Compositions and methods for compartment-specific cargo delivery

Abstract

To provide fusosome compositions and methods.SOLUTION: The present disclosure provides technologies relating to fusosomes and their use to deliver membrane proteins to target cells. In some embodiments, a fusosome comprises a lipid bilayer, a lumen surrounded by the lipid bilayer, a fusogen, and a cargo that includes a membrane protein payload agent. In some embodiments, such a cargo may be or comprise a nucleic acid that encodes (or is complementary to a nucleic acid that encodes) a membrane protein.SELECTED DRAWING: None

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is a subsidiary of "COMPOSITIONS AND This application claims priority to U.S. Provisional Application No. 62 / 767,394, entitled "METHODS FOR COMPARTMENT-SPECIFIC CARGO DELIVERY," the contents of which are incorporated by reference in their entirety for all purposes.

[0002] Incorporation by reference to sequence listing This application has been submitted with an electronic Sequence Listing. The Sequence Listing is provided as a file entitled 186152002641SEQLIST.TXT, created on November 14, 2019, and is 807 kilobytes in size. The information in the electronic format of the Sequence Listing is incorporated by reference in its entirety.

[0003] Cell-cell fusion is required for diverse biological processes such as fertilization, development, immune response, and tumorigenesis. Summary of the Invention [Means for solving the problem]

[0004] The present disclosure provides technology relating to fusosomes and their use for delivering membrane proteins to target cells. In some embodiments, the fusosomes comprise a lipid bilayer, a lumen surrounded by the lipid bilayer, a fusogen, and a cargo comprising a membrane protein payload agent. In some embodiments, such cargo may be or may comprise a nucleic acid encoding (or complementary to) a membrane protein.

[0005] Enumeration of Embodiments membrane delivery 1. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent (e.g., exogenous to or overexpressed in the source cell), i) chimeric antigen receptors, ii) an integrin membrane protein payload, for example selected from Table 7; iii) an ion channel protein selected from Table 8; iv) a pore-forming protein selected, for example, from Tables 9 and 10; v) a Toll-like receptor selected, for example, from Table 11; vi) an interleukin receptor payload, for example selected from Table 12; vii) a cell adhesion protein selected from Tables 13 to 14; viii) a transport protein selected from Table 17; ix) a signal sequence that is heterologous to the naturally occurring membrane protein, or x) a membrane protein payload agent comprising or encoding one or more of the signal sequences listed in Table 6; A fusosome, wherein the fusosome does not contain nucleocapsid protein or viral matrix protein. 2. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent (e.g., exogenous to the source cell or overexpressed) that comprises or encodes a T cell receptor; Optionally, the fusosome does not contain nucleocapsid protein or viral matrix protein. 3. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent that is exogenous to or overexpressed in the source cells; and Including, i) the fusosomes contain or are contained in cellular biological material; ii) the fusogen is present in, e.g., at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies per fusosome, or less, as measured, e.g., by the assay of Example 29; iii) the fusosomes comprise the therapeutic agent at, e.g., at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies or less per fusosome, as measured, e.g., by the assay of Example 43; iv) the fusosomes contain lipids where one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 75% of the corresponding lipid levels in the source cells; v) the fusosomes contain a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; vi) the fusosomes are capable of signaling, e.g., transmitting an extracellular signal, e.g., phosphorylating AKT in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, e.g., at least 10% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; vii) the fusosomes, when administered to a subject, e.g., a mouse, target a tissue, e.g., liver, lung, heart, spleen, pancreas, gastrointestinal tract, kidney, testis, ovary, brain, reproductive organs, central nervous system, peripheral nervous system, skeletal muscle, endothelium, inner ear, or eye, and at least 0.1% or 10% of the fusosomes in the population of administered fusosomes are present in the target tissue after 24 hours, e.g., by an assay of Example 87 or 100; or viii) The fusosomes, wherein the source cell is one or more selected from neutrophils, granulocytes, mesenchymal stem cells, bone marrow stem cells, induced pluripotent stem cells, embryonic stem cells, myeloblasts, myoblasts, hepatocytes, or neurons, e.g., retinal neuronal cells. 4. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent, i) contains DNA encoding a membrane protein, or ii) a membrane protein payload agent comprising RNA, e.g., mRNA, encoding a membrane protein that is exogenous or overexpressed to the source cell; A fusosome, wherein the fusosome does not contain nucleocapsid protein or viral matrix protein. 5. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a non-viral, e.g., mammalian, fusogen that is exogenous to or overexpressed in the source cells, where the mammalian fusogen is not Alzheimer's beta-amyloid peptide or fertilin; (d) a membrane protein payload agent that is exogenous to or overexpressed in the source cell; Optionally, the fusosome does not contain nucleocapsid protein or viral matrix protein. 6. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent that is exogenous to or overexpressed in the source cell; the fusosomes contain enucleated cells; Optionally, the fusosome does not contain nucleocapsid protein or viral matrix protein. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent that is exogenous to or overexpressed in the source cell; i) the fusosomes contain or are contained in cellular biological material; ii) the fusosomes contain enucleated cells; iii) the fusosomes contain inactivated nuclei; iv) the fusosomes fuse with target cells at a rate, e.g., at least at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% higher than with non-target cells, e.g., in the assay of Example 54; v) the fusosomes fuse with target cells at a rate, e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% higher than with non-target fusosomes, e.g., in the assay of Example 54; vi) the fusosomes fuse with the target cells at a rate such that the membrane protein payload agent in the fusosomes is delivered to at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the target cells after 24, 48, or 72 hours, e.g., in the assay of Example 54; vii) the fusogen is present in at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies per fusosome, or less, as measured, for example, by the assay of Example 29; viii) the fusosomes contain at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies or less of the membrane protein payload agent per fusosome, as measured, for example, by the assay of Example 43; ix) The ratio of the copy number of the fusogen to the copy number of the membrane protein payload agent is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 5:1, 5: Between 1 to 2:1, 2:1 to 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. x) the fusosomes contain a lipid composition substantially similar to that of the source cells, or one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75% of the corresponding lipid levels in the source cells; xi) the fusosomes contain a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; xii) the fusosomes comprise a lipid to protein ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 49; xiii) the fusosomes comprise a ratio of protein to nucleic acid (e.g., DNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, e.g., as measured using the assay of Example 50; xiv) the fusosomes comprise a lipid to nucleic acid (e.g., DNA) ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 51; xv) the fusosomes have a half-life in a subject, e.g., a mouse, that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% of the half-life of a reference cell, e.g., a source cell, e.g., by the assay of Example 75; xvi) the fusosomes transport, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% more glucose (e.g., labeled glucose, e.g., 2-NBDG) across the membrane in the absence of glucose than a negative control, e.g., an otherwise similar fusosome, as measured, e.g., using the assay of Example 64; xvii) the fusosomes contain esterase activity in their lumen that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the esterase activity in a reference cell, e.g., a source cell or a mouse embryonic fibroblast, using, e.g., the assay of Example 66; xviii) the fusosomes comprise a level of metabolic activity (e.g., citrate synthase activity) within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the metabolic activity (e.g., citrate synthase activity) in a reference cell, e.g., a source cell, e.g., as described in Example 68; xix) the fusosomes comprise a respiration level (e.g., oxygen consumption rate) within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the respiration level (e.g., oxygen consumption rate) in a reference cell, e.g., a source cell, e.g., as described in Example 69; xx) the fusosomes comprise an annexin V staining level of at most 18,000, 17,000, 16,000, 15,000, 14,000, 13,000, 12,000, 11,000, or 10,000 MFI, e.g., using the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of otherwise similar fusosomes treated with menadione in the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of macrophages treated with menadione in the assay of Example 70. xxi) the fusosomes have miRNA content levels that are at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more than that of the source cells, e.g., by the assay of Example 39; xxii) fusosomes are within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of that of the source cells, e.g., by the assay of Example 47, or, e.g., 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, 5% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50% of that of the source cells , 50%-60%, 60%-70%, 70%-80%, or 80%-90% of the soluble:insoluble protein ratio; xxiii) the fusosomes have LPS levels of 5%, 1%, 0.5%, 0.01%, 0.005%, 0.0001%, 0.00001%, or less of the LPS content of the source cells, as measured by mass spectrometry, e.g., as described in Example 48; xxiv) the fusosomes and / or compositions or preparations thereof are capable of signaling, e.g., transmitting an extracellular signal, e.g., phosphorylating AKT in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; xxv) the fusosomes, when administered to a subject, e.g., a mammal, e.g., a laboratory mammal (e.g., a mouse), a domestic animal (e.g., a pet or livestock), or a human, target a tissue, e.g., the liver, lung, heart, spleen, pancreas, gastrointestinal tract, kidney, testes, ovaries, brain, reproductive organs, central nervous system, peripheral nervous system, skeletal muscle, endothelium, inner ear, or eye, such that at least 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the fusosomes in the population of administered fusosomes are present in the target tissue after 24, 48, or 72 hours, e.g., by the assay of Example 87 or 100; xxvi) the fusosomes have a level of juxtacrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% greater than the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; xxvii) the fusosomes have a level of paracrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% greater than the level of paracrine signaling induced by a reference cell, e.g., a source cell or a macrophage, e.g., by the assay of Example 72; xxviii) the fusosomes polymerize actin at a level within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the level of polymerized actin in a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 73; xxix) the fusosomes have a membrane potential within about 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the membrane potential of a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 74, or the fusosomes have a membrane potential of about -20 to -150 mV, -20 to -50 mV, -50 to -100 mV, or -100 to -150 mV; xxx) the fusosomes and / or compositions or preparations thereof are capable of extravasation from blood vessels, e.g., using the assay of Example 57, at a rate that is at least 1%, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the rate of extravasation of the source cells, and the source cells are neutrophils, lymphocytes, B cells, macrophages, or NK cells; xxxi) the fusosomes and / or compositions or preparations thereof are capable of crossing cell membranes, such as endothelial cell membranes or the blood-brain barrier; xxxii) the fusosomes and / or compositions or preparations thereof are capable of secreting proteins at, for example, at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% greater percentage than a reference cell, e.g., a mouse embryonic fibroblast or source cell, e.g., using the assay of Example 62; xxxiii) the fusosomes meet pharmaceutical or Good Manufacturing Practice (GMP) standards; xxxiv) the fusosomes were produced in accordance with Good Manufacturing Practice (GMP); xxxv) a pharmaceutical preparation comprising a plurality of fusosomes as described herein has a pathogen level below a predetermined reference value, e.g., is substantially pathogen-free; xxxvi) the pharmaceutical formulation comprising a plurality of fusosomes described herein has a contaminant level below a predetermined reference value, e.g., is substantially free of contaminants; xxxvii) a pharmaceutical formulation comprising a plurality of fusosomes as described herein has low immunogenicity, e.g., as described herein; xxxviii) the source cells are selected from neutrophils, granulocytes, mesenchymal stem cells, bone marrow stem cells, induced pluripotent stem cells, embryonic stem cells, myeloblasts, myoblasts, hepatocytes, or neurons, e.g., retinal neuronal cells; or xxxix) Fusosomes, wherein the source cell is one or more of 293 cells, HEK cells, human endothelial cells, or human epithelial cells, monocytes, macrophages, dendritic cells, or cells other than stem cells. 8. A fusosome, (a) a lipid bilayer; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent, e.g., a membrane protein exogenous to the source cell; The fusosomes are derived from the source cell, Fusosomes that have partial or complete nuclear inactivation (e.g., lack an intact nucleus as found in the source cell, have a removed / enucleated nucleus, a non-functioning nucleus, etc.). 9. A fusosome, (a) a lipid bilayer; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous or overexpressed to the target cell, e.g., the fusogen is disposed within a lipid bilayer (e.g., the fusogen is endogenous or exogenous to the source cell); and (d) a membrane protein payload agent (e.g., exogenous to or overexpressed in the source cell), i) comprises or encodes a chimeric antigen receptor; ii) comprises or encodes an integrin membrane protein payload, e.g., selected from Table 7; iii) comprises or encodes an ion channel protein selected from Table 8; iv) comprises or encodes a pore-forming protein, for example, selected from Tables 9 and 10; v) comprises or encodes a Toll-like receptor, for example, selected from Table 11; vi) comprising or encoding an interleukin receptor payload, e.g., selected from Table 12; vii) comprising or encoding a cell adhesion protein selected from Tables 13-14; viii) comprising or encoding a transport protein selected from Table 17; ix) contain or encode a signal sequence that is heterologous to the naturally occurring membrane protein; x) a membrane protein payload agent comprising or encoding a signal sequence listed in Table 6; Fusosomes, wherein the fusosomes do not contain viral capsid or viral envelope proteins. 10. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent (e.g., exogenous to or overexpressed in the source cell), i) lipid-anchored proteins, ii) extracellular proteins that bind to transmembrane proteins; iii) extracellular proteins lacking transmembrane domains; iv) comprises one or more of a protein that partially spans a membrane (e.g., the membrane of a target cell or fusosome) and a protein that does not completely span a membrane (e.g., the protein contains an in-plane membrane helix, or the protein contains a hydrophobic loop that does not completely span the membrane), or v) a membrane protein payload agent, wherein the protein does not contain a transmembrane domain and the protein interacts with the membrane surface, for example, via electrostatic or ionic interactions; A fusosome wherein the fusosome does not contain viral structural proteins, such as viral capsid proteins or viral envelope proteins. 11. A fusosome, (a) a lipid bilayer; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous or overexpressed to the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent; and (e) a functional core; Fusosomes are derived from source cells. 12. The fusosomes of any of the above embodiments, wherein the plurality of fusosomes, when contacted with a target cell population in the presence of an inhibitor of endocytosis, and when contacted with a reference target cell population that has not been treated with an inhibitor of endocytosis, deliver cargo to at least 30%, 40%, 50%, 60%, 70%, or 80% of the number of cells in the target cell population compared to the reference target cell population. 13. The fusosome of any of the above embodiments, (i) when a plurality of fusosomes contact a cell population comprising target cells and non-target cells, the cargo is present in at least 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, or 100-fold greater abundance in target cells than in non-target cells; or (ii) fusosomes, in which multiple fusosomes fuse with target cells at a rate at least 50% higher than with non-target cells; 14. The fusosome of any of the above embodiments, i) the fusogen is present in a copy number of at least 1,000 copies, as measured, for example, by the assay of Example 29, or ii) The ratio of the copy number of the fusogen to the copy number of the membrane protein payload agent is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 5:1, 5:1 to 2 fusosomes, between :1, 2:1 to 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. 15. The fusosome of any of the above embodiments, wherein the fusosome comprises the membrane protein payload agent at a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 43. 16. A fusosome according to any of the above embodiments, wherein the membrane protein payload agent is a membrane protein located within the fusosome lipid bilayer. 17. A fusosome according to any of the above embodiments, wherein the membrane protein payload agent is a nucleic acid located in the fusosome lumen that encodes a membrane protein. 18. The fusosome of embodiment 17, wherein the nucleic acid is or comprises RNA. 19. The fusosome of embodiment 18, wherein the RNA is or comprises pre-mRNA or mRNA. 20. The fusosome of embodiment 17, wherein the nucleic acid is or comprises DNA. 21. The fusosome of embodiment 20, wherein the DNA is or comprises gDNA or cDNA. 22. A fusosome according to any of embodiments 17 to 21, wherein the nucleic acid further comprises one or more sequences encoding one or more signal sequences, e.g., a target cell translocates the protein comprising the signal sequence to the cell membrane of the target cell. 23. The fusosome of embodiment 22, wherein the one or more signal sequences is or comprises a sequence selected from Table 6. 24. A fusosome according to any of embodiments 17 to 23, wherein the nucleic acid comprises one or more regulatory elements directing the expression of the sequence encoding the membrane protein by the target cell. 25. The fusosome of any of the previous embodiments, wherein the membrane protein payload agent is or comprises a sequence of SEQ ID NOs: 8144-16131 of U.S. Patent Publication No. 2016 / 0289674. 26. A fusosome according to any of embodiments 1 to 24, wherein the membrane protein payload agent is or comprises a fragment, variant, or homologue of the sequence of SEQ ID NOs: 8144 to 16131 of US Patent Publication No. 2016 / 0289674. 27. A fusosome according to any of embodiments 1 to 24, wherein the membrane protein payload agent is or comprises a nucleic acid encoding a protein comprising the sequence of SEQ ID NOs: 8144 to 16131 of US Patent Publication No. 2016 / 0289674. 28. A fusosome according to any of embodiments 1 to 24, wherein the membrane protein payload agent is or comprises a nucleic acid encoding a protein comprising a fragment, variant, or homologue of the sequence of SEQ ID NOs: 8144 to 16131 of US Patent Publication No. 2016 / 0289674. 29. The fusosome of any of embodiments 1-24, wherein the membrane protein payload agent is or comprises a protein selected from Tables 7-17. 30. The fusosome of any of embodiments 1-24, wherein the membrane protein payload agent is or comprises a fragment, variant, or homologue of a protein selected from Tables 7-17. 31. The fusosome of any of embodiments 1-24, wherein the membrane protein payload agent is or comprises a nucleic acid encoding a protein selected from Tables 7-17, or a protein comprising the same. 32. The fusosome of any of embodiments 1-24, wherein the membrane protein payload agent is or comprises a nucleic acid encoding a protein comprising a fragment, variant, or homologue of a protein selected from Tables 7-17. 33. A fusosome according to any of embodiments 1 to 24, wherein the membrane protein payload agent is or comprises a chimeric antigen receptor (CAR) comprising an antigen-binding domain. 34. The fusosome of embodiment 33, wherein the CAR is or comprises a first-generation CAR comprising an antigen-binding domain, a transmembrane domain, and a signaling domain. 35. The fusosome of embodiment 33, wherein the CAR is or comprises a second-generation CAR comprising an antigen-binding domain, a transmembrane domain, and two signaling domains. 36. The fusosome of embodiment 33, wherein the CAR is or comprises a third-generation CAR comprising an antigen-binding domain, a transmembrane domain, and at least three signaling domains. 37. The fusosome of embodiment 33, wherein the CAR is or comprises a fourth-generation CAR comprising an antigen-binding domain, a transmembrane domain, three or four signaling domains, and a domain that induces cytokine gene expression upon successful signaling of the CAR. 38. The fusosome of any of embodiments 33 to 37, wherein the antigen-binding domain is or comprises an scFv or Fab. 39. A fusosome according to any of embodiments 33 to 38, wherein the antigen-binding domain targets an antigen characteristic of neoplastic cells. 40. Antigens characteristic of neoplastic cells include cell surface receptors, ion channel-linked receptors, enzyme-linked receptors, G protein-coupled receptors, receptor tyrosine kinases, tyrosine kinase-associated receptors, receptor-like tyrosine phosphatases, receptor serine / threonine kinases, receptor guanylyl cyclases, histidine kinase-associated receptors, epidermal growth factor receptors (EGFRs) (including ErbB1 / EGFR, ErbB2 / HER2, ErbB3 / HER3, and ErbB4 / HER4), fibroblast growth factor receptors (FGFRs) (including FGF1, FGF2, FGF3, FGF4, FGF5, FGF6, FGF7, FGF18, and FGF21), vascular endothelial growth factor receptors (VEGFRs) (including VEGF-A, VEGF-B, VEGF-C, VEGF-D, and VEGF-P). (including EphA1, EphA2, EphA3, EphA4, EphA5, EphA6, EphA7, EphA8, EphA9, EphA10, EphB1, EphB2, EphB3, EphB4, and EphB6), RET receptors and the Eph receptor family (including EphA1, EphA2, EphA3, EphA4, EphA5, EphA6, EphA7, EphA8, EphA9, EphA10, EphB1, EphB2, EphB3, EphB4, and EphB6), CXCR1, CXCR2, CXCR3, CXCR4, CXCR6, CCR1, CCR2, CCR3, CCR 4, CCR5, CCR6, CCR8, CFTR, CIC-1, CIC-2, CIC-4, CIC-5, CIC-7, CIC-Ka, CIC-Kb, bestrophin, TMEM16A, GABA receptor, glycine receptor, ABC transporter, NAV1.1, NAV1.2, NAV1.3, NAV1.4, NAV1.5, NAV1.6, NAV1.7, NAV1.8, NAV1.9, sphingosine-1-phosphate receptor (S1P1R), NMDA channel, transmembrane protein, multispanning transmembrane protein, T cell receptor motif; T cell α chain; T cell β chain; T cell γ chain; T cell δ chain; CCR7; CD3; CD4; CD5; CD7; CD8; CD11b; CD11c; CD16; CD19; CD20; CD21; CD22; CD25; CD28; CD34; CD35; CD40; CD45RA; CD45RO; CD52; CD56; CD62L;CD68;CD80;CD95;CD117;CD127;CD133;CD137(4-1BB);CD163;F4 / 80;IL-4Ra;Sca-1;CTLA-4;GITR;GARP;LAP;Granzyme B;LFA-1;Transferrin receptor;NKp46, perforin, CD4+;Th1;Th2;Th17;Th40;Th22;Th9;Tfh, classical Treg.FoxP3+;Tr1;Th3;Treg17;T. RE G; CDCP1, NT5E, EpCAM, CEA, gpA33, mucin, TAG-72, carbonic anhydrase IX, PSMA, folate-binding protein, gangliosides (e.g., CD2, CD3, GM2), Lewis-γ 2, VEGF, VEGFR1 / 2 / 3, αVβ3, α5β1, ErbB1 / EGFR, ErbB1 / HER2, ErB3, c-MET, IGF1R, EphA3, TRAIL-R1, TRAIL-R2, RANKL, FAP, tenascin, PDL-1, BAFF, HDAC, ABL , FLT3, KIT, MET, RET, IL-1β, ALK, RANKL, mTOR, CTLA-4, IL-6, IL-6R, JAK3, BRAF, PTCH, Smoothened, PIGF, ANPEP, TIMP1, PLAUR, PTPRJ, LTBR, ​​or ANTXR 1, folate receptor α (FRa), ERBB2 (Her2 / neu), EphA2, IL-13Ra2, epidermal growth factor receptor (EGFR), mesothelin, TSHR, CD19, CD123, CD22, CD30, CD171, CS-1, CLL-1, CD33, EGFRvIII, G D2, GD3, BCMA, MUC16(CA125), L1CAM, LeY, MSLN, IL13Rα1, L1-CAM, TnAg, prostate-specific membrane antigen (PSMA), ROR1, FLT3, FAP, TAG72, CD38, CD44v6, CEA, EPCAM, B7H3, KI T, interleukin-11 receptor α (IL-11Ra), PSCA, PRSS21, VEGFR2, LewisY, CD24, platelet-derived growth factor receptor β (PDGFR-β), SSEA-4, CD20, MUC1, NCAM, prostase, PAP, ELF2M, ephrin B2, IGF-1 receptor, CAIX, LMP2, gplOO, bcr-abl, telomerase, fucosyl GM1, sLe, GM3, TGS5, HMWMAA, o-acetyl-GD2, folate receptor β, TEM1 / CD248, TEM7R, CLDN6, GPRC5D, CXORF61 , CD97, CD179a, ALK, polysialic acid, PLACl, GloboH, NY-BR-1, UPK2, HAVCR1, ADRB3, PANX3, GPR20, LY6K, OR51E2, TARP, WT1, NY-ESO-1, LAGE-la, MAGE-A1, legumain, HPVE6, E7, ETV6-AML, sperm protein 17, XAGE1, Tie2, MAD-CT-1, MAD-CT-2, Fos-related antigen 1, p53, p53 mutant, prostein, survivin, telomerase, PCTA-1 / galectin 8, MelanA / MART1,Ras mutant, hTERT, sarcoma translocation breakpoint, ML-IAP, ERG (TMPRSS2ETS fusion gene), NA17, PAX3, androgen receptor, cyclin B1, MYCN, RhoC, TRP-2, CYPIBI, BORIS, SART3, PAX5, OY-TES1, LCK, AKAP-4, SSX2, RAGE-1, human telomerase reverse transcriptase, RU1, RU2, intestinal carboxylesterase, mut 40. The fusosome of embodiment 39, wherein the antigen is selected from hsp70-2, CD79a, CD79b, CD72, LAIR1, FCAR, LILRA2, CD300LF, CLEC12A, BST2, EMR2, LY75, GPC3, FCRL5, IGLL1, neoantigens, CD133, CD15, CD184, CD24, CD56, CD26, CD29, CD44, HLA-A, HLA-B, HLA-C, (HLA-A, B, C)CD49f, CD151, CD340, CD200, tkrA, trkB, trkC, or an antigenic fragment or portion thereof. 41. The fusosome of any of embodiments 33-38, wherein the antigen-binding domain targets an antigen characteristic of T cells. 42. The fusosome of embodiment 41, wherein the antigen characteristic of T cells is selected from cell surface receptors, membrane transport proteins (e.g., active or passive transport proteins such as ion channel proteins, pore-forming proteins), transmembrane receptors, membrane enzymes, and / or cell adhesion proteins characteristic of T cells.In some embodiments, the antigen characteristic of T cells is a G protein-coupled receptor, a receptor tyrosine kinase, a tyrosine kinase-associated receptor, a receptor-like tyrosine phosphatase, a receptor serine / threonine kinase, a receptor guanylyl cyclase, a histidine kinase-associated receptor, AKT1; AKT2; AKT3; ATF2; BCL10; CALM1; CD3D (CD3δ); CD3E (CD3ε); CD3G (CD3γ); CD4; CD8; CD28; CD45; CD80 (B7-1); CD86(B7-2);CD247(CD3ζ);CTLA4(CD152);ELK1;ERK1(MAPK3);ERK2;FOS;FYN;GRAP2(GADS);GRB2;HLA-DRA;HLA-DRB1;HLA-DRB3;H LA-DRB4;HLA-DRB5;HRAS;IKBKA(CHUK);IKBKB;IKBKE;IKBKG(NEMO);IL2;ITPR1;ITK;JUN;KRAS2;LAT;LCK;MAP2K1(MEK1);MAP2K2( MEK2);MAP2K3(MKK3);MAP2K4(MKK4);MAP2K6(MKK6);MAP2K7(MKK7);MAP3K1(MEKK1);MAP3K3;MAP3K4;MAP3K5;MAP3K8;MAP3K14(N IK);MAPK8(JNK1);MAPK9(JNK2);MAPK10(JNK3);MAPK11(p38β);MAPK12(p38γ);MAPK13(p38δ);MAPK14(p38α);NCK;NFAT1;NFAT2;N It can be FKB1; NFKB2; NFKBIA; NRAS; PAK1; PAK2; PAK3; PAK4; PIK3C2B; PIK3C3 (VPS34); PIK3CA; PIK3CB; PIK3CD; PIK3R1; PKCA; PKCB; PKCM; PKCQ; PLCY1; PRF1 (perforin); PTEN; RAC1; RAF1; RELA; SDF1; SHP2; SLP76; SOS; SRC; TBK1; TCRA; TEC; TRAF6; VAV1; VAV2; or ZAP70. 43. The fusosome of any of embodiments 33-38, wherein the antigen-binding domain targets an antigen characteristic of an autoimmune or inflammatory disorder. 44. The autoimmune or inflammatory disorder is selected from chronic graft-versus-host disease (GVHD), lupus, arthritis, immune complex glomerulonephritis, Goodpasture's disease, uveitis, hepatitis, systemic sclerosis or scleroderma, type I diabetes, multiple sclerosis, cold agglutinin disease, pemphigus vulgaris, Graves' disease, autoimmune hemolytic anemia, thrombocytopenia A, primary Sjogren's syndrome, thrombotic thrombocytopenic purpura, neuromyelopathic optic neuropathy, Evan's syndrome, IgM-mediated neuropathy, thyroglobulinemia, dermatomyositis, idiopathic thrombocytopenia, ankylosing spondylitis, bullous pemphigoid, acquired angioedema, chronic urticaria, antiphospholipid demyelinating polyneuropathy, and autoimmune thrombocytopenia or neutropenia or pure red blood cell aplasia, while illustrative, non-limiting examples of alloimmune diseases include allosensitization (e.g., see Blazar et al. al., 2015, Am. J. Transplant, 15(4):931-41) or sensitization to foreign antigens such as may occur due to xenosensitization from hematopoietic or solid organ transplantation, blood transfusions, pregnancies with fetal allosensitization, neonatal alloimmune thrombocytopenia, hemolytic disease of the newborn, enzyme or protein replacement therapy, blood products, and replacement of congenital or acquired defect disorders treated with gene therapy. 45. The fusosome of embodiment 43 or embodiment 44, wherein the antigen characteristic of an autoimmune or inflammatory disorder is selected from a cell surface receptor, an ion channel-linked receptor, an enzyme-linked receptor, a G protein-coupled receptor, a receptor tyrosine kinase, a tyrosine kinase-associated receptor, a receptor-like tyrosine phosphatase, a receptor serine / threonine kinase, a receptor guanylyl cyclase, or a histidine kinase-associated receptor. In some embodiments, the CAR antigen-binding domain binds to a ligand expressed on B cells, plasma cells, plasmablasts, CD10, CD19, CD20, CD22, CD24, CD27, CD38, CD45R, CD138, CD319, BCMA, CD28, TNF, an interferon receptor, GM-CSF, ZAP-70, LFA-1, CD3γ, CD5, or CD2. 46. The fusosome of any of embodiments 33-38, wherein the antigen-binding domain targets an antigen characteristic of an infectious disease. 47. The fusosome of embodiment 46, wherein the infectious disease is selected from HIV, hepatitis B virus, hepatitis C virus, human herpesvirus, human herpesvirus 8 (HHV-8, Kaposi's sarcoma-associated herpesvirus (KSHV)), human T-lymphotropic virus-1 (HTLV-1), Merkel cell polyomavirus (MCV), simian virus 40 (SV40), Epstein-Barr virus, CMV, and human papillomavirus. 48. The fusosome of embodiment 46 or embodiment 47, wherein the antigen characteristic of the infectious disease is selected from cell surface receptors, ion channel-linked receptors, enzyme-linked receptors, G protein-coupled receptors, receptor tyrosine kinases, tyrosine kinase-associated receptors, receptor-like tyrosine phosphatases, receptor serine / threonine kinases, receptor guanylyl cyclases, histidine kinase-associated receptors, HIV Env, gp120, or CD4-inducible epitopes on HIV-1 Env. 49. A fusosome according to any of embodiments 33 to 48, wherein the transmembrane domain comprises at least the transmembrane region of the α, β, or ζ chain of a T-cell receptor, CD28, CD3ε, CD45, CD4, CD5, CD8, CD9, CD16, CD22, CD33, CD37, CD64, CD80, CD86, CD134, CD137, CD154, or a functional variant thereof. 50. The fusosome of any of embodiments 33 to 49, wherein the transmembrane domain comprises at least one of the transmembrane region(s) of CD8α, CD8β, 4-1BB / CD137, CD28, CD34, CD4, FcεRIγ, CD16, OX40 / CD134, CD3ζ, CD3ε, CD3γ, CD3δ, TCRα, TCRβ, TCRζ, CD32, CD64, CD64, CD45, CD5, CD9, CD22, CD37, CD80, CD86, CD40, CD40L / CD154, VEGFR2, FAS, and FGFR2B, or functional variants thereof. 51.CAR is B7-1 / CD80, B7-2 / CD86, B7-H1 / PD-L1, B7-H2, B7-H3, B7-H4, B7-H6, B7-H7, BTLA / CD272, CD28, CTLA-4, Gi24 / VISTA / B7-H5, ICOS / CD278, PD- 1, PD-L2 / B7-DC, PDCD6), 4-1BB / TNFSF9 / CD137, 4-1BB ligand / TNFSF9, BAFF / BLyS / TNFSF13B, BAFFR / TNFRSF13C, CD27 / TNFRSF7, CD27 ligand / TNFSF7, CD30 / TNFRSF8, CD30 ligand / TNFSF8, CD40 / TNFRSF5, CD40 / TNFSF5, CD40 ligand / TNFSF5, DR3 / TNFRSF25, GITR / TNFRSF18, GITR ligand / TNFSF18, HVEM / TNFRSF14, L IGHT / TNFSF14, lymphotoxin-α / TNF-β, OX40 / TNFRSF4, OX40 ligand / TNFSF4, RELT / TNFRSF19L, TACI / TNFRSF13B, TL1A / TNFSF15, TNF-α, TNFRII / TNFRSF1B), 2 B4 / CD244 / SLAMF4, BLAME / SLAMF8, CD2, CD2F-10 / SLAMF9, CD48 / SLAMF2, CD58 / LFA-3, CD84 / SLAMF5, CD229 / SLAMF3, CRACC / SLAMF7, NTB-A / SLAMF6, SLAM / CD150), CD2, CD7, CD53, CD82 / Kai-1, CD90 / Thy1, CD96, CD160, CD200, CD300a / LMIR1, HLA class I, HLA-DR, Ikaros, integrin α4 / CD49d, integrin α4β1, integrin α4β7 / LPAM-1, LAG-3, TCL1A, TCL1B, CRTAM, CAP12, Dectin-1 / CLEC7A, DPPIV / CD26, EphB6, TIM-1 / KIM-1 / HAVCR, TIM-4, TSLP, TSLPR, lymphocyte function-associated antigen-1 (LFA-1), NKG2C, CD3ζ domain, immunoreceptor tyrosine-based activation motif (ITAM), CD27, CD28, 4-1BB, CD134 / OX40, CD30, CD40, PD-1, ICOS, lymphocyte function-associated antigen-1 (LFA-1), CD2, CD7, LIGHT,The fusosome according to any one of embodiments 33 to 50, comprising at least one signaling domain selected from one or more of a ligand that specifically binds to NKG2C, B7-H3, CD83, or a functional fragment thereof. 52. A fusosome according to any of embodiments 33 to 51, wherein the CAR comprises a CD3ζ domain, or an immunoreceptor tyrosine-based activation motif (ITAM), or a functional variant thereof. 53. A fusosome according to any of embodiments 33 to 51, wherein the CAR comprises (i) a CD3ζ domain, or an immunoreceptor tyrosine-based activation motif (ITAM), or a functional variant thereof, and (ii) a CD28 domain, or a 4-1BB domain, or a functional variant thereof. 54. A fusosome described in any of embodiments 33 to 51, wherein the CAR comprises (i) a CD3ζ domain, or an immunoreceptor tyrosine-based activation motif (ITAM), or a functional variant thereof; (ii) a CD28 domain, or a functional variant thereof; and (iii) a 4-1BB domain, or a CD134 domain, or a functional variant thereof. 55. A fusosome described in any of embodiments 33 to 53, wherein the CAR comprises (i) a CD3ζ domain, or an immunoreceptor tyrosine-based activation motif (ITAM), or a functional variant thereof; (ii) a CD28 domain, or a functional variant thereof; (iii) a 4-1BB domain, or a CD134 domain, or a functional variant thereof; and (iv) a cytokine or costimulatory ligand transgene. 56. A fusosome according to any of embodiments 33 to 53, wherein the CAR further comprises one or more spacers. 57. The fusosome of embodiment 56, wherein the spacer is a first spacer between the antigen-binding domain and the transmembrane domain. 58. A fusosome according to embodiment 56 or embodiment 57, wherein the first spacer comprises at least a portion of an immunoglobulin constant region or a variant or modified version thereof. 59. A fusosome according to any of embodiments 56 to 58, wherein the spacer is a second spacer between the transmembrane domain and the signaling domain. 60. The fusosome of embodiment 59, wherein the second spacer is an oligopeptide. 61. The fusosome of embodiment 60, wherein the oligopeptide comprises a glycine-serine doublet. 62. Membrane proteins include cell surface receptors, ion channel-linked receptors, enzyme-linked receptors, G protein-coupled receptors, receptor tyrosine kinases, tyrosine kinase-associated receptors, receptor-like tyrosine phosphatases, receptor serine / threonine kinases, receptor guanylyl cyclases, histidine kinase-associated receptors, epidermal growth factor receptors (EGFRs) (including ErbB1 / EGFR, ErbB2 / HER2, ErbB3 / HER3, and ErbB4 / HER4), fibroblast growth factor receptors (FGFRs) (including FGF1, FGF2, FGF3, FGF4, FGF5, FGF6, FGF7, FGF18, and FGF21), and vascular endothelial growth factor receptors (VEGFRs) (including VEGF-A, VEGF-B, VEGF-C, VEGF-D, and PIGF). , RET receptors and the Eph receptor family (including EphA1, EphA2, EphA3, EphA4, EphA5, EphA6, EphA7, EphA8, EphA9, EphA10, EphB1, EphB2, EphB3, EphB4, and EphB6), CXCR1, CXCR2, CXCR3, CXCR4, CXCR6, CCR1, CCR2, CCR3, CCR4 , CCR5, CCR6, CCR8, CFTR, CIC-1, CIC-2, CIC-4, CIC-5, CIC-7, CIC-Ka, CIC-Kb, Bestrophin, TMEM16A, GABA receptor, Glycine receptor, ABC transporter, NAV1.1, NAV1.2, NAV1.3, NAV1.4, NAV1.5, NAV1.6, NAV1.7, NAV1.8, NAV1.9, sphingosine-1-phosphate receptor (S1P1R), NMDA channel, transmembrane protein, multispanning transmembrane protein, T cell receptor motif; T cell α chain; T cell β chain; T cell γ chain; T cell δ chain; CCR7; CD3; CD4; CD5; CD7; CD8; CD11b; CD11c; CD16; CD19; CD20; CD21; CD22; CD25; CD28; CD34; CD35; CD40; CD45RA; CD45RO; CD52; CD56; CD62L;CD68;CD80;CD95;CD117;CD127;CD133;CD137(4-1BB);CD163;F4 / 80;IL-4Ra;Sca-1;CTLA-4;GITR;GARP;LAP;Granzyme B;LFA-1;Transferrin receptor;NKp46, perforin, CD4+;Th1;Th2;Th17;Th40;Th22;Th9;Tfh, classical Treg.FoxP3+;Tr1;Th3;Treg17;T. RE G; CDCP1, NT5E, EpCAM, CEA, gpA33, mucin, TAG-72, carbonic anhydrase IX, PSMA, folate-binding protein, gangliosides (e.g., CD2, CD3, GM2), Lewis-γ 2, VEGF, VEGFR1 / 2 / 3, αVβ3, α5β1, ErbB1 / EGFR, ErbB1 / HER2, ErB3, c-MET, IGF1R, EphA3, TRAIL-R1, TRAIL-R2, RANKL, FAP, tenascin, PDL-1, BAFF, HDAC, ABL , FLT3, KIT, MET, RET, IL-1β, ALK, RANKL, mTOR, CTLA-4, IL-6, IL-6R, JAK3, BRAF, PTCH, Smoothened, PIGF, ANPEP, TIMP1, PLAUR, PTPRJ, LTBR, ​​or ANTXR 1, folate receptor α (FRa), ERBB2 (Her2 / neu), EphA2, IL-13Ra2, epidermal growth factor receptor (EGFR), mesothelin, TSHR, CD19, CD123, CD22, CD30, CD171, CS-1, CLL-1, CD33, EGFRvIII, G D2, GD3, BCMA, MUC16(CA125), L1CAM, LeY, MSLN, IL13Rα1, L1-CAM, TnAg, prostate-specific membrane antigen (PSMA), ROR1, FLT3, FAP, TAG72, CD38, CD44v6, CEA, EPCAM, B7H3, KI T, interleukin-11 receptor α (IL-11Ra), PSCA, PRSS21, VEGFR2, LewisY, CD24, platelet-derived growth factor receptor β (PDGFR-β), SSEA-4, CD20, MUC1, NCAM, prostase, PAP, ELF2M, ephrin B2, IGF-1 receptor, CAIX, LMP2, gplOO, bcr-abl, telomerase, fucosyl GM1, sLe, GM3, TGS5, HMWMAA, o-acetyl-GD2, folate receptor β, TEM1 / CD248, TEM7R, CLDN6, GPRC5D, CXORF61 , CD97, CD179a, ALK, polysialic acid, PLACl, GloboH, NY-BR-1, UPK2, HAVCR1, ADRB3, PANX3, GPR20, LY6K, OR51E2, TARP, WT1, NY-ESO-1, LAGE-la, MAGE-A1, legumain, HPVE6, E7, ETV6-AML, sperm protein 17, XAGE1, Tie2, MAD-CT-1, MAD-CT-2, Fos-related antigen 1, p53, p53 mutant, prostein, survivin, telomerase, PCTA-1 / galectin 8, MelanA / MART1,Ras mutant, hTERT, sarcoma translocation breakpoint, ML-IAP, ERG (TMPRSS2ETS fusion gene), NA17, PAX3, androgen receptor, cyclin B1, MYCN, RhoC, TRP-2, CYPIBI, BORIS, SART3, PAX5, OY-TES1, LCK, AKAP-4, SSX2, RAGE-1, human telomerase reverse transcriptase, RU1, RU2, intestinal carboxylesterase, mut The fusosome according to any one of embodiments 18 to 32, wherein the fusosome is selected from hsp70-2, CD79a, CD79b, CD72, LAIR1, FCAR, LILRA2, CD300LF, CLEC12A, BST2, EMR2, LY75, GPC3, FCRL5, IGLL1, neoantigens, CD133, CD15, CD184, CD24, CD56, CD26, CD29, CD44, HLA-A, HLA-B, HLA-C, (HLA-A, B, C)CD49f, CD151, CD340, CD200, tkrA, trkB, or trkC. 63. The fusosome of any of the above embodiments, wherein the fusosome enters the target cell by endocytosis, e.g., the level of membrane protein payload agent delivered via the endocytic pathway of a given fusosome is 0.01-0.6, 0.01-0.1, 0.1-0.3, or 0.3-0.6, or at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more greater than chloroquine-treated reference cells, e.g., using the assay of Example 91. 64. The fusosome of any of the above embodiments, wherein the fusosome enters the target cell by a non-endocytic pathway, e.g., the level of membrane protein payload agent delivered via the non-endocytic pathway of a given fusosome is 0.1-0.95, 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-0.95, or at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more greater than chloroquine-treated reference cells, e.g., using the assay of Example 90. 65. A fusosome according to any of the above embodiments, i) the membrane protein payload agent is a membrane protein or a nucleic acid (e.g., DNA, gDNA, cDNA, RNA, pre-mRNA, mRNA) encoding or complementary to a membrane protein, such as a chimeric antigen receptor (CAR) encoding one; ii) the membrane protein is or comprises a receptor, such as an antigen receptor, which in some embodiments may be a natural receptor or an engineered receptor, e.g., a CAR; iii) the membrane protein is or comprises an integrin; iv) the membrane protein is or comprises a T cell receptor; v) the membrane protein is or comprises a membrane transport protein, such as an ion channel protein or a pore-forming protein (e.g., hemolysin or colicin); vi) the membrane protein is or comprises a Toll-like receptor; vii) the membrane protein is or comprises an interleukin receptor; viii) the membrane protein is or comprises a membrane enzyme, or ix) Fusosomes, in which the membrane protein is or comprises a cell adhesion protein (e.g., a cadherin protein, a selectin protein, a mucin protein, etc.). 66. The fusosome according to any of the above embodiments, i) the membrane protein is an integral membrane protein; ii) the membrane protein is a peripheral membrane protein; iii) membrane proteins transiently associate with membranes; iv) the membrane protein is a protein that is associated with and / or spans entirely or partially (e.g., as a transmembrane protein) the membrane of the target cell; v) the membrane protein is an integral monotopic protein (i.e., associated with only one side of the membrane); vi) the membrane protein is associated with or becomes associated with the outer surface of the membrane of the target cell (e.g., is partially or entirely present on the outer surface); or vii) Fusosomes, in which membrane proteins are associated with or become associated with (e.g., reside partially or entirely on) the inner surface of the target cell's membrane. 67. A fusosome according to any of the above embodiments, i) the membrane protein is a therapeutic membrane protein, or ii) fusosomes, in which the membrane protein is or comprises a receptor (e.g., a cell surface receptor and / or a transmembrane receptor), a cell surface ligand, a membrane transport protein (e.g., an ion channel protein, a pore-forming protein (e.g., a toxin protein), etc.), a membrane enzyme, and / or a cell adhesion protein). 68. A fusosome according to any of the above embodiments, i) the membrane protein comprises the sequence of a naturally occurring membrane protein; ii) the membrane protein is or comprises a variant or modified version of a naturally occurring membrane protein; iii) the membrane protein is or comprises an engineered membrane protein, or iv) Fusosomes, in which the membrane protein is or comprises a fusion protein. 69. A fusosome according to any of the above embodiments, wherein the fusosome delivers a membrane protein payload agent to the membrane of a target cell, e.g., as described herein. 70. The fusosome of embodiment 69, wherein the fusosome is further capable of delivering (e.g., delivers) one or more agents, such as proteins, nucleic acids (e.g., DNA, gDNA, cDNA, RNA, pre-mRNA, mRNA, etc.), organelles, or and / or metabolites, to the cytosol of the target cell. 71. A fusosome composition or preparation comprising a plurality of fusosomes, wherein at least one fusosome is (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a membrane protein payload agent, e.g., as described herein, and a fusosome composition or preparation. 72. A frozen purified fusosome composition or preparation comprising a plurality of fusosomes containing a membrane protein payload agent as described herein, wherein the preparation is frozen at a temperature of 4, 0, -4, -10, -12, -16, -20, -80, or -160°C or below. 73. The fusosome composition of embodiment 71 or embodiment 72, wherein at least one fusosome of the plurality of fusosomes is derived from a source cell. 74. The fusosome composition of any of embodiments 71-73, wherein the fusosomes are at a temperature of less than 4, 0, -4, -10, -12, -16, -20, -80, or -160°C. 75. Multiple fusosomes, at least about 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 10 9 , 10 10, 10 11 , 10 12 , 10 13 , 10 14 , or 10 15 75. The fusosome composition of any one of embodiments 71 to 74, comprising fusosomes. 76. The fusosome composition of any of embodiments 71-75, wherein the multiple fusosomes are the same. 77. At least 0.01% to 0.05%, 0.05% to 0.1%, 0.1% to 0.5%, 0.5% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, 5% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, or 80% to 90% of the fusosomes in the fusosome composition are Contains the same fusogens Produced using the same type of source cell, or 77. The fusosome composition of embodiment 76, wherein the fusosomes are the same if they share at least one property selected from: 78. The fusosome composition of any of embodiments 71-75, wherein the fusosomes are different. 79. The fusosome composition of any of embodiments 71-77, wherein the multiple fusosomes are derived from more than one type of source cell. 80. The fusosome composition of any of embodiments 71-79, having a volume of at least 1 μL, 2 μL, 5 μL, 10 μL, 20 μL, 50 μL, 100 μL, 200 μL, 500 μL, 1 mL, 2 mL, 5 mL, or 10 mL. 81. The fusosome composition of any of embodiments 71-80, wherein the plurality of fusosomes comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, which do not contain a functional nucleus. 82. The fusosome composition of any of embodiments 71-81, wherein the plurality of fusosomes comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, which do not contain nuclei. 83. The fusosome composition of any of embodiments 71-82, wherein the plurality of fusosomes comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, which are substantially free of nuclear DNA. 84. The fusosome composition of any of embodiments 71 to 83, wherein the plurality of fusosomes comprises at least 0.01% to 0.05%, 0.05% to 0.1%, 0.1% to 0.5%, 0.5% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, 5% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, or 80% to 90% fusosomes, which do not contain functional mitochondria. 85. The fusosome composition of any of embodiments 71 to 84, wherein the plurality of fusosomes comprises at least 0.01% to 0.05%, 0.05% to 0.1%, 0.1% to 0.5%, 0.5% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, 5% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, or 80% to 90% fusosomes, which do not contain mitochondria. 86. The fusosome composition of any of embodiments 71-85, comprising less than 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, or 10% of the source cells by protein mass, or less than 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, or 10% of the source cells have functional nuclei. 87. The fusosome composition comprises at least 0.01% to 0.05%, 0.05% to 0.1%, 0.1% to 0.5%, 0.5% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, 5% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, or 80% to 90% fusosomes; i) the fusogen is present at a copy number of at least 1,000 copies per fusosome, as measured, for example, by the assay of Example 29, or ii) The ratio of the copy number of the fusogen to the copy number of the membrane protein payload agent per fusosome is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 5:1, 5:1 to 2:1, 2:1 87. The fusosome composition of any of embodiments 71-86, wherein the fusosome composition is between 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. 88. The fusosome composition of any of embodiments 71-87, wherein the fusosome composition comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, and wherein the membrane protein payload agent is present at a copy number of at least 1,000 copies per fusosome, as measured, for example, by the assay of Example 43. 89. The fusosome composition of any of embodiments 71-77, wherein the plurality of fusosomes have an average diameter of at least about 50 nm, about 80 nm, about 100 nm, about 200 nm, about 500 nm, about 1000 nm, about 1200 nm, about 1400 nm, or about 1500 nm. 90. The fusosome composition of any of embodiments 71-89, wherein the plurality of fusosomes comprises fusosomes having a diameter within the range of about 10 nm to about 100 μm. 91. The fusosome composition of any of embodiments 71 to 89, comprising a plurality of fusosomes having a size within the range of about 20 nm to about 200 nm, about 50 nm to about 200 nm, about 50 nm to about 100 nm, about 50 nm to about 150 nm, or about 100 nm to about 150 nm. 92. The fusosome composition of any of embodiments 71-91, wherein at least 50% of the plurality of fusosomes have a diameter within 10%, 20%, 30%, 40%, or 50% of the average diameter of the fusosomes in the fusosome composition. 93. Multiple, approximately 500 nm 3 ~about 0.0006mm 3 , or about 4,000 nm 3 ~about 0.005μm 3 , about 65,000nm 3 ~about 0.005μm 3 , about 65,000nm 3 ~about 0.0006μm 3 , about 65,000nm 3 ~about 0.002μm 3 , or approximately 0.0006 μm3 ~about 0.002μm 3 93. The fusosome composition of any one of embodiments 71 to 92, comprising fusosomes having a volume in the range of 94. A fusosome composition described in any of embodiments 71-93, wherein at least 50% of the plurality of fusosomes have a volume within 10%, 20%, 30%, 40%, or 50% of the average volume of fusosomes in the fusosome composition. 95. A fusosome composition described in any of embodiments 71-94, wherein at least 50% of the plurality of fusosomes have a fusogen copy number within 10%, 20%, 30%, 40%, or 50% of the average fusogen copy number of fusosomes in the fusosome composition. 96. A fusosome composition described in any of embodiments 71 to 95, wherein at least 50% of the plurality of fusosomes have a protein membrane payload copy number within 10%, 20%, 30%, 40%, or 50% of the average protein membrane payload copy number of fusosomes in the fusosome composition. 97. A fusosome composition or pharmaceutical composition according to any of the above embodiments, i) the membrane protein payload agent is located partially or entirely within the fusosome lumen; ii) the membrane protein payload agent is associated with (e.g., located partially or entirely within) the lipid bilayer of the fusosome; or i) A fusosome composition or pharmaceutical composition in which the relevant membrane protein is associated with and / or partially or entirely displayed on the outer surface of the fusosome. 98. A method for producing a fusosome composition, comprising: a) providing source cells, including, for example, expressing a fusogen; b) producing fusosomes from the source cells, the fusosomes comprising a lipid bilayer, a lumen, a fusogen, and a membrane protein payload agent, thereby creating fusosomes; c) formulating the fusosomes, e.g., as a pharmaceutical composition suitable for administration to a subject; i) the source cells are other than 293 cells, HEK cells, human endothelial cells, or human epithelial cells; ii) the fusogen is other than a viral protein; iii) the fusosomes and / or compositions or preparations thereof have a density other than between 1.08 g / mL and 1.12 g / mL; iv) the fusosomes and / or compositions or preparations thereof have a density of 1.25 g / mL + / - 0.05, e.g., as measured by the assay of Example 33; v) fusosomes are not captured by the scavenger system in the circulation or by Kupffer cells in the sinuses of the liver; vi) the fusosomes are not trapped by the reticuloendothelial system (RES) of the subject, e.g., by the assay of Example 76; vii) when a plurality of fusosomes are administered to a subject, less than 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the plurality are not captured by the RES after 24 hours, e.g., by the assay of Example 76; viii) the fusosomes have a diameter of greater than 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 20 μm, 50 μm, 100 μm, 150 μm, or 200 μm; ix) the fusosomes contain cell biological material; x) the fusosome contains enucleated cells, or xi) the fusosome contains an inactivated nucleus. 99. The method of embodiment 98, wherein providing source cells that express a fusogen comprises expressing an exogenous fusogen in the source cells or upregulating expression of an endogenous fusogen in the source cells. 100. The method of embodiment 98 or embodiment 99, comprising inactivating the nuclei of the source cells. 101. A method according to any of embodiments 98 to 100, comprising introducing a membrane protein payload (e.g., a nucleic acid or a protein) into fusosomes, for example by electroporation. 102. A method for producing a fusosome pharmaceutical composition, comprising: a) providing a plurality of fusosomes, for example according to any of embodiments 1 to 70, a fusosome composition according to any of embodiments 71 to 97, or a pharmaceutical composition according to embodiment 97; b) assaying one or more fusosomes from the plurality to determine whether one or more (e.g., two, three, or all) of the following criteria are met: i) the fusosomes fuse with target cells, e.g., at least at least 10% more frequently than with non-target cells, e.g., in the assay of Example 54; ii) the fusosomes fuse with target cells, e.g., at least 50% more frequently than other fusosomes, e.g., in the assay of Example 54; iii) the fusosomes fuse with the target cells at a rate such that the agent in the fusosomes is delivered to at least 10% of the target cells after 24 hours, e.g., in the assay of Example 54; iv) the fusogen is present in a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 29; v) the fusosomes contain a copy number of the membrane protein payload agent of at least 1,000 copies, e.g., as measured by the assay of Example 43; vi) The ratio of the copy number of the fusogen to the copy number of the membrane protein payload agent is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 5:1, 5: Between 1 to 2:1, 2:1 to 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. vii) the fusosomes comprise a lipid composition in which one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 75% of the corresponding lipid levels in the source cells; viii) the fusosomes contain a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; ix) the fusosomes comprise a lipid to protein ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 49; x) the fusosomes comprise a ratio of protein to nucleic acid (e.g., DNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, e.g., as measured using the assay of Example 50; xi) the fusosomes comprise a lipid to nucleic acid (e.g., DNA) ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 51; xii) the fusosomes have a half-life in a subject, e.g., a mouse, that is within 90% of the half-life of a reference cell, e.g., a source cell, e.g., by the assay of Example 75; xiii) the fusosomes transport glucose (e.g., labeled glucose, e.g., 2-NBDG) across the membrane in the absence of glucose, e.g., at least 10% more than a negative control, e.g., an otherwise similar fusosome, as measured, e.g., using the assay of Example 64; xiv) the fusosomes contain esterase activity in the lumen that is within 90% of the esterase activity in a reference cell, e.g., a source cell or a mouse embryonic fibroblast, e.g., using the assay of Example 66; xv) the fusosomes comprise a metabolic activity level within 90% of the metabolic activity (e.g., citrate synthase activity) in a reference cell, e.g., a source cell, e.g., as described in Example 68; xvi) the fusosomes comprise a respiration level (e.g., oxygen consumption rate) within 90% of the respiration level in a reference cell, e.g., a source cell, e.g., as described in Example 69; xvii) the fusosomes comprise an Annexin V staining level of up to 18,000, 17,000, 16,000, 15,000, 14,000, 13,000, 12,000, 11,000, or 10,000 MFI, e.g., using the assay of Example 70; or or the fusosomes comprise a level of Annexin V staining that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the level of Annexin V staining of otherwise similar fusosomes treated with menadione in the assay of Example 70, or the fusosomes comprise a level of Annexin V staining that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the level of Annexin V staining of macrophages treated with menadione in the assay of Example 70. xviii) the fusosomes have an miRNA content level that is at least 1% of that of the source cells, e.g., by the assay of Example 39; xix) the fusosomes have a soluble:insoluble protein ratio that is within 90% of that of the source cells, e.g., by the assay of Example 47; xx) the fusosomes have an LPS level of less than 5% of the lipid content of the fusosomes, as measured, for example, by the assay of Example 48; xxi) the fusosomes and / or compositions or preparations thereof are capable of signaling, e.g., transmitting an extracellular signal, e.g., phosphorylating AKT in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, at least 10% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; xxii) the fusosomes have a level of juxtacrine signaling that is at least 5% greater than the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; xxiii) the fusosomes have a level of paracrine signaling that is at least 5% greater than the level of paracrine signaling induced by a reference cell, e.g., a source cell or a macrophage, e.g., by the assay of Example 72; xxiv) the fusosomes polymerize actin at a level within 5% of the level of polymerized actin in a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 73; xxv) the fusosomes have a membrane potential within about 5% of the membrane potential of a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 74, or the fusosomes have a membrane potential of about -20 to -150 mV, -20 to -50 mV, -50 to -100 mV, or -100 to -150 mV; xxvi) the fusosomes and / or compositions or preparations thereof are capable of secreting protein at a rate that is at least 5% greater than that of a reference cell, e.g., a mouse embryonic fibroblast, e.g., using the assay of Example 62; or xxvii) the fusosomes have low immunogenicity, e.g., as described herein; c) (optionally) authorizing the release of the plurality of fusosomes or fusosome compositions if one or more of the criteria are met; This method results in the production of a fusosome pharmaceutical composition. 103. A method for producing a fusosome composition, comprising: a) providing source cells, including, for example, expressing a fusogen; b) producing fusosomes from the source cells, the fusosomes comprising a lipid bilayer, a lumen, a fusogen, and a membrane protein payload agent, thereby creating fusosomes; c) formulating the fusosomes, for example, as a pharmaceutical composition suitable for administration to a subject. 104. A method for producing a fusosome composition, comprising: a) providing, e.g., producing, a plurality of fusosomes or fusosome preparations described herein; b) analyzing a plurality of samples (e.g., of a preparation) to determine whether one or more (e.g., two, three, or more) criteria are met. 105. The criteria(s) are: i) fusosomes in the sample fuse with target cells at a rate, e.g., at least at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% higher than with non-target cells, e.g., in the assay of Example 54; ii) the fusosomes in the sample fuse with target cells at a rate, e.g., at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% higher than with other fusosomes, e.g., in the assay of Example 54; iii) the fusosomes in the sample fuse with the target cells at a rate such that the membrane protein payload agent in the fusosomes is delivered to at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the target cells after 24, 48, or 72 hours, e.g., in the assay of Example 54; iv) the fusogen is present at a copy number of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies per fusosome (e.g., on average across the sample), as measured, for example, by the assay of Example 29; v) the membrane protein payload agent is detectable in fusosomes of a sample (on average across the sample) at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies or less, as measured, for example, by the assay of Example 43; vi) The ratio of the copy number of the fusogen to the copy number of the membrane protein payload agent is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 5:1, 5: Between 1 to 2:1, 2:1 to 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. vii) the fusosomes of the sample are characterized by a lipid composition substantially similar to that of the source cells, or one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or 75% of the corresponding lipid levels in the source cells; viii) the fusosomes of the sample are characterized by a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; ix) the sample fusosomes are characterized by a lipid to protein ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 49; x) the sample fusosomes are characterized by a protein to nucleic acid (e.g., DNA) ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 50; xi) the sample fusosomes are characterized by a lipid to nucleic acid (e.g., DNA) ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 51; xii) the fusosomes of the sample are characterized by a half-life in a subject, e.g., an experimental animal such as a mouse, that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% of the half-life of a reference cell, e.g., a source cell, e.g., by the assay of Example 75; xiii) the fusosomes of the sample transport, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% more glucose (e.g., labeled glucose, e.g., 2-NBDG) across the membrane in the absence of glucose than a negative control, e.g., an otherwise similar fusosome, as measured, e.g., using the assay of Example 64; xiv) the sample fusosomes are characterized by an esterase activity in the lumen that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the esterase activity in a reference cell, e.g., a source cell or a mouse embryonic fibroblast, using, e.g., the assay of Example 66; xv) the fusosomes of the sample are characterized by a level of metabolic activity (e.g., citrate synthase activity) that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the metabolic activity, e.g., citrate synthase activity, in a reference cell, e.g., a source cell, e.g., as described in Example 68; xvi) the fusosomes of the sample are characterized by a respiration level (e.g., oxygen consumption rate) within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the respiration level in a reference cell, e.g., a source cell, e.g., as described in Example 69; xvii) the fusosomes of the sample are characterized by an annexin V staining level of at most 18,000, 17,000, 16,000, 15,000, 14,000, 13,000, 12,000, 11,000, or 10,000 MFI, e.g., using the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of otherwise similar fusosomes treated with menadione in the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of macrophages treated with menadione in the assay of Example 70. xviii) the fusosomes of the sample are characterized by an miRNA content level that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more than that of the source cells, e.g., by the assay of Example 39; xix) the fusosomes are within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or greater than that of the source cells, e.g., by the assay of Example 47, or have a soluble:insoluble protein ratio within, e.g., 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% of that of the source cells; xx) the sample fusosomes are characterized by an LPS level of 5%, 1%, 0.5%, 0.01%, 0.005%, 0.0001%, 0.00001%, or less of the LPS content of the source cells or reference cells, e.g., as measured by the assay of Example 48; xxi) the fusosomes of the sample are capable of signaling, e.g., sending an extracellular signal, e.g., AKT phosphorylation in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; xxii) the fusosomes of the sample are characterized by a level of juxtacrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% greater than the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; xxiii) the fusosomes of the sample are characterized by a level of paracrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% greater than the level of paracrine signaling induced by a reference cell, e.g., a source cell or macrophage, e.g., by the assay of Example 72; xxiv) the fusosomes of the sample are characterized by polymerizing actin at a level that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the level of polymerized actin in a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 73; xxv) the fusosomes of the sample are characterized by a membrane potential within about 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% of the membrane potential of a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 74, or the fusosomes have a membrane potential of about -20 to -150 mV, -20 to -50 mV, -50 to -100 mV, or -100 to -150 mV; xxvi) the fusosomes of the sample are capable of secreting protein at a rate, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% greater than that of reference cells, e.g., mouse embryonic fibroblast cells, using, e.g., the assay of Example 62; xxvii) The method of embodiment 104, wherein the fusosomes of the sample are selected from: characterized by low immunogenicity, e.g., as described herein. 106. The method of embodiment 104 or 105, further comprising: c) approving the release of the plurality of fusosomes or fusosome compositions if one or more of the criteria are met, or (optionally) formulating the plurality of fusosomes or fusosome preparation as a pharmaceutical product if one or more of the criteria are met. 107. A method for producing a fusosome composition, comprising: a) providing source cells, including, for example, expressing a fusogen; b) producing fusosomes from the source cells, the fusosomes comprising a lipid bilayer, a lumen, a fusogen, and a membrane protein payload agent, thereby creating fusosomes; c) formulating the fusosomes, e.g., as a pharmaceutical composition suitable for administration to a subject; i) the source cells are other than 293 cells, HEK cells, human endothelial cells, or human epithelial cells; ii) the fusogen is other than a viral protein; iii) the fusosomes and / or compositions or preparations thereof have a density other than between 1.08 g / mL and 1.12 g / mL; iv) the fusosomes and / or compositions or preparations thereof have a density of 1.25 g / mL + / - 0.05, e.g., as measured by the assay of Example 33; v) fusosomes are not captured by the scavenger system in the circulation or by Kupffer cells in the sinuses of the liver; vi) the fusosomes are not trapped by the reticuloendothelial system (RES) of the subject, e.g., by the assay of Example 76; vii) when a plurality of fusosomes are administered to a subject, less than 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the plurality are not captured by the RES after 24 hours, e.g., by the assay of Example 76; viii) the fusosomes have a diameter of greater than 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 20 μm, 50 μm, 100 μm, 150 μm, or 200 μm; ix) the fusosomes contain cell biological material; x) the fusosome contains enucleated cells, or xi) the fusosome contains an inactivated nucleus. 108. A method for producing a fusosome composition, comprising: a) providing a plurality of fusosomes, fusosome compositions, or pharmaceutical compositions described herein; b) assaying one or more fusosomes from the plurality to determine whether one or more (e.g., two, three, or all) of the following criteria are met: i) the fusosomes fuse with target cells, e.g., at least at least 10% more frequently than with non-target cells, e.g., in the assay of Example 54; ii) the fusosomes fuse with target cells, e.g., at least 50% more frequently than other fusosomes, e.g., in the assay of Example 54; iii) the fusosomes fuse with the target cells at a rate such that the agent in the fusosomes is delivered to at least 10% of the target cells after 24 hours, e.g., in the assay of Example 54; iv) the fusogen is present in a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 29; v) the fusosomes contain a copy number of the membrane protein payload agent of at least 1,000 copies, e.g., as measured by the assay of Example 43; vi) The ratio of the copy number of the fusogen to the copy number of the membrane protein payload agent is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 5:1, 5: Between 1 to 2:1, 2:1 to 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. vii) the fusosomes comprise a lipid composition in which one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 75% of the corresponding lipid levels in the source cells; viii) the fusosomes contain a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; ix) the fusosomes comprise a lipid to protein ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 49; x) the fusosomes comprise a ratio of protein to nucleic acid (e.g., DNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, e.g., as measured using the assay of Example 50; xi) the fusosomes comprise a lipid to nucleic acid (e.g., DNA) ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 51; xii) the fusosomes have a half-life in a subject, e.g., a mouse, that is within 90% of the half-life of a reference cell, e.g., a source cell, e.g., by the assay of Example 75; xiii) the fusosomes transport glucose (e.g., labeled glucose, e.g., 2-NBDG) across the membrane in the absence of glucose, e.g., at least 10% more than a negative control, e.g., an otherwise similar fusosome, as measured, e.g., using the assay of Example 64; xiv) the fusosomes contain esterase activity in the lumen that is within 90% of the esterase activity in a reference cell, e.g., a source cell or a mouse embryonic fibroblast, e.g., using the assay of Example 66; xv) the fusosomes comprise a metabolic activity level within 90% of the metabolic activity (e.g., citrate synthase activity) in a reference cell, e.g., a source cell, e.g., as described in Example 68; xvi) the fusosomes comprise a respiration level (e.g., oxygen consumption rate) within 90% of the respiration level in a reference cell, e.g., a source cell, e.g., as described in Example 69; xvii) the fusosomes comprise an annexin V staining level of at most 18,000, 17,000, 16,000, 15,000, 14,000, 13,000, 12,000, 11,000, or 10,000 MFI, e.g., using the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of otherwise similar fusosomes treated with menadione in the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of macrophages treated with menadione in the assay of Example 70. xviii) the fusosomes have an miRNA content level that is at least 1% of that of the source cells, e.g., by the assay of Example 39; xix) the fusosomes have a soluble:insoluble protein ratio that is within 90% of that of the source cells, e.g., by the assay of Example 47; xx) the fusosomes have an LPS level of less than 5% of the lipid content of the fusosomes, as measured, for example, by the assay of Example 48; xxi) the fusosomes and / or compositions or preparations thereof are capable of signaling, e.g., transmitting an extracellular signal, e.g., phosphorylating AKT in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, at least 10% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; xxii) the fusosomes have a level of juxtacrine signaling that is at least 5% greater than the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; xxiii) the fusosomes have a level of paracrine signaling that is at least 5% greater than the level of paracrine signaling induced by a reference cell, e.g., a source cell or a macrophage, e.g., by the assay of Example 72; xxiv) the fusosomes polymerize actin at a level within 5% of the level of polymerized actin in a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 73; xxv) the fusosomes have a membrane potential within about 5% of the membrane potential of a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 74, or the fusosomes have a membrane potential of about -20 to -150 mV, -20 to -50 mV, -50 to -100 mV, or -100 to -150 mV; xxvi) the fusosomes and / or compositions or preparations thereof are capable of secreting protein at a rate that is at least 5% greater than that of a reference cell, e.g., a mouse embryonic fibroblast, e.g., using the assay of Example 62; or xxvii) the fusosomes have low immunogenicity, e.g., as described herein; c) (optionally) authorizing the release of the plurality of fusosomes or fusosome compositions if one or more of the criteria are met; This method results in the production of a fusosome pharmaceutical composition. 109. A method for delivering a membrane protein payload agent to a subject, comprising administering to the subject a fusosome composition comprising a plurality of fusosomes according to any of embodiments 1 to 70, a fusosome composition described in any of embodiments 71 to 97, or a pharmaceutical composition described in embodiment 97, wherein the fusosome composition is administered in an amount and / or for a time such that the membrane protein payload agent is delivered. 110. A method of delivering a fusosome composition or preparation comprising a membrane protein payload agent, e.g., as described herein, to a human subject, target tissue, or cell, the method comprising administering to the human subject or contacting the target tissue or cell with a fusosome composition comprising a plurality of fusosomes described herein, a fusosome composition described herein, or a pharmaceutical composition described herein, thereby administering the fusosome composition to the subject. 111. A method for delivering a membrane protein payload agent to a subject, target tissue, or cell, comprising administering to the subject or contacting the target tissue or cell with a fusosome composition or preparation described herein (e.g., a pharmaceutical composition described herein), wherein the fusosome composition or preparation is administered in an amount and / or for a time such that the membrane protein payload agent is delivered. 112. A method for delivering a membrane protein payload agent to a subject, comprising, for example: a) administering a first fusogen to a subject under conditions that allow for location of the first fusogen in one or more target cells of the subject; i) administering the first fusogen comprises administering a nucleic acid encoding the first fusogen under conditions that allow expression of the first fusogen in one or more target cells; or ii) administering a first fusogen that does not contain a coiled-coil motif; b) administering to a human subject a fusosome composition or preparation as described herein comprising a plurality of fusosomes comprising a second fusogen and a membrane protein payload agent, wherein the second fusogen is compatible with the first fusogen and the plurality of fusosomes further comprise the membrane protein payload agent; thereby delivering a membrane protein payload agent to a subject. 113. A method for regulating, e.g., enhancing, a biological function in a subject, comprising: a) administering a first fusogen to a subject under conditions that allow for location of the first fusogen in one or more target cells of the subject; i) administering the first fusogen comprises administering a nucleic acid encoding the first fusogen under conditions that allow expression of the first fusogen in one or more target cells; or ii) administering a first fusogen that does not contain a coiled-coil motif; b) administering to a human subject a fusosome composition or preparation as described herein comprising a plurality of fusosomes comprising a second fusogen, wherein the second fusogen is compatible with the first fusogen, and the plurality of fusosomes further comprises a membrane protein payload agent; thereby regulating a biological function in the subject. 114. A method for delivering or targeting a membrane protein function to a subject, comprising administering to the subject a fusosome composition or preparation described herein comprising a membrane protein payload agent, wherein the fusosome composition or preparation is administered in an amount and / or for a time such that the membrane protein function is delivered or targeted in the subject, and optionally, the subject has cancer, an inflammatory disorder, an autoimmune disease, a chronic disease, inflammation, impaired organ function, an infectious disease, a degenerative disorder, a genetic disease, or an injury. 115. A method of administering a fusosome composition to a human subject, comprising: a) administering a first fusogen to a subject under conditions that allow for location of the first fusogen in one or more target cells of the subject; i) administering the first fusogen comprises administering a nucleic acid encoding the first fusogen under conditions that allow expression of the first fusogen in one or more target cells; or ii) administering a first fusogen that does not contain a coiled-coil motif; b) administering to a human subject a fusosome composition comprising a plurality of fusosomes comprising a second fusogen, wherein the second fusogen is compatible with the first fusogen, and the plurality of fusosomes further comprise a membrane protein payload agent; This method involves administering a fusosome composition to a subject. 116. A method for delivering a membrane protein payload agent to a subject, comprising: a) administering a first fusogen to a subject under conditions that allow for location of the first fusogen in one or more target cells of the subject; i) administering the first fusogen comprises administering a nucleic acid encoding the first fusogen under conditions that allow expression of the first fusogen in one or more target cells; or ii) administering a first fusogen that does not contain a coiled-coil motif; b) administering to a human subject a fusosome composition comprising a plurality of fusosomes comprising a second fusogen and a therapeutic agent, wherein the second fusogen is compatible with the first fusogen, and the plurality of fusosomes further comprise a membrane protein payload agent; thereby delivering a membrane protein payload agent to a subject. 117. A method for regulating, e.g., enhancing, a biological function in a subject, comprising: a) administering a first fusogen to a subject under conditions that allow for location of the first fusogen in one or more target cells of the subject; i) administering the first fusogen comprises administering a nucleic acid encoding the first fusogen under conditions that allow expression of the first fusogen in one or more target cells; or ii) administering a first fusogen that does not contain a coiled-coil motif; b) administering to a human subject a fusosome composition comprising a plurality of fusosomes comprising a second fusogen, wherein the second fusogen is compatible with the first fusogen, and the plurality of fusosomes further comprise a membrane protein payload agent; thereby regulating a biological function in the subject. 118. Biological functions a) modulating, e.g., increasing or decreasing, the interaction between two cells; b) modulating, e.g., increasing or decreasing, the immune response; c) modulating, e.g., increasing or decreasing, cell recruitment to target tissues; d) reduce the rate of cancer growth, or e) reducing the number of cancer cells in a subject. 119. The method of any of embodiments 115-118, wherein the membrane protein payload agent is exogenous to or overexpressed in the source cells. 120. A membrane protein payload agent is i) chimeric antigen receptors, ii) an integrin membrane protein payload, for example selected from Table 7; iii) an ion channel protein selected from Table 8; iv) a pore-forming protein selected, for example, from Tables 9 and 10; v) a Toll-like receptor selected, for example, from Table 11; vi) an interleukin receptor payload, for example selected from Table 12; vii) a cell adhesion protein selected from Tables 13 to 14; viii) a transport protein selected from Table 17; ix) a signal sequence that is heterologous to the naturally occurring membrane protein, or x) The method of any of embodiments 115-119, comprising or encoding one or more of the signal sequences listed in Table 6. 121. The method of any of embodiments 115-120, wherein the membrane protein payload agent is other than, does not comprise, does not encode, or is not complementary to a sequence encoding a connexin, CFTR, thyrotropin receptor, myelin protein zero, melacortin 4, myelin proteolipid protein, low density lipoprotein receptor, ABC transporter, CD81, mCAT-1, CXCR4, CD4, CCR5, sialic acid-rich protein, claudin, CD21, T cell receptor, B cell receptor, TNFR1, CD63, GLUT4, VEGF, or ICAM. 122. The method of any of embodiments 115-121, wherein the membrane protein payload agent comprises or encodes a chimeric protein that does not bind to a cell surface marker of a target cell or a target cell moiety and does not contain a fluorescent protein. 123. A membrane protein payload agent is a) a therapeutic protein, including, for example, a therapeutic protein described herein; b) comprising a Golgi apparatus protein, a secretory protein, or an endoplasmic reticulum protein, or a combination thereof; c) does not contain one or more of a dimer (e.g., a dimer that is exogenous to the source cell), a heterodimer (e.g., a heterodimer that is exogenous to the source cell), or a dimerization domain (e.g., a dimerization domain of a polypeptide that is exogenous to the source cell); d) The method of any of embodiments 115 to 122, comprising a nucleic acid (e.g., DNA or RNA) encoding a membrane protein. 124. A membrane protein payload agent is a) membrane proteins containing transmembrane domains; b) lipid-anchored proteins; c) proteins that bind to transmembrane proteins (e.g., extracellular proteins that bind to the extracellular portion of a transmembrane protein, or intracellular proteins that bind to the intracellular portion of a transmembrane protein); d) proteins lacking a transmembrane domain; e) proteins that partially span the membrane (e.g., the membrane of a target cell or fusosome) and proteins that do not completely span the membrane (e.g., proteins that contain in-plane membrane helices or that contain hydrophobic loops that do not completely span the membrane), or f) The method of any of embodiments 115 to 123, comprising or encoding a protein that does not contain a transmembrane domain, wherein the protein interacts with the membrane surface, for example, via electrostatic or ionic interactions. 125. The method of any of embodiments 115-124, wherein the first fusogen is not a lipopeptide. 126. The method of any of embodiments 109-125, further comprising monitoring cancer progression, tumor regression, tumor volume, reduction in neoplastic cell number, amount of fused cells, amount of fused cells containing a membrane protein payload agent, amount of fused cells expressing a nucleic acid protein payload, and amount of membrane protein disposed in the membrane of the fused cells. 127. A membrane protein payload agent is A) Sequences SEQ ID NOs: 8144 to 16131 of U.S. Patent Publication No. 2016 / 0289674; b) fragments, variants, or homologs of the sequences set forth in SEQ ID NOs: 8144 to 16131 of U.S. Patent Publication No. 2016 / 0289674; c) a nucleic acid encoding a protein comprising the sequence of SEQ ID NOs: 8144 to 16131 of U.S. Patent Publication No. 2016 / 0289674; or d) A fusosome, fusosome composition, fusosome preparation, or method according to any of the preceding embodiments, which is or comprises a nucleic acid encoding a protein comprising a fragment, variant, or homolog of SEQ ID NOs: 8144-16131 of U.S. Patent Publication No. 2016 / 0289674. 128. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the membrane protein payload agent is: a) a protein selected from Tables 7 to 17; b) a fragment, variant, or homologue of a protein selected from Tables 7 to 17; c) a nucleic acid encoding a protein that is or comprises a protein selected from Tables 7 to 17; or d) A fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, which is or comprises a nucleic acid encoding a protein comprising a fragment, variant, or homologue of a protein selected from Tables 7 to 17. 129. The membrane protein payload agent is a chimeric antigen receptor containing an antigen-binding domain. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, which is or comprises (CAR). 130. The fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, wherein the membrane protein provided by or as a membrane protein payload agent described herein is or comprises an immunoglobulin moiety or entity (e.g., an antibody, Fab, scFV, scFab, sdAb, duobody, minibody, nanobody, diabody, zybody, camelid antibody, BiTE, quadroma, or bsDb). 131. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the membrane protein provided by, or as a membrane protein payload agent described herein, is or comprises one or more cell surface ligands (e.g., 1, 2, 3, 4, 5, 10, 20, 50, or more cell surface ligands), and / or the membrane protein provided by, or as a membrane protein payload agent described herein, presents one or more cell surface ligands, e.g., to a target cell. 132. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof comprises (and can deliver to a target cell) multiple agents (e.g., at least 2, 3, 4, 5, 10, 20, or 50 agents), at least one agent is or comprises a membrane protein payload, and optionally, one or more of the agents is or comprises an inhibitory nucleic acid (e.g., siRNA or miRNA) and / or mRNA. 133. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof comprises (e.g., can be delivered to) a membrane protein payload agent capable of reprogramming or transdifferentiation of a target cell, e.g., wherein the fusosome (and / or composition thereof) comprises one or more agents that induce reprogramming or transdifferentiation of a target cell. 134. The fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, a) the fusosomes deliver at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% of the membrane protein payload agent (e.g., a therapeutic agent, e.g., a therapeutic agent that is endogenous or exogenous to the source cell) comprised by the fusosomes to the target cell; b) the fusosomes that fuse with the target cell(s) deliver, on average, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% of the membrane protein payload agent (e.g., a therapeutic membrane protein payload agent, e.g., an endogenous therapeutic membrane protein payload agent or a therapeutic membrane protein payload agent that is exogenous to the source cell) comprised by the fusosomes that fuse with the target cell(s) to the target cell; and / or c) A fusosome, fusosome composition, fusosome preparation, or method wherein the fusosome composition delivers at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% of the membrane protein payload agent (e.g., a membrane protein payload agent, e.g., a therapeutic membrane protein payload agent that is exogenous to the source cell) comprised by the fusosome composition to the target tissue. 135. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof delivers or is capable of delivering (e.g., delivers) a membrane protein payload agent (e.g., a therapeutic agent) characterized by a half-life in a subject that is, e.g., at least 10%, 20%, 50%, 2-fold, 5-fold, or 10-fold longer than the half-life of the fusosome. 136. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 306, wherein the fusosomes deliver a therapeutic agent to a target cell, and optionally the agent is present after the fusosomes are no longer present or detectable. 137. A fusosome, fusosome composition, fusosome preparation, or method wherein the fusosomes are transported with a therapeutic membrane protein payload agent, e.g., a therapeutic membrane protein payload agent, e.g., a therapeutic membrane protein payload agent that is exogenous or endogenous to the source cell, optionally wherein the therapeutic membrane protein payload agent is selected from one or more of a protein, e.g., a transmembrane protein, a cell surface protein, a secreted protein, a receptor, an antibody, a nucleic acid, e.g., DNA, a chromosome (e.g., a human artificial chromosome), RNA, or mRNA. Nuclear delivery 138. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a nuclear payload agent, e.g., a nuclear protein payload agent (e.g., exogenous to or overexpressed in the source cell); i) upon contact of the target cell with a plurality of fusosomes, the nucleoprotein payload agent or the protein encoded therein is present in the nucleus of the target cell at a level that is at least 10%, 20%, 50%, 100%, 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, or 100-fold higher than the level of the nucleoprotein payload agent in the cytoplasm of the target cell, e.g., by an assay of any of Examples 117-122; ii) upon contacting the population of target cells with a plurality of fusosomes, the nucleoprotein payload agent or the protein encoded therein is enriched in the nuclei of at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the cells in the population of target cells (e.g., present in the nuclei of the target cells at levels that are at least 50% greater than the levels of the nucleoprotein payload agent in the cytoplasm of the target cells), e.g., as measured in any of the assays of Examples 117-122; iii) upon contact of the population of target cells with the plurality of fusosomes, the nucleoprotein payload agent or the protein encoded therein becomes present in a subpopulation of the population of target cells (the "fusion population"), and the nucleoprotein payload agent or the protein encoded therein becomes enriched in the nuclei of at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the cells in the fusion population (e.g., becomes present in the nuclei of target cells at levels at least 50% higher than the level of the nucleoprotein payload agent in the cytosol of the target cells), e.g., as measured in the assays of any of Examples 117-122; iv) upon contact of the population of target cells with the plurality of fusosomes, the nucleoprotein payload agent or the protein encoded therein becomes present in a subpopulation of the population of target cells (the "recipient cell population"), such that the nucleoprotein payload agent or the protein encoded therein is enriched in the nuclei of at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the cells in the recipient cell population (e.g., becomes present in the nuclei of target cells at levels that are at least 50% greater than the levels of the nucleoprotein payload agent in the cytoplasm of the target cells), e.g., as measured in the assays of any of Examples 117-122; v) at least 1, 2, 5, 10, 20, 50, 100, 200, 500, or 1,000 copies of the nucleoprotein payload agent, or the protein encoded by the nucleic acid nucleoprotein payload agent, are present in the nucleus in the target cell, e.g., as measured by the assay of Example 117 or 118; vi) the nucleoprotein payload agent comprises or encodes one or more of a transcriptional activator, a transcriptional repressor, an epigenetic modifier, a histone acetyltransferase, a histone deacetylase, a histone methyltransferase, a DNA methyltransferase, a DNA nickase, a site-specific DNA editing enzyme such as a deaminase, a DNA transposase, a DNA integrase, an RNA editor, an RNA splicing factor, a PIWI protein; vii) the nucleoprotein payload agent comprises or encodes one or more of a basic helix-loop-helix motif, a leucine zipper motif, a helix-turn-helix motif, a homeodomain motif, a winged-helix motif, a winged-helix-turn motif, an HMG-box domain, a Wor3 domain, an OB-fold domain, a zinc finger motif, a TAL effector, or a B3 domain; viii) the nucleoprotein payload agent comprises a complex comprising a homodimer, heterodimer, homotrimer, heterotrimer, homotetramer, or heterotetramer; ix) the nucleoprotein payload agent comprises or encodes a heterologous nuclear localization signal, and the nucleoprotein payload agent does not comprise a site-specific nuclease such as Cre; x) the nucleoprotein payload agent comprises or encodes a nuclear localization signal listed in Table 6-1, and optionally the NLS comprises an amino acid sequence set forth in any one of SEQ ID NOs: 128-507 and 605-626; or xi) the nucleoprotein payload agent comprises or encodes the nucleoplasm, nucleolus, perinucleolar region, Cajal bodies, clastosomes, GEM nuclear structures, histone locus bodies (HLBs), nuclear speckles, nuclear stress bodies, paraspeckles, PML bodies, or polycomb bodies; xii) The nucleoprotein payload agent comprises or encodes a protein containing a first domain that binds to an endogenous protein present (at least partially) in the cytoplasm of the target cell, and a second domain that promotes nuclear import, e.g., an NLS-containing protein, a fusosome. 139. A fusosome according to embodiment 138, wherein the payload in the endocytic vesicle is in the cytoplasm of the target cell. 140. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a nuclear payload agent, e.g., a nuclear protein payload agent (e.g., exogenous to or overexpressed in the source cell); i) the fusosomes contain or are contained in cellular biological material; ii) the fusogen is present in a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 29; iii) the fusosomes contain a therapeutic agent in a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 43; iv) the fusosomes contain lipids where one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 75% of the corresponding lipid levels in the source cells; v) the fusosomes contain a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; vi) the fusosomes are capable of signaling, e.g., transmitting an extracellular signal, e.g., phosphorylating AKT in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, e.g., at least 10% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; vii) the fusosomes, when administered to a subject, e.g., a mouse, target a tissue, e.g., liver, lung, heart, spleen, pancreas, gastrointestinal tract, kidney, testis, ovary, brain, reproductive organs, central nervous system, peripheral nervous system, skeletal muscle, endothelium, inner ear, or eye, and at least 0.1% or 10% of the fusosomes in the population of administered fusosomes are present in the target tissue after 24 hours, e.g., by the assay of Example 87 or 100; or viii) Fusosomes, wherein the source cell is selected from a neutrophil, a granulocyte, a mesenchymal stem cell, a bone marrow stem cell, an induced pluripotent stem cell, an embryonic stem cell, a myeloblast, a myoblast, a hepatocyte, or a neuron, e.g., a retinal neuron. 141. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a fusosome comprising (i) a nucleic acid, and (ii) a nuclear payload agent comprising a protein that promotes nuclear import of the nucleic acid. 142. A nucleoprotein payload agent (e.g., exogenous to the source cell or overexpressed) is i) a transcriptional activator, e.g., a transcriptional activator of Table 17-1; ii) a transcriptional repressor, e.g., a transcriptional repressor in Table 17-1; iii) epigenetic modifiers, e.g., epigenetic modifiers in Table 17-1; iv) histone acetyltransferases, e.g., histone acetyltransferases of Table 17-1; v) histone deacetylases, e.g., histone deacetylases of Table 17-1; vi) histone methyltransferases, e.g., histone methyltransferases of Table 17-1; vii) DNA methyltransferases, e.g., the DNA methyltransferases of Table 17-1; viii) a DNA nickase, such as a DNA nickase described herein; ix) site-specific DNA editing enzymes, such as deaminases in Table 17-1; x) a DNA transposase, such as a DNA transposase described herein; xi) a DNA integrase, such as a DNA integrase described herein; xii) an RNA editor, e.g., an RNA editor in Table 17-1; xiii) an RNA splicing factor, e.g., an RNA splicing factor in Table 17-1; or xiv) A fusosome according to any of the above embodiments, comprising or encoding one or more of the PIWI proteins, such as the PIWI proteins described herein. 143. A fusosome according to any of the above embodiments, wherein the nucleoprotein payload agent comprises or encodes a protein having an NLS, wherein the NLS is the same as the NLS in the protein's naturally occurring counterpart. 144. A fusosome according to any of the above embodiments, wherein the nucleoprotein payload agent comprises or encodes a protein having an NLS that is not contained by the protein's naturally occurring counterpart. 145. The fusosome of any of the above embodiments, wherein the nucleoprotein payload agent comprises or encodes a transcription factor, a nuclease, a recombinase, an epigenetic factor, a post-transcriptional RNA modifier (e.g., an mRNA splicing factor), a non-coding RNA (e.g., an snRNA or snoRNA), or a ribonucleoprotein (e.g., an snRNP or snoRNP), a structural protein (e.g., a lamin or a karysokeletal protein). 146. The fusosome of any of the above embodiments, wherein the nucleoprotein payload agent comprises or encodes an antibody molecule, e.g., a Fab, scFv, scFab, sdAb, duobody, minibody, nanobody, diabody, zybody, camelid antibody, BiTE, quadroma, or bsDb. 147. A fusosome according to any of the above embodiments, wherein the nucleoprotein payload agent comprises or encodes a fusion protein comprising an effector domain and a localization domain. 148. The fusosome of embodiment 147, wherein the localization domain comprises a TAL domain, a zinc finger domain, a Cas9 domain, or a meganuclease domain. 149. The fusosome of embodiment 147 or 148, wherein the effector domain comprises a nuclease, recombinase, integrase, base editor (deaminase), transcription factor, or epigenetic modifier. 150. A fusosome according to any of the above embodiments, wherein the nucleoprotein payload agent comprises or encodes a gene-editing protein or nucleic acid, for example, Cas9 or a guide RNA. 151. A fusosome according to any of the above embodiments, wherein the nuclear payload agent comprises functional RNA. 152. A fusosome according to any of the above embodiments, wherein the nuclear payload agent comprises a nuclear protein payload agent, such as a protein or an mRNA encoding a protein. 153. A fusosome according to any of the above embodiments, wherein the nuclear payload agent comprises (i) a nucleic acid, and (ii) a protein that promotes nuclear import of the nucleic acid. 154. The fusosome of embodiment 153, wherein the nucleic acid comprises a binding site and a protein that promotes nuclear import binds to the binding site. 155. The fusosome of embodiment 154, wherein the binding site comprises a TetR binding site and the protein comprises TetR. 156. The fusosome according to any of the above embodiments, wherein the nuclear payload agent comprises a synthetic transcription factor, e.g., a fusion protein comprising (i) a DNA-binding domain, e.g., a specific DNA-binding domain, e.g., a TAL domain, a ZF domain, or a Cas9 domain, and (ii) a transcriptional activator domain or a transcriptional repressor domain. 157. A fusosome according to any of the above embodiments, wherein the nuclear payload agent comprises a synthetic epigenetic modifier, for example a fusion protein comprising (i) a DNA binding domain and (ii) an epigenetic modifier domain. 158. The fusosome of any of the above embodiments, wherein the nucleoprotein payload agent is or comprises a protein selected from Table 17-1. 159. The fusosome of any of the above embodiments, wherein the nucleoprotein payload agent is or comprises a fragment, variant, or homologue of a protein selected from Table 17-1. 160. The fusosome of any of the above embodiments, wherein the nucleoprotein payload agent is, or is a nucleic acid encoding, a protein selected from Table 17-1, or comprises the same. 161. The fusosome of any of the above embodiments, wherein the nucleoprotein payload agent is or comprises a nucleic acid encoding a protein, including a fragment, variant, or homologue of a protein selected from Table 17-1. Organelle Delivery 162. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) A lumen surrounded by a lipid bilayer; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an organelle payload agent, e.g., an organelle protein payload agent (e.g., exogenous to or overexpressed in the source cell), and wherein upon contact of the target cell with a plurality of fusosomes, the organelle protein payload agent or a polypeptide encoded therein is enriched in the mitochondria of the target cell at a level at least 10%, 20%, 50%, 100%, 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, or 100-fold greater than the level of the organelle protein payload agent in the cytoplasm or the target cell plasma membrane. 163. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) A lumen surrounded by a lipid bilayer; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an organelle protein payload agent that comprises or encodes a heterologous signal sequence for the organelle protein payload agent (e.g., a signal sequence of Table 6 or 6-1) sufficient to enrich the organelle protein payload agent or a polypeptide encoded therein in a cytoplasmic organelle of a target cell, and optionally, the heterologous signal sequence is set forth in any one of SEQ ID NOs: 39-127 and 605-626. 164. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer, the lumen not containing organelles; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an organellar protein payload agent (e.g., exogenous to or overexpressed in the source cell), and wherein upon contact of the target cell with a plurality of fusosomes, the organellar protein payload agent or the polypeptide encoded therein is enriched in one or more of the target cell's Golgi apparatus, endoplasmic reticulum, vacuole, acrosome, autophagosome, centriole, glycosome, glyoxysome, hydromenosome, melanosome, mitosome, cnidocyst, peroxisome, proteasome, vesicle, or stress granule, relative to the target cell's cyosol or plasma membrane. 165. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer, the lumen not containing organelles; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an organelle protein payload agent comprising a nucleic acid encoding a polypeptide, wherein upon contact of a target cell with a plurality of fusosomes, the encoded polypeptide is enriched in lysosomes and / or endosomes relative to the cytosol or plasma membrane of the target cell. 166. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) A lumen surrounded by a lipid bilayer; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an exogenous or overexpressed organelle protein payload agent, wherein the organelle protein payload agent comprises or encodes a polypeptide selected from a mitochondrial membrane protein, a mitochondrial outer membrane protein, a mitochondrial inner membrane protein, a mitochondrial inner boundary membrane protein, a mitochondrial crystalline membrane protein, a mitochondrial DNA protein, a mitochondrial intermembrane space protein, a mitochondrial matrix protein, a mitochondrial matrix granule protein, a mitochondrial cristae protein, a mitochondrial ribosomal protein, a mitochondrial intracristal protein, a mitochondrial peripheral space protein, a membrane protein, a peroxisomal crystalline core protein, a peroxisomal matrix protein, and a peroxin. 167. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) A lumen surrounded by a lipid bilayer; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an exogenous or overexpressed organelle protein payload agent, wherein the organelle protein payload agent is i) metabolic proteins (e.g., electron transport chain proteins or ATP synthase); ii) proteases, iii) chaperones; iv) protein transport proteins; v) mitochondrial ribosomal proteins, vi) a mitochondrial transcription protein, or vii) A fusosome comprising or encoding a polypeptide selected from mitochondrial replication proteins. 168. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) A lumen surrounded by a lipid bilayer; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a fusosome comprising an organelle protein payload agent (e.g., exogenous to or overexpressed in the source cell) that comprises or encodes a first domain that binds to an endogenous protein present (at least partially) in the cytosol or nucleus of the target cell, and a second domain that facilitates import into a cytoplasmic organelle of the target cell. 169. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) A lumen surrounded by a lipid bilayer; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) a fusosome comprising (i) a nucleic acid, and (ii) an organelle protein payload agent comprising a protein that facilitates the transfer of the nucleic acid into a cytoplasmic organelle. 170. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) A lumen surrounded by a lipid bilayer; (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an organelle protein payload agent (e.g., exogenous to or overexpressed in the source cell), wherein the organelle protein payload agent comprises a nucleic acid (e.g., DNA or RNA), e.g., a functional RNA or a nucleic acid encoding a protein. 171. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an organellar payload agent, e.g., an organellar protein payload agent (e.g., exogenous to or overexpressed in the source cell); ix) the fusosomes contain or are contained in cellular biological material; ii) the fusogen is present in a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 29; xi) the fusosomes contain at least 1,000 copies of the therapeutic agent, e.g., as measured by the assay of Example 43; xii) the fusosomes contain lipids where one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 75% of the corresponding lipid levels in the source cells; xiii) the fusosomes contain a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; xiv) the fusosomes are capable of signaling, e.g., transmitting an extracellular signal, e.g., phosphorylating AKT in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, e.g., at least 10% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; xv) the fusosomes, when administered to a subject, e.g., a mouse, target a tissue, e.g., liver, lung, heart, spleen, pancreas, gastrointestinal tract, kidney, testes, ovaries, brain, reproductive organs, central nervous system, peripheral nervous system, skeletal muscle, endothelium, inner ear, or eye, and at least 0.1% or 10% of the fusosomes in the population of administered fusosomes are present in the target tissue after 24 hours, e.g., by the assay of Example 87 or 100; or xvi) Fusosomes, wherein the source cell is selected from a neutrophil, a granulocyte, a mesenchymal stem cell, a bone marrow stem cell, an induced pluripotent stem cell, an embryonic stem cell, a myeloblast, a myoblast, a hepatocyte, or a neuron, e.g., a retinal neuron. 172. A fusosome, (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) an organellar payload agent, e.g., an organellar protein payload agent (e.g., exogenous to or overexpressed in the source cell); i) the fusosomes contain or are contained in cellular biological material; ii) the fusosomes contain enucleated cells; iii) the fusosomes contain inactivated nuclei; iv) fusosomes fuse with target cells at a rate, e.g., at least at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 2-fold, 3-fold, 4-fold, 5-fold, 10-fold, 20-fold, 50-fold, or 100-fold higher, than with non-target cells, e.g., in the assay of Example 54; v) the fusosomes fuse with target cells at, e.g., at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%, 2-fold, 3-fold, 4-fold, 5-fold, 10-fold, 20-fold, 50-fold, or 100-fold higher rates than with other fusosomes, e.g., in the assay of Example 54; vi) the fusosomes fuse with the target cells at a rate such that the agent in the fusosomes is delivered to at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the target cells after 24, 48, or 72 hours, e.g., in the assay of Example 54; vii) the fusogen is present in at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies or less, as measured, for example, by the assay of Example 29; viii) the fusosomes contain the therapeutic agent in at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies or less, as measured, for example, by the assay of Example 43 or 156; ix) The ratio of the copy number of the fusogen to the copy number of the therapeutic drug is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 5:1, 5:1 to 2:1 , 2:1 to 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. x) the fusosomes contain a lipid composition substantially similar to that of the source cells, or one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75% of the corresponding lipid levels in the source cells; xi) the fusosomes contain a proteomic composition similar to that of the source cells, e.g., using the assays of Examples 42 or 155; xii) the fusosomes comprise a lipid to protein ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 49; xiii) the fusosomes comprise a ratio of protein to nucleic acid (e.g., DNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, e.g., as measured using the assay of Example 50; xiv) the fusosomes comprise a lipid to nucleic acid (e.g., DNA) ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Examples 51 or 159; xv) the fusosomes have a half-life in a subject, e.g., a mouse, that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% of the half-life of a reference cell, e.g., a source cell, e.g., by the assay of Example 75; xvi) the fusosomes transport, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% more (e.g., about 11.6% more) glucose (e.g., labeled glucose, e.g., 2-NBDG) across the membrane in the absence of glucose than a negative control, e.g., an otherwise similar fusosome, as measured, e.g., using the assay of Example 64; xvii) the fusosomes contain esterase activity in their lumen that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the esterase activity in a reference cell, e.g., a source cell or a mouse embryonic fibroblast, using, e.g., the assay of Example 66; xviii) the fusosomes comprise a metabolic activity level within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the citrate synthase activity in a reference cell, e.g., a source cell, e.g., as described in Example 68; xix) the fusosomes comprise a respiration level (e.g., oxygen consumption rate) within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the respiration level in a reference cell, e.g., a source cell, e.g., as described in Example 69; xx) the fusosomes comprise an annexin V staining level of at most 18,000, 17,000, 16,000, 15,000, 14,000, 13,000, 12,000, 11,000, or 10,000 MFI, e.g., using the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of otherwise similar fusosomes treated with menadione in the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of macrophages treated with menadione in the assay of Example 70. xxi) the fusosomes have miRNA content levels that are at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more than that of the source cells, e.g., by the assay of Example 39; xxii) the fusosomes are within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of that of the source cells, e.g., by the assay of Example 47, or have a soluble:insoluble protein ratio within, e.g., 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% of that of the source cells; xxiii) the fusosomes have an LPS level of less than 5%, 1%, 0.5%, 0.01%, 0.005%, 0.0001%, 0.00001%, or less than the LPS content of the source cells, e.g., in the assay of Example 48; xxiv) the fusosomes are capable of signaling, e.g., sending an extracellular signal, e.g., AKT phosphorylation in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; xxv) the fusosomes, when administered to a subject, e.g., a mouse, target a tissue, e.g., liver, lung, heart, spleen, pancreas, gastrointestinal tract, kidney, testis, ovary, brain, reproductive organs, central nervous system, peripheral nervous system, skeletal muscle, endothelium, inner ear, or eye, and at least 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the fusosomes in the administered population of fusosomes are present in the target tissue after 24, 48, or 72 hours, e.g., by the assay of Example 87 or 100; xxvi) the fusosomes have a level of juxtacrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% greater than the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; xxvii) the fusosomes have a level of paracrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% greater than the level of paracrine signaling induced by a reference cell, e.g., a source cell or a macrophage, e.g., by the assay of Example 72; xxviii) the fusosomes polymerize actin at a level within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the level of polymerized actin in a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 73; xxix) the fusosomes have a membrane potential within about 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the membrane potential of a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 74, or the fusosomes have a membrane potential of about -20 to -150 mV, -20 to -50 mV, -50 to -100 mV, or -100 to -150 mV; xxx) the fusosomes are capable of extravasation from blood vessels, e.g., using the assay of Example 57, at a rate that is at least 1%, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the rate of extravasation of source cells or cells of the same type as the source cells, and the source cells are neutrophils, lymphocytes, B cells, macrophages, or NK cells; xxxi) the fusosomes are capable of crossing cell membranes, such as endothelial cell membranes or the blood-brain barrier; xxxii) the fusosomes are capable of secreting protein at, for example, at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% greater rates than reference cells, e.g., mouse embryonic fibroblast cells, using, for example, the assay of Example 62; xxxiii) the fusosomes meet pharmaceutical or Good Manufacturing Practice (GMP) standards; xxxiv) the fusosomes were produced in accordance with Good Manufacturing Practice (GMP); xxxv) the fusosomes have a pathogen level below a predetermined reference value, e.g., are substantially free of pathogens; xxxvi) the fusosomes have contaminant levels below a predetermined reference value, e.g., are substantially free of contaminants; xxvii) the fusosomes have low immunogenicity, e.g., as described herein; xxxviii) the source cells are selected from neutrophils, granulocytes, mesenchymal stem cells, bone marrow stem cells, induced pluripotent stem cells, embryonic stem cells, myeloblasts, myoblasts, hepatocytes, or neurons, e.g., retinal neuronal cells; or xxxix) Fusosomes, wherein the source cell is other than a 293 cell, an HEK cell, a human endothelial cell, or a human epithelial cell, a monocyte, a macrophage, a dendritic cell, or a stem cell. 173. The fusosome of any of the above embodiments, wherein the cytoplasmic organelle is selected from a mitochondrion, Golgi apparatus, lysosome, endoplasmic reticulum, vacuole, endosome, acrosome, autophagosome, centriole, glycosome, glyoxysome, hydrogenosome, melanosome, mitosome, cnidocyst, peroxisome, proteasome, vesicle, or stress granule. 174. A fusosome according to any of the above embodiments, wherein the cytoplasmic organelle is a membrane-bound organelle. 10a. The fusosome of any of the above embodiments, wherein the organellar payload agent is enriched in one or more of the mitochondrial matrix, the mitochondrial intermembrane space, the mitochondrial outer membrane, the mitochondrial inner membrane, or the mitochondrial cristae. 175. The fusosome of any of the above embodiments, wherein the organelle protein payload agent or the polypeptide encoded therein comprises a protein in Table 17-2. 176. The fusosome of any of the above embodiments, wherein upon contact of the population of target cells with a plurality of fusosomes, the organelle protein payload agent or the polypeptide encoded therein is enriched in the cytoplasmic organelles of at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the cells in the population of target cells (e.g., is present in the cytoplasmic organelles of the target cells at a level that is at least 50% higher than the level of the organelle protein payload agent in the cytoplasm of the target cells), e.g., as measured in the assay of Example 123 or 124. 177. The fusosome of any of the above embodiments, wherein upon contact of the population of target cells with a plurality of fusosomes, the organellar protein payload agent or the protein encoded therein becomes present in a subpopulation of the population of target cells (the "fusion population"), and the organellar protein payload agent or the protein encoded therein becomes enriched in the cytoplasmic organelles of at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the cells in the fusion population (e.g., becomes present in the cytoplasm of the target cells at a level that is at least 50% higher than the level of the organellar protein payload agent or the polypeptide encoded therein in the cytosol of the target cells), e.g., as measured in the assays of Examples 123-124. 178. A fusosome according to any of the above embodiments, wherein at least 1, 2, 5, 10, 20, 50, 100, 200, 500, or 1,000 copies of the organelle protein payload agent, or the polypeptide encoded therein, are present in a cytoplasmic organelle in a target cell that has contacted multiple fusosomes. 179. The fusosome of any of the above embodiments, wherein the organelle protein payload agent comprises or encodes one or more of a basic helix-loop-helix motif, a leucine zipper motif, a helix-turn-helix motif, a homeodomain motif, a winged-helix motif, a winged-helix-turn motif, an HMG-box domain, a Wor3 domain, an OB-fold domain, a zinc finger motif, a TAL effector, or a B3 domain. 180. The fusosome of any of the above embodiments, wherein the organelle protein payload agent comprises or encodes a protein complex comprising a homodimer, heterodimer, homotrimer, heterotrimer, homotetramer, or heterotetramer. 181. The fusosome of any of the above embodiments, wherein the organelle protein payload agent comprises or encodes a protein having a signal sequence that is the same as the signal sequence in the protein's naturally occurring counterpart. 182. A fusosome according to any of the above embodiments, wherein the organelle protein payload agent comprises or encodes a protein having a signal sequence not included by the protein's naturally occurring counterpart. 183. The fusosome of any of the above embodiments, wherein the organelle protein payload agent comprises or encodes an antibody molecule, e.g., a Fab, scFv, scFab, sdAb, duobody, minibody, nanobody, diabody, zybody, camelid antibody, BiTE, quadroma, or bsDb. 184. The fusosome of any of the above embodiments, wherein the organelle payload agent comprises functional RNA. 185. The fusosome of any of the above embodiments, wherein the organelle payload agent comprises an organelle protein payload agent, such as a protein or an mRNA encoding a protein. 186. A fusosome according to any of the above embodiments, wherein the organelle payload agent does not contain or encode a reporter protein or a fluorescent protein, for example, GFP. 187. The fusosome of any of the above embodiments, wherein the lumen does not contain an organelle. 188. The fusosome of any of the above embodiments, wherein the organelle protein payload agent, or the protein encoded therein, is not a cell membrane protein or a secreted protein. 189. A fusosome according to any of the above embodiments, wherein the amount of viral capsid protein in the fusosome composition is less than 1% of the total protein. 190. Fusosomes, containing chondrisomes and fusogens. 191. The fusosome of any of the above embodiments, having partial or complete nuclear inactivation (e.g., nucleus removal). 192. A fusosome according to any of the above embodiments, wherein the source cells are cells grown under adherent or suspension conditions. 193. The fusosome of any of the above embodiments, wherein the source cell is a primary cell, a cultured cell, an immortalized cell, or a cell line (e.g., a myelobast cell line, e.g., C2C12). 194. The source cells may be endothelial cells, fibroblasts, blood cells (e.g., macrophages, neutrophils, granulocytes, leukocytes), stem cells (e.g., mesenchymal stem cells, umbilical cord stem cells, bone marrow stem cells, hematopoietic stem cells, induced pluripotent stem cells, e.g., induced pluripotent stem cells derived from cells of a subject), embryonic stem cells (e.g., stem cells from embryonic yolk sac, placenta, umbilical cord, fetal skin, adolescent skin, blood, bone marrow, adipose tissue, erythropoietic tissue, hematopoietic tissue), myoblasts, parenchymal cells (e.g., hepatocytes), alveolar cells, neurons (e.g., retinal neurons), progenitor cells (e.g., retinal

[0023] The fusosome of any of the above embodiments is a membrane progenitor cell, myeloblast, myeloid progenitor cell, thymocyte, meiocyte, megakaryoblast, promegakaryoblast, melanocyte, lymphoblast, myeloid progenitor cell, normoblast, or hemangioblast), progenitor cell (e.g., cardiac progenitor cell, satellite cell, radial glial cell, bone marrow stromal cell, pancreatic progenitor cell, endothelial progenitor cell, blast cell), or immortalized cell (e.g., HeLa, HEK293, HFF-1, MRC-5, WI-38, IMR90, IMR91, PER.C6, HT-1080, or BJ cell). 195. The fusosome of any of the above embodiments, wherein the source cells are allogeneic, e.g., obtained from a different organism of the same species as the target cells. 196. A fusosome according to any of the above embodiments, wherein the source cells are autologous, e.g., obtained from the same organism as the target cells. 197. A fusosome according to any of the above embodiments, wherein the source cells are heterologous, e.g., obtained from an organism of a different species than the target cells. 198. The fusosome of any of the above embodiments, wherein the source cell is selected from a leukocyte or a stem cell. 199. The fusosome of any of the above embodiments, wherein the source cell is selected from a neutrophil, a lymphocyte (e.g., a T cell, a B cell, a natural killer cell), a macrophage, a granulocyte, a mesenchymal stem cell, a bone marrow stem cell, an induced pluripotent stem cell, an embryonic stem cell, or a myeloblast. 200. The fusosome of any of the above embodiments, wherein the source cell is other than a 293 cell, an HEK cell, a human endothelial cell, or a human epithelial cell, a monocyte, a macrophage, a dendritic cell, or a stem cell. 201. The fusosome of any of the above embodiments, i) the source cells are not transformed or immortalized, or ii) Fusosomes, in which the source cells are transformed or immortalized using methods other than adenovirus-mediated immortalization, for example, immortalized by spontaneous mutation or telomerase expression. 202. The fusosome of any of the above embodiments, wherein the fusosome is derived from a source cell having a modified genome, e.g., reduced immunogenicity (e.g., by genome editing to remove MHC complexes). 203. The fusosome of any of the above embodiments, wherein the source cells are derived from a cell culture treated with an anti-inflammatory signal. 204. The fusosome of any of the above embodiments, wherein the source cell is substantially non-immunogenic, for example, using the assays described herein. 205. The fusosome of any of the above embodiments, wherein the source cell is a recombinant cell. 206. The fusosome of any of the above embodiments, wherein the source cell further comprises a second agent exogenous to the source cell, e.g., a therapeutic agent, e.g., a protein or nucleic acid (e.g., RNA, e.g., mRNA or miRNA). 207. The fusosome of embodiment 206, wherein the second agent is present at at least 10, 20, 50, 100, 200, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, or 1,000,000 copies contained by the fusosome, or at an average level of at least 10, 20, 50, 100, 200, 500, 10,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, or 1,000,000 copies per fusosome, or less. 208. A fusosome according to any of the above embodiments, wherein the fusosome has altered, e.g., increased or decreased levels of one or more endogenous molecules, e.g., proteins or nucleic acids, compared to the source cell, e.g., mammalian source cell, by treating the source cell with siRNA or a gene editing enzyme. 209. The fusosomes of embodiment 208, wherein the fusosomes contain at least 10, 20, 50, 100, 200, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, or 1,000,000 copies or less of an endogenous molecule or are present at an average level of at least 10, 20, 50, 100, 200, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, or 1,000,000 copies or less per fusosome. 210. An endogenous molecule (e.g., RNA or protein) is at least 1, 2, 3, 4, 5, 10, 20, 50, 100, 500, 1000, or 10000% of its concentration in the source cells. 3 , 5.0×10 3 , 10 4 , 5.0×10 4 , 10 5 , 5.0×10 5 , 10 6 , 5.0×10 6 , 1.0×10 7 , 5.0×10 7 , or 1.0 × 10 8 209. The fusosomes of embodiment 208 or embodiment 209, which are present in high concentrations. 211. An endogenous molecule (e.g., RNA or protein) is at least 1, 2, 3, 4, 5, 10, 20, 50, 100, 500, 1 ... 3 , 5.0×10 3 , 10 4 , 5.0×10 4 , 10 5 , 5.0×10 5 , 10 6 , 5.0×106 , 1.0×10 7 , 5.0×10 7 , or 1.0 × 10 8 The fusosomes of embodiment 208 or embodiment 209, which are present in low concentrations. 212. The fusosomes of any of the above embodiments, wherein the fusosomes have an miRNA content level that is at least 1% lower than that of the source cell, e.g., by the assay of Example 39. 213. The fusosome of embodiment 206 or 207, wherein the second agent, e.g., a therapeutic agent, is selected from a protein, a protein complex (e.g., at least 2, 3, 4, 5, 10, 20, or 50 proteins, e.g., at least at least 2, 3, 4, 5, 10, 20, or 50 different proteins), a polypeptide, a nucleic acid (e.g., DNA, a chromosome, or RNA, e.g., mRNA, siRNA, or miRNA), or a small molecule. 214. The fusosome of any of the above embodiments, wherein the fusosome comprises a proteomic composition similar to that of the source cell, e.g., using the assay of Example 42. 215. The fusosomes of any of the above embodiments, wherein the fusosomes have a soluble:insoluble protein ratio within 90% of that of the source cell, e.g., by the assay of Example 47. 216. The fusosome of any of the above embodiments, having a diameter that is less than about 0.01% to 0.05%, 0.05% to 0.1%, 0.1% to 0.5%, 0.5% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, 5% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, or 80% to 90% of the size of the source cell, e.g., as measured by the assay of Example 30. 217. A fusosome according to any of the above embodiments, wherein the fusosome has a diameter that is less than about 0.01% or 1% of that of the source cell, e.g., as measured by the assay of Example 30. 218. The fusosome of any of the above embodiments, having a volume that is less than about 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90%% of the volume of the source cell. 219. A fusosome according to any of the above embodiments, wherein the fusogen is a protein fusogen. 220. A fusosome according to any of the above embodiments, wherein the fusogen is a mammalian fusogen or a viral fusogen. 221. The fusosome of any of the above embodiments, wherein the fusogen does not promote vesicle formation from the source cell. 222. The fusosome of any of the above embodiments, wherein the fusogen comprises an enucleated cell. 223. Fusogen, i) is other than a viral protein; ii) the fusogen is other than a fusogenic glycoprotein; iii) the fusogen is a mammalian protein other than fertilin-β; iv) the fusogen is other than a VSVG, a SNARE protein, or a secretory granule protein; or v) A fusosome according to any of the above embodiments, wherein the fusogen is other than TAT, TAT-HA2, HA-2, gp41, Alzheimer's beta-amyloid peptide, Sendai virus protein, or amphipathic net-negative peptide (WAE 11). 224. A fusosome according to any of the above embodiments, i) the fusogen is present in a copy number of at least 1,000 copies, as measured, for example, by the assay of Example 29; or ii) The ratio of the copy number of the fusogen to the copy number of the payload (e.g., membrane payload agent, nuclear payload agent, or organelle payload agent) is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, or 20:1 to 10:1 , 10:1 to 5:1, 5:1 to 2:1, 2:1 to 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. 225. A fusosome according to any of the above embodiments, the fusosomes were not produced by loading fusosomes with a therapeutic or diagnostic agent; ii) the source cells were not loaded with therapeutic or diagnostic agents; iii) the fusosomes do not contain doxorubicin, dexamethasone, cyclodextrin; polyethylene glycol, microRNA, e.g., miR125, VEGF receptors, ICAM-1, E-selectin, iron oxide, fluorescent proteins, e.g., GFP or RFP, nanoparticles, or RNases, or any form of the above that is exogenous to the source cell; or iv) Fusosomes, wherein the fusosomes are exogenous to the source cell and further comprise a therapeutic agent, including one or more post-translational modifications, e.g., glycosylation. 226. The fusosome of any of the above embodiments, wherein the fusogen is a viral fusogen, such as HA, HIV-1 ENV, gp120, or VSV-G, or wherein the fusogen is a mammalian fusogen, such as a SNARE, syncytin, myomaker, myomixer, myomerger, or FGFRL1. 227. A fusosome or fusosomes according to any of the above embodiments, wherein the fusogen is active at a pH of 4-5, 5-6, 6-7, 7-8, 8-9, or 9-10. 228. A fusosome according to any of the above embodiments, wherein the fusogen is not active at a pH of 4-5, 5-6, 6-7, 7-8, 8-9, or 9-10. 229. The fusosome of any of the above embodiments, wherein the fusogen is a lipid fusogen, such as oleic acid, glycerol monooleate, a glyceride, a diacylglycerol, or a modified unsaturated fatty acid. 230. A fusosome according to any of the above embodiments, wherein the fusogen is a chemical fusogen, for example PEG. 231. A fusosome according to any of the above embodiments, wherein the fusogen is a small molecule fusogen, for example, an NSAID such as halothane, meloxicam, piroxicam, tenoxicam, and chlorpromazine. 232. The fusosome of any of the above embodiments, wherein the fusogen is recombinant. 233. A fusosome according to any of the above embodiments, wherein the fusogen is biochemically incorporated, e.g., the fusogen is provided as a purified protein and contacted with the fusosome lipid bilayer under conditions that allow association of the fusogen with the lipid bilayer, or is biosynthetically incorporated, e.g., expressed in the source cell under conditions that allow association of the fusogen with the fusosome lipid bilayer. 234. Fusosomes have one or more of the following characteristics: i) the fusosomes contain or are contained in cellular biological material; ii) the fusosomes contain or are contained in enucleated cells, or iii) A fusosome according to any of the above embodiments, wherein the fusosome comprises an inactivated nucleus. 234A. A fusosome described in any of the above embodiments, wherein the fusosome comprises a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent) at a copy number of at least 1,000 copies, for example, as measured by the assay of Example 43. 235. Fusosomes have one or more of the following characteristics: i) the fusosomes contain lipids where one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 75% of the corresponding lipid levels in the source cells; ii) the fusosomes comprise a lipid to protein ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 49; iii) the fusosomes comprise a ratio of protein to nucleic acid (e.g., DNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, e.g., as measured using the assay of Example 50; iv) The fusosomes of any of the above embodiments, wherein the fusosomes comprise a ratio of lipid to nucleic acid (e.g., DNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cell, e.g., as measured using the assay of Example 51. 236. A fusosome according to any of the above embodiments, i) the fusosomes fuse with target cells at a rate, e.g., at least at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% (e.g., 10%) higher than with non-target cells, e.g., in the assay of Example 54; ii) the fusosomes fuse with target cells at a rate, e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% (e.g., 50%) higher than with other fusosomes, e.g., in the assay of Example 54; iii) the fusosomes fuse with the target cells at a rate such that the agent in the fusosomes is delivered to at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% (e.g., 10%) of the target cells after 24, 48, or 72 hours, e.g., in the assay of Example 54; vi) the fusosomes transport glucose (e.g., labeled glucose, e.g., 2-NBDG) across the membrane in the absence of glucose, e.g., at least 10% more than a negative control, e.g., an otherwise similar fusosome, as measured, e.g., using the assay of Example 64; v) the fusosomes contain esterase activity in the lumen that is within 90% of the esterase activity in a reference cell, e.g., a source cell or a mouse embryonic fibroblast, e.g., using the assay of Example 66; vi) the fusosomes comprise a metabolic activity level within 90% of the metabolic activity (e.g., citrate synthase activity) in a reference cell, e.g., a source cell, e.g., as described in Example 68; vii) the fusosomes comprise a respiration level (e.g., oxygen consumption rate) within 90% of the respiration level in a reference cell, e.g., a source cell, e.g., as described in Example 69; viii) the fusosomes comprise an annexin V staining level of at most 18,000, 17,000, 16,000, 15,000, 14,000, 13,000, 12,000, 11,000, or 10,000 MFI, e.g., using the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of otherwise similar fusosomes treated with menadione in the assay of Example 70; or the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the annexin V staining level of macrophages treated with menadione in the assay of Example 70. ix) the fusosomes have LPS levels of less than 5% of the lipid content of the fusosomes, as measured, for example, by the assay of Example 48; x) the fusosomes have a level of juxtacrine signaling that is at least 5% greater than the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; xi) the fusosomes have a level of paracrine signaling that is at least 5% greater than the level of paracrine signaling induced by a reference cell, e.g., a source cell or a macrophage, e.g., by the assay of Example 72; xii) the fusosomes polymerize actin at a level within 5% of the level of polymerized actin in a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 73; xiii) fusosomes and / or compositions or preparations thereof are capable of secreting protein at a rate at least 5% greater than a reference cell, e.g., a mouse embryonic fibroblast cell, e.g., using the assay of Example 62. 237. A fusosome according to any of the above embodiments, i) the fusosomes have a membrane potential within about 5% of the membrane potential of a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 74, or the fusosomes have a membrane potential of about -20 to -150 mV, -20 to -50 mV, -50 to -100 mV, or -100 to -150 mV; ii) the fusosomes and / or compositions or preparations thereof are capable of extravasation from blood vessels, e.g., using the assay of Example 57, at a rate that is at least 1%, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the rate of extravasation of cells of the same type as the source cells, and the source cells are neutrophils, lymphocytes, B cells, macrophages, or NK cells; iii) the fusosomes and / or compositions or preparations thereof are capable of crossing a cell membrane, e.g., an endothelial cell membrane or the blood-brain barrier, at a rate that is, e.g., at least 1%, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of that of cells of the same type as the source cells; iv) the fusosomes meet pharmaceutical or Good Manufacturing Practice (GMP) standards; v) the fusosomes were produced in accordance with Good Manufacturing Practice (GMP); vi) the fusosomes have pathogen levels below a predetermined reference value, e.g., are substantially free of pathogens; vii) the fusosomes have contaminant levels below a predetermined reference value, e.g., are substantially free of contaminants; or viii) fusosomes, wherein the fusosomes are one or more of: having low immunogenicity, e.g., as described herein. 238. A fusosome according to any of the above embodiments, wherein the fusosome is or comprises a chondrisome. 239. The fusosome of any of the above embodiments, wherein the fusosome has a half-life in a subject, e.g., a mouse, that is within 90% of the half-life of a reference cell, e.g., a source cell, e.g., by the assay of Example 75. 240. A fusosome according to any of the above embodiments, i) the fusosomes and / or compositions or preparations thereof have a density other than between 1.08 g / mL and 1.12 g / mL; ii) the fusosomes and / or compositions or preparations thereof have a density of greater than 1.12 g / mL, e.g., 1.25 g / mL + / - 0.1, 1.25 g / mL + / - 0.05, e.g., as measured by the assay of Example 33; iii) Fusosomes and / or compositions or preparations thereof having a density of less than 1, 1 to 1.1, 1.05 to 1.15, 1.1 to 1.2, 1.15 to 1.25, 1.2 to 1.3, 1.25 to 1.35, or greater than 1.35 g / mL, e.g., by the assay of Example 33. 241. A fusosome according to any of the above embodiments, i) fusosomes are not captured by the scavenger system in the circulation or by Kupffer cells in the sinusoids of the liver; ii) the fusosomes are not trapped by the reticuloendothelial system (RES) of the subject, e.g., by the assay of Example 76; iii) When multiple fusosomes are administered to a subject, less than 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the fusosomes are not captured by the RES after 24 hours, e.g., by the assay of Example 76. 242. A fusosome according to any of the above embodiments, i) the fusosomes meet pharmaceutical or Good Manufacturing Practice (GMP) standards; ii) the fusosomes were produced according to good manufacturing practice (GMP); iii) the fusosomes have pathogen levels below a predetermined reference value, e.g., are substantially free of pathogens; or iv) Fusosomes having contaminant levels below a predetermined reference value, e.g., substantially free of contaminants. 243. The fusosome of any of the above embodiments, i) the fusosomes have a diameter greater than 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 20 μm, 50 μm, 100 μm, 150 μm, or 200 μm; ii) the fusosomes have a diameter other than between 40 and 150 nm, for example, greater than 150 nm, 200 nm, 300 nm, 400 nm, or 500 nm; iii) the fusosomes have a diameter of at least 80 nm, 100 nm, 200 nm, 500 nm, 1000 nm, 1200 nm, 1400 nm, or 1500 nm; iv) the fusosomes have a diameter of less than 80 nm, 100 nm, 200 nm, 500 nm, 1000 nm, 1200 nm, 1400 nm, or 1500 nm; or v) The fusosome has a diameter of at least about 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, or 200 nm, e.g., as measured by the assay of Example 32. 244. The fusosome of any of the above embodiments, wherein the fusosome comprises in its lumen a polypeptide selected from an enzyme, an antibody, or an antiviral polypeptide. 245. A fusosome according to any of the above embodiments, wherein the fusosome does not contain CD63 or GLUT4. 246. Fusosomes are i) does not contain viruses, is not infectious, or does not replicate in host cells; ii) are not VLPs (virus-like particles); iii) does not contain viral structural proteins, e.g., viral capsid proteins, e.g., viral nucleocapsid proteins, or the amount of viral capsid proteins is less than 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.2%, or 0.1% of the total protein, e.g., by the assay of Example 53; iv) does not contain viral matrix proteins; v) does not contain viral nonstructural proteins; vi) Contains fewer than 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies of a viral structural protein; or vii) A fusosome according to any of the above embodiments which is not a virosome. 247. The fusosome of any of the above embodiments, wherein the fusosome comprises viral structural proteins and / or viral matrix proteins. 248. The fusosome of any of the above embodiments, i) The ratio of the copy number of the fusogen to the copy number of the viral structural protein on the fusosome is at least 1,000,000:1, 100,000:1, 10,000:1, 1,000:1, 100:1, 50:1, 20:1, 10:1, 5:1, or 1:1. ii) Fusosomes in which the ratio of the copy number of the fusogen to the copy number of the viral matrix protein on the fusosome is at least 1,000,000:1, 100,000:1, 10,000:1, 1,000:1, 100:1, 50:1, 20:1, 10:1, 5:1, or 1:1. 249. A fusosome according to any of the above embodiments, wherein the fusosome is unilamellar or multilamellar. 250. The fusosome of any of the above embodiments, i) the fusosomes do not contain water-immiscible droplets; ii) Fusosomes, in which the fusosomes comprise an aqueous lumen and a hydrophilic exterior. 251. The fusosome of any of the above embodiments, wherein the fusosome is substantially free of one or more of the following organelles: mitochondria, Golgi apparatus, lysosomes, endoplasmic reticulum, vacuoles, endosomes, acrosomes, autophagosomes, centrioles, glycosomes, glyoxysomes, hydrogenosomes, melanosomes, mitosomes, cnidocysts, peroxisomes, proteasomes, vesicles, and stress granules. 252. The fusosome of any of the above embodiments, wherein the fusosome has a reduced number of organelles compared to the source cell, and the organelles are selected from mitochondria, Golgi apparatus, lysosomes, endoplasmic reticulum, vacuoles, endosomes, acrosomes, autophagosomes, centrioles, glycosomes, glyoxysomes, hydrogenosomes, melanosomes, mitosomes, cnidocysts, peroxisomes, proteasomes, vesicles, and stress granules. 253. The fusosome of any of the above embodiments, i) the fusosomes are not exosomes; ii) the fusosomes are microvesicles; iii) the fusosomes contain non-mammalian fusogens; iv) fusosomes are engineered to incorporate fusogens; v) the fusosomes contain fusogens that are exogenous to the source cell; vi) the fusosome comprises one or more organelles, such as mitochondria, Golgi apparatus, lysosomes, endoplasmic reticulum, vacuoles, endosomes, acrosomes, autophagosomes, centrioles, glycosomes, glyoxysomes, hydrogenosomes, melanosomes, mitosomes, cnidocysts, peroxisomes, proteasomes, vesicles, stress granules, or combinations thereof; vii) the fusosomes comprise the cytoskeleton or components thereof, such as actin, Arp2 / 3, formin, coronin, dystrophin, keratin, myosin, or tubulin; viii) Fusosomes and / or compositions or preparations thereof are used, for example, in Thery or having a buoyant density of at least 1.18 to 1.25 g / ml, or 1.05 to 1.12 g / ml, for example, in a sucrose gradient centrifugation assay as described in [Illegible Text] et al., "Isolation and characterization of exosomes from cell culture supernatants and biological fluids," Curr Protoc Cell Biol. 2006 Apr; Chapter 3: Unit 3.22. ix) the fusomal lipid bilayer is enriched for ceramide or sphingomyelin, or a combination thereof, compared to the source cells, or the fusomal lipid bilayer is not enriched (e.g., depleted) for glycolipids, free fatty acids, or phosphatidylserine, or a combination thereof, compared to the source cells; x) the fusosomes contain phosphatidylserine (PS) or CD40 ligand, or both PS and CD40 ligand, as measured in the assay of Example 52; xi) the fusosomes are enriched for PS compared to the source cells, e.g., at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the fusosomes are positive for PS; xii) the fusosomes are substantially free of acetylcholinesterase (AChE) or contain less than 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, 500, or 1000 AChE activity units per microgram of protein, e.g., according to the assay of Example 67; xiii) fusosomes express tetraspanin family proteins (e.g., CD63, CD9, or CD81), ESCRT-related proteins (e.g., TSG101, CHMP4A-B, or VPS4B), Alix, TSG101, MHCI, MHCII, GP96, actinin-4, mitofilin, syntenin-1, TSG101, ADAM10, EHD4, syntenin-1, TSG101, EHD1, flotillin-1, heat shock 70-kDa proteins (HSC70 / HSP73, HSP70 / HSP72), or any of these. or is substantially free of any combination of, or contains less than 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 5%, or 10% of any individual exosomal marker protein and / or less than 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 5%, 10%, 15%, 20%, or 25% of the total exosomal marker protein of any of the foregoing proteins, as determined by, for example, the assay of Example 44, or is not enriched for any one or more of these proteins. xiv) the fusosomes contain a level of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) that is less than 500, 250, 100, 50, 20, 10, 5, or 1 ng GAPDH / μg total protein, or less than the level of GAPDH in the source cells, e.g., less than 1%, 2.5%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% less than the level of GAPDH per μg total protein in the source cells (ng / μg), e.g., using the assay of Example 45; xv) the fusosomes contain one or more endoplasmic reticulum proteins (e.g., calnexin), one or more proteasome proteins, if or one or more mitochondrial proteins, or any combination thereof, e.g., the amount of calnexin is greater than 500, 250, 100, 50, 20, 10, 5, or 1 ng calnexin / μg total protein, or the fusosomes contain 1%, 2.5%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% more calnexin per μg total protein compared to the source cells, e.g., using the assay of Example 46. xvi) the fusosomes contain an agent (e.g., a protein, mRNA, or siRNA) that is exogenous to the source cell, as measured, for example, using the assays of Examples 39 or 40; or xvii) Fusosomes, which can be immobilized on a mica surface by atomic force microscopy for at least 30 minutes. 254. The fusosome of any of the above embodiments, i) the fusosomes are exosomes; ii) the fusosomes are not microvesicles; iii) fusosomes do not contain organelles; iv) the fusosomes do not contain the cytoskeleton or its components, such as actin, Arp2 / 3, formin, coronin, dystrophin, keratin, myosin, or tubulin; v) the fusosomes and / or compositions or preparations thereof have a buoyant density of 1.08 to 1.22 g / mL, for example, in a sucrose gradient centrifugation assay; vi) the fusosome lipid bilayer is not enriched (e.g., depleted) for ceramide or sphingomyelin, or a combination thereof, relative to the source cells, or the fusosome lipid bilayer is enriched for glycolipids, free fatty acids, or phosphatidylserine, or a combination thereof, relative to the source cells; vii) the fusosomes do not contain or are depleted relative to the source cells in phosphatidylserine (PS) or CD40 ligand, or both PS and CD40 ligand, as measured in the assay of Example 52; viii) the fusosomes are not enriched (e.g., depleted) for PS compared to the source cells, e.g., less than 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the fusosomes are positive for PS; ix) the fusosomes contain, e.g., at least 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, 500, or 1000 AChE activity units / ug of protein of acetylcholinesterase (AChE), e.g., by the assay of Example 67; x) fusosomes express tetraspanin family proteins (e.g., CD63, CD9, or CD81), ESCRT-related proteins (e.g., TSG101, CHMP4A-B, or VPS4B), Alix, TSG101, MHCI, MHCII, GP96, actinin-4, mitofilin, syntenin-1, TSG101, ADAM10, EHD4, syntenin-1, TSG101, EHD1, flotillin-1, heat shock 70-kDa proteins (HSC70 / HSP73, HSP70 / HSP72), or any of their components; or are enriched for any one or more of the foregoing proteins, including any combination thereof, e.g., by the assay of Example 44, relative to the source cells, including greater than 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 5%, or 10% of any individual exosomal marker protein and / or less than 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, or 25% of the total exosomal marker protein of any of the foregoing proteins. xi) the fusosomes comprise a level of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) greater than 500, 250, 100, 50, 20, 10, 5, or 1 ng GAPDH / μg total protein, or less than the level of GAPDH in the source cells, e.g., at least 1%, 2.5%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% greater than the level of GAPDH per total protein in the source cells, e.g., using the assay of Example 45; xii) the fusosomes are not enriched (e.g., depleted) for one or more endoplasmic reticulum proteins (e.g., calnexin), one or more proteasome proteins, or one or more mitochondrial proteins, or any combination thereof, e.g., the amount of calnexin is less than 500, 250, 100, 50, 20, 10, 5, or 1 ng calnexin / μg total protein, or the fusosomes contain 1%, 2.5%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% less calnexin per μg total protein compared to the source cells, e.g., using the assay of Example 46; or xiii) Fusosomes that cannot be immobilized on a mica surface by atomic force microscopy for at least 30 minutes. 255. A fusosome according to any of the above embodiments, i) the fusosomes do not contain VLPs; ii) the fusosomes are virus-free; iii) the fusosomes are free of replication-competent virus; iv) the fusosomes do not contain viral proteins, e.g., viral structural proteins, e.g., capsid proteins or viral matrix proteins; v) the fusosomes do not contain capsid proteins from enveloped viruses; vi) the fusosomes do not contain nucleocapsid protein, or vii) A fusosome, wherein the fusogen is not a viral fusogen. 256. A fusosome according to any of the above embodiments, wherein the fusosome comprises cytosol. 257. A fusosome according to any of the above embodiments, i) the fusosomes do not form teratomas when transplanted into a subject, e.g., by the assay of Example 102; ii) the fusosomes and / or compositions or preparations thereof are capable of chemotaxis, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% faster than a reference cell, e.g., a macrophage, using, e.g., the assay of Example 58; iii) the fusosomes and / or compositions or preparations thereof are capable of homing, e.g., to sites of injury, and the fusosomes are derived from human cells, e.g., using the assay of Example 59, e.g., the source cells are neutrophils; or iv) The fusosomes and / or compositions or preparations thereof are capable of phagocytosis, e.g., fusosome phagocytosis is detectable within 0.5, 1, 2, 3, 4, 5, or 6 hours using the assay of Example 60, e.g., fusosomes in which the source cell is a macrophage. 258. Fusosomes have one or more of the following characteristics: a) one or more endogenous proteins from the source cell, including, for example, membrane proteins or cytosolic proteins; b) comprises at least 10, 20, 50, 100, 200, 500, 1000, 2000, or 5000 different proteins; c) comprises at least 1, 2, 5, 10, 20, 50, or 100 different glycoproteins; d) at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% by weight of the protein in the fusosomes is naturally occurring protein; e) comprises at least 10, 20, 50, 100, 200, 500, 1000, 2000, or 5000 different RNAs; or f) A fusosome according to any of the above embodiments, comprising at least 2, 3, 4, 5, 10 or 20 different lipids, e.g. selected from CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG. 259. The fusosomes have been engineered to have one, two, three, four, five, or more of the following properties, or the fusosomes are not naturally occurring cells and have one, two, three, four, five, or more of the following properties, or the nucleus does not naturally have one, two, three, four, five, or more of the following properties: i) partial nuclear inactivation results in at least a 50%, 60%, 70%, 80%, 90% or greater reduction in nuclear function, e.g., transcription or DNA replication, or both, e.g., transcription as measured by the assay of Example 19 and DNA replication as measured by the assay of Example 20; ii) the fusosomes are incapable of transcription or have a transcription activity that is less than 1%, 2.5%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of that of the transcription activity of a reference cell, e.g., a source cell, e.g., using the assay of Example 19; iii) the fusosomes are incapable of nuclear DNA replication or have nuclear DNA replication that is less than 1%, 2.5%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the nuclear DNA replication of a reference cell, e.g., a source cell, e.g., using the assay of Example 20; iv) the fusosomes lack chromatin or have a chromatin content that is less than 1%, 2.5%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the chromatin content of a reference cell, e.g., a source cell, e.g., using the assay of Example 37; v) the fusosomes lack a nuclear membrane or have an amount of nuclear membrane that is less than 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, or 1% of that of a reference cell, e.g., a source cell or a Jurkat cell, e.g., by the assay of Example 36; vi) the fusosomes lack functional nuclear pore complexes or have at least 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, or 1% reduced import or export activity, e.g., by the assay of Example 36, or the fusosomes lack one or more nuclear pore proteins, e.g., NUP98 or importin 7; vii) the fusosomes are histone-free or have histone levels that are less than 1% of those of the source cells (e.g., H1, H2a, H2b, H3, or H4), e.g., by the assay of Example 37; viii) the fusosomes contain less than 20, 10, 5, 4, 3, 2, or 1 chromosome; ix) nuclear function is eliminated; x) the fusosomes are from enucleated mammalian cells; xi) the nucleus is removed or inactivated, for example, pushed out by mechanical force, by radiation, or by chemical ablation; or xii) A fusosome according to any of the above embodiments, wherein the fusosome is derived from a mammalian cell whose DNA is completely or partially removed, for example during interphase or mitosis. 260. A fusosome according to any of the above embodiments, wherein the fusosome comprises mtDNA or vector DNA. 261. A fusosome according to any of the above embodiments, which is free of DNA or substantially free of DNA. 262. A fusosome according to any of the above embodiments, wherein the fusosome does not comprise a functional nucleus. 263. A fusosome according to any of the above embodiments, wherein the fusosome does not contain a nucleus. 264. The fusosome of any of the above embodiments, wherein the fusosome is substantially free of nuclear DNA. 265. A fusosome according to any of the above embodiments, ii) the fusosomes do not contain Cre or GFP, e.g., EGFP, or iii) Fusosomes, wherein the fusosomes further comprise a protein that is exogenous to the source cell and is other than Cre or GFP, e.g., EGFP. 266. The fusosome of any of the above embodiments, wherein the fusosome further comprises a nucleic acid (e.g., DNA, gDNA, cDNA, RNA, pre-mRNA, mRNA, miRNA, or siRNA) or a protein (e.g., an antibody), wherein the nucleic acid or protein is exogenous to the source cell, e.g., in the lumen. 267. The fusosome of any of the above embodiments, wherein the fusosome is free of mitochondria or substantially free of mitochondria. 268. The fusosome of any of the above embodiments, which retains any one, two, three, four, five, six, or more of the characteristics for 5 days or less, e.g., 4 days or less, 3 days or less, 2 days or less, 1 day or less, e.g., for about 12 to 72 hours, after administration to a subject, e.g., a human subject. 269. A fusosome according to any of the above embodiments, which associates with and / or binds to a target cell or a surface feature of a target cell. 270. A fusosome according to any of the above embodiments, which fuses with a target cell at the surface of the target cell. 271. A fusosome according to any of the above embodiments, which promotes fusion to a target cell in a lysosome-independent manner. 272. A fusosome according to any of the above embodiments, wherein the fusosome and / or fusomal contents enter the target cell by endocytosis or via a non-endocytic pathway. 273. A fusosome according to any of the above embodiments, wherein at least a portion of the fusosome lipid bilayer becomes integrated into the target cell membrane. 274. The fusosome of embodiment 273, wherein the fusosome enters the target cell by endocytosis, e.g., the level of payload (e.g., membrane payload agent, nuclear payload agent, or organelle payload agent) delivered via a given fusomal endocytic pathway is 0.01 to 0.6, 0.01 to 0.1, 0.1 to 0.3, or 0.3 to 0.6, or at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more greater than chloroquine-treated reference cells, e.g., using the assay of Example 91. 275. The fusosomes of embodiment 273, wherein the fusosomes enter the target cell by a non-endocytic pathway, e.g., the level of payload (e.g., membrane payload agent, nuclear payload agent, or organelle payload agent) delivered via the non-endocytic pathway of a given fusosome is 0.1 to 0.95, 0.1 to 0.2, 0.2 to 0.3, 0.3 to 0.4, 0.4 to 0.5, 0.5 to 0.6, 0.6 to 0.7, 0.7 to 0.8, 0.8 to 0.9, 0.9 to 0.95, or at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more greater than chloroquine-treated reference cells, e.g., using the assay of Example 90. 276. A fusosome according to any of the above embodiments, wherein the target cell is within an organism. 277. A fusosome according to any of the above embodiments, wherein the target cell is a primary cell isolated from an organism. 278. The target cells are endothelial cells, fibroblasts, blood cells (e.g., macrophages, neutrophils, granulocytes, leukocytes), stem cells (e.g., mesenchymal stem cells, umbilical cord stem cells, bone marrow stem cells, hematopoietic stem cells, induced pluripotent stem cells, e.g., induced pluripotent stem cells derived from cells of the subject), embryonic stem cells (e.g., stem cells from the embryonic yolk sac, placenta, umbilical cord, fetal skin, adolescent skin, blood, bone marrow, adipose tissue, erythropoietic tissue, hematopoietic tissue), myoblasts, parenchymal cells (e.g., hepatocytes), alveolar cells, neurons (e.g., retinal neurons), progenitor cells (e.g., retinal progenitor cells), the fusosome of any of the above embodiments is selected from a cell (e.g., a blast, myeloblast, myeloid progenitor, thymocyte, meiocyte, megakaryoblast, promegakaryoblast, melanoblast, lymphoblast, myeloid progenitor, normoblast, or hemangioblast), a progenitor cell (e.g., a cardiac progenitor cell, a satellite cell, a radial glial cell, a bone marrow stromal cell, a pancreatic progenitor cell, an endothelial progenitor cell, a blast cell), or an immortalized cell (e.g., a HeLa, HEK293, HFF-1, MRC-5, WI-38, IMR90, IMR91, PER.C6, HT-1080, or BJ cell). 279. The fusosome of any of the above embodiments, wherein the target cell is other than a HeLa cell, or the target cell is not transformed or immortalized. 280. The fusosome of any of the above embodiments, wherein the target cell is transformed or immortalized. 281. The fusosome of any of the above embodiments, wherein the target cell is selected from a leukocyte or a stem cell. 282. The fusosome of any of the above embodiments, wherein the target cell is selected from a neutrophil, a lymphocyte (e.g., a T cell, a B cell, a natural killer cell), a macrophage, a granulocyte, a mesenchymal stem cell, a bone marrow stem cell, an induced pluripotent stem cell, an embryonic stem cell, or a myeloblast. 283. The fusosome of any of the above embodiments, wherein the fusosome comprises a targeting domain that localizes the fusosome to a target cell. 284. The fusosome of embodiment 283, wherein the targeting domain interacts with a target cell moiety on the target cell. 285. The fusosome of embodiment 284, wherein the target cell moiety is a cell surface feature. 286. The fusosome of embodiment 284 or embodiment 285, wherein the fusosome does not comprise said target cell moiety. 287. A fusosome according to any of the above embodiments, wherein the fusosome comprises a fusogen that interacts with a fusogen-binding partner on a target cell, thereby enabling the fusosome to bind to or fuse with the target cell. 288. The fusosome of embodiment 287, wherein the fusosome does not comprise the fusogen-binding partner. 289. A fusosome according to any of embodiments 283-288, wherein the targeting domain is not part of the fusogen. 290. A fusosome according to any of embodiments 283 to 288, wherein the fusogen comprises a targeting domain. 291. A fusosome according to any of embodiments 283-289, wherein the fusogen-binding partner is a separate entity from or part of the target cell moiety. 292. A fusosome according to any of embodiments 283-289, wherein the fusogen-binding partner is or is part of a target cell moiety. 293. The fusosome of any of the above embodiments, further comprising organelles disposed within the lumen, for example, a therapeutically effective number of organelles. 294. A fusosome according to any of the above embodiments, i) the source cells are other than dendritic cells or tumor cells, for example, the source cells are selected from endothelial cells, macrophages, neutrophils, granulocytes, leukocytes, stem cells (e.g., mesenchymal stem cells, bone marrow stem cells, induced pluripotent stem cells, embryonic stem cells), myeloblasts, myoblasts, hepatocytes, or neurons, for example, retinal neuronal cells; ii) the fusogen is other than a fusogenic glycoprotein; iii) the fusogen is a mammalian protein other than fertilin-β; iv) the fusosomes have low immunogenicity, e.g., as described herein; v) the fusosomes meet pharmaceutical or Good Manufacturing Practice (GMP) standards; vi) the pharmaceutical formulation comprising the plurality of fusosomes is produced in accordance with Good Manufacturing Practice (GMP); vii) the pharmaceutical preparation comprising a plurality of fusosomes has a pathogen level below a predetermined reference value, e.g., is substantially free of pathogens; or viii) A fusosome according to any of the above embodiments, wherein the pharmaceutical formulation comprising a plurality of fusosomes has a contaminant level below a predetermined reference value, e.g. is substantially free of contaminants. 295. A fusosome composition or fusosome preparation comprising a plurality of fusosomes according to any of the above embodiments. 296. A fusosome composition comprising a plurality of fusosomes, wherein at least one fusosome is (a) a lipid bilayer comprising a plurality of lipids derived from a source cell; (b) a lumen surrounded by a lipid bilayer (e.g., containing the cytosol); (c) a fusogen that is exogenous to or overexpressed in the source cell, e.g., the fusogen is disposed within a lipid bilayer; and (d) A fusosome composition comprising a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent), e.g., a membrane protein payload agent, a nuclear protein payload agent, or an organelle protein payload agent described herein. 297. The fusosome composition of embodiment 295 or embodiment 296, wherein at least one fusosome of the plurality of fusosomes is derived from a source cell. 298. The fusosome composition of any of embodiments 295-297, wherein the fusosomes are at a temperature of less than 4, 0, -4, -10, -12, -16, -20, -80, or -160°C. 299. Multiple fusosomes, at least about 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 109 , 10 10 , 10 11 , 10 12 , 10 13 , 10 14 , or 10 15 299. The fusosome composition of any one of embodiments 295 to 298, comprising fusosomes. 300. The fusosome composition of any of embodiments 295-299, wherein the fusosomes are the same. 301. At least 0.01% to 0.05%, 0.05% to 0.1%, 0.1% to 0.5%, 0.5% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, 5% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, or 80% to 90% of the fusosomes in the fusosome composition are Contains the same fusogens Produced using the same type of source cell, or The fusosome composition of embodiment 300, wherein the multiple fusosomes are the same if they share at least one characteristic selected from the following: containing the same payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent). 302. The fusosome composition of any of embodiments 295-299, wherein the fusosomes are different. 303. The fusosome composition of any of embodiments 295-302, wherein the plurality of fusosomes is derived from more than one type of source cell. 304. The fusosome composition of any of embodiments 295 to 303, having a volume of at least 1 μL, 2 μL, 5 μL, 10 μL, 20 μL, 50 μL, 100 μL, 200 μL, 500 μL, 1 mL, 2 mL, 5 mL, or 10 mL. 305. The fusosome composition of any of embodiments 295-304, wherein the plurality of fusosomes comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, which do not contain a functional nucleus. 306. The fusosome composition of any of embodiments 295-305, wherein the plurality of fusosomes comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, which do not contain nuclei. 307. The fusosome composition of any of embodiments 295-306, wherein the plurality of fusosomes comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, which are substantially free of nuclear DNA. 308. The fusosome composition of any of embodiments 295-307, wherein the plurality of fusosomes comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, which do not contain functional mitochondria. 309. The fusosome composition of any of embodiments 295-308, wherein the plurality of fusosomes comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, which do not contain mitochondria. 310. The fusosome composition of any of embodiments 295-309, comprising source cells with less than 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, or 10% by protein mass, or source cells with less than 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, or 10% functional nuclei. 311. The fusosome composition comprises at least 0.01% to 0.05%, 0.05% to 0.1%, 0.1% to 0.5%, 0.5% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, 5% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, or 80% to 90% fusosomes; i) the fusogen is present at a copy number of at least 1,000 copies per fusosome, as measured, for example, by the assay of Example 29, or ii) The ratio of the copy number of the fusogen to the copy number of the payload (e.g., membrane payload agent, nuclear payload agent, or organelle payload agent) per fusogen is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 50:1 The fusosome composition of any of embodiments 295-310, wherein the fusosome ratio is between 1, 5:1 and 2:1, 2:1 and 1:1, 1:1 and 1:2, 1:2 and 1:5, 1:5 and 1:10, 1:10 and 1:20, 1:20 and 1:50, 1:50 and 1:100, 1:100 and 1:1,000, 1:1,000 and 1:10,000, 1:10,000 and 1:100,000, or 1:100,000 and 1:1,000,000. 312. The fusosome composition of any of embodiments 295-311, wherein the fusosome composition comprises at least 0.01%-0.05%, 0.05%-0.1%, 0.1%-0.5%, 0.5%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% fusosomes, and wherein the payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent) is present at a copy number of at least 1,000 copies per fusosome, as measured, for example, by the assay of Example 43. 313. The fusosome composition of any of embodiments 295-312, wherein the plurality of fusosomes have an average diameter of at least about 50 nm, about 80 nm, about 100 nm, about 200 nm, about 500 nm, about 1000 nm, about 1200 nm, about 1400 nm, or about 1500 nm. 314. The fusosome composition of any of embodiments 295-313, wherein the plurality of fusosomes comprises fusosomes having a diameter in the range of about 10 nm to about 100 μm. 315. The fusosome composition of any of embodiments 295-314, comprising a plurality of fusosomes having a size within the range of about 20 nm to about 200 nm, about 50 nm to about 200 nm, about 50 nm to about 100 nm, about 50 nm to about 150 nm, or about 100 nm to about 150 nm. 316. The fusosome composition of any of embodiments 295-315, wherein at least 50% of the plurality of fusosomes have a diameter within 10%, 20%, 30%, 40%, or 50% of the average diameter of the fusosomes in the fusosome composition. 317. Multiple, about 500nm 3 ~about 0.0006mm 3 , or about 4,000 nm 3 ~about 0.005μm 3 , about 65,000nm 3 ~about 0.005μm 3 , about 65,000nm 3 ~about 0.0006μm 3 , about 65,000nm 3 ~about 0.002μm 3 , or approximately 0.0006 μm 3 ~about 0.002μm 3 317. The fusosome composition of any of embodiments 295-316, comprising fusosomes having a volume in the range of: 318. A fusosome composition according to any of embodiments 295-317, wherein at least 50% of the plurality of fusosomes have a volume within 10%, 20%, 30%, 40%, or 50% of the average volume of the fusosomes in the fusosome composition. 319. A fusosome composition according to any of embodiments 295-318, wherein at least 50% of the plurality of fusosomes have a fusogen copy number within 10%, 20%, 30%, 40%, or 50% of the average fusogen copy number of fusosomes in the fusosome composition. 320. The fusosome composition of any of embodiments 295-319, wherein at least 50% of the plurality of fusosomes have a copy number of a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent) within 10%, 20%, 30%, 40%, or 50% of the average payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent) copy number of fusosomes in the fusosome composition. 321. A fusosome composition according to any of the above embodiments, wherein less than 10%, 5%, 4%, 3%, 2%, or 1% of the fusosomes in the composition comprise organelles in their lumen, e.g., the lumen does not comprise one or more of mitochondria, Golgi apparatus, lysosomes, endoplasmic reticulum, mitochondria, vacuoles, endosomes, acrosomes, autophagosomes, centrioles, glycosomes, glyoxysomes, hydrogenosomes, melanosomes, mitosomes, cnidocysts, peroxisomes, proteasomes, vesicles, or granules. 322. A pharmaceutical composition comprising a fusosome composition or preparation according to any of the above embodiments, and a pharmaceutically acceptable carrier. 323. The fusosome composition or pharmaceutical composition of any of the above embodiments, which is maintained at a predetermined temperature for at least 1, 2, 3, 6, or 12 hours; 1, 2, 3, 4, 5, or 6 days; 1, 2, 3, or 4 weeks; 1, 2, 3, or 6 months; or 1, 2, 3, 4, or 5 years. 324. The fusosome composition or pharmaceutical composition of embodiment 323, wherein the predetermined temperature is selected from about 4, 0, -4, -10, -12, -16, -20, -80, or -160°C. 325. Having at least 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the activity of a plurality of activities prior to being maintained at the aforementioned temperatures, e.g., by one or more of the following: i) the fusosomes fuse with target cells, e.g., at least at least 10% more frequently than with non-target cells, e.g., in the assay of Example 54; ii) the fusosomes fuse with target cells, e.g., at least 50% more frequently than with other fusosomes, e.g., in the assay of Example 54; iii) the fusosomes fuse with the target cells at a rate such that the agent in the fusosomes is delivered to at least 10% of the target cells after 24 hours, e.g., in the assay of Example 54; or iv) A fusosome composition or pharmaceutical composition described in embodiment 323 or embodiment 324, wherein the fusogen is present in at least 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the copy number of the fusogen before being maintained at the aforementioned temperature, for example, as measured by the assay of Example 29. The fusosome composition or pharmaceutical composition of any of the above embodiments is storage-stable at a temperature of less than 326.4°C for at least 1, 2, 3, 6, or 12 hours; 1, 2, 3, 4, 5, or 6 days; 1, 2, 3, or 4 weeks; 1, 2, 3, or 6 months; or 1, 2, 3, 4, or 5 years. 327. A fusosome composition or pharmaceutical composition according to any of the above embodiments, which is storage-stable at temperatures below -20°C for at least 1, 2, 3, 6, or 12 hours; 1, 2, 3, 4, 5, or 6 days; 1, 2, 3, or 4 weeks; 1, 2, 3, or 6 months; or 1, 2, 3, 4, or 5 years. 328. A fusosome composition or pharmaceutical composition according to any of the above embodiments, which is storage stable at temperatures below -80°C for at least 1, 2, 3, 6, or 12 hours; 1, 2, 3, 4, 5, or 6 days; 1, 2, 3, or 4 weeks; 1, 2, 3, or 6 months; or 1, 2, 3, 4, or 5 years. 329. A composition is considered stable if it has at least 50%, 60%, 70%, 80%, 90%, 95%, or 99% activity of a plurality of activities prior to storage at the aforementioned temperatures for the aforementioned periods, for example, due to one or more of the following: i) the fusosomes fuse with target cells, e.g., at least at least 10% more frequently than with non-target cells, e.g., in the assay of Example 54; ii) the fusosomes fuse with target cells, e.g., at least 50% more frequently than with other fusosomes, e.g., in the assay of Example 54; iii) the fusosomes fuse with the target cells at a rate such that the agent in the fusosomes is delivered to at least 10% of the target cells after 24 hours, e.g., in the assay of Example 54; or iv) A fusosome composition or pharmaceutical composition described in any of embodiments 326 to 328, wherein the fusogen is present in at least 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the copy number of the fusogen before being maintained at the aforementioned temperature, for example, as measured by the assay of Example 29. 330. Having one or more of the following characteristics: a) the pharmaceutical composition meets drug or Good Manufacturing Practice (GMP) standards; b) the pharmaceutical composition is made in accordance with Good Manufacturing Practice (GMP); c) the pharmaceutical composition has a pathogen level below a predetermined reference value, e.g., is substantially free of pathogens; d) the pharmaceutical composition has a contaminant level below a predetermined reference value, e.g., is substantially free of contaminants, or e) A pharmaceutical composition according to any of embodiments 322 to 329, wherein the pharmaceutical composition has low immunogenicity, for example as described herein. 331. A method for producing a fusosome composition, comprising: a) providing source cells, including, for example, expressing a fusogen; b) producing fusosomes from the source cells, the fusosomes comprising a lipid bilayer, a lumen, a fusogen, and a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent), e.g., a membrane protein payload agent, a nuclear protein payload agent, or an organelle protein payload agent, thereby creating fusosomes; c) formulating the fusosomes, e.g., as a pharmaceutical composition suitable for administration to a subject; xii) the source cells are other than 293 cells, HEK cells, human endothelial cells, or human epithelial cells; xiii) the fusogen is other than a viral protein; xiv) the fusosomes and / or compositions or preparations thereof have a density other than, for example, between 1.08 g / mL and 1.12 g / mL; xv) the fusosomes and / or compositions or preparations thereof have a density of 1.25 g / mL + / - 0.05, e.g., as measured by the assay of Example 33; xvi) fusosomes are not captured by the scavenger system in the circulation or by Kupffer cells in the sinuses of the liver; xvii) the fusosomes are not trapped by the reticuloendothelial system (RES) of the subject, e.g., by the assay of Example 76; xviii) when a plurality of fusosomes are administered to a subject, less than 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the plurality are not captured by the RES after 24 hours, e.g., by the assay of Example 76; xix) the fusosomes have a diameter of more than 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 20 μm, 50 μm, 100 μm, 150 μm, or 200 μm; xx) the fusosomes contain cell biological material; xxi) the fusosome contains enucleated cells, or xxii) The method, wherein the fusosome comprises an inactivated nucleus. 332. The method of embodiment 331, wherein providing source cells that express a fusogen comprises expressing an exogenous fusogen in the source cells or upregulating expression of an endogenous fusogen in the source cells. 333. The method of embodiment 331 or embodiment 332, comprising inactivating the nuclei of the source cells. 334. A method for producing a fusosome composition, comprising: i) providing a plurality of fusosomes according to any one of embodiments 1 to 70, a fusosome composition according to any one of embodiments 71 to 97, or a pharmaceutical composition according to embodiment 97; ii) formulating a plurality of fusosomes, fusosome compositions, or pharmaceutical compositions, e.g., as a fusosome preparation suitable for administration to a subject. 335. The fusosome composition comprises at least about 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 10 9 , 10 10 , 10 11 , 10 12 , 10 13 , 10 14 , or 10 15 The method of any one of embodiments 331 to 334, comprising fusosomes. 336. The method of any of embodiments 331-335, wherein the fusosome composition comprises a volume of at least 10 mL, 20 mL, 50 mL, 100 mL, 200 mL, 500 mL, 1 L, 2 L, 5 L, 10 L, 20 L, or 50 L. 337. The method of any of embodiments 331-336, comprising enucleating the source cells, e.g., mammalian cells, e.g., by chemical enucleation, use of mechanical force, e.g., use of a filter or centrifuge, minimal partial disruption of the cytoskeleton. 338. The method of any of embodiments 331-337, comprising expressing a fusogen or other membrane protein in the source cell. 339. The method of any of embodiments 331-338, comprising one or more of vesicle formation, hypotonic treatment, extrusion, or centrifugation. 340. The method of any of embodiments 331-339, comprising genetically expressing an exogenous agent in the cell or loading the exogenous agent into source cells or fusosomes. 341. The method of any of embodiments 331-340, comprising contacting the source cells with DNA encoding the polypeptide agent, e.g., prior to inactivating the nucleus, e.g., enucleating the source cells. 342. The method of any of embodiments 331-341, comprising contacting the source cells with RNA encoding the polypeptide agent, e.g., before or after inactivating the nucleus, e.g., enucleating the source cells. 343. The method of any of embodiments 331-342, comprising introducing a payload, e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent (e.g., a nucleic acid or a protein), into the fusosome, e.g., by electroporation. 344. The source cells may be endothelial cells, fibroblasts, blood cells (e.g., macrophages, neutrophils, granulocytes, leukocytes), stem cells (e.g., mesenchymal stem cells, umbilical cord stem cells, bone marrow stem cells, hematopoietic stem cells, induced pluripotent stem cells, e.g., induced pluripotent stem cells derived from cells of a subject), embryonic stem cells (e.g., stem cells from embryonic yolk sac, placenta, umbilical cord, fetal skin, adolescent skin, blood, bone marrow, adipose tissue, erythropoietic tissue, hematopoietic tissue), myoblasts, parenchymal cells (e.g., hepatocytes), alveolar cells, neurons (e.g., retinal neurons), progenitor cells (e.g., preretinal cells), 344. The method of any one of embodiments 331-343, wherein the cell is a progenitor cell, myeloblast, myeloid progenitor cell, thymocyte, meiocyte, megakaryoblast, promegakaryoblast, melanocyte, lymphoblast, myeloid progenitor cell, normoblast, or hemangioblast), progenitor cell (e.g., cardiac progenitor cell, satellite cell, radial glial cell, bone marrow stromal cell, pancreatic progenitor cell, endothelial progenitor cell, blast cell), or immortalized cell (e.g., HeLa, HEK293, HFF-1, MRC-5, WI-38, IMR90, IMR91, PER.C6, HT-1080, or BJ cell). 345. The method of any of embodiments 331 to 344, wherein the fusosomes are derived from mammalian cells with a modified genome, e.g., reduced immunogenicity (e.g., by genome editing to remove MHC complexes). 346. The method of any of embodiments 331-345, wherein the source cells are derived from a cell culture treated with an anti-inflammatory signal. 347. The method of any of embodiments 331-346, further comprising contacting the source cells of step a) with an anti-inflammatory signal, e.g., before or after inactivating the nucleus, e.g., enucleating the cells. 348. A method for producing a fusosome pharmaceutical composition, comprising: a) providing a plurality of fusosomes, for example according to any of embodiments 1 to 70, a fusosome composition according to any of embodiments 71 to 97, or a pharmaceutical composition according to embodiment 97; b) assaying one or more fusosomes from the plurality to determine whether one or more (e.g., two, three, or all) of the following criteria are met: i) the fusosomes fuse with target cells, e.g., at least at least 10% more frequently than with non-target cells, e.g., in the assay of Example 54; ii) the fusosomes fuse with target cells, e.g., at least 50% more frequently than other fusosomes, e.g., in the assay of Example 54; iii) the fusosomes fuse with the target cells at a rate such that the agent in the fusosomes is delivered to at least 10% of the target cells after 24 hours, e.g., in the assay of Example 54; iv) the fusogen is present in a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 29; v) the fusosomes contain a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent) at a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 43; vi) The ratio of the copy number of the fusogen to the copy number of the payload (e.g., membrane payload agent, nuclear payload agent, or organelle payload agent) is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, or 20:1 to 1 Between 0:1, 10:1 to 5:1, 5:1 to 2:1, 2:1 to 1:1, 1:1 to 1:2, 1:2 to 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. vii) the fusosomes comprise a lipid composition in which one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 75% of the corresponding lipid levels in the source cells; viii) the fusosomes contain a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; ix) the fusosomes comprise a lipid to protein ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 49; x) the fusosomes comprise a ratio of protein to nucleic acid (e.g., DNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, e.g., as measured using the assay of Example 50; xi) the fusosomes comprise a lipid to nucleic acid (e.g., DNA) ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 51; xii) the fusosomes have a half-life in a subject, e.g., a mouse, that is within 90% of the half-life of a reference cell, e.g., a source cell, e.g., by the assay of Example 75; xiii) the fusosomes transport glucose (e.g., labeled glucose, e.g., 2-NBDG) across the membrane in the absence of glucose, e.g., at least 10% more than a negative control, e.g., an otherwise similar fusosome, as measured, e.g., using the assay of Example 64; xiv) the fusosomes contain esterase activity in the lumen that is within 90% of the esterase activity in a reference cell, e.g., a source cell or a mouse embryonic fibroblast, e.g., using the assay of Example 66; xv) the fusosomes comprise a metabolic activity level within 90% of the metabolic activity (e.g., citrate synthase activity) in a reference cell, e.g., a source cell, e.g., as described in Example 68; xvi) the fusosomes comprise a respiration level (e.g., oxygen consumption rate) within 90% of the respiration level in a reference cell, e.g., a source cell, e.g., as described in Example 69; xvii) the fusosomes comprise an Annexin V staining level of up to 18,000, 17,000, 16,000, 15,000, 14,000, 13,000, 12,000, 11,000, or 10,000 MFI, e.g., using the assay of Example 70; or or the fusosomes comprise a level of Annexin V staining that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the level of Annexin V staining of otherwise similar fusosomes treated with menadione in the assay of Example 70, or the fusosomes comprise a level of Annexin V staining that is at least 5%, 10%, 20%, 30%, 40%, or 50% less than the level of Annexin V staining of macrophages treated with menadione in the assay of Example 70. xviii) the fusosomes have an miRNA content level that is at least 1% of that of the source cells, e.g., by the assay of Example 39; xix) the fusosomes have a soluble:insoluble protein ratio that is within 90% of that of the source cells, e.g., by the assay of Example 47; xx) the fusosomes have an LPS level of less than 5% of the lipid content of the fusosomes, as measured, for example, by the assay of Example 48; xxi) the fusosomes and / or compositions or preparations thereof are capable of signaling, e.g., transmitting an extracellular signal, e.g., phosphorylating AKT in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG) in response to insulin, at least 10% more than a negative control, e.g., otherwise similar fusosomes, in the absence of insulin, e.g., using the assay of Example 63; xxii) the fusosomes have a level of juxtacrine signaling that is at least 5% greater than the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; xxiii) the fusosomes have a level of paracrine signaling that is at least 5% greater than the level of paracrine signaling induced by a reference cell, e.g., a source cell or a macrophage, e.g., by the assay of Example 72; The fusosomes polymerize actin at a level within 5% of the level of polymerized actin in a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 73. The fusosomes have a membrane potential within about 5% of the membrane potential of a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 74, or the fusosomes have a membrane potential of about -20 to -150 mV, -20 to -50 mV, -50 to -100 mV, or -100 to -150 mV. xxvi) the fusosomes and / or compositions or preparations thereof are capable of secreting protein at a rate that is at least 5% greater than that of a reference cell, e.g., a mouse embryonic fibroblast, e.g., using the assay of Example 62; or xxvii) the fusosomes have low immunogenicity, e.g., as described herein; c) (optionally) authorizing the release of the plurality of fusosomes or fusosome compositions if one or more of the criteria are met; This method results in the production of a fusosome pharmaceutical composition. 349. A method for producing a fusosome pharmaceutical composition, comprising: a) providing, e.g., producing, providing, e.g., a plurality of fusosomes according to any of embodiments 1 to 70, a fusosome composition according to any of embodiments 71 to 97, or a pharmaceutical composition according to embodiment 97; b) assaying one or more fusosomes from the plurality to determine the presence or level of one or more of the following factors: i) an immunogenic molecule, e.g., an immunogenic protein, e.g., as described herein; ii) a pathogen, e.g., a bacterium or virus, or iii) pollutants; c) (optionally) authorizing the release of a plurality of fusosomes or fusosome compositions if one or more of the factors is below a reference value; This method results in the production of a fusosome pharmaceutical composition. 350. The method of embodiment 349, wherein if a detectable level, e.g., a value above a reference value, is determined, the sample containing multiple fusosomes or fusosome compositions is discarded. 351. A method for producing a fusosome composition, comprising: a) providing a plurality of fusosomes as described herein or a fusosome composition as described herein; b) formulating the fusosomes, for example, as a pharmaceutical composition suitable for administration to a subject. 352. A method for producing a fusosome composition, comprising: a) providing, e.g., producing, a plurality of fusosomes or fusosome preparations, e.g., as described herein; b) analyzing a plurality of samples (e.g., of a preparation) to determine whether one or more (e.g., two, three, or more) criteria are met. 353. A method for producing a fusosome composition, comprising: a) providing, e.g., producing, a plurality of fusosomes as described herein, or a fusosome composition or preparation as described herein; b) assaying the plurality or preparation of samples to determine the presence or level of one or more of the following factors: i) an immunogenic molecule, e.g., an immunogenic protein, e.g., as described herein; ii) a pathogen, e.g., a bacterium or virus, or iii) contaminants (e.g., components of nuclear structures or nuclear DNA); c) (optionally) approving the plurality of fusosomes or fusosome preparation for release if one or more of the factors deviates significantly (e.g., by more than a specified amount) from the reference value, or (optionally) formulating the plurality of fusosomes or fusosome preparation as a pharmaceutical product if one or more of the factors does not deviate significantly (e.g., does not deviate by more than a specified amount) from the reference value. 354. A method for producing a fusosome composition, comprising: i) providing a plurality of fusosomes, fusosome compositions, or pharmaceutical compositions described herein; ii) formulating a plurality of fusosomes, fusosome compositions, or pharmaceutical compositions, e.g., as a fusosome preparation suitable for administration to a subject. 355. A method for producing a fusosome composition, comprising: a) providing a plurality of fusosomes, fusosome compositions, or pharmaceutical compositions described herein; b) assaying one or more fusosomes from the plurality to determine the presence or level of one or more of the following factors: i) an immunogenic molecule, e.g., an immunogenic protein, e.g., as described herein; ii) a pathogen, e.g., a bacterium or virus, or iii) pollutants; c) (optionally) authorizing the release of a plurality of fusosomes or fusosome compositions if one or more of the factors is below a reference value; This method results in the production of a fusosome pharmaceutical composition. 356. One or more of the following is present: i) the source cells are other than 293 cells, HEK cells, human endothelial cells, or human epithelial cells; ii) the fusogen is other than a viral protein; iii) the preparation containing multiple fusosomes has a density other than 1.08 g / mL to 1.12 g / mL; iv) the preparation comprising a plurality of fusosomes has a density of 1.25 g / mL + / - 0.05, e.g., as measured by the assay of Example 33; v) fusosomes are not substantially captured by the scavenger system in the circulation or by Kupffer cells in the sinuses of the liver; vi) the fusosomes are not substantially trapped by the reticuloendothelial system (RES) of the subject, e.g., by the assay of Example 76; vii) when a plurality of fusosomes are administered to a subject, less than 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the plurality are captured by the RES after 24, 48, or 72 hours, e.g., by the assay of Example 76; viii) the fusosomes have a diameter of greater than 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 20 μm, 50 μm, 100 μm, 150 μm, or 200 μm; ix) the fusosomes contain cell biological material; x) the fusosome contains enucleated cells, or xi) the fusosomes contain an inactivated nucleus. 357. A method for delivering a fusosome composition to a subject, e.g., a human subject, comprising administering to the subject a fusosome composition comprising a plurality of fusosomes according to any of embodiments 1 to 70, a fusosome composition described in any of embodiments 71 to 97, or a pharmaceutical composition described in embodiment 97, thereby administering the fusosome composition to the subject. 358. A method for delivering a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent) to a subject, comprising administering to the subject a fusosomal composition comprising a plurality of fusosomes according to any of embodiments 1 to 70, a fusosomal composition described in any of embodiments 71 to 97, or a pharmaceutical composition described in embodiment 97, wherein the fusosomal composition is administered in an amount and / or for a time such that the payload is delivered. 359. A method for regulating, e.g., enhancing, a biological function in a subject, comprising administering to the subject or contacting a target tissue or cell with a plurality of fusosomes according to any of embodiments 1 to 70, a fusosome composition described in any of embodiments 71 to 97, or a pharmaceutical composition described in embodiment 97, thereby regulating the biological function in the subject. 360. Biological functions a) modulating, e.g., increasing or decreasing, the interaction between two cells; b) modulating, e.g., increasing or decreasing, the immune response; c) modulating, e.g., increasing or decreasing, cell recruitment to target tissues; d) reduce the rate of cancer growth, or e) reducing the number of cancer cells in a subject. 361. A method for delivering a function to a subject, comprising administering to the subject a plurality of fusosomes according to any of embodiments 1-70, a fusosome composition described in any of embodiments 71-97, or a pharmaceutical composition described in embodiment 97, wherein the fusosome composition is administered in an amount and / or for a time such that the function in the subject is delivered. 362. A method for targeting a function in a subject, comprising administering to the subject a plurality of fusosomes according to any of embodiments 1 to 70, a fusosome composition described in any of embodiments 71 to 97, or a pharmaceutical composition described in embodiment 97, wherein the fusosome composition is administered in an amount and / or for a time such that the function in the subject is targeted. 363. A method for delivering or targeting a function to a subject, comprising administering to the subject a fusosome composition, fusosome composition, or pharmaceutical composition comprising a plurality of fusosomes described herein, wherein the fusosome composition is administered in an amount and / or for a time such that the function in the subject is delivered or targeted. 364. A method for treating a disease or disorder in a patient, comprising administering to a subject a plurality of fusosomes according to any of embodiments 1-70, a fusosome composition described in any of embodiments 71-97, or a pharmaceutical composition described in embodiment 97, wherein the fusosome composition is administered in an amount and / or for a time such that the disease or disorder is treated. 365. The method of embodiment 364, wherein the disease or disorder is selected from cancer, an autoimmune disorder, or an infectious disease. 366. The method of any of embodiments 357-365, wherein a plurality of fusosomes has a local effect. 367. The method of any of embodiments 357-365, wherein multiple fusosomes have a distal effect. 368. The method of any of embodiments 357-365, wherein multiple fusosomes have a systemic effect. 369. The method of any of embodiments 357-368, wherein the subject has cancer. 370. The method of embodiment 369, wherein the subject has cancer and the fusosomes contain neoantigens. 371. The method of any of embodiments 357-370, wherein the fusosome composition is administered to the subject at least 1, 2, 3, 4, or 5 times. 372. The method of any of embodiments 357-370, wherein the fusosome composition is administered systemically (e.g., orally, parenterally, subcutaneously, intravenously, intramuscularly, intraperitoneally) or locally to the subject. 373. The method of any of embodiments 357-372, wherein the fusosome composition is administered to a subject so that the fusosome composition reaches a target tissue selected from the liver, lung, heart, spleen, pancreas, gastrointestinal tract, kidney, testes, ovaries, brain, reproductive organs, central nervous system, peripheral nervous system, skeletal muscle, endothelium, inner ear, or eye. 374. The method of any of embodiments 357-373, wherein the fusosome composition is co-administered with an immunosuppressant, such as a glucocorticoid, a cytostatic, an antibody, or an immunophilin modulator. 375. The method of any of embodiments 357-374, wherein the fusosome composition is co-administered with an immunostimulant, such as an adjuvant, interleukin, cytokine, or chemokine. 376. The method of any of the above embodiments, wherein the method comprises delivering an agent to the cytosol of the target cell, and optionally, the cytosol-delivered agent is a protein (or a nucleic acid encoding a protein or complementary to one encoding a protein, such as, for example, DNA, gDNA, cDNA, RNA, pre-mRNA, mRNA, etc., encoding a protein). 377. A method of administering a fusosome composition to a human subject, comprising: a) administering a first fusogen to a subject under conditions that allow for location of the first fusogen in one or more target cells of the subject; i) administering the first fusogen comprises administering a nucleic acid encoding the first fusogen under conditions that allow expression of the first fusogen in one or more target cells; or ii) administering a first fusogen that does not contain a coiled-coil motif; b) administering to a human subject a fusosome composition comprising a plurality of fusosomes comprising a second fusogen, wherein the second fusogen is compatible with the first fusogen, and the plurality of fusosomes further comprise a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent); This method involves administering a fusosome composition to a subject. 378. A method for delivering a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent) to a subject, comprising: a) administering a first fusogen to a subject under conditions that allow for location of the first fusogen in one or more target cells of the subject; i) administering the first fusogen comprises administering a nucleic acid encoding the first fusogen under conditions that allow expression of the first fusogen in one or more target cells; or ii) administering a first fusogen that does not contain a coiled-coil motif; b) administering to a human subject a fusosome composition comprising a plurality of fusosomes comprising a second fusogen and a therapeutic agent, wherein the second fusogen is compatible with the first fusogen and the plurality of fusosomes further comprise a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent); thereby delivering a payload (eg, a membrane payload agent, a nuclear payload agent, or an organelle payload agent) to a subject. 379. A method for modulating, e.g., enhancing, a biological function in a subject, comprising: a) administering a first fusogen to a subject under conditions that allow for location of the first fusogen in one or more target cells of the subject; i) administering the first fusogen comprises administering a nucleic acid encoding the first fusogen under conditions that allow expression of the first fusogen in one or more target cells; or ii) administering a first fusogen that does not contain a coiled-coil motif; b) administering to a human subject a fusosome composition comprising a plurality of fusosomes comprising a second fusogen, wherein the second fusogen is compatible with the first fusogen, and the plurality of fusosomes further comprise a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent); thereby regulating a biological function in the subject. 380. The method of any of embodiments 377-379, wherein the payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent) is exogenous to or overexpressed in the source cell. 381. The payload (e.g., membrane payload agent, nuclear payload agent, or organelle payload agent) is: i) a transcriptional activator, e.g., a transcriptional activator of Table 17-1; ii) a transcriptional repressor, e.g., a transcriptional repressor of Table 171; iii) epigenetic modifiers, e.g., epigenetic modifiers in Table 17-1; iv) histone acetyltransferases, e.g., histone acetyltransferases of Table 17-1; v) histone deacetylases, e.g., histone deacetylases of Table 17-1; vi) histone methyltransferases, e.g., histone methyltransferases of Table 17-1; vii) DNA methyltransferases, e.g., the DNA methyltransferases of Table 17-1; viii) a DNA nickase, such as a DNA nickase described herein; ix) site-specific DNA editing enzymes, such as deaminases in Table 17-1; x) a DNA transposase, such as a DNA transposase described herein; xi) a DNA integrase, such as a DNA integrase described herein; xii) an RNA editor, e.g., an RNA editor in Table 17-1; xiii) an RNA splicing factor, e.g., an RNA splicing factor in Table 17-1; or xiv) The method of any of embodiments 377 to 379, comprising or encoding one or more of the PIWI proteins, such as the PIWI proteins described herein. 382. The method of any of the above embodiments, wherein the multiple fusosomes have a local effect or have a distal effect. 383. The method of any of the above embodiments, comprising providing a source cell that expresses a fusogen (including expressing an exogenous fusogen in the source cell), or upregulating expression of an endogenous fusogen in the source cell. 384. The method of any of the above embodiments, comprising inactivating the nuclei of the source cells. 385. The method of any of the above embodiments, comprising enucleating the mammalian cells, e.g., by chemical enucleation, use of mechanical force, e.g., use of a filter or centrifuge, at least partial disruption of the cytoskeleton, or a combination thereof. 386. The method of any of the above embodiments, comprising expressing a fusogen or other membrane protein in the source cell. 387. The method of any of the above embodiments, comprising one or more of vesicle formation, hypotonic treatment, extrusion, or centrifugation. 388. The method of any of the above embodiments, comprising genetically expressing the exogenous agent in the source cell, or loading the exogenous agent into the source cell or fusosomes. 389. The method of any of the above embodiments, comprising, e.g., contacting the cell with DNA encoding the polypeptide agent before inactivating the nucleus, e.g., enucleating the cell. 390. The method of any of the above embodiments, comprising, e.g., contacting the cell with RNA encoding the polypeptide agent before or after inactivating the nucleus, e.g., enucleating the cell. 391. The method of any of the above embodiments, comprising introducing a therapeutic agent (e.g., a nucleic acid or protein) into fusosomes, e.g., by electroporation. 392. The method of any of the above embodiments, wherein the fusosomes are derived from mammalian cells having a genome that has been modified, e.g., to reduce immunogenicity (e.g., by genome editing, e.g., to remove MHC proteins), and optionally the method further comprises contacting the source cells of step a) with an immunosuppressive substance, e.g., before or after inactivating the nucleus, e.g., enucleating the cells. 393. The method of any of the above embodiments, wherein if a detectable level, e.g., a value above a reference value, is determined, the sample containing multiple fusosomes or fusosome composition or preparation is discarded. 394. A method according to any of the above embodiments, comprising: a) monitoring cancer progression, tumor regression, tumor volume, reduction in neoplastic cell number, amount of fused cells, amount of fused cells containing a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent), amount of fused cells expressing a nucleic acid protein payload, and amount of membrane protein located in the membrane of the fused cells; and / or b) further comprising the step of monitoring the organism for adverse events, optionally including one or more of cytokine release syndrome, fever, tachycardia, chills, anorexia, nausea, vomiting, myalgia, headache, capillary leak syndrome, hypotension, pulmonary edema, coagulopathy, renal dysfunction, renal damage, macrophage activation syndrome, hemophagocytic lymphohistiocytosis, organ failure, cerebral edema, bystander inflammation due to T cell activation, neurological symptoms, encephalopathy, confusion, hallucinations, delirium, coma, aphasia, seizures, B cell hypoplasia, tumor lysis syndrome, and graft versus host disease. 395. The method of any of embodiments 377-379, wherein the first fusogen is not a lipopeptide. 396. The method of any one of embodiments 357-395, further comprising monitoring one or more of the amount of fused cells, the amount of fused cells containing a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent), the amount of fused cells expressing a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent), and the amount of membrane protein located in the nucleus of the fused cells. 397. The method of any of embodiments 357-396, further comprising monitoring an adverse event in the organism. 398. The method of embodiment 397, wherein the adverse events include one or more of cytokine release syndrome, fever, tachycardia, chills, anorexia, nausea, vomiting, myalgia, headache, capillary leak syndrome, hypotension, pulmonary edema, coagulopathy, renal dysfunction, renal impairment, macrophage activation syndrome, hemophagocytic lymphohistiocytosis, organ failure, cerebral edema, bystander inflammation due to T cell activation, neurological symptoms, encephalopathy, confusion, hallucinations, delirium, coma, aphasia, seizures, B cell hypoplasia, tumor lysis syndrome, and graft versus host disease. 399. The method of any of embodiments 357-398, wherein the organism is a human. 400. The method of embodiment 399, wherein the human has a disease, disorder, or condition. 401. The method of embodiment 400, wherein the presence of a payload (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent, e.g., a membrane protein payload agent, a nuclear protein payload agent, or an organelle protein payload agent) in the cell membrane lipid bilayer of a target cell ameliorates one or more symptoms of a disease, disorder, or condition. 402.CAR, a) a first-generation CAR comprising an antigen-binding domain, a transmembrane domain, and a signaling domain (e.g., one, two, or three signaling domains); b) a third-generation CAR comprising an antigen-binding domain, a transmembrane domain, and at least three signaling domains; c) is or comprises a fourth-generation CAR that comprises an antigen-binding domain, a transmembrane domain, three or four signaling domains, and a domain that induces cytokine gene expression upon successful signaling of the CAR; Optionally, the fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the antigen-binding domain is an scFv or Fab. 403. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 401 or 402, wherein the CAR antigen-binding domain binds to a ligand expressed on B cells, plasma cells, plasmablasts, CD10, CD19, CD20, CD22, CD24, CD27, CD38, CD45R, CD138, CD319, BCMA, CD28, TNF, interferon receptor, GM-CSF, ZAP-70, LFA-1, CD3γ, CD5, or CD2. 404. The fusosome, fusosome composition, fusosome preparation, or method according to any of embodiments 401 to 403, wherein the CAR transmembrane domain comprises at least the transmembrane region of the α, β, or ζ chain of the T cell receptor, CD28, CD3ε, CD45, CD4, CD5, CD8, CD9, CD16, CD22, CD33, CD37, CD64, CD80, CD86, CD134, CD137, CD154, or a functional variant thereof. 405. The fusosome, fusosome composition, fusosome preparation, or method of any of embodiments 401-404, wherein the transmembrane domain comprises at least the transmembrane region(s) of CD8α, CD8β, 4-1BB / CD137, CD28, CD34, CD4, FcεRIγ, CD16, OX40 / CD134, CD3ζ, CD3ε, CD3γ, CD3δ, TCRα, TCRβ, TCRζ, CD32, CD64, CD64, CD45, CD5, CD9, CD22, CD37, CD80, CD86, CD40, CD40L / CD154, VEGFR2, FAS, and FGFR2B, or functional variants thereof. 406.CAR is B7-1 / CD80, B7-2 / CD86, B7-H1 / PD-L1, B7-H2, B7-H3, B7-H4, B7-H6, B7-H7, BTLA / CD272, CD28, CTLA-4, Gi24 / VISTA / B7-H5, ICOS / CD278, PD- 1, PD-L2 / B7-DC, PDCD6), 4-1BB / TNFSF9 / CD137, 4-1BB ligand / TNFSF9, BAFF / BLyS / TNFSF13B, BAFFR / TNFRSF13C, CD27 / TNFRSF7, CD27 ligand / TNFSF7, CD30 / TNFRSF8, CD30 ligand / TNFSF8, CD40 / TNFRSF5, CD40 / TNFSF5, CD40 ligand / TNFSF5, DR3 / TNFRSF25, GITR / TNFRSF18, GITR ligand / TNFSF18, HVEM / TNFRSF14, L IGHT / TNFSF14, lymphotoxin-α / TNF-β, OX40 / TNFRSF4, OX40 ligand / TNFSF4, RELT / TNFRSF19L, TACI / TNFRSF13B, TL1A / TNFSF15, TNF-α, TNFRII / TNFRSF1B), 2 B4 / CD244 / SLAMF4, BLAME / SLAMF8, CD2, CD2F-10 / SLAMF9, CD48 / SLAMF2, CD58 / LFA-3, CD84 / SLAMF5, CD229 / SLAMF3, CRACC / SLAMF7, NTB-A / SLAMF6, SLAM / CD150), CD2, CD7, CD53, CD82 / Kai-1, CD90 / Thy1, CD96, CD160, CD200, CD300a / LMIR1, HLA class I, HLA-DR, Ikaros, integrin α4 / CD49d, integrin α4β1, integrin α4β7 / LPAM-1, LAG-3, TCL1A, TCL1B, CRTAM, CAP12, Dectin-1 / CLEC7A, DPPIV / CD26, EphB6, TIM-1 / KIM-1 / HAVCR, TIM-4, TSLP, TSLPR, lymphocyte function-associated antigen-1 (LFA-1), NKG2C, CD3ζ domain, immunoreceptor tyrosine-based activation motif (ITAM), CD27, CD28, 4-1BB, CD134 / OX40, CD30, CD40, PD-1, ICOS, lymphocyte function-associated antigen-1 (LFA-1), CD2, CD7, LIGHT,The fusosome, fusosome composition, fusosome preparation, or method according to any one of embodiments 401 to 405, comprising at least one signaling domain selected from one or more of a ligand that specifically binds to NKG2C, B7-H3, CD83, or a functional fragment thereof. 407. The fusosome, fusosome composition, fusosome preparation, or method of any of embodiments 401-406, wherein the CAR comprises a CD3ζ domain, or an immunoreceptor tyrosine-based activation motif (ITAM), or a functional variant thereof. In some embodiments, the CAR comprises: (i) a CD3ζ domain, or an immunoreceptor tyrosine-based activation motif (ITAM), or a functional variant thereof; (ii) a CD28 domain, or a 4-1BB domain, or a functional variant thereof; and (iii) a 4-1BB domain, or a CD134 domain, or a functional variant thereof. 408. The fusosome, fusosome composition, fusosome preparation, or method according to any of embodiments 401 to 407, wherein the CAR further comprises one or more spacers, e.g., a first spacer between the antigen-binding domain and the transmembrane domain, optionally wherein the first spacer comprises at least a portion of an immunoglobulin constant region or a variant or modified version thereof, and optionally wherein the spacer is a second spacer between the transmembrane domain and the signaling domain, and optionally wherein the second spacer is an oligopeptide, e.g., wherein the oligopeptide comprises a glycine-serine doublet. 409. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the antigen-binding domain targets an antigen characteristic of neoplastic cells. 410. Antigens characteristic of neoplastic cells include cell surface receptors, ion channel-linked receptors, enzyme-linked receptors, G protein-coupled receptors, receptor tyrosine kinases, tyrosine kinase-associated receptors, receptor-like tyrosine phosphatases, receptor serine / threonine kinases, receptor guanylyl cyclases, histidine kinase-associated receptors, epidermal growth factor receptors (EGFRs) (including ErbB1 / EGFR, ErbB2 / HER2, ErbB3 / HER3, and ErbB4 / HER4), fibroblast growth factor receptors (FGFRs) (including FGF1, FGF2, FGF3, FGF4, FGF5, FGF6, FGF7, FGF18, and FGF21), vascular endothelial growth factor receptors (VEGFRs) (including VEGF-A, VEGF-B, VEGF-C, VEGF-D, and PIGF), RET receptors, and the Eph receptor family (EphA1, EphA2, EphB3, EphC1, EphD2, EphE3, EphF4, EphF5, EphF6, EphF7, EphF8, EphF9, EphF10, EphF11, EphF12, EphF13, EphF14, EphF15, EphF16, EphF17, EphF18, EphF19, EphF20, EphF21, EphF22, EphF23, ​​EphF24, EphF25, EphF26, EphF27, EphF28, EphF29, EphF30, EphF31, EphF32, EphF33, EphF34, EphF35, EphF36, EphF37, EphF38, EphF39, A2, EphA3, EphA4, EphA5, EphA6, EphA7, EphA8, EphA9, EphA10, EphB1, EphB2, EphB3, EphB4, and EphB6), CXCR1 , CXCR2, CXCR3, CXCR4, CXCR6, CCR1, CCR2, CCR3, CCR4, CCR5, CCR6, CCR8, CFTR, CIC-1, CIC-2, CIC-4, CIC-5, CIC-7, CIC-Ka, CIC-Kb, bestrophin, TMEM16A, GABA receptor, glycine receptor, ABC transporter, NAV1.1, NAV1.2, NAV1.3, NAV1.4, NAV1.5, NAV1.6, NAV1.7, NAV1.8, NAV1.9, sphingosine-1-phosphate receptor (S1P1R), NMDA channel, transmembrane protein, multispanning transmembrane protein, T cell receptor motif. T cell alpha chain, T cell beta chain, T cell gamma chain, T cell delta chain, CCR7, CD3, CD4, CD5, CD7, CD8, CD11b, CD11c, CD16, CD19, CD20, CD21, CD22, CD25, CD28, CD34, CD35, CD40, CD45RA, C D45RO, CD52, CD56, CD62L, CD68, CD80, CD95, CD117, CD127, CD133, CD137(4-1BB), CD163, F4 / 80, IL-4Ra, Sca-1, CTLA-4, GITR, GARP, LAP, Granzyme B,LFA-1, transferrin receptor, NKp46, perforin, CD4+, Th1, Th2, Th17, Th40, Th22, Th9, Tfh, classical Treg, FoxP3+, Tr1, Th3, Treg17, TREG, CDCP1, NT5E, EpCAM, CEA, gpA33, mucin, TAG-72, carbonic anhydrase IX, PSMA, folate-binding protein, gangliosides (e.g., CD2, CD3, GM2), Lewis-γ2, VEGF, VEGFR1 / 2 / 3, αVβ3, α5β1, ErbB1 / EGFR, ErbB1 / HER2, E rB3, c-MET, IGF1R, EphA3, TRAIL-R1, TRAIL-R2, RANKL, FAP, tenascin, PDL-1, BAFF, HDAC, ABL, FLT3, KIT, MET, RET, IL-1β, ALK, RANKL, mTOR, CTLA-4, IL-6 , IL-6R, JAK3, BRAF, PTCH, Smoothened, PIGF, ANPEP, TIMP1, PLAUR, PTPRJ, LTBR, ​​or ANTXR1, folate receptor alpha (FRa), ERBB2(Her2 / neu), EphA2, IL-13Ra2, epithelial Growth factor receptor (EGFR), mesothelin, TSHR, CD19, CD123, CD22, CD30, CD171, CS-1, CLL-1, CD33, EGFRvIII, GD2, GD3, BCMA, MUC16 (CA125), L1CAM, LeY, MSLN, IL13Rα1, L1-CAM, TnAg, prostate-specific membrane antigen (PSMA), ROR1, FLT3, FAP, TAG72, CD38, CD44v6, CEA, EPCAM, B7H3, KIT, interleukin-11 receptor α (IL-11Ra), PSCA, PRSS21, VEGFR2, Le IsY, CD24, platelet-derived growth factor receptor beta (PDGFR beta), SSEA-4, CD20, MUC1, NCAM, prostase, PAP, ELF2M, ephrin B2, IGF-1 receptor, CAIX, LMP2, gplOO, bcr-abl, telomerase, fucosyl GM1, sLe, GM3, TGS5, HMWMAA, o-acetyl-GD2, folate receptor beta, TEM1 / CD248, TEM7R, CLDN6, GPRC5D, CXORF61, CD97, CD179a, ALK, polysialic acid, PLACl, GloboH, NY-BR-1,UPK2, HAVCR1, ADRB3, PANX3, GPR20, LY6K, OR51E2, TARP, WT1, NY-ESO-1, LAGE-la, MAGE-A1, legumain, HPVE6, E7, ETV6-AML, sperm protein 17, XAGE1, Tie2, MAD-CT-1, MAD-CT-2, Fos-related antigen 1, p53, p53 mutant, prostein, survivin, telomerase, PCTA-1 / galectin 8, MelanA / MART1, Ras mutant, hTERT, sarcoma translocation breakpoint, ML-IAP, ERG (TMPRSS2ETS fusion gene), NA17, PAX3, androgen receptor, cyclin B1, MYCN, RhoC, TRP-2, CYPIBI, BORIS, SART3, PAX5, OY-TES1, LCK , AKAP-4, SSX2, RAGE-1, human telomerase reverse transcriptase, RU1, RU2, intestinal carboxylesterase, muthsp70-2, CD79a, CD79b, CD72, LAIR1, FCAR, LILRA2, CD300LF, CLEC12A, BST2, EMR2, LY75, GPC3, FCRL5, IGLL1, neoantigens, CD133, CD15, CD184, CD24, CD56, CD26, CD29, CD44, HLA-A, HLA-B, HLA-C, (HLA-A, B, C)CD49f, CD151, CD340, CD200, tkrA, trkB, trkC, or an antigenic fragment or portion thereof. 411. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the antigen-binding domain targets an antigen characteristic of T cells. 412. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 411, wherein the antigen characteristic of T cells is selected from a cell surface receptor, a membrane transport protein (e.g., an active or passive transport protein such as an ion channel protein, a pore-forming protein, etc.), a transmembrane receptor, a membrane enzyme, and / or a cell adhesion protein characteristic of T cells. 413. Antigens characteristic of T cells include G protein-coupled receptors, receptor tyrosine kinases, tyrosine kinase-associated receptors, receptor-like tyrosine phosphatases, receptor serine / threonine kinases, receptor guanylyl cyclases, histidine kinase-associated receptors, AKT1; AKT2; AKT3; ATF2; BCL10; CALM1; CD3D (CD3δ); CD3E (CD3ε); CD3G (CD3γ); CD4; CD8; CD28; CD45; CD80 (B7-1); CD86 (B7-2); CD247 ( CD3ζ);CTLA4(CD152);ELK1;ERK1(MAPK3);ERK2;FOS;FYN;GRAP2(GADS);GRB2;HLA-DRA;HLA-DRB1;HLA-DRB3;HLA-DRB4;HLA-DRB5;HRAS; IKBKA(CHUK);IKBKB;IKBKE;IKBKG(NEMO);IL2;ITPR1;ITK;JUN;KRAS2;LAT;LCK;MAP2K1(MEK1);MAP2K2(MEK2);MAP2K3(MKK3);MAP2K4(M KK4);MAP2K6(MKK6);MAP2K7(MKK7);MAP3K1(MEKK1);MAP3K3;MAP3K4;MAP3K5;MAP3K8;MAP3K14(NIK);MAPK8(JNK1);MAPK9(JNK2);MAPK 10(JNK3);MAPK11(p38β);MAPK12(p38γ);MAPK13(p38δ);MAPK14(p38α);NCK;NFAT1;NFAT2;NFKB1;NFKB2;NFKBIA;NRAS;PAK1;PAK2;PAK3 The fusosome, fusosome composition, fusosome preparation, or method described in embodiment 411 or 412 may be ;PAK4;PIK3C2B;PIK3C3 (VPS34);PIK3CA;PIK3CB;PIK3CD;PIK3R1;PKCA;PKCB;PKCM;PKCQ;PLCY1;PRF1 (perforin);PTEN;RAC1;RAF1;RELA;SDF1;SHP2;SLP76;SOS;SRC;TBK1;TCRA;TEC;TRAF6;VAV1;VAV2;or ZAP70. 414. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the antigen-binding domain targets an antigen characteristic of an autoimmune or inflammatory disorder. 415. The autoimmune or inflammatory disorder is selected from chronic graft-versus-host disease (GVHD), lupus, arthritis, immune complex glomerulonephritis, Goodpasture's disease, uveitis, hepatitis, systemic sclerosis or scleroderma, type I diabetes, multiple sclerosis, cold agglutinin disease, pemphigus vulgaris, Graves' disease, autoimmune hemolytic anemia, thrombocytopenia A, primary Sjogren's syndrome, thrombotic thrombocytopenic purpura, neuromyelopathic optic neuropathy, Evan's syndrome, IgM-mediated neuropathy, thyroglobulinemia, dermatomyositis, idiopathic thrombocytopenia, ankylosing spondylitis, bullous pemphigoid, acquired angioedema, chronic urticaria, antiphospholipid demyelinating polyneuropathy, and autoimmune thrombocytopenia or neutropenia or pure red blood cell aplasia, while illustrative, non-limiting examples of alloimmune diseases include allosensitization (e.g., Blazar et al., 415. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 414, wherein the antigen characteristic of the autoimmune or inflammatory disorder is selected from the group consisting of cell surface receptors, ion channel-linked receptors, enzyme-linked receptors, G protein-coupled receptors, receptor tyrosine kinases, tyrosine kinase-associated tumors, receptor-like tyrosine phosphatases, receptor serine / threonine kinases, receptor guanylyl cyclases, and histidine kinase-associated receptors. 416. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the antigen-binding domain targets an antigen characteristic of an infectious disease. 417. The infectious disease is selected from HIV, hepatitis B virus, hepatitis C virus, human herpesvirus, human herpesvirus 8 (HHV-8, Kaposi's sarcoma-associated herpesvirus (KSHV)), human T-lymphotropic virus-1 (HTLV-1), Merkel cell polyomavirus (MCV), simian virus 40 (SV40), Epstein-Barr virus, CMV, and human papillomavirus, and optionally, the antigen characteristic of the infectious disease is selected from cell surface receptors, ion channel-linked receptors, enzyme-linked receptors, G protein-coupled receptors, receptor tyrosine kinases, tyrosine kinase-associated receptors, receptor-like tyrosine phosphatases, receptor serine / threonine kinases, receptor guanylyl cyclases, histidine kinase-associated receptors, HIV, Env, gpl20, or HIV-1. 417. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 416, wherein the epitope is selected from a CD4-inducible epitope on Env. 418. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the target cell comprises aggregated or misfolded membrane proteins. 419. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of reducing (e.g., reduces) the level of aggregated or misfolded protein in a target cell, or wherein the method herein comprises reducing the level of aggregated or misfolded protein in a target cell. 420. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of delivering (e.g., delivers) a membrane protein to the cell membrane of a target cell. 421. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 420, wherein delivering the protein comprises delivering a nucleic acid (e.g., DNA, gDNA, cDNA, RNA, pre-mRNA, mRNA, etc.) encoding the protein to the target cell, whereby the target cell produces the protein and localizes it to its membrane. 422. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 420 or 421, wherein the fusosome comprises a protein or the method comprises delivering a protein, and fusion of the fusosome with a target cell carries the protein to the plasma membrane of the target cell. 423. The fusosome, fusosome composition, fusosome preparation, or method according to any of embodiments 420-422, wherein the protein comprises an antibody that binds to a cell surface ligand or cell surface receptor. 424. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome further comprises, or the method further comprises delivering, a second agent that comprises or encodes a second cell surface ligand or antibody that binds to the cell surface receptor, and optionally further comprises or encodes one or more additional cell surface ligands or antibodies (e.g., 1, 2, 3, 4, 5, 10, 20, 50, or more) that bind to the cell surface receptor. 425. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 424, wherein the first agent and the second agent form a complex, and optionally, the complex further comprises one or more additional cell surface ligands. 426. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the agent comprises or encodes a cell surface receptor, e.g., a cell surface receptor that is exogenous to or overexpressed on the source cell. 427. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome further comprises, or the method further comprises delivering, a second agent that comprises or encodes a second cell surface receptor, and optionally further comprises or encodes one or more additional cell surface receptors (e.g., 1, 2, 3, 4, 5, 10, 20, 50, or more additional cell surface receptors). 428. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 427, wherein the second agent, e.g., therapeutic agent, is selected from a protein, a protein complex (e.g., at least 2, 3, 4, 5, 10, 20, or 50 proteins, e.g., at least at least 2, 3, 4, 5, 10, 20, or 50 different proteins), a polypeptide, a nucleic acid (e.g., DNA, a chromosome, or RNA, e.g., mRNA, siRNA, or miRNA), or a small molecule. 429. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 427 or 428, wherein the first agent and the second agent form a complex, optionally, the complex further comprises one or more additional cell surface receptors, and optionally, the agent comprises or encodes an antigen or antigen-presenting protein. 430. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof delivers or is capable of delivering (e.g., delivers) a secreted agent, e.g., a secreted protein, to a target site (e.g., an extracellular region), e.g., by delivering nucleic acid (e.g., DNA, gDNA, cDNA, RNA, pre-mRNA, mRNA, etc.) encoding the protein to the target cell under conditions that allow the target cell to produce and secrete the protein. 431. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 430, wherein the secreted protein is endogenous or exogenous to the source cell or to the target cell. 432. The fusosome, fusosome composition, fusosome preparation, or method according to embodiment 430 or 431, wherein the secreted protein comprises a therapeutic protein, such as an antibody molecule, a cytokine, an enzyme, an autocrine signaling molecule, a paracrine signaling molecule, or a secretory granule. 433. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof delivers or is capable of delivering (e.g., delivers) a membrane protein, or secreted cell that is or contains an antigen. 434. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 433, wherein the fusosome and / or composition or preparation thereof delivers or is capable of delivering (e.g., delivers) a membrane protein or secreted protein that is or comprises a membrane protein, or an antigen-presenting protein, optionally together with (e.g., in a complex with) an antigen. 435. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof donates or is capable of donating (e.g., donates) one or more cell surface receptors to a target cell (e.g., an immune cell). 436. The fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, wherein the target cell is or comprises a tumor cell. 437. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof delivers or is capable of delivering (e.g., delivers) a membrane or secreted protein that is or comprises an immunostimulatory ligand, an antigen-presenting protein, a tumor suppressor protein, a pro-apoptotic protein, or a receptor or binding partner of any of the foregoing. 438. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome comprises an agent (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent, and optionally at least one second agent) that is immunomodulatory, e.g., immunostimulatory. 439. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of presenting or causing (e.g., causing) an antigen to be presented to a target cell. 440. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof delivers or is capable of delivering (e.g., delivers) a nucleic acid to a target cell, e.g., to transiently modify gene expression in the target cell or to modify, e.g., by integration into the genome of the target cell, e.g., to cause expression of a membrane protein (or secreted protein) described herein. 441. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof delivers or is capable of delivering (e.g., delivers) a protein (e.g., a membrane protein such as a transporter protein, or a secreted protein such as an immunosuppressive protein) to a target cell, thereby at least temporarily relieving a protein deficiency in the target cell. 442. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 441, wherein the membrane protein may comprise one or more covalently attached non-peptide moieties, such as, for example, one or more carbohydrate moieties, lipid moieties, polyethylene glycol moieties, small molecules, and combinations thereof. 443. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of secreting or causing (e.g., secreting) a protein, e.g., a therapeutic protein, to a target cell. 444. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes having a cell surface ligand are derived from a source cell selected from a neutrophil (e.g., and the target cell is a tumor-infiltrating lymphocyte), a dendritic cell (e.g., and the target cell is a naive T cell), or a neutrophil (e.g., and the target is a tumor cell or a virus-infected cell). 445. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 444, wherein the fusosome comprises a membrane complex, e.g., a complex comprising at least two, three, four, or five proteins, e.g., a homodimer, heterodimer, homotrimer, heterotrimer, homotetramer, or heterotetramer. 446. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 444 or 445, wherein the fusosome comprises an antibody, e.g., a toxic antibody, and wherein the fusosome and / or composition or preparation thereof is capable of delivering (e.g., delivers) the antibody to a target site, e.g., by homing to the target site. 447. The fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, wherein the source cell is a NK cell or a neutrophil. 448. Membrane proteins include cell surface receptors, ion channel-linked receptors, enzyme-linked receptors, G protein-coupled receptors, receptor tyrosine kinases, tyrosine kinase-associated receptors, receptor-like tyrosine phosphatases, receptor serine / threonine kinases, receptor guanylyl cyclases, histidine kinase-associated receptors, epidermal growth factor receptors (EGFRs) (including ErbB1 / EGFR, ErbB2 / HER2, ErbB3 / HER3, and ErbB4 / HER4), fibroblast growth factor receptors (FGFRs) (including FGF1, FGF2, FGF3, FGF4, FGF5, FGF6, FGF7, FGF18, and FGF21), vascular endothelial growth factor receptors (VEGFRs) (including VEGF-A, VEGF-B, VEGF-C, VEGF-D, and PIGF), RET receptors, and the Eph receptor family (EphA1, EphA2, CXCR1, C XCR2, CXCR3, CXCR4, CXCR6, CCR1, CCR2, CCR3, CCR4, CCR5, CCR6, CCR8, CFTR, CIC-1, CIC-2, CIC-4, CIC-5, CIC-7, C IC-Ka, CIC-Kb, bestrophin, TMEM16A, GABA receptor, glycine receptor, ABC transporter, NAV1.1, NAV1.2, NAV1.3, NAV1.4, NAV1.5, NAV1.6, NAV1.7, NAV1.8, NAV1.9, sphingosine-1-phosphate receptor (S1P1R), NMDA channel, transmembrane protein, multispanning transmembrane protein, T cell receptor motif. T cell alpha chain, T cell beta chain, T cell gamma chain, T cell delta chain, CCR7, CD3, CD4, CD5, CD7, CD8, CD11b, CD11c, CD16, CD19, CD20, CD21, CD22, CD25, CD28, CD34, CD35, CD40, CD45RA, CD45 RO, CD52, CD56, CD62L, CD68, CD80, CD95, CD117, CD127, CD133, CD137(4-1BB), CD163, F4 / 80, IL-4Ra, Sca-1, CTLA-4, GITR, GARP, LAP, Granzyme B, LFA-1,Transferrin receptor, NKp46, perforin, CD4+, Th1, Th2, Th17, Th40, Th22, Th9, Tfh, classical Treg, FoxP3+, Tr1, Th3, Treg17, TREG, CDCP1, NT5E, EpCAM, CEA, gpA33, mucin, TAG-72, carbonic anhydrase IX, PSMA, folate-binding protein, gangliosides (e.g., CD2, CD3, GM2), Lewis-γ2, VEGF, VEGFR1 / 2 / 3, αVβ3, α5β1, ErbB1 / EGFR, ErbB1 / HER2, ErB3, c- MET, IGF1R, EphA3, TRAIL-R1, TRAIL-R2, RANKL, FAP, tenascin, PDL-1, BAFF, HDAC, ABL, FLT3, KIT, MET, RET, IL-1β, ALK, RANKL, mTOR, CTLA-4, IL-6, IL-6R, JAK3, BRAF, PTCH, Smoothened, PIGF, ANPEP, TIMP1, PLAUR, PTPRJ, LTBR, ​​or ANTXR1, folate receptor alpha (FRa), ERBB2 (Her2 / neu), EphA2, IL-13Ra2, epidermal growth factor receptor EGFR, mesothelin, TSHR, CD19, CD123, CD22, CD30, CD171, CS-1, CLL-1, CD33, EGFRvIII, GD2, GD3, BCMA, MUC16 (CA125), L1CAM, LeY, MSLN, IL13Rα1, L1-CAM, TnAg, prostate-specific membrane antigen (PSMA), ROR1, FLT3, FAP, TAG72, CD38, CD44v6, CEA, EPCAM, B7H3, KIT, interleukin-11 receptor α (IL-11Ra), PSCA, PRSS21, VEGFR2, Lewis Y, CD 24, platelet-derived growth factor receptor beta (PDGFR beta), SSEA-4, CD20, MUC1, NCAM, prostase, PAP, ELF2M, ephrin B2, IGF-1 receptor, CAIX, LMP2, gplOO, bcr-abl, telomerase, fucosyl GM1, sLe, GM3, TGS5, HMWMAA, o-acetyl-GD2, folate receptor beta, TEM1 / CD248, TEM7R, CLDN6, GPRC5D, CXORF61, CD97, CD179a, ALK, polysialic acid, PLACl, GloboH, NY-BR-1, UPK2,HAVCR1, ADRB3, PANX3, GPR20, LY6K, OR51E2, TARP, WT1, NY-ESO-1, LAGE-la, MAGE-A1, legumain, HPVE6, E7, ETV6-AML, sperm protein 17, XAGE1, Tie2, MAD-CT-1, MAD-CT-2, Fos-related antigen 1, p53, p53 mutant, prostein, survivin, telomerase, PCTA-1 / galectin 8, MelanA / MART1, Ras mutant, hTERT, sarcoma translocation breakpoint, ML-IAP, ERG (TMPRSS2ETS fusion gene), NA17, PAX3, androgen receptor, cyclin B1, MYCN, RhoC, TRP-2, CYPIBI, BORIS, SART3, PAX5, OY-T The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the antigen is selected from ES1, LCK, AKAP-4, SSX2, RAGE-1, human telomerase reverse transcriptase, RU1, RU2, intestinal carboxylesterase, muthsp70-2, CD79a, CD79b, CD72, LAIR1, FCAR, LILRA2, CD300LF, CLEC12A, BST2, EMR2, LY75, GPC3, FCRL5, IGLL1, neoantigens, CD133, CD15, CD184, CD24, CD56, CD26, CD29, CD44, HLA-A, HLA-B, HLA-C, (HLA-A, B, C)CD49f, CD151, CD340, CD200, tkrA, trkB, or trkC. 449. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome associates with and / or binds to a target cell or a surface feature of a target cell. 450. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof causes or is capable of causing secretion of a protein from a target cell or presentation of a ligand on the surface of a target cell. 451. The fusosome, fusosome composition, fusosome preparation, or method according to embodiment 450, wherein the fusosome and / or composition or preparation thereof causes or is capable of causing cell death of a target cell. 452. The fusosome, fusosome composition, fusosome preparation, or method according to embodiment 450 or 451, wherein the fusosome is derived from an NK source cell. 453. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of sensing and / or responding to, or transmitting and / or responding to, one or more features of the local environment, such as metabolites, interleukins, antigens, etc., or combinations thereof. 454. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of chemotaxis, extravasation, and / or one or more metabolic activities (e.g., kyneurinin, gluconeogenesis, prostaglandin fatty acid oxidation, adenosine metabolism, urea cycle, and thermogenic respiration). 455. The source cell is: a) neutrophils, and fusosomes and / or compositions or preparations thereof, can home to the site of injury; b) macrophages, and fusosomes and / or compositions or preparations thereof, are capable of phagocytosis, or c) A fusosome, fusosome composition, fusosome preparation, or method described in embodiment 454, wherein the brown adipose tissue cells, and the fusosomes and / or the composition or preparation thereof are capable of lipolysis. 456. Fusosomes are: a) the fusosomes fuse with target cells at a rate, e.g., at least at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% higher than with non-target cells, e.g., in the assay of Example 54; b) the fusosomes fuse with target cells at a rate, e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% higher than with other fusosomes, e.g., in the assay of Example 54; c) A fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, wherein the fusosomes fuse with target cells at a rate such that the agent in the fusosomes is delivered to at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the target cells after 24, 48, or 72 hours, e.g., in the assay of Example 54. 457. Fusosomes are: a) is present in at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies per fusosome, or less, as measured, for example, by the assay of Example 29; or b) The fusosomes, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes are present in a copy number of at least 1,000 copies, e.g., as measured by the assay of Example 29. 458. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% of the fusogens contained by the fusosome are located within the cell membrane. 459. The fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, wherein the fusosome also comprises a fusogen internally, for example within the cytoplasm or organelle. 460. Fusosomes are a) a therapeutic agent (e.g., a therapeutic membrane payload agent, nuclear payload agent, or organelle payload agent) at a copy number of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies per fusosome, or less, as measured, for example, by the assay of Example 43; b) a protein therapeutic at a copy number of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies or less, as measured, for example, by the assay of Example 43; c) nucleic acid therapeutic agents in a copy number of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies; d) DNA therapeutics in copy numbers of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies; e) RNA therapeutics in copy numbers of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies; f) a therapeutic agent that is exogenous to the source cells at a copy number of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies; g) a protein therapeutic that is exogenous to the source cells in a copy number of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies; and / or h) The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, comprising a nucleic acid (e.g., DNA or RNA) therapeutic that is exogenous to the source cell at a copy number of at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies. 461. The ratio of the copy number of the fusogen to the copy number of the therapeutic drug is 1,000,000:1 to 100,000:1, 100,000:1 to 10,000:1, 10,000:1 to 1,000:1, 1,000:1 to 100:1, 100:1 to 50:1, 50:1 to 20:1, 20:1 to 10:1, 10:1 to 5:1, 5:1 to 2:1, 2:1 to 1:1, 1:1 to 1:2, 1:2 or The fusosomes, fusosome composition, fusosome preparation, or method according to any of the preceding embodiments, wherein the concentration is 1:5, 1:5 to 1:10, 1:10 to 1:20, 1:20 to 1:50, 1:50 to 1:100, 1:100 to 1:1,000, 1:1,000 to 1:10,000, 1:10,000 to 1:100,000, or 1:100,000 to 1:1,000,000. 462. Fusosomes are a) at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies of a therapeutic agent (e.g., a therapeutic membrane payload agent, a nuclear payload agent, or an organelle payload agent); b) at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies of the protein therapeutic; c) at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies of the nucleic acid therapeutic agent; d) at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies of the RNA therapeutic; and / or e) A fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments that delivers at least 10, 50, 100, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000 copies of the DNA therapeutic to a target cell. 463. Fusosomes and / or compositions or preparations thereof a) 0.00000001 mg to 1 mg of fusogen per mg of total protein in the fusosome, for example, 0.00000001 to 0.0000001, 0.0000001 to 0.000001, 0.000001 to 0.0001, 0.00001 to 0.0001, 0.0001 to 0.001, 0.001 to 0.01, 0.01 to 0.1, or 0.1 to 1 mg of fusogen per mg of total protein in the fusosome, or b) A fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, comprising 0.00000001 mg to 5 mg of fusogen per mg of lipid in the fusosome, for example, 0.00000001 to 0.0000001, 0.0000001 to 0.000001, 0.000001 to 0.0001, 0.0001 to 0.001, 0.001 to 0.01, 0.01 to 0.1, 0.1 to 1, or 1 to 5 mg of fusogen per mg of lipid in the fusosome. 464. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes and / or composition or preparation thereof are characterized by a lipid composition substantially similar to that of the source cells, or wherein one or more of CL, Cer, DAG, HexCer, LPA, LPC, LPE, LPG, LPI, LPS, PA, PC, PE, PG, PI, PS, CE, SM, and TAG are within 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, e.g., 75%, of the corresponding lipid levels in the source cells. 465. Fusosomes and / or compositions or preparations thereof have a cardiolipin:ceramide ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:ceramide ratio in source cells, or a cardiolipin:diacylglycerol ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:diacylglycerol ratio in source cells, or a cardiolipin:hexosylceramide ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:hexosylceramide ratio in source cells, or a cardiolipin:lysophosphatidate ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:lysophosphatidate ratio in the source cells, or a cardiolipin:lysophosphatidylcholine ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:lysophosphatidylcholine ratio in the source cells, or a cardiolipin:lysophosphatidylethanolamine ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:lysophosphatidylethanolamine ratio in the source cells or a cardiolipin:lysophosphatidylglycerol ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:lysophosphatidylglycerol ratio in the source cells, or a cardiolipin:lysophosphatidylinositol ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:lysophosphatidylserine ratio in the source cells, or a cardiolipin:lysophosphatidylserine ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:lysophosphatidylserine ratio in the source cells. a ratio of cardiolipin:phosphatidylserine, or a ratio of cardiolipin:phosphatidate within 10%, 20%, 30%, 40%, or 50% of the ratio of cardiolipin:phosphatidate in the source cells, or a ratio of cardiolipin:phosphatidylcholine within 10%, 20%, 30%, 40%, or 50% of the ratio of cardiolipin:phosphatidylcholine in the source cells, or a ratio of cardiolipin:phosphatidylethanolamine within 10%, 20%, 30%, 40%, or 50% of the ratio of cardiolipin:phosphatidylethanolamine in the source cells,or a cardiolipin:phosphatidylglycerol ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:phosphatidylglycerol ratio in the source cells, or a cardiolipin:phosphatidylinositol ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:phosphatidylinositol ratio in the source cells, or a cardiolipin:phosphatidylserine ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:phosphatidylserine ratio in the source cells, and a cardiolipin:cholesterol ester ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:cholesterol ester ratio in the source cells, or a cardiolipin:sphingomyelin ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:sphingomyelin ratio in the source cells, or a cardiolipin:triacylglycerol ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:triacylglycerol ratio in the source cells, or a phosphatase activity in the source cells. a phosphatidylcholine: ceramide ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylcholine: diacylglycerol ratio in the source cells, or a phosphatidylcholine: hexosyl ... hexosylceramide ratio in the source cells, or a phosphatidylcholine: lysophosylceramide ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylcholine: hexosylceramide ratio in the source cells. a phosphatidylcholine:lysophosphatidate ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylcholine:lysophosphatidylcholine ratio in the source cells, or a phosphatidylcholine:lysophosphatidylethanolamine ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylcholine:lysophosphatidylethanolamine ratio in the source cells;or a phosphatidylcholine:lysophosphatidylglycerol ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylcholine:lysophosphatidylglycerol ratio in the source cells, or a phosphatidylcholine:lysophosphatidylinositol ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylcholine:lysophosphatidylserine ratio in the source cells. a phosphatidylcholine:lysophosphatidylserine ratio or a phosphatidylcholine:phosphatidylate ratio within 10%, 20%, 30%, 40%, or 50% of the cardiolipin:phosphatidylate ratio in the source cells, or a phosphatidylcholine:phosphatidylethanolamine ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylcholine:phosphatidylglycerol ratio in the source cells; is a cardiolipin:phosphatidylglycerol ratio within 50%, or a phosphatidylcholine:phosphatidylinositol ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylcholine:phosphatidylinositol ratio in the source cells, or a phosphatidylcholine:phosphatidylserine ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylcholine:phosphatidylserine ratio in the source cells, or a phosphatidylcholine:cholesterol ester ratio within 10%, 20%, 30% , a phosphatidylcholine:cholesterol ester ratio within 40% or 50%, or a phosphatidylcholine:sphingomyelin ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylcholine:sphingomyelin ratio in the source cells, or a phosphatidylcholine:triacylglycerol ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylcholine:triacylglycerol ratio in the source cells, or a phosphatidylethanolamine:ceramide ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylcholine:triacylglycerol ratio in the source cells,a phosphatidylethanolamine: ceramide ratio within 40% or 50%, or a phosphatidylethanolamine: diacylglycerol ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine: diacylglycerol ratio in the source cells, or a phosphatidylethanolamine: hexosylceramide ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine: hexosylceramide .... a phosphatidylethanolamine:lysophosphatidate ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine:lysophosphatidate ratio in the source cells, or a phosphatidylethanolamine:lysophosphatidylcholine ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine:lysophosphatidylcholine ratio in the source cells, or a phosphatidylethanolamine:lysophosphatidylcholine ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine:lysophosphatidylethanolamine ratio in the source cells a ratio of phosphatidylethanolamine:lysophosphatidylethanolamine, or a ratio of phosphatidylethanolamine:lysophosphatidylglycerol that is within 10%, 20%, 30%, 40%, or 50% of the ratio of phosphatidylethanolamine:lysophosphatidylglycerol in the source cells, or a ratio of phosphatidylethanolamine:lysophosphatidylinositol that is within 10%, 20%, 30%, 40%, or 50% of the ratio of phosphatidylethanolamine:lysophosphatidylinositol in the source cells; or a ratio of phosphatidylethanolamine:lysophosphatidylserine within 10%, 20%, 30%, 40% or 50% of the ratio of phosphatidylethanolamine:lysophosphatidylserine in the source cells, or a ratio of phosphatidylethanolamine:phosphatidate within 10%, 20%, 30%, 40% or 50% of the ratio of phosphatidylethanolamine:phosphatidate in the source cells, or 10%, 20%, 30% of the ratio of phosphatidylethanolamine:phosphatidylglycerol in the source cells,a phosphatidylethanolamine:phosphatidylglycerol ratio within 40% or 50%, a phosphatidylethanolamine:phosphatidylinositol ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine:phosphatidylinositol ratio in the source cells, or a phosphatidylethanolamine:phosphatidylserine ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine:phosphatidylserine ratio in the source cells, a phosphatidylethanolamine:cholesterol ester ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine:cholesterol ester ratio, or a phosphatidylethanolamine:sphingomyelin ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine:sphingomyelin ratio in the source cells, or a phosphatidylethanolamine:triacylglycerol ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylethanolamine:triacylglycerol ratio in the source cells. a phosphatidylethanolamine:triacylglycerol ratio, or a phosphatidylserine:ceramide ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylserine:diacylglycerol ratio in the source cells, or a phosphatidylserine:diacylglycerol ratio within 10%, 20%, 30%, 40% or 50% of the phosphatidylserine:hexosylceramide ratio in the source cells; a ratio of phosphatidylserine:hexosylceramide, or a ratio of phosphatidylserine:lysophosphatidate within 10%, 20%, 30%, 40%, or 50% of the ratio of phosphatidylserine:lysophosphatidate in the source cells, or a ratio of phosphatidylserine:lysophosphatidylcholine within 10%, 20%, 30%, 40%, or 50% of the ratio of phosphatidylserine:lysophosphatidylethanolamine in the source cells,a phosphatidylserine:lysophosphatidylethanolamine ratio within 40% or 50%, or a phosphatidylserine:lysophosphatidylglycerol ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylserine:lysophosphatidylglycerol ratio in the source cells, or a phosphatidylserine:lysophosphatidylinositol ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylserine:lysophosphatidylinositol ratio in the source cells; or a phosphatidylserine:lysophosphatidyl inositol ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylserine:lysophosphatidylserine ratio in the source cells, or a phosphatidylserine:phosphatidate ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylserine:phosphatidate ratio in the source cells, or a phosphatidylserine:phosphatidylate ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylserine:phosphatidylglycerol ratio in the source cells. a phosphatidylserine:phosphatidylglycerol ratio within 50%, or a phosphatidylserine:phosphatidylinositol ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylserine:phosphatidylinositol ratio in the source cells, or a phosphatidylserine:cholesterol ester ratio within 10%, 20%, 30%, 40%, or 50% of the phosphatidylserine:sphingomyelin ratio in the source cells, a phosphatidylserine:sphingomyelin ratio within 20%, 30%, 40% or 50% of the phosphatidylserine:triacylglycerol ratio in the source cells, or a sphingomyelin:ceramide ratio within 10%, 20%, 30%, 40% or 50% of the sphingomyelin:diacylglycerol ratio in the source cells; a sphingomyelin:diacylglycerol ratio within 0% or 50%, or a sphingomyelin:hexosylceramide ratio within 10%, 20%, 30%, 40%, or 50% of the sphingomyelin:hexosylceramide ratio in the source cells, or a sphingomyelin:lysophosphatidate ratio within 10%, 20%, 30%, 40%, or 50% of the sphingomyelin:lysophosphatidate ratio in the source cells, or 10%, 20%, 30% of the sphingomyelin:lysophosphatidylcholine ratio in the source cells,a ratio of sphingomyelin:lysophosphatidylcholine within 40% or 50%, or a ratio of sphingomyelin:lysophosphatidylethanolamine within 10%, 20%, 30%, 40% or 50% of the ratio of sphingomyelin:lysophosphatidylethanolamine in the source cells, or a ratio of sphingomyelin:lysophosphatidylglycerol within 10%, 20%, 30%, 40% or 50% of the ratio of sphingomyelin:lysophosphatidylglycerol in the source cells, or a ratio of sphingomyelin:lysophosphatidylethanolamine within 10%, 20%, 30%, 40% or 50% of the ratio of sphingomyelin:lysophosphatidylglycerol in the source cells a ratio of sphingomyelin:lysophosphatidylinositol within 10%, 20%, 30%, 40% or 50% of the ratio of lysophosphatidylinositol, or a ratio of sphingomyelin:lysophosphatidylserine within 10%, 20%, 30%, 40% or 50% of the ratio of sphingomyelin:lysophosphatidylserine in the source cells, or a ratio of sphingomyelin:phosphatidate within 10%, 20%, 30%, 40% or 50% of the ratio of sphingomyelin:phosphatidate in the source cells a sphingomyelin:phosphatidylglycerol ratio within 10%, 20%, 30%, 40% or 50% of the sphingomyelin:phosphatidylglycerol ratio in the source cells, or a sphingomyelin:phosphatidylinositol ratio within 10%, 20%, 30%, 40% or 50% of the sphingomyelin:phosphatidylinositol ratio in the source cells, or a sphingomyelin:cholesterol ester ratio within 10%, 20%, 30%, 40% or 50% of the sphingomyelin:cholesterol ester ratio in the source cells. a sphingomyelin:triacylglycerol ratio within 10%, 20%, 30%, 40%, or 50% of the sphingomyelin:triacylglycerol ratio in the source cells, or a cholesterol ester:ceramide ratio within 10%, 20%, 30%, 40%, or 50% of the cholesterol ester:ceramide ratio in the source cells, or a cholesterol ester:diacylglycerol ratio within 10%, 20%, 30%, 40%, or 50% of the cholesterol ester:diacylglycerol ratio in the source cells,or a cholesterol ester:hexosylceramide ratio that is within 10%, 20%, 30%, 40% or 50% of the cholesterol ester:hexosylceramide ratio in the source cells, or a cholesterol ester:lysophosphatidate ratio that is within 10%, 20%, 30%, 40% or 50% of the cholesterol ester:lysophosphatidate ratio in the source cells, or a cholesterol ester:lysophosphatidylcholine ratio that is within 10%, 20%, 30%, 40% or 50% of the cholesterol ester:lysophosphatidylcholine ratio in the source cells. a ratio of cholesterol esters:lysophosphatidylcholine, or a ratio of cholesterol esters:lysophosphatidylethanolamine within 10%, 20%, 30%, 40%, or 50% of the ratio of cholesterol esters:lysophosphatidylethanolamine in the source cells, or a ratio of cholesterol esters:lysophosphatidylglycerol within 10%, 20%, 30%, 40%, or 50% of the ratio of cholesterol esters:lysophosphatidyl inositol in the source cells, a cholesterol ester:lysophosphatidylinositol ratio within 20%, 30%, 40% or 50%, or a cholesterol ester:lysophosphatidylserine ratio within 10%, 20%, 30%, 40% or 50% of the cholesterol ester:lysophosphatidylserine ratio in the source cells, or a cholesterol ester:phosphatidate ratio within 10%, 20%, 30%, 40% or 50% of the cholesterol ester:phosphatidate ratio in the source cells, or a cholesterol ester:phosphatidate ratio within 10%, 20%, 30%, 40% or 50% of the cholesterol ester:phosphatidate ratio in the source cells or a cholesterol ester:phosphatidylglycerol ratio within 10%, 20%, 30%, 40% or 50% of the cholesterol ester:phosphatidylinositol ratio in the source cells, or a cholesterol ester:triacylglycerol ratio within 10%, 20%, 30%, 40% or 50% of the cholesterol ester:triacylglycerol ratio in the source cells.The fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments. 466. Fusosomes and / or compositions or preparations thereof a) a proteomic composition similar to that of the source cells, e.g., using the assay of Example 42; b) a lipid to protein ratio that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 49; c) a ratio of protein to nucleic acid (e.g., DNA or RNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 50; d) a protein to DNA ratio that is greater than the corresponding ratio in, e.g., at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or more than 90% of the source cells, e.g., as measured using the assay of Example 50; e) a ratio of protein to nucleic acid (e.g., DNA) that is within 10%, 20%, 30%, 40%, or 50% of the corresponding ratio in the source cells, as measured, for example, using the assay of Example 51; and / or f) A fusosome, fusosome composition, fusosome preparation, or method according to any of the preceding embodiments, characterized by a protein to DNA ratio that is greater than the corresponding ratio in, e.g., at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or more than 90% of the source cells, e.g., as measured using the assay of Example 51. 467. Fusosomes and / or compositions or preparations thereof a) a half-life within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% of the half-life of a reference cell, e.g., a source cell, in a subject, e.g., a mouse, e.g., by the assay of Example 75, or b) A fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, characterized by a half-life in a subject, e.g., a human subject or a mouse, of at least 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 12 hours, or 24 hours, e.g., by the assay of Example 75. 468. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof transports or is capable of transporting glucose (e.g., labeled glucose, e.g., 2-NBDG) across the membrane in the absence of glucose, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% more than a negative control, e.g., an otherwise similar fusosome, as measured, e.g., using the assay of Example 64. 469. Fusosomes and / or compositions or preparations thereof a) an esterase activity in the lumen that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the esterase activity in a reference cell, e.g., a source cell or a mouse embryonic fibroblast, using, e.g., the assay of Example 66; b) a metabolic activity level (e.g., citrate synthase activity) within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the metabolic activity level in a reference cell, e.g., a source cell, e.g., as described in Example 68; c) a metabolic activity level (e.g., citrate synthase activity) of at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the metabolic activity level in a reference cell, e.g., a source cell, e.g., as described in Example 68; d) a respiration level (e.g., oxygen consumption rate) within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the respiration level in a reference cell, e.g., a source cell, as described, for example, in Example 69; e) a respiration level (e.g., oxygen consumption rate) of at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the respiration level in reference cells, e.g., source cells, as described, e.g., in Example 69; and / or f) The fusosomes, fusomal composition, fusomal preparation, or method of any of the above embodiments, characterized by an annexin V staining level of at most 18,000, 17,000, 16,000, 15,000, 14,000, 13,000, 12,000, 11,000, or 10,000 MFI, e.g., using the assay of Example 70, or wherein the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% less than the annexin V staining level of otherwise similar fusosomes treated with menadione, or a composition or preparation thereof, in the assay of Example 70. 470. The fusosomes and / or composition or preparation thereof, the fusosomes, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes comprise an annexin V staining level that is at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% lower than the annexin V staining level of menadione-treated macrophages in the assay of Example 70. 471. Fusosomes and / or compositions or preparations thereof a) an miRNA content that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more than that of the source cells, e.g., by the assay of Example 39; b) a miRNA content level of at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of the miRNA content level of the source cells (e.g., up to 100% of the miRNA content level of the source cells), e.g., by the assay of Example 39; c) a total RNA content level of at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more (e.g., up to 100% of the total RNA content level of the source cells) as measured, for example, by the assay of Example 108; d) a soluble:insoluble protein ratio that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more of that of the source cells, e.g., within 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, or 80%-90% of that of the source cells, e.g., by the assay of Example 47; and / or e) A fusosome, fusosome composition, fusosome preparation, or method according to any of the preceding embodiments, characterized by an LPS level of less than 5%, 1%, 0.5%, 0.01%, 0.005%, 0.0001%, 0.00001%, or even less than the lipid content of the fusosomes, as measured, for example, by the assay of Example 48. 472. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of signaling, e.g., sending an extracellular signal, e.g., AKT phosphorylation in response to insulin, or uptake of glucose (e.g., labeled glucose, e.g., 2-NBDG), in response to insulin, to at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% more than a negative control, e.g., an otherwise similar fusosome, in the absence of insulin, e.g., using the assay of Example 63. 473. The fusosomes, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes, when administered to a subject, e.g., a mouse, target a tissue, e.g., liver, lung, heart, spleen, pancreas, gastrointestinal tract, kidney, testis, ovary, brain, reproductive organs, central nervous system, peripheral nervous system, skeletal muscle, endothelium, inner ear, or eye, and at least 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the fusosomes in the administered population of fusosomes are present in the target tissue 24, 48, or 72 hours later, e.g., by the assay of Example 87 or 100. 474. Fusosomes and / or compositions or preparations thereof a) a level of juxtacrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% greater than the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; b) a level of juxtacrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% (e.g., up to 100%) of the level of juxtacrine signaling induced by a reference cell, e.g., a source cell or bone marrow stromal cell (BMSC), e.g., by the assay of Example 71; c) a level of paracrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% greater than the level of paracrine signaling induced by a reference cell, e.g., a source cell or macrophage, e.g., by the assay of Example 72; d) a level of paracrine signaling that is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% (e.g., up to 100%) of the level of paracrine signaling induced by a reference cell, e.g., a source cell or macrophage, e.g., by the assay of Example 72; e) a level of polymerized actin that is within 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the level of polymerized actin in a reference cell, e.g., a source cell or a C2C12 cell, e.g., by the assay of Example 73; and / or f) For example, by the assay of Example 74, fusosomes and / or compositions or preparations thereof are characterized by or provided with a membrane potential within about 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% of the membrane potential of a reference cell, e.g., a source cell or a C2C12 cell, or within about -20 to -150 mV, -20 to - The fusosomes, fusosome composition, fusosome preparation, or method of any of the preceding embodiments, characterized by a membrane potential of 50 mV, -50 to -100 mV, or -100 to -150 mV, wherein the fusosomes have a membrane potential of less than -1 mV, -5 mV, -10 mV, -20 mV, -30 mV, -40 mV, -50 mV, -60 mV, -70 mV, -80 mV, -90 mV, or -100 mV. 475. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes and / or composition or preparation thereof are capable of extravasating from blood vessels at a rate that is at least 1%, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the extravasation rate of source cells, e.g., using the assay of Example 57, e.g., where the source cells are neutrophils, lymphocytes, B cells, macrophages, or NK cells, and optionally, the provided fusosomes and / or composition or preparation thereof are capable of chemotaxis, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% (e.g., up to 100%), compared to a reference cell, e.g., a macrophage, e.g., using the assay of Example 58. 476. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of phagocytosis, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% (e.g., up to 100%), compared to a reference cell, e.g., a macrophage, using, e.g., the assay of Example 60. 477. The fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, wherein the fusosome and / or composition or preparation thereof is capable of crossing a cell membrane, for example an endothelial cell membrane or the blood-brain barrier. 478. Fusosomes and / or compositions or preparations thereof a) secrete, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% more protein than a reference cell, e.g., a mouse embryonic fibroblast cell, using, e.g., the assay of Example 62; or b) A fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, which is capable of secreting protein at a greater percentage, e.g., at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% (e.g., up to 100%), compared to a reference cell, e.g., a mouse embryonic fibroblast, using, e.g., the assay of Example 62. 479. Fusosomes and / or compositions or preparations thereof a) is incapable of transcription or has less than 1%, 2.5%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the transcriptional activity of a reference cell, e.g., a source cell, e.g., using the assay of Example 19; or b) A fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, which is incapable of nuclear DNA replication or has nuclear DNA replication that is less than 1%, 2.5%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the nuclear DNA replication of a reference cell, e.g., a source cell, e.g., using the assay of Example 20. 480. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome and / or composition or preparation thereof lacks chromatin or has a chromatin content that is less than 1%, 2.5%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the chromatin content of a reference cell, e.g., a source cell, e.g., using the assay of Example 37. 481. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome, and / or composition or preparation thereof meets pharmaceutical or Good Manufacturing Practice (GMP) standards or is made in accordance with GMP. 482. Fusosomes and / or compositions or preparations thereof a) characterized by pathogen levels below a predetermined reference value, e.g., substantially free of pathogens; b) contains levels of contaminants (e.g., nuclear components such as nuclear DNA) below predetermined thresholds, e.g., is substantially free of one or more specified contaminants; and / or c) A fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, characterized by low immunogenicity, for example as described herein. 483. The source or target cell is an endothelial cell, a fibroblast, a blood cell (e.g., a macrophage, a neutrophil, a granulocyte, a leukocyte), a stem cell (e.g., a mesenchymal stem cell, an umbilical cord stem cell, a bone marrow stem cell, a hematopoietic stem cell, an induced pluripotent stem cell, e.g., an induced pluripotent stem cell derived from a subject's cells), an embryonic stem cell (e.g., a stem cell from an embryonic yolk sac, a placenta, an umbilical cord, a fetal skin, adolescent skin, blood, bone marrow, adipose tissue, erythropoietic tissue, hematopoietic tissue), a myoblast, a parenchymal cell (e.g., a hepatocyte), a lung alveolar cell, a neuron (e.g., a retinal neuron), a progenitor cell (e.g., a retinal progenitor cell, a myeloblast, a myeloid progenitor cell, a thymocyte, a meiocyte, a megakaryoblast, a promegakaryoblast, a melanocyte, a lymphoblast, a myeloid progenitor cell, a normoblast, or a hemangioblast), a progenitor cell (e.g., a cardiac progenitor cell, a satellite cell), a myoblast, a myeloblast, a myeloprogenitor cell ... , radial glial cells, bone marrow stromal cells, pancreatic progenitor cells, endothelial progenitor cells, blast cells), or immortalized cells (e.g., HeLa, HEK293, HFF-1, MRC-5, WI-38, IMR90, IMR91, PER.C6, HT-1080, or BJ cells), and optionally the source cell is other than a 293 cell, HEK cell, human endothelial cell, or human epithelial cell, a monocyte, a macrophage, a dendritic cell, or a stem cell, and optionally the source cell or target cell is selected from a neutrophil, a lymphocyte (e.g., a T cell, a B cell, a natural killer cell), a macrophage, a granulocyte, a mesenchymal stem cell, a bone marrow stem cell, an induced pluripotent stem cell, an embryonic stem cell, or a myeloblast. 484. Source cells are a) Cells grown under adherent or suspension conditions; b) primary cells, cultured cells, immortalized cells, or cell lines (e.g., myeloid blast cell lines, e.g., C2C12); c) allogeneic cells, e.g., obtained from a different organism of the same species as the target cells; d) autologous cells, e.g., obtained from the same organism as the target cells, or e) A fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, which is a heterologous cell, e.g., obtained from an organism of a different species than the target cell. 485. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the source cells comprise a second agent, e.g., a therapeutic agent, e.g., a protein or nucleic acid (e.g., RNA, e.g., mRNA or miRNA), that is exogenous to the source cells. 486. The second agent is at least 10, 20, 50, 100, 200, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 50,000,000, 100,000,000, 500,000,000, or 1,000,000,000. 486. The fusosome, fusosome composition, fusosome preparation, or method of embodiment 485, wherein the fusosomes are present at 0 copies or less, or are present at an average level of at least 10, 20, 50, 100, 200, 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000, 100,000, 200,000, 500,000, or 1,000,000 copies per fusosome or less. 487. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the target cell is within an organism, e.g., a primary cell isolated from the organism. 488. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the targeting domain interacts with a target cell moiety, e.g., a cell surface feature, on the target cell. 489. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome does not comprise said target cell moiety. 490. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosome comprises a fusogen that interacts with a fusogen-binding partner on a target cell, thereby enabling the fusosome to bind to or fuse with the target cell, and optionally the fusosome does not comprise said fusogen-binding partner. 491. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the targeting domain is not part of the fusogen, or the fusogen comprises a targeting domain. 492. The fusosome, fusosome composition, fusosome preparation, or method according to any of the above embodiments, wherein the fusogen-binding partner is a separate entity from, or is part of, the target cell moiety, or wherein the fusogen-binding partner is, or is part of, the target cell moiety. 493. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes enter the target cell by endocytosis, e.g., the level of an agent (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent, and optionally a second agent) delivered via the endocytic pathway is 0.01-0.6, 0.01-0.1, 0.1-0.3, or 0.3-0.6, e.g., using the assay of Example 91, or is at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more greater than chloroquine-treated reference cells contacted with similar fusosomes. 494. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the fusosomes in the fusosome composition or preparation that enter the target cell enter a non-endocytic pathway, e.g., the fusosomes enter the target cell via fusion with the cell surface, and optionally, at least 1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the fusosomes in the fusosome composition or preparation that enter the target cell enter the cytoplasm (e.g., do not enter endosomes or lysosomes). 495. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, or 1% of the fusosomes in the fusosome composition or preparation that enter the target cell enter endosomes or lysosomes. 496. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes enter the target cell by a non-endocytic pathway, e.g., the level of the delivered agent (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent, and optionally a second agent) is at least 90%, 95%, 98%, or 99% of the level in chloroquine-treated reference cells, e.g., using the assay of Example 91. 497. The fusosome, fusosome composition, fusosome preparation, or method of any of the above embodiments, wherein the fusosomes deliver an agent (e.g., a membrane payload agent, a nuclear payload agent, or an organelle payload agent, and optionally a second agent) to a target cell via a dynamin-mediated pathway, e.g., wherein the level of the agent (e.g., a membrane protein payload agent and / or a second agent) delivere...

Claims

[Claim 1] The invention described in the specification.

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