’).

[0304] In some embodiments, the peptide linker is up to 65 amino acids in length. In some embodiments, the peptide linker comprises from or from about 2 to 65 amino acids, 2 to 60 amino acids, 2 to 56 amino acids, 2 to 52 amino acids, 2 to 48 amino acids, 2 to 44 amino acids, 2 to 40 amino acids, 2 to 36 amino acids, 2 to 32 amino acids, 2 to 28 amino acids, 2 to 24 amino acids, 2 to 20 amino acids, 66 sf-5667634186152009940 2 to 18 amino acids, 2 to 14 amino acids, 2 to 12 amino acids, 2 to 10 amino acids, 2 to 8 amino acids, 2 to 6 amino acids, 6 to 65 amino acids, 6 to 60 amino acids, 6 to 56 amino acids, 6 to 52 amino acids, 6 to 48 amino acids, 6 to 44 amino acids, 6 to 40 amino acids, 6 to 36 amino acids, 6 to 32 amino acids, 6 to 28 amino acids, 6 to 24 amino acids, 6 to 20 amino acids, 6 to 18 amino acids, 6 to 14 amino acids, 6 to 12 amino acids, 6 to 10 amino acids, 6 to 8 amino acids, 8 to 65 amino acids, 8 to 60 amino acids, 8 to 56 amino acids, 8 to 52 amino acids, 8 to 48 amino acids, 8 to 44 amino acids, 8 to 40 amino acids, 8 to 36 amino acids, 8 to 32 amino acids, 8 to 28 amino acids, 8 to 24 amino acids, 8 to 20 amino acids, 8 to 18 amino acids, 8 to 14 amino acids, 8 to 12 amino acids, 8 to 10 amino acids, 10 to 65 amino acids, 10 to 60 amino acids, 10 to 56 amino acids, 10 to 52 amino acids, 10 to 48 amino acids, 10 to 44 amino acids, 10 to 40 amino acids, 10 to 36 amino acids, 10 to 32 amino acids, 10 to 28 amino acids, 10 to 24 amino acids, 10 to 20 amino acids, 10 to 18 amino acids, 10 to 14 amino acids, 10 to 12 amino acids, 12 to 65 amino acids, 12 to 60 amino acids, 12 to 56 amino acids, 12 to 52 amino acids, 12 to 48 amino acids, 12 to 44 amino acids, 12 to 40 amino acids, 12 to 36 amino acids, 12 to 32 amino acids, 12 to 28 amino acids, 12 to 24 amino acids, 12 to 20 amino acids, 12 to 18 amino acids, 12 to 14 amino acids, 14 to 65 amino acids, 14 to 60 amino acids, 14 to 56 amino acids, 14 to 52 amino acids, 14 to 48 amino acids, 14 to 44 amino acids, 14 to 40 amino acids, 14 to 36 amino acids, 14 to 32 amino acids, 14 to 28 amino acids, 14 to 24 amino acids, 14 to 20 amino acids, 14 to 18 amino acids, 18 to 65 amino acids, 18 to 60 amino acids, 18 to 56 amino acids, 18 to 52 amino acids, 18 to 48 amino acids, 18 to 44 amino acids, 18 to 40 amino acids, 18 to 36 amino acids, 18 to 32 amino acids, 18 to 28 amino acids, 18 to 24 amino acids, 18 to 20 amino acids, 20 to 65 amino acids, 20 to 60 amino acids, 20 to 56 amino acids, 20 to 52 amino acids, 20 to 48 amino acids, 20 to 44 amino acids, 20 to 40 amino acids, 20 to 36 amino acids, 20 to 32 amino acids, 20 to 28 amino acids, 20 to 26 amino acids, 20 to 24 amino acids, 24 to 65 amino acids, 24 to 60 amino acids, 24 to 56 amino acids, 24 to 52 amino acids, 24 to 48 amino acids, 24 to 44 amino acids, 24 to 40 amino acids, 24 to 36 amino acids, 24 to 32 amino acids, 24 to 30 amino acids, 24 to 28 amino acids, 28 to 65 amino acids, 28 to 60 amino acids, 28 to 56 amino acids, 28 to 52 amino acids, 28 to 48 amino acids, 28 to 44 amino acids, 28 to 40 amino acids, 28 to 36 amino acids, 28 to 34 amino acids, 28 to 32 amino acids, 32 to 65 amino acids, 32 to 60 amino acids, 32 to 56 amino acids, 32 to 52 amino acids, 32 to 48 amino acids, 32 to 44 amino acids, 32 to 40 amino acids, 32 to 38 amino acids, 32 to 36 amino acids, 36 to 65 amino acids, 36 to 60 amino acids, 36 to 56 amino acids, 36 to 52 amino acids, 36 to 48 amino acids, 36 to 44 amino acids, 36 to 40 amino acids, 40 to 65 amino acids, 40 to 60 amino acids, 40 to 56 amino acids, 40 to 52 amino acids, 40 to 48 amino acids, 40 to 44 amino acids, 44 to 65 amino acids, 44 to 60 amino acids, 44 to 56 amino acids, 44 to 52 amino acids, 44 to 48 amino acids, 48 to 65 amino acids, 48 to 60 amino acids, 48 to 56 amino acids, 48 to 52 amino acids, 50 to 65 amino acids, 50 to 60 amino acids, 50 to 56 amino acids, 50 to 52 amino acids, 54 to 65 amino acids, 54 to 60 amino acids, 54 to 56 amino acids, 58 to 65 amino acids, 58 to 60 amino acids, or 60 to 65 67 sf-5667634186152009940 amino acids. In some embodiments, the peptide linker is a polypeptide that is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, or 65 amino acids in length.

[0305] In particular embodiments, the linker is a flexible peptide linker. In some such embodiments, the linker is 1-20 amino acids, such as 1-20 amino acids predominantly composed of glycine. In some embodiments, the linker is 1-20 amino acids, such as 1-20 amino acids predominantly composed of glycine and serine. In some embodiments, the linker is a flexible peptide linker containing amino acids Glycine and Serine, referred to as GS-linkers. In some embodiments, the peptide linker includes the sequences GS, GGS, GGGGS, GGGGGS or combinations thereof. In some embodiments, the polypeptide linker has the sequence (GGS)n, wherein n is 1 to 10. In some embodiments, the polypeptide linker has the sequence (GGGGS)n, wherein n is 1 to 10. In some embodiments, the polypeptide linker has the sequence (GGGGGS)n, wherein n is 1 to 6. In some embodiments, the polypeptide linker has or comprises the amino acid sequence of SEQ ID NO: 405 (GGGGSGGGGSGGGGS). In some embodiments, the retargeted attachment protein comprising a binding domain, a first binding domain, and / or a second binding domain linked to at least one paramyxovirus envelope attachment may comprise an engineered binding domain, such as an artificially generated binding domain. The binding domain may comprise a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer. Any engineered binding domain known in art and suitable for the present invention can be used, for example any such binding domain described in Olaleye et al. Biomolecules.2021 Dec; 11(12): 1791. I. T cell Binding Domains

[0306] In some embodiments, the lipid particles disclosed herein comprise one or more retargeted attachment proteins, each independently comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell. In some embodiments, the targeting moiety is a T cell binding domain, e.g., a T cell binding agent, such as any of those disclosed herein. In some embodiments, the retargeted attachment protein comprises a targeting moiety. In some embodiments, the retargeted attachment protein comprises a targeting moiety that is a T cell binding domain.

[0307] The lipid particles disclosed herein include, in some embodiments, one or more T cell binding domains (e.g., a T cell binding agent) that target the viral vector to a T cell. In some embodiments, the T cell binding agent binds to a molecule expressed on the surface of the T cell. The cell surface molecule may be a receptor, coreceptor, or a GPI-anchored protein. In some embodiments, the T cell binding agent binds CD3, CD4 or CD8. 68 sf-5667634186152009940

[0308] In particular embodiments, a T cell binding agent may be fused to or incorporated in a protein fusogen or attachment protein, thereby retargeting the lipid particle to a T cell. In some embodiments, for re-targeting the T cell binding agent is fused to a protein fusogen or envelope attachment protein that is mutated to reduce binding for the native binding partner of the fusogen or viral envelope protein. In some embodiments, the fusogen is or contains a mutant G protein or a biologically active portion thereof that is a mutant of wild-type NiV-G and exhibits reduced binding to one or both of the native binding partners Ephrin B2 or Ephrin B3, including any as described above. Thus, in some aspects, a fusogen can be retargeted to display altered tropism. In some embodiments, the binding confers re-targeted binding compared to the binding of a wild-type surface glycoprotein protein in which a new or different binding activity is conferred. In particular embodiments, the binding confers re-targeted binding compared to the binding of a wild-type G protein in which a new or different binding activity is conferred. In some embodiments the fusogen is randomly mutated. In some embodiments the fusogen is rationally mutated. In some embodiments the fusogen is subjected to directed evolution. In some embodiments the fusogen is truncated and only a subset of the peptide is used in the viral vector. In some embodiments, amino acid residues in the measles hemagglutinin protein may be mutated to alter the binding properties of the protein, redirecting fusion (doi:10.1038 / nbt942, Molecular Therapy vol.16 no. 8, 1427–1436 Aug.2008, doi:10.1038 / nbt1060, DOI: 10.1128 / JVI.76.7.3558–3563.2002, DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi: 10.1073pnas.0604993103).

[0309] In some embodiments, protein fusogens may be re-targeted by covalently conjugating a T cell binding agent to the attachment protein. In some embodiments, the fusogen and T cell binding agent are covalently conjugated by expression of a chimeric protein comprising the fusogen linked to the T cell binding agent (e.g., retargeted attachment protein). The T cell binding agent can include any targeting protein able to confer specific binding to a target molecule expressed on the surface of a T cell. In some embodiments, a targeting protein can also include an antibody or an antigen-binding fragment thereof (e.g., Fab, Fab', F(ab')2, Fv fragments, scFv antibody fragments, disulfide-linked Fvs (sdFv), a Fd fragment consisting of the VH and CH1 domains, linear antibodies, single domain antibodies such as sdAb (either VL or VH), nanobodies, or camelid VHH domains), an antigen-binding fibronectin type III (Fn3) scaffold such as a fibronectin polypeptide minibody, a ligand, a cytokine, a chemokine, or a T cell receptor (TCRs). In some embodiments, the T cell binding agent is an antibody or antigen binding fragment thereof. In some embodiments, the fusion protein can be engineered to bind the Fc region of an antibody that targets an antigen on a target cell, redirecting the fusion activity towards cells that display the antibody’s target (DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi:10.1038 / nm1192). In some embodiments, altered and non-altered fusogens may be displayed on the same retroviral vector or VLP (doi: 10.1016 / j.biomaterials.2014.01.051). 69 sf-5667634186152009940

[0310] In some embodiments, a single-chain variable fragment (scFv) can be conjugated to fusogens to redirect fusion activity towards T cells that display the scFv binding target (doi:10.1038 / nbt1060, DOI 10.1182 / blood-2012-11-468579, doi:10.1038 / nmeth.1514, doi:10.1006 / mthe.2002.0550, HUMAN GENE THERAPY 11:817– 826, doi:10.1038 / nbt942, doi:10.1371 / journal.pone.0026381, DOI 10.1186 / s12896-015-0142-z). In some embodiments, designed ankyrin repeat proteins (DARPin) can be conjugated to fusogens to redirect fusion activity towards T cells that display the DARPin binding target (doi:10.1038 / mt.2013.16, doi:10.1038 / mt.2010.298, doi: 10.4049 / jimmunol.1500956), as well as combinations of different DARPins (doi:10.1038 / mto.2016.3). In some embodiments, a single domain antibody (e.g., a VHH) can be conjugated to fusogens to redirect fusion activity towards T cells that display the sdAb binding target. In some embodiments, receptor ligands and antigens can be conjugated to fusogens to redirect fusion activity towards T cells that display the target receptor (DOI: 10.1089 / hgtb.2012.054, DOI: 10.1128 / JVI.76.7.3558–3563.2002). a) CD3 Binding Agents

[0311] In some embodiments, the lipid particles disclosed herein comprise one or more retargeted attachment proteins, each independently comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, wherein the target molecule is CD3. In some embodiments, the targeting moiety is a CD3 binding domain, e.g., a CD3 binding agent, such as any of those disclosed herein.

[0312] In some embodiments, CD3 binding domain may be fused to or incorporated in a protein fusogen or lipid particle envelope attachment protein (e.g., a retargeted attachment protein). In some embodiments, the CD3 binding domain may be incorporated into the co-display protein. In some embodiments, a CD3 binding domain may be incorporated into the viral envelope via fusion with a transmembrane domain. In some embodiments, the CD3 binding domain targets the lipid particle to a T cell.

[0313] The lipid particles disclosed herein include, in some embodiments, one or more CD3 binding agents. For example, a CD3 binding agent may be fused to or incorporated in a retargeted attachment protein. In another embodiment, a CD3 binding agent may be incorporated into the lipid particle envelope via fusion with a transmembrane domain.

[0314] Exemplary CD3 binding agents include antibodies and fragments thereof (e.g., scFv, VHH) that bind to CD3. Such antibodies may be derived from any species, and may be for example, mouse, rabbit, human, humanized, or camelid antibodies.

[0315] Exemplary antibodies include OKT3, CRIS-7, I2C, blinatumomab, catumaxomab, muromonab-CD3, A-319, AFM11, AMG 199, AMG 211, AMG 424, AMG 427, AMG 562, AMG 564, APVO436, CC-93269, ERY974, GBR1302, GEM333, GEM2PSCA, GNC-035, HPN424, IGM-2323, 70 sf-5667634186152009940 JNJ-63709178, JNJ-63898081, JNJ-75348780, JNJ-78306358, M701, M802, MGD007, MOR209 / ES414, PF-06671008, REGN5459, RO7283420, SAR442257, SAR443216, TNB-383B, TNB- 486, TNB-585, Y150, acapatamab, cevostamab, cibisatamab, duvortuxizumab, eluvixtamab, emerfetamab, etevritamab, glofitamab, gresonitamab, obrindatamab, pavurutamab, plamotamab, solitomab, tarlatamab, tepoditamab, tidutamab, vibecotamab, vixtimotamab, alnuctamab, dafsolimab setaritox, pacanalotamab, pasotuxizumab, runimotamab, nivatrotamab, elranatamab, ertumaxomab, flotetuzumab, odronextamab, talquetamab, teclistamab, visilizumab, epcoritamab, otelixizumab, 3F8BiAb, CCW702, DKTK CC-1, EMB-06, GEN1044, GEN1047, GTB-3550, HPN217, IMC-C103C, NVG-111, REGN4018, REGN4336, REGN5458, A-2019, A-337, ABP-100, AFM15, AFM21, AMG 701, APVO425, CLN-049, Dow2, EM801, Ektomab, FBTA05, GBR1342, GBR1372, GSK3537142, HBM7020, HLX31, IGM-2644, MG1122, MGD015, ND003, ND007, PF-07062119, RO7293583, STA551, TT19, ZW38; and anti-CD3 antibodies disclosed in US Patent Nos.4361549, 7728114, 9657102, 9587021, and 11007267; US Patent Application Nos. US20120269826, US20180057597, and US20180112000; and PCT Application Nos. WO2005118635, WO2011050106, WO2012162067, WO2014047231, WO2016116626, WO2016180721, and WO2016204966. Other exemplary binding agents include designed ankyrin repeat proteins (DARPins) and binding agents based on fibronectin type III (Fn3) scaffolds.

[0316] In some embodiments, the CD3 binding agent comprises a heavy chain variable (VH) region comprising a CDR-H1, a CDRH-2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO:474, 475, and 476 respectively; and a light chain variable region comprising a CDR-L1, a CDR- L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO:477, 478, and 479, respectively. In some embodiments, the CD3 binding agent comprises a VH region comprising an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO:480, and a VL region comprising an amino acid sequence having at least about 90% sequence identity to the amino acid sequence set forth in SEQ ID NO:481. In some embodiments, the CD3 binding agent comprises a VH region comprising the amino acid sequence set forth in SEQ ID NO:480, and a VL region comprising the amino acid sequence set forth in SEQ ID NO:481. In some embodiments, the CD3 binding agent is an scFv. In some embodiments, the CD3 binding agent comprises the amino acid sequence set forth in SEQ ID NO:482. In some embodiments, the CD3 binding agent comprises the amino acid sequence set forth in SEQ ID NO:802. In some embodiments, the CD3 binding agent is OKT3.

[0317] In some embodiments, the CD3 binding agent is activating (e.g., the CD3 binding agent activates T cells). In some embodiments, the CD3 binding agent is non-activating (e.g., it does not activate T cells). 71 sf-5667634186152009940

[0318] In some embodiments, a CD3 binding agent comprises a humanized antibody molecule, intact IgA, IgG, IgE or IgM antibody; bi- or multi- specific antibody (e.g., Zybodies®, etc.); antibody fragments such as Fab fragments, Fab’ fragments, F(ab’)2fragments, Fd’ fragments, Fd fragments, and isolated CDRs or sets thereof; single chain Fvs; polypeptide-Fc fusions; single domain antibodies (e.g., shark single domain antibodies such as IgNAR or fragments thereof); camelid antibodies; masked antibodies (e.g., Probodies®); Small Modular ImmunoPharmaceuticals (“SMIPsTM”); single chain or Tandem diabodies (TandAb®); VHHs; Anticalins®; Nanobodies®; minibodies; BiTE®s; ankyrin repeat proteins or DARPINs®; Avimers®; DARTs; TCR-like antibodies;, Adnectins®; Affilins®; Trans- bodies®; Affibodies®; TrimerX®; MicroProteins; Fynomers®, Centyrins®; and KALBITOR®s.

[0319] In some embodiments, the CD3 binding agent is a peptide. In some embodiments, the CD3 binding agent is an antibody, such as a single-chain variable fragment (scFv). In some embodiments, the CD3 binding agent is an antibody, such as a single domain antibody. In some embodiments, the antibody can be human or humanized. In some embodiments, the CD3 binding agent is a VHH. In some embodiments, the antibody or portion thereof is naturally occurring. In some embodiments, the antibody or portion thereof is synthetic.

[0320] In some embodiments, the antibody can be generated from phage display libraries to have specificity for a desired target ligand. In some embodiments, the phage display libraries are generated from a VHH repertoire of camelids immunized with various antigens, as described in Arbabi et al., FEBS Letters, 414, 521-526 (1997); Lauwereys et al., EMBO J., 17, 3512-3520 (1998); Decanniere et al., Structure, 7, 361-370 (1999). In some embodiments, the phage display library is generated comprising antibody fragments of a non-immunized camelid. In some embodiments, a library of human single domain antibodies is synthetically generated by introducing diversity into one or more scaffolds.

[0321] In some embodiments, the C-terminus of the CD3 binding agent is attached to the C- terminus of the G protein (e.g., fusogen) or biologically active portion thereof. In some embodiments, the N-terminus of the CD3 binding agent is exposed on the exterior surface of the lipid bilayer.

[0322] In some embodiments, the CD3 binding agent is the only surface displayed non-viral sequence of the viral vector. In some embodiments, the CD3 binding agent is the only membrane bound non-viral sequence of the viral vector. In some embodiments, the viral vector does not contain a molecule that engages or stimulates T cells other than the CD3 binding agent. In some embodiments, the viral vector contains a non-activating CD3 binding agent.

[0323] In some embodiments, viral vectors may display CD3 binding agents that are not conjugated to protein fusogens in order to redirect the fusion activity towards a cell that is bound by the targeting moiety, or to affect homing. 72 sf-5667634186152009940 b) CD4 Binding Agents

[0324] In some embodiments, the lipid particles disclosed herein comprise one or more retargeted attachment proteins, each independently comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, wherein the target molecule is CD4. In some embodiments, the targeting moiety is a CD4 binding domain, e.g., a CD4 binding agent, such as any of those disclosed herein.

[0325] The lipid particles disclosed herein include, in some embodiments, one or more CD4 binding agents. For example, a CD4 binding agent may be fused to or incorporated in a protein fusogen or attachment protein. In another embodiment, a CD4 binding agent may be incorporated into the lipid particle envelope via fusion with a transmembrane domain.

[0326] In some of any of the provided embodiments, the CD4 binding agent is exposed on the surface of the lipid particle. In some embodiments, the CD4 binding agent is fused to a transmembrane domain incorporated in the lipid particle envelope.

[0327] In some embodiments, CD4 binding domain may be fused to or incorporated in a protein fusogen or lipid particle envelope attachment protein (e.g., a retargeted attachment protein). In some embodiments, the CD4 binding domain may be incorporated into the co-display protein. In some embodiments, a CD4 binding domain may be incorporated into the viral envelope via fusion with a transmembrane domain. In some embodiments, the CD3 binding domain targets the lipid particle to a T cell.

[0328] Exemplary CD4 binding agents include antibodies and fragments thereof (e.g., scFv, VHH) that bind to CD4. Such antibodies may be derived from any species, and may be for example, mouse, rabbit, human, humanized, or camelid antibodies. Exemplary antibodies include ibalizumab, zanolimumab, tregalizumab, priliximab, cedelizumab, clenoliximab, keliximab, and anti-CD4 antibodies disclosed in WO2002102853, WO2004083247, WO2004067554, WO2007109052, WO2008134046, WO2010074266, WO2012113348, WO2013188870, WO2017104735, WO2018035001, WO2018170096, WO2019203497, WO2019236684, WO2020228824, US 5,871,732, US 7,338,658, US 7,722,873, US 8,399,621, US 8,911,728, US 9,005,963,US 9,587,022, US 9,745,552, US provisional application no.63 / 326,269, US provisional application no.63 / 341,681; as well as antibodies B486A1, RPA-T4, CE9.1 (Novus Biologicals); GK1.5, RM4-5, RPA-T4 , OKT4, 4SM95, S3.5, N1UG0 (ThermoFisher); GTX50984, ST0488, 10B5, EP204 (GeneTex); GK1.3, 5A8, 10C12, W3 / 25, 8A5, 13B8.2, 6G5 (Absolute Antibody); VIT4, M-T466, M-T321, REA623, (Miltenyi); MEM115, MT310 (Enzo Life Sciences); H129.19, 5B4, 6A17, 18-46, A-1, C-1, OX68 (Santa Cruz); EP204, D2E6M (Cell Signaling Technology). Other exemplary binding agents include designed ankyrin repeat proteins (DARPins) (e.g., the anti-CD4 DARPin disclosed in WO2017182585) and binding agents based on 73 sf-5667634186152009940 fibronectin type III (Fn3) scaffolds. Each of US 9,005,963, US provisional application no.63 / 326,269, and US provisional application no.63 / 341,681 is incorporated by reference herein in its entirety.

[0329] In some embodiments, protein fusogens or attachment proteins may be re-targeted by mutating amino acid residues in a fusion protein or a targeting protein (e.g. the hemagglutinin (H) protein or G protein). In particular embodiments, the fusogen (e.g. G protein) is mutated to reduce binding for the native binding partner of the fusogen. In some embodiments, the fusogen is or contains a mutant G protein or a biologically active portion thereof that is a mutant of wild-type NiV-G and exhibits reduced binding to one or both of the native binding partners Ephrin B2 or Ephrin B3, including any as described above. Thus, in some aspects, a fusogen can be retargeted to display altered tropism. In some embodiments, the binding confers re-targeted binding compared to the binding of a wild-type surface glycoprotein protein in which a new or different binding activity is conferred. In particular embodiments, the binding confers re-targeted binding compared to the binding of a wild-type G protein in which a new or different binding activity is conferred. In some embodiments the fusogen is randomly mutated. In some embodiments the fusogen is rationally mutated. In some embodiments the fusogen is subjected to directed evolution. In some embodiments the fusogen is truncated and only a subset of the peptide is used in the viral vector. In some embodiments, amino acid residues in the measles hemagglutinin protein may be mutated to alter the binding properties of the protein, redirecting fusion (doi:10.1038 / nbt942, Molecular Therapy vol.16 no.8, 1427–1436 Aug.2008, doi:10.1038 / nbt1060, DOI: 10.1128 / JVI.76.7.3558–3563.2002, DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi: 10.1073pnas.0604993103).

[0330] In some embodiments, protein fusogens may be re-targeted by covalently conjugating a CD4 binding agent to the fusion protein or attachment protein (e.g. retargeted attachment protein). In some embodiments, the fusogen and CD4 binding agent are covalently conjugated by expression of a chimeric protein comprising the fusogen linked to the CD4 binding agent (e.g. retargeted attachment protein). In some embodiments, a single-chain variable fragment (scFv) can be conjugated to fusogens to redirect fusion activity towards cells that display the scFv binding target (doi:10.1038 / nbt1060, DOI 10.1182 / blood-2012-11-468579, doi:10.1038 / nmeth.1514, doi:10.1006 / mthe.2002.0550, HUMAN GENE THERAPY 11:817– 826, doi:10.1038 / nbt942, doi:10.1371 / journal.pone.0026381, DOI 10.1186 / s12896-015-0142-z). In some embodiments, designed ankyrin repeat proteins (DARPin) can be conjugated to fusogens to redirect fusion activity towards cells that display the DARPin binding target (doi:10.1038 / mt.2013.16, doi:10.1038 / mt.2010.298, doi: 10.4049 / jimmunol.1500956), as well as combinations of different DARPins (doi:10.1038 / mto.2016.3). In some embodiments, receptor ligands and antigens can be conjugated to fusogens to redirect fusion activity towards cells that display the target receptor (DOI: 10.1089 / hgtb.2012.054, DOI: 10.1128 / JVI.76.7.3558–3563.2002). In some embodiments, a targeting protein can also include an antibody or an antigen-binding fragment thereof (e.g., Fab, Fab', 74 sf-5667634186152009940 F(ab')2, Fv fragments, scFv antibody fragments, disulfide-linked Fvs (sdFv), a Fd fragment consisting of the VH and CH1 domains, linear antibodies, single domain antibodies such as sdAb (either VL or VH), nanobodies, or camelid VHH domains), an antigen-binding fibronectin type III (Fn3) scaffold such as a fibronectin polypeptide minibody, a ligand, a cytokine, a chemokine, or a T cell receptor (TCRs). In some embodiments, protein fusogens may be re-targeted by non-covalently conjugating a CD4 binding agent to the fusion protein or targeting protein (e.g. retargeted attachment protein)). In some embodiments, the fusion protein can be engineered to bind the Fc region of an antibody that targets an antigen on a target cell, redirecting the fusion activity towards cells that display the antibody’s target (DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi:10.1038 / nm1192). In some embodiments, altered and non-altered fusogens may be displayed on the same retroviral vector or VLP (doi: 10.1016 / j.biomaterials.2014.01.051).

[0331] In some embodiments, a CD4 binding agent comprises a humanized antibody molecule, intact IgA, IgG, IgE or IgM antibody; bi- or multi- specific antibody (e.g., Zybodies®, etc.); antibody fragments such as Fab fragments, Fab’ fragments, F(ab’)2fragments, Fd’ fragments, Fd fragments, and isolated CDRs or sets thereof; single chain Fvs; polypeptide-Fc fusions; single domain antibodies (e.g., shark single domain antibodies such as IgNAR or fragments thereof); camelid antibodies; masked antibodies (e.g., Probodies®); Small Modular ImmunoPharmaceuticals (“SMIPsTM”); single chain or Tandem diabodies (TandAb®); VHHs; Anticalins®; Nanobodies®; minibodies; BiTE®s; ankyrin repeat proteins or DARPINs®; Avimers®; DARTs; TCR-like antibodies;, Adnectins®; Affilins®; Trans- bodies®; Affibodies®; TrimerX®; MicroProteins; Fynomers®, Centyrins®; and KALBITOR®s.

[0332] In some embodiments, the CD4 binding agent is a peptide. In some embodiments, the CD4 binding agent is an antibody, such as a single-chain variable fragment (scFv). In some embodiments, the CD4 binding agent is an antibody, such as a single domain antibody. In some embodiments, the antibody can be human or humanized. In some embodiments, the CD4 binding agent is a VHH. In some embodiments, the antibody or portion thereof is naturally occurring. In some embodiments, the antibody or portion thereof is synthetic.

[0333] In some embodiments, the antibody can be generated from phage display libraries to have specificity for a desired target ligand. In some embodiments, the phage display libraries are generated from a VHH repertoire of camelids immunized with various antigens, as described in Arbabi et al., FEBS Letters, 414, 521-526 (1997); Lauwereys et al., EMBO J., 17, 3512-3520 (1998); Decanniere et al., Structure, 7, 361-370 (1999). In some embodiments, the phage display library is generated comprising antibody fragments of a non-immunized camelid. In some embodiments, a library of human single domain antibodies is synthetically generated by introducing diversity into one or more scaffolds. 75 sf-5667634186152009940

[0334] In some embodiments, the C-terminus of the CD4 binding agent is attached to the C- terminus of the G protein (e.g., fusogen) or biologically active portion thereof. In some embodiments, the N-terminus of the CD4 binding agent is exposed on the exterior surface of the lipid bilayer.

[0335] In some embodiments, the CD4 binding agent is the only surface displayed non-viral sequence of the lipid particle. In some embodiments, the CD4 binding agent is the only membrane bound non-viral sequence of the lipid particle. In some embodiments, the lipid particle does not contain a molecule that engages or stimulates T cells other than the CD4 binding agent.

[0336] In some embodiments, lipid particles may display CD4 binding agents that are not conjugated to protein fusogens in order to redirect the fusion activity towards a cell that is bound by the targeting moiety, or to affect homing.

[0337] In some embodiments, a protein fusogen derived from a virus or organism that do not infect humans does not have a natural fusion targets in patients, and thus has high specificity.

[0338] In some of any of the provided embodiments, the CD4 binding agent is an anti-CD4 antibody or an antigen-binding fragment. In some of any of the provided embodiments, the anti-CD4 antibody or antigen-binding fragment is mouse, rabbit, human, or humanized. In some embodiments, the antigen- binding fragment is a single chain variable fragment (scFv). In some embodiments, the antigen-binding fragment is an anti-CD4 scFv.

[0339] In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 260, 261, and 262, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 263, 264, and 265, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 260, 261, and 262, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 263, 264, and 265, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 266, 267, and 268, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 269, 270, and 265, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 266, 267, and 268, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 269, 270, and 265, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 271, 272, and 268, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 269, 270, and 265, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, 76 sf-5667634186152009940 a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 271, 272, and 268, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 269, 270, and 265, respectively. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:273. In some embodiments, the anti-CD4 scFv comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:274. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:273; and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:274. In some embodiments, the VH and VL are joined by a linker. In some embodiments, the linker comprises the amino acid sequence set forth in SEQ ID NO:275. In some embodiments, the anti- CD4 scFv comprises the amino acid sequence set forth in SEQ ID NO:276.

[0340] In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 277, 278, and 279, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 280, 281, and 282, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 277, 278, and 279, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 280, 281, and 282, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 283, 284, and 285, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 286, 287, and 288, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 283, 284, and 285, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 286, 287, and 288, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 289, 290, and 285, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 286, 287, and 282, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 289, 290, and 285, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 286, 287, and 282, respectively. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:291. In some embodiments, the anti-CD4 scFv comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:292. In some embodiments, the anti-CD4 77 sf-5667634186152009940 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:291; and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:292. In some embodiments, the VH and VL are joined by a linker. In some embodiments, the linker comprises the amino acid sequence set forth in SEQ ID NO:275. In some embodiments, the anti- CD4 scFv comprises the amino acid sequence set forth in SEQ ID NO:293.

[0341] In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 294, 295, and 296, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 297, 298, and 299, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 294, 295, and 296, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 297, 298, and 299, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 300, 301, 302, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 303, 304, and 299, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 300, 301, 302, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 303, 304, and 299, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 305, 306, 306, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 303, 304, and 299, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 305, 306, 302, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 224, 225, and 172, respectively. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:307. In some embodiments, the anti-CD4 scFv comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:308. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:307; and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:308. In some embodiments, the VH and VL are joined by a linker. In some embodiments, the linker comprises the amino acid sequence set forth in SEQ ID NO:275. In some embodiments, the anti-CD4 scFv comprises the amino acid sequence set forth in SEQ ID NO:309. 78 sf-5667634186152009940

[0342] In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 310, 311, and 312, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 313, 314, and 315, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 310, 311, and 312, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 313, 314, and 315, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 316, 317, 318, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 319, 320, and 315, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 316, 317, 318, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 319, 320, and 315, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 321, 322, 318, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 319, 321, and 315, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 321, 322, 318, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 319, 320, and 323, respectively. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:323. In some embodiments, the anti-CD4 scFv comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:324. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:323; and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:324. In some embodiments, the VH and VL are joined by a linker. In some embodiments, the linker comprises the amino acid sequence set forth in SEQ ID NO:275. In some embodiments, the anti-CD4 scFv comprises the amino acid sequence set forth in SEQ ID NO:325.

[0343] In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 326, 327, and 328, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 329, 330, and 331, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 326, 327, and 328, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 79 sf-5667634186152009940 comprising the amino acid sequence set forth in SEQ ID NO: 329, 330, and 331, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 332, 333, and 334, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 335, 336, and 331, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 332, 333, and 334, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 335, 336, and 331, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 337, 338, and 334, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 335, 336, and 331, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 337, 338, and 334, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 335, 336, and 331, respectively. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:339. In some embodiments, the anti-CD4 scFv comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:340. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:339; and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:340. In some embodiments, the VH and VL are joined by a linker. In some embodiments, the linker comprises the amino acid sequence set forth in SEQ ID NO:275. In some embodiments, the anti- CD4 scFv comprises the amino acid sequence set forth in SEQ ID NO:341.

[0344] In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 342, 343, and 344, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 345, 346, and 347, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 342, 343, and 344, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 345, 346, and 347, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 348, 349, and 350, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 351, 352, and 347, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ 80 sf-5667634186152009940 ID NO: 242, 243, and 244, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 245, 246, and 198, respectively. In some embodiments, the anti- CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 353, 354, and 350, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 351, 353, and 347, respectively. In some embodiments, the anti-CD4 scFv comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 353, 354, and 350, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 351, 352, and 347, respectively. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:355. In some embodiments, the anti-CD4 scFv comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:356. In some embodiments, the anti-CD4 scFv comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:355; and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:356. In some embodiments, the VH and VL are joined by a linker. In some embodiments, the linker comprises the amino acid sequence set forth in SEQ ID NO:275. In some embodiments, the anti- CD4 scFv comprises the amino acid sequence set forth in SEQ ID NO:357.

[0345] In some embodiments, the anti-CD4 antibody or antigen-binding fragment is a single domain antibody. In some embodiments, the anti-CD4 antibody or antigen-binding fragment is a camelid (e.g. llama, alpaca, camel) anti-CD4 antibody or antigen-binding fragment (e.g. VHH). In some embodiments, the anti-CD4 antibody or antigen-binding fragment is an anti-CD4 VHH. In some embodiments, the anti- CD4 VHH comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 358, 359, and 360, respectively. In some embodiments, the anti-CD4 VHH comprises a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 361, 362, and 363, respectively. In some embodiments, the anti-CD4 VHH comprises a CDR- H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequence set forth in SEQ ID NO: 364, 365, and 363, respectively. In some embodiments, the anti-CD4 VHH comprises the amino acid sequence set forth in SEQ ID NO:366. c) CD7 Binding Agents

[0346] In some embodiments, the lipid particles disclosed herein comprise one or more retargeted attachment proteins, each independently comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, wherein the target molecule is CD7. In some embodiments, the targeting moiety is a CD7 binding domain, e.g., a CD7 binding agent, such as any of those disclosed herein. 81 sf-5667634186152009940

[0347] The lipid particles disclosed herein include, in some embodiments, one or more CD7 binding agents. For example, a CD7 binding agent may be fused to or incorporated in a protein fusogen or attachment protein. In another embodiment, a CD7 binding agent may be incorporated into the lipid particle envelope via fusion with a transmembrane domain.

[0348] In some embodiments, CD7 binding domain may be fused to or incorporated in a protein fusogen or lipid particle envelope attachment protein (e.g., a retargeted attachment protein). In some embodiments, the CD7 binding domain may be incorporated into the co-display protein. In some embodiments, a CD7 binding domain may be incorporated into the viral envelope via fusion with a transmembrane domain. In some embodiments, the CD7 binding domain targets the lipid particle to a T cell.

[0349] Exemplary CD7 binding agents include antibodies and fragments thereof (e.g., scFv, VHH) that bind to CD7. Such antibodies may be derived from any species, and may be for example, mouse, rabbit, human, humanized, or camelid antibodies. Exemplary antibodies include grsinilimab, SPV-T3a and those disclosed in WO2015 / 184941; US10106609; WO2017 / 213979; WO2018 / 098306; WO2019086534; US11447548; WO2019 / 102234; WO2022 / 136887; WO2022 / 136888; WO2020 / 212710; WO2021 / 160267; WO2022 / 095803; WO2022 / 151851. Further exemplary anti-CD7 binding agents and G proteins are described in U.S. provisional application No.63 / 172,518, which is incorporated by reference herein. Other exemplary binding agents include designed ankyrin repeat proteins (DARPins) and binding agents based on fibronectin type III (Fn3) scaffolds.

[0350] In some embodiments, protein fusogens or attachment proteins may be re-targeted by mutating amino acid residues in a fusion protein or a targeting protein (e.g. retargeted attachment protein). In particular embodiments, the fusogen (e.g. G protein) is mutated to reduce binding for the native binding partner of the fusogen. In some embodiments, the fusogen is or contains a mutant G protein or a biologically active portion thereof that is a mutant of wild-type NiV-G and exhibits reduced binding to one or both of the native binding partners Ephrin B2 or Ephrin B3, including any as described above. Thus, in some aspects, a fusogen can be retargeted to display altered tropism. In some embodiments, the binding confers re-targeted binding compared to the binding of a wild-type surface glycoprotein protein in which a new or different binding activity is conferred. In particular embodiments, the binding confers re-targeted binding compared to the binding of a wild-type G protein in which a new or different binding activity is conferred. In some embodiments the fusogen is randomly mutated. In some embodiments the fusogen is rationally mutated. In some embodiments the fusogen is subjected to directed evolution. In some embodiments the fusogen is truncated and only a subset of the peptide is used in the viral vector. In some embodiments, amino acid residues in the measles hemagglutinin protein may be mutated to alter the binding properties of the protein, redirecting fusion (doi:10.1038 / nbt942, Molecular Therapy vol.16 no.8, 1427–1436 Aug.2008, doi:10.1038 / nbt1060, DOI: 82 sf-5667634186152009940 10.1128 / JVI.76.7.3558–3563.2002, DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi: 10.1073pnas.0604993103).

[0351] In some embodiments, protein fusogens (e.g., attachment proteins) may be re-targeted by covalently conjugating a CD7 binding agent to the fusion protein or attachment protein (e.g. retargeted attachment protein). In some embodiments, the fusogen and CD7 binding agent are covalently conjugated by expression of a chimeric protein comprising the fusogen linked to the CD8 binding agent. In some embodiments, a single-chain variable fragment (scFv) can be conjugated to fusogens to redirect fusion activity towards cells that display the scFv binding target (doi:10.1038 / nbt1060, DOI 10.1182 / blood-2012-11-468579, doi:10.1038 / nmeth.1514, doi:10.1006 / mthe.2002.0550, HUMAN GENE THERAPY 11:817– 826, doi:10.1038 / nbt942, doi:10.1371 / journal.pone.0026381, DOI 10.1186 / s12896-015-0142-z). In some embodiments, designed ankyrin repeat proteins (DARPin) can be conjugated to fusogens to redirect fusion activity towards cells that display the DARPin binding target (doi:10.1038 / mt.2013.16, doi:10.1038 / mt.2010.298, doi: 10.4049 / jimmunol.1500956), as well as combinations of different DARPins (doi:10.1038 / mto.2016.3). In some embodiments, receptor ligands and antigens can be conjugated to fusogens to redirect fusion activity towards cells that display the target receptor (DOI: 10.1089 / hgtb.2012.054, DOI: 10.1128 / JVI.76.7.3558–3563.2002). In some embodiments, a targeting protein can also include an antibody or an antigen-binding fragment thereof (e.g., Fab, Fab', F(ab')2, Fv fragments, scFv antibody fragments, disulfide-linked Fvs (sdFv), a Fd fragment consisting of the VH and CH1 domains, linear antibodies, single domain antibodies such as sdAb (either VL or VH), nanobodies, or camelid VHH domains), an antigen-binding fibronectin type III (Fn3) scaffold such as a fibronectin polypeptide minibody, a ligand, a cytokine, a chemokine, or a T cell receptor (TCRs). In some embodiments, protein fusogens may be re-targeted by non-covalently conjugating a CD7 binding agent to the fusion protein or targeting protein (e.g. the hemagglutinin protein). In some embodiments, the fusion protein can be engineered to bind the Fc region of an antibody that targets an antigen on a target cell, redirecting the fusion activity towards cells that display the antibody’s target (DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi:10.1038 / nm1192). In some embodiments, altered and non- altered fusogens may be displayed on the same retroviral vector or VLP (doi: 10.1016 / j.biomaterials.2014.01.051).

[0352] In some embodiments, a CD7 binding agent comprises a humanized antibody molecule, intact IgA, IgG, IgE or IgM antibody; bi- or multi- specific antibody (e.g., Zybodies®, etc.); antibody fragments such as Fab fragments, Fab’ fragments, F(ab’)2 fragments, Fd’ fragments, Fd fragments, and isolated CDRs or sets thereof; single chain Fvs; polypeptide-Fc fusions; single domain antibodies (e.g., shark single domain antibodies such as IgNAR or fragments thereof); cameloid antibodies; masked antibodies (e.g., Probodies®); Small Modular ImmunoPharmaceuticals (“SMIPsTM”); single chain or Tandem diabodies (TandAb®); VHHs; Anticalins®; Nanobodies®; minibodies; BiTE®s; ankyrin repeat 83 sf-5667634186152009940 proteins or DARPINs®; Avimers®; DARTs; TCR-like antibodies;, Adnectins®; Affilins®; Trans- bodies®; Affibodies®; TrimerX®; MicroProteins; Fynomers®, Centyrins®; and KALBITOR®s.

[0353] In some embodiments, the CD7 binding agent is a peptide. In some embodiments, the CD7 binding agent is an antibody, such as a single-chain variable fragment (scFv). In some embodiments, the CD7 binding agent is an antibody, such as a single domain antibody. In some embodiments, the CD7 binding agent is a VHH. In some embodiments, the antibody can be human or humanized. In some embodiments, the antibody or portion thereof is naturally occurring. In some embodiments, the antibody or portion thereof is synthetic.

[0354] In some embodiments, the antibody can be generated from phage display libraries to have specificity for a desired target ligand. In some embodiments, the phage display libraries are generated from a VHH repertoire of camelids immunized with various antigens, as described in Arbabi et al., FEBS Letters, 414, 521-526 (1997); Lauwereys et al., EMBO J., 17, 3512-3520 (1998); Decanniere et al., Structure, 7, 361-370 (1999). In some embodiments, the phage display library is generated comprising antibody fragments of a non-immunized camelid. In some embodiments, a library of human single domain antibodies is synthetically generated by introducing diversity into one or more scaffolds.

[0355] In some embodiments, the C-terminus of the CD7 binding agent is attached to the C- terminus of the G protein (e.g., fusogen) or biologically active portion thereof. In some embodiments, the N-terminus of the CD7 binding agent is exposed on the exterior surface of the lipid bilayer.

[0356] In some embodiments, the CD7 binding agent is the only surface displayed non-viral sequence of the viral vector. In some embodiments, the CD7 binding agent is the only membrane bound non-viral sequence of the viral vector. In some embodiments, the viral vector does not contain a molecule that engages or stimulates T cells other than the CD7 binding agent.

[0357] In some embodiments, viral vectors may display CD7 binding agents that are not conjugated to protein fusogens in order to redirect the fusion activity towards a cell that is bound by the targeting moiety, or to affect homing. d) CD8 Binding Agents

[0358] In some embodiments, the lipid particles disclosed herein comprise one or more retargeted attachment proteins, each independently comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, wherein the target molecule is CD8. In some embodiments, the targeting moiety is a CD8 binding domain, e.g., a CD8 binding agent, such as any of those disclosed herein.

[0359] The lipid particles disclosed herein include, in some embodiments, one or more CD8 binding agents. For example, a CD8 binding agent may be fused to or incorporated in a protein fusogen or 84 sf-5667634186152009940 attachment protein. In another embodiment, a CD8 binding agent may be incorporated into the lipid particle envelope via fusion with a transmembrane domain.

[0360] In some embodiments, CD8 binding domain may be fused to or incorporated in a protein fusogen or lipid particle envelope attachment protein (e.g., a retargeted attachment protein). In some embodiments, the CD8 binding domain may be incorporated into the co-display protein. In some embodiments, a CD8 binding domain may be incorporated into the viral envelope via fusion with a transmembrane domain. In some embodiments, the CD8 binding domain targets the lipid particle to a T cell.

[0361] Exemplary CD8 binding agents include antibodies and fragments thereof (e.g., scFv, VHH) that bind to one or more of CD8 alpha and CD8 beta. Such antibodies may be derived from any species, and may be for example, mouse, rabbit, human, humanized, or camelid antibodies. Exemplary antibodies include those disclosed in WO2014025828, WO2014164553, WO2020069433, WO2015184203, US20160176969, WO2017134306, WO2019032661, WO2020257412, WO2018170096, WO2020060924, US10730944, US20200172620, and the non-human antibodies OKT8; RPA-T8, 12.C7 (Novus); 17D8, 3B5, LT8, RIV11, SP16, YTC182.20, MEM-31, MEM-87, RAVB3, C8 / 144B (Thermo Fisher); 2ST8.5H7, Bu88, 3C39, Hit8a, SPM548, CA-8, SK1, RPA-T8 (GeneTex); UCHT4 (Absolute Antibody); BW135 / 80 (Miltenyi); G42-8 (BD Biosciences); C8 / 1779R, mAb 104 (Enzo Life Sciences); B-Z31 (Sapphire North America); 32-M4, 5F10, MCD8, UCH-T4, 5F2 (Santa Cruz); D8A8Y, RPA-T8 (Cell Signaling Technology). Further exemplary anti-CD8 binding agents and G proteins are described in U.S. provisional application No.63 / 172,518, which is incorporated by reference herein. Other exemplary binding agents include designed ankyrin repeat proteins (DARPins) and binding agents based on fibronectin type III (Fn3) scaffolds.

[0362] In some embodiments, the CD8 binding agent comprises a CDR-H1, a CDR-H2, and a CDR- H3 comprising the amino acid sequence set forth in SEQ ID NO: 483, 484, and 485, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 486, 487, and 488, respectively. In some embodiments, the CD8 binding agent comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:369, and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:370. In some embodiments, the CD8 binding agent comprises the sequence set forth in SEQ ID NO:489.

[0363] In some embodiments, the CD8 binding agent comprises a CDR-H1, a CDR-H2, and a CDR- H3 comprising the amino acid sequence set forth in SEQ ID NO: 490, 491, and 492, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 493, 494, and 495, respectively. In some embodiments, the CD8 binding agent comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:371 and a light chain 85 sf-5667634186152009940 variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:372. In some embodiments, the CD8 binding agent comprises the sequence set forth in SEQ ID NO:496.

[0364] In some embodiments, the CD8 binding agent comprises a CDR-H1, a CDR-H2, and a CDR- H3 comprising the amino acid sequence set forth in SEQ ID NO: 497, 498, and 499, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 486, 487, and 500, respectively. In some embodiments, the CD8 binding agent comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:373, and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:374. In some embodiments, the CD8 binding agent comprises the sequence set forth in SEQ ID NO:501.

[0365] In some embodiments, the CD8 binding agent comprises a CDR-H1, a CDR-H2, and a CDR- H3 comprising the amino acid sequence set forth in SEQ ID NO: 502, 503, and 504, respectively; and a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequence set forth in SEQ ID NO: 505, 506, and 507, respectively. In some embodiments, the CD8 binding agent comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:375, and a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO:376. In some embodiments, the CD8 binding agent comprises the sequence set forth in SEQ ID NO:508.

[0366] In some embodiments, the CD8 binding agent comprises a CDR-H1, a CDR-H2, and a CDR- H3 comprising the amino acid sequence set forth in SEQ ID NO: 509, 510, and 511, respectively. In some embodiments, the CD8 binding agent comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:377. In some embodiments, the CD8 binding agent comprises the sequence set forth in SEQ ID NO:377.

[0367] In some embodiments, the CD8 binding agent comprises any CD8 binding agent as described in US 2019 / 0144885, incorporated by reference herein in its entirety.

[0368] In some embodiments, the CD8 binding agent is an scFv that contains a VH and VL set forth from any as below, in which the VH and VL are separated by linker. In some embodiments, the CD8 binding agent is a VHH having the sequence set forth below. In some embodiments, the CD8 binding agent is linked to the C-terminus of a truncated NiV-G set forth in SEQ ID NO: 19 to provide a re- targeted NiV-G. In some embodiments, the retargeted NiV-G is pseudotyped on a lentiviral vector with the NiV-F (e.g. set forth in SEQ ID NO:227). In some embodiments, the lentiviral vector further contains a payload gene encoding an anti-CD19 CAR. In some embodiments, the anti-CD19 CAR contains an anti-CD19 FMC63 scFv binding domain set forth in SEQ ID NO:239, a CD8 hinge set forth in SEQ ID NO:367, a CD8 transmembrane domain set forth in SEQ ID NO: 368, a 4-1bb signaling domain set forth in SEQ ID NO:248. a CD3zeta signaling domain set forth in SEQ ID NO: 249.

[0369] CD8_1 86 sf-5667634186152009940 VH (SEQ ID NO.: 369): QVQLVQSGAEVKKPGASVKVSCKASGGTFSSYAISWVRQAPGQGLEWMGIIDPSDGNTNYAQN FQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCAKERAAAGYYYYMDVWGQGTTVTVSS VL (SEQ ID NO.: 370): DIQMTQSPSSLSASVGDRVTITCRASQSISSYLNWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSG SGTDFTLTISSLQPEDFATYYCQQSYSTPLTFGGGTKVEIKR

[0370] CD8_2 VH (SEQ ID NO.:371): QVQLVQSGAEVKKPGASVKVSCKASGYTFTDYYIQWVRQAPGQGLEWMGWINPNSGGTSYAQ KFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCAKEGDYYYGMDAWGQGTMVTVSS VL (SEQ ID NO.:372): DIVMTQSPLSLPVTPGEPASISCRSSQSLLHSNGYNYLDWYLQKPGQSPQLLIYLGSNRASGVPD RFSGSGSGTDFTLKISRVEAEDVGVYYCMQGLQTPHTFGQGTKVEIKR

[0371] CD8_3 VH (SEQ ID NO.:373): QVQLVQSGAEVKKPGASVKVSCKASGYTFTSYYMHWVRQAPGQGLEWMGGFDPEDGETIYA QKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCARDQGWGMDVWGQGTTVTVSS VL(SEQ ID NO.:374): DIQMTQSPSSLSASVGDRVTITCRASQSISSYLNWYQQKPGKAPKLLIYAASSLQSGVPSRFSGSG SGTDFTLTISSLQPEDFATYYCQQTYSTPYTFGQGTKLEIKR

[0372] CD8_4 VH (SEQ ID NO.:375): QVQLVQSGAEVKKPGASVKVSCKASGYTFTNHYMHWVRQAPGQGLEWMGWMNPNSGNTGY AQKFQGRVTMTRDTSTSTVYMELSSLRSEDTAVYYCASSESGSDLDYWGQGTLVTVSS VL (SEQ ID NO.:376): DIQMTQSPSSLSASVGDRVTITCRASQTIGNYVNWYQQKPGKAPKLLIYGASNLHTGVPSRFSGS GSGTDFTLTISSLQPEDFATYYCQQTYSAPLTFGGGTKVEIKR

[0373] In some embodiments, the CD8 binding agent is VHH set forth as: VHH (SEQ ID NO.:377): QVQLVESGGGLVQAGGSLRLSCAASGRTFSGYVMGWFRQAPGKQRKFVAAISRGGLSTSYADS VKGRFTISRDNAKNTVFLQMNTLKPEDTAVYYCAADRSDLYEITAASNIDSWGQGTLVTVSS

[0374] In some embodiments, protein fusogens or attachment proteins may be re-targeted by mutating amino acid residues in a fusion protein or a targeting protein (e.g. retargeted attachment protein). In particular embodiments, the fusogen (e.g. G protein) is mutated to reduce binding for the native binding partner of the fusogen. In some embodiments, the fusogen is or contains a mutant G 87 sf-5667634186152009940 protein or a biologically active portion thereof that is a mutant of wild-type NiV-G and exhibits reduced binding to one or both of the native binding partners Ephrin B2 or Ephrin B3, including any as described above. Thus, in some aspects, a fusogen can be retargeted to display altered tropism. In some embodiments, the binding confers re-targeted binding compared to the binding of a wild-type surface glycoprotein protein in which a new or different binding activity is conferred. In particular embodiments, the binding confers re-targeted binding compared to the binding of a wild-type G protein in which a new or different binding activity is conferred. In some embodiments the fusogen is randomly mutated. In some embodiments the fusogen is rationally mutated. In some embodiments the fusogen is subjected to directed evolution. In some embodiments the fusogen is truncated and only a subset of the peptide is used in the viral vector. In some embodiments, amino acid residues in the measles hemagglutinin protein may be mutated to alter the binding properties of the protein, redirecting fusion (doi:10.1038 / nbt942, Molecular Therapy vol.16 no.8, 1427–1436 Aug.2008, doi:10.1038 / nbt1060, DOI: 10.1128 / JVI.76.7.3558–3563.2002, DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi: 10.1073pnas.0604993103).

[0375] In some embodiments, protein fusogens (e.g., attachment proteins) may be re-targeted by covalently conjugating a CD8 binding agent to the fusion protein or attachment protein (e.g. retargeted attachment protein). In some embodiments, the fusogen and CD8 binding agent are covalently conjugated by expression of a chimeric protein comprising the fusogen linked to the CD8 binding agent. In some embodiments, a single-chain variable fragment (scFv) can be conjugated to fusogens to redirect fusion activity towards cells that display the scFv binding target (doi:10.1038 / nbt1060, DOI 10.1182 / blood-2012-11-468579, doi:10.1038 / nmeth.1514, doi:10.1006 / mthe.2002.0550, HUMAN GENE THERAPY 11:817– 826, doi:10.1038 / nbt942, doi:10.1371 / journal.pone.0026381, DOI 10.1186 / s12896-015-0142-z). In some embodiments, designed ankyrin repeat proteins (DARPin) can be conjugated to fusogens to redirect fusion activity towards cells that display the DARPin binding target (doi:10.1038 / mt.2013.16, doi:10.1038 / mt.2010.298, doi: 10.4049 / jimmunol.1500956), as well as combinations of different DARPins (doi:10.1038 / mto.2016.3). In some embodiments, receptor ligands and antigens can be conjugated to fusogens to redirect fusion activity towards cells that display the target receptor (DOI: 10.1089 / hgtb.2012.054, DOI: 10.1128 / JVI.76.7.3558–3563.2002). In some embodiments, a targeting protein can also include an antibody or an antigen-binding fragment thereof (e.g., Fab, Fab', F(ab')2, Fv fragments, scFv antibody fragments, disulfide-linked Fvs (sdFv), a Fd fragment consisting of the VH and CH1 domains, linear antibodies, single domain antibodies such as sdAb (either VL or VH), nanobodies, or camelid VHH domains), an antigen-binding fibronectin type III (Fn3) scaffold such as a fibronectin polypeptide minibody, a ligand, a cytokine, a chemokine, or a T cell receptor (TCRs). In some embodiments, protein fusogens may be re-targeted by non-covalently conjugating a CD8 binding agent to the fusion protein or targeting protein (e.g. the hemagglutinin protein). In some embodiments, 88 sf-5667634186152009940 the fusion protein can be engineered to bind the Fc region of an antibody that targets an antigen on a target cell, redirecting the fusion activity towards cells that display the antibody’s target (DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi:10.1038 / nm1192). In some embodiments, altered and non- altered fusogens may be displayed on the same retroviral vector or VLP (doi: 10.1016 / j.biomaterials.2014.01.051).

[0376] In some embodiments, a CD8 binding agent comprises a humanized antibody molecule, intact IgA, IgG, IgE or IgM antibody; bi- or multi- specific antibody (e.g., Zybodies®, etc.); antibody fragments such as Fab fragments, Fab’ fragments, F(ab’)2fragments, Fd’ fragments, Fd fragments, and isolated CDRs or sets thereof; single chain Fvs; polypeptide-Fc fusions; single domain antibodies (e.g., shark single domain antibodies such as IgNAR or fragments thereof); cameloid antibodies; masked antibodies (e.g., Probodies®); Small Modular ImmunoPharmaceuticals (“SMIPsTM”); single chain or Tandem diabodies (TandAb®); VHHs; Anticalins®; Nanobodies®; minibodies; BiTE®s; ankyrin repeat proteins or DARPINs®; Avimers®; DARTs; TCR-like antibodies;, Adnectins®; Affilins®; Trans- bodies®; Affibodies®; TrimerX®; MicroProteins; Fynomers®, Centyrins®; and KALBITOR®s.

[0377] In some embodiments, the CD8 binding agent is a peptide. In some embodiments, the CD8 binding agent is an antibody, such as a single-chain variable fragment (scFv). In some embodiments, the CD8 binding agent is an antibody, such as a single domain antibody. In some embodiments, the CD8 binding agent is a VHH. In some embodiments, the antibody can be human or humanized. In some embodiments, the antibody or portion thereof is naturally occurring. In some embodiments, the antibody or portion thereof is synthetic.

[0378] In some embodiments, the antibody can be generated from phage display libraries to have specificity for a desired target ligand. In some embodiments, the phage display libraries are generated from a VHH repertoire of camelids immunized with various antigens, as described in Arbabi et al., FEBS Letters, 414, 521-526 (1997); Lauwereys et al., EMBO J., 17, 3512-3520 (1998); Decanniere et al., Structure, 7, 361-370 (1999). In some embodiments, the phage display library is generated comprising antibody fragments of a non-immunized camelid. In some embodiments, a library of human single domain antibodies is synthetically generated by introducing diversity into one or more scaffolds.

[0379] In some embodiments, the C-terminus of the CD8 binding agent is attached to the C- terminus of the G protein (e.g., fusogen) or biologically active portion thereof. In some embodiments, the N-terminus of the CD8 binding agent is exposed on the exterior surface of the lipid bilayer.

[0380] In some embodiments, the CD8 binding agent is the only surface displayed non-viral sequence of the viral vector. In some embodiments, the CD8 binding agent is the only membrane bound non-viral sequence of the viral vector. In some embodiments, the viral vector does not contain a molecule that engages or stimulates T cells other than the CD8 binding agent. 89 sf-5667634186152009940

[0381] In some embodiments, viral vectors may display CD8 binding agents that are not conjugated to protein fusogens in order to redirect the fusion activity towards a cell that is bound by the targeting moiety, or to affect homing. II. HSC Binding Domains

[0382] In some embodiments, the lipid particles disclosed herein comprise one or more retargeted attachment proteins, each independently comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell. In some embodiments, the targeting moiety is an HSC binding domain, e.g., an HSC binding agent, such as any of those disclosed herein.

[0383] In some embodiments, an HSC binding domain may be fused to or incorporated in a protein fusogen or lipid particle envelope attachment protein (e.g., a retargeted attachment protein). In some embodiments, the HSC binding domain may be incorporated into the co-display protein. In some embodiments, an HSC binding domain may be incorporated into the viral envelope via fusion with a transmembrane domain. In some embodiments, the HSC binding domain targets the lipid particle to a T cell.

[0384] The lipid particles disclosed herein include, in some embodiments, one or more HSC binding domains (e.g., HSC binding agent) that target the viral vector to a cell that is an HSC. In some embodiments, the HSC binding agent binds to a molecule expressed on the surface of the HSC. The cell surface molecule may be a receptor, coreceptor, or a GPI-anchored protein. In some embodiments, the HSC binding agent binds ASCT2, CD105, CD110, CD117, CD133, CD146, CD164, CD34, CD46, CD49f, CD90, EPCR, or ITGA3. In some embodiments, a HSC binding agent may be fused to or incorporated in a protein fusogen or lipid particle envelope attachment protein (e.g., a retargeted attachment protein). In some embodiments, a HSC binding agent may be incorporated into the viral envelope via fusion with a transmembrane domain. In some embodiments, the HSC binding agent targets the lipid particle to a HSC.

[0385] In particular embodiments, a HSC binding agent may be fused to or incorporated in a protein fusogen or attachment protein, thereby retargeting the lipid particle to a HSC. In some embodiments, for re-targeting the HSC binding agent is fused to a protein fusogen or envelope attachment protein that is mutated to reduce binding for the native binding partner of the fusogen or viral envelope protein. In some embodiments, the fusogen is or contains a mutant G protein or a biologically active portion thereof that is a mutant of wild-type NiV-G and exhibits reduced binding to one or both of the native binding partners Ephrin B2 or Ephrin B3, including any as described above. Thus, in some aspects, a fusogen can be retargeted to display altered tropism. In some embodiments, the binding confers re-targeted binding compared to the binding of a wild-type surface glycoprotein protein in which a new or different binding 90 sf-5667634186152009940 activity is conferred. In particular embodiments, the binding confers re-targeted binding compared to the binding of a wild-type G protein in which a new or different binding activity is conferred. In some embodiments the fusogen is randomly mutated. In some embodiments the fusogen is rationally mutated. In some embodiments the fusogen is subjected to directed evolution. In some embodiments the fusogen is truncated and only a subset of the peptide is used in the viral vector. In some embodiments, amino acid residues in the measles hemagglutinin protein may be mutated to alter the binding properties of the protein, redirecting fusion (doi:10.1038 / nbt942, Molecular Therapy vol.16 no.8, 1427–1436 Aug.2008, doi:10.1038 / nbt1060, DOI: 10.1128 / JVI.76.7.3558–3563.2002, DOI: 10.1128 / JVI.75.17.8016– 8020.2001, doi: 10.1073pnas.0604993103).

[0386] In some embodiments, protein fusogens may be re-targeted by covalently conjugating a HSC binding agent to the attachment protein. In some embodiments, the fusogen and HSC binding agent are covalently conjugated by expression of a chimeric protein comprising the fusogen linked to the HSC binding agent (e.g., retargeted attachment protein). The HSC binding agent can include any targeting protein able to confer specific binding to a target molecule expressed on the surface of a HSC. In some embodiments, a targeting protein can also include an antibody or an antigen-binding fragment thereof (e.g., Fab, Fab', F(ab')2, Fv fragments, scFv antibody fragments, disulfide-linked Fvs (sdFv), a Fd fragment consisting of the VH and CH1 domains, linear antibodies, single domain antibodies such as sdAb (either VL or VH), nanobodies, or camelid VHH domains), an antigen-binding fibronectin type III (Fn3) scaffold such as a fibronectin polypeptide minibody, a ligand, a cytokine, a chemokine, or a T cell receptor (TCRs). In some embodiments, the HSC binding agent is an antibody or antigen binding fragment thereof. In some embodiments, the fusion protein can be engineered to bind the Fc region of an antibody that targets an antigen on a target cell, redirecting the fusion activity towards cells that display the antibody’s target (DOI: 10.1128 / JVI.75.17.8016–8020.2001, doi:10.1038 / nm1192). In some embodiments, altered and non-altered fusogens may be displayed on the same retroviral vector or VLP (doi: 10.1016 / j.biomaterials.2014.01.051).

[0387] In some embodiments, a single-chain variable fragment (scFv) can be conjugated to fusogens to redirect fusion activity towards HSCs that display the scFv binding target (doi:10.1038 / nbt1060, DOI 10.1182 / blood-2012-11-468579, doi:10.1038 / nmeth.1514, doi:10.1006 / mthe.2002.0550, HUMAN GENE THERAPY 11:817– 826, doi:10.1038 / nbt942, doi:10.1371 / journal.pone.0026381, DOI 10.1186 / s12896-015-0142-z). In some embodiments, designed ankyrin repeat proteins (DARPin) can be conjugated to fusogens to redirect fusion activity towards HSCs that display the DARPin binding target (doi:10.1038 / mt.2013.16, doi:10.1038 / mt.2010.298, doi: 10.4049 / jimmunol.1500956), as well as combinations of different DARPins (doi:10.1038 / mto.2016.3). In some embodiments, a single domain antibody (e.g., a VHH) can be conjugated to fusogens to redirect fusion activity towards HSCs that display the sdAb binding target. In some embodiments, receptor ligands and antigens can be conjugated 91 sf-5667634186152009940 to fusogens to redirect fusion activity towards HSCs that display the target receptor (DOI: 10.1089 / hgtb.2012.054, DOI: 10.1128 / JVI.76.7.3558–3563.2002).

[0388] In some embodiments, the target cell is a CD34+ progenitor cells. In some embodiments, the target cell molecule is expressed on at least a subset of CD34+ progenitor cells.

[0389] In some embodiments, the cell surface molecule is expressed on HSCs. In some embodiments, the cell surface molecule is expressed on MPPs. In some embodiments, the cell surface molecule is expressed on MLPs. In some embodiments, the cell surface molecule is expressed on ETPs. In some embodiments, the cell surface molecule is expressed on MEPs. In some embodiments, the cell surface molecule is expressed on CMPs. In some embodiments, the cell surface molecule is expressed on GMPs. In some embodiments, the cell surface molecule is expressed on any combination of the foregoing CD34+ progenitor subpopulations. In some embodiments, the cell surface molecule is expressed on HSCs and MPPs. In some embodiments, the cell surface molecule is expressed on myeloid progenitors. In some embodiments, the cell surface molecule is expressed on lymphoid progenitors. In some embodiments, the cell surface molecule is expressed on myeloid progenitors. In some embodiments, the cell surface molecule is expressed on HSCs, MPPs, MEPs, CMPs, and GMPs.

[0390] In some embodiments, the cell surface molecule is ASCT2. In some embodiments, the target cell is ASCT2+.

[0391] In some embodiments, the cell surface molecule is CD105. In some embodiments, the target cell is CD105+.

[0392] In some embodiments, the cell surface molecule is CD110. In some embodiments, the target cell is CD110+.

[0393] In some embodiments, the cell surface molecule is CD117. In some embodiments, the target cell is CD117+.

[0394] In some embodiments, the cell surface molecule is CD133. In some embodiments, the target cell is CD133+.

[0395] In some embodiments, the cell surface molecule is CD146. In some embodiments, the target cell is CD146+.

[0396] In some embodiments, the cell surface molecule is CD164. In some embodiments, the target cell is CD164+.

[0397] In some embodiments, the cell surface molecule is CD34. In some embodiments, the target cell is CD34+.

[0398] In some embodiments, the cell surface molecule is CD46. In some embodiments, the target cell is CD46+. 92 sf-5667634186152009940

[0399] In some embodiments, the cell surface molecule is CD49f. In some embodiments, the target cell is CD49f+.

[0400] In some embodiments, the ta cell surface molecule is CD90. In some embodiments, the target cell is CD90+.

[0401] In some embodiments, the cell surface molecule is EPCR. In some embodiments, the target cell is EPCR+.

[0402] In some embodiments, the cell surface molecule is ITGA3. In some embodiments, the target cell is ITGA3+.

[0403] In some embodiments, the target molecule is CD133. In some embodiments, the target cell is CD133+. In some embodiments, the targeting agent is an anti-CD133 antibody. Exemplary anti-CD133 antibodies include CART133, AC133, 293C3-SDIE, CMab-43, RW03, 293C3H9 (293C3), and W6B3H10 (W6B3); and anti-CD133 antibodies disclosed in US Patent Nos. US8722858, US9249225, US9624303, US10106623, US10711068, US11098109, US11214628, US11352435, and US11220551; US Patent Application Nos. US20130224202; PCT Application Nos. WO200901840, WO2011089211, WO2011149493, WO2014128185, WO2015121383, WO2016154623, WO2018045880, WO2018072025, and WO2022022718; and Canadian Patent Application No. CA2962157.

[0404] In some embodiments, the lipid particles disclosed herein comprise one or more retargeted attachment proteins, each independently comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, wherein the target molecule is CD133. In some embodiments, the targeting moiety is a CD133 binding domain, e.g., a CD133 binding agent, such as any of those disclosed herein.

[0405] In some embodiments, the lipid particles comprise one or more HSC binding domains that is a CD133 binding agent that targets the viral vector to a cell that is an HSC. In some embodiments, the lipid particles comprise two or more HSC binding domains that are each a CD133 binding agent that targets the viral vector to a cell that is an HSC. In some embodiments, each of the two or more HSC binding domains that are each a CD133 binding agent bind distinct epitopes of the same target molecule (CD133). In some embodiments, the lipid particle comprises two or more, e.g., two, three, four, or five or more, CD133 binding agents.

[0406] In some embodiments, the lipid particle comprises one or more targeting moieties, e.g., HSC binding domains, in which the CD133 binding agent is an antibody or antigen-binding fragment. In some embodiments, the CD133 binding agent is a single chain antibody, such as a single chain variable fragment (scFv). In some embodiments, the CD133 binding agent contains a variable heavy (VH) chain comprising a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID NOs: 536, 537, and 538, respectively, and a variable light (VL) chain comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 540, 541, and 542, respectively; 93 sf-5667634186152009940 (b) a VH chain comprising a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID NOs: 545, 546, and 547, respectively, and a VL chain comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 549, 550, and 551, respectively; (c) a VH chain comprising a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID NOs: 518, 519, and 520, respectively, and a VL chain comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 522, 523, and 524, respectively; (d) a VH chain comprising a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID NOs: 527, 528, and 529, respectively, and a VL chain comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 531, 532, and 533, respectively; or (e) a VH chain comprising a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID NOs: 554, 555, and 556, respectively, and a VL chain comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 558, 559, and 560, respectively.

[0407] In some embodiments, the lipid particle comprises one or more targeting moieties, e.g., HSC binding domains, that is a CD133 binding agent which is a single chain antibody, such as a single chain variable fragment (scFv) comprising a VH and a VL selected from: (a) a VH comprising a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID NOs: 289, 565, and 538, respectively, and a VL comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 540, 541, and 542, respectively; (b) a VH comprising a CDR-H1, a CDR- H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID NOs: 566, 567, and 547, respectively, and a VL comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 549, 550, and 551, respectively; (c) a VH comprising a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID Nos: 568, 569, and 520, respectively, and a VL comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 522, 523, and 524, respectively; (d) a VH comprising a CDR-H1, a CDR-H2, and a CDR- H3 comprising the amino acid sequences of SEQ ID NOs: 570, 571, and 529, respectively, and a VL comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID NOs: 531, 532, and 533, respectively; and (e) a VH comprising a CDR-H1, a CDR-H2, and a CDR-H3 comprising the amino acid sequences of SEQ ID NOs: 572, 573, and 556, respectively, and a VL comprising a CDR-L1, a CDR-L2, and a CDR-L3 comprising the amino acid sequences of SEQ ID Nos: 558, 559, and 560, respectively.

[0408] In some embodiments, the lipid particle comprises one or more, e.g., one, two, three, or more, targeting moieties, e.g., HSC binding domains, independently selected from: (a) a CD133 binding agent comprising a heavy chain variable (VH) region comprising the amino acid sequence of SEQ ID NO: 535, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; and a light chain variable (VL) region comprising the amino acid 94 sf-5667634186152009940 sequence of SEQ ID NO: 539, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; (b) a CD133 binding agent comprising a VH region comprising the amino acid sequence of SEQ ID NO: 544, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; and a VL region comprising the amino acid sequence of SEQ ID NO: 548, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; (c) a CD133 binding agent comprising a VH region comprising the amino acid sequence of SEQ ID NO: 517, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; and a VL region comprising the amino acid sequence of SEQ ID NO: 521, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; (d) a CD133 binding agent comprising a VH region comprising the amino acid sequence of SEQ ID NO: 526, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; and a VL region comprising the amino acid sequence of SEQ ID NO: 530, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; and (e) a CD133 binding agent comprising a VH region comprising the amino acid sequence of SEQ ID NO: 553, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; and a VL region comprising the amino acid sequence of SEQ ID NO: 557, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto.

[0409] In some embodiments, the lipid particle comprises one or more, e.g., one, two, three, or more, targeting moieties, e.g., HSC binding domains, independently selected from: (a) a CD133 binding agent comprising a heavy chain variable (VH) region comprising the amino acid sequence of SEQ ID NO: 535 and a light chain variable (VL) region comprising the amino acid sequence of SEQ ID NO: 539; (b) a CD133 binding agent comprising a VH region comprising the amino acid sequence of SEQ ID NO: 544 and a VL region comprising the amino acid sequence of SEQ ID NO: 548; (c) a CD133 binding agent comprising a VH region comprising the amino acid sequence of SEQ ID NO: 517 and a VL region comprising the amino acid sequence of SEQ ID NO: 521; (d) a CD133 binding agent comprising a VH region comprising the amino acid sequence of SEQ ID NO: 526 and a VL region comprising the amino acid sequence of SEQ ID NO: 530; and (e) a CD133 binding agent comprising a VH region comprising the amino acid sequence of SEQ ID NO: 553 and a VL region comprising the amino acid sequence of SEQ ID NO: 557.

[0410] In some embodiments, the lipid particle comprises one or more targeting moieties, e.g., HSC binding domains, that is an scFv comprising an amino acid sequence independently selected from the group consisting of SEQ ID NOs: 516, 525, 534, 543, and 552, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto. In some 95 sf-5667634186152009940 embodiments, each of the one or more CD133 binding agents is independently an scFv comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 516, 525, 534, 543, and 552, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto.

[0411] In some embodiments, the lipid particle comprises a first CD133 binding agent that is an scFv comprising the amino acid sequence of SEQ ID NO: 516 or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto, and a second CD133 binding agent that is an scFv comprising the amino acid sequence of SEQ ID NO: 525 or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto.

[0412] In some embodiments, the target molecule is CD105. In some embodiments, the target cell is CD105+. In some embodiments, the targeting agent is an anti-CD105 antibody. Exemplary anti-CD105 antibodies include carotuximab, TRC105, huRH105, and TCR205; and anti-CD105 antibodies disclosed in US Patent Nos. US8221753, US8609094, US9150652, US95181212, US9926375, US9944714, US10155820, and US10336831; US Patent Application Nos. US20100098692, US20100196398, US20170007714, and US20220233591; PCT Application Nos. WO2010039873, WO2011041441, WO2016077451, WO2018067819, WO2010032059, WO2012149412, WO2015118031, WO2021118955, and WO2021118957; and Korean Patent No. KR101398707B1.

[0413] In some embodiments, the lipid particles disclosed herein comprise one or more retargeted attachment proteins, each independently comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, wherein the target molecule is CD117. In some embodiments, the targeting moiety is a CD117 binding domain, e.g., a CD117 binding agent, such as any of those disclosed herein.

[0414] In some embodiments, the target molecule is CD117. In some embodiments, the target cell is CD117+. In some embodiments, the targeting moiety is a CD117 binding agent that is an anti-CD117 antibody. In some embodiments, the CD117 binding agent is a single domain antibody, such as a VHH. In some embodiments, the lipid particles comprise one or more HSC binding domains that is a CD117 binding agent that targets the viral vector to a cell that is an HSC. In some embodiments, the lipid particle comprises one or more targeting moieties, e.g., HSC binding domains, that is a CD117 binding agent comprising an amino acid sequence independently selected from the group consisting of SEQ ID NOs: 512-515 and 575-621, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto.

[0415] In some embodiments, the lipid particle comprises one or more targeting moieties, e.g., HSC binding domains, selected from: (a) a CD117 binding agent comprising a VHH comprising the amino acid sequence of SEQ ID NO: 512, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 96 sf-5667634186152009940 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; (b) a CD117 binding agent comprising a VHH comprising the amino acid sequence of SEQ ID NO: 513, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; (c) a CD117 binding agent comprising a VHH comprising the amino acid sequence of SEQ ID NO: 514, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto; and (d) a CD117 binding agent comprising a VHH comprising the amino acid sequence of SEQ ID NO: 515, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity thereto.

[0416] In some embodiments, the lipid particle comprises one or more targeting moieties, e.g., HSC binding domains, each independently comprising a VHH comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 512-515 and 575-621, or an amino acid sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity to an amino acid sequence selected from the group consisting of SEQ ID NOs: 512-515 and 575-621, wherein the target molecule is CD117.

[0417] In some embodiments, the lipid particle comprises one or more targeting moieties, e.g., HSC binding domains, each independently comprising a VHH comprising a CDR-H1, a CDR-H2, and a CDR- H3 contained within an amino acid sequence selected from the group consisting of SEQ ID NOs: 512- 515 and 575-621, wherein the target molecule is CD117.

[0418] In some embodiments, the target molecule is EPCR. In some embodiments, the target cell is EPCR+. In some embodiments, the targeting agent is an anti-EPCR antibody. Exemplary anti-EPCR antibodies include JRK1494, JRK1535; and anti-EPCR antibodies disclosed in US Patent Application Nos. US20210355231 and US20220127374; and PCT Application Nos. WO2020051277 and WO2020161478.

[0419] In some embodiments, the target molecule is CD34. In some ...

Claims

186152009940 CLAIMS WHAT IS CLAIMED:

1. A lipid particle, comprising: (a) a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, (b) a co-display protein; and (c) at least one paramyxovirus fusion (F) protein; and wherein the co-display protein increases the potency and / or specificity of the lipid particle as compared to a lipid particle not comprising the co-display protein, wherein the protein in (a), (b) and (c) are exposed on the outside of the lipid bilayer / embedded in the lipid bilayer.

2. A lipid particle, comprising: (a) a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, (b) a co-display protein for increasing the potency and / or specificity of the lipid particle as compared to a lipid particle not comprising the co-display protein; and (c) at least one paramyxovirus fusion (F) protein; and wherein the protein in (a), (b) and (c) are exposed on the outside of the lipid bilayer / embedded in the lipid bilayer.

3. A lipid particle, comprising: (a) a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a first target molecule expressed on the surface of a target cell, (b) a co-display protein comprising a binding means for specifically interacting with a second target molecule expressed on the surface of the target cell; and (c) at least one paramyxovirus fusion (F) protein; and wherein the protein in (a), (b) and (c) are exposed on the outside of the lipid bilayer / embedded in the lipid bilayer.

4. A lipid particle, comprising: (a) a Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof, and (b) a co-display protein comprising a binding means for specifically interacting with a target molecule expressed on the surface of the target cell; and wherein the protein in (a) and (b) are exposed on the outside of the lipid bilayer / embedded in the lipid bilayer. 368 sf-5667634186152009940 5. The lipid particle of any of claims 1-4, wherein the co-display protein is an immune stimulating protein and / or is a transduction adjuvant.

6. A lipid particle, comprising: (a) a retargeted attachment protein comprising (i) a paramyxovirus envelope attachment protein; and (ii) a targeting moiety directed to a target molecule expressed on the surface of a target cell, (b) a co-display protein selected from an immune stimulating protein and a transduction adjuvant; and (c) at least one paramyxovirus fusion (F) protein; and wherein the protein in (a), (b) and (c) are embedded in the lipid bilayer.

7. The lipid particle of claims 1-6, wherein the co-display protein is selected from the group comprising of a glycoprotein, transmembrane protein, receptor, integrin, antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide.

8. The lipid particle of any of claims 1-7, wherein the co-display protein increases specificity to the target cell.

9. The lipid particle of any of claims 1-8, wherein the co-display protein increases specificity to a target cell selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells.

10. The lipid particle of any of claims 1-9, wherein the co-display protein increases specificity to a target cell selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell..

11. The lipid particle of any of claims 1-10, wherein the co-display protein increases specificity to a target cell that is a hematopoietic stem cell. 369 sf-5667634186152009940 12. The lipid particle of claim 11, wherein the cell surface molecule is selected from CD34, CD105, or CD117.

13. The lipid particle of any of claims 1-10, wherein the co-display protein increases specificity to a target cell that is a T cell.

14. The lipid particle of claim 13, wherein the cell surface molecule is selected from CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3.

15. The lipid particle of any of claims 1-10, wherein the co-display protein increases specificity to a target cell that is a hepatocyte.

16. The lipid particle of claim 15, wherein the cell surface molecule is selected from ASGR1, ASGR2 and TM4SF5.

17. The lipid particle of any of claims 1-3, and 5-16, wherein the co-display protein binds to a different protein than the targeting moiety of the retargeted attachment protein.

18. The lipid particle of claim 1, wherein the co-display protein does not include a paramyxovirus envelope attachment protein or a fragment thereof.

19. The lipid particle of any of claims 1-10, 13, 14, 17 or 18, wherein the co-display protein is an immune stimulating protein and the immune stimulating protein stimulates a T cell activity or function.

20. The lipid particle of claim 19, wherein the immune stimulating protein comprises (i) an extracellular domain, (ii) a linker, and (iii) an anchor.

21. The lipid particle of claim 20, wherein the extracellular domain of the immune stimulating protein binds to a T cell stimulatory receptor.

22. The lipid particle of claim 21, wherein the T cell stimulatory receptor is selected from CD3, CD2, CD28, CD27. 370 sf-5667634186152009940 23. The lipid particle of claims 20-22, wherein the extracellular domain of the immune stimulating protein binds to CD3.

24. The lipid particle of claims 20-23, wherein the extracellular domain is selected from the group comprising an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide.

25. The lipid particle of claims 20-24, wherein the extracellular domain of the immune stimulating protein is an anti-CD3 antibody or single chain fragment thereof.

26. The lipid particle of any of claims 1-18, wherein the co-display protein is a transduction adjuvant that increases transduction efficiency of the lipid particle as compared to a lipid particle that does not have a co-display protein comprising a transduction adjuvant.

27. The lipid particle of any of claims 1-18, and 26, wherein the co-display protein is a transduction adjuvant that binds to a surface molecule on target cells to enhance transduction.

28. The lipid particle of claim 26 or 27 wherein the transduction adjuvant comprises (i) an extracellular domain, (ii) a linker, and (iii) an anchor.

29. The lipid particle of claim 28, wherein the extracellular domain of the transduction adjuvant binds an integrin binding domain.

30. The lipid particle of claims 28 or 29, wherein the extracellular domain of the transduction adjuvant comprises the extracellular domain of fibronectin, retronectin, or a functional variant thereof.

31. The lipid particle of any of claims 20-30, wherein the linker is derived from a human protein. 371 sf-5667634186152009940 32. The lipid particle of any of claims 20-31, wherein the linker is a derived from human CD8α, IgG3 hinge, IgG1 hinge, IgG4 heavy chain, IgG4, or CD28.

33. The lipid particle of any of claims 20-32, wherein the linker is modified to remove a cysteine residue.

34. The lipid particle of any of claims 20-33, wherein the linker is rigid or wherein the linker is flexible.

35. The lipid particle of any of claims 20-34, wherein the anchor is a peptide anchor that is a transmembrane domain.

36. The lipid particle of any of claims 20-35, wherein the anchor is a transmembrane domain that is a transmembrane domain of a protein selected from PDGFR, VSV-G, CD8α, ICAM1, HLA-DRB, CD49d, or Transferrin.

37. The lipid particle of any of claims 20-34, wherein the anchor is a GPI lipid anchor.

38. The lipid particle of any of claims 1-3, and 5-37, wherein the targeting moiety is selected from the group consisting of an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide.

39. The lipid particle of any of claims 1-3, and 5-38, wherein the targeting moiety binds to a cell surface molecule present on a target cell.

40. The lipid particle of claim 39, wherein the cell surface molecule is a protein, glycan, or lipid.

41. The lipid particle of any of claims 1-3, and 5-40, wherein the target cell is selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells.

42. The lipid particle of any of claims 1-3, and 5-41, wherein the target cells is selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem 372 sf-5667634186152009940 cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell.

43. The lipid particle of any of claims 1-3, and 5-42, wherein the target is a hematopoietic stem cell.

44. The lipid particle of any of claim 43, wherein the cell surface molecule is selected from CD34, CD105, or CD117.

45. The lipid particle of any of claims 1-3, and 5-42, wherein the target cell is a T cell.

46. The lipid particle of claim 45, wherein the cell surface molecule is selected from the group consisting of CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3.

47. The lipid particle of any of claims 1-3, and 5-42, wherein the target cell is a hepatocyte.

48. The lipid particle of claim 47, wherein the cell surface molecule is selected from the group consisting of ASGR1, ASGR2 and TM4SF5.

49. The lipid particle of any of claims 1-3, and 5-48, wherein the targeting moiety is selected from the group consisting of a single domain antibody or a single chain variable fragment (scFv).

50. The lipid particle of claim 49, wherein the single domain antibody is a VHH.

51. The lipid particle of any of claims 1-3, and 5-50, wherein the retargeted attachment protein is linked to a (i) first targeting moiety directed to a first target molecule expressed on the surface of a target cell, and a (ii) second targeting moiety directed to a second target molecule expressed on the surface of a target cell. 373 sf-5667634186152009940 52. The lipid particle of any of claims 1-3, and 5-51, wherein the paramyxovirus envelope attachment protein of the retargeted attachment protein is a first paramyxovirus envelope attachment protein and the lipid particle further comprises a second paramyxovirus envelope attachment protein.

53. The lipid particle of any of claims 1-3, and 5-52, wherein the second paramyxovirus envelope attachment protein is linked to the first paramyxovirus envelope attachment protein in tandem.

54. The lipid particle of any of claims 1-3, and 5-53, wherein the retargeted attachment protein comprising the first paramyxovirus envelope attachment protein and the second paramyxovirus envelope attachment protein are each separately exposed the outside of the lipid bilayer / embedded in the lipid bilayer.

55. The lipid particle of any of claims 1-3, and 5-54, wherein the second paramyxovirus attachment protein is a retargeted attachment protein.

56. The lipid particle of claim 55, wherein the second retargeted attachment protein comprises (i) a second paramyxovirus envelope attachment protein; and (ii) a second targeting moiety directed to a target molecule expressed on the surface of a target cell.

57. The lipid particle of any of claims 51-56, wherein the targeting moiety is selected from the group consisting of an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide.

58. The lipid particle of claim 56 or 57, wherein the target cell is selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells.

59. The lipid particle of any of claims 56-58, wherein the target cells is selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell. 374 sf-5667634186152009940 60. The lipid particle of any of claims 56-59, wherein the target is a hematopoietic stem cell.

61. The lipid particle of any of claim 60, wherein the cell surface molecule is selected from CD34, CD105, or CD117.

62. The lipid particle of any of claims 56-60, wherein the target cell is a T cell.

63. The lipid particle of claim 62, wherein the cell surface molecule is selected from the group consisting of CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3.

64. The lipid particle of any of claims 56-60, wherein the target cell is a hepatocyte.

65. The lipid particle of claim 64, wherein the cell surface molecule is selected from the group consisting of ASGR1, ASGR2 and TM4SF5.

66. The lipid particle of any of claims 56-65, wherein the targeting moiety is selected from the group consisting of a single domain antibody or a single chain variable fragment (scFv).

67. The lipid particle of claim 66, wherein the single domain antibody is a VHH.

68. The lipid particle of claim 4, wherein the BaEV envelope glycoprotein is a truncated BaEV envelope glycoprotein comprising a cytoplasmic tail with a partial fusion inhibitory R peptide relative to the inhibitory R peptide of a wild-type BaEV envelope glycoprotein, wherein the partial fusion inhibitory R peptide comprises at least one amino-terminal amino acid but less than the full length of the inhibitory R peptide of the wild-type BaEV envelope glycoprotein.

69. The lipid particle of claim 4 or 68, wherein the BaEV envelope glycoprotein is a truncated BaEV envelope glycoprotein comprising a cytoplasmic tail with a partial fusion inhibitory R peptide relative to a wild-type BaEV envelope glycoprotein, wherein the cytoplasmic tail is 25 amino acids in length and contains 8 contiguous amino-terminal acids of the inhibitory R peptide (R+8) of the full length inhibitory R peptide of wild-type BaEV envelope glycoprotein. 375 sf-5667634186152009940 70. The lipid particle of claims 68 or 69, wherein the truncated BaEV glycoprotein comprises: (i) a glycoprotein 70 (g70) subunit or a biologically active portion thereof, and (ii) a portion of the glycoprotein p20E (p20E) subunit comprising the cytoplasmic tail with the partial inhibitory R peptide.

71. The lipid particle of claims 68-70, wherein the BaEV envelope glycoprotein binds an ASCT-2 or ASCT-1 receptor.

72. The lipid particle of any of claims 68-71, wherein the truncated BaEV envelope glycoprotein is truncated relative to SEQ ID NO: 622 and lacks up to 16 contiguous amino acids from the C-terminal cytoplasmic tail of SEQ ID NO:

622.

73. The lipid particle of any of claims 68-72, wherein the partial fusion inhibitory R peptide is set forth as amino acids 1 to 8 of SEQ ID NO: 623, optionally wherein the cytoplasmic tail is set forth in SEQ ID NO: 624 (R+8).

74. The lipid particle of any of claims 68-73, wherein the truncated BaEV envelope glycoprotein is set forth in SEQ ID NO:

625.

75. A lipid particle, comprising a variant Baboon Endogenous Virus (BaEV) fusogen wherein the fusogen is exposed on the outside of the lipid bilayer / embedded in the lipid bilayer.

76. The lipid particle of claim 75, wherein the variant BaEV envelope glycoprotein has the amino acid sequence set forth in SEQ ID NO: 795 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:

795.

77. The lipid particle of claim 75, wherein the variant BaEV envelope glycoprotein has the amino acid sequence set forth in SEQ ID NO: 796 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 376 sf-5667634186152009940 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:

796.

78. The lipid particle of claim 75, wherein the variant BaEV envelope glycoprotein has the amino acid sequence set forth in SEQ ID NO: 797 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:

797.

79. The lipid particle lipid particle of claim 75, wherein the BaEV Baboon Endogenous Virus (BaEV) is a BaEVTR fusogen.

80. The lipid particle lipid particle of claim 79, wherein the BaEV Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof comprises a protease site modification.

81. The lipid particle of claim 80, wherein the protease site modification comprises modifying a MLV-A cleavage site to a MA / CA cleavage site.

82. The lipid particle of any of claims 1-3, and 5-67, wherein the paramyxovirus envelope attachment protein is an envelope attachment protein from a Nipah virus, Hendra virus, or Measles virus, or is a variant or biologically active portion thereof of any of the foregoing.

83. The lipid particle of any of claims 1-3, 5-67, or 82, wherein the paramyxovirus envelope attachment protein is a wild-type paramyxovirus G protein, H protein or HN protein or is a variant or biologically active portion of any of the foregoing.

84. The lipid particle of claim 82 or claim 83 wherein the paramyxovirus envelope attachment protein is a wild-type Nipah virus G (NiV-G) protein or is a variant or biologically active portion of a NiV-G.

85. The lipid particle of claims 1-3, 5-67, or 82-84, wherein the paramyxovirus envelope attachment protein is a variant paramyxovirus envelope attachment protein. 377 sf-5667634186152009940 86. The lipid particle of claim 85, wherein the variant paramyxovirus envelope attachment protein comprises one or more mutations that reduces native tropism relative to the wild-type paramyxovirus envelope attachment protein not comprising the one or more mutations.

87. The lipid particle of any of claims 1-3, 5-67, or 82-86, wherein the paramyxovirus envelope attachment protein is a variant NiV-G that is a variant or a biologically active portion of a wild- type NiV-G.

88. The lipid particle of any one of claims 85-87, wherein the variant is a variant NiV-G that is a variant of a wild-type Nipah virus G (NiV-G) protein or a biologically active portion thereof.

89. The lipid particle of claim 87 or 88, wherein the variant NiV-G is truncated by up to 40 contiguous amino acids at or near the N-terminus of the wild-type NiV-G set forth in SEQ ID NO:

1.

90. The lipid particle of any of claims 87-89, wherein the variant NiV-G has a truncation of amino acids 2-34 of the wild-type NiV-G set forth in SEQ ID NO:

1.

91. The lipid particle of any of claims 87-90, wherein the variant NiV-G exhibits reduced binding to Ephrin B2 or Ephrin B3.

92. The lipid particle of claim 91, wherein the variant NiV-G comprises: one or more amino acid substitutions corresponding to amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:

1.

93. The lipid particle of claim 91 or claim 92, wherein the variant NiV-G comprises amino acid substitutions E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:

1.

94. The lipid particle of any of claims 87-93, wherein the variant NiV-G has the amino acid sequence set forth in SEQ ID NO: 228 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:

228. 378 sf-5667634186152009940 95. The lipid particle of any of claims 87-94, wherein the variant NiV-G has the amino acid sequence set forth in SEQ ID NO:

228.

96. The lipid particle of any of claims 1-95, wherein the particle further comprises an additional attachment protein that is a paramyxovirus envelope attachment protein that is a variant NiV-G that is a variant or a biologically active portion of a wild-type NiV-G.

97. The lipid particle of claim 96, wherein the variant NiV-G exhibits reduced binding to Ephrin B2 or Ephrin B3.

98. The lipid particle of claim 97, wherein the variant NiV-G comprises: one or more amino acid substitutions corresponding to amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:

1.

99. The lipid particle of any of claims 1-3, 5-67, and 82-98, wherein the at least one paramyxovirus fusion (F) protein is an F protein from a henipavirus or is a biologically active portion thereof or variant thereof.

100. The lipid particle of claim 99, wherein the henipavirus is a Hendra virus.

101. The lipid particle of claim 99, wherein the henipavirus is a Nipah virus.

102. The lipid particle of any of claims 1-3, 5-67, and 82-98, wherein the paramyxovirus F protein is a wild-type NiV-F protein or a variant or a biologically active portion thereof.

103. The lipid particle of any of claims 1-3, 5-67, and 82-98, wherein the paramyxovirus F protein is a variant NiV-F that is a variant or a biologically active portion of a wild-type NiV-F protein.

104. The lipid particle of claim 103, wherein the variant NiV-F is truncated by up to 22 contiguous amino acids the at the C-terminus of the wild-type NiV-F set forth in SEQ ID NO:235, optionally not include the initial methionine.

105. The lipid particle of claim 103 or claim 104, wherein the variant NiV-F protein is a truncated NiV-F that lacks amino acids 525-546 of SEQ ID NO:

235. 379 sf-5667634186152009940 106. The lipid particle of any of claims 103-105, wherein the variant NiV-F has the amino acid sequence set forth in SEQ ID NO: 227 or an amino acid sequence having at or about 80%, at least at or about 81%, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91%, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:

227.

107. The lipid particle of any of claims 103-106, wherein the variant NiV-F has the amino acid sequence set forth in SEQ ID NO:

227.

108. The lipid particle of any of claims 1-3, 5-67, and 82-103, wherein the paramyxovirus F protein is an F0 precursor or is a proteolytically cleaved form thereof comprising F1 and F2 subunits.

109. The lipid particle of claim 108, wherein the proteolytically cleaved form is a cathepsin L cleavage product.

110. The lipid particle of any of claims 1-109, wherein the targeting moiety and the paramyxovirus envelope attachment protein or biologically active portion thereof is attached via a linker.

111. The lipid particle of claim 110, wherein the linker is a peptide linker.

112. The lipid particle of claim 111, wherein the peptide linker is 2 to 65 amino acids in length.

113. The lipid particle of claim 111 or claim 112, wherein the peptide linker is a flexible linker that comprises GS, GGS, GGGGS, GGGGGS or combinations thereof.

114. The lipid particle of any of claims 111-113, wherein the peptide linker is selected from: (GGS)n, wherein n is 1 to 10; (GGGGS)n, wherein n is 1 to 10; or (GGGGGS)n, wherein n is 1 to 6.

115. The lipid particle of any of claims 1-114, wherein the paramyxovirus fusion (F) protein exhibits fusogenic activity with a target cell upon binding of at least one paramyxovirus envelope attachment protein o to the target molecule on the target cell. 380 sf-5667634186152009940 116. The lipid particle of any of claims 1-115, wherein the lipid particle comprises a viral nucleic acid.

117. The lipid particle of claim 116, wherein the viral nucleic acid comprises one or more of (e.g., all of) the following nucleic acid sequences: 5’ LTR (e.g., comprising U5 and lacking a functional U3 domain), Psi packaging element (Psi), Central polypurine tract (cPPT) / central termination sequence (CTS) (e.g. DNA flap), Poly A tail sequence, a posttranscriptional regulatory element (e.g. WPRE), a Rev response element (RRE), and 3’ LTR (e.g., comprising U5 and lacking a functional U3).

118. The lipid particle of any of claims 1-117, wherein the lipid particle is a viral vector.

119. The lipid particle of any of claims 1-117, that is a retroviral vector.

120. The lipid particle of any of claims 1-119, that is a lentiviral vector.

121. The lipid particle of any of claims 1-117, wherein the lipid particle is devoid of viral genomic DNA.

122. The lipid particle of any of claims 1-117 and 121, that is a viral-like particle.

123. The lipid particle of any of claims 1-117, 121, and 122, that is a retroviral-like particle.

124. The lipid particle of any of claims 1-117, 121-123, that is a lentiviral-like particle.

125. The lipid particle of claim 120 or 124, wherein the lentiviral vector or the lentiviral-like particle is derived from HIV.

126. The lipid particle lipid particle of claim 4 and 125, wherein the Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof is a BaEVTR fusogen.

127. The lipid particle lipid particle of claim 4 and 125, wherein the Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof comprises a protease site modification. 381 sf-5667634186152009940 128. The lipid particle of claim 127, wherein the protease site modification comprises modifying a MLV-A cleavage site to a MA / CA cleavage site.

129. The lipid particle of any of claims 1-128, wherein the lipid particle is produced as a preparation with increased titer compared to a reference lipid particle preparation that is similarly produced but with only the first retargeted attachment protein.

130. The lipid particle of claim 129, wherein the titer is increased by at or greater than 1.2- fold, 1.3-fold, 1.4-fold, 1.5-fold, 1.6-fold, 1.7-fold, 1.8-fold, 2-fold, 2.5-fold, 3-fold, 4-fold, 5-fold, 6- fold, 7-fold, 8-fold, 9-fold, 10-fold, or more.

131. The lipid particle of any of claims 1-130, further comprising an exogenous agent for delivery to a target cell.

132. The lipid particle of claim 131, wherein the exogenous agent is present in the lumen.

133. The lipid particle of claim 131 or claim 132, wherein the exogenous agent is a protein or a nucleic acid, optionally wherein the nucleic acid is a DNA or RNA.

134. The lipid particle of any of claims 131-133, wherein the exogenous agent is a nucleic acid encoding a cargo for delivery to the target cell.

135. The lipid particle of any of claims 131-134, wherein the exogenous agent is or encodes a therapeutic agent, a diagnostic agent or a genome-modifying enzyme.

136. The lipid particle of any of claims 131-135, wherein the exogenous agent encodes a membrane protein, optionally wherein the membrane protein is an antigen receptor for targeting cells expressed by or associated with a disease or condition.

137. The lipid particle of claim 136, wherein the membrane protein is a chimeric antigen receptor (CAR).

138. The lipid particle of any of claims 131-136, wherein the exogenous agent is a nucleic acid comprising a payload gene for correcting a genetic deficiency, optionally a genetic deficiency in the target cell, optionally wherein the genetic deficiency is associated with a liver cell or a hepatocyte. 382 sf-5667634186152009940 139. The lipid particle of any of claims 131-138, wherein binding of the paramyxovirus envelope attachment protein or biologically active portion thereof to a target molecule expressed on the surface of a target cell mediates fusion of the particle with the target cell and delivery of the exogenous agent to the target cell.

140. The lipid particle of any of claims 131-139, wherein at or greater than 10%, 20%, 30%, 40%, 50%, 60% of the target cells are delivered the exogenous agent.

141. The lipid particle of any of claims 131-140, wherein delivery of the exogenous cell to the target cell is increased compared to a reference particle preparation that is similarly produced but with only a retargeted attachment protein (e.g., no co-display protein).

142. The lipid particle of claim 141, wherein the delivery to the target cell is increased by at or greater than 1.2-fold, 1.3-fold, 1.4-fold, 1.5-fold, 1.6-fold, 1.7-fold, 1.8-fold, 2-fold, 2.5-fold, 3-fold, 4-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, 10-fold, or more.

143. A producer cell comprising (a) a nucleic acid encoding a retargeted attachment protein comprising a paramyxovirus envelope attachment protein; and (i) a targeting moiety directed to a target molecule expressed on the surface of a target cell, (b) a nucleic acid encoding a co-display protein, and (c) a nucleic acid encoding at least one paramyxovirus F protein.

144. A producer cell comprising (a) a nucleic acid encoding a retargeted attachment protein comprising a Baboon Endogenous Virus (BaEV) fusogen or functional variant thereof expressed on the surface of a target cell, and (b) a nucleic acid encoding a co-display protein.

145. The producer cell of claim 143 or claim 144, wherein the cell further comprises a viral nucleic acid(s).

146. The producer cell of claim 145, wherein the viral nucleic acid(s) are lentiviral nucleic acids.

147. The producer cell of any of claims 143-146, wherein the cell is a mammalian cell. 383 sf-5667634186152009940 148. The producer cell of any of claims 143-147, wherein the producer cell is selected from the group consisting of CHO cells, BHK cells, MDCK cells, C3H 10T1 / 2 cells, FLY cells, Psi-2 cells, BOSC 23 cells, PA317 cells, WEHI cells, COS cells, BSC 1 cells, BSC 40 cells, BMT 10 cells, VERO cells, W138 cells, MRC5 cells, A549 cells, HT1080 cells, 293 cells, 293T cells, B-50 cells, 3T3 cells, NIH3T3 cells, HepG2 cells, Saos-2 cells, Huh7 cells, HeLa cells, W163 cells, 211 cells, and 211A cells.

149. The producer cell of any of claims 143-148, wherein the producer cell comprises 293T cells.

150. The producer cell of any of claims 143-149, wherein the viral nucleic acid(s) lacks one or more genes involved in viral replication.

151. The producer cell of any of claims 143-150, wherein the viral nucleic acid comprises a nucleic acid encoding a viral packaging protein selected from one or more of Gag, Pol, Rev and Tat.

152. The producer cell of any of claims 143-151, wherein the viral nucleic acid comprises: one or more of (e.g., all of) the following nucleic acid sequences: 5’ LTR (e.g., comprising U5 and lacking a functional U3 domain), Psi packaging element (Psi), Central polypurine tract (cPPT) / central termination sequence (CTS) (e.g. DNA flap), Poly A tail sequence, a posttranscriptional regulatory element (e.g. WPRE), a Rev response element (RRE), and 3’ LTR (e.g., comprising U5 and lacking a functional U3).

153. The producer cell of any of claims 143-152, wherein the co-display protein increases specificity to the target cell.

154. The producer cell of any of claims 143-153, wherein the co-display protein increases specificity to a target cell selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells.

155. The producer cell of any of claims 143-154, wherein the co-display protein increases specificity to a target cell selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a 384 sf-5667634186152009940 Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell.

156. The producer cell of any of claims 143-155, wherein the co-display protein increases specificity to a target cell that is a hematopoietic stem cell.

157. The producer cell of claim 156, wherein the cell surface molecule is selected from CD34, CD105, or CD117.

158. The producer cell of any of claims 143-155, wherein the co-display protein increases specificity to a target cell that is a T cell.

159. The producer cell of claim 158, wherein the cell surface molecule is selected from CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3.

160. The producer cell of any of claims 143-155, wherein the co-display protein increases specificity to a target cell that is a hepatocyte.

161. The producer cell of claim 160, wherein the cell surface molecule is selected from ASGR1, ASGR2 and TM4SF5.

162. The producer cell of any of claims 143, and 145-161, wherein the co-display protein binds to a different protein than the targeting moiety of the retargeted attachment protein.

163. The producer cell of any of claims 143-162, wherein the co-display protein does not include a paramyxovirus envelope attachment protein or a fragment thereof.

164. The producer cell of any of claims 143-155, 158, 159, 162, or 163, wherein the co- display protein is an immune stimulating protein and the immune stimulating protein stimulates a T cell activity or function.

165. The producer cell of claim 164, wherein the immune stimulating protein comprises (i) an extracellular domain, (ii) a linker, and (iii) an anchor. 385 sf-5667634186152009940 166. The producer cell of claim 165, wherein the extracellular domain of the immune stimulating protein binds to a T cell stimulatory receptor.

167. The producer cell of claim 166, wherein the T cell stimulatory receptor is selected from CD3, CD2, CD28, CD27.

168. The producer cell of claims 165-167, wherein the extracellular domain of the immune stimulating protein binds to CD3.

169. The producer cell of claims 165-168, wherein the extracellular domain is selected from the group comprising an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide.

170. The producer cell of claims 165-169, wherein the extracellular domain of the immune stimulating protein is an anti-CD3 antibody or single chain fragment thereof.

171. The producer cell of any of claims 143-170, wherein the co-display protein is a transduction adjuvant that increases transduction efficiency of the lipid particle as compared to a lipid particle that does not have a co-display protein comprising a transduction adjuvant.

172. The producer cell of any of claims 143-171, wherein the co-display protein is a transduction adjuvant that binds to a surface molecule on target cells to enhance transduction.

173. The producer cell of claim 171 or 172 wherein the transduction adjuvant comprises (i) an extracellular domain, (ii) a linker, and (iii) an anchor.

174. The producer cell of claim 173, wherein the extracellular domain of the transduction adjuvant binds an integrin binding domain.

175. The producer cell of claims 173 or 174, the extracellular domain of the transduction adjuvant comprises the extracellular domain of fibronectin, retronectin, or a functional variant thereof. 386 sf-5667634186152009940 176. The producer cell of any of claims 165-175, wherein the linker is derived from a human protein.

177. The producer cell of any of claims 165-176, wherein the linker is a derived from human CD8α, IgG3 hinge, IgG1 hinge, IgG4 heavy chain, IgG4, or CD28.

178. The producer cell of any of claims 165-177, wherein the linker is modified to remove a cysteine residue.

179. The producer cell of any of claims 165-178, wherein the linker is rigid or wherein the linker is flexible.

180. The producer cell of any of claims 165-179, wherein the anchor is a peptide anchor that is a transmembrane domain.

181. The producer cell of any of claims 165-180, wherein the anchor is a transmembrane domain that is a transmembrane domain of a protein selected from PDGFR, VSV-G, CD8α, ICAM1, HLA-DRB, CD49d, or Transferrin.

182. The producer cell of any of claims 165-179, wherein the anchor is a GPI lipid anchor.

183. The producer cell of any of claims 143, and 145-182, wherein the targeting moiety is selected from the group consisting of an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide.

184. The producer cell of any of claims 143, and 145-183, wherein the targeting moiety binds to a cell surface molecule present on a target cell.

185. The producer cell of claim 184, wherein the cell surface molecule is a protein, glycan, or lipid.

186. The producer cell of any of claims 143, and 145-185, wherein the target cell is selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus- 387 sf-5667634186152009940 infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells.

187. The producer cell of any of claims 143, and 145-186, wherein the target cells is selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell.

188. The producer cell of any of claims 143, and 145-187, wherein the target is a hematopoietic stem cell.

189. The producer cell of any of claim 188, wherein the cell surface molecule is selected from CD34, CD105, or CD117.

190. The producer cell of any of claims 143, and 145-187, wherein the target cell is a T cell.

191. The producer cell of claim 190, wherein the cell surface molecule is selected from the group consisting of CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3.

192. The producer cell of any of claims 143, and 145-187, wherein the target cell is a hepatocyte.

193. The producer cell of claim 192, wherein the cell surface molecule is selected from the group consisting of ASGR1, ASGR2 and TM4SF5.

194. The producer cell of any of claims 143, and 145-193, wherein the targeting moiety is selected from the group consisting of a single domain antibody or a single chain variable fragment (scFv).

195. The producer cell of claim 194, wherein the single domain antibody is a VHH. 388 sf-5667634186152009940 196. The producer cell of any of claims 143, and 145-195, wherein the retargeted attachment protein is a first attachment protein and the lipid particle further comprises a second retargeted attachment protein.

197. The producer cell of claim 196, wherein the second retargeted attachment protein comprises (i) a second paramyxovirus envelope attachment protein; and (ii) a second targeting moiety directed to a target molecule expressed on the surface of a target cell.

198. The producer cell of any of claims 196 or 197, wherein the second targeting moiety is selected from the group consisting of an antibody or antigen-binding fragment, an engineered binding domain, a nanobody, a DARPin, an Aptamer, an Affimer, an Affibody, a Knottin, an Avimer, a Monobody, an Anticalin, a Fynomer, and a targeting peptide.

199. The producer cell of claim 197 or 198, wherein the target cell is selected from the group consisting of tumor-infiltrating lymphocytes, T cells, neoplastic or tumor cells, virus-infected cells, stem cells, central nervous system (CNS) cells, hematopoietic stem cells (HSCs), and liver cells.

200. The producer cell of any of claims 197-199, wherein the target cells is selected from the group consisting of a CD3+ T cell, a CD4+ T cell, a CD8+ T cell, a hepatocyte, a hematopoietic stem cell, a CD34+ hematopoietic stem cell, a CD105+ hematopoietic stem cell, a CD117+ hematopoietic stem cell, a CD105+ endothelial cell, a B cell, a CD20+ B cell, a CD19+ B cell, a cancer cell, a CD133+ cancer cell, an EpCAM+ cancer cell, a CD19+ cancer cell, a Her2 / Neu+ cancer cell, a GluA2+ neuron, a GluA4+ neuron, a NKG2D+ natural killer cell, a SLC1A3+ astrocyte, a SLC7A10+ adipocyte, or a CD30+ lung epithelial cell.

201. The producer cell of any of claims 197-200, wherein the target is a hematopoietic stem cell.

202. The producer cell of any of claim 201, wherein the cell surface molecule is selected from CD34, CD105, or CD117.

203. The producer cell of any of claims 197-200, wherein the target cell is a T cell. 389 sf-5667634186152009940 204. The producer cell of claim 203, wherein the cell surface molecule is selected from the group consisting of CD3, CD4, CD7 CD8, ASCT2, CD110, CD133, CD146, CD164, CD46, CD49f, CD90, EPCR, and ITGA3.

205. The producer cell of any of claims 197-200, wherein the target cell is a hepatocyte.

206. The producer cell of claim 205, wherein the cell surface molecule is selected from the group consisting of ASGR1, ASGR2 and TM4SF5.

207. The producer cell of any of claims 197-206, wherein the targeting moiety is selected from the group consisting of a single domain antibody or a single chain variable fragment (scFv).

208. The producer cell of claim 207, wherein the single domain antibody is a VHH.

209. The producer cell of claim 144, wherein the BaEV envelope glycoprotein is a truncated BaEV envelope glycoprotein comprising a cytoplasmic tail with a partial fusion inhibitory R peptide relative to the inhibitory R peptide of a wild-type BaEV envelope glycoprotein, wherein the partial fusion inhibitory R peptide comprises at least one amino-terminal amino acid but less than the full length of the inhibitory R peptide of the wild-type BaEV envelope glycoprotein.

210. The producer cell of claim 144 or 209, wherein the BaEV envelope glycoprotein is a truncated BaEV envelope glycoprotein comprising a cytoplasmic tail with a partial fusion inhibitory R peptide relative to a wild-type BaEV envelope glycoprotein, wherein the cytoplasmic tail is 25 amino acids in length and contains 8 contiguous amino-terminal acids of the inhibitory R peptide (R+8) of the full length inhibitory R peptide of wild-type BaEV envelope glycoprotein.

211. The producer cell of claim 209 or 210, wherein the truncated BaEV glycoprotein comprises: (i) a glycoprotein 70 (g70) subunit or a biologically active portion thereof, and (ii) a portion of the glycoprotein p20E (p20E) subunit comprising the cytoplasmic tail with the partial inhibitory R peptide.

212. The producer cell of claims 209-211, wherein the BaEV envelope glycoprotein binds an ASCT-2 or ASCT-1 receptor. 390 sf-5667634186152009940 213. The producer cell of any of claims 209-212, wherein the truncated BaEV envelope glycoprotein is truncated relative to SEQ ID NO: 622 and lacks up to 16 contiguous amino acids from the C-terminal cytoplasmic tail of SEQ ID NO:

622.

214. The producer cell of any of claims 209-213, wherein the partial fusion inhibitory R peptide is set forth as amino acids 1 to 8 of SEQ ID NO: 623, optionally wherein the cytoplasmic tail is set forth in SEQ ID NO: 624 (R+8).

215. The producer cell of any of claims 209-214, wherein the truncated BaEV envelope glycoprotein is set forth in SEQ ID NO:

625.

216. The producer cell of any of claims 136, and 138-208, wherein the paramyxovirus envelope attachment protein is an envelope attachment protein from a Nipah virus, Hendra virus, or Measles virus, or is a variant or biologically active portion thereof of any of the foregoing.

217. The producer cell of any of claims 143, and 145-208, and 216, wherein the paramyxovirus envelope attachment protein is a wild-type paramyxovirus G protein, H protein or HN protein or is a variant or biologically active portion of any of the foregoing.

218. The producer cell of claim 216 or claim 217, wherein the paramyxovirus envelope attachment protein is a wild-type Nipah virus G (NiV-G) protein or is a variant or biologically active portion of a NiV-G.

219. The producer cell of claims 143, and 145-208, and 218, wherein the paramyxovirus envelope attachment protein is a variant paramyxovirus envelope attachment protein.

220. The producer cell of claim 219, wherein the variant paramyxovirus envelope attachment protein comprises one or more mutations that reduces native tropism relative to the wild-type paramyxovirus envelope attachment protein not comprising the one or more mutations.

221. The producer cell of any of claims 143, and 145-220, wherein the paramyxovirus envelope attachment protein is a variant NiV-G that is a variant or a biologically active portion of a wild- type NiV-G. 391 sf-5667634186152009940 222. The producer cell of any one of claims 218-221, wherein the variant is a variant NiV-G that is a variant of a wild-type Nipah virus G (NiV-G) protein or a biologically active portion thereof.

223. The producer cell of claim 221 or 222, wherein the variant NiV-G is truncated by up to 40 contiguous amino acids at or near the N-terminus of the wild-type NiV-G set forth in SEQ ID NO:

1.

224. The producer cell of any of claims 218-223, wherein the variant NiV-G has a truncation of amino acids 2-34 of the wild-type NiV-G set forth in SEQ ID NO:

1.

225. The producer cell of any of claims 218-224, wherein the variant NiV-G exhibits reduced binding to Ephrin B2 or Ephrin B3.

226. The producer cell of claim 225, wherein the variant NiV-G comprises: one or more amino acid substitutions corresponding to amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:

1.

227. The producer cell of claim 225 or claim 226, wherein the variant NiV-G comprises amino acid substitutions E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:

1.

228. The producer cell of any of claims 218-227, wherein the variant NiV-G has the amino acid sequence set forth in SEQ ID NO: 228 or an amino acid sequence having at or about 80%, at least at or about 81 %, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91 %, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:

228.

229. The producer cell of any of claims 218-228, wherein the variant NiV-G has the amino acid sequence set forth in SEQ ID NO:

228.

230. The producer cell of any of claims 143-229, wherein the particle further comprises an additional attachment protein that is a paramyxovirus envelope attachment protein that is a variant NiV-G that is a variant or a biologically active portion of a wild-type NiV-G. 392 sf-5667634186152009940 231. The producer cell of claim 230, wherein the variant NiV-G exhibits reduced binding to Ephrin B2 or Ephrin B3.

232. The producer cell of claim 231, wherein the variant NiV-G comprises: one or more amino acid substitutions corresponding to amino acid substitutions selected from the group consisting of E501A, W504A, Q530A and E533A with reference to numbering set forth in SEQ ID NO:

1.

233. The producer cell of any of claims 143-232, wherein the at least one paramyxovirus fusion (F) protein is an F protein from a henipavirus or is a biologically active portion thereof or variant thereof.

234. The producer cell of claim 233, wherein the henipavirus is a Hendra virus.

235. The producer cell of claim 233, wherein the henipavirus is a Nipah virus.

236. The producer cell of any of claims 143, 145-208, and 216-235, wherein the paramyxovirus F protein is a wild-type NiV-F protein or a variant or a biologically active portion thereof.

237. The producer cell of any of claims 143-236, wherein the paramyxovirus F protein is a variant NiV-F that is a variant or a biologically active portion of a wild-type NiV-F protein.

238. The producer cell of claim 237, wherein the variant NiV-F is truncated by up to 22 contiguous amino acids the at the C-terminus of the wild-type NiV-F set forth in SEQ ID NO:235, optionally not include the initial methionine.

239. The producer cell of claim 237 or claim 238, wherein the variant NiV-F protein is a truncated NiV-F that lacks amino acids 525-546 of SEQ ID NO:

235.

240. The producer cell of any of claims 237-239, wherein the variant NiV-F has the amino acid sequence set forth in SEQ ID NO: 227 or an amino acid sequence having at or about 80%, at least at or about 81%, at least at or about 82%, at least at or about 83%, at or about 84%, at least at or about 85%, at least at or about 86%, or at least at or about 87%, at least at or about 88%, or at least at or about 89%, at least at or about 90%, at least at or about 91%, at least at or about 92%, at least at or about 93%, at least at or about 94%, at least at or about 95%, at or about 96%, at least at or about 97%, at least at or about 98%, or at least at or about 99% sequence identity to SEQ ID NO:

227. 393 sf-5667634186152009940 241. The producer cell of any of claims 237-240, wherein the variant NiV-F has the amino acid sequence set forth in SEQ ID NO:

227.

242. The producer cell of any of claims 143-241, wherein the paramyxovirus F protein is an F0 precursor or is a proteolytically cleaved form thereof comprising F1 and F2 subunits.

243. The producer cell of claim 242, wherein the proteolytically cleaved form is a cathepsin L cleavage product.

244. The producer cell of any of claims 143-243, wherein the targeting moiety and the paramyxovirus envelope attachment protein or biologically active portion thereof is attached via a linker.

245. The producer cell of claim 244, wherein the linker is a peptide linker.

246. The producer cell of claim 245, wherein the peptide linker is 2 to 65 amino acids in length.

247. The producer cell of claim 245 or claim 246, wherein the peptide linker is a flexible linker that comprises GS, GGS, GGGGS, GGGGGS or combinations thereof.

248. The producer cell of any of claims 245-247, wherein the peptide linker is selected from: (GGS)n, wherein n is 1 to 10; (GGGGS)n, wherein n is 1 to 10; or (GGGGGS)n, wherein n is 1 to 6.

249. The producer cell of any of claims 143-248, wherein the paramyxovirus fusion (F) protein exhibits fusogenic activity with a target cell upon binding of at least one paramyxovirus envelope attachment protein o to the target molecule on the target cell.

250. The producer cell of any of claims 143-249, wherein the lipid particle comprises a viral nucleic acid.

251. The producer cell of claim 250, wherein the viral nucleic acid comprises one or more of (e.g., all of) the following nucleic acid sequences: 5’ LTR (e.g., comprising U5 and lacking a functional U3 domain), Psi packaging element (Psi), Central polypurine tract (cPPT) / central termination sequence 394 sf-5667634186152009940 (CTS) (e.g. DNA flap), Poly A tail sequence, a posttranscriptional regulatory element (e.g. WPRE), a Rev response element (RRE), and 3’ LTR (e.g., comprising U5 and lacking a functional U3).

252. The producer cell of any of claims 143-251, wherein the lipid particle is a viral vector.

253. The producer cell of any of claims 143-252, that is a retroviral vector.

254. The producer cell of any of claims 143-253, that is a lentiviral vector.

255. The producer cell of any of claims 143-249, wherein the lipid particle is devoid of viral genomic DNA.

256. The producer cell of any of claims 143-249 and 252, that is a viral-like particle.

257. The producer cell of any of claims 143-249, 252, and 256, that is a retroviral-like particle.

258. The producer cell of any of claims 143-249, 252, and 256, that is a lentiviral-like particle.

259. The producer cell of any of claims 143-258, wherein the lipid particle is produced as a preparation with increased titer compared to a reference lipid particle preparation that is similarly produced but with only the first retargeted attachment protein.

260. The producer cell of claim 259, wherein the titer is increased by at or greater than 1.2- fold, 1.3-fold, 1.4-fold, 1.5-fold, 1.6-fold, 1.7-fold, 1.8-fold, 2-fold, 2.5-fold, 3-fold, 4-fold, 5-fold, 6- fold, 7-fold, 8-fold, 9-fold, 10-fold, or more.

261. The producer cell of any of claims 143-260, further comprising an exogenous agent for delivery to a target cell.

262. The producer cell of claim 261, wherein the exogenous agent is present in the lumen.

263. The producer cell of claim 261 or claim 262, wherein the exogenous agent is a protein or a nucleic acid, optionally wherein the nucleic acid is a DNA or RNA. 395 sf-5667634186152009940 264. The producer cell of any of claims 261-263, wherein the exogenous agent is a nucleic acid encoding a cargo for delivery to the target cell.

265. The producer cell of any of claims 261-264, wherein the exogenous agent is or encodes a therapeutic agent, a diagnostic agent or a genome-modifying enzyme.

266. The producer cell of any of claims 261-265, wherein the exogenous agent encodes a membrane protein, optionally wherein the membrane protein is an antigen receptor for targeting cells expressed by or associated with a disease or condition.

267. The producer cell of claim 266, wherein the membrane protein is a chimeric antigen receptor (CAR).

268. The producer cell of any of claims 261-267, wherein the exogenous agent is a nucleic acid comprising a payload gene for correcting a genetic deficiency, optionally a genetic deficiency in the target cell, optionally wherein the genetic deficiency is associated with a liver cell or a hepatocyte.

269. The producer cell of any of claims 261-268, wherein binding of the paramyxovirus envelope attachment protein or biologically active portion thereof to a target molecule expressed on the surface of a target cell mediates fusion of the particle with the target cell and delivery of the exogenous agent to the target cell.

270. The producer cell of any of claims 261-269, wherein at or greater than 10%, 20%, 30%, 40%, 50%, 60% of the target cells are delivered the exogenous agent.

271. The producer cell of any of claims 261-270, wherein delivery of the exogenous cell to the target cell is increased compared to a reference particle preparation that is similarly produced but with only a retargeted attachment protein (e.g., no co-display protein).

272. The producer cell of claim 271, wherein the delivery to the target cell is increased by at or greater than 1.2-fold, 1.3-fold, 1.4-fold, 1.5-fold, 1.6-fold, 1.7-fold, 1.8-fold, 2-fold, 2.5-fold, 3-fold, 4-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, 10-fold, or more.

273. A method of making a lipid particle, comprising: 396 sf-5667634186152009940 a) providing a producer cell of any of claims 143-272; b) culturing the cell under conditions that allow for production of the lipid particle, and c) separating, enriching, or purifying the lipid particle from the cell, thereby making the lipid particle.

274. The method of claim 273, wherein the lipid particle is a pseudotyped lentiviral vector.

275. A lipid particle produced by the method of claim 273 or claim 274.

276. A composition comprising a plurality of lipid particles of any of claims 1-142 and 275.

277. The composition of claim 276 further comprising a pharmaceutically acceptable carrier.

278. A method of transducing a cell comprising contacting a cell with a lipid particle of any of claims 1-142 and 275 or a composition of claim 276 or claim 277.

279. A method of delivering an exogenous agent into a target cell, the method comprising contacting a lipid particle of any of claims 131-142 and 275 or a composition of claim 276 or claim 277 with a target cell.

280. The method of claim 278 or claim 279, wherein the contacting is in vitro or ex vivo.

281. The method of claim 278 or claim 279, wherein the contacting is in vivo in a subject.

282. A method of delivering an exogenous agent to a cell in a subject, the method comprising administering to the subject a lipid particle of any of claims 131-142 and 275 or a composition of claim 276 or claim 277.

283. The method of claim 282, wherein the exogenous agent is or encodes a therapeutic agent for treating a disease or condition in the subject.

284. A method of treatment, the method comprising administering to a subject a lipid particle of any of claims 131-142 and 275 or a composition of claim 276 or claim 277. 397 sf-5667634186152009940 285. The method of any of claims 279-284, wherein the exogenous agent is or encodes a membrane protein, optionally a chimeric antigen receptor, for targeting an antigen associated with a disease or condition in the subject.

286. The method of any of claims 279-285, wherein the exogenous agent is for use in gene therapy to correct a genetic deficiency or replaces a deficient or missing gene in the subject.

287. The method of any of claims 279-286, wherein the subject is a human subject.

288. A co-display polypeptide, comprising one or more of: a leader domain; one or more fibronectin fragments; a hinge domain; an anchor domain; and a intracellular domain.

289. The co-display polypeptide of claim 288, wherein the co-display polypeptide is partially derived or derived from one or more recombinant fibronectin fragments.

290. The co-display polypeptide of claim 288 or 289, wherein the one or more recombinant fibronectin fragments are selected from: CH296-A, CH296-B, CH296-C, CH296-D, CH296-E, and CH296-F.

291. A co-display polypeptide, comprising one or more of: a leader domain; a CS-1 domain; a linker; a C-domain; a hinge domain; an anchor domain; and a intracellular domain. 398 sf-5667634

Images