Antiviral compositions and methods of using the same

Abstract

The present disclosure provides antibody-drug conjugates or drug-Fc conjugates for treating and / or preventing an influenza viral infection in a subject in need thereof.

Description

Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ANTIVIRAL COMPOSITIONS AND METHODS OF USING THE SAME CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial Nos.63 / 690,257, filed September 3, 2024; 63 / 724,841, filed November 25, 2024; 63 / 738,219, filed December 23, 2024; and 63 / 818,527, filed June 5, 2025; the contents of which are hereby incorporated by reference in their entirety. REFERENCE TO AN ELECTRONIC SEQUENCE LISTING

[0002] The content of the electronic sequence listing (P0218.xml; Size: 146,770 bytes; and Date of Creation: August 15, 2025) is herein incorporated by reference in its entirety. BACKGROUND

[0003] Current flu vaccines face several limitations. Firstly, they are designed to target specific strains of the influenza virus prevalent in each flu season, necessitating annual updates to match circulating strains. However, their effectiveness can vary due to antigenic drift or shift, reducing their ability to provide broad protection. Additionally, the production of flu vaccines predominantly relies on egg-based methods, which can be time-consuming and pose challenges such as allergies and suboptimal growth of certain strains. Furthermore, the continuous evolution of flu viruses poses a perpetual challenge, necessitating ongoing research and development efforts to improve vaccine technology, surveillance, distribution, and uptake strategies to mitigate the impact of influenza.

[0004] Accordingly, methods for preventing and / or treating influenza viral infections are of utmost clinical importance. BACKGROUND

[0005] Current flu vaccines face several limitations. Firstly, they are designed to target specific strains of the influenza virus prevalent in each flu season, necessitating annual updates to match circulating strains. However, their effectiveness can vary due to antigenic drift or shift, reducing their ability to provide broad protection. Additionally, the production of flu vaccines predominantly relies on egg-based methods, which can be time-consuming and pose challenges such as allergies and suboptimal growth of certain strains. Furthermore, the continuous evolution of flu viruses poses a perpetual challenge, necessitating ongoing research and development efforts to improve vaccine technology, surveillance, distribution, and uptake strategies to mitigate the impact of influenza.

[0006] Accordingly, methods for preventing and / or treating influenza viral infections are of utmost clinical importance. 1Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT SUMMARY

[0007] Anti-influenza antibody-drug conjugates (ADCs) or drug-Fc conjugates (DFCs) could potentially offer several advantages in the fight against influenza. ADCs and DFCs can be designed to target specific components of the influenza virus, where the specificity could minimize off-target effects and maximize the effectiveness of the treatment. By coupling potent cytotoxic agents to antibodies, ADCs deliver cytotoxic agent directly to virus-infected cells, enhancing potency offering a more targeted approach to treatment, which could potentially reduce side effects compared to broad- spectrum antiviral drugs that affect both infected and healthy cells. Further, some strains of influenza virus may develop resistance over time, such that ADCs or DFCs with unique mechanisms of action could potentially overcome this resistance and provide an alternative treatment option.

[0008] The present disclosure, in one embodiment, provides a method of preventing an influenza viral infection in a subject in need thereof, comprising administering to the subject an effective amount of a conjugate as described herein. In one embodiment, provided is a method of treating an influenza viral infection in a subject in need thereof, comprising administering to the subject an effective amount of a conjugate as described herein. In some embodiments, the influenza is influenza A, influenza B, or a combination thereof.

[0009] In some embodiments, the conjugate is selected from Table 2, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof.

[0010] In one embodiment, provided is a conjugate of Formula I: I or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein: A is a polypeptide; each ;each L1is independently a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or 2Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; L2is a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each X2is independently cycloalkylene, heterocyclylene, heteroarylene, -O-, -S-, -NH-, or -C(O)-; wherein the cycloalkylene, heterocyclylene, heteroarylene are each optionally substituted; each L3is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each L4is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each m is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; and y is an integer from 1-20.

[0011] In some embodiments, y is from 5-15.

[0012] In some embodiments, the polypeptide is an anti-influenza antibody or antigen-binding fragment thereof. In some embodiments, the polypeptide is a human IgG antibody or a fragment thereof. In some embodiments, the IgG antibody is an IgG1 antibody. In some embodiments, the IgG1 3Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT antibody is an anti-SARS-CoV-2 antibody. In some embodiments, the IgG1 antibody is an anti- influenza antibody. In some embodiments, the anti-influenza antibody is an anti-hemagglutinin (HA) antibody. In some embodiments, the anti-SARS-CoV-2 antibody or the anti-influenza antibody is selected from Tables 3A-C. In some embodiments, the anti-influenza antibody comprises: i) a heavy chain variable region comprising a complementary determining region (CDR) H1 of SEQ ID NO: 7, a CDRH2 of SEQ ID NO: 8, a CDRH3 of SEQ ID NO: 9; and ii) a light chain variable region comprising a CDRL1 of SEQ ID NO: 10, a CDRL2 of SEQ ID NO: 11, and a CDRL3 of SEQ ID NO: 12. In some embodiments, the anti-influenza antibody comprises a heavy chain variable region of SEQ ID NO: 1 and a light chain variable region of SEQ ID NO: 2. In some embodiments, the anti- influenza antibody comprises: i) a heavy chain of SEQ ID NO: 5 and a light chain of SEQ ID NO: 4; or ii) a heavy chain of SEQ ID NO: 6 and a light chain of SEQ ID NO: 4. In some embodiments, the anti-influenza antibody comprises a heavy chain variable region comprising the sequence of SEQ ID NO: 33 and a light chain variable region comprising the sequence of SEQ ID NO: 23. In some embodiments, the anti-influenza antibody comprises a heavy chain comprising the sequence of SEQ ID NO: 34 and a light chain comprising the sequence of SEQ ID NO: 24. In some embodiments, the polypeptide comprises a human IgG Fc polypeptide that comprises an Fc fragment without an antigen-binding fragment. In some embodiments, the Fc polypeptide consists or consists essentially of a human IgG Fc fragment, a hinge, and at least part of a CH1 domain. In some embodiments, the IgG Fc polypeptide is an IgG1 Fc polypeptide. In some embodiments, the IgG Fc polypeptide comprises SEQ ID NO:137, 138, 139140, 141 or 142. In some embodiments, the IgG Fc polypeptide is a variant IgG Fc polypeptide. In some embodiments, the variant IgG Fc polypeptide comprises, consists, or consists essentially of SEQ ID NO: 140. In some embodiments, the variant IgG Fc polypeptide comprises, consists, or consists essentially of SEQ ID NO: 142. In some embodiments, the conjugate has a drug to antibody ratio (DAR) of about 5 to 15.

[0013] Also provided herein are pharmaceutical compositions comprising a conjugate as disclosed herein, e.g., of Formula I or IA, or a pharmaceutically acceptable salt or solvate thereof, and a pharmaceutically acceptable excipient, where the average drug to antibody ratio (DAR) of the conjugate in the composition is about 5 to 15. In some embodiments, the methods use a composition of a conjugate as disclosed herein where the DAR, LAR, or both, are a range (e.g., 1-15, 5-15, etc., as disclosed herein). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the figures, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the figures are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale and some of these elements are enlarged and positioned to improve figure legibility. Further, the shapes of the elements as drawn, are not 4Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT intended to convey any information regarding the actual shape of the particular elements and have been solely selected for ease of recognition in the figures.

[0015] FIG.1A-C show that the tested conjugates effectively neutralized vaccine isolates and resistant mutations.

[0016] FIG.2A-Dshow that the tested ADCs had remarkable breadth across panel of flu strains in enzymatic inhibition assay with live viruses (A and B), pseudoviruses (C) and viruses through evolution (D).

[0017] FIG.3 shows that the tested ADCs has broad activity against zoonotic flu strains.

[0018] FIG.4 shows that the tested ADCs had strong in vivo prophylactic efficacy against influenza challenges.

[0019] FIG.5 shows that the tested ADCs and DFC (drug-Fc conjugates) had strong in vivo prophylactic efficacy even at low doses.

[0020] FIG.6 shows that the ADCs retained the anti-HA activities of the antibodies and effectively prevented viral entry.

[0021] FIG.7A-B show that ADC with both flu vs. non-flu antibodies has strong in vivo activities.

[0022] FIG.8 shows that the ADCs fewer escape mutations on the neuraminidase.

[0023] FIG.9 shows the neutralization activities of tested ADCs, in comparison to naked antibodies and neuraminidase inhibitor (NAI) payloads.

[0024] FIG.10 shows the neutralization activities of the ADCs required the antibody’s binding specificity.

[0025] FIG.11 presents in vivo potency testing results of Flu_Ab ADC across multiple strains.

[0026] FIG.12 shows reduction of lung virus titers by each tested ADC.

[0027] FIG.13 shows the lung virus titer reduction curve for each tested ADC.

[0028] FIG.14 shows measurement of the neuraminidase inhibition (NAI) by each tested ADC. DETAILED DESCRIPTION Definitions

[0029] As used in the present specification, the following words, phrases and symbols are generally intended to have the meanings as set forth below, except to the extent that the context in which they are used indicates otherwise. 5Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0030] It is to be noted that the term “a” or “an” entity refers to one or more of that entity; for example, “an antibody,” is understood to represent one or more antibodies. As such, the terms “a” (or “an”), “one or more,” and “at least one” can be used interchangeably herein.

[0031] As used herein, the term “polypeptide” is intended to encompass a singular “polypeptide” as well as plural “polypeptides,” and refers to a molecule composed of monomers (amino acids) linearly linked by amide bonds (also known as peptide bonds). The term “polypeptide” refers to any chain or chains of two or more amino acids, and does not refer to a specific length of the product. Thus, peptides, dipeptides, tripeptides, oligopeptides, “protein,” “amino acid chain,” or any other term used to refer to a chain or chains of two or more amino acids, are included within the definition of “polypeptide,” and the term “polypeptide” may be used instead of, or interchangeably with any of these terms. The term “polypeptide” is also intended to refer to the products of post-expression modifications of the polypeptide, including without limitation glycosylation, acetylation, phosphorylation, amidation, derivatization by known protecting / blocking groups, proteolytic cleavage, or modification by non- naturally occurring amino acids. A polypeptide may be derived from a natural biological source or produced by recombinant technology, but is not necessarily translated from a designated nucleic acid sequence. It may be generated in any manner, including by chemical synthesis.

[0032] The term “isolated” as used herein with respect to cells, nucleic acids, such as DNA or RNA, refers to molecules separated from other DNAs or RNAs, respectively, that are present in the natural source of the macromolecule. The term “isolated” as used herein also refers to a nucleic acid or peptide that is substantially free of cellular material, viral material, or culture medium when produced by recombinant DNA techniques, or chemical precursors or other chemicals when chemically synthesized. Moreover, an “isolated nucleic acid” is meant to include nucleic acid fragments which are not naturally occurring as fragments and would not be found in the natural state. The term “isolated” is also used herein to refer to cells or polypeptides which are isolated from other cellular proteins or tissues. Isolated polypeptides is meant to encompass both purified and recombinant polypeptides.

[0033] As used herein, the term “recombinant” as it pertains to polypeptides or polynucleotides intends a form of the polypeptide or polynucleotide that does not exist naturally, a non-limiting example of which can be created by combining polynucleotides or polypeptides that would not normally occur together.

[0034] “Homology” or “identity” or “similarity” refers to sequence similarity between two peptides or between two nucleic acid molecules. Homology can be determined by comparing a position in each sequence which may be aligned for purposes of comparison. When a position in the compared sequence is occupied by the same base or amino acid, then the molecules are homologous at that 6Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT position. A degree of homology between sequences is a function of the number of matching or homologous positions shared by the sequences. An “unrelated” or “non-homologous” sequence shares less than 40% identity, though preferably less than 25% identity, with one of the sequences of the present disclosure.

[0035] A polynucleotide or polynucleotide region (or a polypeptide or polypeptide region) has a certain percentage (for example, 60 %, 65 %, 70 %, 75 %, 80 %, 85 %, 90 %, 95 %, 98 % or 99 %) of “sequence identity” to another sequence means that, when aligned, that percentage of bases (or amino acids) are the same in comparing the two sequences. This alignment and the percent homology or sequence identity can be determined using software programs known in the art, for example those described in Ausubel et al. eds. (2007) Current Protocols in Molecular Biology. Preferably, default parameters are used for alignment. One alignment program is BLAST, using default parameters. In particular, programs are BLASTN and BLASTP, using the following default parameters: Genetic code = standard; filter = none; strand = both; cutoff = 60; expect = 10; Matrix = BLOSUM62; Descriptions = 50 sequences; sort by = HIGH SCORE; Databases = non-redundant, GenBank + EMBL + DDBJ + PDB + GenBank CDS translations + SwissProtein + SPupdate + PIR. Biologically equivalent polynucleotides are those having the above-noted specified percent homology and encoding a polypeptide having the same or similar biological activity.

[0036] As used herein, an “antibody” or “antigen-binding polypeptide” refers to a polypeptide or a polypeptide complex that specifically recognizes and binds to an antigen. An antibody can be a whole antibody and any antigen binding fragment or a single chain thereof. Thus the term “antibody” includes any protein or peptide containing molecule that comprises at least a portion of an immunoglobulin molecule having biological activity of binding to the antigen. Examples of such include, but are not limited to a complementarity determining region (CDR) of a heavy or light chain or a ligand binding portion thereof, a heavy chain or light chain variable region, a heavy chain or light chain constant region, a framework (FR) region, or any portion thereof, or at least one portion of a binding protein.

[0037] The terms “antibody fragment” or “antigen-binding fragment”, as used herein, is a portion of an antibody such as F(ab')2, F(ab)2, Fab', Fab, Fv, scFv and the like. Regardless of structure, an antibody fragment binds with the same antigen that is recognized by the intact antibody. The term “antibody fragment” includes aptamers, spiegelmers, and diabodies. The term “antibody fragment” also includes any synthetic or genetically engineered protein that acts like an antibody by binding to a specific antigen to form a complex.

[0038] A “single-chain variable fragment” or “scFv” refers to a fusion protein of the variable regions of the heavy (VH) and light chains (VL) of immunoglobulins. In some aspects, the regions are connected with a short linker peptide of ten to about 25 amino acids. The linker can be rich in glycine 7Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT for flexibility, as well as serine or threonine for solubility, and can either connect the N-terminus of the VHwith the C-terminus of the VL, or vice versa. This protein retains the specificity of the original immunoglobulin, despite removal of the constant regions and the introduction of the linker. ScFv molecules are known in the art and are described, e.g., in US patent 5,892,019.

[0039] The term antibody encompasses various broad classes of polypeptides that can be distinguished biochemically. Those skilled in the art will appreciate that heavy chains are classified as gamma, mu, alpha, delta, or epsilon (γ, μ, α, δ, ε) with some subclasses among them (e.g., γ l- γ4). It is the nature of this chain that determines the “class” of the antibody as IgG, IgM, IgA IgG, or IgE, respectively. The immunoglobulin subclasses (isotypes) e.g., IgG1, IgG2, IgG3, IgG4, IgG5, etc. are well characterized and are known to confer functional specialization. Modified versions of each of these classes and isotypes are readily discernable to the skilled artisan in view of the instant disclosure and, accordingly, are within the scope of the instant disclosure. All immunoglobulin classes are clearly within the scope of the present disclosure, the following discussion will generally be directed to the IgG class of immunoglobulin molecules. With regard to IgG, a standard immunoglobulin molecule comprises two identical light chain polypeptides of molecular weight approximately 23,000 Daltons, and two identical heavy chain polypeptides of molecular weight 53,000-70,000. The four chains are typically joined by disulfide bonds in a “Y” configuration wherein the light chains bracket the heavy chains starting at the mouth of the “Y” and continuing through the variable region.

[0040] Antibodies, antigen-binding polypeptides, variants, or derivatives thereof of the disclosure include, but are not limited to, polyclonal, monoclonal, multispecific, human, humanized, primatized, or chimeric antibodies, single chain antibodies, epitope-binding fragments, e.g., Fab, Fab' and F(ab')2, Fd, Fvs, single-chain Fvs (scFv), single-chain antibodies, disulfide-linked Fvs (sdFv), fragments comprising either a VK or VH domain, fragments produced by a Fab expression library, and anti- idiotypic (anti-Id) antibodies (including, e.g., anti-Id antibodies to LIGHT antibodies disclosed herein). Immunoglobulin or antibody molecules of the disclosure can be of any type (e.g., IgG, IgE, IgM, IgD, IgA, and IgY), class (e.g., IgGl, IgG2, IgG3, IgG4, IgAl and IgA2) or subclass of immunoglobulin molecule.

[0041] Light chains are classified as either kappa or lambda (Κ, λ). Each heavy chain class may be bound with either a kappa or lambda light chain. In general, the light and heavy chains are covalently bonded to each other, and the “tail” portions of the two heavy chains are bonded to each other by covalent disulfide linkages or non-covalent linkages when the immunoglobulins are generated either by hybridomas, B cells or genetically engineered host cells. In the heavy chain, the amino acid sequences run from an N-terminus at the forked ends of the Y configuration to the C-terminus at the bottom of each chain. 8Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0042] Both the light and heavy chains are divided into regions of structural and functional homology. The terms “constant” and “variable” are used functionally. In this regard, it will be appreciated that the variable domains of both the light (VK) and heavy (VH) chain portions determine antigen recognition and specificity. Conversely, the constant domains of the light chain (CK) and the heavy chain (CH1, CH2 or CH3) confer important biological properties such as secretion, transplacental mobility, Fc receptor binding, complement binding, and the like. By convention the numbering of the constant region domains increases as they become more distal from the antigen- binding site or amino- terminus of the antibody. The N-terminal portion is a variable region and at the C-terminal portion is a constant region; the CH3 and CK domains actually comprise the carboxy- terminus of the heavy and light chain, respectively.

[0043] As indicated above, the variable region allows the antibody to selectively recognize and specifically bind epitopes on antigens. That is, the VK domain and VH domain, or subset of the complementarity determining regions (CDRs), of an antibody combine to form the variable region that defines a three dimensional antigen-binding site. This quaternary antibody structure forms the antigen-binding site present at the end of each arm of the Y. More specifically, the antigen-binding site is defined by three CDRs on each of the VH and VK chains (i.e. CDR-H1, CDR-H2, CDR-H3, CDR-L1, CDR-L2 and CDR-L3). In some instances, e.g., certain immunoglobulin molecules derived from camelid species or engineered based on camelid immunoglobulins, a complete immunoglobulin molecule may consist of heavy chains only, with no light chains. See, e.g., Hamers-Casterman et al., Nature 363:446-448 (1993).

[0044] In naturally occurring antibodies, the six “complementarity determining regions” or “CDRs” present in each antigen-binding domain are short, non-contiguous sequences of amino acids that are specifically positioned to form the antigen-binding domain as the antibody assumes its three dimensional configuration in an aqueous environment. The remainder of the amino acids in the antigen-binding domains, referred to as “framework” regions, show less inter-molecular variability. The framework regions largely adopt a β-sheet conformation and the CDRs form loops which connect, and in some cases form part of, the β -sheet structure. Thus, framework regions act to form a scaffold that provides for positioning the CDRs in correct orientation by inter-chain, non-covalent interactions. The antigen-binding domain formed by the positioned CDRs defines a surface complementary to the epitope on the immunoreactive antigen. This complementary surface promotes the non-covalent binding of the antibody to its cognate epitope. The amino acids comprising the CDRs and the framework regions, respectively, can be readily identified for any given heavy or light chain variable region by one of ordinary skill in the art, since they have been precisely defined (see “Sequences of Proteins of Immunological Interest,” Kabat, E., et al., U.S. Department of Health and Human Services, (1983); and Chothia and Lesk, J. MoI. Biol., 196:901-917 (1987)). 9Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0045] In the case where there are two or more definitions of a term which is used and / or accepted within the art, the definition of the term as used herein is intended to include all such meanings unless explicitly stated to the contrary. A specific example is the use of the term “complementarity determining region” (“CDR”) to describe the non-contiguous antigen combining sites found within the variable region of both heavy and light chain polypeptides. This particular region has been described by Kabat et al., U.S. Dept. of Health and Human Services, “Sequences of Proteins of Immunological Interest” (1983) and by Chothia et al., J. MoI. Biol.196:901-917 (1987), which are incorporated herein by reference in their entireties. The CDR definitions according to Kabat and Chothia include overlapping or subsets of amino acid residues when compared against each other. Nevertheless, application of either definition to refer to a CDR of an antibody or variants thereof is intended to be within the scope of the term as defined and used herein. The appropriate amino acid residues which encompass the CDRs as defined by each of the above cited references are set forth in the table below as a comparison. The exact residue numbers which encompass a particular CDR will vary depending on the sequence and size of the CDR. Those skilled in the art can routinely determine which residues comprise a particular CDR given the variable region amino acid sequence of the antibody. Kabat Chothia

[0046] Kabat et al. also defined a numbering system for variable domain sequences that is applicable to any antibody. One of ordinary skill in the art can unambiguously assign this system of “Kabat numbering” to any variable domain sequence, without reliance on any experimental data beyond the sequence itself. As used herein, “Kabat numbering” refers to the numbering system set forth by Kabat et al., U.S. Dept. of Health and Human Services, “Sequence of Proteins of Immunological Interest” (1983).

[0047] Throughout this application, amino acid numbers are according to Kabat numbering system, unless specified otherwise. 10Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0048] Antibodies disclosed herein may be from any animal origin including birds and mammals. Preferably, the antibodies are human, murine, donkey, rabbit, goat, guinea pig, camel, llama, horse, or chicken antibodies.

[0049] As used herein, the term “heavy chain constant region” includes amino acid sequences derived from an immunoglobulin heavy chain. A polypeptide comprising a heavy chain constant region comprises at least one of: a CH1 domain, a hinge (e.g., upper, middle, and / or lower hinge region) domain, a CH2 domain, a CH3 domain, or a variant or fragment thereof. For example, an antigen-binding polypeptide for use in the disclosure may comprise a polypeptide chain comprising a CH1 domain; a polypeptide chain comprising a CH1 domain, at least a portion of a hinge domain, and a CH2 domain; a polypeptide chain comprising a CH1 domain and a CH3 domain; a polypeptide chain comprising a CH1 domain, at least a portion of a hinge domain, and a CH3 domain, or a polypeptide chain comprising a CH1 domain, at least a portion of a hinge domain, a CH2 domain, and a CH3 domain. In another embodiment, a polypeptide of the disclosure comprises a polypeptide chain comprising a CH3 domain. Further, an antibody for use in the disclosure may lack at least a portion of a CH2 domain (e.g., all or part of a CH2 domain). As set forth above, it will be understood by one of ordinary skill in the art that the heavy chain constant region may be modified such that they vary in amino acid sequence from the naturally occurring immunoglobulin molecule.

[0050] The heavy chain constant region of an antibody disclosed herein may be derived from different immunoglobulin molecules. For example, a heavy chain constant region of a polypeptide may comprise a CH1 domain derived from an IgGlmolecule and a hinge region derived from an IgG3molecule. In another example, a heavy chain constant region can comprise a hinge region derived, in part, from an IgGlmolecule and, in part, from an IgG3molecule. In another example, a heavy chain portion can comprise a chimeric hinge derived, in part, from an IgGlmolecule and, in part, from an IgG4molecule.

[0051] As used herein, the term “light chain constant region” includes amino acid sequences derived from antibody light chain. Preferably, the light chain constant region comprises at least one of a constant kappa domain or constant lambda domain.

[0052] A “light chain-heavy chain pair” refers to the collection of a light chain and heavy chain that can form a dimer through a disulfide bond between the CL domain of the light chain and the CH1 domain of the heavy chain.

[0053] As previously indicated, the subunit structures and three dimensional configuration of the constant regions of the various immunoglobulin classes are well known. As used herein, the term “VH domain” includes the amino terminal variable domain of an immunoglobulin heavy chain and the term “CH1 domain” includes the first (most amino terminal) constant region domain of an 11Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT immunoglobulin heavy chain. The CH1 domain is adjacent to the VH domain and is amino terminal to the hinge region of an immunoglobulin heavy chain molecule.

[0054] As used herein the term “CH2 domain” includes the portion of a heavy chain molecule that extends, e.g., from about residue 244 to residue 360 of an antibody using conventional numbering schemes (residues 244 to 360, Kabat numbering system; and residues 231-340, EU numbering system; see Kabat et al., U.S. Dept. of Health and Human Services, “Sequences of Proteins of Immunological Interest” (1983). The CH2 domain is unique in that it is not closely paired with another domain. Rather, two N-linked branched carbohydrate chains are interposed between the two CH2 domains of an intact native IgG molecule. It is also well documented that the CH3 domain extends from the CH2 domain to the C-terminal of the IgG molecule and comprises approximately 108 residues.

[0055] As used herein, the term “hinge region” includes the portion of a heavy chain molecule that joins the CH1 domain to the CH2 domain. This hinge region comprises approximately 25 residues and is flexible, thus allowing the two N-terminal antigen-binding regions to move independently. Hinge regions can be subdivided into three distinct domains: upper, middle, and lower hinge domains (Roux et al., J. Immunol 161:4083 (1998)).

[0056] By “specifically binds” or “has specificity to,” it is generally meant that an antibody binds to an epitope via its antigen-binding domain, and that the binding entails some complementarity between the antigen-binding domain and the epitope. According to this definition, an antibody is said to “specifically bind” to an epitope when it binds to that epitope, via its antigen-binding domain more readily than it would bind to a random, unrelated epitope. The term “specificity” is used herein to qualify the relative affinity by which a certain antibody binds to a certain epitope. For example, antibody “A” may be deemed to have a higher specificity for a given epitope than antibody “B,” or antibody “A” may be said to bind to epitope “C” with a higher specificity than it has for related epitope “D.”

[0057] As used herein, the terms “treat” or “treatment” refer to both therapeutic treatment and prophylactic or preventative measures, wherein the object is to prevent or slow down (lessen) an undesired physiological change or disorder, such as the progression of cancer. Beneficial or desired clinical results include, but are not limited to, alleviation of symptoms, diminishment of extent of disease, stabilized (i.e., not worsening) state of disease, delay or slowing of disease progression, amelioration or palliation of the disease state, and remission (whether partial or total), whether detectable or undetectable. “Treatment” can also mean prolonging survival as compared to expected survival if not receiving treatment. Those in need of treatment include those already with the condition or disorder as well as those prone to have the condition or disorder or those in which the condition or disorder is to be prevented. 12Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0058] The term “preventing”, as used herein, is the prevention of the onset, recurrence or spread, in whole or in part, of the disease or condition as described herein, or a symptom thereof.

[0059] The “affinity” of an antibody for an antigen (e.g., IgE for purposes of the present disclosure) is expressed in terms of the KDof the antibody. The KDof an antibody refers to the equilibrium constant for the dissociation equilibrium of the antibody-antigen interaction, where KDis equal to kon / koff. The dissociation constant, KD, and affinity are inversely related; the greater the KDvalue for an antibody binding to an antigen, the weaker the binding affinity of that antibody to that antigen.

[0060] The binding properties of an antibody for a particular antigen may also be expressed in terms of the koffof the antibody. The koffof an antibody refers to the first-order rate constant for the dissociation of the antibody-antigen complex. Assuming a constant kon, a higher koffcorresponds to a higher KDand a lower affinity.

[0061] A dash (“-”) that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -C(O)NH2is attached through the carbon atom. A dash at the front or end of a chemical group is a matter of convenience; chemical groups may be depicted with or without one or more dashes without losing their ordinary meaning. A wavy line drawn through a line in a structure indicates a point of attachment of a group. Unless chemically or structurally required, no directionality is indicated or implied by the order in which a chemical group is written or named.

[0062] The prefix “Cu-v” indicates that the following group has from u to v carbon atoms. For example, “C1-6alkyl” indicates that the alkyl group has from 1 to 6 carbon atoms.

[0063] Reference to “about” a value or parameter herein includes (and describes) embodiments that are directed to that value or parameter per se. In certain embodiments, the term “about” includes the indicated amount ± 10%. In other embodiments, the term “about” includes the indicated amount ± 5%. In certain other embodiments, the term “about” includes the indicated amount ± 1%. Also, to the term “about X” includes description of “X”. Also, the singular forms “a” and “the” include plural references unless the context clearly dictates otherwise. Thus, e.g., reference to “the compound” includes a plurality of such compounds and reference to “the assay” includes reference to one or more assays and equivalents thereof known to those skilled in the art.

[0064] “Alkyl” refers to an unbranched or branched saturated hydrocarbon chain. As used herein, alkyl has 1 to 20 carbon atoms (i.e., C1-20alkyl), 1 to 8 carbon atoms (i.e., C1-8alkyl), 1 to 6 carbon atoms (i.e., C1-6alkyl), or 1 to 4 carbon atoms (i.e., C1-4alkyl). Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, pentyl, 2-pentyl, isopentyl, neopentyl, hexyl, 2-hexyl, 3-hexyl, and 3-methylpentyl. When an alkyl residue having a specific number of carbons is named by chemical name or identified by molecular formula, all positional isomers having that number of carbons may be encompassed; thus, for example, “butyl” includes n- 13Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT butyl (i.e. -(CH2)3CH3), sec-butyl (i.e. -CH(CH3)CH2CH3), isobutyl (i.e. -CH2CH(CH3)2) and tert- butyl (i.e. -C(CH3)3); and “propyl” includes n-propyl (i.e. -(CH2)2CH3) and isopropyl (i.e. -CH(CH3)2).

[0065] “Alkenyl” refers to an alkyl group containing at least one carbon-carbon double bond and having from 2 to 20 carbon atoms (i.e., C2-20alkenyl), 2 to 8 carbon atoms (i.e., C2-8alkenyl), 2 to 6 carbon atoms (i.e., C2-6alkenyl), or 2 to 4 carbon atoms (i.e., C2-4alkenyl). Examples of alkenyl groups include ethenyl, propenyl, butadienyl (including 1,2-butadienyl and 1,3-butadienyl).

[0066] “Alkynyl” refers to an alkyl group containing at least one carbon-carbon triple bond and having from 2 to 20 carbon atoms (i.e., C2-20alkynyl), 2 to 8 carbon atoms (i.e., C2-8alkynyl), 2 to 6 carbon atoms (i.e., C2-6alkynyl), or 2 to 4 carbon atoms (i.e., C2-4alkynyl). The term “alkynyl” also includes those groups having one triple bond and one double bond.

[0067] “Alkoxy” refers to the group “alkyl-O-”. Examples of alkoxy groups include methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, tert-butoxy, sec-butoxy, n-pentoxy, n-hexoxy, and 1,2- dimethylbutoxy.

[0068] “Haloalkyl” refers to an unbranched or branched alkyl group as defined above, wherein one or more hydrogen atoms are replaced by a halogen. For example, where a residue is substituted with more than one halogen, it may be referred to by using a prefix corresponding to the number of halogen moieties attached. Dihaloalkyl and trihaloalkyl refer to alkyl substituted with two (“di”) or three (“tri”) halo groups, which may be, but are not necessarily, the same halogen. Examples of haloalkyl include difluoromethyl (-CHF2) and trifluoromethyl (-CF3).

[0069] “Haloalkoxy” refers to an alkoxy group as defined above, wherein one or more hydrogen atoms are replaced by a halogen.

[0070] “Alkylthio” refers to the group “alkyl-S-”.

[0071] “Acyl” refers to a group -C(O)R, wherein R is hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroalkyl, or heteroaryl; each of which may be optionally substituted, as defined herein. Examples of acyl include formyl, acetyl, cyclohexylcarbonyl, cyclohexylmethyl-carbonyl, and benzoyl.

[0072] “Amido” refers to both a “C-amido” group which refers to the group -C(O)NRyRzand an “N- amido” group which refers to the group -NRyC(O)Rz, wherein Ryand Rzare independently selected from the group consisting of hydrogen, alkyl, aryl, haloalkyl, or heteroaryl; each of which may be optionally substituted.

[0073] “Amino” refers to the group -NRyRzwherein Ryand Rzare independently selected from the group consisting of hydrogen, alkyl, haloalkyl, aryl, or heteroaryl; each of which may be optionally substituted. 14Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0074] “Aryl” refers to an aromatic carbocyclic group having a single ring (e.g., monocyclic) or multiple rings (e.g., bicyclic or tricyclic) including fused systems. As used herein, aryl has 6 to 20 ring carbon atoms (i.e., C6-20aryl), 6 to 12 carbon ring atoms (i.e., C6-12aryl), or 6 to 10 carbon ring atoms (i.e., C6-10aryl). Examples of aryl groups include phenyl, naphthyl, fluorenyl, and anthryl. Aryl, however, does not encompass or overlap in any way with heteroaryl defined below. If one or more aryl groups are fused with a heteroaryl, the resulting ring system is heteroaryl. If one or more aryl groups are fused with a heterocyclyl, the resulting ring system is heterocyclyl.

[0075] “Carbamoyl” refers to both an “O-carbamoyl” group which refers to the group –O- C(O)NRyRzand an “N-carbamoyl” group which refers to the group -NRyC(O)ORz, wherein Ryand Rzare independently selected from the group consisting of hydrogen, alkyl, aryl, haloalkyl, or heteroaryl; each of which may be optionally substituted.

[0076] “Carboxyl ester” refers to both -OC(O)R and -C(O)OR, wherein R is hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroalkyl, or heteroaryl; each of which may be optionally substituted, as defined herein.

[0077] “Cycloalkyl” refers to a saturated or partially unsaturated cyclic alkyl group having a single ring or multiple rings including fused, bridged, and spiro ring systems. The term “cycloalkyl” includes cycloalkenyl groups (i.e. the cyclic group having at least one double bond). As used herein, cycloalkyl has from 3 to 20 ring carbon atoms (i.e., C3-20cycloalkyl), 3 to 12 ring carbon atoms (i.e., C3-12cycloalkyl), 3 to 10 ring carbon atoms (i.e., C3-10cycloalkyl), 3 to 8 ring carbon atoms (i.e., C3-8cycloalkyl), or 3 to 6 ring carbon atoms (i.e., C3-6cycloalkyl). Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

[0078] “Imino” refers to a group -C(NR)R, wherein each R is alkyl, cycloalkyl, heterocyclyl, aryl, heteroalkyl, or heteroaryl; each of which may be optionally substituted, as defined herein.

[0079] “Halogen” or “halo” includes fluoro, chloro, bromo, and iodo.

[0080] “Heteroalkyl” refers to an alkyl group in which one or more of the carbon atoms (and any associated hydrogen atoms) are each independently replaced with the same or different heteroatomic group. The term “heteroalkyl” includes unbranched or branched saturated chain having carbon and heteroatoms. By way of example, 1, 2 or 3 carbon atoms may be independently replaced with the same or different heteroatomic group. Heteroatomic groups include, but are not limited to, -NR-, -O-, -S-, -S(O)-, -S(O)2-, and the like, where R is H, alkyl, aryl, cycloalkyl, heteroalkyl, heteroaryl or heterocyclyl, each of which may be optionally substituted. Examples of heteroalkyl groups include - OCH3, -CH2OCH3, -SCH3, -CH2SCH3, -NRCH3, and -CH2NRCH3, where R is hydrogen, alkyl, aryl, arylalkyl, heteroalkyl, or heteroaryl, each of which may be optionally substituted. As used herein, heteroalkyl include 1 to 10 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms; and 1 to 3 heteroatoms, 1 to 2 heteroatoms, or 1 heteroatom. 15Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0081] “Heteroalkylene” refers to a divalent heteroalkyl group. “Heteroalkylene” groups must have at least one carbon and at least one heteroatomic group within the chain. The term “heteroalkylene” includes unbranched or branched saturated chain having carbon and heteroatoms. By way of example, 1, 2 or 3 carbon atoms may be independently replaced with the same or different heteroatomic group. Heteroatomic groups include, but are not limited to, -NRy-, -O-, -S-, -S(O)-, - S(O)2-, and the like, wherein Ryis hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclyl, aryl, heteroalkyl or heteroaryl; each of which may be optionally substituted, as defined herein. Examples of heteroalkylene groups include, e.g., -CH2OCH2-, -CH(CH3)OCH2-, -CH2CH2OCH2-, -OCH2-, -CH(CH3)O-, -CH2CH2O-, -CH2CH2OCH2CH2OCH2-, -CH2CH2OCH2CH2O-, -CH2SCH2-, -CH(CH3)SCH2-, -CH2CH2SCH2-, -CH2CH2SCH2CH2SCH2-, -SCH2-, -CH(CH3)S-, -CH2CH2S-, -CH2CH2SCH2CH2S-, -CH2S(O)2CH2-, -CH(CH3)S(O)2CH2-, -CH2CH2S(O)2CH2-, -CH2CH2S(O)2CH2CH2OCH2-, -CH2NRyCH2-, -CH(CH3)NRyCH2-, -CH2CH2NRyCH2-, -CH2CH2NRyCH2CH2NRyCH2-, etc., where Ryis hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclyl, aryl, heteroalkyl, or heteroaryl; each of which may be optionally substituted, as defined herein). As used herein, heteroalkylene includes 1 to 10 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms; and 1 to 3 heteroatoms, 1 to 2 heteroatoms, or 1 heteroatom. As used herein, the term “heteroalkylene” does not include groups such as amides or other functional groups having an oxo present on one or more carbon atoms.

[0082] “Heteroaryl” refers to an aromatic group having a single ring, multiple rings, or multiple fused rings, with one or more ring heteroatoms independently selected from nitrogen, oxygen, and sulfur. As used herein, heteroaryl includes 1 to 20 ring carbon atoms (i.e., C1-20heteroaryl), 3 to 12 ring carbon atoms (i.e., C3-12heteroaryl), or 3 to 8 carbon ring atoms (i.e., C3-8heteroaryl); and 1 to 5 heteroatoms, 1 to 4 heteroatoms, 1 to 3 ring heteroatoms, 1 to 2 ring heteroatoms, or 1 ring heteroatom independently selected from nitrogen, oxygen, and sulfur. Examples of heteroaryl groups include pyrimidinyl, purinyl, pyridyl, pyridazinyl, benzothiazolyl, and pyrazolyl. Examples of the fused-heteroaryl rings include, but are not limited to, benzo[d]thiazolyl, quinolinyl, isoquinolinyl, benzo[b]thiophenyl, indazolyl, benzo[d]imidazolyl, pyrazolo[1,5-a]pyridinyl, and imidazo[1,5- a]pyridinyl, where the heteroaryl can be bound via either ring of the fused system. Any aromatic ring, having a single or multiple fused rings, containing at least one heteroatom, is considered a heteroaryl regardless of the attachment to the remainder of the molecule (i.e., through any one of the fused rings). Heteroaryl does not encompass or overlap with aryl as defined above.

[0083] “Heterocyclyl” refers to a saturated or unsaturated cyclic alkyl group, with one or more ring heteroatoms independently selected from nitrogen, oxygen and sulfur. The term “heterocyclyl” includes heterocycloalkenyl groups (i.e. the heterocyclyl group having at least one double bond), bridged-heterocyclyl groups, fused-heterocyclyl groups, and spiro-heterocyclyl groups. A heterocyclyl may be a single ring or multiple rings wherein the multiple rings may be fused, bridged, 16Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT or spiro. Any non-aromatic ring containing at least one heteroatom is considered a heterocyclyl, regardless of the attachment (i.e., can be bound through a carbon atom or a heteroatom). Further, the term heterocyclyl is intended to encompass any non-aromatic ring containing at least one heteroatom, which ring may be fused to an aryl or heteroaryl ring, regardless of the attachment to the remainder of the molecule. As used herein, heterocyclyl has 2 to 20 ring carbon atoms (i.e., C2-20heterocyclyl), 2 to 12 ring carbon atoms (i.e., C2-12heterocyclyl), 2 to 10 ring carbon atoms (i.e., C2-10heterocyclyl), 2 to 8 ring carbon atoms (i.e., C2-8heterocyclyl), 3 to 12 ring carbon atoms (i.e., C3-12heterocyclyl), 3 to 8 ring carbon atoms (i.e., C3-8heterocyclyl), or 3 to 6 ring carbon atoms (i.e., C3-6heterocyclyl); having 1 to 5 ring heteroatoms, 1 to 4 ring heteroatoms, 1 to 3 ring heteroatoms, 1 to 2 ring heteroatoms, or 1 ring heteroatom independently selected from nitrogen, sulfur or oxygen. Examples of heterocyclyl groups include pyrrolidinyl, piperidinyl, piperazinyl, oxetanyl, dioxolanyl, azetidinyl, and morpholinyl. As used herein, the term “bridged- heterocyclyl” refers to a four- to ten-membered cyclic moiety connected at two non-adjacent atoms of the heterocyclyl with one or more (e.g., 1 or 2) four- to ten-membered cyclic moiety having at least one heteroatom where each heteroatom is independently selected from nitrogen, oxygen, and sulfur. As used herein, bridged- heterocyclyl includes bicyclic and tricyclic ring systems. Also used herein, the term “spiro-heterocyclyl” refers to a ring system in which a three- to ten-membered heterocyclyl has one or more additional ring, wherein the one or more additional ring is three- to ten-membered cycloalkyl or three- to ten- membered heterocyclyl, where a single atom of the one or more additional ring is also an atom of the three- to ten-membered heterocyclyl. Examples of the spiro-heterocyclyl rings include bicyclic and tricyclic ring systems, such as 2-oxa-7-azaspiro[3.5]nonanyl, 2-oxa-6-azaspiro[3.4]octanyl, and 6- oxa-1-azaspiro[3.3]heptanyl. Examples of the fused-heterocyclyl rings include, but are not limited to, 1,2,3,4-tetrahydroisoquinolinyl, 4,5,6,7-tetrahydrothieno[2,3-c]pyridinyl, indolinyl, and isoindolinyl, where the heterocyclyl can be bound via either ring of the fused system.

[0084] “Sulfonyl” refers to the group -S(O)2R, where R is alkyl, haloalkyl, heterocyclyl, cycloalkyl, heteroaryl, or aryl. Examples of sulfonyl are methylsulfonyl, ethylsulfonyl, phenylsulfonyl, and toluenesulfonyl.

[0085] “Alkylsulfonyl” refers to the group -S(O)2R, where R is alkyl.

[0086] “Alkylsulfinyl” refers to the group -S(O)R, where R is alkyl.

[0087] Certain commonly used alternative chemical names may be used. For example, a divalent group such as a divalent “alkyl” group, a divalent “aryl” group, etc., may also be referred to as an “alkylene” group or an “alkylenyl” group, an “arylene” group or an “arylenyl” group, respectively. Also, unless indicated explicitly otherwise, where combinations of groups are referred to herein as one moiety, e.g., arylalkyl, the last mentioned group contains the atom by which the moiety is attached to the rest of the molecule. 17Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0088] The terms “optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances in which it does not. Also, the term “optionally substituted” refers to any one or more hydrogen atoms on the designated atom or group may or may not be replaced by a moiety other than hydrogen.

[0089] As used herein, the term “compound,” is meant to include all stereoisomers, geometric isomers, tautomers, and isotopes of the structures depicted. Compounds herein identified by name or structure as one particular tautomeric form are intended to include other tautomeric forms unless otherwise specified.

[0090] Some of the compounds exist as tautomers. Tautomers are in equilibrium with one another. For example, amide containing compounds may exist in equilibrium with imidic acid tautomers. Regardless of which tautomer is shown, and regardless of the nature of the equilibrium among tautomers, the compounds are understood by one of ordinary skill in the art to comprise both amide and imidic acid tautomers. Thus, the amide containing compounds are understood to include their imidic acid tautomers. Likewise, the imidic acid containing compounds are understood to include their amide tautomers.

[0091] Any formula or structure given herein, is also intended to represent unlabeled forms as well as isotopically labeled forms of the compounds. Isotopically labeled compounds have structures depicted by the formulas given herein except that one or more atoms are replaced by an atom having a selected atomic mass or mass number. Examples of isotopes that can be incorporated into compounds of the disclosure include isotopes of hydrogen, carbon, nitrogen, oxygen, phosphorous, fluorine and chlorine, such as, but not limited to2H (deuterium, D),3H (tritium),11C,13C,14C,15N,18F,31P,32P,35S,36Cl and125I. Various isotopically labeled compounds of the present disclosure, for example those into which radioactive isotopes such as3H,13C and14C are incorporated. Such isotopically labelled compounds may be useful in metabolic studies, reaction kinetic studies, detection or imaging techniques, such as positron emission tomography (PET) or single-photon emission computed tomography (SPECT) including drug or substrate tissue distribution assays or in radioactive treatment of patients.

[0092] The disclosure also includes “deuterated analogs” of compounds of Formula I in which from 1 to n hydrogens attached to a carbon atom is / are replaced by deuterium, in which n is the number of hydrogens in the molecule. Such compounds exhibit increased resistance to metabolism and are thus useful for increasing the half-life of any compound of Formula I when administered to a mammal, particularly a human. See, for example, Foster, “Deuterium Isotope Effects in Studies of Drug Metabolism,” Trends Pharmacol. Sci.5(12):524-527 (1984). Such compounds are synthesized by 18Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT means well known in the art, for example by employing starting materials in which one or more hydrogens have been replaced by deuterium.

[0093] Deuterium labelled or substituted therapeutic compounds of the disclosure may have improved DMPK (drug metabolism and pharmacokinetics) properties, relating to distribution, metabolism and excretion (ADME). Substitution with heavier isotopes such as deuterium may afford certain therapeutic advantages resulting from greater metabolic stability, for example increased in vivo half-life, reduced dosage requirements and / or an improvement in therapeutic index. An18F labeled compound may be useful for PET or SPECT studies. Isotopically labeled compounds of this disclosure and prodrugs thereof can generally be prepared by carrying out the procedures disclosed in the schemes or in the examples and preparations described below by substituting a readily available isotopically labeled reagent for a non-isotopically labeled reagent. It is understood that deuterium in this context is regarded as a substituent in the compound of Formula I.

[0094] The concentration of such a heavier isotope, specifically deuterium, may be defined by an isotopic enrichment factor. In the compounds of this disclosure any atom not specifically designated as a particular isotope is meant to represent any stable isotope of that atom. Unless otherwise stated, when a position is designated specifically as “H” or “hydrogen”, the position is understood to have hydrogen at its natural abundance isotopic composition. Accordingly, in the compounds of this disclosure any atom specifically designated as a deuterium (D) is meant to represent deuterium.

[0095] In many cases, the compounds of this disclosure are capable of forming acid and / or base salts by virtue of the presence of amino and / or carboxyl groups or groups similar thereto.

[0096] Provided are also pharmaceutically acceptable salts, hydrates, solvates, tautomeric forms, polymorphs, and prodrugs of the compounds described herein. “Pharmaceutically acceptable” or “physiologically acceptable” refer to compounds, salts, compositions, dosage forms and other materials which are useful in preparing a pharmaceutical composition that is suitable for veterinary or human pharmaceutical use.

[0097] The term “pharmaceutically acceptable salt” of a given compound refers to salts that retain the biological effectiveness and properties of the given compound and which are not biologically or otherwise undesirable. “Pharmaceutically acceptable salts” or “physiologically acceptable salts” include, for example, salts with inorganic acids and salts with an organic acid. In addition, if the compounds described herein are obtained as an acid addition salt, the free base can be obtained by basifying a solution of the acid salt. Conversely, if the product is a free base, an addition salt, particularly a pharmaceutically acceptable addition salt, may be produced by dissolving the free base in a suitable organic solvent and treating the solution with an acid, in accordance with conventional procedures for preparing acid addition salts from base compounds. Those skilled in the art will recognize various synthetic methodologies that may be used to prepare nontoxic pharmaceutically 19Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT acceptable addition salts. Pharmaceutically acceptable acid addition salts may be prepared from inorganic and organic acids. Salts derived from inorganic acids include, e.g., hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid and the like. Salts derived from organic acids include, e.g., acetic acid, propionic acid, gluconic acid, glycolic acid, pyruvic acid, oxalic acid, malic acid, malonic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, p-toluene-sulfonic acid, salicylic acid, and the like. Likewise, pharmaceutically acceptable base addition salts can be prepared from inorganic and organic bases. Salts derived from inorganic bases include, by way of example only, sodium, potassium, lithium, aluminum, ammonium, calcium, and magnesium salts. Salts derived from organic bases include, but are not limited to, salts of NH3, or primary, secondary, tertiary amines, such as salts derived from a N-containing heterocycle, a N-containing heteroaryl, or derived from an amine of formula N(RN)3(e.g., HN+(RN)3or (alkyl)N+(RN)3) where each RNis independently hydrogen, alkyl, alkenyl, alkynyl, haloalkyl, cycloalkyl, heterocyclyl, aryl, or heteroaryl, wherein each is optionally substituted, such as by one or more (e.g., 1-5 or 1-3) substituents (e.g., halo, cyano, hydroxy, amino, alkyl, alkenyl, alkynyl, haloalkyl, alkoxy, or haloalkoxy). Specific examples of suitable amines include, by way of example only, isopropylamine, trimethyl amine, diethyl amine, tri(iso-propyl) amine, tri(n-propyl) amine, ethanolamine, 2- dimethylaminoethanol, piperazine, piperidine, morpholine, N-ethylpiperidine, and the like.

[0098] The term “substituted” means that any one or more hydrogen atoms on the designated atom or group is replaced with one or more substituents other than hydrogen, provided that the designated atom’s normal valence is not exceeded. The one or more substituents include, but are not limited to, alkyl, alkenyl, alkynyl, alkoxy, acyl, amino, amido, amidino, aryl, azido, carbamoyl, carboxyl, carboxyl ester, cyano, guanidino, halo, haloalkyl, haloalkoxy, heteroalkyl, heteroaryl, heterocyclyl, hydroxy, hydrazino, imino, oxo, nitro, alkylsulfinyl, sulfonic acid, alkylsulfonyl, thiocyanate, thiol, thione, or combinations thereof. Polymers or similar indefinite structures arrived at by defining substituents with further substituents appended ad infinitum (e.g., a substituted aryl having a substituted alkyl which is itself substituted with a substituted aryl group, which is further substituted by a substituted heteroalkyl group, etc.) are not intended for inclusion herein. Unless otherwise noted, the maximum number of serial substitutions in compounds described herein is three. For example, serial substitutions of substituted aryl groups with two other substituted aryl groups are limited to ((substituted aryl)substituted aryl) substituted aryl. Similarly, the above definitions are not intended to include impermissible substitution patterns (e.g., methyl substituted with 5 fluorines or heteroaryl groups having two adjacent oxygen ring atoms). Such impermissible substitution patterns are well known to the skilled artisan. When used to modify a chemical group, the term “substituted” may describe other chemical groups defined herein. Unless specified otherwise, where a group is described as optionally substituted, any substituents of the group are themselves unsubstituted. For 20Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT example, in some embodiments, the term “substituted alkyl” refers to an alkyl group having one or more substituents including hydroxyl, halo, alkoxy, cycloalkyl, heterocyclyl, aryl, and heteroaryl. In other embodiments, the one or more substituents may be further substituted with halo, alkyl, haloalkyl, hydroxyl, alkoxy, cycloalkyl, heterocyclyl, aryl, or heteroaryl, each of which is substituted. In other embodiments, the substituents may be further substituted with halo, alkyl, haloalkyl, alkoxy, hydroxyl, cycloalkyl, heterocyclyl, aryl, or heteroaryl, each of which is unsubstituted.

[0099] As used herein, “pharmaceutically acceptable carrier” or “pharmaceutically acceptable excipient” includes any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents and the like. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active ingredient, its use in the therapeutic compositions is contemplated. Supplementary active ingredients can also be incorporated into the compositions.

[0100] The term “therapeutic compound” as used herein is meant to include, without limitation, all compounds of Formula I, or pharmaceutically acceptable salts or solvates thereof, and compositions (e.g., pharmaceutical compositions) wherein a compound of Formula I, or a pharmaceutically acceptable salt or solvate thereof is a component of the composition.

[0101] The term “administration” or “administering” refers to a method of giving a dosage of a compound or pharmaceutical composition to a vertebrate or invertebrate, including a mammal, a bird, a fish, or an amphibian. The method of administration can vary depending on various factors, e.g., the components of the pharmaceutical composition, the site of the disease, and the severity of the disease.

[0102] The terms “effective amount” or “effective dosage” or “pharmaceutically effective amount” or “therapeutically effective amount,” as used herein, refer to a sufficient amount of a chemical entity (e.g., a compound of Formula I, or a pharmaceutically acceptable salt or solvate thereof) being administered which will relieve to some extent one or more of the symptoms of the disease or condition being treated, and can include curing the disease. “Curing” means that the symptoms of active disease are eliminated. The result includes reduction and / or alleviation of the signs, symptoms, or causes of a disease, or any other desired alteration of a biological system. For example, an “effective amount” for therapeutic uses is the amount of the composition comprising a compound as disclosed herein required to provide a clinically significant decrease in disease symptoms. An appropriate “effective” amount in any individual case is determined using any suitable technique, such as a dose escalation study. In some embodiments, a “therapeutically effective amount” of a compound as provided herein refers to an amount of the compound that is effective as a monotherapy or combination therapy.

[0103] The term “excipient” or “pharmaceutically acceptable excipient” means a pharmaceutically- acceptable material, composition, or vehicle, such as a liquid or solid filler, diluent, carrier, solvent, or 21Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT encapsulating material. In some embodiments, each component is “pharmaceutically acceptable” in the sense of being compatible with the other ingredients of a pharmaceutical formulation, and suitable for use in contact with the tissue or organ of humans and animals without excessive toxicity, irritation, allergic response, immunogenicity, or other problems or complications, commensurate with a reasonable benefit / risk ratio. See, e.g., Remington: The Science and Practice of Pharmacy, 21st ed.; Lippincott Williams & Wilkins: Philadelphia, PA, 2005; Handbook of Pharmaceutical Excipients, 6th ed.; Rowe et al., Eds.; The Pharmaceutical Press and the American Pharmaceutical Association: 2009; Handbook of Pharmaceutical Additives, 3rd ed.; Ash and Ash Eds.; Gower Publishing Company: 2007; Pharmaceutical Preformulation and Formulation, 2nd ed.; Gibson Ed.; CRC Press LLC: Boca Raton, FL, 2009.

[0104] The term “pharmaceutical composition” refers to a mixture of a compound of Formula I, or a pharmaceutically acceptable salt or solvate thereof as provided herein with other chemical components (referred to collectively herein as “excipients”), such as carriers, stabilizers, diluents, dispersing agents, suspending agents, and / or thickening agents. The pharmaceutical composition facilitates administration of the compound to an organism. Multiple techniques of administering a compound exist in the art including, but not limited to, rectal, oral, intravenous, aerosol, parenteral, ophthalmic, pulmonary, and topical administration.

[0105] The terms “subject”, “patient”, or “individual”, as used herein, are used interchangeably and refers to any animal, including mammals such as mice, rats, other rodents, rabbits, dogs, cats, swine, cattle, sheep, horses, primates, and humans. In some embodiments, the term refers to a subject, particularly a mammalian subject, for whom diagnosis, prognosis, or therapy is desired or needed. In some embodiments, the subject is a human. In some embodiments, the subject has experienced and / or exhibited at least one symptom of the disease, disorder, or condition to be treated and / or prevented.

[0106] The terms “treatment regimen” and “dosing regimen” are used interchangeably to refer to the dose and timing of administration of each therapeutic agent in a combination.

[0107] The term “combination therapy” as used herein refers to a dosing regimen of two different therapeutically active agents (i.e., the components or combination partners of the combination), wherein the therapeutically active agents are administered together or separately in a manner prescribed by a medical care taker or according to a regulatory agency as defined herein.

[0108] The term “modulate,” “modulating,” or “modulation,” as used herein, refers to a regulation or an adjustment (e.g., increase or decrease) and can include, for example agonism, partial agonism or antagonism. 22Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Peramivir-Polypeptide Conjugates

[0109] In one aspect, provided herein are polypeptide-drug conjugates for treating and / or preventing an influenza viral infection in a subject in need thereof. The conjugates described herein comprise an polypeptide (A), bound to a drug portion (e.g., peramivir), via a linker. In some embodiments, the polypeptide is an anti-influenza antibody or anti-influenza antibody fragment, for example an anti- hemagglutinin antibody or fragment thereof. In other embodiments, the polypeptide is an Fc polypeptide or fragment thereof, for example, a human IgG Fc polypeptide or fragment thereof.

[0110] Provided herein are antiviral compositions and methods of using the same. In some embodiments, conjugates (e.g., antibody-drug conjugates or ADCs, or Drug-Fc conjugates or DFCs) are provided that comprise (i) (a) an antibody or (b) Fc polypeptide conjugated to (ii) a compound comprising or consisting of an active component (i.e., “drug” represented by R1) that is capable of antiviral activity (e.g., in the context of the ADC or DFC and optionally outside the context of the ADC or DFC). In some embodiments, compounds are provided which are capable of antiviral activity and, in certain embodiments, are amenable to conjugation to a carrier molecule, e.g., to an antibody to form an ADC, or to an Fc polypeptide to form a DFC. In some embodiments, a compound comprises a modified form (e.g., a derivative) of a neuraminidase inhibitor. In some embodiments, a compound comprises a modified form (e.g., a derivative) of oseltamivir, zanamivir, laninamivir, or peramivir.

[0111] An antibody of a conjugate may, for example, have binding specificity for an antigen from an influenza A virus, an influenza B virus, or both, or a coronavirus (e.g., a SARS-CoV-2 virus). In some embodiments, a conjugate has antiviral activity against at least one respiratory virus. In some embodiments, a conjugate has antiviral activity against two or more respiratory viruses. In certain embodiments, a conjugate may possess antiviral activity against a first virus and against a second virus, wherein the first virus is a virus recognized by the antibody of the conjugate, and wherein compound (drug) of the conjugate has antiviral activity against the second virus. The antibody of a conjugate can have antiviral activity against its target, and the compound of the conjugate can have antiviral activity against its target.

[0112] In some embodiments, the conjugate is represented by Formula I: I or a stereoisomer, mixture o stereosomers, tautomer, or pharmaceutically acceptable salt thereof, wherein: A is a polypeptide, such as an antibody or antigen-binding fragment thereof, or a Fc fragment or a polypeptide that includes all or part of the Fc fragment; 23Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ; rising at least one alkylene, alkenylene, alkynylene,cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; L2is a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each X2is independently cycloalkylene, heterocyclylene, heteroarylene, -O-, -S-, -NH-, or -C(O)-; wherein the cycloalkylene, heterocyclylene, heteroarylene are each optionally substituted; each L3is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each L4is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each m is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; x is 1, 2, 3, 4, 5, or 6; and 24Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT y is an integer from 1-20.

[0113] As described herein, conjugates that comprise an antibody (i.e., A) can comprise various drug-to-antibody ratios (DARs) (i.e., the ratio of the total number of active small molecules (i.e., R1) attached to the antibody; DAR is typically reported as an average across the conjugate molecules within a sample), various linker-to-antibody ratios (LARs) (i.e., the total number of conjugations-to- linker sites per antibody; LAR may be reported as an average across the conjugate molecules within a sample), or both. In certain embodiments, two conjugate molecules may possess different DARs but the same LAR. In other embodiments, two conjugate molecules possess different LARs but the same – or different – DAR. In some embodiments, a DAR can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 21, 32, or greater. In some embodiments, DAR is 1-5, 6-10, 11-15, 16-20, 21-25, 26-30, 31-35, or greater than 35. In some embodiments, DAR is 1-8, 9-12, 13-18, 19-22, 23-28, 29-32, 33-38, or greater than 38.

[0114] In some embodiments, a LAR can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In some embodiments, LAR is 1-5, 6-10, 11-15, or 16-20. In some embodiments, LAR is 1- 8, 9-12, or 13-18.

[0115] In some embodiments, a ratio of drug molecules:linker molecules in a conjugate is 1:1, 2:1, 4:1, or greater. In certain embodiments, a conjugate can comprise: a LAR of 7 and a DAR of 7; a LAR of 4 and a DAR of 8; a LAR of 5 and a DAR of 10; a LAR of 6 and a DAR of 12; a LAR of 16 and a DAR of 32; or a LAR of 8 and a DAR of 32. In some embodiments, the conjugate has a LAR of 5 and a DAR of 10. In some embodiments, the conjugate has a LAR of 6 and a DAR of 12. A comparison of DAR to LAR in a conjugate may be expressed as DAR / LAR, for example, a conjugate comprising DAR 3 and LAR 3 has a DAR / LAR of 1. As another example, a conjugate comprising DAR 6 and LAR 3 has a DAR / LAR of 2. As yet another example, a conjugate comprising DAR 12 and LAR 3 has a DAR / LAR of 4.

[0116] DAR or LAR may be determined, for example, by intact mass spectrometry analysis of a de- glycosylated conjugate. The molecular weight of the small molecule and the antibody components are used to match each peak in the spectra to a DAR or LAR. In some embodiments, for the purposes of defining each batch of prepared conjugate, the DAR or LAR reported refers to the highest intensity peak of the mass distribution. In some embodiments, the DAR or LAR is reported as an average across the conjugate molecules within a sample. 25Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0117] In some embodiments, eac .

[0118] In some embodiments, eac mprising at least one alkylene orheteroalkylene; wherein each alkylene or heteroalkylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl.

[0119] In some embodiments, each L1is independently C2-10heteroalkylene; wherein each is independently optionally substituted with oxo.

[0120] In some embodiments, each L2is independently a linear linker.

[0121] In some embodiments, each L2is independently a branched linker.

[0122] In some embodiments, each L2is independently a bivalent linker or a trivalent linker.

[0123] As used herein, a “bivalent linker” refers to a contiguous chain of atoms that connects one peramivir moiety (one R1) to the antibody or antibody fragment (A). Unless otherwise stated, a bivalent linker may be optionally substituted. Exemplary bivalent linkers comprise one or more of the following linker fragments: ;wherein n is an integer greater than 0 (e.g., 1-10).

[0124] As used herein, a “trivalent linker” refers to a contiguous chain of atoms that includes a branching atom such that one linker connects two peramivir moieties (two R1) to the antibody or antibody fragment (A). Unless otherwise stated, a trivalent linker may be optionally substituted. Exemplary trivalent linkers include the following structures: ;wherein n is an integer greater than 0 (e.g., 1-10). 26Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0125] As used herein, a “tetravalent linker” refers to a contiguous chain of atoms that includes a branching atom such that one linker connects three peramivir moieties (three R1) to the antibody or antibody fragment (A). Unless otherwise stated, a tetravalent linker may be optionally substituted. Exemplary bivalent linkers include the following structures: ;

[0126] In some embodiments, each occurrence of L1independently comprises alkylene, triazolyl, -(CH2CH2O)-, -(OCH2CH2)-, -C(=O)NH- or -NHC(=O)-. In certain embodiments, each occurrence of L1is independently a bivalent linker or a trivalent linker.

[0127] In some embodiments, L1is a non-cleavable linker. The term “non-cleavable linker” refers to a linker that is covalently bound to two or more additional portions of the compound of Formula II (or subformula thereof) or conjugate of Formula I or IA that is not cleaved (i.e., no covalent bonds are broken) under normal physiological conditions. Generally, “normal physiological conditions” include a temperature ranging from about 20 to 40°C, an atmospheric pressure of about 1 atm (101 kPa or 14.7 psi), a pH of about 6 to 8, a glucose concentration of about 1 to 20 mM, atmospheric oxygen concentration, and earth gravity. In some embodiments, physiological conditions include the presence of enzymes (i.e., proteases, or nucleases).

[0128] In some embodiments, each occurrence of L1and L2are independently non-cleavable linkers. In some embodiments, each occurrence of L1, L2, and L3are independently non-cleavable linkers. In certain embodiments, L1, L2, L3, and L4are independently non-cleavable linkers.

[0129] In some embodiments, a contiguous chain of atoms connecting two or more portions of Formula I, IA, II, etc. (i.e., a linker such as L1, L2, L3, and L4) consists of carbon-carbon bonds, carbon-oxygen bonds, carbon-nitrogen bonds, wherein the chain of atoms can be linear or branched, and optionally substituted (e.g., oxo).

[0130] It is understood that a linker (e.g., L1, L2, L3, and L4) may also include other bond types (e.g., carbon-hydrogen, nitrogen-hydrogen, etc.) that are not part of the contiguous chain of atoms connecting two or more portions of the compound or conjugate.

[0131] In certain embodiments, each occurrence of L1independently comprises the following structure: 27Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCTeach occurrence of L1ais independently a direct bond or C1-C6alkylene.

[0132] In some embodiments, each occurrence of L1independently has the following structure:each occurrence of L1ais independently a direct bond or C1-C6alkylene.

[0133] In some embodiments, each occurrence of L1independently comprises the following structure:w ere n: each occurrence of L1bis independently alkylene or heteroalkylene.

[0134] In some embodiments, each occurrence of L1independently comprises the following structure: .

[0135] In some embodiments, each occurrence of L1independently has the following structure: .28Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0136] In some embodiments, each occurrence of L1independently comprises the following structure: .

[0137] f L1independently has the following structure: .

[0138] g g cates a range of “1-5”, the number range given include compounds where the variable is 1, 2, 3, 4, and 5. Similarly, in each foregoing embodiment which indicates a range of “1-20”, the number range of 1-20 includes a range from 1-15, 1-12, 1-10, 1-8, 1-5, and 1-3.

[0139] In some embodiments, each occurrence of L1independently comprises the following structure:wherein each occurrence of L1cis independently C1-C8alkylene.

[0140] In some embodiments, each occurrence of L1independently has the following structure:wherein each occurrence of L1cis independently C1-C8alkylene.

[0141] In some embodiments, each occurrence of L1independently comprises the following structure:29Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT wherein each occurrence of L1din independently C1-C8alkylene; and each occurrence of L1eis independently C1-C8alkylene, C1-C4heteroalkylene, or a direct bond.

[0142] In the foregoing embodiment, the number range of 1-20 includes a range from 1-15, 1-12, 1- 10, 1-8, 1-5, and 1-3.

[0143] In some embodiments, each occurrence of L1independently has the following structure:each occurrence of L1din independently C1-C8alkylene; and each occurrence of L1eis independently C1-C8 alkylene, C1-C4 heteroalkylene, or a direct bond.

[0144] In the foregoing embodiment, the number range of 1-20 includes a range from 1-15, 1-12, 1- 10, 1-8, 1-5, and 1-3.

[0145] In some embodiments, each occurrence of L1independently comprises the following structure: .

[0146] In the foregoing embodiment, the number range of 1-4 includes a range from 1-3 and 1-2. In the foregoing embodiment, the number range of 1-10 includes a range from 1-8, 1-7, 1-6, 1-5, 1-4, 1- 3, and 1-2.

[0147] In some embodiments, each occurrence of L1independently has the following structure: 30Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT .

[0148] of 1-4 includes a range from 1-3 and 1-2. In the foregoing embodiment, the number range of 1-10 includes a range from 1-8, 1-7, 1-6, 1-5, 1-4, 1- 3, and 1-2.

[0149] In some embodiments, each occurrence of L1independently comprises one of the following structures: ; ; ;31Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ;owing structures: ; ; ;32Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ; .1-3 and 1-2.

[0152] In some embodiments, each occurrence of L1independently has one of the following structures: ; ;33Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ; .structures: ; ; ;34Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ; .1-3 and 1-2.

[0155] In some embodiments, each occurrence of L1independently has one of the following structures: ; ; ;35Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ; .IA or, , , ptable salt thereof, wherein: A is a polypeptide, such as an antibody or antigen-binding fragment thereof, or a Fc fragment or a polypeptide that includes all or part of the Fc fragment; p is 0, 1, 2, 3, 4, 5, or 6; q is 0 or 1; r is 0, 1, 2, or 3; L2is a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or 36Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each X2is independently cycloalkylene, heterocyclylene, heteroarylene, -O-, -S-, -NH-, or -C(O)-; wherein the cycloalkylene, heterocyclylene, heteroarylene are each optionally substituted; each L3is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each L4is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each m is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; x is 1, 2, 3, 4, 5, or 6; and y is an integer from 1-20.

[0157] In certain embodiments, each occurrence of L2is independently a bivalent linker, a trivalent linker, a tetravalent linker, or a pentavalent linker. In some embodiments, each occurrence of L2is independently a bivalent linker or a trivalent linker. In certain specific embodiments, L2comprises alkylene, triazolyl, -C(=O)-, -(CH2CH2O)-, -(OCH2CH2)-, -C(=O)NH-, -NHC(=O)-, -NHC(=O)O-, -OC(=O)NH-, or -NHC(=O)NH-.

[0158] In some embodiments, L2comprises one of the following structures:wherein each occurrence of L2ais independently a direct bond or C1-C6alkylene.

[0159] In some embodiments, L2has the following structure: 37Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCTene.

[0160] In some embodiments, L2comprises following structure:L2bis independently C1-C6alkylene.

[0161] In some embodiments, L2comprises one of the following structures: ,6.

[0162] In the foregoing embodiment, the number range of 1-20 includes a range from 1-15, 1-12, 1- 10, 1-8, 1-5, and 1-3.

[0163] In some embodiments, L2has following structure:wherein L2bis C1-C6alkylene.

[0164] In some embodiments, L2has one of the following structures: ,wherein L2bis C1-C6alkylene. 38Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0165] In the foregoing embodiment, the number range of 1-20 includes a range from 1-15, 1-12, 1- 10, 1-8, 1-5, and 1-3.

[0166] In certain embodiments, L2has one of the following structures: or, ;

[0168] In some embodiments, L has one of the following structures: ;

[0169] In some embodiments, L2has one of the following structures: 39Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT .

[0170] 1-8, 1-7, 1-6, 1- 5, 1-4, and 1-3.

[0171] In some embodiments, each L2is independently C2-20heteroalkylene optionally substituted with oxo.

[0172] In some embodiments, the compound is represented by Formula IB: IBsalt thereof wherein: A is a polypeptide, such as an antibody or antigen-binding fragment thereof, or a Fc fragment or a polypeptide that includes all or part of the Fc fragment; p is 0, 1, 2, 3, 4, 5, or 6; q is 0 or 1; r is 0, 1, 2, or 3; L2ais N, NH, C(H)m-1or a 5-6 membered heteroarylene; s is 0 or 1; L2cis C2-20heteroalkylene; each X2is independently cycloalkylene, heterocyclylene, heteroarylene, -O-, -S-, -NH-, or -C(O)-; wherein the cycloalkylene, heterocyclylene, heteroarylene are each optionally substituted; 40Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT each L3is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each L4is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each m is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; x is 1, 2, 3, 4, 5, or 6; and y is an integer from 1-20.

[0173] In some embodiments, each X2is independently -O-, -S-, -NH-, -C(O)-, optionally substituted cycloalkyl, or optionally substituted heterocyclyl.

[0174] In some embodiments, each X2is independently optionally substituted cycloalkyl, or optionally substituted heterocyclyl.

[0175] In some embodiments, each X2is independently: ,eac n s n epen en y , , , , , , , , , or ; an each R2is independently fluoro, chloro, or bromo. 41Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0176] In some embodiments, each L3is a linker comprising one to three independently selected alkylene, cycloalkylene, or heteroalkylene, wherein each L3is independently optionally substituted with oxo.

[0177] In some embodiments, each L3is independently -O-, -S-, -NH-, or -C(O)-.

[0178] In some embodiments, x is 1.

[0179] In some embodiments, y is from 5-15.

[0180] In some embodiments, eac .

[0181] In some embodiments, eac ..42Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0184] In some embodiments, eac .

[0185] In some embodiments of Lnitrogen of the triazole portion of the molecule is to L2. In some embodiments, the covalent bond to the 8-membered ring portion of the molecule is to L2.

[0186] In some embodiments, each L3compris .

[0187] In some embodiments, eac .

[0188] In some embodiments, each L4; wherein each occurrence of R4ais independently alkylene or heteroayene.

[0189] In the foregoing embodiment, the number range of 1-20 includes a range from 1-15, 1-12, 1- 10, 1-8, 1-5, and 1-3.

[0190] In some embodiments, eac ; wherein each occurrence of L4b, L4c, and L4dare independently alkylene

[0191] In some embodiments, each occurrence of L4band L4care independently C1-C6alkylene. 43Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0192] In some embodiments, each occurrence of L4dhas the following structure .mbodiment, the number range of 1-20 includes a range from 1-15, 1-12, 1- 10, 1-8, 1-5, and 1-3. ,, ,

[0196] In the foregoing embodiment, the number range of 0-20 includes a range from 0-15, 0-12, 0- 10, 0-8, 0-5, and 0-3. In the foregoing embodiments, the number range of 0-20 includes a range from 1-15, 1-12, 1-10, 1-8, 1-5, and 1-3. 44Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT , ,

[0098] In t e oregong embod ment, t e number range o 0- 0 nc udes a range rom 0- 5, 0- , 0- 10, 0-8, 0-5, and 0-3. In the foregoing embodiments, the number range of 0-20 includes a range from 1-15, 1-12, 1-10, 1-8, 1-5, and 1-3.

[0199] In some embodiments, eac .

[0200] In some embodiments, L4is connected to A via an amide bond. In some embodiments, L4is connected to A via an amide bond wherein the nitrogen of the amide bond is from a lysine of the antibody’s amino acid sequence.

[0201] In some embodiments, each occurrence of n is 1. 45Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0202] In certain embodiments, each occurrence of n is 1. In some embodiments, at least one occurrence of n is 1. In some embodiments, each occurrence of n is 2. In some embodiments, at least one occurrence of n is 2. In some embodiments, each occurrence of n is 3. In some embodiments, at least one occurrence of n is 3. In some embodiments, each occurrence of n is 4. In some embodiments, at least one occurrence of n is 4.

[0203] In some embodiments, each occurrence of n is 1 and each occurrence of L1is a divalent linker. In certain embodiments of Structure (II), each occurrence of n is 2 and each occurrence of L1is a trivalent linker. In some embodiments, each occurrence of n is 3 and each occurrence of L1is a tetravalent linker. In some embodiments, each occurrence of n is 4 and each occurrence of L1is a pentavalent linker.

[0204] In some embodiments, at least one occurrence of m is 1. In some embodiments, each occurrence of m is 1. In some embodiments, at least one occurrence of m is 2. In some embodiments, each occurrence of m is 2. In some embodiments, at least one occurrence of m is 3. In some embodiments, each occurrence of m is 3. In some embodiments, at least one occurrence of m is 4. In some embodiments, each occurrence of m is 4. In some embodiments, at least one occurrence of m is 5, 6, 7, 8, 9, or 10. In some embodiments, each occurrence of m is 5, 6, 7, 8, 9, or 10.

[0205] In some embodiments, each occurrence of m is 1 and each occurrence of L2is a divalent linker. In some embodiments, each occurrence of m is 2 and each occurrence of L2is a trivalent linker. In some embodiments, each occurrence of m is 3 and each occurrence of L2is a tetravalent linker. In some embodiments, each occurrence of m is 3 and each occurrence of L2is a pentavalent linker.

[0206] In some embodiments, each occurrence of L3is a divalent linker. In some embodiments, each occurrence of L3is a trivalent linker. In some embodiments, each occurrence of L3is a tetravalent linker.

[0207] In some embodiments, at least one occurrence of x is 1. In some embodiments, each occurrence of x is 1. In some embodiments, at least one occurrence of x is 2. In some embodiments, each occurrence of x is 2. In some embodiments, at least one occurrence of x is 3. In some embodiments, each occurrence of x is 3. In some embodiments, at least one occurrence of x is 4. In some embodiments, each occurrence of x is 4. In some embodiments, at least one occurrence of x is 5, 6, 7, 8, 9, or 10. In some embodiments, each occurrence of x is 5, 6, 7, 8, 9, or 10.

[0208] In some embodiments, each occurrence of x is 1 and each occurrence of L4is a divalent linker. In some embodiments, each occurrence of x is 2 and each occurrence of L4is a trivalent linker. 46Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT In some embodiments, each occurrence of x is 3 and each occurrence of L4is a tetravalent linker. In some embodiments, each occurrence of x is 3 and each occurrence of L4is a pentavalent linker.

[0209] In some embodiments, y is 1, y is 2, y is 3, y is 4, or y is 5. In some embodiments, y is 6, y is 7, y is 8, y is 9, or y is 10. In some embodiments, y is 11, y is 12, y is 13, y is 14, or y is 15. In some embodiments, y is 16, y is 17, y is 18, y is 19, or y is 20. In some embodiments, y is 4, 6, 8, 10, 12, 14 or 16.

[0210] In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 0.1 to 10. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 10 to 20. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 0.1 to 5. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 5 to 10. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 10 to 15. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 15 to 20.

[0211] In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 1 to 3. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 3 to 5. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 5 to 7. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 7 to 9. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 9 to 11. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 11 to 13. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 13 to 15. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 15 to 17. In some embodiments, a plurality of conjugates of Formula I or IA have an average y ranging from 17 to 19.

[0212] A conjugate may comprise a variable number of occurrences of R1for a given combination of the variables n, m, x, and y. For example, if n is 2, m is 1, x is 2, and y is 2, the number of occurrences of R1for the conjugate would be 8. A DAR would then be expressed as 8:1 (expressing the ratio of molecules of antiviral drug, R1relative to molecule of antibody).

[0213] Additionally, a ratio of the number of linker units per antibody or LAR is expressed as the variable “y”. In the aforementioned example, a LAR would be expressed as 2:1 (i.e., the ratio of linker-drug molecules relative to the antibody).

[0214] In some embodiments, an individual conjugate has a DAR of 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, or more. In a composition or sample comprising a plurality of conjugates, 47Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT the DAR may vary between one conjugate and another, such that an average DAR of the total conjugates present in the composition or sample may be expressed; e.g., a DAR of 6:1, or a DAR of 6.8:1, or a DAR of 7.4:1. Thus, an average DAR can be expressed as a non-integer value, and the DARs of individual conjugates within a sample may be present in a range; e.g., from 5 to 7, or from 5 to 6, or from 6 to 7. In some embodiments, DAR is 1-5, 6-10, 11-15, 16-20, 21-25, 26-30, 31-35, or greater than 35. In some embodiments, DAR is 1-8, 9-12, 13-18, 19-22, 23-28, 29-32, 33-38, or greater than 38.

[0215] In some embodiments, a composition comprises conjugates of Formula I or IA and the DAR is expressed as an average of the conjugates present in the composition. Accordingly, in some embodiments, the average DAR for a plurality of conjugates ranges from 9.5 to 12.5, from 10 to 12, or from 10.5 to 11.5. In certain embodiments, the average DAR for a plurality of conjugates is 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8.9.9, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, or 13.0.

[0216] In some embodiments, a conjugate of Formula I or IA includes an unbranched or linear linker. That is, in some embodiments, a composition comprises conjugates of Formula I or IA the LAR is expressed as an average of the conjugates present in the composition. Accordingly, in some embodiments, the LAR is the same as the average DAR for a plurality of conjugates. In some embodiments, the average LAR for a plurality of conjugates ranges from 9.5 to 12.5, from 10 to 12, or from 10.5 to 11.5. In certain embodiments, the average LAR for a plurality of conjugates is 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8.9.9, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, or 13.0.

[0217] In some embodiments, the conjugates of Formula I or IA have a branched linker that includes two drug molecules attached to each linker moiety. That is, in some embodiments, the LAR is half the average DAR for a plurality of conjugates. More specifically, in some embodiments, the average LAR for a plurality of conjugates ranging from 4.75 to 6.25, from 5 to 6, or from 5.25 to 6.75. In some embodiments, the average LAR for a plurality of conjugates is 4.5, 4.55, 4.6, 4.65, 4.7, 4.75, 4.8, 4.85, 4.9, 4.95, 5.0, 5.05, 5.1, 5.15, 5.2, 5.25, 5.3, 5.35, 5.4, 5.45, 5.5, 5.55, 5.6, 5.65, 5.7, 5.75, 5.8, 5.85, 5.9, 5.95, 6.0, 6.05, 6.1, 6.15, 6.2, 6.25, 6.3, 6.35, 6.4, 6.45, or 6.5.

[0218] In some embodiments, the DAR for a plurality of conjugates ranging from 9.5 to 12.5, from 10 to 12, or from 10.5 to 11.5 and the LAR for the plurality of conjugates ranging from 4.75 to 6.25, from 5 to 6, or from 5.25 to 6.75, respectively. Additionally, in some embodiments, the average DAR for a plurality of conjugates is 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8.9.9, 10.0, 10.1, 10.2, 10.3, 10.4, 48Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, or 13.0 and the average LAR for the plurality of conjugates is 4.5, 4.55, 4.6, 4.65, 4.7, 4.75, 4.8, 4.85, 4.9, 4.95, 5.0, 5.05, 5.1, 5.15, 5.2, 5.25, 5.3, 5.35, 5.4, 5.45, 5.5, 5.55, 5.6, 5.65, 5.7, 5.75, 5.8, 5.85, 5.9, 5.95, 6.0, 6.05, 6.1, 6.15, 6.2, 6.25, 6.3, 6.35, 6.4, 6.45, or 6.5, respectively.

[0219] In some embodiments, the DAR ranges from 9 to 12 and the LAR ranges from 1.5 to 3.5 for a plurality of conjugates. In some embodiments, the DAR is 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8.9.9, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, or 13.0 and the average LAR for the plurality of conjugates is 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.5 for a plurality of conjugates.

[0220] One embodiment provides a composition comprising a plurality of conjugates, each conjugate being described by Formula I or IA. In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 1:1 to about 50:1. In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 1:1 to about 40:1. In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 1:1 to about 32:1. In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 1:1 to about 16:1. In certain embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 1:1 to about 8:1. In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 1:1 to about 4:1. In certain embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 1:1 to about 2:1

[0221] In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 2:1 to about 50:1, from about 2:1 to about 40:1, from about 2:1 to about 30:1, from about 2:1 to about 20:1, from about 2:1 to about 10:1, or from about 2:1 to about 5:1.

[0222] In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 3:1 to about 55:1, from about 3:1 to about 45:1, from about 3:1 to about 35:1, from about 3:1 to about 25:1, from about 3:1 to about 15:1, or from about 3:1 to about 7.5:1. In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 9.5:1 to about 12.5:1, from about 10:1 to about 12:1, or from about 10.5:1 to about 11.5:1. In some embodiments, the plurality of conjugates has an average ratio of R1to A ranging from 10:1 to 12:1.

[0223] In some embodiments, the plurality of conjugates have an average ratio of R1to A ranging from about 4:1 to about 42:1, from about 4:1 to about 37:1, from about 4:1 to about 32:1, from about 49Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 4:1 to about 27:1, from about 4:1 to about 22:1, from about 4:1 to about 17:1, or from about 4:1 to about 12:1.

[0224] In some embodiments, the plurality of conjugates have an average y ranging from about 1-50, 1-25, 1-20, 1-15, 1-10, 1-5, 2-45, 2-30, 2-22, 2-17, 2-12, 2-7, 3-8, 3-9, 3-14, 3-19, 3-27, 3-35, 3-37, 3- 42, 4-6, or 4-16. In certain embodiments, the plurality of conjugates have an average y ranging from about 4-8. In some embodiments, the plurality of conjugates have an average y ranging from about 4- 6. In some embodiments, the plurality of conjugates has an average y ranging from about 5-6. In some embodiments, the plurality of conjugates has an average y of 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, or 6.5. In some embodiments, the plurality of conjugates have an average y ranging from 0.5-2.5. In some embodiments, the plurality of conjugates have an average y ranging from 0.75-2.25. Peramivir-Linker Compounds

[0225] The conjugates disclosed herein can be prepared using a peramivir-linker compound and a suitably functionalized antibody, such that upon contact under suitable reaction conditions, at least one peramivir-linker compound is covalently bonded to the functionalized antibody. Thus, in one aspect, provided herein are peramivir-linker compounds, as well as precoursers thereof.

[0226] In one aspect, provided herein is a compound of Formula II: II or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof; wherein: each ; eachp y y g C1-4alkyl; each L1is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally 50Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; L2is a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4 alkyl, C1-4 alkoxy, and C1-4 haloalkyl; X1is cycloalkynyl, heterocyclylalkynyl, alkynyl, -OH, -SH, -N3, -NH2, an activated ester, or maleimide; wherein the cycloalkynyl, heterocyclylalkynyl, alkynyl, activated ester, or maleimide are each optionally substituted; and m is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0227] In some embodiments, each R1is: .

[0228] In some embodiments, eacer comprising at least one alkylene or heteroalkylene; wherein each alkylene or heteroalkylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl.

[0229] In some embodiments, each L1is independently C5-10heteroalkylene; wherein each is independently optionally substituted with oxo.

[0230] In some embodiments, L1is represented by -L1a-L1b-L1c-; wherein: L1ais a bond, -O-, -S-, -NH-, C1-8alkylene, C2-15heteroalkylene, C2-8alkenylene, C2-8alkynylene, or C3-8cycloalkylene; L1bis -O-, -S-, -NH-, -NHC(O)-, -NHC(O)NH-, -NHC(O)O-, C1-6alkylene, C2-15heteroalkylene, C2-8alkenylene, C2-8alkynylene, C3-8cycloalkylene, a 4-8 membered heterocyclylene, C6arylene, or a 5-6 membered heteroarylene; and L1cis a bond, -O-, -S-, -NH-, C1-8alkylene, or C2-15heteroalkylene; 51Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT wherein each alkylene, heteroalkylene, alkenylene, alkynylene, cycloalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl.

[0231] In some embodiments, the compound is represented by Formula IIA: IA or a sterely acceptable salt thereof; wherein: p is 0, 1, 2, 3, 4, 5, or 6; q is 0 or 1; r is 0, 1, 2, or 3; L2is a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; X1is cycloalkynyl, heterocyclylalkynyl, alkynyl, -OH, -SH, -N3, -NH2, an activated ester, or maleimide; wherein the cycloalkynyl, heterocyclylalkynyl, alkynyl, activated ester, or maleimide are each optionally substituted; and m is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0232] In some embodiments, L2is a linear linker.

[0233] In some embodiments, L2is a branched linker.

[0234] In some embodiments, L2is a bivalent linker or a trivalent linker.

[0235] In some embodiments,, wherein L2is C2-20heteroalkylene optionally substituted with oxo.

[0236] In some embodiments, L2is represented by -L2a-L2b-L2c-; wherein: 52Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT L2ais C(H)m-1, N(H)m-1, C3-8cycloalkylene, a 4-8 membered heterocyclylene, C6arylene, or a 5-6 membered heteroarylene; L2bis -O-, -S-, -NH-, -NHC(O)-, -NHC(O)NH-, -NHC(O)O-, C1-6alkylene, C2-15heteroalkylene, C2-8alkenylene, C2-8alkynylene, C3-8cycloalkylene, a 4-8 membered heterocyclylene, C6arylene, or a 5-6 membered heteroarylene; and L2cis C1-6alkylene, C2-20heteroalkylene, C2-8alkenylene, C2-8alkynylene, C3-8cycloalkylene, a 4-8 membered heterocyclylene, C6arylene, or a 5-6 membered heteroarylene; wherein each alkylene, heteroalkylene, alkenylene, alkynylene, cycloalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl.

[0237] In some embodiments, the compound is represented by Formula IIB: IBy acceptable salt thereof, wherein: p is 0, 1, 2, 3, 4, 5, or 6; q is 0 or 1; r is 0, 1, 2, or 3; L2ais C or 5-6 membered heteroarylene, and m is 3; CH, N, or 5-6 membered heteroarylene, and m is 2; or CH2, NH, or 5-6 membered heteroarylene, and m is 1; s is 0 or 1; L2cis C2-20heteroalkylene; X1is cycloalkynyl, heterocyclylalkynyl, alkynyl, -OH, -SH, -N3, -NH2, an activated ester, or maleimide; wherein the cycloalkynyl, heterocyclylalkynyl, alkynyl, activated ester, or maleimide are each optionally substituted; and 53Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT m is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0238] In some embodiments, the compound is represented by Formula IIB: IB acceptable saltthereof, wherein: p is 0, 1, 2, 3, 4, 5, or 6; q is 0 or 1; r is 0, 1, 2, or 3; L2ais C(H)m-1or a 5-6 membered heteroarylene; s is 0 or 1; L2cis C2-20heteroalkylene; X1is cycloalkynyl, heterocyclylalkynyl, alkynyl, -OH, -SH, -N3, -NH2, an activated ester, or maleimide; wherein the cycloalkynyl, heterocyclylalkynyl, alkynyl, activated ester, or maleimide are each optionally substituted; and m is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0239] In some embodiments, each moiety is independently selected from:,54Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0240] In some embodiments, X1is an activated ester. “Activated ester” refers to an ester functional group that is highly susceptible toward nucleophilic attack. Activation can be imparted by modifications of the oxo alkoxy component of a normal ester (e.g., modification with one or more electronegative substituents). In some embodiments, the activated ester is an N-succinimide ester, sulfo-N-succinimidyl ester, imidoester, acid chloride, nitrophenyl ester, tetrafluorophenyl ester, hydroxybenzotriazole, or perflourophenyl ester. 55Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0241] “Maleimide” is a functional group with the following structu .

[0242] In some embodiments, X1is -OH, -SH, -NH2, -N3, optionallyd cycloalkynyl, optionally substituted heterocyclylalkenyl, or optionally substituted heterocyclylalkynyl.

[0243] In some embodiments, X1is an optionally substituted cycloalkynyl or an optionally substituted heterocyclylalkynyl.

[0244] In certain embodiments, X1is:each occurrence of R2is independently fluoro, chloro, or bromo, n1 is 0, 1, 2, 3, or 4.

[0245] In some embodiments, X1is: orweren eac s nepenen y op ona y sus ue w , , , or ao.

[0246] In some embodiments .56Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0247] In some embodiments .

[0248] In some embodiments-NH2, or -N3.

[0249] In some embodiments, X1is -SH or -N3.

[0250] In some embodiments, X1is –SH.

[0251] In some embodiments, X1is -N3.

[0252] In some embodiments .

[0253] In some embodimentsd of Table 1, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof. 57Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Table 1. Compounds No. Compound Structure58Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Compound Structure59Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Compound Structure60Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Compound Structure61Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Compound Structure62Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Compound Structure63Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Compound Structure64Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Compound Structure65Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Compound Structure

[0254] In some embodiments, provided is a conjugate selected from Table 2, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein A is as defined herein. Table 2. Conjugates No. Conjugate Structure66Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure67Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure68Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure O69Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure70Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure S71Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure72Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure73Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure74Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure75Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure76Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure77Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure78Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT No. Conjugate Structure

[0255] The compounds of Formula I provided herein encompass stereochemical forms of the compounds, for example, optical isomers, such as enantiomers, diastereomers, as well as mixtures thereof, e.g., mixtures of enantiomers and / or diastereomers, including racemic mixtures, as well as equal or non-equal mixtures of individual enantiomers and / or diastereomers. All stereochemical forms are contemplated in this disclosure. Unless otherwise indicated, when a disclosed compound is named or depicted by a structure without specifying the stereochemistry and has one or more chiral centers, it is understood to represent all possible stereoisomers of the compound.

[0256] The compounds of Formula I include pharmaceutically acceptable salts thereof. In addition, the compounds of Formula I also include other salts of such compounds which are not necessarily pharmaceutically acceptable salts, and which may be useful as intermediates for preparing and / or purifying compounds of Formula I and / or for separating enantiomers of compounds of Formula I. Non-limiting examples of pharmaceutically acceptable salts of compounds of Formula I include trifluoroacetic acid salts. 79Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0257] In some embodiments, A is a polypeptide, such as an antibody or antigen-binding fragment thereof, or a Fc fragment or a polypeptide that includes all or part of the Fc fragment. Antibodies and Fc Polypeptides

[0258] Certain embodiments of a conjugate of the present disclosure comprise a polypeptide such as an antibody; such conjugates can be referred-to as antibody-drug conjugates or ADCs. The following description refers to certain structures and functions of antibodies, separate from structure and function of the same when in the context of a conjugate or an ADC. However, when in the context of a conjugate or an ADC, an antibody can, in some embodiments, retain or substantially retain one or more functions of the antibody outside the context of the conjugate or ADC.

[0259] Furthermore, in other embodiments, a conjugate of the present disclosure comprises an Fc polypeptide which is not coupled to an antigen binding domain. Such a conjugate can be referred to as a drug-Fc conjugate or DFC. The Fc polypeptide, in some embodiments, includes the entire Fc fragment of an IgG antibody and optionally some or all of a CH1 domain along with the hinge region between the CH1 and Fc fragment. The following description also refers to certain structures and functions of the Fc portion of an antibody, which can also be applied to the Fc portion of a DFC. When in the context of a conjugate or a DFC, an Fc polypeptide can, in some embodiments, retain or substantially retain one or more functions of the Fc polypeptide outside the context of the conjugate or DFC.

[0260] Terms understood by those in the art of antibody technology are each given the meaning acquired in the art, unless expressly defined differently herein. For example, the term “antibody” refers to an intact antibody comprising at least two heavy (H) chains (HCs) and two light (L) chains (LCs) inter-connected by disulfide bonds (i.e LC-HC-HC-LC, as a bivalent tetramer molecule). The term encompasses intact or full-length antibodies, including antibodies of any class or sub-class, including IgG and sub-classes thereof (e.g., IgG1, IgG2, IgG3, IgG4), IgM, IgE, IgA, and IgD. In some embodiments, an ADC of the present disclosure comprises a full-length antibody (e.g., a full- length human IgG1 antibody or an engineered variant thereof); it will be understood that a “full- length” antibody in this context includes an antibody in which a C-terminal lysine has been removed, e.g., by clipping during antibody production in a host cell. A full-length antibody also refers to an antibody in which a C-terminal glycine-lysine motif (G-K) is removed.

[0261] The terms “VL” or “VL” and “VH” or “VH” refer to the variable binding region (also called a “variable region” or “variable domain”) from an antibody light chain and an antibody heavy chain, respectively. The variable binding regions comprise discrete, well-defined sub-regions known as “complementarity determining regions” (CDRs) and “framework regions” (FRs). The terms “complementarity determining region,” and “CDR,” are synonymous with “hypervariable region” or 80Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT “HVR,” and refer to sequences of amino acids within antibody variable regions, which, in general, together confer the antigen specificity and / or binding affinity of the antibody, wherein consecutive CDRs (i.e, CDR1 and CDR2, CDR2 and CDR3) are separated from one another in primary structure by a framework region. There are three CDRs in each variable region (HCDR1, HCDR2, HCDR3; LCDR1, LCDR2, LCDR3; also referred to as CDRHs and CDRLs, respectively). In certain embodiments, an antibody VH comprises four FRs and three CDRs as follows: FR1-HCDR1-FR2- HCDR2-FR3-HCDR3-FR4; and an antibody VL comprises four FRs and three CDRs as follows: FR1-LCDR1-FR2-LCDR2-FR3-LCDR3-FR4. In general, the VH and the VL together form the antigen-binding site through their respective CDRs. However, in some cases, a VH alone, a VL alone, or one, two, three, four, or five of the CDRs are involved in antigen-binding.

[0262] It will be understood that heavy chain-only antibodies (typically comprising two heavy chains, but no light chains) are also contemplated for use in a conjugate of the present disclosure.

[0263] Numbering of CDR and framework regions may be according to any known method or scheme, such as the Kabat, Chothia, EU, IMGT, and Aho numbering schemes (see, e.g., Kabat et al., “Sequences of Proteins of Immunological Interest, US Dept. Health and Human Services, Public Health Service National Institutes of Health, 1991, 5thed.; Chothia and Lesk, J. Mol. Biol.196:901- 917 (1987)); Lefranc et al., Dev. Comp. Immunol.27:55, 2003; Honegger and Plückthun, J. Mol. Bio. 309:657-670 (2001); and the antibody numbering method developed by the Chemical Computing Group (CCG); e.g., using Molecular Operating Environment (MOE) software (www.chemcomp.com). Other CDR numbering schemes include North (described in “A New Clustering of Antibody CDR Loop Conformations”, Journal of Molecular Biology, 406,

[0264] 228-256 (2011)), AbM, and Martin (also referred to as Enhanced Chothia). Equivalent residue positions can be annotated and for different molecules to be compared using Antigen receptor Numbering and Receptor Classification (ANARCI) software tool (2016, Bioinformatics 15:298-300). Accordingly, identification of CDRs of an exemplary variable domain (VH or VL) sequence as provided herein according to one numbering scheme is not exclusive of an antibody comprising CDRs of the same variable domain as determined using a different numbering scheme.

[0265] In some embodiments, CDRs of a variable domain or region (VH or VL)

[0266] sequence as provided herein are a combination of CDRs according any two or more of the following numbering schemes: Kabat, Chothia, IMGT, CCG, AHo, AbM, Martin, North, and EU.

[0267] “Fv” is a small antibody fragment that contains a complete antigen-recognition and antigen- binding site. This fragment generally consists of a dimer of one heavy- and one light-chain variable region domain in tight, non-covalent association. However, even a single variable domain (or half of 81Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT an Fv comprising only three CDRs specific for an antigen) can recognize and bind antigen, although sometimes at a lower affinity than the entire binding site. Disulfide-stabilized Fvs (dsFv) are known and may be used to make conjugates of the present disclosure.

[0268] “Single-chain Fv” also abbreviated as “sFv” or “scFv”, are antibody fragments that comprise the VHand VLantibody domains connected into a single polypeptide chain. In some embodiments, the scFv polypeptide comprises a polypeptide linker disposed between and linking the VHand VLdomains that enables the scFv to retain or form the desired structure for antigen binding. Such a peptide linker can be incorporated into a fusion polypeptide using standard techniques well known in the art. For a review of scFv, see Pluckthun in The Pharmacology of Monoclonal Antibodies, vol. 113, Rosenburg and Moore eds., Springer-Verlag, New York, pp.269-315 (1994); Borrebaeck 1995, infra. In certain embodiments, the antibody comprises a scFv comprising a VH domain, a VL domain, and a peptide linker linking the VH domain to the VL domain. In some embodiments, a scFv comprises a VH domain linked to a VL domain by a peptide linker, which can be in a VH-linker-VL orientation or in a VL-linker-VH orientation. Any scFv of the present disclosure may be engineered so that the C-terminal end of the VL domain is linked by a short peptide sequence to the N-terminal end of the VH domain, or vice versa (i.e, (N)VL(C)-linker-(N)VH(C) or (N)VH(C)-linker-(N)VL(C). Alternatively, in some embodiments, a linker may be linked to an N-terminal portion or end of the VH domain, the VL domain, or both. Peptide linker sequences may be chosen, for example, based on: (1) their ability to adopt a flexible extended conformation; (2) their inability or lack of ability to adopt a secondary structure that could interact with functional epitopes on the first and second polypeptides and / or on a target molecule; and / or (3) the lack or relative lack of hydrophobic or charged residues that might react with the polypeptides and / or target molecule. Other considerations regarding linker design (e.g., length) can include the conformation or range of conformations in which the VH and VL can form a functional antigen-binding site. In certain embodiments, peptide linker sequences contain, for example, Gly, Asn, and Ser residues. Other near neutral amino acids, such as Thr and Ala, may also be included in a linker sequence. Other amino acid sequences which may be usefully employed as linker include those disclosed in Maratea et al., Gene 40:3946 (1985); Murphy et al., Proc. Natl. Acad. Sci. USA 83:82588262 (1986); U.S. Pat. No.4,935,233, and U.S. Pat. No.4,751,180. Other illustrative and non-limiting examples of linkers may include, for example, Glu-Gly-Lys-Ser-Ser-Gly- Ser-Gly-Ser-Glu-Ser-Lys-Val-Asp (Chaudhary et al., Proc. Natl. Acad. Sci. USA 87:1066-1070 (1990)) and Lys-Glu-Ser-Gly-Ser-Val-Ser-Ser-Glu-Gln-Leu-Ala-Gln-Phe-Arg-Ser-Leu-Asp (Bird et al., Science 242:423-426 (1988)) and the pentamer Gly-Gly-Gly-Gly-Ser when present in a single iteration or repeated 1 to 5 or more times, or more. Any suitable linker may be used, and in general can be about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 1523, 24, 25, 26, 27, 28, 29, 30, 40, 50, 60, 70, 80, 90, 100 amino acids in length, or less than about 200 amino acids in length, and will preferably comprise a flexible structure (can provide flexibility and room for 82Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT conformational movement between two regions, domains, motifs, fragments, or modules connected by the linker), and will preferably be biologically inert and / or have a low risk of immunogenicity in a human. ScFvs can be constructed using any combination of the VH and VL sequences or any combination of the CDRH1, CDRH2, CDRH3, CDRL1, CDRL2, and CDRL3 sequences disclosed herein. In some embodiments, linker sequences are not required; for example, when the first and second polypeptides have non-essential N-terminal amino acid regions that can be used to separate the functional domains and prevent steric interference.

[0269] The term “CL” refers to an “immunoglobulin light chain constant region” or a “light chain constant region,” i.e., a constant region from an antibody light chain. The term “CH” refers to an “immunoglobulin heavy chain constant region” or a “heavy chain constant region,” which is further divisible, depending on the antibody isotype into CH1, CH2, and CH3 (IgA, IgD, IgG), or CH1, CH2, CH3, and CH4 domains (IgE, IgM). The Fc region of an antibody heavy chain is described further herein. In any of the presently disclosed embodiments, an antibody of the present disclosure comprises a CL, a CH1, a CH2, and a CH3.

[0270] A “Fab” (fragment antigen binding) is the part of an antibody that binds to antigen(s) and includes the variable region and CH1 of the heavy chain linked to the light chain via an inter-chain disulfide bond. Each Fab fragment is monovalent with respect to antigen binding, i.e., it has a single antigen-binding site. Pepsin treatment of an antibody yields a single large F(ab′)2 fragment that roughly corresponds to two disulfide linked Fab fragments having divalent antigen-binding activity and is still capable of cross-linking antigen. Both the Fab and F(ab′)2 are examples of “antigen- binding fragments.” Fab′ fragments differ from Fab fragments by having additional few residues at the carboxy terminus of the CH1 domain including one or more cysteines from the antibody hinge region. Fab′-SH is the designation herein for Fab′ in which the cysteine residue(s) of the constant domains bear a free thiol group. F(ab′)2 antibody fragments originally were produced as pairs of Fab′ fragments that have hinge cysteines between them. Other chemical couplings of antibody fragments are also known. An “Fd” refers to a fragment comprised of VH+CH1 of the heavy chain. Fabs may be provided in single-chain format, e.g., a scFab wherein a linker connects the Fd to the light chain (e.g., a linker connects the C-terminus of the CH1 to the N-terminus of the VL).

[0271] An antibody can be multispecific, e.g., bispecific, trispecific, or the like. In certain embodiments, an antibody of the present disclosure is monospecific (e.g., binds to a single epitope) or is multispecific (e.g., binds to multiple epitopes and / or target molecules). Antibodies and antigen binding fragments may be constructed in various formats. Exemplary antibody formats disclosed in Spiess et al., Mol. Immunol.67(2):95 (2015), and in Brinkmann and Kontermann, mAbs 9(2):182-212 (2017), which formats and methods of making the same are incorporated herein by reference and include, for example, Bispecific T cell Engagers (BiTEs), DARTs, Knobs-Into-Holes (KIH) 83Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT assemblies, scFv-CH3-KIH assemblies, KIH Common Light-Chain antibodies, TandAbs, Triple Bodies, TriBi Minibodies, Fab-scFv, scFv-CH-CL-scFv, F(ab′)2-scFv2, tetravalent Hcabs, Intrabodies, CrossMabs, Dual Action Fabs (DAFs) (two-in-one or four-in-one), DutaMabs, DT-IgG, Charge Pairs, Fab-arm Exchange, SEEDbodies, Triomabs, LUZ-Y assemblies, Fcabs, κλ-bodies, orthogonal Fabs, DVD-Igs (e.g., US Patent No.8,258,268, which formats are incorporated herein by reference in their entirety), IgG(H)-scFv, scFv-(H)IgG, IgG(L)-scFv, scFv-(L)IgG, IgG(L,H)-Fv, IgG(H)-V, V(H)-IgG, IgG(L)-V, V(L)-IgG, KIH IgG-scFab, 2scFv-IgG, IgG-2scFv, scFv4-Ig, Zybody, and DVI-IgG (four-in-one), as well as so-called FIT-Ig (e.g., PCT Publication No. WO 2015 / 103072, which formats are incorporated herein by reference in their entirety), so-called WuxiBody formats (e.g., PCT Publication No. WO 2019 / 057122, which formats are incorporated herein by reference in their entirety), and so-called In-Elbow-Insert Ig formats (IEI-Ig; e.g., PCT Publication Nos. WO 2019 / 024979 and WO 2019 / 025391, which formats are incorporated herein by reference in their entirety).

[0272] Certain embodiments of presently disclosed conjugates comprise an antibody comprising an Fc polypeptide (e.g., comprising an Fc polypeptide dimer). An “Fc” dimer comprises the carboxy- terminal portions (i.e., the CH2 and CH3 domains of IgG) of both antibody H chains held together by disulfides. An Fc may comprise a dimer comprised of two Fc polypeptides (e.g., two CH2-CH3 polypeptides). The two Fc polypeptides may be the same (may form a homodimer) or different (may form a heterodimer). The two Fc polypeptides may be the same (may form a homodimer) or different (may form a heterodimer).

[0273] In some embodiments, an Fc heterodimer comprises modified CH3 domain amino acid sequences, wherein each modified CH3 domain amino acid sequence does not significantly interact with a CH3 domain amino acid sequence that does not contain the modification(s). In some embodiments, orthogonal modifications in CH3 domains comprise mutations that generate one or more engineered disulfide bridges between a first CH3 domain and a second CH3 domain, wherein, optionally, the one or more mutations that generate engineered disulfide bridges comprise a S354C mutation in the first CH3 domain, and a 349C in the other CH3 domain, wherein numbering of the mutations corresponds to amino acid positions of a human IgG1 heavy chain according to the EU Index as set forth in Kabat.

[0274] In some embodiments, an Fc polypeptide heterodimer comprises knob-in-hole mutations, wherein, optionally, the knob-in hole mutations are a T366W mutation in one Fc polypeptide, and a T366S, L368A, and aY407V mutation in the other Fc polypeptide, wherein numbering of the mutations corresponds to amino acid positions of a human IgG1 heavy chain according to the EU Index as set forth in Kabat. In some embodiments, an Fc polypeptide heterodimer comprises one or more charge-pair mutations, wherein, optionally, the one or more charge-pair mutations comprises a 84Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT T366K mutation in one Fc polypeptide, and a L351D mutation in the other Fc polypeptide, wherein numbering of the mutations corresponds to amino acid positions of a human IgG1 heavy chain according to the EU Index as set forth in Kabat. In some embodiments, Fc polypeptides of a dimer comprise one or more mutations for heterodimerization disclosed in PCT / US2021 / 062951 and / or US Provisional Application No.63 / 123,915, which mutations are incorporated herein by reference. In some embodiments, the Fc polypeptides of a dimer comprise one or more mutations to promote heterodimerization, wherein the one or more mutations are so-called “AzymetricTM” mutations from Zymeworks, Inc. In some embodiments, the Fc polypeptides of a dimer comprise one or more mutations to promote heterodimerization, wherein the one or more mutations are selected from mutations disclosed in any one or more of: U.S. Patent No.9,562,109 B2; U.S. Patent No.9,574,010 B2; and U.S. Publication No. U.S.2013 / 0336973 A1, which mutations are incorporated herein by reference. In some embodiments, an antibody comprises a SEEDbody. In some embodiments, and antibody comprises a knobs-into-holes assembly.

[0275] It will be understood that, for example, production in a mammalian cell line can remove one or more C-terminal lysine of an antibody heavy chain (see, e.g., Liu et al. mAbs 6(5):1145-1154 (2014)). Accordingly, an antibody of the present disclosure can comprise a heavy chain, a CH1-CH3, a CH3, or an Fc polypeptide wherein a C-terminal lysine residue is present or is absent; in other words, encompassed are embodiments where the C-terminal residue of a heavy chain, a CH1-CH3, or an Fc polypeptide is not a lysine, and embodiments where a lysine is the C-terminal residue. In certain embodiments, a composition comprises a plurality of an antibody of the present disclosure, wherein one or more antibody does not comprise a lysine residue at the C-terminal end of the heavy chain, CH1-CH3, or Fc polypeptide, and wherein one or more antibody comprises a lysine residue at the C- terminal end of the heavy chain, CH1-CH3, or Fc polypeptide. Also, contemplated embodiments include wherein a C-terminal glycine-lysine (G-K) motif is not present in the heavy chain of an antibody.

[0276] Antibody “effector functions” refer to those biological activities attributable to the Fc region (a native sequence Fc region or amino acid sequence variant Fc region) of an antibody and vary with the antibody isotype. Examples of antibody effector functions include: C1q binding and complement dependent cytotoxicity; Fc receptor binding; antibody-dependent cell-mediated cytotoxicity (ADCC); phagocytosis; down regulation of cell surface receptors (e.g., B cell receptor); and B cell activation.

[0277] As discussed herein, modifications (e.g., amino acid substitutions) may be made to an Fc domain to modify (e.g., improve, reduce, or ablate) one or more functionality of an Fc-containing polypeptide (e.g., an antibody of the present disclosure). Such functions include, for example, Fc receptor (FcR) binding, antibody half-life modulation (e.g., by binding to FcRn), ADCC function, protein A binding, protein G binding, and complement binding. Amino acid modifications that modify 85Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT (e.g., improve, reduce, or ablate) Fc functionalities include, for example, the T250Q / M428L, M252Y / S254T / T256E (also referred to as “YTE”), H433K / N434F, M428L / N434S, M428L / 434A, E233P / L234V / L235A / G236 + A327G / A330S / P331S, E333A, S239D / A330L / I332E, P257I / Q311, K326W / E333S, S239D / I332E / G236A, A330L / I332E / G236A, N297Q, K322A, S228P, L235E + E318A / K320A / K322A, L234A / L235A (also referred to herein as “LALA”), G236R / L328R (also referred to herein as “GRLR”), and L234A / L235A / P329G mutations, certain of which mutations are summarized and annotated in “Engineered Fc Regions”, published by InvivoGen (2011) and available at invivogen.com / PDF / review / review-Engineered-Fc-Regions-invivogen.pdf? utm_source=review&utm_medium=pdf&utm_campaign=review&utm_content=Engineered-Fc- Regions, and are incorporated herein by reference.

[0278] For example, to activate the complement cascade, the C1q protein complex can bind to at least two molecules of IgG1 or one molecule of IgM when the immunoglobulin molecule(s) is attached to the antigenic target (Ward, E. S., and Ghetie, V., Ther. Immunol.2 (1995) 77-94). Burton, D. R., described (Mol. Immunol.22 (1985) 161-206) that the heavy chain region comprising amino acid residues 318 to 337 is involved in complement fixation. Duncan, A. R., and Winter, G. (Nature 332 (1988) 738-740), using site directed mutagenesis, reported that Glu318, Lys320 and Lys322 form the binding site to C1q. The role of Glu318, Lys320 and Lys 322 residues in the binding of C1q was confirmed by the ability of a short synthetic peptide containing these residues to inhibit complement mediated lysis.

[0279] For example, FcR binding can be mediated by the interaction of the Fc moiety (of an antibody) with Fc receptors (FcRs), which are specialized cell surface receptors on cells including hematopoietic cells. Fc receptors belong to the immunoglobulin superfamily and shown to mediate both the removal of antibody-coated pathogens by phagocytosis of immune complexes, and the lysis of erythrocytes and various other cellular targets (e.g., tumor cells) coated with the corresponding antibody, via antibody dependent cell mediated cytotoxicity (ADCC; Van de Winkel, J. G., and Anderson, C. L., J. Leukoc. Biol.49 (1991) 511-524). FcRs are defined by their specificity for immunoglobulin classes; Fc receptors for IgG antibodies are referred to as FcγR, for IgE as FcεR, for IgA as FcαR and so on and neonatal Fc receptors are referred to as FcRn. Fc receptor binding is described for example in Ravetch, J. V., and Kinet, J. P., Annu. Rev. Immunol.9 (1991) 457-492; Capel, P. J., et al., Immunomethods 4 (1994) 25-34; de Haas, M., et al., J Lab. Clin. Med.126 (1995) 330-341; and Gessner, J. E., et al., Ann. Hematol.76 (1998) 231-248.

[0280] Cross-linking of receptors by the Fc domain of native IgG antibodies (FcγR) triggers a wide variety of effector functions including phagocytosis, antibody-dependent cellular cytotoxicity, and release of inflammatory mediators, as well as immune complex clearance and regulation of antibody production. Fc moieties providing cross-linking of receptors (e.g., FcγR) are contemplated herein. In 86Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT humans, three classes of FcγR have been characterized to-date, which are: (i) FcγRI (CD64), which binds monomeric IgG with high affinity and is expressed on macrophages, monocytes, neutrophils and eosinophils; (ii) FcγRII (CD32), which binds complexed IgG with medium to low affinity, is widely expressed, in particular on leukocytes, is believed to be a central player in antibody-mediated immunity, and which can be divided into FcγRIIA, FcγRIIB and FcγRIIC, which perform different functions in the immune system, but bind with similar low affinity to the IgG-Fc, and the ectodomains of these receptors are highly homologous; and (iii) FcγRIII (CD16), which binds IgG with medium to low affinity and has been found in two forms: FcγRIIIA, which has been found on NK cells, macrophages, eosinophils, and some monocytes and T cells, and is believed to mediate ADCC; and FcγRIIIB, which is highly expressed on neutrophils.

[0281] FcγRIIA is found on many cells involved in killing (e.g., macrophages, monocytes, neutrophils) and seems able to activate the killing process. FcγRIIB seems to play a role in inhibitory processes and is found on B-cells, macrophages and on mast cells and eosinophils. Importantly, it has been shown that 75% of all FcγRIIB is found in the liver (Ganesan, L. P. et al., 2012: “FcγRIIb on liver sinusoidal endothelium clears small immune complexes,” Journal of Immunology 189: 4981– 4988). FcγRIIB is abundantly expressed on Liver Sinusoidal Endothelium, called LSEC, and in Kupffer cells in the liver and LSEC are the major site of small immune complexes clearance (Ganesan, L. P. et al., 2012: FcγRIIb on liver sinusoidal endothelium clears small immune complexes. Journal of Immunology 189: 4981–4988).

[0282] In some embodiments, the antibodies disclosed herein comprise an Fc polypeptide or fragment thereof for binding to FcγRIIb, in particular an Fc region, such as, for example IgG-type antibodies. Moreover, it is possible to engineer the Fc moiety to enhance FcγRIIB binding by introducing the mutations S267E and L328F as described by Chu, S. Y. et al., 2008: Inhibition of B cell receptor-mediated activation of primary human B cells by co-engagement of CD19 and FcγRIIb with Fc-engineered antibodies. Molecular Immunology 45, 3926–3933. Thereby, the clearance of immune complexes can be enhanced (Chu, S., et al., 2014: Accelerated Clearance of IgE In Chimpanzees Is Mediated By Xmab7195, An Fc-Engineered Antibody With Enhanced Affinity For Inhibitory Receptor FcγRIIb. Am J Respir Crit, American Thoracic Society International Conference Abstracts). In some embodiments, the antibodies of the present disclosure, or the antigen binding fragments thereof, comprise an engineered Fc moiety with the mutations S267E and L328F, in particular as described by Chu, S. Y. et al., 2008: Inhibition of B cell receptor-mediated activation of primary human B cells by coengagement of CD19 and FcγRIIb with Fc-engineered antibodies. Molecular Immunology 45, 3926–3933.

[0283] On B cells, FcγRIIB may function to suppress further immunoglobulin production and isotype switching to, for example, the IgE class. On macrophages, FcγRIIB is thought to inhibit phagocytosis 87Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT as mediated through FcγRIIA. On eosinophils and mast cells, the B form may help to suppress activation of these cells through IgE binding to its separate receptor.

[0284] Regarding FcγRI binding, modification in native IgG of at least one of E233-G236, P238, D265, N297, A327 and P329 reduces binding to FcγRI. IgG2 residues at positions 233-236, substituted into corresponding positions IgG1 and IgG4, reduces binding of IgG1 and IgG4 to FcγRI by 103-fold and eliminated the human monocyte response to antibody-sensitized red blood cells (Armour, K. L., et al. Eur. J. Immunol.29 (1999) 2613-2624).

[0285] Regarding FcγRII binding, reduced binding for FcγRIIA is found, e.g., for IgG mutation of at least one of E233-G236, P238, D265, N297, A327, P329, D270, Q295, A327, R292 and K414.

[0286] Two allelic forms of human FcγRIIA are the “H131” variant, which binds to IgG1 Fc with higher affinity, and the “R131” variant, which binds to IgG1 Fc with low affinity. See, e.g., Bruhns et al., Blood 113:3716-3725 (2009).

[0287] Regarding FcγRIII binding, reduced binding to FcγRIIIA is found, e.g., for mutation of at least one of E233-G236, P238, D265, N297, A327, P329, D270, Q295, A327, S239, E269, E293, Y296, V303, A327, K338 and D376. Mapping of the binding sites on human IgG1 for Fc receptors, the above-mentioned mutation sites, and methods for measuring binding to FcγRI and FcγRIIA, are described in Shields, R. L., et al., J. Biol. Chem.276 (2001) 6591-6604.

[0288] Two allelic forms of human FcγRIIIA are the “F158” variant, which binds to IgG1 Fc with lower affinity, and the “V158” variant, which binds to IgG1 Fc with higher affinity. See, e.g., Bruhns et al., Blood 113:3716-3725 (2009).

[0289] Regarding binding to FcγRII, two regions of native IgG Fc appear to be involved in interactions between FcγRIIs and IgGs, namely (i) the lower hinge site of IgG Fc, in particular amino acid residues L, L, G, G (234 – 237, EU numbering), and (ii) the adjacent region of the CH2 domain of IgG Fc, in particular a loop and strands in the upper CH2 domain adjacent to the lower hinge region, e.g., in a region of P331 (Wines, B.D., et al., J. Immunol.2000; 164: 5313 – 5318). Moreover, FcγRI appears to bind to the same site on IgG Fc, whereas FcRn and Protein A bind to a different site on IgG Fc, which appears to be at the CH2-CH3 interface (Wines, B.D., et al., J. Immunol.2000; 164: 5313 – 5318).

[0290] Also contemplated are mutations that increase binding affinity of an Fc polypeptide or fragment thereof of the present disclosure to a (i.e., one or more) Fcγ receptor (e.g., as compared to a reference Fc polypeptide or fragment thereof or containing the same that does not comprise the mutation(s)). See, e.g., Delillo and Ravetch, Cell 161(5):1035-1045 (2015) and Ahmed et al., J. Struc. 88Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Biol.194(1):78 (2016), the Fc mutations and techniques of which are incorporated herein by reference.

[0291] In some embodiments, an antibody comprises a Fc polypeptide comprising the following mutations selected from G236A; S239D; A330L; and I332E; or a combination comprising any two or more of the same; e.g., S239D / I332E; S239D / A330L / I332E; G236A / S239D / I332E; G236A / A330L / I332E (also referred to herein as “GAALIE”) (EU numbering with reference to human IgG1); or G236A / S239D / A330L / I332E. In some embodiments, the Fc polypeptide or fragment thereof does not comprise S239D. In some embodiments, the Fc polypeptide or fragment thereof comprises S at position 239. GAALIE improves binding affinity to FcRγIIa and FcγRIIIa and reduces binding affinity to FcγRIIb.

[0292] In certain embodiments, the Fc polypeptide may comprise or consist of at least a portion of an Fc polypeptide that is involved in binding to FcRn binding. In certain embodiments, the Fc polypeptide comprises one or more amino acid modifications that improve binding affinity for (e.g., enhance binding to) FcRn (e.g., at a pH of about 6.0) and, in some embodiments, thereby extend in vivo half-life of a molecule comprising the Fc polypeptide (e.g., as compared to a reference Fc polypeptide or antibody that is otherwise the same but does not comprise the modification(s)). In certain embodiments, the Fc polypeptide comprises or is derived from an IgG (e.g., IgG1, such as human IgG1) Fc and a half-life-extending mutation comprises any one or more of: M428L; N434S; N434H; N434A; M252Y; S254T; T256E; T250Q; P257I Q311I; D376V; T307A; E380A (EU numbering with reference to human IgG1). In certain embodiments, a half-life-extending mutation comprises M428L / N434S (also referred to herein as “MLNS” or “LS”) or comprises M428L / N434A (also referred to herein as “MLNA” or “LA”). In certain embodiments, a half-life-extending mutation comprises M252Y / S254T / T256E (also referred to as “YTE”). In certain embodiments, a half-life- extending mutation comprises T250Q / M428L. In certain embodiments, a half-life-extending mutation comprises P257I / Q311I. In certain embodiments, a half-life-extending mutation comprises P257I / N434H. In certain embodiments, a half-life-extending mutation comprises D376V / N434H. In certain embodiments, a half-life-extending mutation comprises T307A / E380A / N434A.

[0293] In some embodiments, an antibody includes a Fc polypeptide that comprises the substitution mutations M428L / N434S. In some embodiments, an antibody includes a Fc polypeptide that comprises the substitution mutations M428L / N434A. In some embodiments, an antibody includes a Fc polypeptide that comprises the substitution mutations G236A / A330L / I332E. In certain embodiments, an antibody includes a (e.g., IgG1) Fc moiety that comprises a G236A mutation, an A330L mutation, and a I332E mutation (GAALIE), and does not comprise a S239D mutation (e.g., comprises a native S at position 239). In some embodiments, an antibody includes an Fc polypeptide that comprises the substitution mutations: M428L / N434S and G236A / A330L / I332E, and optionally 89Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT does not comprise S239D. In certain embodiments, an antibody includes a Fc polypeptide that comprises the substitution mutations: M428L / N434S and G236A / S239D / A330L / I332E. In certain embodiments, an antibody includes an Fc polypeptide that comprises the substitution mutations: M428L / N434A and G236A / A330L / I332E, and optionally does not comprise S239D. In certain embodiments, an antibody includes a Fc polypeptide that comprises the substitution mutations: M428L / N434A and G236A / S239D / A330L / I332E.

[0294] In certain embodiments, antibodies comprising a variant Fc polypeptide of the present disclosure provide surprising advantages, such as any one or more of the following: increased binding affinity (e.g., as determined by surface plasmon resonance, e.g., using a Biacore instrument and / or as determined by a electrochemiluminescence assay, such as a meso scale discovery (MSD) assay) for and / or inducing increased signaling (e.g., as determined using (1) an Fc variant antibody (2) antigen- expressing target cells and (3) reporter cells expressing one or more human FcγRA, optionally driving expression of a reporter gene such as, for example, GFP or luciferase) by one or more human FcγRA, as compared to the antibody comprising a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state; decreased binding affinity for and / or inducing decreased signaling of human FcγRIIB, as compared to the antibody comprising a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state; a unique and optionally improved binding profile across human FcγRIIA-H, human FcγRIIA-R, human FcγRIIB, human FcγRIIIA-F, and human FcγRIIIA-V, wherein improved binding comprises an overall increase in binding to and / or activation of FcγRA signaling relative to binding to and / or activation of inhibitory FcγR signaling, as compared to the antibody comprising a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state; increased binding affinity for human C1q , as compared to the antibody comprising a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state; no detrimental effect or no substantial detrimental effect on thermal stability, a reduced negative effect on thermal stability as compared to a variant Fc polypeptide or fragment thereof not comprising the mutation(s) and / or fucosylation state (e.g., a human IgG1 Fc comprising the mutations G236A, A330L, and I332E (e.g., having a smaller decreasing effect, or no decreasing effect, on melting temperature as compared to the antibody comprising a human IgG1 Fc comprising the mutations G236A, A330L, and I332E), or having a higher melting temperature than the antibody comprising a human IgG1 Fc comprising the mutations G236A, A330L, and I332E)); increasing specific lysis (e.g., via ADCC) by natural killer cells and / or PBMCs (e.g., expressing F158 / V158 or V158 / V158 FcγRIIIA) against antigen-expressing target cells, as compared to the antibody comprising a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state (e.g., the antibody comprising a human IgG1 Fc comprising the mutations G236A, A330L, and I332E); increasing ADCP by monocytes (e.g., CD14+ monocytes, optionally expressing F158 / V158 FcγRIIA and R131 / H131 FcγRIIA or F158 / F158 FcγRIIA and R131 / H131 FcγRIIA) against antigen-expressing target cells, as compared to the antibody comprising 90Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state; increasing the percentage of CD83+ cells (e.g., moDCs) and / or increasing expression of CD83 by moDCs in a sample when provided in combination with the antigen, as compared to the antibody comprising a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state, when provided in combination with the antigen; increasing production of one or more cytokine (optionally selected from the group consisting of IL-1β, IFN-γ, IL-6, and TNF-α) by moDCs in a sample when provided in combination with the antigen, as compared to the antibody comprising a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state, when provided in combination with the antigen; and / or increasing the ability of moDCs to stimulate antigen-specific CD4+ T cells when provided to the moDCs in combination with the antigen, as compared to the antibody comprising a reference Fc polypeptide not comprising the mutation(s) and / or fucosylation state, when provided to the moDCs in combination with the antigen, wherein, optionally, (1) the moDCs and the CD4+ T cells are from the same (optionally antigen-vaccinated) subject and / or (2) stimulation of antigen-specific CD4+ T cells is determined by an increase in CD25 expression and / or an increase in proliferation (e.g., as determined by a reduction in CFSE staining over time) and / or an increase in expression of CD69 and / or an increase in expression of NFAT and / or an increase in expression of CD44, by the antigen- specific CD4+ T cells.

[0295] In some embodiments, an engineered Fc or Fc fragment of the present disclosure (or a polypeptide comprising the same) comprises two or more substitution mutations as compared to a reference wild-type Fc or Fc fragment, and the combined effect of the two or more substitutions is different than, and is optionally greater than, would be expected based on the effects of the individual component substitution mutations and / or based on the effects of a subset of the two or more substitution mutations. In other words, in some embodiments, combination mutations comprise a non- additive or synergistic effect with reference to the individual component mutations and / or to a subset thereof.

[0296] In some embodiments, presently disclosed antibodies comprising an Fc variant possess characteristics such as effector functions, ability to bind human C1q, ability to induce FcγRA- mediated cell signaling, ability to bind to human FcRn, ability to promote ADCP, ability to promote ADCC, ability to promote activation of CD4+ T cells, and the like.

[0297] Presently disclosed polypeptides include those that comprise a variant of: an IgG Fc polypeptide or a fragment thereof, wherein the variant comprises one or more modifications as compared to the IgG Fc polypeptide or fragment thereof. It will be understood that, unless stated otherwise, a “reference” polypeptide or antibody (e.g., reference IgG Fc polypeptide or fragment thereof, reference antibody, reference CH2 polypeptide, reference IgG hinge-CH2, reference IgG hinge-Fc polypeptide, reference CH3 polypeptide) is preferably identical to the recited molecule (e.g., 91Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT variant of an Fc polypeptide or fragment thereof; polypeptide comprising such a variant; antibody comprising a variant of an Fc polypeptide) except for the recited difference or differences.

[0298] For example, it will be understood that for a variant IgG1 Fc polypeptide that comprises an alanine (A) amino acid at EU position 236, a reference Fc polypeptide includes an IgG1 Fc polypeptide that is otherwise identical to the variant except that a native glycine (G) amino acid is found at EU position 236. As another example, for a variant of an Fc polypeptide fragment (e.g., containing a CH2 and a portion of a CH3), a reference Fc polypeptide fragment is preferably of an identical length to the variant and preferably differs from the variant only by the recited features (e.g., amino acid mutation or mutations present in the variant). In some embodiments, a reference Fc polypeptide, Fc polypeptide fragment, or antibody comprises a wild-type amino acid sequence (e.g., wild-type human IgG1). Excepting the recited differences present in the variant, a reference Fc polypeptide, Fc polypeptide fragment, or antibody will be of the same isotype, and, preferably, of the same allotype, as the variant. In the case of a reference antibody, the Fabs domains will preferably be identical to those present in the specified antibody comprising a variant Fc polypeptide or fragment thereof.

[0299] In some embodiments, variants of IgG Fc polypeptides or fragments thereof include one or more amino acid substitution as compared to a reference (e.g., wild-type) IgG Fc polypeptide (e.g., SEQ ID NO:137) or fragment thereof. Herein, the position of an amino acid in a variant IgG Fc polypeptide or fragment may be described by referencing the “EU position”; it will be understood that “the EU position” follows the EU numbering system as set forth in Kabat. By way of illustration, it will be understood that in the example of a human IgG1 CH1-CH3 amino acid sequence provided below, the first amino acid (A) corresponds to EU position 118, and the last amino acid (K) corresponds to EU position 447.

[0300] Accordingly, it will be understood that unless otherwise indicated, the position of a recited amino acid(s) follows EU numbering for human IgG1 even if a complete antibody heavy chain, complete CH1-CH3, complete CH2-CH3, or the like is not present or is not explicitly recited. In other words, for example, if only a hinge-CH2 is described and a CH3 and / or CH1 may not be present, the position of the amino acids in the hinge-CH2 is described with reference to EU numbering, unless stated otherwise. Correspondence between EU numbering, Kabat numbering, IMGT exon numbering, and IMGT unique numbering for immunoglobulin G heavy chain constant domain is known in the art and is shown, for example, in the IMGT Scientific chart (www.imgt.org / IMGTScientificChart / Numbering / Hu_IGHGnber.html; created May 17, 2001, accessed May 23, 2021, last updated January 20, 2020). 92Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0301] In some embodiments, an antibody comprises, in an (e.g., human) IgG1 heavy chain, the amino acid mutation(s) set forth in any one of (i)-(xviii): (i) G236A, L328V, and Q295E; (ii) G236A, P230A, and Q295E; (iii) G236A, R292P, and I377N; (iv) G236A, K334A, and Q295E; (v) G236S, R292P, and Y300L; (vi) G236A and Y300L; (vii) G236A, R292P, and Y300L; (viii) G236S, G420V, G446E, and L309T; (ix) G236A and R292P; (x) R292P and Y300L; (xi) G236A and R292P; (xii) Y300L; (xiii) E345K, G236S, L235Y, and S267E; (xiv) E272R, L309T, S219Y, and S267E; (xv) G236Y; (xvi) G236W; (xvii) F243L, G446E, P396L, and S267E; (xviii) G236A, S239D, and H268E, wherein the numbering of amino acid residues is according to the EU index as set forth in Kabat. In certain embodiments, the antibody is afucosylated. In certain embodiments, an antibody comprising an IgG1 Fc polypeptide or fragment thereof comprising GALVQE is afucosylated. In some embodiments, the antibody further comprises one or more mutation that enhances binding to a human FcRn, such as M428L and N434S mutations or M428L and N434A mutations (EU numbering) or any other mutation(s) that enhance binding to a human FcRn, such as those described herein. In certain embodiments, the antibody fragment is afucosylated. In some embodiments, the IgG1 heavy chain comprises a CH1-CH3 or a CH2-CH3 or a hinge-CH2-CH3, wherein the CH1-CH3 or CH2-CH3 or hinge-CH2-CH3 has at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity (or similarity) to a wild-type human IgG1 CH1-CH3 or CH2-CH3 or hinge-CH2-CH3, respectively.

[0302] In some embodiments, the antibody comprises a kappa light chain. In certain embodiments, the antibody is capable of eliciting continued protection in vivo in a subject even once no detectable levels of the antibody can be found in the subject (i.e., when the antibody has been cleared from the subject following administration). Such protection is referred to herein as a vaccinal effect. Without wishing to be bound by theory, it is believed that dendritic cells can internalize complexes of antibody and antigen and thereafter induce or contribute to an endogenous immune response against antigen. In certain embodiments, an antibody comprises one or more modifications, such as, for example, mutations in the Fc comprising G236A, A330L, and I332E, that can activate dendritic cells that may induce, e.g., T cell immunity to the antigen. In any of the presently disclosed embodiments, the antibody comprises a Fc polypeptide or a fragment thereof, including a CH2 (or a fragment thereof, a CH3 (or a fragment thereof), or a CH2 and a CH3, wherein the CH2, the CH3, or both can be of any isotype and may contain amino acid substitutions or other modifications as compared to a corresponding wild-type CH2 or CH3, respectively. In certain embodiments, a Fc of the present disclosure comprises two CH2-CH3 polypeptides that associate to form a dimer.

[0303] In certain embodiments, the antibody comprises a mutation that alters glycosylation, wherein the mutation that alters glycosylation comprises N297A, N297Q, or N297G, and / or the antibody is 93Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT partially or fully aglycosylated and / or is partially or fully afucosylated. Host cell lines and methods of making partially or fully aglycosylated or partially or fully afucosylated antibodies are known (see, e.g., PCT Publication No. WO 2016 / 181357; Suzuki et al. Clin. Cancer Res.13(6):1875-82 (2007); Huang et al. Mabs 6:1-12 (2018)).

[0304] In certain embodiments, the antibody is capable of eliciting continued protection in vivo in a subject even once no detectable levels of the antibody can be found in the subject (i.e., when the antibody has been cleared from the subject following administration). Such protection is referred to herein as a vaccinal effect. Without wishing to be bound by theory, it is believed that dendritic cells can internalize complexes of antibody and antigen and thereafter induce or contribute to an endogenous immune response (e.g., T cell immunity) against antigen.

[0305] An antibody may be of any allotype or combination of allotypes. “Allotype” refers to the allelic variation found among the IgG subclasses. For example, an allotype may comprise G1m1 (or G1m(a)), G1m2 (or G1m(x)), G1m3 (or G1m(f)), G1m17 (or Gm(z))m), G1m27, and / or G1m28 (G1m27 and G1m28 have been described as “alloallotypes”).

[0306] The G1m3 and G1m17 allotypes are located at the same position in the CH1 domain (position 214 according to EU numbering). G1m3 comprises R214 (EU), while G1m17 comprises K214 (EU). The G1m1 allotype is in the CH3 domain (at positions 356 and 358 (EU)) and refers to the replacements E356D and M358L. The G1m2 allotype refers to a replacement of the alanine in position 431 (EU) by a glycine. G1m allotypes, alloallotypes, and features thereof are known in the art and described at, for example, www.imgt.org / IMGTrepertoire / Proteins / allotypes / human / IGH / IGHC / G1m_allotypes.html and Lefranc, M.-P. and Lefranc, G. Human Gm, Km and Am allotypes and their molecular characterization: a remarkable demonstration of polymorphism In: B. Tait, F. Christiansen (Eds.), Immunogenetics, chap.34, Humana Press, Springer, New York, USA. Methods Mol. Biol.2012; 882, 635-680. PMID: 22665258, LIGM: 406, the contents and allotypes and allotype information of which are incorporated herein by reference.

[0307] The G1m1 allotype may be combined, for example, with the G1m3, G1m17, G1m27, G1m2, and / or G1m28 allotype. In some embodiments, an allotype is G1m3 with no G1m1 (G1m3,-1). In some embodiments, an allotype is G1m17,1 allotype. In some embodiments, an allotype is G1m3,1. In some embodiments, an allotype is G1m17 with no G1m1 (G1m17,-1). Optionally, these allotypes may be combined (or not combined) with the G1m2, G1m27 or G1m28 allotype. For example, an allotype may be G1m17,1,2. 94Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0308] In some embodiments, an antibody of the present disclosure comprises a G1m3 allotype or a G1m3,1 allotype. In some embodiments, an antibody of the present disclosure comprises a G1m3 allotype and comprises M428L and N434S or M428L and N434A mutations or any other mutation(s) that enhance binding to a human FcRn, such as those described herein. In some embodiments, an antibody of the present disclosure comprises a G1m3,1 allotype and comprises M428L and N434S or M428L and N434A mutations or any other mutation(s) that enhance binding to a human FcRn, such as those described herein. In some embodiments, an antibody of the present disclosure comprises a G1m17, 1 allotype. In some embodiments, an antibody of the present disclosure comprises a G1m17, 1 allotype and comprises M428L and N434S or M428L and N434A mutations or any other mutation(s) that enhance binding to a human FcRn, as described further herein.

[0309] In certain embodiments, an antibody comprises a CH3 sequence engineered to reduce potential immunogenicity of the antibody by replacing specific amino acids of one allotype with those of another allotype (these may be referred to as isoallotype mutations), as described in more detail in Stickler et al. (Genes Immun.2011 Apr; 12(3): 213-221), which is herein incorporated by reference in its entirety, including, for example, the isoallotype mutations disclosed therein. In particular embodiments, specific amino acids of the Glml allotype are replaced. In a preferred embodiment, isoallotype mutations D356E and L358M are made in the CH3 sequence.

[0310] An antibody of the present disclosure can be fucosylated (e.g., comprising one or more fucosyl moiety, and typically comprising a native (wild-type) fucosylation pattern or a fucosylation pattern that includes one or more additional, or fewer, fucosyl moieties as compared to native), or can be afucosylated. In particular, native IgG1 antibodies carry a glycan site at N297, and this is typically the only site where a core fucose moiety may be found in the antibody, though some glycan sites may arise through mutation (e.g., in the variable domains) during antibody development. Fucosylation of an antibody, can be affected by introducing amino acid mutations to introduce or disrupt a fucosylation site (e.g., a mutation at N297, such as N297Q or N297A, to disrupt formation of a glycan that can include a core fucose moiety), though typically it is preferred to maintain N297 and the glycan thereof, such as by expressing the antibody in a host cell which has been genetically engineered to lack the ability (or have an inhibited or compromised ability) to fucosylate the antibody; by expressing the antibody under conditions in which a host cell is impaired in its ability to fucosylate the polypeptide (e.g., in the presence of 2-fluoro-L-fucose (2FF)), or the like. An afucosylated antibody can comprise no fucose moieties, or substantially no fucose moieties, and / or can be expressed by a host cell that is genetically engineered to lack the ability (or have an inhibited or compromised ability) to fucosylate the antibody and / or can be expressed under conditions in which a host cell is impaired in its ability to fucosylate the antibody (e.g., in the presence of 2-fluoro-L-fucose (2FF)). In some embodiments, an antibody does not comprise a core fucose moiety at Asn297. In 95Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT some embodiments, afucosylated antibodies have increased binding to FcγRIIIA. In some contexts, addition of 2FF to a culture media comprising host cells expressing an antibody result in about 85% or more of the antibodies not carrying a fucose moiety. Accordingly, a plurality of antibodies may be described as “afucosylated” when the plurality was produced in the presence of 2FF or like reagent. In some contexts, a plurality of antibodies may be described as, for example, afucosylated, meaning that about 85% or more of the single antibody molecules of the plurality do not comprise a fucose moiety. In certain preferred embodiments, an afucosylated antibody or a population or a plurality thereof comprises an asparagine (N) at EU position 297. Fucosylation or lack thereof can be assessed using, for example, mass spectrometry (e.g., Electrospray mass spectrometry (ESI-MS)). In some embodiments, compositions are provided that comprise a plurality of any one or more of the presently disclosed antibodies, wherein the composition comprises afucosylated antibodies.

[0311] In any of the presently disclosed embodiments, the antibody can be monoclonal. The term “monoclonal antibody” (mAb) as used herein refers to an antibody obtained from a population of substantially homogeneous antibodies, i.e., individual antibodies comprising the population are identical except for possible naturally occurring mutations that may be present, in some cases in minor amounts. Monoclonal antibodies are highly specific, being directed against a single antigenic site. Furthermore, in contrast to polyclonal antibody preparations that include different antibodies directed against different epitopes, each monoclonal antibody is directed against a single epitope of the antigen. In addition to their specificity, the monoclonal antibodies are advantageous in that they may be synthesized uncontaminated by other antibodies. The term “monoclonal” is not to be construed as requiring production of the antibody by any method. For example, monoclonal antibodies useful in the present disclosure may be prepared by the hybridoma methodology first described by Kohler et al., Nature 256:495 (1975), or may be made using recombinant DNA methods in bacterial, eukaryotic animal, or plant cells (see, e.g., U.S. Patent No.4,816,567). Monoclonal antibodies may also be isolated from phage antibody libraries using the techniques described in Clackson et al., Nature, 352:624-628 (1991) and Marks et al., J. Mol. Biol., 222:581-597 (1991), for example. Monoclonal antibodies may also be obtained using methods disclosed in PCT Publication No. WO 2004 / 076677A2.

[0312] A “human antibody” is an antibody containing only sequences that are present in an antibody that is produced by a human. However, as used herein, human antibodies may comprise residues or modifications not found in a naturally occurring human antibody (e.g., an antibody that is isolated from a human), including those modifications and variant sequences described herein. These are typically made to further refine or enhance antibody performance. In some instances, human antibodies are produced by transgenic animals. For example, see U.S. Patent Nos.5,770,429; 6,596,541 and 7,049,426. 96Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0313] Conjugation of a compound to an antibody is described further herein. Antibody structures amenable to conjugation include, for example, lysine amino acid residues, cysteine amino acid residues, non-natural amino acids (e.g., amino acid analogs), carbohydrate moieties, and N-termini of heavy and light chains (or of VH and VL). Such structures may be native to the antibody, or may be introduced (e.g., a native non-lysine or non-cysteine amino acid of the antibody may be replaced by a lysine or cysteine, and / or a lysine or cysteine may be inserted into the amino acid sequence of the antibody, as an additional amino acid). Also contemplated are conjugation techniques in which a protein with a strong interaction with an antibody (e.g., FcRn, Protein A, Protein G, or fragments of these) is conjugated to a compound and non-covalent interaction between the protein and the antibody effectively couples the compound to the antibody, as well as modification in nucleotide-binding sites (e.g., for modification by photoaffinity labeling), or in catalytic sites (if present). Non-limiting examples of antibody conjugation technologies and mutations to facilitate conjugation are disclosed in, for example, PCT Publication Nos. WO 2006 / 034488, WO 2011 / 005481, WO 2011 / 156328, WO 2016 / 040856, WO 2015 / 157595, WO 2013 / 093809, WO 2005 / 018572, WO 1996 / 014339, WO 2008 / 070593, WO 2009 / 092011, WO 2020 / 191306, WO 2006 / 074397, WO 2008 / 038024, WO 2010 / 141902, and WO 2004 / 042017, as well as in Sang et al., Methods Mol. Biol.2078:235-250 (2020), Haque et al. Chem. Commun.57:10689-10702 (2021), Brun and Gauzy-Lazo, Methods Mol. Biol.1045:173-187 (2013), and Yoder et al., Mol. Pharmaceuticals 16(9):3926-3927 (2019); the techniques, linkers, conjugation sites and conjugation chemistries, and mutations described in the foregoing documents are incorporated herein by reference. Non-limiting examples of mutations include the following (all residue positions according to EU numbering of human IgG1): A118C, S239C, T289C, A330C, and S442C in the heavy chain, and K149C in the light chain.

[0314] An antibody of a conjugate can comprise one or more native lysine, one or more native cysteine, one or more introduced lysine, one or more introduced cysteine, or any combination thereof. In embodiments where an antibody comprises its native lysines, its native cysteines, or both. In some embodiments, an antibody does not comprise modifications in its amino acid sequence for conjugation. Conjugation may comprise forming conjugates at all, or at fewer than all, of the available conjugation sites.

[0315] In some embodiments, an antibody of a conjugate is capable of binding to a SARS-CoV-2 antigen (e.g., a spike protein). In some embodiments, an antibody of a conjugate is capable of binding to an influenza antigen (e.g., a hemagglutinin or a neuraminidase). Tables 3A-C provide variable domain and heavy chain and light chain SEQ ID NOs. of certain antibodies useful in the preparation of conjugates in accordance with the present disclosure. These sequences are provided in the Table 4 of Sequences. It will be understood that antibodies may be expressed in isotypes and allotypes other than in accordance with the sequences as shown in Table 3A-C and may contain Fc mutations as 97Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT shown in certain heavy chain sequences in Table 5, or may contain other Fc mutations, or may contain no Fc mutations. It will also be understood that a heavy chain may or may not comprise a lysine as its C-terminal amino acid and may or may not comprise a glycine-lysine as its C-terminal amino acids. Accordingly, contemplated embodiments include conjugates comprising an antibody of Tables 3A-C wherein a C-terminal lysine or C-terminal glycine-lysine is not present in the heavy chain of the antibody. Table 3A. Antibodies to Influenza A hemagglutinin Antibody VH HC VL LC Flu_Ab 1 3 2 4 T. Antibody VH HC VL LC FNI9-v8.1 (G1m3 with M428L and N434S) 13 14 15 1698Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Antibody VH HC VL LC FNI1279 80Table 3C. Antibodies to SARS-CoV-2 S protein Antibody VH HC VL LC S2X324 (G1m3 with M428L and N434S)17 18 19 20Antibodies Targeting Influenza A Hemagglutinin

[0316] In certain embodiments, a conjugate of the present disclosure includes an antibody or antigen- binding fragment having specificity to an influenza virus, such as targeting the influenza A hemagglutinin of the influenza virus. 99Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0317] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:1 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:2. In some embodiments, the CDRH1, CDRH2, CDRH3, CDRL1, CDRL2, and CDRL3 are according to IMGT (see e.g., imgt.org / IMGTScientificChart / Numbering / IMGTIGVLsuperfamily.html). In some embodiments, the CDRH1, CDRH2, CDRH3, CDRL1, CDRL2, and CDRL3 are according to Kabat. In some embodiments, the CDRH1, CDRH2, CDRH3, CDRL1, CDRL2, and CDRL3 are according to Chothia. In some embodiments, the CDRH1, CDRH2, CDRH3, CDRL1, CDRL2, and CDRL3 are according to Aho. In some embodiments, the CDRH1, CDRH2, CDRH3, CDRL1, CDRL2, and CDRL3, respectively, include the amino acid sequences of SEQ ID NO:7, 8, 9, 10, 11 and 12. In certain embodiments, the VH includes the sequence of SEQ ID NO:1 and the VL includes the sequence of SEQ ID NO:2.

[0318] In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:3 and a light chain that includes the sequence of SEQ ID NO:4. In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:5 and a light chain that includes the sequence of SEQ ID NO:4. In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:6 and a light chain that includes the sequence of SEQ ID NO:4.

[0319] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:21 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:23. In certain embodiments, the VH includes the sequence of SEQ ID NO:21 and the VL includes the sequence of SEQ ID NO:23.In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:22 and a light chain that includes the sequence of SEQ ID NO:24.

[0320] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:25 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:23. In certain embodiments, the VH includes the sequence of SEQ ID NO:25 and the VL includes the sequence of SEQ ID NO:23.In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:26 and a light chain that includes the sequence of SEQ ID NO:24.

[0321] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:27 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:23. In certain embodiments, the VH includes the sequence of SEQ ID NO:27 and the VL includes the sequence of SEQ ID NO:23.In 100Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:28 and a light chain that includes the sequence of SEQ ID NO:24.

[0322] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:29 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:23. In certain embodiments, the VH includes the sequence of SEQ ID NO:29 and the VL includes the sequence of SEQ ID NO:23.In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:30 and a light chain that includes the sequence of SEQ ID NO:24.

[0323] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:31 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:23. In certain embodiments, the VH includes the sequence of SEQ ID NO:31 and the VL includes the sequence of SEQ ID NO:23.In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:32 and a light chain that includes the sequence of SEQ ID NO:24.

[0324] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:33 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:23. In certain embodiments, the VH includes the sequence of SEQ ID NO:33 and the VL includes the sequence of SEQ ID NO:23. In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:34 and a light chain that includes the sequence of SEQ ID NO:24.

[0325] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:43 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:44. In certain embodiments, the VH includes the sequence of SEQ ID NO:43 and the VL includes the sequence of SEQ ID NO:44.

[0326] In some embodiments, a conjugate comprises a VH and a VL that respectively comprise the VH CDRs and VL CDRs of the anti-influenza antibodies disclosed in US8871207B2 (e.g., FI6 variants 1 and 2), US9587010 (e.g., FI6 variants 3-5), and US10294292B2 (e.g., FluB-100; FluB mAbs such as FBC-39 FTL).

[0327] In certain embodiments, a conjugate of the present disclosure includes an antibody or antigen- binding fragment having specificity to an influenza virus, such as targeting the influenza neuraminidase of the influenza virus. Examples of such antibodies or antigen-binding fragments are provided in Table 3B. 101Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Antibodies Targeting SARS-CoV-2

[0328] In certain embodiments, a conjugate of the present disclosure includes an antibody or antigen- binding fragment having specificity to a coronavirus, such as targeting the SARS-CoV-2 S protein of the SARS-CoV-2 virus.

[0329] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:17 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:19. In certain embodiments, the VH includes the sequence of SEQ ID NO:17 and the VL includes the sequence of SEQ ID NO:19.In certain embodiments, the antibody or antigen-binding fragment includes a heavy chain that includes the sequence of SEQ ID NO:18 and a light chain that includes the sequence of SEQ ID NO:20.

[0330] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:37 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:38. In certain embodiments, the VH includes the sequence of SEQ ID NO:37 and the VL includes the sequence of SEQ ID NO:38.

[0331] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:39 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:40. In certain embodiments, the VH includes the sequence of SEQ ID NO:39 and the VL includes the sequence of SEQ ID NO:40.

[0332] In certain embodiments, the antibody or antigen-binding fragment includes a VH and a VL, wherein the VH includes the CDRH1, CDRH2, and CDRH3 of SEQ ID NO:41 and wherein the VL includes the CDRL1, CDRL2, and CDRL3 of SEQ ID NO:42. In certain embodiments, the VH includes the sequence of SEQ ID NO:41 and the VL includes the sequence of SEQ ID NO:42.

[0333] Any of the foregoing antibodies or fragments may alternatively comprise a different allotype or combination of allotypes than is comprised in the antibody heavy chain sequence shown in Tables 3A-C. Additionally or alternatively, one or more alternative Fc fragments as disclosed herein can be used, such as an Fc with M428L and N434S (“LS”), EU numbering, or an Fc with G236A / A330L / I332E (“GAALIE”), EU numbering. In some embodiments, the antibody or fragment includes an Fc or Fc portion as shown in Table 5.

[0334] It will be appreciated that variant antibodies (e.g., comprising one or more amino acid substitution, insertion, or deletion, and preferably comprising one or more conservative amino acid substitution and / or an amino acid substation in a non-CDR or non-V-region amino acid sequence, such as a Fc mutation as described herein) are contemplated for use in conjugates of the present 102Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT disclosure. In some embodiments, an antibody of a conjugate comprises all, or substantially all, of its native lysine amino acid residues, of its native cysteine amino acid residues, or both.

[0335] Antibodies can be made by using a host cell that comprises a polynucleotide that encodes an antibody or a portion thereof (e.g., a CDR, a VH, a VL, a heavy chain, or a light chain). The polynucleotide can be codon-optimized for expression in a host cell. From a known a coding sequence, codon optimization can be performed using known techniques and tools, e.g., using the GenScript® OptimiumGeneTMtool or Gene Synthesis by GeneArt® (ThermoFisher); see also Scholten et al., Clin. Immunol.119:135, 2006). Codon-optimized sequences include sequences that are partially codon-optimized (i.e., one or a plurality of codons is optimized for expression in the host cell) and those that are fully codon-optimized.

[0336] Polynucleotides encoding antibodies may possess different nucleotide sequences while still encoding a same antibody due to, for example, the degeneracy of the genetic code, splicing, and the like.

[0337] A polynucleotide encoding an antibody can be comprised in a polynucleotide that includes other sequences and / or features for, e.g., expression of the antibody in a host cell. Exemplary features include a promoter sequence, a polyadenylation sequence, a sequence that encodes a signal peptide (e.g., located at the N-terminus of an expressed antibody heavy chain or light chain), or the like.

[0338] A polynucleotide can comprise deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). RNA can comprise messenger RNA (mRNA).

[0339] Vectors can be used that comprise or contain a polynucleotide encoding an antibody. A vector can comprise any one or more of the vectors disclosed herein. For example, some vectors comprise a DNA plasmid construct encoding the antibody or a portion thereof (e.g., so-called “DMAb”; see, e.g., Muthumani et al., J Infect Dis.214(3):369-378 (2016); Muthumani et al., Hum Vaccin Immunother 9:2253-2262 (2013)); Flingai et al., Sci Rep.5:12616 (2015); and Elliott et al., NPJ Vaccines 18 (2017). A DNA plasmid construct can comprise a single open reading frame encoding a heavy chain and a light chain (or a VH and a VL) of the antibody wherein the sequence encoding the heavy chain and the sequence encoding the light chain are optionally separated by polynucleotide encoding a protease cleavage site and / or by a polynucleotide encoding a self-cleaving peptide. The substituent components of the antibody can be encoded by a polynucleotide comprised in a single plasmid or can be encoded by a polynucleotide comprised in two or more plasmids (e.g., a first plasmid comprises a polynucleotide encoding a heavy chain, VH, or VH+CH, and a second plasmid comprises a polynucleotide encoding the cognate light chain, VL, or VL+CL). An exemplary expression vector is pVax1, available from Invitrogen®. A DNA plasmid can be delivered to a subject by, for example, 103Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT electroporation (e.g., intramuscular electroporation), or with an appropriate formulation (e.g., hyaluronidase). A vector can comprise a nucleotide sequence encoding a signal peptide. The signal peptide may or may not be present (e.g., can be enzymatically cleaved from) on the mature antibody. In some embodiments, a vector comprises a polyadenylation signal sequence.

[0340] A vector can comprise a CMV promoter.

[0341] Examples of host cells useful for expressing an antibody include but are not limited to, eukaryotic cells, e.g., yeast cells, animal cells, insect cells, plant cells; and prokaryotic cells, including E. coli. In some embodiments, the cells are mammalian cells. In certain such embodiments, the cells are a mammalian cell line such as CHO cells (e.g., DHFR- CHO cells (Urlaub et al., PNAS 77:4216 (1980)), human embryonic kidney cells (e.g., HEK293T cells), PER.C6 cells, Y0 cells, Sp2 / 0 cells. NS0 cells, human liver cells, e.g., Hepa RG cells, myeloma cells or hybridoma cells. Other examples of mammalian host cell lines include mouse sertoli cells (e.g., TM4 cells); monkey kidney CV1 line transformed by SV40 (COS-7); baby hamster kidney cells (BHK); African green monkey kidney cells (VERO-76); monkey kidney cells (CV1); human cervical carcinoma cells (HELA); human lung cells (W138); human liver cells (Hep G2); canine kidney cells (MDCK; buffalo rat liver cells (BRL 3A); mouse mammary tumor (MMT 060562); TRI cells; MRC 5 cells; and FS4 cells. Mammalian host cell lines suitable for antibody production also include those described in, for example, Yazaki and Wu, Methods in Molecular Biology, Vol.248 (B. K. C. Lo, ed., Humana Press, Totowa, N.J.), pp. 255-268 (2003).

[0342] A host cell can be a prokaryotic cell, such as an E. coli. The expression of peptides in prokaryotic cells such as E. coli is well established (see, e.g., Pluckthun, A. Bio / Technology 9:545- 551 (1991). For example, antibodies may be produced in bacteria, when glycosylation and Fc effector function are not needed. For expression of antibody polypeptides in bacteria, see, e.g., U.S. Patent Nos.5,648,237; 5,789,199; and 5,840,523.

[0343] A host cell may be transfected with a vector according to the present description with an expression vector. The term “transfection” refers to the introduction of nucleic acid molecules, such as DNA or RNA (e.g., mRNA) molecules, into cells, such as into eukaryotic cells. In the context of the present description, the term “transfection” encompasses any method known to the skilled person for introducing nucleic acid molecules into cells, such as into eukaryotic cells, including into mammalian cells. Such methods encompass, for example, electroporation, lipofection, e.g., based on cationic lipids and / or liposomes, calcium phosphate precipitation, nanoparticle-based transfection, virus-based transfection, or transfection based on cationic polymers, such as DEAE-dextran or polyethylenimine, etc. The introduction can be non-viral. 104Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0344] Moreover, host cells may be transfected stably or transiently with a vector, e.g., for expressing an antibody. The cells may be stably transfected with the vector. Alternatively, cells may be transiently transfected with a vector comprising a polynucleotide encoding an antibody. A polynucleotide may be heterologous to the host cell.

[0345] Recombinant host cells can be engineered to heterologously express an antibody. For example, the cell may be of a species that is different to the species from which the antibody was fully or partially obtained (e.g., CHO cells expressing a human antibody or an engineered human antibody). In some embodiments, the cell type of the host cell does not express the antibody in nature. Moreover, the host cell may impart a post-translational modification (PTM; e.g., glycosylation or fucosylation) on an antibody that is not present in a native state of the antibody (or in a native state of a parent antibody from which the antibody was engineered or derived). Such a PTM may result in a functional difference (e.g., reduced immunogenicity). Accordingly, an antibody that is produced by a host cell as disclosed herein may include one or more post-translational modification that is distinct from the antibody (or parent antibody) in its native state (e.g., a human antibody produced by a CHO cell can comprise a more post-translational modification that is distinct from the antibody when isolated from the human and / or produced by the native human B cell or plasma cell).

[0346] Insect cells useful expressing an antibody are known in the art and include, for example, Spodoptera frugipera Sf9 cells, Trichoplusia ni BTI-TN5B1-4 cells, and Spodoptera frugipera SfSWT01 “MimicTM” cells. See, e.g., Palmberger et al., J. Biotechnol.153(3-4):160-166 (2011). Numerous baculoviral strains have been identified which may be used in conjunction with insect cells, particularly for transfection of Spodoptera frugiperda cells.

[0347] Eukaryotic microbes such as filamentous fungi or yeast are also suitable hosts for cloning or expressing protein-encoding vectors and include fungi and yeast strains with “humanized” glycosylation pathways, resulting in the production of an antibody with a partially or fully human glycosylation pattern. See Gerngross, Nat. Biotech.22:1409-1414 (2004); Li et al., Nat. Biotech.24:210-215 (2006).

[0348] Plant cells can also be utilized as hosts for expressing an antibody. For example, PLANTIBODIES™ technology (described in, for example, U.S. Patent Nos.5,959,177; 6,040,498; 6,420,548; 7,125,978; and 6,417,429) employs transgenic plants to produce antibodies.

[0349] A host cell can comprise a mammalian cell, such as, for example, a CHO cell, a HEK293 cell, a PER.C6 cell, a Y0 cell, a Sp2 / 0 cell, a NS0 cell, a human liver cell, a myeloma cell, or a hybridoma cell. 105Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0350] Methods for producing an antibody can comprise culturing a host cell of the present disclosure under conditions and for a time sufficient to produce the antibody. Methods useful for isolating and purifying recombinantly produced antibodies, by way of example, may include obtaining supernatants from suitable host cell / vector systems that secrete the recombinant antibody into culture media and then concentrating the media using a commercially available filter. Following concentration, the concentrate may be applied to a single suitable purification matrix or to a series of suitable matrices, such as an affinity matrix or an ion exchange resin. One or more reverse phase HPLC steps may be employed to further purify a recombinant polypeptide. These purification methods may also be employed when isolating an immunogen from its natural environment. Methods for large scale production of an isolated / recombinant antibody include batch cell culture, which is monitored and controlled to maintain appropriate culture conditions. Purification of soluble antibodies may be performed according to methods described herein and known in the art and that comport with laws and guidelines of domestic and foreign regulatory agencies.

[0351] In certain embodiments, a method comprises administering the compound, conjugate, or pharmaceutical composition to the subject once (e.g., a single dose, or a single regimen comprising two or more doses) in a twelve-month period, once in a six-month period, once in a three-month period, about once yearly, about once every six months, or about once every three months. In some embodiments, a method comprises administering the compound, conjugate, or pharmaceutical composition to the subject prior to, or in the early stages of, a seasonal or yearly period in which an increase in infections in a population of subjects is expected or has historically been observed; e.g., a method may comprise administering the compound, conjugate, or pharmaceutical composition as a preventive measure shortly prior to or during the fall or winter, e.g., during August, September, October, November, December, January, or February in the northern hemisphere.

[0352] Compositions comprising a compound or conjugate of the present disclosure may also be administered simultaneously with, prior to, or after administration of one or more other therapeutic agents. Such combination therapy may include administration of a single pharmaceutical dosage formulation which contains a compound or conjugate of the disclosure and one or more additional active agents, as well as administration of compositions comprising a compound or conjugate of the disclosure and each active agent in its own separate dosage formulation. For example, an antibody as described herein and the other active agent can be administered to the subject together in a single parenteral dosage composition such as in a saline solution or other physiologically acceptable solution, or each agent administered in separate parenteral dosage formulations. Where separate dosage formulations are used, the compositions comprising a compound or conjugate and one or more additional active agents can be administered at essentially the same time, i.e., concurrently, or at 106Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT separately staggered times, i.e., sequentially and in any order; combination therapy is understood to include all these regimens.

[0353] In certain embodiments, a combination therapy is provided that comprises one or more compound, conjugate, or pharmaceutical composition of the present disclosure and one or more anti- inflammatory agent and / or one or more anti-viral agent. In particular embodiments, the one or more anti-inflammatory agent comprises a corticosteroid such as, for example, dexamethasone, prednisone, or the like. In some embodiments, the one or more anti-inflammatory agents comprise a cytokine antagonist such as, for example, an antibody that binds to IL6 (such as siltuximab), or to IL-6R (such as tocilizumab), or to IL-1β, IL-7, IL-8, IL-9, IL-10, FGF, G-CSF, GM-CSF, IFN-γ, IP-10, MCP-1, MIP-1A, MIP1-B, PDGR, TNF-α, or VEGF. In some embodiments, anti-inflammatory agents such as ruxolitinib and / or anakinra are used. In some embodiments, the one or more anti-viral agents comprise nucleotide analogs or zanamivir analog prodrugs such as, for example, remdesivir, sofosbuvir, acyclovir, and zidovudine. In particular embodiments, an anti-viral agent comprises lopinavir, ritonavir, favipiravir, oseltamivir, peramivir, zanamivir, or any combination thereof. In some embodiments, a combination therapy comprises leronlimab. Anti-inflammatory agents for use in a combination therapy of the present disclosure also include non-steroidal anti-inflammatory drugs (NSAIDS). It will be appreciated that in such a combination therapy, the one or more compound, conjugate, or pharmaceutical composition and the one or more anti-inflammatory agent and / or one or the more antiviral agent can be administered in any order and any sequence, or together.

[0354] In some embodiments, a compound, conjugate, or pharmaceutical composition is administered to a subject who has previously received one or more anti-inflammatory agent and / or one or more antiviral agent. In some embodiments, one or more anti-inflammatory agent and / or one or more antiviral agent is administered to a subject who has previously a compound, conjugate, or pharmaceutical composition. In a related aspect, uses of the presently disclosed compounds, conjugates and pharmaceutical compositions are provided.

[0355] In certain embodiments, a compound, conjugate, or pharmaceutical composition is provided for use in a method of treating (e.g., treating an existing infection or preventing an infection or preventing a severe infection) a respiratory virus infection in a subject.

[0356] In certain embodiments, a compound, conjugate, or pharmaceutical composition is provided for use in a method of manufacturing or preparing a medicament for treating (e.g., treating an existing infection or preventing an infection or preventing a severe infection) a respiratory virus infection in a subject. Table 4. Antibody Sequences 107Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceL T L T P S H P E L V L T P S H P E L V L T P S H P E L V L T P S H P E L V L F108Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceL F K Y W Y W Y P S H P E L V L W L W Y E L T L T T V E D A109Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceP N K T K T D W L T L T S G T E Y T D L D L D F Y L T L T S110Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceG T E Y T D L T L T S G T E Y T D L T L T S G T E Y T D L T L T S G T E Y T D111Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceL T L T S G T E Y T D L T S G T E Y T D W Y L W W Y L T L T K T W Y112Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceK A L T L D W Y L W W Y L W W Y L W W Y L W W Y L F W Y113Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceL W W Y L F W Y L W W Y L W W Y L W W Y L W W Y L W W Y114Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceL W W Y L F W Y L W W Y L F W Y L W W Y L W W Y L W W Y115Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceL W W Y L W W Y L W W Y L W W Y L W W Y L W W Y L W W Y116Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceL W W Y L W W Y L W W Y L W W Y L W W Y L W117Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceW Y L W W Y L W W Y L W W Y L W W Y L W W Y118Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceL W W Y L W W Y L W W Y L W W Y L W W Y L W119Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT DescriptionSEQ IDNO: SequenceW Y L W W Y L W W Y L W

[0357] In certain embodiments, a polypeptide of a conjugate of the present disclosure consists of an Fc polypeptide or a fragment thereof. In certain embodiments, a polypeptide of a conjugate of the present disclosure comprises an Fc polypeptide or a fragment thereof without further comprising an antigen binding domain (e.g. VH and VL regions). Such conjugates can be referred-to as drug-Fc conjugates or DFCs. In some embodiments, the Fc polypeptide comprises a CH2 domain and a CH3 domain. In some embodiments, the Fc polypeptide further comprises a hinge domain. In some embodiments, the Fc polypeptide further comprises a CH1 domain or a portion thereof. In some embodiments, the Fc polypeptide comprises or consists of a portion of a CH1 domain, a hinge domain, a CH2 domain, and a CH3 domain. In certain embodiments, the Fc polypeptide of a conjugate described herein comprises or consists of an Fc sequence of any one of SEQ ID NO: 137- 142. In certain embodiments, the Fc polypeptide of a conjugate comprises or consists of SEQ ID NO: 140. In certain embodiments, the Fc polypeptide (“YTE” version) of a conjugate comprises or consists of SEQ ID NO: 142. An example antibody with the Fc (YTE), Flu_Ab (YTE), includes a heavy chain sequence of SEQ ID NO:143, and a light chain sequence of SEQ ID NO:4. Another 120Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT example, FHF11v9 (YTE), includes a heavy chain sequence of SEQ ID NO:144, and a light chain sequence of SEQ ID NO:24. Table 5. Fc Sequences Description SEQ ID NO: Sequence Fc fragment ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVH S D C F F L V P F L V P F L V P F L V P F H S D C F121Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT YPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVF SCSVMHEALHNHYTQKSLSLSPGK, ,

[0358] The methods described herein may be applied to cell populations in vivo or ex vivo. “In vivo” means within a living individual, as within an animal or human. In this context, the methods described herein may be used therapeutically in an individual. “Ex vivo” means outside of a living individual. Examples of ex vivo cell populations include in vitro cell cultures and biological samples including fluid or tissue samples obtained from individuals. Such samples may be obtained by methods well known in the art. Exemplary biological fluid samples include blood, cerebrospinal fluid, urine, and saliva. In this context, the compounds and compositions described herein may be used for a variety of purposes, including therapeutic and experimental purposes. For example, the compounds and compositions described herein may be used ex vivo to determine the optimal schedule and / or dosing of administration of a compound of the present disclosure for a given indication, cell type, individual, and other parameters. Information gleaned from such use may be used for experimental purposes or in the clinic to set protocols for in vivo treatment. Other ex vivo uses for which the compounds and compositions described herein may be suited are described below or will become apparent to those skilled in the art. The selected compounds may be further characterized to examine the safety or tolerance dosage in human or non-human subjects. Such properties may be examined using commonly known methods to those skilled in the art.

[0359] Also provided herein are methods for using of a compound, conjugate, or pharmaceutical composition of the present disclosure to prevent or treat a respiratory virus infection in a subject. “Treat,” “treatment,” or “ameliorate” refers to medical management of a disease, disorder, or condition of a subject (e.g., a human or non-human mammal, such as a primate, horse, cat, dog, goat, mouse, or rat). In general, an appropriate dose or treatment regimen comprising an antibody or composition of the present disclosure is administered in an amount sufficient to elicit a therapeutic or prophylactic benefit. Therapeutic or prophylactic / preventive benefit includes improved clinical outcome; lessening or alleviation of symptoms associated with a disease; decreased occurrence of symptoms; improved quality of life; longer disease-free status; diminishment of extent of disease, stabilization of disease state; delay or prevention of disease progression; remission; survival; prolonged survival; or any combination thereof. In certain embodiments, therapeutic or prophylactic / preventive benefit includes reduction or prevention of hospitalization for treatment of a respiratory virus infection (i.e., in a statistically significant manner). In certain embodiments, therapeutic or prophylactic / preventive benefit includes a reduced duration of hospitalization for treatment of a respiratory virus infection (i.e., in a statistically significant manner). In certain 122Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT embodiments, therapeutic or prophylactic / preventive benefit includes a reduced or abrogated need for respiratory intervention, such as intubation and / or the use of a respirator device. In certain embodiments, therapeutic or prophylactic / preventive benefit includes reversing a late-stage disease pathology and / or reducing mortality.

[0360] A “therapeutically effective amount” or “effective amount” of a compound, conjugate, or pharmaceutical composition of this disclosure refers to an amount of the composition, conjugate, or pharmaceutical composition, respectively, sufficient to result in a therapeutic effect, including improved clinical outcome; lessening or alleviation of symptoms associated with a disease; decreased occurrence of symptoms; improved quality of life; longer disease-free status; diminishment of extent of disease, stabilization of disease state; delay of disease progression; remission; survival; or prolonged survival in a statistically significant manner. When referring to an individual active ingredient (e.g., compound, conjugate, or pharmaceutical composition, administered alone, a therapeutically effective amount refers to the effects of that ingredient. When referring to a combination, a therapeutically effective amount refers to the combined amounts of active ingredients that results in a therapeutic effect, whether administered serially, sequentially, or simultaneously.

[0361] “Antiviral” or “antiviral activity” refers to inhibiting the replication, multiplication, or spread of a virus. The inhibition encompasses various mechanisms, including (1) preventing viral attachment or entry (e.g., blocking an interaction between the virus and a host cell receptor), (2) interfering with viral replication (e.g., inhibiting the synthesis of viral proteins or nucleic acids), (3) disrupting viral assembly or release (e.g., disrupting viral assembly or release), and / or (4) modulating a host’s immune system response (e.g., enhancing the immune system’s ability to fight off the virus). In some embodiments, the compounds or conjugates of the present disclosure have a minimum inhibitor concentration or other relevant quantitative data demonstrating the antiviral activity.

[0362] Accordingly, in certain embodiments, methods are provided for treating a respiratory virus infection (e.g., influenza, coronavirus (e.g., SARS-CoV-2)) infection in a subject, wherein the methods comprise administering to the subject an effective amount of a conjugate or pharmaceutical composition as disclosed herein.

[0363] Subjects that can be treated by the present disclosure are, in general, human, and other primate subjects, such as monkeys and apes for veterinary medicine purposes. Other model organisms, such as mice and rats, may also be treated according to the present disclosure. In any of the aforementioned embodiments, the subject may be a human subject. The subjects can be male or female and can be any suitable age, including infant, juvenile, adolescent, adult, and geriatric subjects.

[0364] In certain embodiments, a human subject treated according to the present disclosure is an infant, a child, a young adult, an adult of middle age, or an elderly person. In certain embodiments, a human subject treated according to the present disclosure is less than 1 year old, or is 1 to 5 years old, 123Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT or is between 5 and 125 years old (e.g., 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, or 125 years old, including any and all ages therein or therebetween). In certain embodiments, a human subject treated according to the present disclosure is 0-19 years old, 20-44 years old, 45-54 years old, 55-64 years old, 65-74 years old, 75-84 years old, or 85 years old and older. In particular embodiments, the human subject is 45-54 years old, 55-64 years old, 65-74 years old, 75-84 years old, or 85 years old and older. In some embodiments, the human subject is male. In some embodiments, the human subject is female.46. In some embodiments, the subject is 65 years of age or older.

[0365] In some embodiments, the conjugate or pharmaceutical composition provided herein is administered prior to the subject having been exposed to an influenza virus.

[0366] In certain embodiments, methods are provided for preventing an influenza viral infection in a subject in need thereof, comprising administering to the subject an effective amount of a conjugate or pharmaceutical composition as disclosed herein.

[0367] In certain embodiments, the influenza is influenza A, influenza B, or a combination thereof. In certain embodiments, the influenza is influenza A. In certain embodiments, the influenza is influenza B. In certain embodiments, the influenza is influenza A and influenza B.

[0368] In some embodiments, the subject has a comorbidity for influenza. In some embodiments, the comorbidity is selected from the group consisting of a chronic respiratory disease, a cardiovascular disorder, a chronic kidney disease, a neurological disorder, an endocrine or metabolic disorder, cancer, a weakened immune system, obesity, and pregnancy, or a combination thereof. In some embodiments, the chronic respiratory disease is chronic obstructive pulmonary disease (COPD), cystic fibrosis, or asthma. In some embodiments, the cardiovascular disorder is congestive heart failure, a coronary artery disease, or a congenital heart defect. In some embodiments, the neurological disorder is cerebral palsy or epilepsy. In some embodiments, the endocrine or metabolic disorder is diabetes. In some embodiments, the weakened immune system is a result of a human immunodeficiency virus (HIV) infection, cancer treatment, or chronic steroid use.

[0369] In certain embodiments, provided are methods for treating an influenza viral infection in a subject in need thereof, comprising administering to the subject an effective amount of a conjugate or pharmaceutical composition as disclosed herein.

[0370] In certain embodiments, provided is a conjugate or pharmaceutical composition as disclosed herein for use in preventing an influenza viral infection. 124Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0371] In certain embodiments, provided is the use of a conjugate as disclosed herein in the manufacture of a medicament for the prevention of an influenza viral infection, such as for use in treating an influenza viral infection.

[0372] In certain embodiments, provided is the use of a conjugate as disclosed herein in the manufacture of a medicament for the treatment of an influenza viral infection.

[0373] In certain embodiments, treatment is administered as pre-exposure prophylaxis. In certain embodiments, treatment is administered as peri-exposure prophylaxis. In certain embodiments, treatment is administered as post-exposure prophylaxis.

[0374] In certain embodiments, a composition, compound, conjugate, or pharmaceutical composition is administered in combination with (before, concurrently with, or after) a vaccine, such as, but not limited to, an influenza vaccine.

[0375] Typical routes of administering the presently disclosed compositions thus include, without limitation, oral, topical, transdermal, inhalation, parenteral, sublingual, buccal, rectal, vaginal, and intranasal. The term “parenteral”, as used herein, includes subcutaneous injections, intravenous, intramuscular, intrasternal injection, or infusion techniques. In certain embodiments, administering comprises administering by a route that is selected from oral, intravenous, parenteral, intragastric, intrapleural, intrapulmonary, intrarectal, intradermal, intraperitoneal, intratumoral, subcutaneous, topical, transdermal, intracisternal, intrathecal, intranasal, and intramuscular. In particular embodiments, a method comprises orally administering the compound, conjugate, or pharmaceutical composition to the subject.

[0376] In certain embodiments, a conjugate or pharmaceutical composition is administered as prophylaxis (e.g., pre-exposure, peri-exposure, or post-exposure) against a respiratory virus infection to a subject. In further embodiments, the composition, compound, conjugate, or pharmaceutical composition is administered via intramuscular injection. In some embodiments, the subject is an elderly subject (e.g., is aged 65 years or more) and / or has a pre-existing lung disease (e.g., asthma, lung cancer, COPD, emphysema, pneumonia, tuberculosis, lung scarring, lung damage following smoke inhalation, pulmonary hypertension, a chronic lung disease, or the like). In certain embodiments, the prophylaxis is effective against influenza A, influenza B, or both. In certain further embodiments, the prophylaxis is effective against SARS-CoV-2.

[0377] In certain embodiments, the administering comprises intranasal, intramuscular, subcutaneous, or intravenous administration. In some embodiments, the composition is formulated such that the administration is once per 6-month influenza season. In some embodiments, the administering comprises intramuscular injection. In some embodiments, the intramuscular injection is in the deltoid muscle. 125Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0378] Pharmaceutical compositions according to certain embodiments of the present disclosure are formulated to allow the active ingredients contained therein to be bioavailable upon administration of the composition to a patient. Compositions that will be administered to a subject or patient may take the form of one or more dosage units, where for example, a tablet may be a single dosage unit, and a container of a herein described compound, conjugate, or pharmaceutical composition in aerosol form may hold a plurality of dosage units. Actual methods of preparing such dosage forms are known, or will be apparent, to those skilled in this art; for example, see Remington: The Science and Practice of Pharmacy, 20thEdition (Philadelphia College of Pharmacy and Science, 2000). The composition to be administered will, in any event, contain an effective amount of a compound, conjugate, or pharmaceutical composition of the present disclosure, for treatment of a disease or condition of interest in accordance with teachings herein.

[0379] A composition may be in the form of a solid or liquid. In some embodiments, the carrier(s) are particulate, so that the compositions are, for example, in tablet or powder form. The carrier(s) may be liquid, with the compositions being, for example, an oral oil, injectable liquid, or an aerosol, which is useful in, for example, inhalatory administration.

[0380] The composition may be in the form of a liquid, for example, an elixir, syrup, solution, emulsion, or suspension. The liquid may be for oral administration or for delivery by injection, as two examples. In a composition intended to be administered by injection, one or more of a surfactant, preservative, wetting agent, dispersing agent, suspending agent, buffer, stabilizer, and isotonic agent may be included.

[0381] Liquid pharmaceutical compositions, whether they be solutions, suspensions or other like form, may include one or more of the following adjuvants: sterile diluents such as water for injection, saline solution, preferably physiological saline, Ringer’s solution, isotonic sodium chloride, fixed oils such as synthetic mono or diglycerides which may serve as the solvent or suspending medium, polyethylene glycols, glycerin, propylene glycol or other solvents; antibacterial agents such as benzyl alcohol or methyl paraben; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates, or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic. Physiological saline is a preferred adjuvant. An injectable pharmaceutical composition is preferably sterile.

[0382] A liquid composition intended for either parenteral or oral administration should contain an amount of a compound, conjugate, or pharmaceutical composition as herein disclosed such that a suitable dosage will be obtained. Typically, this amount is at least 0.01% of the compound or conjugate in the pharmaceutical composition. 126Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0383] The pharmaceutical compositions may be prepared by methodology well known in the pharmaceutical art. For example, a composition intended to be administered by injection can be prepared by combining a composition that comprises a compound or conjugate as described herein and optionally, one or more of salts, buffers, and / or stabilizers, with sterile, distilled water so as to form a solution. A surfactant may be added to facilitate the formation of a homogeneous solution or suspension. Surfactants are compounds (e.g., anionic, non-ionic, cationic, or amphoteric compounds) that non-covalently interact with the peptide composition so as to facilitate dissolution or homogeneous suspension of the compound or conjugate in the aqueous delivery system.

[0384] In general, an appropriate dose and treatment regimen provide the composition(s) in an amount sufficient to provide therapeutic and / or prophylactic benefit (such as described herein, including an improved clinical outcome (e.g., a longer disease-free and / or overall survival, or a lessening of symptom severity). For prophylactic use, a dose should be sufficient to prevent, delay the onset of, or diminish the severity of a disease associated with disease or disorder. Prophylactic benefit of the compositions administered according to the methods described herein can be determined by performing pre-clinical (including in vitro and in vivo animal studies) and clinical studies and analyzing data obtained therefrom by appropriate statistical, biological, and clinical methods and techniques, all of which can readily be practiced by a person skilled in the art.

[0385] Compositions are administered in an effective amount (e.g., to treat a respiratory virus infection), which will vary depending upon a variety of factors including the activity of the specific compound or conjugate employed; the metabolic stability and length of action of the compound or conjugate; the age, body weight, general health, sex, and diet of the subject; the mode and time of administration; the rate of excretion; the drug combination; the severity of the particular disorder or condition; and the subject undergoing therapy. In certain embodiments, following administration of therapies according to the formulations and methods of this disclosure, test subjects will exhibit about a 10% up to about a 99% reduction in one or more symptoms associated with the disease or disorder being treated as compared to placebo-treated or other suitable control subjects.

[0386] In certain embodiments, a method comprises administering the compound, conjugate, or pharmaceutical composition to the subject at 2, 3, 4, 5, 6, 7, 8, 9, 10 times, or more.

[0387] In certain embodiments, a method comprises administering the compound, conjugate, or pharmaceutical composition to the subject a plurality of times, wherein a second or successive administration is performed at about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 24, about 48, about 74, about 96 hours, or more, following a first or prior administration, respectively.

[0388] In certain embodiments, a method comprises administering the compound, conjugate, or pharmaceutical composition at least one time prior to the subject being infected by a respiratory virus. 127Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0389] In certain embodiments, a method comprises administering the compound, conjugate, or pharmaceutical composition to the subject once (e.g., a single dose, or a single regimen comprising two or more doses) in a twelve-month period, once in a six-month period, once in a three-month period, about once yearly, about once every six months, or about once every three months. In some embodiments, a method comprises administering the compound, conjugate, or pharmaceutical composition to the subject prior to, or in the early stages of, a seasonal or yearly period in which an increase in infections in a population of subjects is expected or has historically been observed; e.g., a method may comprise administering the compound, conjugate, or pharmaceutical composition as a preventive measure shortly prior to or during the fall or winter, e.g., during August, September, October, November, December, January, or February in the northern hemisphere.

[0390] In certain embodiments, a compound, conjugate, or pharmaceutical composition is provided for use in a method of treating (e.g., treating an existing infection or preventing an infection or preventing a severe infection) a respiratory virus infection in a subject.

[0391] In certain embodiments, a compound, conjugate, or pharmaceutical composition is provided for use in a method of manufacturing or preparing a medicament for treating (e.g., treating an existing infection or preventing an infection or preventing a severe infection) a respiratory virus infection in a subject.

[0392] Improvements in any of the foregoing response criteria are specifically provided by the methods of the present disclosure.

[0393] Compositions comprising a compound or conjugate of the present disclosure may also be administered simultaneously with, prior to, or after administration of one or more other therapeutic agents. Such combination therapy may include administration of a single pharmaceutical dosage formulation which contains a compound or conjugate of the disclosure and one or more additional active agents, as well as administration of compositions comprising a compound or conjugate of the disclosure and each active agent in its own separate dosage formulation. For example, a compound, conjugate, pharmaceutical composition as described herein and the other active agent can be administered to the patient together in a single oral dosage composition such as a tablet or capsule, or each agent administered in separate oral dosage formulations. Similarly, an antibody as described herein and the other active agent can be administered to the subject together in a single parenteral dosage composition such as in a saline solution or other physiologically acceptable solution, or each agent administered in separate parenteral dosage formulations. Where separate dosage formulations are used, the compositions comprising a compound or conjugate and one or more additional active agents can be administered at essentially the same time, i.e., concurrently, or at separately staggered times, i.e., sequentially and in any order; combination therapy is understood to include all these regimens. 128Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0394] In certain embodiments, a combination therapy is provided that comprises one or more compound, conjugate, or pharmaceutical composition of the present disclosure and one or more anti- inflammatory agent and / or one or more anti-viral agent. In particular embodiments, the one or more anti-inflammatory agent comprises a corticosteroid such as, for example, dexamethasone, prednisone, or the like. In some embodiments, the one or more anti-inflammatory agents comprise a cytokine antagonist such as, for example, an antibody that binds to IL6 (such as siltuximab), or to IL-6R (such as tocilizumab), or to IL-1β, IL-7, IL-8, IL-9, IL-10, FGF, G-CSF, GM-CSF, IFN-γ, IP-10, MCP-1, MIP-1A, MIP1-B, PDGR, TNF-α, or VEGF. In some embodiments, anti-inflammatory agents such as ruxolitinib and / or anakinra are used. In some embodiments, the one or more anti-viral agents comprise nucleotide analogs or zanamivir analog prodrugs such as, for example, remdesivir, sofosbuvir, acyclovir, and zidovudine. In particular embodiments, an anti-viral agent comprises lopinavir, ritonavir, favipiravir, oseltamivir, peramivir, zanamivir, or any combination thereof. In some embodiments, a combination therapy comprises leronlimab. Anti-inflammatory agents for use in a combination therapy of the present disclosure also include non-steroidal anti-inflammatory drugs (NSAIDS). It will be appreciated that in such a combination therapy, the one or more compound, conjugate, or pharmaceutical composition and the one or more anti-inflammatory agent and / or one or the more antiviral agent can be administered in any order and any sequence, or together.

[0395] In some embodiments, a compound, conjugate, or pharmaceutical composition is administered to a subject who has previously received one or more anti-inflammatory agent and / or one or more antiviral agent. In some embodiments, one or more anti-inflammatory agent and / or one or more antiviral agent is administered to a subject who has previously a compound, conjugate, or pharmaceutical composition. In a related aspect, uses of the presently disclosed compounds, conjugates and pharmaceutical compositions are provided. Synthesis of the Compounds

[0396] The compounds may be prepared using the methods disclosed herein and routine modifications thereof, which will be apparent given the disclosure herein and methods well known in the art. Conventional and well-known synthetic methods may be used in addition to the teachings herein. The synthesis of typical compounds described herein may be accomplished as described in the following examples. If available, reagents may be purchased commercially, e.g., from Sigma Aldrich or other chemical suppliers. General Synthesis

[0397] Typical embodiments of compounds described herein may be synthesized using the general reaction schemes described below. It will be apparent given the description herein that the general schemes may be altered by substitution of the starting materials with other materials having similar structures to result in products that are correspondingly different. Descriptions of syntheses follow to 129Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT provide numerous examples of how the starting materials may vary to provide corresponding products. Given a desired product for which the substituent groups are defined, the necessary starting materials generally may be determined by inspection. Starting materials are typically obtained from commercial sources or synthesized using published methods. For synthesizing compounds which are embodiments described in the present disclosure, inspection of the structure of the compound to be synthesized will provide the identity of each substituent group. The identity of the final product will generally render apparent the identity of the necessary starting materials by a simple process of inspection, given the examples herein. In general, compounds described herein are typically stable and isolatable at room temperature and pressure.

[0398] The compounds may be prepared using the methods disclosed herein and routine modifications thereof, which will be apparent given the disclosure herein and methods well known in the art. Conventional and well-known synthetic methods may be used in addition to the teachings herein. The synthesis of typical compounds described herein may be accomplished as described in the following examples. If available, reagents and starting materials may be purchased commercially, e.g., from Sigma Aldrich or other chemical suppliers.

[0399] It will be appreciated that where typical or preferred process conditions (i.e., reaction temperatures, times, mole ratios of reactants, solvents, pressures, etc.) are given, other process conditions can also be used unless otherwise stated. Optimum reaction conditions may vary with the particular reactants or solvent used, but such conditions can be determined by one skilled in the art by routine optimization procedures.

[0400] Additionally, conventional protecting groups may be necessary to prevent certain functional groups from undergoing undesired reactions. Suitable protecting groups for various functional groups as well as suitable conditions for protecting and deprotecting particular functional groups are well known in the art. For example, numerous protecting groups are described in Wuts, P. G. M., Greene, T. W., & Greene, T. W. (2006). Greene’s protective groups in organic synthesis. Hoboken, N.J., Wiley-Interscience, and references cited therein.

[0401] Furthermore, the compounds of this disclosure may contain one or more chiral centers. Accordingly, if desired, such compounds can be prepared or isolated as pure stereoisomers, i.e., as individual enantiomers or diastereomers or as stereoisomer-enriched mixtures. All such stereoisomers (and enriched mixtures) are included within the scope of this disclosure, unless otherwise indicated. Pure stereoisomers (or enriched mixtures) may be prepared using, for example, optically active starting materials or stereoselective reagents well-known in the art. Alternatively, racemic mixtures of such compounds can be separated using, for example, chiral column chromatography, chiral resolving agents, and the like. 130Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0402] The starting materials for the following reactions are generally known compounds or can be prepared by known procedures or obvious modifications thereof. For example, many of the starting materials are available from commercial suppliers such as Aldrich Chemical Co. (Milwaukee, Wisconsin, USA), Bachem (Torrance, California, USA), Emka-Chemce or Sigma (St. Louis, Missouri, USA). Others may be prepared by procedures or obvious modifications thereof, described in standard reference texts such as Fieser and Fieser’s Reagents for Organic Synthesis, Volumes 1-15 (John Wiley, and Sons, 1991), Rodd’s Chemistry of Carbon Compounds, Volumes 1-5, and Supplementals (Elsevier Science Publishers, 1989) organic Reactions, Volumes 1-40 (John Wiley, and Sons, 1991), March’s Advanced Organic Chemistry, (John Wiley, and Sons, 5th Edition, 2001), and Larock’s Comprehensive Organic Transformations (VCH Publishers Inc., 1989).

[0403] Conjugates of the disclosure (e.g., Formula IA) can be prepared according to Scheme I, where p, q, r, m, L2, X1, L3, x, L4, y, and A are each independently as defined herein, and X2ais a functional group capable of spontaneous conjugation to a compatible chemical group on X1when the two groups come into contact under suitable conditions (e.g., thiol-maleimide chemistry or copper free Click chemistry conditions). In some instances, the chemoselective ligation group is capable of conjugation to a compatible chemical group when the two groups come into contact in the presence of a catalyst or other reagent (e.g., copper catalyzed Click chemistry conditions). Scheme I131Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT EXAMPLES

[0404] The following examples are included to demonstrate specific embodiments of the disclosure. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques to function well in the practice of the disclosure, and thus can be considered to constitute specific modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the disclosure. Synthetic Examples

[0405] The following Synthetic Examples, which are directed to the synthesis of the compounds and conjugates of the disclosure, and the following Biological Examples, are provided as a guide to assist in the practice of the disclosure and are not intended as a limitation on the scope of the disclosure.

[0406] In the Preparations and Examples below, unless otherwise indicated all temperatures are set forth in degrees Celsius. Commercially available reagents were purchased from suppliers such as Sigma Aldrich, Alfa Aesar, Combi-Blocks, Oakwood Chemicals, Matrix Scientific, TCI, BroadPharm, etc. and were used without further purification unless otherwise indicated. The reactions set forth below were done generally under a positive pressure of nitrogen, argon, or with a drying tube (unless otherwise stated) in anhydrous solvents, and the reaction flasks were typically fitted with rubber septa for the introduction of substrates and reagents via syringe. Glassware was oven dried and / or heat dried. Yields were not optimized. Melting points were determined on a Büchi hot-stage apparatus and are uncorrected.1H NMR,19F, and13C NMR data were obtained in deuterated CDCI3, DMSO-d6, CD3OD, CD3CN, or acetone-d6solvent solutions with chemical shifts (δ) reported in parts- per-million (ppm) relative to trimethylsilane (TMS) or the residual non-deuterated solvent peaks as the reference standard. Data are reported as follows, if applicable: chemical shift, multiplicity, coupling constant in Hz, and number of protons, fluorine, or carbon atoms. When peak multiplicities are reported, the following abbreviates are used: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet, br (broadened), dd (doublet of doublets), dt (doublet of triplets). Coupling constants, when given, are reported in Hz (Hertz). 132Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Example 1: Synthesis of Compounds Intermediate 1

[0407] ((5-bromopentyl)o) was synthesized using the starting material and reagents shown above. A reaction yield of 83% was achieved. Intermediate 2

[0408] ethyl 7-((tert- uty p eny s y)oxy)- -et y eptanoate ( nterme ate ) was synthesized using the starting material and reagents shown above. A reaction yield of 83% was achieved. Intermediate 3

[0409] 7-((tert-butyldiphenylsilyl)oxy)-2-ethylheptanal (Intermediate 3) was synthesized using the starting material and reagents shown above. 133Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Intermediate 4

[0410] (E)-7-((tere 4) was synthesized using the starting material and reagents shown above. Intermediate 5

[0411] mety (3aR, R,6S,6aS)- -((tert-butoxycarbony )am no)-3-(8-((tert- butyldiphenylsilyl)oxy)octan-3-yl)-3a,5,6,6a-tetrahydro-4H-cyclopenta[d]isoxazole-6-carboxylate (Intermediate 5) was synthesized using the starting material and reagents shown above. Intermediate 6134Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0412] methyl (1S,2S,3S,4R)-3-((1R)-1-amino-2-ethyl-7-hydroxyheptyl)-4-((tert- butoxycarbonyl)amino)-2-hydroxycyclopentane-1-carboxylate (Intermediate 6) was synthesized using the starting material and reagents shown above. Intermediate 7

[0413] methy, , , rt- butoxycarbonyl)amino)-2-hydroxycyclopentane-1-carboxylate (Intermediate 7) was synthesized using the Intermediate 8

[0414] methyl (1S,2S,3R,4R)-3-((1R)-1-acetamido-2-ethyl-7-hydroxyheptyl)-4-amino-2- hydroxycyclopentane-1-carboxylate (Intermediate 8) was synthesized using the starting material and reagents shown above. 135Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Intermediate 9

[0415] methy)-2,3-bis(tert- butoxycarbonyl)guanidino)-2-hydroxycyclopentane-1-carboxylate (Intermediate 9) was synthesized using the starting material and reagents shown above. Intermediate 10

[0416] methyl (1S,2S,3R,4R)-3-((1R)-1-acetamido-2-ethyl-7-(tosyloxy)heptyl)-4-((E)-2,3-bis(tert- butoxycarbonyl)guanidino)-2-hydroxycyclopentane-1-carboxylate (Intermediate 10) was synthesized using the starting material and reagents shown above. 136Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Intermediate 11

[0417] methy,3-bis(tert- butoxycarbonyl)guanidino)-2-hydroxycyclopentane-1-carboxylate (Intermediate 11) was synthesized using the starting material and reagents shown above. Intermediate 12

[0418] methyl (1S,2S,3R,4R)-3-((1R,2S)-1-acetamido-7-amino-2-ethylheptyl)-4-((E)-2,3-bis(tert- butoxycarbonyl)guanidino)-2-hydroxycyclopentane-1-carboxylate (Intermediate 12) was synthesized using the starting material and reagents shown above. SFC separation was used to obtain the desired stereoisomer. Separation was performed after optional protection of the primary amine with Boc. Approximately ½ of the material (i.e., the undesired stereoisomer) was discarded. 137Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Intermediate 13

[0419] methyl (uanidino-2- hydroxycyclopentane-1-carboxylate (Intermediate 13) was synthesized using the starting material and reagents shown above. Intermediate 14

[0420] 3,3′-((2-(((((1R,8S,9S)-bicyclo[6.1.0]non-4-yn-9-yl)methoxy)carbonyl)amino)propane-1,3- diyl)bis(oxy))dipropionic acid (Intermediate 14): In a 20 mL vial 2-amino-1,3- bis(carboxylethoxy)propane HCl salt 14-2 (581.4 mg, 2.14 mmol) and endo-BCN-PNP-carbonate (680.5 mg, 2.16 mmol) 14-1 were suspended in DCM (8.0 mL) under inert atmosphere. TEA (0.75 mL, 5.4 mmol, 2.5 eq) was added dropwise resulting in partial dissolution of 14-2 and reaction mixture turning yellow (PNP). After stirring for 18 h at r.t. entire reaction mixture was loaded onto a 138Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 25 g C18 Biotage Bio Sfär column and purified using 5à28% MeCN / water with 0.1% ammonium formate gradient. Compound 3 eluted in multiple peaks, which were combined, concentrated, and repurified on a 25 g C18 Biotage Bio Sfär column using 5à35% MeCN / water (no modifier) gradient. Intermediate 14 (135 mg, 15% yield) was obtained. Synthesis of Compound I-3

[0421] To a 20mL va under nert atmosp ere were added -3 (36.6 mg, 0.089 mmol), H5b (109.2 mg, 0.231 mmol, 2.6 eq), DMF (3.0 mL), EDC.HCl (51.9 mg, 0.271 mmol, 3.0 eq), HOBt (36.8 mg, 0.272 mmol, 3.1 eq), followed by DIPEA (0.12 mL, 0.69 mmol, 7.7 eq) dropwise. After stirring for 18 h at r.t. entire reaction mixture was loaded onto a 30 g C18 Biotage Sfär column and purified using 5à100% MeCN / water with 0.1% ammonium formate gradient. Fraction containing Compound I-3- diMe ester were combined, concentrated, and repurified on a 10 g C4 Biotage Sfär column using the following set of gradients: 1) slow 5 to 45% MeCN / water (no modifier); 2) fast 45 to 100% MeCN / water (no modifier); 3) fast 90 to 100% MeCN / water with 0.1% ammonium formate. Compound I-3-diMe ester came off the column during the 3rdgradient and following concentration 16 (15.6 mg, 16% yield) was obtained.

[0422] To a 20 mL vial under inert atmosphere were added Compound I-3-diMe ester (44.6 mg, 0.038 mmol), methanol (1.5 mL), water (0.5 mL), and LiOH hydrate (18.5 mg, 0.441 mmol, 12 eq). Reaction mixture was stirred at 25oC for 30-90 min and was monitored by LC-MS. Following 139Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT completion reaction mixture was directly loaded onto a 25 g Biotage C4 Sfär column and purified using 5à40% MeCN / water (no modifier). Compound I-3 partially eluted at 30%, the remainder was eluted using 90à100% MeCN / water with 0.1% ammonium formate. Following concentration Compound I-3 (15.2 mg, 35% yield) was obtained. Synthesis of Des-Et Peramivir Intermediate 15140Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0423] Step 1: To a solution of 15-1 (23 g, 173.98 mmol, 1 eq) in ACN (360 mL) and Hexane (1080 mL) was added TBSCl (26.22 g, 173.98 mmol, 21.32 mL, 1 eq) and TEA (26.41 g, 260.97 mmol, 36.32 mL, 1.5 eq). The mixture was stirred at 20°C for 12 h. TLC (petroleum ether / ethyl acetate= 10 / 1, Rf= 0.4) showed the reaction was completed. The reaction mixture was concentrated under reduced pressure to give a residue. The residue was purified by column chromatography (SiO2, 141Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Petroleum ether / Ethyl acetate= 100 / 1 to 5 / 1) to give 15-2 (27 g, 109.55 mmol, 62.97% yield) as a colorless oil. LCMS-product (ESI+): m / z 247.0 [M+H]+, Rt: 0.735 min.

[0424] Step 2: To a solution of oxalyl chloride (11.33 g, 89.26 mmol) in DCM (100 mL) was added DMSO (13.95 g, 178.53 mmol) at -78°C. The reaction mixture was stirred at -78°C for 10 min. To the reaction mixture was added the solution of VIR-J01_2 (20 g, 81.15 mmol) in DCM (200 mL) at - 78°C. The reaction mixture was stirred at -78°C for 40 min. To the reaction mixture was added TEA (41.06 g, 405.74 mmol) at -78°C. The reaction mixture was stirred at -78°C for 1 h. TLC (petroleum ether / ethyl acetate=10 / 1, Rf=0.6) indicated the VIR-J01_2 was consumed completely and one new spot formed. To the resulting mixture was added H2O at 0°C. The combined mixture was partitioned between ethyl acetate (0.6 L) and water (0.3 L), and then the aqueous phase was further extracted with ethyl acetate (3 × 0.5 L). The organic phase was washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure to give a residue which was purified by column chromatography (SiO2, Petroleum ether / Ethyl acetate=100 / 1 to 10 / 1) to give VIR-J01_3 (15 g, yield 61.36%) as a colorless oil.1H NMR: (CHLOROFORM-d, 400MHz) δ = 9.76 (s, 1H), 3.60 (s, 2H), 2.42 (d, J = 1.7 Hz, 2H), 1.68 - 1.60 (m, 2H), 1.55 - 1.47 (m, 2H), 1.38 - 1.31 (m, 4H), 1.05 (s, 2H), 0.89 (s, 9H), 0.04 (s, 6H)

[0425] Step 3: To a solution of 15-3 (10 g, 40.91 mmol) in DCM (100 mL) was added NH2OH.HCl (7.11 g, 102.22 mmol) and TEA (12.42 g, 122.72 mmol) at 20°C. The reaction mixture was stirred at 20°C for 16 h. TLC (Petroleum ether / Ethyl acetate= 10 / 1, Rf= 0.2) indicated the 15-3 was consumed completely and one new spot formed. The resulting mixture was partitioned between ethyl acetate (1 L) and water (500 mL), and then the aqueous phase was further extracted with ethyl acetate (3 × 500 mL). The organic phase was washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure to give 15-4 (7.5 g, yield 70.66%) as yellow oil which was used into the next step without further purification.1H NMR: (CHLOROFORM-d, 400MHz) δ = 7.38 (t, J = 6.1 Hz, 1H), 6.67 (t, J = 5.5 Hz, 1H), 3.55 (t, J = 2.0, 6.5 Hz, 2H), 2.33 (t, J = 5.5, 7.5 Hz, 1H), 2.19 - 2.11 (m, 1H), 1.51 - 1.41 (m, 4H), 1.35 - 1.26 (m, 4H), 0.85 (s, 9H), 0.00 (d, J = 0.6 Hz, 6H)

[0426] Step 4: To a solution of 15-4B (2.32 g, 9.64 mmol), TEA (585 mg, 5.78 mmol) and 15-4 (5 g, 19.27 mmol) in DCM (50 mL) was added NaClO (50 mL, 10% purity) at 0°C. The reaction mixture was stirred at 45°C for 16 h. LC-MS showed the reactant was consumed completely and one main peak with desired mass was detected. The combined resulting mixture was partitioned between ethyl acetate (0.3 L) and water (0.3 L), and then the aqueous phase was further extracted with ethyl acetate (3 × 0.2 L). The organic phase was washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure to give a residue which was purified by column chromatography (SiO2, Petroleum ether / Ethyl acetate=50 / 1 to 4 / 1) to give 15-5 (2 g, yield 20.12%) as a yellow oil. LCMS- reaction (ESI): m / z 499.4 [M+H], Rt: 0.960 min.1H NMR: (CHLOROFORM-d, 400MHz) δ = 4.30 - 142Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 3.96 (m, 1H), 3.77 (s, 2H), 3.73 - 3.57 (m, 3H), 3.45 - 3.15 (m, 1H), 2.58 - 1.97 (m, 4H), 1.77 - 1.42 (m, 13H), 1.40 - 1.31 (m, 4H), 1.28 - 1.02 (m, 2H), 0.90 (s, 9H), 0.05 (s, 6H)

[0427] Step 5: To a solution of 15-5 (2 g, 2.81 mmol) in MeOH (200 mL) and HCl (12 M, 0.4 mL) and was added PtO2(0.956 g, 4.21 mmol) at 20°C. The reaction mixture was stirred at 30°C for 16 h under H2at 50 psi. LCMS (LCMS_ET38556-185-P1A) showed the 15-5 was consumed completely and one main peak with desired mass was detected. The precipitate was filtered using a Buchner funnel. The filter cake was washed with MeOH, and the filtrate was concentrated under high vacuum to give an amine hydrochloride salt intermediate which was used to next step. To this amine hydrochloride salt in DCM (100 mL) was added TEA (0.284 g, 2.81 mmol) and Ac2O (0.315 g, 3.09 mmol) at 20°C. The reaction mixture was stirred at 20°C for 16 h. LCMS (LCMS_ET38556-185- P1D) showed one main peak with desired mass was detected. Two vials were set up as described above. Three reaction mixtures were combined. The resulting mixture was partitioned between DCM (100 mL) and water (100 mL), and then the aqueous phase was further extracted with DCM (3 × 100 mL). The organic phase was washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure to give a residue which was purified by column chromatography (SiO2, Petroleum ether / Ethyl acetate=3 / 1 to 1 / 2) to give 15-6 (0.8 g, yield 66.19 %) as a colorless oil. LCMS-reaction (ESI+): m / z 389.3 (M+H)+, Rt: 0.607 min. LCMS-reaction (ESI+): m / z 431.3 (M+H)+, Rt: 0.626 min.

[0428] Step 6: To 15-6 (0.8 g, 1.86 mmol) was added HCl / dioxane (4 M, 10 mL) at 20°C. The reaction mixture was stirred at 20°C for 1 h. LCMS showed the reactant was consumed completely and one main peak with desired mass was detected. The resulting mixture was concentrated to give 15-7 (0.9 g, yield 70.15%, HCl salt) as white oil which was used into the next step without further purification. LCMS-reaction (ESI+): m / z 331.3 [M+H]+, Rt: 0.471 min.

[0429] Step 7: To a solution of 15-7 (0.9 g, 2.45 mmol, HCl salt) in MeOH (10 mL) was added TEA (0.87 g, 8.59 mmol) and 15-7B (0.84 g, 2.70 mmol) at 20°C. The reaction mixture was stirred at 20°C for 16 h. LCMS showed the 15-7 was consumed completely and one main peak with desired mass was detected. The resulting mixture was concentrated, then was partitioned between ethyl acetate (10 mL) and water (5 mL), and the aqueous phase was further extracted with ethyl acetate (10 × 2 mL). The organic phase was washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure to give a residue. The residue was purified by column chromatography (SiO2, Petroleum ether / Ethyl acetate=3 / 1 to 0 / 1) to give 15-8 (1 g, yield 71.78%) as a white solid. LCMS-reaction (ESI+): m / z 573.3 [M+H]+, Rt: 1.340 min. LCMS-product (ESI+): m / z 573.3 [M+H]+, Rt: 1.230 min. 143Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0430] Step 8: A mixture of 15-8 (900 mg, 1.57 mmol), PhI(OAc)2(556.8 mg, 1.88 mmol), TEMPO (74.14 mg, 0.47 mmol) and NaHCO3 (660.1 mg, 7.86 mmol) in DCM (10 mL) was degassed and purged with N2for 3 times, and then the mixture was stirred at 20°C for 24 hr under N2atmosphere. TLC (petroleum ether / ethyl acetate= 0 / 1, Rf= 0.2) showed the reaction was completed. The reaction mixture was concentrated under reduced pressure to give a residue. The residue was purified by column chromatography (SiO2, Petroleum ether / Ethyl acetate= 10 / 1 to 0 / 1) to give 15-9 (800 mg, 89.20% yield) as a white solid. LCMS-product (ESI+): m / z 571.4 [M+H]+, Rt: 2.466 min.

[0431] Step 9: To a solution of 15-9 (300 mg, 525.69 umol) and K2CO3(290.6 mg, 2625 umol) in MeOH (3 mL) was added 1-diazo-1-dimethoxyphosphoryl-propan-2-one (302.9 mg, 1580 umol) at 25°C under N2. The reaction mixture was stirred at 25°C for 72 h under N2. TLC (petroleum ether / ethyl acetate= 0 / 1, Rf= 0.4) showed the reaction was completed. The reaction mixture was concentrated under reduced pressure to give a residue. The residue was purified by column chromatography (SiO2, Petroleum ether / Ethyl acetate= 10 / 1 to 0 / 1) to give 15-10 (200 mg, 67.14% yield) as a yellow solid. LCMS-product (ESI+): m / z 567.4 [M+H]+, Rt: 1.363 min.1H NMR: (CHLOROFORM-d, 400MHz) δ = 8.66 - 8.49 (m, 2H), 5.32 - 5.26 (s, 1H), 4.54 - 4.45 (m, 1H), 4.37 - 4.28 (m, 2H), 4.23 - 4.07 (m, 2H), 3.70 (s, 3H), 2.86 - 2.77 (m, 1H), 2.57 - 2.46 (m, 1H), 2.34 - 2.23 (m, 1H), 2.12 - 2.09 (m, 3H), 2.04 - 2.03 (m, 1H), 1.93 - 1.82 (m, 3H), 1.49 (d, J = 11.0 Hz, 22H), 1.28 - 1.22 (m, 2H)

[0432] Step 10: To a solution of 15-10B (62.01 mg, 105.88 umol) and 15-10 (60 mg, 105.88 umol,) in t-BuOH (0.5 mL) and H2O (0.5 mL) was added CuSO4.5H2O (10.57 mg, 42.35 umol) and VC-Na (16.78 mg, 84.70 umol). The mixture was stirred at 20°C for 3 h. TLC (ethyl acetate / methanol = 10 / 1, Rf= 0.5) showed the reaction was completed. The reaction mixture was concentrated under reduced pressure to give a residue. The residue was purified by Prep-TLC (SiO2, ethyl acetate / methanol= 10 / 1) to give 15-11 Step 11: A solution of 15-11 (50 mg, 43.4 umol,) in TFA (1 mL) was stirred at 20°C for 2 h. LC-MS showed the reaction was completed. The reaction mixture was concentrated under reduced pressure to give 15-12 (30 mg, 72.62% yield, TFA salt) as a yellow solid. LCMS-reaction (ESI+): m / z 952.7 [M+H]+, Rt: 0.889 min.

[0433] Step 12: To a solution of 15-12 (40 mg, 8.69 umol, 1 eq, TFA salt) in MeOH (1.5 mL) was added aqueous solution LiOH.H2O (2 M, 0.5 mL). The mixture was stirred at 20°C for 10 min. LC- MS showed the reaction was completed. The reaction mixture was purified by prep-HPLC to give Intermediate 15 (5 mg, 14.88% yield) as a white solid. Prep-HPLC method: Instrument: Shimadzu LC-8A preparative HPLC; Column: Phenomenex Luna C1880×30mm×3um; Mobile phase: A for H2O (0.1% TFA) and B for CAN; Gradient: B from 5% to 30% in 8min; Flow rate: 25mL / min; Wavelength: 220&254nm. LCMS product (ESI+): m / z 896.4 [M+H]+, Rt: 1.810 min. 144Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Alternate Synthesis of Intermediate 13a and Intermediate 13145Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0434] Step 1: To a solution of 5-bromopentan-1-ol (150 g, 0.9 mol, 1.0 eq) in THF (4500 mL) was added imidazole (61.3 g, 0.9 mol, 1.0 eq) and TBDPSCl (247.4 g, 0.9 mol, 1.0 eq) at 0 °C under N2protection. The resulting mixture was stirred at 20 °C for 16 h. The reaction mixture was diluted with 2000 mL of water, extracted with ethyl acetate (2000 mL x 3). The combined organic layers were washed with brine (1500 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: EtOAc=10: 1 to afford 226.0 g (61.0% yield) of 13-1 as colorless oil.

[0435] Step 2: To a solution of HMPA (159.8 g, 0.89 mol, 1.6 eq) in THF (1400mL) was added LDA (392 mL, 0.78 mol, 1.4 eq) dropwise at -78 °C under N2protection. The resulting mixture was stirred 146Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT at -78 °C for 1 h. Then ethyl butyrate (84.1 g, 0.72 mol, 1.3 eq) in THF (450 mL) was added dropwise at -78 °C. The reaction mixture was stirred at -78 °C for 2 h. Then 13-1 (226.0 g, 0.56 mol, 1.0 eq) in THF (450 mL) was added dropwise at -78 °C. The reaction mixture was stirred at -78 °C - 20 °C for 5 h. The reaction mixture was quenched with 2000 mL of aqueous solution NH4Cl, extracted with ethyl acetate (1500 mL x 3). The combined organic layers were washed with brine (500 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: EtOAc = 10: 1 to afford 157.1 g (64.0% yield) of 13-2 as colorless oil.

[0436] Step 3: To a solution of 13-2 (157.1 g, 0.36 mol, 1.0 eq) in THF (1600 mL) was added LiAlH4(18.4 g, 0.54 mol, 1.5 eq) in several portions at -10 °C under N2protection. The reaction mixture was stirred at 0 °C for 6 h. The reaction mixture was quenched with 18.4 mL of water, 18.4 mL 15% NaOH (aq) and 55.2 mL of water at 0 °C. The reaction mixture was filtered out and the filtrate was concentrated under vacuum. The residue was purified by silica gel chromatography eluted with PE: EtOAc = 7: 1 to afford 91.9 g (64.6% yield) of 13-3 as light yellow oil.

[0437] Step 4: To a solution of oxalyl chloride (35.1 g, 0.27 mol, 1.2 eq) in DCM (900 mL) was added DMSO (41.3 g, 0.53 mol, 2.3 eq) dropwise at -78 °C under N2protection. The resulting mixture was stirred at -78 °C for 40 min. Then 13-3 (91.9 g, 0.23 mol, 1.0 eq) in DCM (900 mL) was added dropwise at -78 °C. The reaction mixture was stirred at -78 °C for 1 h. Then TEA (116.1 g, 1.15 mol, 5.0 eq) was added dropwise at -78 °C. The reaction mixture was stirred at 20 °C for 3 h. The reaction mixture was quenched with 2000 mL of water, extracted with DCM (1000 mL x 3). The combined organic layers were washed with brine (500 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure to afford 64.1 g (curde) of 13-4 as yellow oil.

[0438] Step 5: To a solution of 13-4 (64.1 g, 0.16 mol, 1.0 eq) in DCM (640 mL) was added NH2OH•HCl (27.8 g, 0.4 mol, 2.5 eq) and TEA (48.5 g, 0.48 mol, 3.0 eq) at 0 °C under N2protection. The reaction mixture was stirred at 20 °C for 16 h. The reaction mixture was diluted with 500 mL of water, extracted with DCM (500 mL x 3). The combined organic layers were washed with brine (500 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: EtOAc = 10: 1 to afford 49.3 g (51.9% yield) of 13-5 as yellow oil. LC-MS m / z (ESI): [M+H]+412.1

[0439] Step 6: To a solution of 13-5 (49.3 g, 120 mmol, 1.0 eq) in DMF (500 mL) was added NCS (40.0 g, 300 mmol, 2.5 eq) in several portions at 0 °C under N2protection. The reaction mixture was stirred at 25 °C for 4 h. The reaction mixture was diluted with 500 mL of water, extracted with DCM (500 mL x 3). The combined organic layers were washed with brine (300 mL x 3), dried over Na2SO4, 147Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: EtOAc = 10: 1 to afford 31.2 g (57.4% yield) of 13-5A as yellow oil.

[0440] Step 7: To a solution of 13-5A (31.2 g, 70 mmol, 1.5 eq) in DCM (310 mL) was added (1S, 4R)-methyl 4-((tert-butoxycarbonyl) amino) cyclopent-2-enecarboxylate (11.3 g, 46.7 mmol, 1.0 eq) and TEA (14.2 g, 140 mmol, 3.0 eq) at 20 °C under N2protection. The reaction mixture was stirred at 40 °C for 16 h. After cooled to room temperature, and diluted with 500 mL of water, extracted with DCM (300 mL x 3). The combined organic layers were washed with brine (200 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: EtOAc = 10: 1 to afford 32 g (70.1% yield) of 13-6 as yellow oil.

[0441] Step 7: To a solution of 13-6 (32 g, 0.05 mol, 1.0 eq) and NiCl2•6H2O (11.9 g, 0.05 mol, 1.0 eq) in MeOH (300 mL) was added NaBH4(5.0 g, 0.13 mol, 2.5 eq) in several portions at -20 °C under N2protection. The reaction mixture was stirred at 0 °C for 3 h. The reaction mixture was diluted with 300 mL of water, extracted with DCM (300 mL x 3). The combined organic layers were washed with brine (200 mL x 2), dried over Na2SO4, then filtered and concentrated under reduced pressure to afford 19.7 g (crude) of 13-7 as yellow oil.

[0442] Step 8: To a solution of 13-7 (19.7 g, 0.03 mol, 1.0 eq) in DCM (200 mL) was added TEA (9.1 g, 0.09 mol, 3.0 eq) and Ac2O (3.1 g, 0.03 mol, 1.0 eq) dropwise at 0 °C under N2protection. The reaction mixture was stirred at 20 °C for 12 h. The reaction mixture was diluted with 200 mL of water, extracted with DCM (200 mL x 3). The combined organic layers were washed with brine (200 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: EtOAc = 1: 10 to afford 16.1 g (45.8% yield of two steps) of 13-8 as yellow oil. LC-MS m / z (ESI): [M+H]+697.6

[0443] Step 9: To a solution of 13-8 (16.1 g, 0.023 mol, 1.0 eq) in DCM (160 mL) was added HCl (4 M in dioxane, 160 mL) dropwise at 0 °C under N2protection. The reaction mixture was stirred at 20 °C for 12 h. The reaction mixture was concentrated under reduced pressure to afford crude product. The crude product was slurry with EtOAc: PE = 1:10 to afford 8.4 g (85.1% yield) of 13-9 as yellow solid.

[0444] Step 10: To a solution of 13-9 (8.4 g, 0.02 mol, 1.0 eq) in MeOH (84 mL) was added TEA (6.1 g, 0.06 mmol, 3.0 eq) and 13-5-INT (6.8 g, 0.022 mol, 1.1 eq) at 0 °C under N2protection. The reaction mixture was stirred at 20 °C for 16 h. The reaction mixture was diluted with 50 mL of water, extracted with ethyl acetate (50 mL x 3). The combined organic layers were washed with brine (50 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was 148Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT purified by silica gel chromatography eluted with PE: EtOAc = 1: 2 to afford 6.5 g (51.0% yield) of 13-10 as yellow solid. LC-MS m / z (ESI): [M+H]+601.3

[0445] Step 11: To a solution of 13-10 (6.5 g, 0.01 mol, 1.0 eq) in DCM (190 mL) was added TEA (4.1 g, 0.04 mol, 4.0 eq), DMAP (122 mg, 1.0 mmol, 0.1 eq) and TsCl (2.86 g, 0.015 mol, 1.5 eq) at 0 °C under N2protection. The reaction mixture was stirred at 20 °C for 24 h. The reaction mixture was diluted with 20 mL of water, extracted with DCM (50 mL x 3). The combined organic layers were washed with brine (50 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: EtOAc = 1: 1 to afford 5.7 g (79.4% yield) of 13-11 as yellow solid. LC-MS m / z (ESI): [M+H]+755.3

[0446] Step 12: To a solution of 13-11 (5.7 g, 7.55 mmol, 1.0 eq) in THF (60 mL) was added TBAF (4.39 g, 16.61 mmol, 2.2 eq) and TMSN3(1.92 g, 16.61 mmol, 2.2 eq) at 20 °C under N2protection. The reaction mixture was stirred at 60 °C for 12 h. After cooled at 10 °C, quenched with 200 mL of ice / water, and extracted with ethyl acetate (200 mL x 3). The combined organic layers were washed with brine (100 mL x 3), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: EtOAc = 1: 1 to afford 3.3 g (69.8% yield) of 13-12 as yellow oil. LC-MS m / z (ESI): [M+H]+626.4

[0447] Step 13: To a solution of 13-12 (3.3 g, 5.27 mmol, 1.0 eq), Zn (1.72 g, 26.35 mmol, 5.0 eq) in THF (30 mL) was added saturated NH4Cl aqueous solution (8 mL) dropwise at 20 °C under N2protection. The reaction mixture was stirred at 30 °C for 4 h. The reaction mixture was filtered out and the filtrate was concentrated under vacuum to afford 3.0 g (crude) of 13-13 as yellow oil.

[0448] Step 14: To a solution of 13-13 (3.0 g, 5.0 mmol, 1.0 eq) in THF (30 mL) was added (Boc)2O (1.3 g, 6.0 mmol, 1.2 eq) and TEA (1.5 g, 15 mmol, 3.0 eq) at 0 °C. The reaction mixture was stirred at 30 °C for 12 h. The reaction mixture was diluted with 200 mL of water, extracted with ethyl acetate (100 mL x 3). The combined organic layers were washed with brine (50 mL x 2), dried over Na2SO4, then filtered and concentrated under reduced pressure. The residue was purified by silica gel chromatography eluted with PE: THF = 1: 1 to afford 1.3 g (35.2% yield of two steps) of 13-14 as white solid. LC-MS m / z (ESI): [M+H]+700.6

[0449] Step 15: 13-14 (1.3 g) was purified by SFC to afford 510 mg (39.2% yield) of 13a as off- white solid and 530 mg (40.8% yield) of 13 as off-white solid.

[0450] Step 15: To a solution of 13-14a (510 mg, 0.73 mmol, 1.0 eq) in MeOH (3.6 mL) was added HCl (4 M in dioxane, 1.5 mL) dropwise at 0 °C under N2protection. The reaction mixture was stirred at 20 °C for 12 h. The reaction mixture was concentrated under reduced pressure to afford crude product. The residue was purified by prep-HPLC (HCl-MeCN system) and dried by lyophilization to 149Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT afford 160.1 mg (47.1% yield) of 13a as yellow solid.1H NMR (400 MHz, Methanol-d4) δ 7.62-7.45 (m, 0.81H), 5.49-5.45 (m, 0.34H), 4.68-4.62 (m, 0.87H), 4.39-4.22 (m, 1.28H), 4.05-3.95 (m, 0.86H), 3.78-3.72 (m, 3.09H), 3.69-3.60 (m, 0.54H), 3.48-3.45 (m, 0.43H), 3.05-2.91 (m, 3.58H), 2.89-2.82 (m, 1.24H), 2.85-2.75 (m, 1.0H), 2.32-2.22 (m, 0.85H), 2.11(s, 1H), 2.05-1.95 (m, 2.61H), 1.91-1.82 (m, 0.35H), 1.81-1.68 (m, 4.18H), 1.67-1.35 (m, 9H), 1.19-1.07 (m, 2H), 0.99-0.91 (m, 4H).

[0451] Step 15: To a solution of 13-14b (530 mg, 0.76 mmol, 1.0 eq) in MeOH (3.7 mL) was added HCl (4 M in dioxane, 1.6 mL) dropwise at 0 °C under N2protection. The reaction mixture was stirred at 20 °C for 12 h. The reaction mixture was concentrated under reduced pressure to afford crude product. The residue was purified by prep-HPLC (HCl-MeCN system) and dried by lyophilization to afford 203 mg (57.1% yield) of Intermediate 13 as yellow solid.1H NMR (400 MHz, Methanol-d4) δ 7.90-7.72 (m, 0.5H), 7.45-7.30 (m, 0.5H), 5.46-5.42 (m, 0.34H), 4.62-4.51 (m, 1H), 4.39-4.30 (m, 1.35H), 4.03-3.94 (m, 1H), 3.78-3.72 (m, 3.36H), 3.68-3.63 (m, 0.6 H), 3.05-2.81 (m, 4.7H), 2.73- 2.65 (m, 1H), 2.28-2.18 (m, 0.9H), 2.11(s, 1H), 2.05-1.96 (m, 2.74H), 1.90-1.53 (m, 8H), 1.52-1.15 (m, 6.6H), 1.13-0.93 (m, 6H). Alternate Separation Conditions for 13-14

[0452] 13-14 (1.02 g) was purified by chiral Prep-HPLC to afford 430 mg (98.7% ee) of 13 and 390 mg of 13a. Instrument Model: Prep-HPLC-Flash Brix 1860; Column Name: YMC CHIRAL ART Amylose-C NEO, 250*30mm, 5um; Mobile Phase: A: n-Hexane; B: IPA; Isocratic elution: A: B = 95:5 (V / V); Total Flow: 40 mL / min; Column temp.: room temperature; Retention Time (min): 15 min (Product peak); 35 min (isomers peak); Running Time: 40 min. Synthesis of Compound I-14 150Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCTp p p g g amide formation followed by saponification using LiOH dissolved in MeOH / H2O. Example 2: Synthesis of Conjugates

[0454] Conjugates of the disclosure were, or can be, provided by the following protocol: 1. Buffer exchange antibody 2. Linker reaction (room temperature for 2 hours) – in some embodiments, a linker comprising NHS-ester PEG linker with maleimide or azide can be used for this step 3. Removal of unreacted linker via desalting column 4. Confirm antibody-linker intermediate LAR via intact mass spectroscopy (deglyc) 5. Small molecule reaction to add drug (approximately 20 hours at room temperature) – in some embodiments, a peramivir derivative with a free thiol or strained cyclooctyne can be used 6. Remove unreacted small molecule via desalting column 7. Quality control – measure concentration, mass spectrometry measurement, endotoxin, neutralization

[0455] Each desalting step provides about a 70% yield. Overall, the 3 desalting steps give about a 35% cumulative yield. It was observed that the yield was impacted by the scale of the reaction. A 151Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT larger scale reaction has a higher volume and a higher yield; a smaller scale has a lower volume and a lower yield. Example 3: Synthesis of Conjugate II-8 via Cu-free Click Chemistry

[0456] A represents an antibody in the above reaction scheme. The desired conjugate was synthesized using the starting material and reagents shown above. Generally, 4x equivalents of the peramivir-linker compound to achieve an LAR of x. For example, 16 equivalents of compound I-3 relative to an azide-PEG functionalized antibody is used to achieve an LAR of 4:1 and a DAR of 8:1. Example 4: Additional ADC Synthesis

[0457] The following different linker to antibody ratios were tested to determine for conjugation of Flu_Ab and DBCO as a linker. DBCO has the following structure: 152Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCTted in a linker to antibody ratio (LAR; average) of 5:1 as tested by MS (results not shown). This compares to 16:1 for a comparable azide containing linker (i.e., in lieu of a cyclooctyne) that is required to achieve a LAR of 5:1. Other ratios averaged LAR values of 8 (for 16:1 ratio) and 12 (32:1 ratio).

[0459] BCN was also tested as a linker. BCN has the following structure:, , , . 16:1 ratio of BCN to antibody resulted in an LAR of 5, which is similar to the ratio required for a comparable azide analog needed to achieve a LAR of 5.

[0461] Intermediates were then tested using linker-drugs and proved that DAR values of about 4 (on average) could be achieved and verified via mass spectrometry (results not shown). Example 5: Hydrophobic Interaction Chromatography Analysis

[0462] Very broad peaks were observed for conjugates when analyzed using hydrophobic interaction chromatography (HIC). This is presumably due to heterogeneity within the population of conjugates. Assessment of DAR was not possible via HIC analysis. HIC retention time is correlated to the antibody species. Example 6: Size Exclusion Chromatography Analysis

[0463] Tested conjugates were analyzed using size exclusion chromatography (SEC) to determine whether conjugates formed higher order structures (e.g., antibody dimers, trimers, etc.) when conjugated to linker-drug moieties. Tested conjugates were approximately 85% monomer when analyzed by SEC. Additionally, no correlation was shown between DAR and increased high molecular weight species (HMWS) or low molecular weight species (LMWS). Results are shown the table below: 153Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Antibody1DAR Dimer % Monomer % LMWS % Antibody only None 0 100 0Example 7: Differential Scanning Fluorimetry Analysis

[0464] The stability of conjugates was tested using nano differential scanning fluorimetry (nDSF) against the parent antibody (Flu_Ab). The results showed that the nDSF was driven by the antibody with no obvious impact due to the small molecule (i.e., linker-drug moieties) of the conjugates. The tested conjugates tested include the parameters shown in the table below. Conjugate 4-1 Conjugate 4-2Example 8: DMS Testing of ADCs

[0465] ADCs were tested using a deep-mutational scanning (DMS) library of NA based on Cal09 N1. Results for FNI9 anti-NA mAb showed binding escapes from N1 DMS library. It was discovered that FNI9 binding escape substitutions were extremely rare in natural isolates from 2000 to 2020 and were associated with a fitness cost for the virus. ADC binding excapes were a subset of FNI9 binding escapes, with a few exceptions unique to the ADC which were determined to be false positives by NAI testing. Results indicated that ADCs had fewer escape positions compared to anti-NA mAb (e.g., FNI9 and a variant). ADC had high NAI activity against a panel of Cal09 VLP carrying FNI9 escape mutations.

[0466] Two methods were used for testing: fluorescent labeling of the mAb directly (method A) or labeling the mAb / ADC via secondary (method B). In turn, library preparation, sequencing, and variant calling were performed externally for method A and internally for method B. 154Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Example 9: Pharmacokinetics of different linker chemistries

[0467] Compounds were tested to determine if linker chemistry had any effect on pharmacokinetics (PK). Samples were tested with either a thiol-maleimide linkage or copper-free Click chemistry linkage. The thiol-maleimide compound had a DAR = 6 and an LAR = 6. Mass spectrometry analysis was used to determine that ADCs were produced having the following linkage prepared using copper- free Click chemistry:spectrometry analysis showed that an average LAR of 4 and an average DAR of 8 was obtained for these ADCs. Biological Activity Testing

[0469] The peramivir-based conjugates disclosed herein were shown to be highly potent against a panel of contemporary influenza A and influenza B viruses, including oseltamivir-resistant strains, in vitro. As provided by the data presented herein, a conjugate comprising Flu_Ab (LS) had high in vivo efficacy (prophylaxis against influenza in mice) as compared to Flu_Ab alone. A conjugate comprising an antibody and a peramivir derivative compound I-4 also had in vivo efficacy (prophylaxis against influenza in mice). The prophylactic efficacy was similar to that observed with anti-NA antibodies. Increasing DAR appears to improve efficacy of the antibody-drug conjugates. In vivo therapy experiments in mice using antibody-drug conjugates comprising compound I-4 were conducted; no advantage was shown over anti-NA antibody or anti-HA / anti-NA combination. Click chemistry was utilized to develop further antibody-drug conjugates, which were tested (e.g., an antibody-drug conjugate comprising compound I-6 was made using Cu-free Click chemistry).

[0470] In further studies, production of antibody-drug conjugates (using antibodies as shown in Tables 3A-C) with alternative linkers and DAR are tested for stability, PK, potency, and efficacy. To test resistance to viral escape and in vitro breadth, serial viral passaging is performed to attempt generation of escape mutants, and antibody-drug conjugates comprising drugs with NAI activity are tested against a panel of zoonotic NA pseudo particles. Enzymatic inhibition 155Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0471] A Neuraminidase Inhibition (NAI) assay was performed to evaluate the inhibitory activity of the conjugates or small molecules against a diverse panel of live virus NA enzymes using the 2'-(4- Methylumbelliferyl)-α-D-N-acetylneuraminic acid (MUNANA) substrate. In this assay, the viral neuraminidase cleaves the substrate MUNANA, releasing a fluorescent product, 4- methylumbelliferone. Briefly, live virus stocks are diluted in PBS to a pre-determined concentration which would result in a non-saturated fluorescent signal after 1 hour incubation with MUNANA. The diluted viruses are mixed with a 10-point serial dilution of the conjugates or small molecules and incubated for 30 min at room temperature. Then the MUNANA substrate is added and the reaction is allowed to proceed for 1 hour at 37C. The fluorescent signal is measured on an EnSight plate reader at excitation and emission wavelengths of 364 nm and 450 nm, respectively. The percent inhibition is calculated by subtracting the mean fluorescent signal of the no-virus wells from all the data points and then normalizing the experimental wells to the no-treatment control wells. Data were analyzed and graphed using GraphPad Prism software. The half maximal effective concentration (EC50) values were calculated using a non-linear regression model (variable slope model, 4 parameters) of log(inhibitor) versus response and the EC50values were interpolated from the curve at y=50. Live virus neutralization

[0472] A live virus neutralization assay was performed to determine the in vitro antiviral potency of conjugates, antibodies, and small molecules. Briefly, microneutralization assays were conducted using MDCK-LN and MDCK-SIAT cells seeded in 96-well plates and cultured for 24 hours. Virus stocks were diluted to 70FFU / well and added to the cells, followed by the addition of a 9-point serial dilution of the therapeutic agents mixed with colloidal cellulose. The cells were then incubated and viral replication was measured using an EnSight plate reader. A parallel TCID50 assay was performed to confirm the virus input, involving serial dilution of the virus and incubation with MDCK cells under similar conditions. Evaluation of viral replication and calculation of EC50

[0473] The percent neutralization was determined by intercellular staining of influenza A or B nuclear protein. To control for background, the mean count of positive cells in uninfected wells was calculated and subtracted from all data points. All positive cell counts were normalized to the no- antibody treatment control. Data were analyzed and graphed using GraphPad Prism software. The half maximal effective concentration (EC50) values were calculated using a non-linear regression model (variable slope model, 4 parameters) of log(inhibitor) versus response and the EC50values were interpolated from the curve at y=50. The geometric mean of two independent experiments in which the antibody was tested in triplicate was calculated in Excel. 156Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Example 10: Neutralization of vaccine isolates and resistant mutations

[0474] This example tested the activity of an antibody-drug conjugate (ADC) for the neutralization of vaccine isolates and resistant mutations.

[0475] The ADC, referred to as Flu_Ab (LS)-Peramivir, included an anti-influenza A hemagglutinin antibody Flu_Ab (LS) (Table 3A), conjugated to molecule I-19. The drug-antibody ratio was 12. As references, a naked Flu_Ab (with WT Fc) antibody, a naked FNI19v3 antibody, peramivir alone, and a Flu_Ab (WT Fc) + Peramivir combination, were also tested.

[0476] These molecules were tested with various vaccine isolates with or without resistant mutations in the antigen. As shown in FIG.1A and 1B, the ADC Flu_Ab (LS)-Peramivir had significantly higher neutralization activity against all of the isolates than the other tested molecules, including naked antibodies, drugs, and their combination.

[0477] In a similar experiment, Flu_Ab (LS)-Peramivir (“ADC”) showed >10-fold improved potency compared to Flu_Ab, plus expanded breadth to IBV (FIG.1C). Flu_Ab (LS)-Peramivir neutralized oseltamivir / peramivir-resistant strains with high potency (e.g., +H275Y). The comparison to an ADC with no anti-HA activity (“ADC with non anti-HA Ab”) shows that Flu_Ab (LS)-Peramivir prevented viral entry, and had higher anti-HA potency compared to naked antibody Flu_Ab (LS). Example 11: Broad Cross-panel Activity against Flu strains

[0478] The anti-viral activities of antibody FNI9, OSE (Oseltamivir), peramivir, and an ADC with an antibody not specific to flu conjugated to I-19 (DAR 10) (in FIG.2A) or an ADC of Flu_Ab (LS)- peramivir (in FIG.2B-D) were tested against a large panel of flu strains. The activities were determined with an enzymatic inhibition assay, measuring neuraminidase inhibition (NAI) on viral- like particles (VLPs).

[0479] As shown in FIG.2A-C, both OSE and peramivir exhibited strong activities against the majority of the strains, while naked antibody FNI9’s activity was relatively lower (FIG.2A-B: live viruses; FIG.2C: pseudoviruses). Interestingly, for many strains, the ADC showed >10-fold improvement of IC50as compared to FNI9, OSE and peramivir, even though the antibody did not target the flu viruses per se. The ADC maintained high potency even for strains with resistance to the NAI small molecule (indicated by bracket). In particular, H1N1-H275Y (black box) reached 98.5% of circulating H1N1 prior to the 2009 pandemic. These results, therefore, indicate that I-19, and more generally the instantly disclosed molecules and their associated ADC platform, has strong and broad anti-flu activities, which do not necessarily require a specific anti-flu antibody. Therefore, when the 157Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ADC platform incorporates an antibody having a different / orthogonal specificity, the resulting ADC molecule would have both strong and broad cross-strain / cross-species activities.

[0480] It was observed that H3N2 strains prior to 2014 were inhibited with high potency by FNI9 (indicated by inverse triangles in black boxes in upper panel of FIG.2D). A 2006 strain carrying a drug-resistant mutation (R292K), however, was an escape for FNI9 (FIG.2D, upper panel). In addition, H3N2 evolution (new glycan at 245 plus additional NA mutations) has steadily eroded the potency of FNI9 since 2014. Interestingly, the tested ADC maintained high potency across all such H3N2 strains (FIG.2C, lower panel). Example 12: Activity against Zoonotic Flu Strains

[0481] Using the method of Example 11, this example further tested the activity of Flu_Ab (LS) ADC (Flu_Ab (LS) conjugated to I-19, DAR: 12), an ADC (DAR: 10) with no specificity to flu, and peramivir against a panel of zoonotic flu strains.

[0482] As shown in FIG.3, peramivir and both ADCs exhibited potent inhibition of avian, swine, and canine NA proteins. Such data, therefore, highlight the instant ADC platform’s potential in a pandemic setting. Example 13. In vivo Prophylactic Efficacy

[0483] This example tested the in vivo prophylactic efficacy of ADC in Balb / c mice against influenza challenges.

[0484] Five animals were included in each group. ADC or naked antibodies (Flu_Ab (LS) and FNI17) were dosed at day -1 at 1 mg / kg (IV). The ADC included Flu_Ab (LS) conjugated to I-19 (DAR: 6). Peramivir was dosed at day -1 at 0.02 mg (IV), equivalent small molecule concentration as ADC. OSE was dosed orally at 10 mg / kg, day -1 to day 5 (approx. equivalent to human px dose).

[0485] The body weights following PR8 H1N1 challenge are charted in FIG.4. As shown in the figure, the ADC exhibited high in vivo prophylactic efficacy against influenza.

[0486] In an extension of the above experiment, the prophylactic efficacy of a Flu_Ab (LS) / I-16 ADC (DAR: 10) was tested. Naked antibodies Flu_Ab (LS) and FNI9-v8.1, drug OSE (Oseltamivir), as well as a Drug-Fc Conjugate (DFC) with peramivir, were used as references. As shown in FIG.5, even at low doses (e.g., 0.3 mg / kg), the ADC and DFC exhibited high prophylactic efficacy against IAV PR8in Balb / C mice. 158Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Example 14. ADC Retained Anti-HA Activity and Prevented Viral Entry

[0487] This example tested whether the ADC retained the activity of the antibodies. The molecules examined in Example 13 were tested for their activity of neutralizing an A / CA / 09 strain. As shown in FIG.6, upper panel, molecules with anti-HA antibodies reached 100% neutralization while those with an anti-NA antibody (e.g., FNI19v3) did not reach 100% neutralization.

[0488] A single-round infection test was conducted for these molecules. Infection was virtualized with red fluorescence (gray color in FIG.6, lower panel). Likewise, the molecule with anti-HA activity achieved complete prevention of viral entry. Example 15. Efficacy of ADC with Flu vs. non-Flu Antibodies

[0489] This example compared the in vivo prophylactic efficacy of Flu_Ab (LS) / I-19 ADC (DAR: 6) to an ADC that included the same payload conjugated to a non-flu antibody (Non-Flu Ab / I-19 ADC; DAR: 6) at three different doses, 0.2 mg / kg, 0.6 mg / kg and 2 mg / kg. A lethal dose of H1N1 was administered to the Balb / c mice (5 per group) at day 0.

[0490] Changes of body weight were measured. As shown in FIG.7A-B, both ADCs (with flu- antibody and with non-flu-antibody) exhibited similarly strong in vivo prophylactic efficacy at all tested doses. Example 16. Effector Function Did not Impact ADC Prophylactic Efficacy

[0491] This example examined the impacts of effector functions of the antibodies in ADCs on the in vivo prophylactic efficacy.

[0492] It was known that the G236R / L328R (“GRLR”) mutations abrogate the antibody Fc receptor interaction. The GRLR mutations were introduced to the antibodies in the Flu_Ab (LS) / I-19 ADC (DAR: 4) and the Non-Flu Ab / I-19 ADC (DAR: 4). FcgR activation reporter cell assays with NA- transfected target cells were conducted to confirm that the GRLR mutations in both ADCs effectively inhibited their activation of Jurkat-FcgRIIIa (V158) and Jurkat-FcgRIIA (H131).

[0493] The same in vivo prophylactic efficacy assay was used as in Example 14, and the results are shown in Table 6 below. Table 6. In vivo prophylactic efficacy measured as % survival Non-Flu Ab / I-19 ADC Flu_Ab (LS) / I-19 ADC159Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 0.3 mg / kg 100 100 100 100 0.1 mg / kg 40 20 40 60 tions

[0494] This example screened for amino acid residues in the neuraminidase to identify escape mutations for each of the naked antibody FNI9-v8.1 and the Flu_Ab (LS) / I-19 ADC.

[0495] In FIG.8, upper panel, letters on plots indicate observed binding escapes. Overall, these substitutions are rare in natural isolates from 2000 to 2020 and are associated with a fitness cost for the virus. Empty blue boxes indicate mutations at these positions (T148I and R152K) which appeared in earlier dataset with FNI9. FNI9 activity was reduced for some mutations. Mutations were also associated with decreased sialidase activity which suggests they have a fitness cost for the virus. The ADC had fewer escape mutations (FIG.8). Testing of ADC-specific DMS escapes by NAI showed no loss in potency.

[0496] The comparison shows that the ADC was not sensitive or only modestly sensitive to a panel of FNI9 DMS escapes. Example 18. Stability Testing

[0497] This example tested the stability of the antibodies prior to and following conjugation.

[0498] Two types of conjugation chemistry were used, including (A) thiol-maleimide and (B) Cu- free Click. It was determined that the ADC activity was undiminished after two months of circulation in mice. Antibody half-life was either unchanged or enhanced vs un-conjugated antibody for both types of conjugation chemistry. Example 19. Pharmacokinetic and Pharmacodynamic

[0499] This example evaluated the impact of various Fc mutations and the conjugates on the PK / PD of antibodies. Table 7. YTE mutations on pharmacokinetic properties UnitFlu_Ab (LS)5m / k Flu_Ab-YTE FHF11-LS FHF11-YTE160Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT Table 8. Pharmacokinetic with conjugates UnitFlu_Ab (LS)Flu_Ab (LS)- 5mg / kg ADC 5mg / kgDFCT1 / 2Day 11.4 15.0 13.4 own in Table 7, greatlyincreased the half-life of the antibodies. In Table 8, lower clearance and higher exposure was observed for the ADC than for the unconjugated antibody, suggesting that antibody conjugation did not have a detrimental impact on the PK performance of the antibodies. Example 20. Additional Testing of the ADCs

[0501] This example provides additional testing results for ADCs with antibodies Flu_Ab (LS) (“ADC”) and FHF11v9 (YTE) (“FHF11v9 (YTE) ADC)”), as compared to the naked antibodies and payload (Peramivir).

[0502] FIG.9 shows the results of neutralization experiments performed with clinically isolated flu viruses, representative of historical and recent H1N1, H3N2 and Flu B. As shown in the figure, ADC and FHF11v9 (YTE) ADC neutralized every tested strain with high potency. Their in vitro potent was superior to the naked antibodies and payloads.

[0503] In FIG.10, the maximal neutralization of the tested molecules was measured. ADC and FHF11v9 (YTE) ADC inhibited viral entry of Flu A strains due to anti-HA activity of the antibodies (maximal inhibition was near 100% for Flu A). The payloads alone, with only neuraminidase inhibitor activities, exhibited lower maximal neutralization compared to the antibodies and ADCs.

[0504] FIG.11 shows that the ADC had higher potency than the antibody (Flu_Ab) and payload (peramivir) alone in vivo across multiple strains of mouse. Example 21. In vivo Evaluation of the ADCs

[0505] This example measured the in vivo efficacy of three ADCs in reducing virus titers in the lung. The three tested ADCs were Flu_Ab (LS) (“ADC”), FHF11v9 (YTE) (“FHF11v9 (YTE) ADC)”), and FHF11v9 (G1m3 with M428L and N434S) ADC (“FHF11v9 (LS) ADC”). OSE (Oseltamivir) and Peramivir were included as controls.

[0506] As shown in FIG.12 and 13, each of the three ADCs dose-dependently reduced virus titers in the lung. At about 3.0 mg / kg, each ADC was able to totally eliminate the virus titers. 161Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT

[0507] In addition, the neuraminidase inhibition (NAI) by each ADC was measured side by side for each ADC, with Peramivir as control. Three ADCs had similar NAI IC50 (FIG.14), demonstrating that they are all excellent candidates. * * *

[0508] The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and / or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications, and publications to provide yet further embodiments.

[0509] These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 162

Claims

Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT CLAIMS:

1. A compound of Formula II: II or a stereoisomer, mixture of or pharmaceutically acceptable saltthereof; wherein: ;1-4alkyl; each L1is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; L2is a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; X1is cycloalkynyl, heterocyclylalkynyl, alkynyl, -OH, -SH, -N3, -NH2, an activated ester, or maleimide; wherein the cycloalkynyl, heterocyclylalkynyl, alkynyl, activated ester, or maleimide are each optionally substituted; and m is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

2. The compound of claim 1, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each R1is: 163Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT .

3. The compound of claim 1 oure of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each L1is independently a linker comprising at least one alkylene or heteroalkylene; wherein each alkylene or heteroalkylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl.

4. The compound of any one of claims 1-3, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each L1is independently C5-10heteroalkylene; wherein each is independently optionally substituted with oxo.

5. The compound of any one of claims 1-3, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein L1is represented by -L1a-L1b-L1c-; wherein: L1ais a bond, -O-, -S-, -NH-, C1-8alkylene, C2-15heteroalkylene, C2-8alkenylene, C2-8alkynylene, or C3-8cycloalkylene; L1bis -O-, -S-, -NH-, -NHC(O)-, -NHC(O)NH-, -NHC(O)O-, C1-6alkylene, C2-15heteroalkylene, C2-8alkenylene, C2-8alkynylene, C3-8cycloalkylene, a 4-8 membered heterocyclylene, C6arylene, or a 5-6 membered heteroarylene; and L1cis a bond, -O-, -S-, -NH-, C1-8 alkylene, or C2-15 heteroalkylene; wherein each alkylene, heteroalkylene, alkenylene, alkynylene, cycloalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl.

6. The compound of claim 1, wherein the compound is represented by Formula IIA: 164Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT IA or a stereoiso cceptable saltthereof, wherein: p is 0, 1, 2, 3, 4, 5, or 6; q is 0 or 1; and r is 0, 1, 2, or 3.

7. The compound of any one of claims 1-6, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein L2is a linear linker.

8. The compound of any one of claims 1-6, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein L2is a branched linker.

9. The compound of claim 8, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein L2is a bivalent linker or a trivalent linker.

10. The compound of any one of claims 1-9, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein L2is C2-20heteroalkylene optionally substituted with oxo.

11. The compound of any one of claims 1-10, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein L2is represented by -L2a-L2b-L2c-; wherein: L2ais C(H)m-1, N(H)m-1, C3-8cycloalkylene, a 4-8 membered heterocyclylene, C6arylene, or a 5-6 membered heteroarylene; L2bis -O-, -S-, -NH-, -NHC(O)-, -NHC(O)NH-, -NHC(O)O-, C1-6alkylene, C2-15heteroalkylene, C2-8alkenylene, C2-8alkynylene, C3-8cycloalkylene, a 4-8 membered heterocyclylene, C6arylene, or a 5-6 membered heteroarylene; and L2cis C1-6alkylene, C2-20heteroalkylene, C2-8alkenylene, C2-8alkynylene, C3-8cycloalkylene, a 4-8 membered heterocyclylene, C6arylene, or a 5-6 membered heteroarylene; 165Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT wherein each alkylene, heteroalkylene, alkenylene, alkynylene, cycloalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl.

12. The compound of claim 1, wherein the compound is represented by Formula IIB: IIB or a sterble salt thereof; wherein: p is 0, 1, 2, 3, 4, 5, or 6; q is 0 or 1; r is 0, 1, 2, or 3; L2ais C(H)m-1or a 5-6 membered heteroarylene; s is 0 or 1; and L2cis C2-20heteroalkylene.

13. The compound of any one of claims 1-12, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein X1is -OH, -SH, -NH2, -N3, optionally substituted cycloalkynyl, optionally substituted heterocyclylalkenyl, or optionally substituted heterocyclylalkynyl.

14. The compound of any one of claims 1-13, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein X1is: 166Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ;15. The compound of any one of claims 1-14, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein X1is: .

16. The compound of any one of claimsa stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein X1is: .

17. The compound of any one of claims 1-14, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein X1is -OH, -SH, -NH2, or -N3.

18. A compound having a structure as set forth in Table 1, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof.

19. A conjugate of Formula I: I or a stereoisomer, mixtu, , pharmaceutically acceptable salt thereof, wherein: A is a polypeptide; 167Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT ; rising at least one alkylene, alkenylene, alkynylene,cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; L2is a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each X2is independently cycloalkylene, heterocyclylene, heteroarylene, -O-, -S-, -NH-, or -C(O)-; wherein the cycloalkylene, heterocyclylene, heteroarylene are each optionally substituted; each L3is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each L4is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each m is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; and y is an integer from 1-20. 168Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 20. The conjugate of claim 19, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each R1is: .

21. The conjugate of claim 19xture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each L1is independently a linker comprising at least one alkylene or heteroalkylene; wherein each alkylene or heteroalkylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl.

22. The conjugate of any one of claims 19-21, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each L1is independently C2-10heteroalkylene; wherein each is independently optionally substituted with oxo.

23. The conjugate of any one of claims 19-22, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each L2is independently a linear linker.

24. The conjugate of any one of claims 19-22, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each L2is independently a branched linker.

25. The conjugate of claim 24, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each L2is independently a bivalent linker or a trivalent linker.

26. The conjugate of any one of claims 19-25, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each L2is independently C2-20heteroalkylene optionally substituted with oxo.

27. The conjugate of claim 19, wherein the compound is represented by Formula IB: 169Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT IB or a sterwherein: A is a polypeptide; p is 0, 1, 2, 3, 4, 5, or 6; q is 0 or 1; r is 0, 1, 2, or 3; L2ais N, NH, C(H)m-1or a 5-6 membered heteroarylene; s is 0 or 1; L2cis C2-20heteroalkylene; each X2is independently cycloalkylene, heterocyclylene, heteroarylene, -O-, -S-, -NH-, or -C(O)-; wherein the cycloalkylene, heterocyclylene, heteroarylene are each optionally substituted; each L3is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; each L4is independently a bond or a linker comprising at least one alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, heteroarylene, or heteroatomic linker; wherein each alkylene, alkenylene, alkynylene, cycloalkylene, heteroalkylene, heterocyclylene, arylene, or heteroarylene is independently optionally substituted with one to five substituents independently selected from oxo, hydroxy, halo, C1-4alkyl, C1-4alkoxy, and C1-4haloalkyl; x is 1, 2, 3, 4, 5, or 6; and 170Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT y is an integer from 1-20.

28. The conjugate of any one of claims 19-27, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each X2is independently -O-, -S-, - NH-, -C(O)-, optionally substituted cycloalkyl, or optionally substituted heterocyclyl.

29. The conjugate of any one of claims 19-28, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, wherein each X2is independently optionally substituted cycloalkyl, or optionally substituted heterocyclyl.

30. The conjugate of any one of claims 19-29, wherein each X2is independently: N N N ,each R2is independently fluoro, chloro, or bromo.

31. The conjugate of any one of claims 19-30, wherein each L3is a linker comprising one to three independently selected alkylene, cycloalkylene, or heteroalkylene, wherein each L3is independently optionally substituted with oxo.

32. The conjugate of any one of claims 19-31, wherein each L3is independently -O-, -S-, -NH-, or -C(O)-.

33. A conjugate, or a stereoisomer, mixture of stereoisomers, tautomer, or pharmaceutically acceptable salt thereof, selected from Table 2, wherein A is a polypeptide.

34. The conjugate of any one of claims 19-33, wherein y is from 5-15.

35. The conjugate of any one of claims 19-34, wherein the polypeptide is an anti-influenza antibody or antigen-binding fragment thereof.

36. The conjugate of claim 35, wherein the polypeptide is a human IgG antibody or a fragment thereof. 171Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 37. The conjugate of claim 36, wherein the IgG antibody is an IgG1 antibody.

38. The conjugate of claim 37, wherein the IgG1 antibody is an anti-SARS-CoV-2 antibody.

39. The conjugate of claim 37, wherein the IgG1 antibody is an anti-influenza antibody.

40. The conjugate of claim 39, wherein the anti-influenza antibody is an anti-hemagglutinin (HA) antibody.

41. The conjugate of claim 38 or 39, wherein the anti-SARS-CoV-2 antibody or the anti- influenza antibody is selected from Tables 3A-C.

42. The conjugate of claim 40, wherein the anti-influenza antibody comprises: i) a heavy chain variable region comprising a complementary determining region (CDR) H1 of SEQ ID NO: 7, a CDRH2 of SEQ ID NO: 8, a CDRH3 of SEQ ID NO: 9; and ii) a light chain variable region comprising a CDRL1 of SEQ ID NO: 10, a CDRL2 of SEQ ID NO: 11, and a CDRL3 of SEQ ID NO:

12.

43. The conjugate of claim 42, wherein the anti-influenza antibody comprises a heavy chain variable region of SEQ ID NO: 1 and a light chain variable region of SEQ ID NO:

2.

44. The conjugate of claim 43, wherein the anti-influenza antibody comprises: i) a heavy chain of SEQ ID NO: 5 and a light chain of SEQ ID NO: 4; ii) a heavy chain of SEQ ID NO: 6 and a light chain of SEQ ID NO: 4, or iii) a heavy chain of SEQ ID NO: 143 and a light chain of SEQ ID NO:

4.

45. The conjugate of claim 40, wherein the anti-influenza antibody comprises a heavy chain variable region comprising the sequence of SEQ ID NO: 33 and a light chain variable region comprising the sequence of SEQ ID NO:

23.

46. The conjugate of claim 45, wherein the anti-influenza antibody comprises i) a heavy chain comprising the sequence of SEQ ID NO: 34 and a light chain comprising the sequence of SEQ ID NO: 24 or ii) a heavy chain comprising the sequence of SEQ ID NO: 144 and a light chain comprising the sequence of SEQ ID NO:

24.

47. The conjugate of any one of claims 19-34, wherein the polypeptide comprises a human IgG Fc polypeptide that comprises an Fc fragment without an antigen-binding fragment.

48. The conjugate of claim 35, wherein the Fc polypeptide consists or consists essentially of a human IgG Fc fragment, a hinge, and at least part of a CH1 domain.

49. The conjugate of claim 47 or 48, wherein the IgG Fc polypeptide is an IgG1 Fc polypeptide.

50. The conjugate of claim 49, wherein the IgG Fc polypeptide comprises SEQ ID NO:137, 138, 139140, 141 or 142. 172Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 51. The conjugate of claim 49 or 50, wherein the IgG Fc polypeptide is a variant IgG Fc polypeptide.

52. The conjugate of claim 51, wherein the variant IgG Fc polypeptide comprises, consists, or consists essentially of SEQ ID NO: 140 or 142.

53. The conjugate of any one of claims 19-52, wherein the conjugate has a drug to antibody ratio (DAR) of about 5 to 15.

54. A conjugate selected from Table 2, or pharmaceutically acceptable salt thereof, wherein A is an anti-influenza antibody comprising a heavy chain variable region of SEQ ID NO: 1 and a light chain variable region of SEQ ID NO:

2.

55. The conjugate of claim 54, wherein the anti-influenza antibody comprises: i) a heavy chain of SEQ ID NO: 5 and a light chain of SEQ ID NO: 4; or ii) a heavy chain of SEQ ID NO: 6 and a light chain of SEQ ID NO:

4.

56. A conjugate selected from Table 2, or pharmaceutically acceptable salt thereof, wherein A is an anti-influenza antibody comprises a heavy chain variable region comprising the sequence of SEQ ID NO: 33 and a light chain variable region comprising the sequence of SEQ ID NO:

23.

57. The conjugate of claim 56, wherein the anti-influenza antibody comprises a heavy chain comprising the sequence of SEQ ID NO: 34 and a light chain comprising the sequence of SEQ ID NO:

24.

58. A composition comprising a mixture of the conjugates of any one of claims 19-40, wherein the average drug to antibody ratio (DAR) of the conjugate in the composition is about 5 to 15.

59. The composition of claim 58, where in the DAR of the conjugate in the composition is about 10 to 12.

60. The composition of claim 58, wherein the DAR of the conjugate in the composition is about 12.

61. A method of preventing an influenza viral infection in a subject in need thereof, comprising administering to the subject an effective amount of the conjugate of any one of claims 19-57.

62. The method of claim 61, wherein the influenza is influenza A, influenza B, or a combination thereof.

63. The method of claim 61 or 62, wherein the administering comprises intranasal, intramuscular, subcutaneous, or intravenous administration.

64. The method of claim 63, wherein the administering comprises intramuscular injection.

65. The method of claim 64, wherein the intramuscular injection is in the deltoid muscle. 173Attorney Docket No.: 95KG-386881-WO Vir Ref No: P0218.WO1PCT 66. The method of any one of claims 61-65, wherein the subject is 65 years of age or older.

67. The method of any one of claims 61-66, wherein the subject has a comorbidity for influenza.

68. The method of any one of claims 61-67, wherein the conjugate of any one of claims 19-57 is administered prior to the subject having been exposed to an influenza virus.

69. A method of treating an influenza viral infection in a subject in need thereof, comprising administering to the subject an effective amount of the conjugate of any one of claims 19-57.

70. The conjugate of any one of claims 19-57 for use in preventing an influenza viral infection.

71. Use of a conjugate of any one of claims 19-57 in the manufacture of a medicament for the prevention of an influenza viral infection.

72. The conjugate of any one of claims 19-57 for use in treating an influenza viral infection.

73. Use of a conjugate of any one of claims 19-57 in the manufacture of a medicament for the treatment of an influenza viral infection. 174

Images