Half-life extending FC domain variants and uses thereof

Abstract

Fc domain variants having altered binding affinity for human FcRn, and polypeptides comprising the Fc domain variants. Also provided herein are nucleic acid encoding Fc domain variants or the polypeptides comprising the Fc domain variants, host cells comprising the encoding nucleic acid for making the variants or polypeptides, and methods for increasing the half-life of a polypeptide and using polypeptides comprising the Fc domain variants to treat disease.

Description

[0001]Attorney Docket: 064802-505001WO HALF-LIFE EXTENDING FC DOMAIN VARIANTS AND USES THEREOF CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of the filing date of U.S. Provisional Application No.63 / 615,822, filed December 29, 2023, the entire contents of which is incorporated by reference herein. SEQUENCE LISTING The instant application contains a Sequence Listing which has been filed electronically in XML format and is hereby incorporated by reference in its entirety. Said XML copy, created on December 20, 2024, is named “064802-505001WO_Seq-Listing_ST26.xml” and is 75,574 bytes in size. BACKGROUND IgG is a class of antibody that comprises 2 heavy chains and 2 light chains. The IgG heavy chain consists of four immunoglobulin domains arranged from N- to C-terminus as VH- CH1-CH2-CH3. The CH2-CH3 interface that forms the Fc region is critical for Fc receptor binding. In IgG, the Fc region contains a site between the CH2 and CH3 domains that directly interacts with FcRn in a pH-dependent manner. This interaction facilitates the recycling of endocytosed antibodies back into the bloodstream, contributing to favorable serum half-lives ranging from one to three weeks. Additionally, Fc-FcRn binding plays a significant role in antibody transport. A polypeptide’s serum half-life is influenced by several factors, such as stability, serum aggregation, enzymatic degradation, inherent immunogenicity, and FcRn-mediated uptake. Therefore, there is a demand for polypeptide modifications that enhance their overall pharmacokinetic profile. SUMMARY The present disclosure is based, at least in part, on the development of IgG Fc domain variants having desired binding affinity to Fc receptors, for example, enhanced binding affinity to human neonatal Fc receptor (FcRn) at an acidic pH condition as relative to their wild-type counterparts. Proteins (e.g., antibodies and Fc-fusion polypeptides) comprising such IgG Fc domain variants showed extended half-life in a subject relative to counterpart proteins having the wild-type counterpart Fc domains. Such proteins would be expected to exhibit superior Attorney Docket: 064802-505001WO therapeutic effects. Accordingly, provided herein are IgG Fc domain variants with increased binding affinity to human FcRn at an acidic pH, proteins (e.g., polypeptides) comprising such, and nucleic acids encoding the IgG Fc domain variants and proteins comprising such. Also provided herein are methods for producing the IgG Fc domain variants and proteins comprising such, as well as methods of using proteins comprising the IgG Fc domain variants to achieve desired effects such as therapeutic effects. In some aspects, the present disclosure provides a polypeptide comprising an IgG Fc domain variant. Relative to a wild-type counterpart, the IgG Fc domain variant comprises: (i) an amino acid residue substitution at position M428, position N434, or a combination thereof; and (ii) an amino acid residue substitution at one or more of positions M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, and N389 (e.g., V259, E269, L309, N361, and / or N389). The IgG Fc domain variant has an increased binding affinity to a human neonatal Fc receptor (FcRn) at an acidic pH (e.g., about pH 6.0) as compared with the wild- type counterpart..Unless indicated otherwise, the Fc residue numbering used herein is based on EU numbering of human IgG Fc domain. In some embodiments, the amino acid residue substitution at position M428 is M428V, M428L, or M428I (e.g., M428L). In some embodiments, the amino acid residue substitution at position N434 is N434Q, N434S, N434T, or N434Y (e.g., N434S or N434Y). In some embodiments, the amino acid residue substitution at position M252 is M252V, M252I, M252V, M252F, M252Y, or M252W (e.g., M252I or M252Y). In some embodiments, the amino acid residue substitution at position T256 is T256D or T256E (e.g., T256E). In some embodiments, the amino acid residue substitution at position V259 is V259I, V259L or V259M (e.g., V259I). In some embodiments, the amino acid residue substitution at position E269 is E269E or E269D (e.g., E269D). In some embodiments, the amino acid residue substitution at position L309 is L309A or L309G (e.g., L309G). In some embodiments, the amino acid residue substitution at position Q311 is D311H, D311K, or D311R (e.g., Q311R). In some embodiment, the amino acid residue substitution at position D312 is D312H, D312K, D312R, D312S, D312T (e.g., D312R or D312S). Attorney Docket: 064802-505001WO In some embodiment, the amino acid residue substitution at position N315 is N315D or N315E (e.g., N315D). In some embodiment, the amino acid residue substitution at position T359 is T359A or T359G (e.g., T359A). In some embodiment, the amino acid residue substitution at position N361 is N361E or N361D (e.g., N361D). In some embodiments, the amino acid residue substitution at position N389 is N389S or N389T (e.g., N389T). In some instances, the IgG Fc domain variant may comprise: (i) the amino acid residue substitution at position M428, position N434, or a combination thereof; and (ii) the amino acid residue substitution(s) at the following position(s): (a) V259, (b) L309 and N361, (c) E269 and N389, (d) M252 and D312, (e) Q311, (f) D312, (g) L309, (h) T256 and V259, (i) T256, V259, and Q311, (j) M252 and Q311, (k) T359, (l) N361 and N389, (m) T359 and N389, (n) N361, (o) N315 and N389, or (p) Q311, N315, and N389. In some examples, the IgG Fc domain variant comprises amino acid residue substitutions at the following combined positions: (a) V259, M428, and N434, (b) L309, N361, and N434, (c) E269, N389, M428, and N434, (d) M252, D312, M428, and N434, (e) Q311, M428, and N434, (f) D312, M428, and N434, (g) L309, M428, and N434, (h) T256, V259, M428, and N434, (i) T256, V259, Q311, M428, and N434, (j) M252, Q311, and N434, (k) T359, M428, and N434, (l) N361, N389, M428, and N434, (m) T359, N389, M428, and N434, (n) N361, M428, and N434, (o) N315, N389, M428, and N434, or (p) Q311, N315, N389, and M428. In specific examples, the IgG Fc domain variant comprises the following amino acid residue substitutions: (a) V259I, M428L, and N434S, (b) L309G, N361D, and N434Y, (c) E269D, N389T, M428L, and N434S, (d) M252I, D312R, M428L, and N434T, (e) Q311R, M428L, and N434S, (f) D312S, M428L, and N434S, (g) L309G, M428L, and N434S, (h) T256E, V259I, M428L, and N434S, (i) L309G, M428L, and N434T, (j) T256E, V259I, Q311R, M428L, and N434S, (k) M252Y, Q311R, and N434Y, (m) T359A, M428L, and N434S, (n) N361D, N389T, M428L, and N434S, (m) T359A, N389T, M428L, and N434S, (o) N361D, M428L, and N434S, (p) N315D, N389T, M428L, and N434S, or (q) Q311R, N315D, N389T, and M428L. Any of the IgG Fc domain variants provided herein may comprise no further amino acid residue substitutions in a binding site for the human fcRn, for example, no further amino acid residue substitutions at amino acid residues T250-T254, T307-Q311 and H433-Y436. In Attorney Docket: 064802-505001WO some instances, the IgG Fc domain variant provided herein may comprises residue K286, N288, H310, L314, E345, H429, E430, and / or K439. Any of the IgG Fc domain variants provided herein may have a reduced binding affinity to the human FcRn relative to the wild-type counterpart at a physiological condition, for example, at a neutral pH (e.g., about 7.0 or about 7.5). In some instances, the IgG Fc domain variant provided herein may further comprise at least one amino acid substitution that alters Fc effector function, for example, at least one amino acid substitution that alters Fc effector function is at position D265 (e.g., D265S or D265T). Alternatively or in addition, the IgG Fc domain variant provided herein may further comprise at least one amino acid substitution that alters binding to a human FcγR, for example, at position L234 (e.g., L234A or L234G) and / or L235 (e.g., L235A or L235G). Alternatively or in addition, the IgG Fc domain variant provided herein may further comprise at least one amino acid substitution that alters binding to human C1q. Alternatively or in addition, the IgG Fc domain variant provided herein may further comprise at least one amino acid substitution that alters antibody-dependent cellular cytotoxicity (ADCC). In some embodiments, the IgG Fc domain variant provided herein can be a human IgG1 Fc domain variant. In some instances, such an IgG Fc domain variant may comprise an amino acid sequence at least 85% (e.g., at least 90%, at least 95%, at least 97%, or above) identical to SEQ ID NO: 1 and the amino acid residue substitutions provided herein. the IgG Fc domain variant comprises an amino acid sequence of any one of SEQ ID NOs: 8-24, (e.g., SEQ ID NO: 11, 17, or 23). In some embodiments, the IgG Fc domain variant provided herein can be a human IgG4 Fc domain variant. In some instances, such an IgG Fc domain variant may comprise an amino acid sequence at least 85% (e.g., at least 90%, at least 95%, at least 97%, or above) identical to SEQ ID NO: 59 and the amino acid residue substitutions provided herein. In specific examples, In specific examples, the IgG Fc domain variant comprises an amino acid sequence of any one of SEQ ID NOs: 25-41 (e.g., SEQ ID NO: 28, 34, or 40). In some aspects, provided herein is a protein comprising any of the IgG Fc domain variants provided herein. In some embodiment, the protein is a polypeptide comprising the IgG Fc domain variant. In some examples, the polypeptide can be a heavy chain of an antibody comprising a heavy chain variable region. In other examples, the polypeptide can be an Fc- fusion polypeptide comprising a polypeptide fragment (a fusion partner) fused to the IgG Fc domain variant. The fusion partner may be an antigen-binding moiety, for example, a single Attorney Docket: 064802-505001WO chain variable fragment (scFv) or a single-domain antibody fragment. Alternatively, the fusion partner can be a cytokine. In other aspects, the present disclosure provides a nucleic acid comprising a nucleotide sequence encoding a polypeptide comprising any of the IgG Fc domain variants provided herein. In some embodiments, the nucleic acid may be a vector, for example, an expression vector. Also provided herein are host cells comprising the encoding nucleic acid (e.g., a vector such as an expression vector). In yet other aspects, the present disclosure provides a method for producing a polypeptide comprising the IgG Fc domain variant as disclosed herein. The method comprises culturing the host cell comprising the encoding nucleic acid under conditions allowing for expression of the polypeptide. Further, the present disclosure provides a composition comprising the polypeptide or protein disclosed herein, comprising any of the IgG Fc domain variants disclosed herein, or the encoding nucleic acid as also disclosed herein, and a pharmaceutically acceptable carrier. Moreover, the present disclosure features a method for enhancing half-life of an Fc- containing protein in a subject, the method comprising introducing into the Fc domain in the Fc-containing protein the amino acid residue substitutions disclosed herein to produce a protein comprising a variant Fc domain. A protein comprising the variant Fc domain has an increased half-life in a subject as compared with the parent Fc-containing protein comprising a wildtype counterpart IgG Fc domain. In some instances, the Fc-containing protein is an antibody or an Fc-fusion polypeptide. Also provided herein are proteins comprising any of the IgG Fc domain variants disclosed herein as a medication for use in treating a target disease of interest, as well as uses of such proteins for manufacturing a medicament for treatment of the target disease of interest. Provided below are specific embodiments, each of which is within the scope of the present disclosure. Embodiment 1: A polypeptide comprising an IgG Fc domain variant, wherein the IgG Fc domain variant comprises amino acid substitutions at amino acid residues selected from: (a) T256, V259, M428, and N434; (b) L309, N361, and N434; (c) T359, M428, and N434; (d) N361, N389, M428, and N434, (e) T359, N389, M428, and N434; (f) N361, M428, and N434; (g) Q311, N315, N389, and M428; (h) E269, N389, M428, and N434; (i) N315, N389, M428, and N434; and (j) T256, V259, Q311, M428, and N434, wherein residue numbering is based on EU numbering of a human IgG Fc domain, and wherein the IgG Fc domain variant has increased binding affinity to human FcRn at an acidic pH. Attorney Docket: 064802-505001WO Embodiment 2: A polypeptide comprising an IgG Fc domain variant, wherein the IgG Fc domain variant comprises (i) an amino acid substitution at amino acid residues M428 and / or N434, and (ii) amino acid substitutions at amino acid residues from selected from: (a) T256 and V259; (b) L309 and N361; (c) T359; (d) N361 and N389; (e) T359 and N389; (f) N361; (g) Q311, N315, and N389; (h) E269 and N389; (i) N315 and N389; and (j) T256, V259 and Q311, wherein residue numbering is based on EU numbering of a human IgG Fc domain, and wherein the IgG Fc domain variant has increased binding affinity to human FcRn at an acidic pH. Embodiment 3: The polypeptide of Embodiment 1 or Embodiment 2, wherein the amino acid substitution at amino acid residue T256 is selected from T256E and T256N; the amino acid substitution at amino acid residue V259 is selected from V259I and V259T; the amino acid substitution at amino acid residue E269 is selected from E269D and E269G; the amino acid substitution at amino acid residue L309 is selected from L309G, L309K, L309P, L309R and L309S; the amino acid substitution at amino acid residue Q311 is Q311R; the amino acid substitution at amino acid residue N315 is N315D; the amino acid substitution at amino acid residue T359 is T359A; the amino acid substitution at amino acid residue N361 is selected from N361D and N361S; the amino acid substitution at amino acid residue N389 is selected from N389K, N389R and N389T; the amino acid substitution at amino acid residue M428 is selected from M428D, M428E and M428L; and / or the amino acid substitution at amino acid residue N434 is selected from N434H, N434T, N434W, N434S and N434Y. Embodiment 4: The polypeptide of Embodiment 1 or Embodiment 2, wherein the amino acid substitution at amino acid residue T256 is T256E; the amino acid substitution at amino acid residue V259 is selected from V259I and V259T; the amino acid substitution at amino acid residue E269 is E269D; the amino acid substitution at amino acid residue L309 is L309G; the amino acid substitution at amino acid residue Q311 is Q311R; the amino acid substitution at amino acid residue N315 is N315D; the amino acid substitution at amino acid residue T359 is T359A; the amino acid substitution at amino acid residue N361 is N361D; the amino acid substitution at amino acid residue N389 is N389T; the amino acid substitution at amino acid residue M428 is M428L; and / or the amino acid substitution at amino acid residue N434 is selected from N434S and N434Y. Embodiment 5: A polypeptide comprising an IgG Fc domain variant, wherein the IgG Fc domain variant comprises: (a) at least one amino acid substitution selected from M428L, N434S, N434T and N434Y; and (b) at least two amino acid substitutions selected from: M252I, M252Y, T256E, V259I, E269D, L309G, Q311R, D312S, D312R, N315D, T359A, Attorney Docket: 064802-505001WO N361D, and N389T; wherein residue numbering is based on EU numbering of a human IgG Fc domain, and wherein the IgG Fc domain variant has increased binding affinity to human FcRn at an acidic pH. Embodiment 6: The polypeptide of Embodiment 5, wherein the at least one amino acid substitution of (a) is selected from: (i) M428L and N434S, (ii) M428L and N434T, (iii) N434Y, and (iv) M428L. Embodiment 7: The polypeptide of Embodiment 5 or Embodiment 6, wherein the at least two amino acid substitutions of (b) is selected from: (i) M252I and D312R, (ii) T256E and V259I, (iii) T256E, V259I and Q311R, (iv) M252Y and Q311R, (v) N361D and N389T, (vi) T359A and N389T, (vii) N315D and N389T, (viii) E269D and N389T, and (ix) Q311R and N315D. Embodiment 8: A polypeptide comprising an IgG Fc domain variant, wherein the IgG Fc domain variant comprises (i) an amino acid substitution at amino acid residues M428 and / or N434, and (ii) amino acid substitutions selected from: (a) M252I and D312R; (b) T256E and V259I; (c) T256E, V259I and Q311R; (d) M252Y and Q311R; (e) N361D and N389T; (f) T359A and N389T: (g) N315D and N389T: (h) E269D and N389T; or (i) Q311R, N315D and N389T; wherein residue numbering is based on EU numbering of a human IgG Fc domain. Embodiment 9: The polypeptide of Embodiment 8, wherein the amino acid substitution of (i) is selected from M428L, N434S, N434T and N434Y. Embodiment 10: The polypeptide of Embodiment 8 or Embodiment 9, wherein the amino acid substitution of (i) is selected from M428L and N434S; M428L and N434T; N434Y; and M428L. Embodiment 11: A polypeptide comprising an IgG Fc domain variant, wherein the IgG Fc domain variant comprises amino acid substitutions selected from: (a) M252I, D312R, M428L, and N343T; (b) Q311R, M428L, and N434S; (c) D312S, M428L, and N434S; (d) L309G, M428L, and N434S; (e) T256E, V259I, M428L, and N434S; (f) L309G, M428L, N434T; (g) T256E, V259I, Q311R, M428L and N434S; (h) M252Y, Q311R, and N434Y; (i) T259A, M428L and N434S; (j) N361D, N389T, M428L and N434S; (k) T359A, N389T, M428L and N434S: (l) N361D, M428L, and N434S; (m) N315D, N389T, M428L and N434S: (n) E269D, N389T, M428L, and N434S; and (o) Q311R, N315D, N389T and M428L; wherein residue numbering is based on EU numbering of a human IgG Fc domain. Embodiment 12: The polypeptide of any one of Embodiments 8-11, wherein the IgG Fc domain variant has increased binding affinity to human FcRn at an acidic pH. Embodiment 13: The polypeptide of any one of Embodiments 1-7 and 12, wherein the Attorney Docket: 064802-505001WO acidic pH is about 6. Embodiment 14: The polypeptide of any one of Embodiments 1-7 and 12-13; wherein increased binding affinity to human FcRn is relative to a wild-type human IgG Fc domain or a human IgG Fc domain without the amino acid substitutions of the IgG Fc domain variant. Embodiment 15: The polypeptide of any one of Embodiments 1-14, wherein the IgG Fc domain variant has reduced binding affinity to human FcRn at physiological conditions. Embodiment 16: The polypeptide of Embodiment 15, wherein physiological conditions comprise a neutral pH. Embodiment 17: The polypeptide of Embodiment 15, wherein physiological conditions comprise a pH of about 7 to about 7.5. Embodiment 18: The polypeptide of any one of Embodiments 15-17, wherein reduced binding affinity to human FcRn is relative to a wild-type human IgG Fc domain or a human IgG Fc domain without the amino acid substitutions of the IgG Fc domain variant. Embodiment 19: The polypeptide of any one of Embodiments 1-18, wherein the polypeptide has an increased half-life relative to a polypeptide comprising a wild-type human IgG Fc domain or a polypeptide comprising a human IgG Fc domain without the amino acid substitutions of the IgG Fc domain variant. Embodiment 20: The polypeptide of any one of Embodiments 1-19, wherein the Fc domain variant comprises an amino acid sequence selected from SEQ ID NOs: 8-24 or an amino acid sequence having at least 80%, 90%, 95%, 96%, 97%, 98% or 99% identity to an amino acid sequence selected from SEQ ID Nos: 8-24. Embodiment 21: The polypeptide of any one of Embodiments 1-19, wherein the Fc domain variant comprises an amino acid sequence selected from SEQ ID NOs: 25-41 or an amino acid sequence having at least 80%, 90%, 95%, 96%, 97%, 98% or 99% identity to an amino acid sequence selected from SEQ ID Nos: 25-41. Embodiment 22: The polypeptide of any one of Embodiments 1-21, wherein the IgG Fc domain variant does not comprise amino acid substitutions at amino acid residues H310 and / or H429. Embodiment 23: The polypeptide of any one of Embodiments 1-22, wherein the IgG Fc domain variant comprises at least one amino acid substitution at amino acid residues not involved in human FcRn binding and / or does not alter binding affinity to human FcRn at an acidic pH. Embodiment 24: The polypeptide of any one of Embodiments 1-23, wherein the IgG Fc domain variant does not comprise additional amino acid substitutions in the binding site for Attorney Docket: 064802-505001WO human FcRn, wherein the binding site comprises amino acid residues T250-T254, T307-Q311 and H433-Y436, and optionally amino acid residues T256, K286, N288, L314, E345, M428, E430 and K439. Embodiment 25: The polypeptide of any one of Embodiments 1-24, wherein the IgG Fc domain variant comprises at least one amino acid substitution that alters Fc effector function. Embodiment 26: The polypeptide of Embodiment 25, wherein the at least one amino acid substitution that alters Fc effector function is D265S. Embodiment 27: The polypeptide of any one of Embodiments 1-26, wherein the IgG Fc domain variant comprises at least one amino acid substitution that alters binding to a human FcγR. Embodiment 28: The polypeptide of Embodiment 27, wherein the at least one amino acid substitution is L234A and / or L235A. Embodiment 29: The polypeptide of any one of Embodiments 1-28, wherein the IgG Fc domain variant comprises at least one amino acid substitution that alters binding to human C1q. Embodiment 30: The polypeptide of any one of Embodiments 1-29, wherein the IgG Fc domain variant comprises at least one amino acid substitution that alters antibody-dependent cellular cytotoxicity (ADCC). Embodiment 31: The polypeptide of any one of Embodiments 1-30, wherein the IgG Fc domain variant is an IgG1 Fc domain variant. Embodiment 32: The polypeptide of any one of Embodiments 1-30, wherein the IgG Fc domain variant is an IgG4 Fc domain variant. Embodiment 33: The polypeptide of any one of Embodiments 1-32, wherein the polypeptide is an antibody or an antibody fragment thereof. Embodiment 34: The polypeptide of any one of Embodiments 1-32, wherein the polypeptide comprises a cytokine. Embodiment 35: The polypeptide of any one of Embodiments 1-32, wherein the polypeptide comprises an antigen binding region. Embodiment 36: A nucleic acid encoding the polypeptide of any one of Embodiments 1-35. Embodiment 37: A vector comprising the nucleic acid of Embodiment 36. Embodiment 38: A host cell comprising the nucleic acid of Embodiment 36 or the vector of Embodiment 37. Attorney Docket: 064802-505001WO Embodiment 39: A method for producing a polypeptide, comprising maintaining the host cell of Embodiment 37 under conditions permitting expression of the polypeptide. Embodiment 40: A composition comprising the polypeptide of any one of Embodiments 1-35. Embodiment 41: The composition of Embodiment 40, comprising a pharmaceutically acceptable carrier or salt thereof. Embodiment 42: A method for increasing half-life of a polypeptide comprising an IgG Fc domain, wherein the method comprises substituting amino acids residues of the IgG Fc domain, wherein the amino acid residues are selected from: (a) T256, V259, M428, and N434; (b) L309, N361, and N434; (c) T359, M428, and N434; (d) N361, N389, M428, and N434, (e) T359, N389, M428, and N434; (f) N361, M428, and N434; (g) Q311, N315, N389, and M428; (h) E269, N389, M428, and N434; (i) N315, N389, M428, and N434; and (j) T256, V259, Q311, M428, and N434; wherein residue numbering is based on EU numbering of a human IgG Fc domain. Embodiment 43: A method for increasing half-life of a polypeptide comprising an IgG Fc domain, wherein the method comprises substituting amino acids residues of the IgG Fc domain, wherein the amino acid residues comprise (i) M428 and / or N434, and (ii) amino acid residues from selected from: (a) T256 and V259; (b) L309 and N361; (c) T359; (d) N361 and N389; (e) T359 and N389; (f) N361; (g) Q311, N315, and N389; (h) E269 and N389; (i) N315 and N389; and (j) T256, V259 and Q311; wherein residue numbering is based on EU numbering of a human IgG Fc domain. Embodiment 44: The method of Embodiment 42 or Embodiment 43, wherein the amino acid substitution at amino acid residue T256 is selected from T256E and T256N; the amino acid substitution at amino acid residue V259 is selected from V259I and V259T; the amino acid substitution at amino acid residue E269 is selected from E269D and E269G; the amino acid substitution at amino acid residue L309 is selected from L309G, L309K, L309P, L309R and L309S; the amino acid substitution at amino acid residue Q311 is Q311R; the amino acid substitution at amino acid residue N315 is N315D; the amino acid substitution at amino acid residue T359 is T359A; the amino acid substitution at amino acid residue N361 is selected from N361D and N361S; the amino acid substitution at amino acid residue N389 is selected from N389K, N389R and N389T; the amino acid substitution at amino acid residue M428 is selected from M428D, M428E and M428L; and / or the amino acid substitution at amino acid residue N434 is selected from N434H, N434T, N434W, N434S and N434Y. Embodiment 45: The method of Embodiment 42 or Embodiment 43, wherein the amino Attorney Docket: 064802-505001WO acid substitution at amino acid residue T256 is T256E; the amino acid substitution at amino acid residue V259 is selected from V259I and V259T; the amino acid substitution at amino acid residue E269 is E269D; the amino acid substitution at amino acid residue L309 is L309G; the amino acid substitution at amino acid residue Q311 is Q311R; the amino acid substitution at amino acid residue N315 is N315D; the amino acid substitution at amino acid residue T359 is T359A; the amino acid substitution at amino acid residue N361 is N361D; the amino acid substitution at amino acid residue N389 is N389T; the amino acid substitution at amino acid residue M428 is M428L; and / or the amino acid substitution at amino acid residue N434 is selected from N434S and N434Y. Embodiment 46: A method for increasing half-life of a polypeptide comprising an IgG Fc domain, wherein the method comprises substituting amino acids residues of the IgG Fc domain, wherein the amino acid substitutions comprise: (a) at least one amino acid substitution selected from M428L, N434S, N434T and N434Y; and (b) at least two amino acid substitutions selected from: M252I, M252Y, T256E, V259I, E269D, L309G, Q311R, D312S, D312R, N315D, T359A, N361D, and N389T; wherein residue numbering is based on EU numbering of a wild-type IgG Fc domain. Embodiment 47: The method of claim 46, wherein at least one amino acid substitution of (a) is selected from: (i) M428L and N434S, (ii) M428L and N434T, (iii) N434Y, and (iv) M428L. Embodiment 48: The method of Embodiment 46 or Embodiment 47, wherein the at least two amino acid substitutions of (b) is selected from: (i) M252I and D312R, (ii) T256E and V259I, (iii) T256E, V259I and Q311R, (iv) M252Y and Q311R, (v) N361D and N389T, (vi) T359A and N389T, (vii) N315D and N389T, (viii) E269D and N389T, and (ix) Q311R and N315D. Embodiment 49: A method for increasing half-life of a polypeptide comprising an IgG Fc domain, wherein the method comprises substituting amino acids residues of the IgG Fc domain, wherein the amino acid substitutions comprise (i) an amino acid substitution at amino acid residues M428 and / or N434, and (ii) amino acid substitutions selected from: (a) M252I and D312R; (b) T256E and V259I; (c) T256E, V259I and Q311R; (d) M252Y and Q311R; (e) N361D and N389T; (f) T359A and N389T: (g) N315D and N389T: (h) E269D and N389T; and (i) Q311R, N315D and N389T; wherein residue numbering is based on EU numbering of a wild-type IgG Fc domain. Embodiment 50: The method of Embodiment 49, wherein the amino acid substitution of (i) is selected from M428L, N434S, N434T and N434Y. Attorney Docket: 064802-505001WO Embodiment 51: The method of Embodiment 49 or Embodiment 50, wherein the amino acid substitution of (i) is selected from M428L and N434S; M428L and N434T; N434Y; and M428L. Embodiment 52: A method for increasing half-life of a polypeptide comprising an IgG Fc domain, wherein the method comprises substituting amino acids residues of the IgG Fc domain, wherein the amino acid substitutions comprise substitutions selected from: (a) M252I, D312R, M428L, and N434T; (b) Q311R, M428L, and N434S; (c) D312S, M428L, and N434S; (d) L309G, M428L, N434S; (e) T256E, V259I, M428L, and N434S; (f) L309G, M428L, N434T; (g) T256E, V259I, Q311R, M428L and N434S; (h) M252Y, Q311R, and N434Y; (i) T259A, M428L and N434S; (j) N361D, N389T, M428L and N434S; (k) T359A, N389T, M428L and N434S: (l) N361D, M428L, and N434S; (m) N315D, N389T, M428L and N434S: (n) E269D, N389T, M428L, and N434S; and (o) Q311R, N315D, N389T and M428L; wherein residue numbering is based on EU numbering of a wild-type IgG Fc domain. Embodiment 53: The method of any one of Embodiments 42-52, wherein the polypeptide has increased binding affinity to human FcRn at an acidic pH. Embodiment 54: The method of Embodiment 53, wherein the acidic pH is about 6. Embodiment 55: The method of Embodiment 53 or Embodiment 54, wherein increased binding affinity to human FcRn is relative to a polypeptide comprising a wild-type human IgG Fc domain or a human IgG Fc domain without the amino acid substitutions. Embodiment 56: The method of any one of Embodiments 42-55, wherein the polypeptide has reduced binding affinity to human FcRn at physiological conditions. Embodiment 57: The method of Embodiment 56, wherein physiological conditions comprise a neutral pH. Embodiment 58: The method of Embodiment 56, wherein physiological conditions comprise a pH of about 7 to about 7.5. Embodiment 59: The method of any one of Embodiments 56-58, wherein reduced binding affinity to human FcRn is relative to a polypeptide comprising a wild-type human IgG Fc domain or a human IgG Fc domain without the amino acid substitutions. Embodiment 60: The method of any one of Embodiments 42-59, wherein increased half-life is relative to a polypeptide comprising a wild-type human IgG Fc domain or a polypeptide comprising a human IgG Fc domain without the amino acid substitutions of the IgG Fc domain variant. Embodiment 61: The method of any one of Embodiments 42-60, wherein the Fc domain comprises an amino acid sequence selected from SEQ ID NOs: 8-24 or an amino acid Attorney Docket: 064802-505001WO sequence having at least 80%, 90%, 95%, 96%, 97%, 98% or 99% identity to an amino acid sequence selected from SEQ ID Nos: 8-24. Embodiment 62: The method of any one of Embodiments 42-60, wherein the Fc domain variant comprises an amino acid sequence selected from SEQ ID NOs: 25-41 or an amino acid sequence having at least 80%, 90%, 95%, 96%, 97%, 98% or 99% identity to an amino acid sequence selected from SEQ ID Nos: 25-41. Embodiment 63: The method of any one of Embodiments 42-62, wherein the IgG Fc domain does not comprise amino acid substitutions at amino acid residues H310 and / or H429. Embodiment 64: The method of any one of Embodiment 42-63, wherein the IgG Fc domain variant comprises at least one amino acid substitution at amino acid residues not involved in human FcRn binding and / or does not alter binding affinity to human FcRn at an acidic pH. Embodiment 65: The method of any one of Embodiments 42-64, wherein the IgG Fc domain variant does not comprise additional amino acid substitutions in the binding site for human FcRn, wherein the binding site comprises amino acid residues T250-T254, T307-Q311 and H433-Y436, and optionally amino acid residues T256, K286, N288, L314, E345, M428, E430 and K439. Embodiment 66: The method of any one of Embodiments 42-65, wherein the IgG Fc domain comprises at least one amino acid substitution that alters Fc effector function. Embodiment 67: The method of Embodiment 66, wherein at least one amino acid substitution that alters Fc effector function is D265S. Embodiment 68: The method of any one of Embodiments 42-67, wherein the IgG Fc domain comprises at least one amino acid substitution that alters binding to a human FcγR. Embodiment 69: The method of Embodiment 68, wherein the at least one amino acid substitution is L234A and / or L235A. Embodiment 70: The method of any one of Embodiments 42-69, wherein the IgG Fc domain variant comprises at least one amino acid substitution that alters binding to human C1q. Embodiment 71: The method of any one of Embodiments 42-70, wherein the IgG Fc domain variant comprises at least one amino acid substitution that alters antibody-dependent cellular cytotoxicity (ADCC). Embodiment 72: The method of any one of Embodiments 42-71, wherein the IgG Fc domain is an IgG1 Fc domain. Attorney Docket: 064802-505001WO Embodiment 73: The method of any one of Embodiments 42-72, wherein the IgG Fc domain is an IgG4 Fc domain. Embodiment 74: The method of any one of Embodiments 42-72, wherein the polypeptide is an antibody or an antibody fragment thereof. Embodiment 75: The method of any one of Embodiments 42-72, wherein the polypeptide comprises a cytokine. Embodiment 76: The method of any one of Embodiments 42-72, wherein the polypeptide comprises an antigen binding region. The details of one or more embodiments of the invention are set forth in the description below. Other features or advantages of the present invention will be apparent from the following drawings and detailed description of several embodiments, and also from the appended claims. BRIEF DESCRIPTION OF THE FIGURES The patent or application file contains at least one drawing executed in color. Color copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. FIG.1 provides the amino acid sequence (SEQ ID NO: 1) of the CH2 and CH3 domain of a human IgG1 constant region with residues targeted for mutagenesis numbered based on EU numbering and bolded. FIG.2 provides a schematic of the surface plasmon resonance (SPR) capture method for measuring FcRn binding. Anti-his antibody is amine coupled to the surface of an SPR chip. Fc variants are then captured to the surface during immobilization step directly from lysate. Tag free FcRn is then screened as the analyte at pH 6. FIGs.3A-3C provides sensorgrams showing binding kinetics based on SPR shown in FIG.2 for polypeptides having IgG Fc domains with YTE mutations (M252Y / S254T / T256E) (FIG.3B) or LS mutations (M428L / N434S) (FIG.3C) relative to wild-type (FIG.3A). FIG.4 provides graphs showing kinetic parameters of rational designed IgG Fc domain variants with improved FcRn binding at pH 6. FIG.5 provides a graph showing FcRn binding of IgG Fc domain variants designed by artificial intelligence. Variants were ranked by fitness scores using ESM, ProteinMPNN, and BLOSUM80 and top 160 screened using FcRn binding workflow described in FIG.2. FIGs.6A-6B include diagrams showing FcRn binding affinity of Fc domain variants in IgG1 and IgG4 formats at pH 6. FIG.6A: binding affinity to human FcRn at pH 6. FIG.6B: binding affinity to Rhesus FcRn at pH 6. Attorney Docket: 064802-505001WO DETAILED DESCRIPTION The present disclosure is based, at least in part, on the discovery of amino acid substitutions in an Fc domain that alter its binding to a FcRn to modulate the half-life of a protein (e.g., a polypeptide) comprising the resultant Fc domain variant. A number of amino acid residue positions in the wild-type IgG Fc domain (based on the EU numbering system) has been identified by rational design and optionally in combination with artificial intelligence (AI) design as candidate positions for variations to enhance binding affinity to human neonatal Fc receptor (FcRn) at acidic conditions and subsequently half-life of proteins such as antibodies comprising such a Fc variant. Exemplary IgG1 and IgG4 Fc variants having a combination of amino acid residue substitutions at those identified positions exhibited enhanced binding affinity to human FcRn at an acidic pH condition as compared with the wild-type counterpart or the reference YTE or LS Fc variants. Antibodies containing such Fc variants also showed enhanced half-life as evidenced by the absolute antibody recycling concentrations as compared with antibodies having the wild-type Fc domain or the reference Fc domain variants. Accordingly, proteins comprising the IgG Fc domain variants disclosed herein (e.g., antibodies or Fc-fusion polypeptides) are expected to have extended half-life in the body, which would benefit therapeutic uses of such proteins in various aspects (e.g., lower doses required, superior therapeutic effects, minimized side effects, etc.). Accordingly, the disclosure provides, in some aspects, compositions of polypeptides comprising an Fc domain variant described herein and methods for making and using the same. I. IgG Fc Domain Variants In some aspects, the present disclosure provides IgG Fc domain variants (e.g., IgG1 or IgG4 Fc variants) having enhanced binding affinity to human FcRn at acidic conditions. The IgG Fc domain variants can be a component of a polypeptide (e.g., an Fc-fusion polypeptide) or a protein (e.g., the Fc region in an antibody heavy chain). As described herein, an “IgG Fc domain” is a C-terminal region of an immunoglobulin heavy chain that contains at least a portion of the constant region, e.g., the CH2 and CH3 regions of an IgG heavy chain constant region. As described herein, an “IgG Fc domain variant” refers to an IgG Fc domain comprising at least one amino acid mutation relative to a wild-type IgG Fc domain (a wild-type counterpart), for example, a human wild-type IgG Fc domain. In some embodiments, the Fc domain variant comprises a human Fc domain sequence (e.g., a human IgG1, IgG2, IgG3 or IgG4 Fc domain) comprising an amino acid modification (e.g., a substitution) at one or more amino acid residue positions relative to the wild-type Attorney Docket: 064802-505001WO counterpart. In some examples, the Fc domain variant provided herein comprises a human IgG1 Fc domain sequence with an amino acid modification (e.g., a substitution) at one or more amino acid residue positions relative to the wild-type human IgG1 Fc domain sequence. In other examples, the Fc domain variant provided herein comprises a human IgG4 Fc domain sequence with an amino acid modification (e.g., a substitution) at one or more amino acid residue positions relative to the wild-type human IgG4 Fc domain sequence. Mutation of residues within Fc receptor binding sites can result in altered effector function, such as altered ADCC, CDC activity, and / or altered half-life. Mutations include, for example, insertion, deletion, and / or substitution of one or more residues as described in more detail above, including substitution with alanine, a conservative substitution, a non- conservative substitution, and / or replacement with a corresponding amino acid residue at the same position from a different IgG subclass (e.g., replacing an IgG1 residue with a corresponding IgG2 residue at that position). As used herein, a “conservative amino acid substitution” refers to an amino acid substitution that does not alter the relative charge or size characteristics of the protein in which the amino acid substitution is made. Variants can be prepared according to methods for altering polypeptide sequence known to one of ordinary skill in the art such as are found in references which compile such methods, e.g., Molecular Cloning: A Laboratory Manual, J. Sambrook, et al., eds., Second Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, 1989, or Current Protocols in Molecular Biology, F.M. Ausubel, et al., eds., John Wiley & Sons, Inc., New York. Conservative substitutions of amino acids include substitutions made amongst amino acids within the following groups: (a) M, I, L, V; (b) F, Y, W; (c) K, R, H; (d) A, G; (e) S, T; (f) Q, N; and (g) E, D. A. Fc Domain Variants with Altered FcRn Binding & Increased Serum Half-Life In some aspects, the Fc domain variants described herein have altered binding affinity to the neonatal Fc receptor (FcRn) (e.g., increased binding affinity to the FcRn receptor under acidic conditions). Fc domains comprise a binding site for FcRn, which comprises amino acid residues located at T250-T254, T307-Q311 and H433-Y436, following the EU numbering. The IgG Fc domain variants provided herein may comprise at least two amino acid substitutions within the FcRn binding site. In some embodiments, the Fc domain variant comprises 2-6 amino acid substitutions within the FcRn binding site. In some embodiments, the Fc domain variant comprises 2-4 amino acid substitutions within the FcRn binding site. In some examples, the Fc domain variant comprises at least three amino acid Attorney Docket: 064802-505001WO substitutions within the FcRn binding site. In some examples, the Fc domain variant comprises at least four amino acid substitutions within the FcRn binding site. In some examples, the Fc domain variant comprises at least five amino acid substitutions within the FcRn binding site. In some examples, the Fc domain variant comprises at least six amino acid substitutions within the FcRn binding site. In other examples, the Fc domain variant comprises no more than two amino acid substitutions within the FcRn binding site. In some examples, the Fc domain variant comprises no more than three amino acid substitutions within the FcRn binding site. In some examples, the Fc domain variant comprises no more than four amino acid substitutions within the FcRn binding site. In some examples, the Fc domain variant comprises no more than five amino acid substitutions within the FcRn binding site. In examples, the Fc domain variant comprises no more than six amino acid substitutions within the FcRn binding site. Binding affinity, represented by the equilibrium constant for the dissociation (KD) of a target (e.g., FcRn) with a target-binding protein (e.g., Fc domain variant), is a measure for the binding strength between the target and the target-binding protein: the lesser the value of the KD, the stronger the binding strength. Alternatively, affinity can also be expressed as the affinity constant (KA), which is 1 / KD. As will be clear to the skilled person, affinity can be determined in a manner known per se, depending on the specific target of interest. KDcan be measured by any suitable assay. For example, in some embodiments, KDis measured by a radiolabeled antigen-binding assay (RIA) (see, e.g., Chen et al., J. Mol. Biol. 293:865-881 (1999); Presta et al., Cancer Res.57:4593-4599 (1997)). In some embodiments, KDis measured using a surface plasmon resonance assay (e.g., using a BIACORE®-2000 or a BIACORE®-3000). In some embodiments, KDis measured using a competitive ELISA. In some embodiments, binding of an Fc domain to FcRn is measured by surface plasmon resonance assay. In some embodiments, an Fc domain or the FcRn is immobilized onto a biosensor chip and the FcRn or Fc domain, respectively, is injected over the sensor chip. In some embodiments, an Fc domain or FcRn is bound to the sensor chip via amine coupling. In some embodiments, amine coupling is via lysine residues and an N-terminal amino group. Avidity is the measure of the strength of binding between a target-binding molecule and the pertinent target. Avidity is related to both the affinity between a target and its target binding site on the target-binding molecule, and the number of pertinent binding sites present on the target-binding molecule. Typically, target-binding proteins will bind to their cognate or specific target with a dissociation constant (KD of 10-5to 10-12M or less, and preferably 10-7to 10-12M or less and more preferably 10-8to 10-12M (i.e., with an association constant (KA) of Attorney Docket: 064802-505001WO 105to 1012M-1or more, and preferably 107to 1012M-1or more and more preferably 108to 1012M-1). Any KD value greater than 10-4M (or any KA value lower than 104M-1) is generally considered to indicate non-specific binding. The KDfor biological interactions which are considered meaningful (e.g., specific) are typically in the range of 10-10M (0.1 nM) to 10-5M (10000 nM). The stronger an interaction is, the lower is its KD. Specific binding of a target- binding protein to target can be determined in any suitable manner known per se, including, for example, Scatchard analysis and / or competitive binding assays, such as radioimmunoassays (RIA), enzyme immunoassays (EIA) and sandwich competition assays, and the different variants thereof known per se in the art; as well as other techniques as mentioned herein. The term “kon,” as used herein, is intended to refer to the rate constant for association of a target-binding molecule to a target. The term “koff,” as used herein, is intended to refer to the rate constant for dissociation of a target- molecule thereof from the target-binding molecule / target complex. In some aspects, proteins such as polypeptides comprising an Fc domain variant described herein have increased serum half-lives. Serum half-life is the amount of time required for the serum concentration of a molecule to be reduced by 50%. Serum half-life can be evaluated by any suitable assay. In some embodiments, serum half-life is evaluated by measuring the concentration of polypeptide comprising an Fc domain variant over time with LC-MS / MS. In some embodiments, the serum half-life is evaluated fluorometrically using the Phadia System. In some embodiments, the serum half-life and the Fc domain variant were evaluated with surface plasmon resonance (SPR). In some embodiments, the serum half-life was evaluated with an enzyme-linked immunosorbent assay (ELISA). In some embodiments, the polypeptides comprising an Fc domain variant described herein have increased serum half-lives relative to a polypeptide comprising an IgG Fc domain comprising mutations M252Y, S254T and T256E (the YTE Fc domain variant). In some embodiments, the serum half-life of a polypeptide comprising an Fc domain variant described herein is at least 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 20-, 30-, 40-, 50-, 60-, 70-, 80-, 90, or 100- fold higher than the serum half-life of a polypeptide comprising the YTE Fc variant. In some embodiments, the polypeptides comprising an Fc domain variant described herein have increased serum half-lives relative to a polypeptide comprising an IgG Fc domain comprising mutations M428L and N434S (the LS Fc domain variant). In some embodiments, the serum half-life of a polypeptide comprising an Fc domain variant described herein is at least 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 20-, 30-, 40-, 50-, 60-, 70-, 80-, 90, or 100-fold higher than the serum half-life of a polypeptide comprising the LS Fc domain variant. Attorney Docket: 064802-505001WO In some embodiments, the Fc domain variants described herein have altered binding affinity for the FcRn. Fc domain variants with improved affinity for FcRn are anticipated to have longer serum half-lives. In some embodiments, an Fc domain variant has increased binding affinity to an FcRn at an acidic pH. In some embodiments, an acidic pH is a pH value less than 7. In some embodiments, a polypeptide comprising an Fc domain variant has increased binding to an FcRn at about pH 6. In some embodiments, increased binding to FcRn at an acidic pH is relative to a human wild-type Fc domain or a human Fc domain not comprising the amino acid substitutions of the Fc domain variant described herein. In some embodiments, increased binding affinity to human FcRn at an acidic pH is relative to an IgG Fc domain comprising mutations M252Y, S254T and T256E. In some embodiments, increased binding affinity to human FcRn at an acidic pH is relative to an IgG Fc domain comprising mutations M428L and N434S. In some embodiments, the IgG Fc domain variant has similar binding affinity to human FcRn at an acidic pH as an IgG Fc domain comprising mutations M252Y, S245T, and T256E. In some embodiments, the IgG Fc domain variant has similar binding affinity to human FcRn at an acidic pH as an IgG Fc domain comprising mutations M428L and N434S. In some embodiments, the binding affinity of Fc domain variant described herein to a human FcRn at an acidic pH is at least 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 20-, 30-, 40-, 50-, 60- , 70-, 80-, 90, or 100-fold higher than the binding affinity of the YTE Fc domain variant to a human FcRn. In some embodiments, the binding affinity of Fc domain variant described herein to a human FcRn at an acidic pH is at least 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 20-, 30-, 40-, 50- , 60-, 70-, 80-, 90, or 100-fold higher than the binding affinity of the YTE Fc domain variant to a human FcRn. In some embodiments, an Fc domain variant has reduced binding affinity to an FcRn at physiological conditions. In some embodiments, physiological conditions comprise a pH of about 7 to about 7.5. In some embodiments, reduced binding to FcRn at physiological conditions is relative to a human wild-type Fc domain or a human Fc domain not comprising the amino acid substitutions of the Fc domain variant described herein. In some embodiments, reduced binding affinity to human FcRn is relative to a wild-type human IgG Fc domain or a human IgG Fc domain without the amino acid substitutions of the IgG Fc domain variant. In some embodiments, reduced binding affinity to human FcRn at physiological conditions is relative to the YTE Fc domain variant. In some embodiments, reduced binding affinity to human FcRn at physiological conditions is relative to the LS Fc domain variant. In some embodiments, the IgG Fc domain variant has similar binding affinity to human FcRn at Attorney Docket: 064802-505001WO physiological conditions as the YTE Fc domain variant. In some embodiments, the IgG Fc domain variant has similar binding affinity at physiological conditions to human FcRn as the LS Fc domain variant. In some embodiments, the binding affinity of Fc domain variant described herein to a human FcRn at physiological conditions is at least 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 20-, 30-, 40-, 50-, 60-, 70-, 80-, 90, or 100-fold lower than the binding affinity of the YTE Fc domain variant to a human FcRn. In some embodiments, the binding affinity of Fc domain variant described herein to a human FcRn at physiological conditions is at least 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 20-, 30-, 40-, 50-, 60-, 70-, 80-, 90, or 100-fold lower than the binding affinity of the LS Fc domain variant to a human FcRn. In some embodiments, an Fc domain variant disclosed herein may comprise a mutation (e.g., amino acid substitution) at one or more of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. For example, the Fc domain variant may comprise mutations at two or more of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at three or more of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at four or more of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at five or more of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at six or more of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at seven or more of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at eight or more of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. Alternatively, the Fc domain variant may comprise mutations at no more than eight of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at no more than seven of the following amino acid residues: L234, M252, T256, Attorney Docket: 064802-505001WO V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at no more than six of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at no more than five of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at no more than four of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at no more than three of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some examples, the Fc domain variant may comprise mutations at no more than two of the following amino acid residues: L234, M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, N389, M428, and N434. In some embodiments, the Fc domain variant may comprise a combination of mutations of: (i) an amino acid residue substitution at position M428, at position N434, or at positions M428 and N434; and (ii) an amino acid residue substitution at one or more of positions M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, and N389. In some examples, the Fc domain variant may comprise a combination of mutations of: (i) an amino acid residue substitution at position M428, at position N434, or at positions M428 and N434; and (ii) an amino acid residue substitution at one or more of positions V259, E269, L309, N361, and N389. Specific examples of such Fc domain variants are provided herein, each of which is within the scope of the present disclosure. In some embodiments, the mutation is an amino acid substitution. In some embodiments, an amino acid substitution at residue M252 can be I, L, or Y, or a conservative substitution thereof. See disclosures above for conservative substitutions of amino acid residues. In some examples, an Fc domain variant disclosed herein comprises the M252I substitution. In some examples, an Fc domain variant disclosed herein comprises the M252L substitution. In some examples, an Fc domain variant disclosed herein comprises the M252Y substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of I, L, or Y at the M252 position. In some embodiments, an amino acid substitution at residue T256 can be E or N, or a conservative substitution thereof. In some examples, an Fc domain variant disclosed herein comprises the T256E substitution. In some examples, an Fc domain variant disclosed herein Attorney Docket: 064802-505001WO comprises the T256N substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of E or N at the T256 position. In some embodiments, an amino acid substitution at residue V259 can be I or T, or a conservative substitution thereof. In some examples, an Fc domain variant disclosed herein comprises the V259I substitution. In some examples, an Fc domain variant disclosed herein comprises the V259T substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of I or T at the T259 position. In some embodiments, an amino acid substitution at residue E269 can be D or G, or a conservative substitution thereof. In some examples, an Fc domain variant disclosed herein comprises the E269D substitution. In some examples, an Fc domain variant disclosed herein comprises the E269G substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of D or G at the E269 position. In some embodiments, an amino acid substitution at residue L309 can be G, K, P, R, or S, or a conservative substitution thereof. In some examples, an Fc domain variant disclosed herein comprises the L309G substitution. In some examples, an Fc domain variant disclosed herein comprises the L309K substitution. In some examples, an Fc domain variant disclosed herein comprises the L309P substitution. In some examples, an Fc domain variant disclosed herein comprises the L309R substitution. In some examples, an Fc domain variant disclosed herein comprises the L309S substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of G, K, P, R, or S at the L309 position. In some embodiments, an amino acid substitution at residue Q311 can be R. In some examples, an Fc domain variant disclosed herein comprises the Q311R substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of R at the Q311 position. In some embodiments, an amino acid substitution at residue D312 can be R and S. In some examples, an Fc domain variant disclosed herein comprises the D312R substitution. In some examples, an Fc domain variant disclosed herein comprises the D312S substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of R or S at the D312 position. In some embodiments, an amino acid substitution at residue N315 can be D. In some examples, an Fc domain variant disclosed herein comprises the N315D substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of D at the N315 position. In some embodiments, an amino acid substitution at residue T359 can be A. In some Attorney Docket: 064802-505001WO examples, an Fc domain variant disclosed herein comprises the T359A substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of A at the T359 position. In some embodiments, an amino acid substitution at residue N361 can be D or S. In some examples, an Fc domain variant disclosed herein comprises the N361D substitution. In some examples, an Fc domain variant disclosed herein comprises the N361S substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of D or S at the N361 position. In some embodiments, an amino acid substitution at residue N389 can be K, R, or T. In some examples, an Fc domain variant disclosed herein comprises the N389K substitution. In some examples, an Fc domain variant disclosed herein comprises the N389R substitution. In some examples, an Fc domain variant disclosed herein comprises the N389T substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of K, R, or T at the N389 position. In some embodiments, an amino acid substitution at residue M428 can be D, E, or L. In some examples, an Fc domain variant disclosed herein comprises the M428D substitution. In some examples, an Fc domain variant disclosed herein comprises the M428E substitution. In some examples, an Fc domain variant disclosed herein comprises the M428L substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of D, E, or L at the M428 position. In some embodiments, an amino acid substitution at residue N434 can be H, S, T, W, or Y. In some examples, an Fc domain variant disclosed herein comprises the N434H substitution. In some examples, an Fc domain variant disclosed herein comprises the N434S substitution. In some examples, an Fc domain variant disclosed herein comprises the N434T substitution. In some examples, an Fc domain variant disclosed herein comprises the N434W substitution. In some examples, an Fc domain variant disclosed herein comprises the N434Y substitution. In other examples, the Fc domain variant disclosed herein comprises a conservative substitution of H, S, T, W, or Y at the N434 position. In some embodiments, an Fc domain variant as disclosed herein may comprise a mutation selected from the following amino acid residues: M252I, M252Y, T256E, V259I, E269D, L309G, Q311R, D312R, D312S, N315D, T359A, N361D, N389T, M428L, N434S, N434T, N434Y. In some embodiments, the Fc domain variant may comprise at least 2 mutations from the following amino acid residues: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, Attorney Docket: 064802-505001WO N434T, or N434Y. In some embodiments, the Fc domain variant may comprise at least 3 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some embodiments, the Fc domain variant may comprise at least 4 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some embodiments, the Fc domain variant may comprise at least 5 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some embodiments, the Fc domain variant may comprise at least 6 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some embodiments, the Fc domain variant may comprise at least 7 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some embodiments, the Fc domain variant may comprise at least 8 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some embodiments, the Fc domain variant disclosed herein may comprise a combination of no more than 8 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some examples, the Fc domain variant disclosed herein may comprise a combination of no more than 7 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some examples, the Fc domain variant disclosed herein may comprise a combination of no more than 6 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some examples, the Fc domain variant disclosed herein may comprise a combination of no more than 5 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some examples, the Fc domain variant disclosed herein may comprise a combination of no more than 4 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, Attorney Docket: 064802-505001WO M428L, and N434S, N434T, or N434Y. In some examples, the Fc domain variant disclosed herein may comprise a combination of no more than 3 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some examples, the Fc domain variant disclosed herein may comprise a combination of no more than 2 mutations selected from the following: M252I or M252Y, T256E, V259I, E269D, L309G, Q311R, D312R or D312S, N315D, T359A, N361D, N389T, M428L, and N434S, N434T, or N434Y. In some embodiments, an Fc domain comprises mutations at amino acid residues M252, D312, M428, and N434. In some embodiments, an Fc domain comprises mutations M252I, D312R, M428L, and N343T. In some embodiments, at Fc domain comprises mutations at amino acid residues Q311, M428, and N434. In some embodiments, an Fc domain comprises mutations Q311R, M428L, and N434S. In some embodiments, an Fc domain comprises mutations at amino acid residues D312, M428, and N434. In some embodiments, an Fc domain comprises mutations D312S, M428L, and N434S. In some embodiments, an Fc domain comprises mutations at amino acid residues V259, M428, and N434. In some embodiments, an Fc domain comprises mutations V259I, M428L, and N434S. In some embodiments, an Fc domain comprises mutations at amino acid residues L309, M428, and N434. In some embodiments, an Fc domain comprises mutations L309G, M428L, and N434S. In some embodiments, an Fc domain comprises mutations L309G, M428L, and N434T. In some embodiments, an Fc domain comprises mutations at amino acid residues T256, V259I, M428, and N434. In some embodiments, an Fc domain comprises mutations T256E, V259I, M428L, andN434S. In some embodiments, an Fc domain comprises mutations at amino acid residues T256, V259, Q311, M428, and N434. In some embodiments, an Fc domain comprises t mutations T256E, V259I, Q311R, M428L, and N434S. In some embodiments, an Fc domain comprises mutations at amino acid residues M252, Q311, and N434. In some embodiments, and Fc domain comprises mutations M252Y, Q311R, andN434Y. In some embodiments, an Fc domain comprises mutations at amino acid residues L309, N361, and N434. In some embodiments, an Fc domain comprises mutations L309G, N361D, and N434Y. In some embodiments, an Fc domain comprises mutations at amino acid residues T359, N389, M428, and N434. In some embodiments, an Fc domain comprises mutations T359A, M428L, andN434S. In some embodiments, an Fc domain comprises mutations at amino acid residues N361, N389, M428, and N434. In some embodiments, an Fc domain comprises mutations N361D, N389T, M428L, and N434S. In some embodiments, an Fc domain comprises mutations at amino acid residues T359, N389, M428, and N434. In some embodiments, an Fc Attorney Docket: 064802-505001WO domain comprises mutations T359A, N389T, M428L, andN434S. In some embodiments, an Fc domain comprises mutations at amino acid residues N361, M428, and N434. In some embodiments, an Fc domain comprises mutations N361D, M428L, andN434S. In some embodiments, an Fc domain comprises mutations at amino acid residues N315, N389, M428, and N434. In some embodiments, an Fc domain comprises mutations N315D, N318T, M428L, andN434S. In some embodiments, an Fc domain comprises mutations at amino acid residues E269, N389, M428, and N434. In some embodiments, an Fc domain comprises mutations E269E, N389T, M428L, andN434S. In some embodiments, an Fc domain comprises mutations at amino acid residues Q311, N315, N389, and M428. In some embodiments, an Fc domain comprises mutations Q311R, N315D, N389T, and M428L. In some embodiments, the Fc domain variant (e.g., IgG1 or IgG4) may comprise amino acid substitutions at a combination of positions (i) M428 and / or N434; and (ii) V259, E269, L309, and / or N361. In some examples, the Fc domain variant (e.g., IgG1 or IgG4) may comprise amino acid substitutions at positions V259, M428, and N434, e.g., any amino acid residue substitutions at the corresponding positions as disclosed herein. Specific examples include V259I, M428L, and N434S. In other examples, the Fc domain variant (e.g., IgG1 or IgG4) may comprise amino acid substitutions at positions L309, N361, and N434, e.g., any amino acid residue substitutions at the corresponding positions as disclosed herein. Specific examples include L309G, N361D, and N434Y, In yet other examples, the Fc domain variant (e.g., IgG1 or IgG4) may comprise amino acid substitutions at positions E269, N389, M428, and N434, e.g., any amino acid residue substitutions at the corresponding positions as disclosed herein. Specific examples include E269D, N389T, M428L, and N434S, In some embodiments, an Fc domain does not comprise additional amino acid substitutions that impact FcRn binding. In some embodiments, an Fc domain does not comprise amino acid substitutions at H310 or H429. In some embodiments, an Fc domain does not comprise an amino acid substitution at H310. In some embodiments, an Fc domain does not comprise an amino acid substitution at H429. In some embodiments, an Fc domain does not comprise amino acid substitutions at H310 and H429. Alternatively or in addition, the Fc domain variant includes one or more of the following residues: K286, N288, H310, L314, E345, H429, E430, and / or K439 (as in the wild-type counterpart). In some embodiments, the Fc domain variant can be an IgG1 Fc variant comprising any of the amino acid residue substitutions disclosed herein. In some examples, the IgG1 Fc variant may comprise an amino acid sequence at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to an amino acid sequence selected from SEQ ID Nos: 8-24 (e.g., SEQ ID NO: 11, 17, Attorney Docket: 064802-505001WO or 23). In some instances, the Fc domain variant comprises an amino acid sequence having at least 80% identity to an amino acid sequence selected from SEQ ID Nos: 8-24. In some instances, an Fc domain variant comprises an amino acid sequence having at least 90% identity to an amino acid sequence selected from SEQ ID Nos: 8-24. In some instances, an Fc domain variant comprises an amino acid sequence having at least 95% identity to an amino acid sequence selected from SEQ ID Nos: 8-24. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 8. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 8. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 8. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 8. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 8. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 9. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 9. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 9. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 9. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 9. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 10. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 10. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 10. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 10. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 10. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 11. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 11. In some embodiments, an Fc domain variant comprises an amino acid sequence Attorney Docket: 064802-505001WO having at least 80% identity to SEQ ID NO: 11. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 11. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 11. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 12. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 12. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 12. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 12. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 12. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 13. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 13. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 13. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 13. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 13. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 14. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 14. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 14. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 14. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 14. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 15. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 15. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 15. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 15. In some Attorney Docket: 064802-505001WO embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 15. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 16. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 16. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 16. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO:16. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 16. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 17. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 17. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 17. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 17. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 17. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 18. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 18. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 18. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 18. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 18. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 19. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 19. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 19. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 19. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 19. Attorney Docket: 064802-505001WO In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 20. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 20. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 20. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 20. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 20. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 21. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 21. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 21. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 21. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 21. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 22. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 22. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 22. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 22. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 22. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 23. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 23. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 23. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 23. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 23. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 24. In some embodiments, an Fc domain variant comprises an amino acid Attorney Docket: 064802-505001WO sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 24. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 24. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 24. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 24. In some specific examples, the Fc domain variant comprises the amino acid sequence of SEQ ID NO: 11. In some specific examples, the Fc domain variant comprises the amino acid sequence of SEQ ID NO: 17. In some specific examples, the Fc domain variant comprises the amino acid sequence of SEQ ID NO: 23. In some embodiments, the Fc domain variant is an IgG4 Fc variant. Such an Fc domain variant may comprise an amino acid sequence selected from SEQ ID NOs: 25-41. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to an amino acid sequence selected from SEQ ID Nos: 25-41. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to an amino acid sequence selected from SEQ ID Nos: 25-41. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to an amino acid sequence selected from SEQ ID Nos: 25-41. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to an amino acid sequence selected from SEQ ID Nos: 25-41. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 25. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 25. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 25. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 25. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 25. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 26. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 26. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 26. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 26. In some Attorney Docket: 064802-505001WO embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 26. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 27. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 27. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 27. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 27. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 27. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 28. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 28. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 28. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 28. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 28. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 29. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 29. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 29. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 29. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 29. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 30. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 30. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 30. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 30. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 30. Attorney Docket: 064802-505001WO In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 31. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 31. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 31. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 31. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 31. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 32. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 32. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 32. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 32. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 32. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 33. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 33. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 33. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 33. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 33. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 34. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 34. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 34. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 34. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 34. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 35. In some embodiments, an Fc domain variant comprises an amino acid Attorney Docket: 064802-505001WO sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 35. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 35. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 35. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 35. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 36. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 36. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 36. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 36. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 36. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 37. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 37. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 37. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 37. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 37. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 38. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 38. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 38. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 38. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 38. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 39. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 39. In some embodiments, an Fc domain variant comprises an amino acid sequence Attorney Docket: 064802-505001WO having at least 80% identity to SEQ ID NO: 39. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 39. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 39. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 40. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 40. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 40. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 40. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 40. In some embodiments, an Fc domain variant comprises the amino acid sequence of SEQ ID NO: 41. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 70%, 80%, 90%, 95%, 96%, 97%, 98%, or 99% identity to SEQ ID NO: 41. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 80% identity to SEQ ID NO: 41. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 90% identity to SEQ ID NO: 41. In some embodiments, an Fc domain variant comprises an amino acid sequence having at least 95% identity to SEQ ID NO: 41. In some specific examples, the Fc domain variant comprises the amino acid sequence of SEQ ID NO: 28. In some specific examples, the Fc domain variant comprises the amino acid sequence of SEQ ID NO: 34. In some specific examples, the Fc domain variant comprises the amino acid sequence of SEQ ID NO: 40. The “percent identity” of two amino acid sequences is determined using the algorithm of Karlin and Altschul Proc. Natl. Acad. Sci. USA 87:2264-68, 1990, modified as in Karlin and Altschul Proc. Natl. Acad. Sci. USA 90:5873-77, 1993. Such an algorithm is incorporated into the NBLAST and XBLAST programs (version 2.0) of Altschul, et al. J. Mol. Biol.215:403-10, 1990. BLAST protein searches can be performed with the XBLAST program, score=50, wordlength=3 to obtain amino acid sequences homologous to the protein molecules of the invention. Where gaps exist between two sequences, Gapped BLAST can be utilized as described in Altschul et al., Nucleic Acids Res.25(17):3389-3402, 1997. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. Attorney Docket: 064802-505001WO B. Fc Domain Variants with Altered Effector Function In some embodiments, an Fc domain variant described herein may comprise at least one amino acid substitution at an amino acid residue not involved in human FcRn binding and / or does not alter the binding affinity to human FcRn at an acidic pH. For example, the Fc domain variant may comprise at least one amino acid substitution that alters Fc effector function. Effector function is mediated by binding of an Fc domain to an Fc receptor. Fc- gamma receptors (FcγR) bind got IgG class antibodies, Fc-alpha receptors (FcαR) bind to IgA class antibodies, and Fc-epsilon receptors (FCεr) bind to IgE class antibodies. The FcγRs belong to a family that includes several members, e.g., FcγRI, FcγRIIa, FcγRIIb, FcγRIIIa, and FcγRIIIb. In some embodiments, an Fc domain variant described herein exhibits enhanced effector functions. In some embodiments, an Fc domain variant described herein exhibits reduced effector functions. In some embodiments, an Fc domain variant comprises at least one amino acid substitution that alters binding to an FcγR at any of the following residues: L234 or L235. In some embodiments, an Fc domain variant comprises no more than one amino acid substitution that alters binding to an FcγR at any of the following residues: L234 or L235. In some embodiments, an Fc domain variant comprises at least two amino acid substitutions that alter binding to an FcγR at any of the following residues: L234 or L235. In some embodiments, an Fc domain variant comprises no more than two amino acid substitutions that alter binding to an FcγR at any of the following residues: L234 or L235. In some embodiments, an Fc domain variant comprises at least one of the following mutations: L234A or L235A. In some embodiments, an Fc domain variant comprises the mutations L234A and L235A. In some embodiments, an Fc domain variant comprises a mutation at D265. In some embodiments, an Fc domain variant comprises the mutation D265S. In some embodiments, an Fc domain variant described herein exhibits reduced C1q binding. C1q binding assays may also be carried out to confirm that the polypeptide is able or unable to bind C1q and, hence, contains or lacks CDC activity (Idusogie et al., J. Immunol. 164: 4178-84 (2000)). To assess complement activation, a CDC assay may be performed (see, e.g., Gazzano-Santoro et al., J. Immunol. Methods 202:163 (1996); Cragg, M. S. et al., Blood 101:1045-52 (2003); and Cragg et al., Blood 103:2738-43 (2004)). In some embodiments, one or more amino acids are substituted with a different amino acid residue such that the antibody has altered Clq binding and / or reduced or abolished Attorney Docket: 064802-505001WO complement dependent cytotoxicity (CDC). This approach is described in further detail in U.S. Pat. No.6,194,551 by Idusogie et al. In some embodiments, the Fc variant comprises one or more amino acid substitutions to alter the ability of the antibody to fix complement. This approach is described further in PCT Publication WO 94 / 29351 by Bodmer et al. In some embodiments, an Fc domain variant provided herein comprises a mutation at amino acid position 329, 331, and / or 322 (using Kabat numbering), and exhibits reduced Clq binding and / or CDC activity. In some embodiments, Clq binding activity and / or CDC activity of an antibody is reduced by mutating amino acid residue 318, 320, and / or 322 (using Kabat numbering) of a heavy chain; replacing residue 297 (Asn) may result in removal of lytic activity of an antibody. II. Proteins Comprising an Fc Domain Variant In some aspects, the disclosure provides a protein such as a polypeptide comprising an Fc domain variant as described herein. As used herein, the terms “protein", “peptide” and “polypeptide" are used to designate a series of amino acid residues connected to each other by peptide bonds between the alpha- amino and carboxy groups of adjacent residues. The terms "protein", “peptide” and “polypeptide” refer to a polymer of amino acids, including modified amino acids (e.g., phosphorylated, glycated, glycosylated, etc.) and amino acid analogs, regardless of its size or function. “Protein” and “polypeptide” are often used in reference to relatively large polypeptides, whereas the term “peptide” is often used in reference to small polypeptides, but usage of these terms in the art overlaps. In some instances, a protein can be a multi-chain molecule. The terms “protein”, “peptide” and “polypeptide” are used herein when referring to a gene product and fragments thereof. The term “fusion protein” as used herein refers to a polypeptide that comprises an amino acid sequence of an antibody or fragment thereof and an amino acid sequence of a heterologous polypeptide (i.e., an unrelated polypeptide). In some embodiments, a polypeptide comprising the constant region of an immunoglobulin excludes the first constant region immunoglobulin domain and, in some cases, part of the hinge. In some embodiments, the Fc domain variant comprises the last two constant region immunoglobulin domains of IgA, IgD, and IgG, the last three constant region immunoglobulin domains of IgE and IgM, and the flexible hinge N-terminal to these domains. For IgA and IgM, Fc may include the J chain. In some embodiments, the polypeptide is a fusion protein comprising a protein or protein fragment (e.g., a cytokine) and an Fc domain variant described herein. In some Attorney Docket: 064802-505001WO embodiments, the polypeptide is any protein or protein fragment where extension of half-life is sought after. Antibodies with an Fc Domain Variant In some aspects, polypeptide is an antibody or antigen-binding fragment comprising an Fc domain variant described herein. As used herein, the term “antibody” refers to an immunoglobulin (Ig) whether natural or partly or wholly synthetically produced. The term also covers any polypeptide or protein having a binding domain which is, or is homologous to, an antigen-binding domain. The term further includes “antigen-binding fragments” and other interchangeable terms for similar binding fragments such as described below. An antibody includes, but is not to be limited to, any specific binding member, immunoglobulin class and / or isotype (e.g., IgG1, IgG2, IgG3, IgG4, IgM, IgA, IgD, IgE and IgM), and biologically relevant fragment or specific binding member thereof. Thus, an antibody includes, for example, monoclonal antibodies, chimeric antibodies, humanized antibodies, human antibodies, recombinant antibodies, chemically engineered antibodies, deimmunized antibodies, affinity-matured antibodies, multispecific antibodies (for example, bispecific antibodies and polyreactive antibodies), heteroconjugate antibodies, antibody fragments, and combinations thereof (e.g., a monoclonal antibody that is also deimmunized, a humanized antibody that is also deimmunized, etc.). Native antibodies and native immunoglobulins are usually heterotetrametric glycoproteins of about 150,000 Daltons, composed of two identical light (L) chains and two identical heavy (H) chains. Each light chain is typically linked to a heavy chain by one covalent disulfide bond, while the number of disulfide linkages varies among the heavy chains of different immunoglobulin isotypes. Each heavy and light chain also has regularly spaced intrachain disulfide bridges. Each heavy chain has at one end a variable domain (“VH”) followed by a number of constant domains (“CH”). Each light chain has a variable domain at one end (“VL”) and a constant domain (“CL”) at its other end; the constant domain of the light chain is aligned with the first constant domain of the heavy chain, and the light-chain variable domain is aligned with the variable domain of the heavy chain. Particular amino acid residues are believed to form an interface between the light- and heavy-chain variable domains. The antibodies or antigen-binding fragment thereof of the present disclosure can comprise a deletion at an end of a light chain. The antibodies or antigen-binding fragment thereof of the disclosure can comprise a deletion of 3 or more amino acids at an end of the light chain. The antibodies or antigen-binding fragment thereof of the disclosure can comprise a Attorney Docket: 064802-505001WO deletion of 7 or less amino acids at an end of the light chain. The antibodies or antigen-binding fragment thereof of the disclosure can comprise a deletion of 3, 4, 5, 6, or 7 amino acids at an end of the light chain. The antibodies or antigen-binding fragment thereof of the present disclosure can comprise an insertion in a light chain. The antibodies or antigen-binding fragment thereof of the disclosure can comprise an insertion of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, or more amino acids in the light chain. The antibodies or antigen-binding fragment thereof of the disclosure can comprise an insertion of 3 amino acids in the light chain. A “variable region” of an antibody refers to the variable region of the antibody light chain or the variable region of the antibody heavy chain, either alone or in combination. The variable regions of the heavy and light chain each consist of four framework regions (FR) connected by three complementarity-determining regions (CDRs) also known as hypervariable regions. The CDRs in each chain are held together in close proximity by the FRs and, with the CDRs from the other chain, contribute to the formation of the antigen-binding site of antibodies. There are at least two techniques for determining CDRs: (1) an approach based on cross-species sequence variability (e.g., Kabat et al. Sequences of Proteins of Immunological Interest (5thed., 1991, National Institutes of Health, Bethesda Md.)); and (2) an approach based on crystallographic studies of antigen-antibody complexes (Allazikani et al. (1997) J. Molec. Biol.273:927-48). A CDR may refer to CDRs defined by either approach or by a combination of both approaches. A “constant region” of an antibody refers to the constant region of the antibody light chain or the constant region of the antibody heavy chain, either alone or in combination. The constant region does not vary with respect to antigen specificity. As used herein, the term "heavy chain region" includes amino acid sequences derived from the constant domains of an immunoglobulin heavy chain. A polypeptide comprising a heavy chain 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. In an embodiment, an antibody or an antigen-binding fragment thereof may comprise the Fc region of an immunoglobulin heavy chain (e.g., a hinge portion, a CH2 domain, and a CH3 domain). In another embodiment, an antibody or an antigen-binding fragment thereof lacks at least a region of a constant domain (e.g., all or part of a CH2 domain). In certain embodiments, at least one, and preferably all, of the constant domains are derived from a human immunoglobulin heavy chain. For example, in one preferred embodiment, the heavy chain region comprises a fully human hinge domain. In other preferred embodiments, the Attorney Docket: 064802-505001WO heavy chain region comprising a fully human Fc region (e.g., hinge, CH2 and CH3 domain sequences from a human immunoglobulin). In certain embodiments, the constituent constant domains of the heavy chain region are from different immunoglobulin molecules. For example, a heavy chain region of a polypeptide may comprise a domain derived from an IgG1 molecule, and a hinge region derived from an IgG3 or IgG4 molecule. In other embodiments, the constant domains are chimeric domains comprising regions of different immunoglobulin molecules. For example, a hinge may comprise a first region from an IgG1 molecule and a second region from an IgG3 or IgG4 molecule. As set forth above, it will be understood by one of ordinary skill in the art that the constant domains of the heavy chain region may be modified such that they vary in amino acid sequence from the naturally occurring (wild type) immunoglobulin molecule. That is, the polypeptides of the disclosure disclosed herein may comprise alterations or modifications to one or more of the heavy chain constant domains (CH1, hinge, CH2 or CH3) and / or to the light chain constant domain (CL). Exemplary modifications include additions, deletions, or substitutions of one or more amino acids in one or more domains. The antibodies or antigen-binding fragment thereof of the present disclosure can comprise a CDR3 region that is a length of at least about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 amino acids in length. The antibodies or antigen- binding fragment thereof of the present disclosure can comprise a CDR3 region that is at least about 18 amino acids in length. As used herein, the term "hinge region" includes the region 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.1998161:4083). As used herein, the term "Fv" is the minimum antibody fragment that contains a complete antigen-recognition and -binding site. This fragment consists of a dimer of one heavy- and one light-chain variable region domain in tight, non-covalent association. “Heavy chain variable region” or “VH” with regard to an antibody refers to the fragment of the heavy chain that contains three CDRs interposed between flanking stretches known as framework regions, these framework regions are generally more highly conserved than the CDRs and form a scaffold to support the CDRs. Six hypervariable loops (three loops each from the H and L chain) contribute the amino acid residues for antigen-binding and confer antigen-binding specificity to the antibody. However, even a single variable domain (or half of an Fv comprising only three CDRs specific Attorney Docket: 064802-505001WO for an antigen) has the ability to recognize and bind antigen, although at a lower affinity than the entire binding site. "Framework" or FR residues are those variable domain residues other than the hypervariable region residues. It is understood in the art that an antibody is a glycoprotein having at least two heavy (H) chains and two light (L) chains interconnected by disulfide bonds, or an antigen-binding portion thereof. A heavy chain is comprised of a heavy chain variable region (VH) and a heavy chain constant region (CH1, CH2 and CH3). A light chain is comprised of a light chain variable region (VL) and a light chain constant region (CL). The variable regions of both the heavy and light chains comprise framework regions (FRs or FWRs) and hypervariable regions (HVRs). The HVRs are the amino acid residues of an antibody that are responsible for antigen binding. The hypervariable region generally comprises amino acid residues from a complementarity determining region (CDR), which have the highest sequence variability and / or involved in antigen recognition. With the exception of CDR1 in VH, CDRs generally comprise the amino acid residues that form the hypervariable loops. CDRs also comprise “specificity determining residues,” or “SDRs,” which are residues that contact antigen. SDRs are contained within regions of the CDRs called abbreviated-CDRs, or a-CDRs. Exemplary a-CDRs (a-CDR-L1, a- CDR-L2, a-CDR-L3, a-CDR-H1, a-CDR-H2, and a-CDR-H3) occur at amino acid residues 31- 34 of L1, 50-55 of L2, 89-96 of L3, 31-35B of H1, 50-58 of H2, and 95-102 of H3. (See, e.g., Fransson, Front. Biosci.13:1619-33 (2008).) Unless otherwise indicated, HVR residues and other residues in the variable domain (e.g., FR residues) are numbered herein according to Kabat et al., supra. A variable region is the domain of an antibody heavy or light chain that is involved in binding the antibody to antigen. (See, e.g., Kindt et al. Kuby Immunology, 6th ed., W.H. Freeman and Co., p.91 (2007)). A single VHor VLdomain may be sufficient to confer antigen-binding specificity. Furthermore, antibodies that bind a particular antigen may be isolated using a VHor VLdomain from an antibody that binds the antigen to screen a library of complementary VLor VHdomains, respectively. (See, e.g., Portolano et al., J. Immunol.150 :880-87 (1993); Clarkson et al., Nature 352 :624-28 (1991)). The four FWR regions are typically more conserved while CDR regions (CDR1, CDR2 and CDR3) represent hypervariable regions and are arranged from NH2 terminus to the COOH terminus as follows: FWR1, CDR1, FWR2, CDR2, FWR3, CDR3, and FWR4. The variable regions of the heavy and light chains contain a binding domain that interacts with an antigen while, depending on the isotype, the constant region(s) may mediate the binding of the immunoglobulin to host tissues or factors. An antibody also Attorney Docket: 064802-505001WO includes chimeric antibodies, humanized antibodies, and recombinant antibodies, human antibodies generated from a transgenic non-human animal, as well as antibodies selected from libraries using enrichment technologies available to the artisan. The term “antibody heavy chain,” refers to the larger of the two types of polypeptide chains present in antibody molecules in their naturally occurring conformations, and which normally determines the class to which the antibody belongs. The term “antibody light chain,” refers to the smaller of the two types of polypeptide chains present in antibody molecules in their naturally occurring conformations. Kappa (“κ”) and lambda (“λ”) light chains refer to the two major antibody light chain isotypes. An antibody or antigen-binding fragment thereof “specifically binds” or “preferentially binds” to a target antigen if it binds with greater affinity and / or avidity than it binds to epitopes on unrelated polypeptides. The specificity of an antibody or antigen-binding fragment or portion thereof can be determined based on affinity and / or avidity. Methods to determine such specific binding are also well known in art. The affinity, represented by the equilibrium constant for the dissociation (KD) of an antigen with an antigen-binding protein, is a measure for the binding strength between an antigenic determinant and an antigen-binding site on the antigen-binding protein: the lesser the value of the KD, the stronger the binding strength between an antigenic determinant and the antigen-binding molecule. Alternatively, the affinity can also be expressed as the affinity constant (KA), which is 1 / KD). As will be clear to the skilled person, affinity can be determined in a manner known per se, depending on the specific antigen of interest. Accordingly, an antibody or antigen-binding fragment thereof as defined herein is said to be "specific for" a first target or antigen compared to a second target or antigen when it binds to the first antigen with an affinity (as described above, and suitably expressed, for example as a KDvalue) that is at least 50 times, such as at least 100 times, and preferably at least 1000 times, and up to 10,000 times or more better than the affinity with which said amino acid sequence or polypeptide binds to another target or polypeptide. Preferably, when an antibody or antigen- binding fragment thereof is "specific for" a target or antigen, compared to another target or antigen, it can bind the target or antigen, but does not bind the other target or antigen. However, as understood by one of ordinary skill in the art, in some embodiments, where a binding site on a target is shared or partially shared by multiple, different ligands, an antibody or antigen-binding fragment thereof can specifically bind to a target and have the functional effect of, for example, inhibiting / preventing disease or inflammation. In some embodiments, an antibody provided herein has a dissociation constant (KD) of Attorney Docket: 064802-505001WO about 1 μM, 100 nM, 10 nM, 5 nM, 2 nM, 1 nM, 0.5 nM, 0.1 nM, 0.05 nM, 0.01 nM, or 0.001 nM or less (e.g., 10−8M or less, e.g., from 10−8M to 10−13M, e.g., from 10−9M to 10−13M). Another aspect of the disclosure provides for an antibody or antigen-binding fragment thereof with an increased affinity for its target, for example, an affinity matured antibody. An affinity matured antibody is an antibody with one or more alterations in one or more hypervariable regions (HVRs), compared to a parent antibody which does not possess such alterations, such alterations resulting in an improvement in the affinity of the antibody for antigen. These antibodies can bind to antigen with a KD of about 5×10−9M, 2×10−9M, 1×10−9M, 5×10−10M, 2×10−9M, 1×10−10M, 5×10−11M, 1×10−11M, 5×10−12M, 1×10−12M, or less. In some embodiments, the present disclosure provides an antibody or antigen-binding fragment thereof which has an increased affinity of at least 1.5-fold, 2-fold, 2.5-fold, 3-fold, 4-fold, 5 fold, 10 fold, 20 fold or greater as compared to a germline antibody containing the heavy chain sequence and light chain sequence, or both. III. Generating Fc Domain Variants and Polypeptides In some aspects, the disclosure provides methods for making Fc domain variants and proteins / polypeptides described herein. In some embodiments, the Fc domain variants provided herein or a protein / polypeptide comprising such may be produced by the conventional recombinant technology via introduction of encoding nucleic acids into suitable host cells for producing the Fc domain variant or the protein / polypeptide comprising such. A. Nucleic Acids In some aspects, the disclosure provides nucleic acids encoding an Fc domain variant and / or polypeptide comprising an Fc domain variant as described herein. Nucleic acids can be obtained using standard molecular biology techniques. For antibodies expressed by hybridomas (e.g., hybridomas prepared from transgenic mice carrying human immunoglobulin genes as described further below), cDNAs encoding the light and heavy chains of the antibody made by the hybridoma can be obtained by standard PCR amplification or cDNA cloning techniques. For antibodies obtained from an immunoglobulin gene library (e.g., using phage display techniques), nucleic acid encoding the antibody can be recovered from the library. Once DNA fragments encoding VH and VL segments are obtained, these DNA fragments can be further manipulated by standard recombinant DNA techniques, for example to convert the variable region genes to full-length antibody chain genes, to Fab fragment genes or to a scFv gene. In these manipulations, a VL- or VH-encoding DNA fragment is operatively linked to another Attorney Docket: 064802-505001WO DNA fragment encoding another protein, such as an antibody constant region or a flexible linker. The term “operatively linked,” as used in this context, is intended to mean that the two DNA fragments are joined such that the amino acid sequences encoded by the two DNA fragments remain in-frame. The isolated DNA encoding the VH region can be converted to a full-length heavy chain gene by operatively linking the VH-encoding DNA to another DNA molecule encoding heavy chain constant regions (CH1, CH2 and CH3). The sequences of human heavy chain constant region genes are known in the art (see e.g., Kabat, E. A., et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No.91-3242) and DNA fragments encompassing these regions can be obtained by standard PCR amplification. The heavy chain constant region can be an IgG1, IgG2, IgG3, IgG4, IgA, IgE, IgM or IgD constant region, but most preferably is an IgG1 or IgG4 constant region. For a Fab fragment heavy chain gene, the VH-encoding DNA can be operatively linked to another DNA molecule encoding only the heavy chain CH1 constant region. The isolated DNA encoding the VL region can be converted to a full-length light chain gene (as well as a Fab light chain gene) by operatively linking the VL-encoding DNA to another DNA molecule encoding the light chain constant region, CL. The sequences of human light chain constant region genes are known in the art (see e.g., Kabat, E. A., et al. (1991) and DNA fragments encompassing these regions can be obtained by standard PCR amplification. The light chain constant region can be a kappa or lambda constant region, but most preferably is a kappa constant region. To create a scFv gene, the VH- and VL-encoding DNA fragments are operatively linked to another fragment encoding a flexible linker, e.g., encoding the amino acid sequence (Gly-4-Ser)3, such that the VH and VL sequences can be expressed as a contiguous single-chain protein, with the VL and VH regions joined by the flexible linker (see e.g., Bird et al. (1988) Science 242:423-26; Huston et al. (1988) Proc. Natl. Acad. Sci. USA 85:5879-83; McCafferty et al., (1990) Nature 348:552-54). Nucleic acids comprising a nucleotide sequence substantially different from those described above but which, due to the degeneracy of the genetic code, still encode at least antibody or antigen binding fragment thereof as described herein and / or as it is known in the art are also contemplated. Of course, the genetic code is well known in the art. Therefore, it would be routine for one skilled in the art to generate such degenerate nucleic acid variants encoding specific antibodies of the present disclosure. See for example, Ausubel et al., Supra, and such nucleic acid variants are included in the present disclosure. Starting from in silico reconstructed nucleic acid sequences, polypeptides, including Fc Attorney Docket: 064802-505001WO domain variants, may be synthesized, and purified using conventional procedures. In some embodiments, an artificial gene construct encoding a polypeptide thereof is synthesized (see, e.g., Khorana, H.G. et al., J. Mol. Biol.72(2):209-17 (1972); Itakura, K. et al., Science 198(4321):1056-63 (1977); and Edge, M.D. et al. Nature 292(5825):756-62 (1981)). The DNA template for the synthetic gene construct may then be cloned into a suitable expression vector and operably linked to a regulatory control sequence, transformed into an appropriate host for amplification, and the resulting amplified quantities of expression vector purified and transfected into an appropriate host for transient expression of the final resulting polypeptide (see, e.g., Vazquez-Lombardi, R. et al., Nat. Protoc.13(1):99-117 (2018)). Using the information provided herein, for example, the reconstructed nucleic acid and amino acid sequences of the polypeptides; a nucleic acid encoding the polypeptides thereof can be obtained. Such a nucleic acid can be obtained, for example, using conventional methods disclosed in the art. Nucleic acids of the present disclosure may be in the form of RNA, such as mRNA, hnRNA, tRNA or any other form, or in the form of DNA, including but not limited to, cDNA and genomic DNA obtained by cloning or produced synthetically, or any combinations thereof. The DNA may be triplex, duplex, or single-stranded, or any combination thereof. Any portion of at least one strand of the DNA or RNA may be the coding strand, also known as the sense strand, or it can be the antisense strand, also known as the antisense strand. “Polynucleotide,” or “nucleic acid as used interchangeably herein, refer to polymers of nucleotides of any length, and include DNA and RNA. The nucleotides can be deoxyribonucleotides, ribonucleotides, modified nucleotides, or bases, and / or their analogs, or any substrate that can be incorporated into a polymer by DNA or RNA polymerase. A nucleic acid can comprise modified nucleotides, such as methylated nucleotides and their analogs. If present, modification to the nucleotide structure may be imparted before or after assembly of the polymer. The sequence of nucleotides may be interrupted by non-nucleotide components. A polynucleotide may be further modified after polymerization, such as by conjugation with a labeling component. Other types of modifications include, for example, “caps”, substitution of one or more of the naturally occurring nucleotides with an analog, internucleotide modifications such as, for example, those with uncharged linkages (e.g., methyl phosphonates, phosphotriesters, phosphoamidates, carbamates, etc.) and with charged linkages (e.g., phosphorothioates, phosphorodithioates, etc.), those containing pendant moieties, such as, for example, proteins (e.g., nucleases, toxins, antibodies, signal peptides, ply-L-lysine, etc.), those with intercalators (e.g., acridine, psoralen, etc.), those containing chelators (e.g., metals, radioactive metals, boron, oxidative metals, etc.), those containing alkylators, those with Attorney Docket: 064802-505001WO modified linkages (e.g., alpha anomeric nucleic acids, etc.), as well as unmodified forms of the polynucleotide(s). Further, any of the hydroxyl groups ordinarily present in the sugars may be replaced, for example, by phosphonate groups, phosphate groups, protected by standard protecting groups, or activated to prepare additional linkages to additional nucleotides, or may be conjugated to solid supports. The 5′ and 3′ terminal OH can be phosphorylated or substituted with amines or organic capping group moieties of from 1 to 20 carbon atoms. Other hydroxyls may also be derivatized to standard protecting groups. Polynucleotides can also contain analogous forms of ribose or deoxyribose sugars that are generally known in the art, including, for example, 2′-O-methyl-, 2′-O-allyl, 2′-fluoro- or 2′-azido-ribose, carbocyclic sugar analogs, α-anomeric sugars, epimeric sugars such as arabinose, xyloses or lyxoses, pyranose sugars, furanose sugars, sedoheptuloses, acyclic analogs and abasic nucleoside analogs such as methyl riboside. One or more phosphodiester linkages may be replaced by alternative linking groups. These alternative linking groups include, but are not limited to, embodiments wherein phosphate is replaced by P(O)S(“thioate”), P(S)S (“dithioate”), “(O)NR2 (“amidate”), P(O)R, P(O)OR′, CO or CH2 (“formacetal”), in which each R or R′ is independently H or substituted or unsubstituted alkyl (1-20 C) optionally containing an ether (—O—) linkage, aryl, alkenyl, cycloalkyl, cycloalkenyl or araldyl. Not all linkages in a polynucleotide need be identical. The preceding description applies to all polynucleotides referred to herein, including isolated nucleic acid, RNA and DNA. In the context of the present disclosure, the following abbreviations for the commonly occurring nucleic acid bases are used. “A” refers to adenosine, “C” refers to cytosine, “G” refers to guanosine, “T” refers to thymidine, and “U” refers to uridine. In some embodiments, the nucleic acid molecule comprises an isolated nucleic acid. The nucleic acids can be present in whole cells, in a cell lysate, or in a partially purified or substantially pure form. A nucleic acid is “isolated” or “rendered substantially pure” when purified away from other cellular components or other contaminants, e.g., other cellular nucleic acids or proteins, by standard techniques, including, but not limited to alkaline / SDS treatment, CsCl banding, column chromatography, agarose gel electrophoresis and others well known in the art. (See, F. Ausubel, et al., ed. (1987) Current Protocols in Molecular Biology, Greene Publishing and Wiley Interscience, New York). A nucleic acid according to at least some embodiments of the disclosure can be, for example, DNA or RNA and may or may not contain intronic sequences. In a preferred embodiment, the nucleic acid is a cDNA molecule. In some embodiments, the nucleic acid is one that encodes for any of the amino acid sequences for the polypeptides in the Sequence Table. In some embodiments, the nucleic acid Attorney Docket: 064802-505001WO sequence is one that is at least 80% identical to a nucleic acid encoding any of the amino acid sequences for the polypeptides in the in the Sequence Table, for example, at least 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% identical. In some embodiments, the nucleic acid is one that hybridizes to any one or more of the nucleic acid sequences provided herein. In some of the embodiments, hybridization is under moderate conditions. In some embodiments, the hybridization is under highly stringent conditions, such as: at least about 6X SSC and 1% SDS at 65ºC, with a first wash for 10 minutes at about 42ºC with about 20% (v / v) formamide in 0.1X SSC, and with a subsequent wash with 0.2 X SSC and 0.1% SDS at 65ºC. Nucleic acids can be constructed using recombinant DNA techniques conventional in the art. In some embodiments, a nucleic acid disclosed herein is placed in an expression vector that is suitable for expression in a selected host cell. Vectors comprising nucleic acids that encode the antibodies or antigen binding fragment herein are provided. Vectors comprising nucleic acids that encode a heavy chain and / or a light chain are also provided. Such vectors include, but are not limited to, DNA vectors, phage vectors, viral vectors, retroviral vectors, etc. In some embodiments, the nucleic acid coding for the light chain and that coding for the heavy chain are isolated separately by the procedures outlined above. In some embodiments, the isolated nucleic acid encoding the light chain and that coding for the heavy chain may be inserted into separate expression plasmids, or together in the same plasmid, so long as each is under suitable promoter and translation control. In some embodiments, the suitable promoter is an inducible promoter. In some embodiments a suitable promoter is a constitutive promoter. In some embodiments, the heavy chain and light chain are expressed as part of a single polypeptide, such as, for example, when the antibody is an scFv. In some embodiments, a first vector comprises a nucleic acid that encodes a heavy chain and a second vector comprises a nucleic acid that encodes a light chain. In some embodiments, the first vector and second vector are transfected into host cells in similar amounts (such as similar molar amounts or similar mass amounts). In some embodiments, a mole- or mass-ratio of between 5:1 and 1:5 of the first vector and the second vector is transfected into host cells. In some embodiments, a mass ratio of between 1:1 and 1:5 for the vector encoding the heavy chain and the vector encoding the light chain is used. In some embodiments, a mass ratio of 1:2 for the vector encoding the heavy chain and the vector encoding the light chain is used. In some embodiments, a vector is selected that is optimized for expression of polypeptides in CHO or CHO-derived cells, or in NSO cells. Exemplary such vectors are described, for example, in Running Deer et al., Biotechnol. Prog (20):880-89 (2004). Attorney Docket: 064802-505001WO B. Artificial Gene Synthesis A variety of standard recombinant DNA techniques may be used for manipulating domains or functional segments within an antibody nucleic acid sequence. Once DNA fragments encoding VH and VL segments are obtained, these DNA fragments can be further manipulated, for example to convert the variable region genes to full-length antibody chain genes, to Fab fragment genes or to a scFv gene. In these manipulations, a VL- or VH-encoding DNA fragment is operatively linked to another DNA fragment encoding another protein, such as an antibody constant region or a flexible linker. The term “operatively linked,” as used in this context, is intended to mean that the two DNA fragments are joined such that the amino acid sequences encoded by the two DNA fragments remain in-frame. The isolated DNA encoding the VHregion can be converted to a full-length heavy chain gene by operatively linking the VH-encoding DNA to another DNA molecule encoding heavy chain constant regions (CH1, CH2 and CH3). The sequences of human heavy chain constant region genes are known in the art (see e.g., Kabat, E. A. et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242) and DNA fragments encompassing these regions can be obtained by standard PCR amplification. The heavy chain constant region can be IgG1, IgG2, IgG3, IgG4, IgA, IgE, IgM or IgD constant region, but most preferably is an IgG1 or IgG4 constant region. For a Fab fragment heavy chain gene, the VH-encoding DNA can be operatively linked to another DNA molecule encoding only the heavy chain CH1 constant region. The isolated DNA encoding the VLregion can be converted to a full-length light chain gene (as well as a Fab light chain gene) by operatively linking the VL-encoding DNA to another DNA molecule encoding the light chain constant region, CL. The sequences of human light chain constant region genes are known in the art (see e.g., Kabat, E. A. et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242) and DNA fragments encompassing these regions can be obtained by standard PCR amplification. The light chain constant region can be a kappa or lambda constant region, but most preferably is a kappa constant region. To create a scFv gene, the VH- and VL-encoding DNA fragments are operatively linked to another fragment encoding a flexible linker, e.g., encoding the amino acid sequence (Gly-Gly- Gly-Gly-Ser)3, such that the VH and VL sequences can be expressed as a contiguous single-chain protein, with the VLand VHregions joined by the flexible linker (see, e.g., Bird et al. (1988) Science 242:423-26; Huston et al. (1988) Proc. Natl. Acad. Sci. USA 85:5879-83; McCafferty et al., (1990) Nature 348:552-54). Attorney Docket: 064802-505001WO C. Selection and Transformation of Host Cells In some aspects, provided herein is a host cell that comprises the isolated nucleic acids described above or a vector comprising said isolated nucleic acids described above. The vector can be a cloning vector or an expression vector. Suitable host cells for cloning or expressing the DNA in the vectors herein are the prokaryote, yeast, or higher eukaryote cells described above. Suitable prokaryotes for this purpose include eubacteria, such as Gram-negative or Gram-positive organisms, for example, Enterobacteriaceae such as Escherichia, e.g., E. coli, Enterobacter, Erwinia, Klebsiella, Proteus, Salmonella, e.g., Salmonella typhimurium, Serratia, e.g., Serratia marcescens, and Shigella, as well as Bacilli such as B. subtilis and B. licheniformis (e.g., B. licheniformis 41 P disclosed in DD 266,710 published Apr.12, 1989), Pseudomonas such as P. aeruginosa, and Streptomyces. One preferred E. coli cloning host is E. coli 294 (ATCC 31,446), although other strains such as E. coli B, E. coli Xl 776 (ATCC 31,537), and E. coli W3110 (ATCC 27,325) are suitable. These examples are illustrative rather than limiting. In addition to prokaryotes, eukaryotic microbes such as filamentous fungi or yeast are suitable cloning or expression hosts for antibody-encoding vectors. Saccharomyces cerevisiae, or common baker's yeast, is the most commonly used among lower eukaryotic host microorganisms. However, a number of other genera, species, and strains are commonly available and useful herein, such as Schizosaccharomyces pombe; Kluyveromyces hosts such as, e.g., K. lactis, K. fragilis (ATCC 12,424), K. bulgaricus (ATCC 16,045), K. wickeramii (ATCC 24,178), K. waltii (ATCC 56,500), K. drosophilarum (ATCC 36,906), K. thermotolerans, and K. marxianus; yarrowia (EP 402,226); Pichia pastors (EP 183,070); Candida; Trichoderma reesia (EP 244,234); Neurospora crassa; Schwanniomyces such as Schwanniomyces occidentalis; and filamentous fungi such as, e.g., Neurospora, Penicillium, Tolypocladium, and Aspergillus hosts such as A. nidulans and A. niger. Suitable host cells for the expression of glycosylated polypeptide are derived from multicellular organisms. Examples of invertebrate cells include plant and insect cells. Numerous baculoviral strains and variants and corresponding permissive insect host cells from hosts such as Spodoptera frugiperda (caterpillar), Aedes aegypti (mosquito), Aedes albopictus (mosquito), Drosophila melanogaster (fruitfly), and Bombyx mori have been identified. A variety of viral strains for transfection are publicly available, e.g., the L-1 variant of Autographa californica NPV and the Bm-5 strain of Bombyx mori NP\7, and such viruses may be used as the virus herein according to the present disclosure, particularly for transfection of Spodoptera frugiperda cells. Attorney Docket: 064802-505001WO Plant cell cultures of cotton, com, potato, soybean, petunia, tomato, tobacco, lemna, and other plant cells can also be utilized as hosts. However, interest has been greatest in vertebrate cells, and propagation of vertebrate cells in culture (tissue culture) has become routine procedure. Examples of useful mammalian host cell lines are Chinese hamster ovary cells, including CHOKl cells (ATCC CCL61), DXB-11, DG-44, and Chinese hamster ovary cells / -DHFR (CHO, Urlaub et al., Proc. Natl. Acad. Sci. USA 77: 4216 (1980)); monkey kidney CVl line transformed by SV40 (COS-7, ATCC CRL 1651); human embryonic kidney line (293 or 293 cells subcloned for growth in suspension culture, [Graham et al., J. Gen Viral. 36: 59 (1977)]; baby hamster kidney cells (BHK, ATCC CCL 10); mouse sertoli cells (TM4, Mather, Biol. Reprod.23: 243-51 (1980)); monkey kidney cells (CVl ATCC CCL 70); African green monkey kidney cells (VER0-76, ATCC CRL-1587); human cervical carcinoma cells (HELA, ATCC CCL 2); canine kidney cells (MDCK, ATCC CCL 34); buffalo rat liver cells (BRL 3A, ATCC CRL 1442); human lung cells (W138, ATCC CCL 75); human liver cells (Hep G2, HB 8065); mouse mammary tumor (MMT 060562, ATCC CCL51); TRI cells (Mather et al., Annals N.Y Acad. Sci.383: 44-68 (1982)); MRC 5 cells; FS4 cells; and a human hepatoma line (Hep G2). Host cells are transformed or transfected with the above-described expression or cloning vectors for polypeptide production and cultured in conventional nutrient media modified as appropriate for inducing promoters, selecting transformants, or amplifying the genes encoding the desired sequences. In addition, novel vectors, and transfected cell lines with multiple copies of transcription units separated by a selective marker are particularly useful for the expression of polypeptides, described herein. For transfection of the expression vectors and production of the polypeptides described herein, the recipient cell line can be a myeloma cell. Myeloma cells can synthesize, assemble, and secrete polypeptides encoded by transfected nucleic acid sequences and possess the mechanism for glycosylation of the polypeptide. For example, in some embodiments, the recipient cell is the recombinant Ig-producing myeloma cell SP2 / 0 (ATCC #CRL 8287). SP2 / 0 cells produce only immunoglobulin encoded by the transfected genes. Myeloma cells can be grown in culture or in the peritoneal cavity of a mouse, where secreted immunoglobulin can be obtained from ascites fluid. Other suitable recipient cells include lymphoid cells such as B lymphocytes of human or non-human origin, hybridoma cells of human or non-human origin, or interspecies hetero-hybridoma cells. An expression vector carrying a polypeptide described herein can be introduced into an appropriate host cell by any of a variety of suitable means, including such biochemical means as transformation, transfection, conjugation, protoplast Attorney Docket: 064802-505001WO fusion, calcium phosphate -precipitation, and application with polycations such as diethylaminoethyl (DEAE) dextran, and such mechanical means as electroporation, direct microinjection, and microprojectile bombardment. Johnston et al., 240 Science 1538 (1988), as known to one of ordinary skill in the art. Yeast provides certain advantages over bacteria to produce immunoglobulin H and L chains. Yeasts carry out post-translational peptide modifications including glycosylation. Several recombinant DNA strategies exist that utilize strong promoter sequences and high copy number plasmids which can be used for production of the desired proteins in yeast. Yeast recognizes leader sequences of cloned mammalian gene products and secretes peptides bearing leader sequences (i.e., pre-peptides). Hitzman et al., 11thIntl. Conf. Yeast, Genetics & Molec. Biol. (Montpelier, France, 1982). Yeast gene expression systems can be routinely evaluated for the levels of production, secretion, and the stability of polypeptides. Any of a series of yeast gene expression systems incorporating promoter and termination elements from the actively expressed genes coding for glycolytic enzymes produced in large quantities when yeasts are grown in media rich in glucose can be utilized. Known glycolytic genes can also provide very efficient transcription control signals. For example, the promoter and terminator signals of the phosphoglycerate kinase (PGK) gene can be utilized. Several approaches can be taken for evaluating optimal expression plasmids for the expression of cloned immunoglobulin cDNAs in yeast. Bacterial strains can also be utilized as hosts to produce the polypeptides described herein, E. coli K12 strains such as E. coli W3110 (ATCC 27325), Bacillus species, enterobacteria such as Salmonella typhimurium or Serratia marcescens, and various Pseudomonas species can be used. Plasmid vectors containing replicon and control sequences which are derived from species compatible with a host cell are used in connection with these bacterial hosts. The vector carries a replication site, as well as specific genes which can provide phenotypic selection in transformed cells. Several approaches can be taken for evaluating the expression plasmids for the production of polypeptides encoded by the cloned cDNAs or CDRs in bacteria (see Glover, 1985; Ausubel, 1987, 1993; Sambrook, 1989; Colligan, 1992-1996). Host mammalian cells can be grown in vitro or in vivo. Mammalian cells provide post- translational modifications to immunoglobulin protein molecules including leader peptide removal, folding and assembly of H and L chains, glycosylation of the antibody molecules, and secretion of functional antibody protein. Mammalian cells which can be useful as hosts to produce antibody proteins, in addition to the cells of lymphoid origin described above, include cells of fibroblast origin, such as Vero (ATCC CRL 81) or CHO-K1 (ATCC CRL 61) cells. Attorney Docket: 064802-505001WO Exemplary eukaryotic cells that can be used to express polypeptides include, but are not limited to, COS cells, including COS 7 cells; 293 cells, including 293-6E cells; CHO cells, including CHO-S and DG44 cells; PER.C6® cells (Crucell); and NSO cells. In some embodiments, a particular eukaryotic host cell is selected based on its ability to make desired post-translational modifications to the variable heavy chains and / or variable light chains. For example, in some embodiments, CHO cells produce polypeptides that have a higher level of sialylation than the same polypeptide produced in 293 cells. In some embodiments, polypeptides are produced in vivo in an animal that has been engineered or transfected with one or more nucleic acid molecules encoding the polypeptides, according to any suitable method. In some embodiments, a polypeptide is produced in a cell-free system. Non-limiting exemplary cell-free systems are described, e.g., in Sitaraman et al., Methods Mol. Biol.498: 229-44 (2009); Spirin, Trends Biotechnol.22: 538-45 (2004); and Endo et al., Biotechnol. Adv. 21: 695-713 (2003). Many vector systems are available for the expression of H and L chain nucleic acid sequence in mammalian cells (see Glover, 1985). Different approaches can be followed to obtain complete H2L2antibodies. As discussed above, it is possible to co-express H and L chains in the same cells to achieve intracellular association and linkage of H and L chains into complete tetrameric H2L2antibodies and / or antigen-binding fragment peptides. The co- expression can occur by using either the same or different plasmids in the same host. Genes for both H and L chains and / or CDR3 regions peptides can be placed into the same plasmid, which is then transfected into cells, thereby selecting directly for cells that express both chains. Alternatively, cells can be transfected first with a plasmid encoding one chain, for example the L chain, followed by transfection of the resulting cell line with an H chain plasmid containing a second selectable marker. Cell lines producing antigen-binding peptide fragments and / or H2L2molecules via either route could be transfected with plasmids encoding additional copies of peptides, H, L, or H plus L chains in conjunction with additional selectable markers to generate cell lines with enhanced properties, such as higher production of assembled H2L2 antibody molecules or enhanced stability of the transfected cell lines. Additionally, plants have emerged as a convenient, safe, and economical alternative main-stream expression systems for polypeptide production, which are based on large scale culture of microbes or animal cells. Polypeptides can be expressed in plant cell culture, or plants grown conventionally. The expression in plants may be systemic, limited to sub-cellular plastids, or limited to seeds (endosperms). Several plant-derived antibodies have reached Attorney Docket: 064802-505001WO advanced stages of development (see, e.g., Biolex, NC). In some aspects, provided herein are methods and systems for the production of a humanized antibody, which is prepared by a process which comprises maintaining a host transformed with a first expression vector which encodes the light chain of the humanized antibody and with a second expression vector which encodes the heavy chain of the humanized antibody under such conditions that each chain is expressed and isolating the humanized antibody formed by assembly of the thus-expressed chains. The first and second expression vectors can be the same vector. Also provided herein are DNA sequences encoding the light chain or the heavy chain of the humanized antibody; an expression vector which incorporates a said DNA sequence; and a host transformed with a said expression vector. Generating a humanized antibody from the sequences and information provided herein can be practiced by those of ordinary skill in the art without undue experimentation. In one approach, there are four general steps employed to humanize a monoclonal antibody. These are: (1) determining the nucleotide and predicted amino acid sequence of the starting antibody light and heavy variable domains;(2) designing the humanized antibody, i.e., deciding which antibody framework region to use during the humanizing process; (3) the actual humanizing methodologies / techniques; and (4) the transfection and expression of the humanized antibody. D. Purification In some aspects, disclosed herein is a purified polypeptide described herein. Once expressed, the polypeptide can be recovered and purified by known techniques, e.g., immunoadsorption or immunoaffinity chromatography, chromatographic methods such as HPLC (high performance liquid chromatography), ammonium sulfate precipitation, gel electrophoresis, or any combination of these. See generally, Scopes, PROTEIN PURIF. (Springer-Verlag, NY, 1982). Substantially pure polypeptide of at least about 90% to 95% homogeneity are advantageous, as are those with 98% to 99% or more homogeneity, particularly for pharmaceutical uses. When using recombinant techniques, the polypeptide can be produced intracellularly, in the periplasmic space, or directly secreted into the medium, including from microbial cultures. If the polypeptide is produced intracellularly, as a first step, the particulate debris, either host cells or lysed fragments, is removed, for example, by centrifugation or ultrafiltration. Better et al. Science 240: 1041-43 (1988); ICSU Short Reports 10: 105 (1990); and Proc. Natl. Acad. Sci. USA 90: 457-61 (1993) describe a procedure for isolating antibodies which are secreted to the periplasmic space of E. coli. (See also, [Carter et al., Bio / Technology Attorney Docket: 064802-505001WO 10: 163-67 (1992)]. The polypeptide composition prepared from microbial, or mammalian cells can be purified using, for example, hydroxyapatite chromatography cation or avian exchange chromatography, and affinity chromatography, with affinity chromatography being the preferred purification technique. The suitability of protein A as an affinity ligand depends on the species and isotype of any immunoglobulin Fc domain that is present in the antibody. Protein A can be used to purify antibodies that are based on human γl, γ2, or γ4 heavy chains (Lindmark et al., J. Immunol. Meth.62: 1-13 (1983)). Protein G is recommended for all mouse isotypes and for human y3 (Guss et al., EMBO J.5: 1567-75 (1986)). The matrix to which the affinity ligand is attached is most often agarose, but other matrices are available. Mechanically stable matrices such as controlled pore glass or poly(styrene divinyl)benzene allow for faster flow rates and shorter processing times than can be achieved with agarose. Where the antibody comprises a CH3 domain, the Bakerbond ABX™ resin (J. T. Baker, Phillipsburg, N.J.) is useful for purification. Other techniques for protein purification such as fractionation on an ion- exchange column, ethanol precipitation, Reverse Phase HPLC, chromatography on silica, chromatography on heparin SEPHAROSE™ chromatography on an anion or cation exchange resin (such as a polyaspartic acid column), chromatofocusing, SDS-PAGE, and ammonium sulfate precipitation are also available depending on the antibody to be recovered. Once purified, partially or to homogeneity as desired, a humanized or composite human antibody can then be used therapeutically or in developing and performing assay procedures, immunofluorescent staining, and the like. See generally, Vols. I & II Immunol. Meth. (Lefkovits & Pernis, eds., Acad. Press, NY, 1979 and 1981). IV. Pharmaceutical Compositions In some aspects, the present disclosure provides a composition comprising a polypeptide comprising an Fc domain variant disclosed herein and / or a nucleic acid encoding the polypeptide. In some embodiments, the polypeptide or nucleic acid encoding the polypeptide is formulated into pharmaceutical compositions, pharmaceutical formulations, or medicaments, for administration, e.g., subcutaneous, intravenous, intradermal, intraperitoneal, oral, intramuscular, intracranial, or other routs of administration. In some embodiments, the polypeptides, or nucleic acids encoding the polypeptides are administered along with any pharmaceutically acceptable carrier, excipient, or diluent, which results in an effective treatment and / or effective prophylaxis in the subject. Thus, in one aspect, the present disclosure provides pharmaceutical compositions comprising one or more polypeptides and / or Attorney Docket: 064802-505001WO nucleic acids encoding the one or more polypeptides in combination with one or more pharmaceutically acceptable carrier, excipient, or diluent. The phrase "pharmaceutically acceptable" refers to those compounds, materials, compositions, and / or dosage forms which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of human beings and animals without excessive toxicity, irritation, allergic response, or other problem or complication, commensurate with a reasonable benefit / risk ratio. The phrase "pharmaceutically acceptable carrier" as used herein means a pharmaceutically acceptable material, composition or vehicle, such as a liquid or solid filler, diluent, excipient, solvent, media, encapsulating material, manufacturing aid (e.g., lubricant, talc magnesium, calcium or zinc stearate, or steric acid), or solvent encapsulating material, involved in maintaining the stability, solubility, or activity of, a polypeptide thereof of the present disclosure. Examples include, but are not limited to, any of a number of standard pharmaceutical carriers such as sterile phosphate buffered saline solutions, bacteriostatic water, and the like. A variety of aqueous carriers may be used, e.g., water, buffered water, 0.4% saline, 0.3% glycine and the like, and may include other proteins for enhanced stability, such as albumin, lipoprotein, globulin, etc., subjected to mild chemical modifications or the like. Each carrier must be "acceptable" in the sense of being compatible with the other ingredients of the formulation and not injurious to the patient. The terms "excipient", "carrier", "pharmaceutically acceptable carrier", or the like are used interchangeably herein. The compositions of the present disclosure may further comprise one or more pharmaceutically acceptable carriers, excipients, and other agents that are incorporated into formulations to provide improved transfer, delivery, tolerance, and the like (herein collectively referred to as “pharmaceutically acceptable carriers or diluents”). A multitude of appropriate formulations can be found in the formulary known to all pharmaceutical chemists: Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, Pa. These formulations include, for example, powders, pastes, ointments, jellies, waxes, oils, lipids, lipid (cationic or anionic) containing vesicles (such as LIPOFECTIN™), DNA conjugates, anhydrous absorption pastes, oil-in-water and water-in-oil emulsions, emulsions carbowax (polyethylene glycols of various molecular weights), semi- solid gels, and semi-solid mixtures containing carbowax. See also Powell et al. “Compendium of excipients for parenteral formulations” PDA, 1998, J. Pharm. Sci. Technol.52:238-311. Acceptable carriers, excipients, or stabilizers are nontoxic to recipients at the dosages and concentrations employed, and include buffers such as phosphate, citrate, and other organic acids; antioxidants including ascorbic acid and methionine; preservatives (such as octadecyl dimethyl benzyl ammonium chloride; hexamethonium chloride; benzalkonium chloride, Attorney Docket: 064802-505001WO benzethonium chloride; phenol, butyl or benzyl alcohol; alkyl parabens such as methyl or propyl paraben; catechol; resorcinol; cyclohexanol; 3-pentanol; and m-cresol); low molecular weight (less than about 10 residues) polypeptides; proteins, such as serum albumin, gelatin, or immunoglobulins; hydrophilic polymers such as polyvinylpyrrolidone; amino acids such as glycine, glutamine, asparagine, histidine, arginine, or lysine; monosaccharides, disaccharides, and other carbohydrates including glucose, mannose, or dextrins; chelating agents such as EDTA; sugars such as sucrose, mannitol, trehalose or sorbitol; salt-forming counter-ions such as sodium; metal complexes (e.g., Zn-protein complexes); and / or non-ionic surfactants such as TWEEN®, PLURONICS® or polyethylene glycol (PEG). Optionally, the formulations comprising the compositions described herein contain a pharmaceutically acceptable salt, typically, e.g., sodium chloride, and preferably at about physiological concentrations. Optionally, the formulations of the disclosure can contain a pharmaceutically acceptable preservative. In some embodiments the preservative concentration ranges from 0.1 to 2.0%, typically v / v. Suitable preservatives include those known in the pharmaceutical arts. Benzyl alcohol, phenol, m-cresol, methylparaben, and propylparaben are examples of preservatives. Optionally, the formulations of the disclosure can include a pharmaceutically acceptable surfactant at a concentration of 0.005 to 0.02%. The compositions described herein can be specially formulated for administration of the polypeptide thereof to a subject in solid, liquid or gel form, including those adapted for the following: (a) parenteral administration, for example, by subcutaneous, intramuscular, intravenous or epidural injection as, for example, a sterile solution or suspension, or sustained- release formulation; (b) topical application, for example, as a cream, ointment, or a controlled- release patch or spray applied to the skin; (c) intravaginally or intrarectally, for example, as a pessary, cream or foam; (d) ocularly; (e) transdermally; (f) transmucosally; or (g) nasally. Additionally, an antibody or antigen binding fragment thereof, or compositions of the present disclosure can be implanted into a patient or injected using a drug delivery system. See, e.g., Urquhart et al., 24 Ann. Rev. Pharmacol. Toxicol.199 (1984); Controlled Release of Pesticides & Pharmaceuticals (Lewis, ed., Plenum Press, New York, 1981); U.S. Patents No.3,773,919, No.3,270,960. In some embodiments, sustained-release preparations can be used. Suitable examples of sustained-release preparations include semipermeable matrices of solid hydrophobic polymers containing an antibody or antigen binding fragment of the present disclosure, in which the matrices are in the form of shaped articles, e.g., films, or microcapsule. Examples of sustained- release matrices include polyesters, hydrogels (for example, poly(2-hydroxyethyl- Attorney Docket: 064802-505001WO methacrylate), or poly(vinylalcohol)), polylactides (U.S. Patent No.3,773,919), copolymers of L-glutamic acid and y ethyl-L-glutamate, non-degradable ethylene-vinyl acetate, degradable lactic acid-glycolic acid copolymers such as the LUPRON DEPOT™ (injectable microspheres composed of lactic acid-glycolic acid copolymer and leuprolide acetate), and poly-D-(-)-3- hydroxybutyric acid. While polymers such as ethylene-vinyl acetate and lactic acid-glycolic acid enable release of molecules for over 100 days, certain hydrogels release proteins for shorter time periods. When encapsulated antibodies remain in the body for a long time, they can denature or aggregate as a result of exposure to moisture at 37°C, resulting in a loss of biological activity and possible changes in immunogenicity. Rational strategies can be devised for stabilization depending on the mechanism involved. For example, if the aggregation mechanism is discovered to be intermolecular S--S bond formation through thio-disulfide interchange, stabilization can be achieved by modifying sulfhydryl residues, lyophilizing from acidic solutions, controlling moisture content, using appropriate additives, and developing specific polymer matrix compositions. In certain situations, the pharmaceutical composition can be delivered in a controlled release system. In some embodiments, a pump may be used (see Langer R. Science 249(4976):1527-1533 (1990); Sefton 1987 CRC Crit. Ref. Biomed. Eng.14:201). In another embodiment, polymeric materials can be used. In yet another embodiment, a controlled release system can be placed in proximity of the composition's target, thus requiring only a fraction of the systemic dose (see, e.g., Goodson, in R.S. Langer and D.L. Wise (eds.), MEDICAL APPLICATIONS OF CONTROLLED RELEASE, vol.2, pp.115–38 (CRC Press, Boca Raton, 1984)). A pharmaceutical composition of the present disclosure can be delivered, e.g., subcutaneously, or intravenously with a standard needle and syringe. In addition, with respect to subcutaneous delivery, a pen delivery device readily has applications in delivering a pharmaceutical composition of the present disclosure. Such a pen delivery device can be reusable or disposable. A reusable pen delivery device generally utilizes a replaceable cartridge that contains a pharmaceutical composition. Once all of the pharmaceutical composition within the cartridge has been administered and the cartridge is empty, the empty cartridge can readily be discarded and replaced with a new cartridge that contains the pharmaceutical composition. The pen delivery device can then be reused. In a disposable pen delivery device, there is no replaceable cartridge. Rather, the disposable pen delivery device comes prefilled with the pharmaceutical composition held in a reservoir within the device. Once the reservoir is emptied of the pharmaceutical composition, the entire device is discarded. Numerous reusable pens and autoinjector delivery devices have applications in the subcutaneous delivery of a Attorney Docket: 064802-505001WO pharmaceutical composition of the present disclosure. Examples include, but certainly are not limited to AUTOPEN™ (Owen Mumford, Inc., Woodstock, UK), DISETRONIC™ pen (Disetronic Medical Systems, Burghdorf, Switzerland), HUMALOG MIX 75 / 25™ pen, HUMALOG™ pen, HUMALIN70130™ pen (Eli Lilly and Co., Indianapolis, Ind.), NOVOPEN™ I, II and III (Novo Nordisk, Copenhagen, Denmark), NOVOPEN JUNIOR™ (Novo Nordisk, Copenhagen, Denmark), BD™ pen (Becton Dickinson, Franklin Lakes, N.J.), OPTIPEN™, OPTIPEN PRO™, OPTIPEN STARLET™, and OPTICLIK™ (Sanofi-Aventis, Frankfurt, Germany), to name only a few. Examples of disposable pen delivery devices having applications in subcutaneous delivery of a pharmaceutical composition include, but certainly are not limited to the SOLOSTAR™ pen (Sanofi-Aventis), the FLEXPEN™ (Novo Nordisk), and the KWIKPEN™ (Eli Lilly). The injectable preparations may include dosage forms for intravenous, subcutaneous, intracutaneous, and intramuscular injections, drip infusions, etc. These injectable preparations may be prepared by methods known. For example, the injectable preparations may be prepared, e.g., by dissolving, suspending or emulsifying the antibody or its salt described above in a sterile aqueous medium or an oily medium conventionally used for injections. As the aqueous medium for injections, there are, for example, physiological saline, an isotonic solution containing glucose and other auxiliary agents, etc., which may be used in combination with an appropriate solubilizing agent such as an alcohol (e.g., ethanol), a polyalcohol (e.g., propylene glycol, polyethylene glycol), a nonionic surfactant [e.g., polysorbate 80, HCO-50 (polyoxymethylene (50 mol) adduct of hydrogenated castor oil)], etc. As the oily medium, there are employed, e.g., sesame oil, soybean oil, etc., which may be used in combination with a solubilizing agent such as benzyl benzoate, benzyl alcohol, etc. The injection thus prepared is preferably filled in an appropriate ampoule. Compositions of the present disclosure can be in the form of, for example, granules, powders, tablets, capsules, syrup, suppositories, injections, emulsions, elixirs, suspensions, or solutions. The amount of the aforesaid polypeptide contained can be about 5 to about 500 mg per dosage form in a unit dose; especially in the form of injection, it is preferred that the aforesaid polypeptide is contained in about 5 to about 100 mg and in about 10 to about 250 mg for the other dosage forms. For oral, buccal, and sublingual administration, powders, suspensions, granules, tablets, pills, capsules, gelcaps, and caplets are acceptable as solid dosage forms. These can be prepared, for example, by mixing one or more compounds of the instant disclosure, or pharmaceutically acceptable salts or tautomers thereof, with at least one additive such as a Attorney Docket: 064802-505001WO starch or other additive. Suitable additives are sucrose, lactose, cellulose sugar, mannitol, maltitol, dextran, starch, agar, alginates, chitins, chitosans, pectins, tragacanth gum, gum arabic, gelatins, collagens, casein, albumin, synthetic or semi-synthetic polymers or glycerides. Optionally, oral dosage forms can contain other ingredients to aid in administration, such as an inactive diluent, or lubricants such as magnesium stearate, or preservatives such as paraben or sorbic acid, or antioxidants such as ascorbic acid, tocopherol or cysteine, a disintegrating agent, binders, thickeners, buffers, sweeteners, flavoring agents, or perfuming agents. Tablets and pills may be further treated with suitable coating materials known in the art. Liquid dosage forms for oral administration may be in the form of pharmaceutically acceptable emulsions, syrups, elixirs, suspensions, and solutions, which may contain an inactive diluent, such as water. Pharmaceutical formulations and medicaments may be prepared as liquid suspensions or solutions using a sterile liquid, such as, but not limited to, an oil, water, an alcohol, and combinations of these. Pharmaceutically suitable surfactants, suspending agents, emulsifying agents, may be added for oral or par- enteral administration. In some embodiments, pharmaceutical compositions can be prepared in a lyophilized form. The lyophilized preparations can comprise a cryoprotectant known in the art. The term “cryoprotectants” as used herein generally includes agents, which provide stability to the protein from freezing-induced stresses. Examples of cryoprotectants include polyols such as, for example, mannitol, and include saccharides such as, for example, sucrose, as well as including surfactants such as, for example, polysorbate, poloxamer or polyethylene glycol, and the like. Cryoprotectants also contribute to the tonicity of the formulations. Pharmaceutically suitable surfactants, suspending agents, emulsifying agents, may be added for oral or par- enteral administration. As noted above, suspensions may include oils. Such oils include, but are not limited to, peanut oil, sesame oil, cottonseed oil, corn oil and olive oil. Suspension preparation may also contain esters of fatty acids such as ethyl oleate, isopropyl myristate, fatty acid glycerides and acetylated fatty acid glycerides. Suspension formulations may include alcohols, such as, but not limited to, ethanol, iso-propyl alcohol, hexadecyl alcohol, glycerol, and propylene glycol. Ethers, such as but not limited to, poly(ethylene glycol), petroleum hydrocarbons such as mineral oil and petrolatum; and water may also be used in suspension formulations. For nasal administration, the pharmaceutical formulations and medicaments may be a spray or aerosol containing an appropriate solvent(s) and optionally other compounds such as, but not limited to, stabilizers, antimicrobial agents, antioxidants, pH modifiers, surfactants, bio-availability modifiers and combinations of these. A propellant for an aerosol formulation Attorney Docket: 064802-505001WO may include compressed air, nitrogen, carbon dioxide, or a hydrocarbon based low boiling solvent. Injectable dosage forms generally include aqueous suspensions or oil suspensions which may be prepared using a suitable dispersant or wetting agent and a suspending agent. Injectable forms may be in solution phase or in the form of a suspension, which is prepared with a solvent or diluent. Acceptable solvents or vehicles include sterilized water, Ringer's solution, or an isotonic aqueous saline solution. Alternatively, sterile oils may be employed as solvents or suspending agents. Preferably, the oil or fatty acid is non-volatile, including natural or synthetic oils, fatty acids, mono-, di-, or triglycerides. For injections, the pharmaceutical formulation and / or medicament may be a powder suitable for reconstitution with an appropriate solution as described above. Examples of these include, but are not limited to, freeze dried, rotary dried or spray dried powders, amorphous powders, granules, precipitates, or particulates. For injection, the formulations may optionally contain stabilizers, pH modifiers, surfactants, bioavailability modifiers and combinations of these. For rectal administration, the pharmaceutical formulations and medicaments may be in the form of a suppository, an ointment, an enema, a tablet, or a cream for release of compound in the intestines, sigmoid flexure and / or rectum. Rectal suppositories are prepared by mixing one or more compounds of the instant disclosure, or pharmaceutically acceptable salts or tautomers of the compound, with acceptable vehicles, for example, cocoa butter or polyethylene glycol, which is present in a solid phase at normal storing temperatures, and present in a liquid phase at those temperatures suitable to release a drug inside the body, such as in the rectum. Oils may also be employed in the preparation of formulations of the soft gelatin type and suppositories. Water, saline, aqueous dextrose, and related sugar solutions, and glycerols may be employed in the preparation of suspension formulations which may also contain suspending agents such as pectins, carbomers, methyl cellulose, hydroxypropyl cellulose or carboxymethyl cellulose, as well as buffers and preservatives. The concentration of a polypeptide thereof in these compositions can vary widely, i.e., from less than about 10%, usually at least about 25% to as much as 75% or 90% by weight and will be selected primarily by fluid volumes, viscosities, etc., in accordance with the particular mode of administration selected. Actual methods for preparing orally, topically, and parenterally administrable compositions will be known or apparent to those skilled in the art and are described in detail in, for example, Remington's Pharmaceutical Science, 19th ed., Mack Publishing Co., Easton, Pa. (1995), which is incorporated herein by reference. Attorney Docket: 064802-505001WO In another embodiment of the disclosure, an article of manufacture containing materials useful for prophylaxis against or treatment of a disease or disorder including those associated with an inflammatory response, cancer, and / or tuberculosis. The article of manufacture comprises a container and a label. Suitable containers include, for example, bottles, vials, syringes, and test tubes. The containers may be formed from a variety of materials such as glass or plastic. The container holds a composition which is effective for treating the condition and may have a sterile access port (for example the container may be an intravenous solution bag or a vial having a stopper pierceable by a hypodermic injection needle). The active agent in the composition is the antibody of the disclosure. The label on or associated with, the container indicates that the composition is used for treating the condition of choice. The article of manufacture may further comprise a second container comprising a pharmaceutically- acceptable buffer, such as phosphate-buffered saline, Ringer's solution, and dextrose solution. It may further include other materials desirable from a commercial and user stand- point, including other buffers, diluents, filters, needles, syringes, and package inserts with instructions for use. V. Applications of Polypeptides Comprising Fc Domain Variants In some aspects, the present disclosure provides methods of use of a polypeptide comprising an Fc domain variant disclosed herein and / or a nucleic acid encoding the polypeptide, or compositions described herein. In some embodiments the polypeptide comprises a binding domain and the polypeptide reduces or eliminates cells bearing an epitope recognized by the binding domain of the polypeptide. In some embodiments, the polypeptide reduces the concentration of or eliminates soluble antigen in the circulation. In some embodiments, the polypeptides comprising an Fc domain variant are useful for the treatment of a disease or disorder including, but not limited to, an antibody related disorder, or an antibody responsive disorder, condition, or disease. As used herein, the terms “antibody related disorder” or “antibody responsive disorder” or “condition” or “disease” refer to or describe a disease or disorder that may be ameliorated by the administration of a pharmaceutical composition comprising an antibody or binding polypeptide of the present disclosure. In some embodiments, the polypeptides comprising an Fc domain variant are useful for the treatment of cancer. As used herein, the terms “cancer” or “cancerous” refer to or describe the physiological condition that is typically characterized by unregulated cell growth. Examples of cancer include but are not limited to carcinoma, lymphoma, blastoma, sarcoma Attorney Docket: 064802-505001WO (including liposarcoma), neuroendocrine tumors, mesothelioma, schwanoma, meningioma, adenocarcinoma, melanoma, and leukemia or lymphoid malignancies. More particular examples of such cancers include squamous cell cancer (e.g. epithelial squamous cell cancer), lung cancer including small-cell lung cancer, non-small cell lung cancer, adenocarcinoma of the lung and squamous carcinoma of the lung, cancer of the peritoneum, hepatocellular cancer, gastric or stomach cancer including gastrointestinal cancer, pancreatic cancer, glioblastoma, cervical cancer, ovarian cancer, liver cancer, bladder cancer, hepatoma, breast cancer, colon cancer, rectal cancer, colorectal cancer, endometrial or uterine carcinoma, salivary gland carcinoma, kidney or renal cancer, prostate cancer, vulval cancer, thyroid cancer, hepatic carcinoma, anal carcinoma, penile carcinoma, testicular cancer, esophageal cancer, tumors of the biliary tract, as well as head and neck cancer. In some embodiments, the polypeptides comprising an Fc domain variant treat other disorders, including, without limitation, infectious diseases, autoimmune disorders, inflammatory disorders, lung diseases, neuronal or neurodegenerative diseases, liver diseases, diseases of the spine, diseases of the uterus, depressive disorders, and the like. Non-limiting examples of infectious diseases include those caused by RNA viruses (e.g., orthomyxoviruses (e.g., influenza), paramyxoviruses (e.g., respiratory syncytial virus, parainfluenza virus, metapneumovirus), rhabdoviruses (e.g., rabies virus), coronaviruses, alphaviruses (e.g., Chikungunya virus) lentiviruses (e.g., HIV) and the like) or DNA viruses. Examples of infectious diseases also include, without limitation, bacterial infectious diseases, caused by, e.g., Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus, Streptococcus, Escherichia coli, and other infectious diseases including, e.g., those caused by Candida albicans. Other infectious diseases include, without limitation, malaria, SARS, yellow fever, Lyme borreliosis, leishmaniasis, anthrax and meningitis. Exemplary autoimmune disorders include, but are not limited to, psoriasis, rheumatoid arthritis, Sjogren’s Syndrome, graft rejection, Grave’s disease, myasthenia gravis and lupus (e.g., systemic lupus erythematosus). Accordingly, this disclosure relates to a method of treating various conditions that would benefit from using a subject binding polypeptide having, e.g., enhanced half-life. One skilled in the art would be able, by routine experimentation, to determine what an effective, non-toxic amount of a polypeptide comprising an Fc domain variant would be for the purpose of treating a disease or condition. For example, a therapeutically active amount of a polypeptide of the present disclosure may vary according to factors such as the disease stage (e.g., stage I versus stage IV), age, sex, medical complications (e.g., immunosuppressed conditions or diseases) and weight of the subject, and the ability of the modified antibody to Attorney Docket: 064802-505001WO elicit a desired response in the subject. The dosage regimen may be adjusted to provide the optimum therapeutic response. For example, several divided doses may be administered daily, or the dose may be proportionally reduced as indicated by the exigencies of the therapeutic situation. General techniques The practice of the present disclosure will employ, unless otherwise indicated, conventional techniques of molecular biology (including recombinant techniques), microbiology, cell biology, biochemistry, and immunology, which are within the skill of the art. Such techniques are explained fully in the literature, such as Molecular Cloning: A Laboratory Manual, second edition (Sambrook, et al., 1989) Cold Spring Harbor Press; Oligonucleotide Synthesis (M. J. Gait, ed.1984); Methods in Molecular Biology, Humana Press; Cell Biology: A Laboratory Notebook (J. E. Cellis, ed., 1989) Academic Press; Animal Cell Culture (R. I. Freshney, ed.1987); Introuction to Cell and Tissue Culture (J. P. Mather and P. E. Roberts, 1998) Plenum Press; Cell and Tissue Culture: Laboratory Procedures (A. Doyle, J. B. Griffiths, and D. G. Newell, eds.1993-8) J. Wiley and Sons; Methods in Enzymology (Academic Press, Inc.); Handbook of Experimental Immunology (D. M. Weir and C. C. Blackwell, eds.): Gene Transfer Vectors for Mammalian Cells (J. M. Miller and M. P. Calos, eds., 1987); Current Protocols in Molecular Biology (F. M. Ausubel, et al. eds.1987); PCR: The Polymerase Chain Reaction, (Mullis, et al., eds.1994); Current Protocols in Immunology (J. E. Coligan et al., eds., 1991); Short Protocols in Molecular Biology (Wiley and Sons, 1999); Immunobiology (C. A. Janeway and P. Travers, 1997); Antibodies (P. Finch, 1997); Antibodies: a practice approach (D. Catty., ed., IRL Press, 1988-1989); Monoclonal antibodies: a practical approach (P. Shepherd and C. Dean, eds., Oxford University Press, 2000); Using antibodies: a laboratory manual (E. Harlow and D. Lane (Cold Spring Harbor Laboratory Press, 1999); The Antibodies (M. Zanetti and J. D. Capra, eds. Harwood Academic Publishers, 1995); DNA Cloning: A practical Approach, Volumes I and II (D.N. Glover ed. 1985); Nucleic Acid Hybridization (B.D. Hames & S.J. Higgins eds.(1985»; Transcription and Translation (B.D. Hames & S.J. Higgins, eds. (1984»; Animal Cell Culture (R.I. Freshney, ed. (1986»; Immobilized Cells and Enzymes (lRL Press, (1986»; and B. Perbal, A practical Guide To Molecular Cloning (1984); F.M. Ausubel et al. (eds.). It is to be understood that this application is not limited to particular formulations or process parameters, as these may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is Attorney Docket: 064802-505001WO not intended to be limiting. Further, it is understood that a number of methods and materials similar or equivalent to those described herein can be used in the practice of the present disclosure. Without further elaboration, it is believed that one skilled in the art can, based on the above description, utilize the present invention to its fullest extent. The following specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. All publications cited herein are incorporated by reference for the purposes or subject matter referenced herein. EXAMPLES While the present disclosure has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the disclosure. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective, spirit, and scope of the present disclosure. All such modifications are intended to be within the scope of the disclosure. Example 1. Computational Design of Fc Domain Variants To identify human IgG Fc domain variants that increase half-life by modulating recycling through human FcRn binding, a rational engineering approach was developed. Key Fc domain amino acid residues were identified by analyzing the structure-function relationship of residues that modulate FcRn binding.18 high impact sites were chosen for rational design of the variants (FIG.1). Using a rational design approach, a library of 89 variants were designed that contain between 3-5 amino acid substitutions across the C2-CH3 domains. A rational engineering approach coupled with surface plasmon resonance (SPR) and visual inspection of the Fc domain and FcRn binding interference were used to identify mutations or combination mutations. A machine learning approach utilized protein language models to design, rank, and predict variants with improved FcRn binding. Amino acid substitutions were engineered into an IgG1 scaffold for screening binding affinity to FcRn The 18 high impact sites were considered for AI design of Fc domain variants. The library was screened in silico by computing scores from 3 computational approaches, ESM, ProteInMPNN, and BLOSUM80. Using the 3 scores, a library of 208 Fc domain variants (164 unique variants) was generated. The top 58 triple mutants were identified by using an averaged Attorney Docket: 064802-505001WO ranking from all three scores. The top 50 quadruple mutants that contained the M428L mutation were identified by using an averaged ranking from all three scores. The top 50 quadruple mutants were identified using an averaged ranking from all three scores.50 triple mutations were randomly sampled. Amino acid substitutions were engineered into an IgG1 or IgG4 scaffold for screening binding affinity to FcRn. Example 2. Validation of Fc Domain Variants with Surface Plasmon Resonance To evaluate the kinetics of the rationally designed or AI designed Fc domain variants from Example 1, surface plasmon resonance (SPR) was utilized. Briefly, an Fc fragment truncated at the upper hinge region was fused to an N-terminal SUMO tag, specifically designed for high expression in prokaryotic hosts. The Fc domain variants were directly captured from lysate using an anti-HIS tag monoclonal antibody and placed onto an SPR chip (e.g., Carterra LSA) (FIG.2.). The FcRn was flowed as an analyte and the association and disassociation kinetics between the Fc domain variants and FcRns was recorded. Fc domain variants that include LS and YTE mutations were included as positive controls. The LS and YTE mutations are known in the art to improve FcRn binding and antibody half-life (FIG.3). The Fc variants designed by rational design exhibited improved FcRn binding at pH 6.0. Specifically, there were significant increases in KON values as compared to wildtype Fc (FIG. 4). The Fc variants designed by AI design were ranked by fitness scores using ESM, ProteinMPNN, and BLOSUM80 and the binding kinetics were evaluated via SPR (FIG.5).17 Fc variants identified through AI design and rational design were identified that that bind with higher affinity to FcRn than LS and YTE were identified. The Kd values of the 17 Fc variants were calculated and are summarized in Table 1. The 17 Fc variants were reformatted as IgG4 monoclonal antibodies and screened at pH 6 and 7.4 for binding to human or Rhesus FcRn (see Table 2). Several Fc variants exhibited improved pH-dependent binding to human FcRn and Rhesus FcRn compared to the LS and YTE mutations and showed that mutation sites are universal across IgG class. There was a near perfect correlation indicating mutations are compatible in multiple IgG subclasses. Since mutational sites are conserved in all human IgGs, it is expected that these mutations will have a universal effect on FcRn binding across the IgG isotype. (FIG.6A-6B). Attorney Docket: 064802-505001WO Table 1. Kd Values of Fc domain variants. Fc Variant SEQ ID NO. of Fc SEQ ID NO. of Fc Engineering KD SPR Domain Variant Domain Variant source (nM) I 1 I 4 Table 2. Binding Properties of Antibodies with IgG4 Fc Variants. Fc Fc Variant Full Heavy Full Light Engineering KD FcRn mAb Avg Variants Sequence Chain Chain (nM) species / pH KD (nM) 1 6 7 6 3 2 .3 .7 Attorney Docket: 064802-505001WO Fc Fc Variant Full Heavy Full Light Engineering KD FcRn mAb Avg Variants Sequence Chain Chain (nM) species / pH KD (nM) S S 0 9 5 6 .0 .2 3 8 0 .6 .6 .7 .7 7 .9 .2 .1 Attorney Docket: 064802-505001WO Fc Fc Variant Full Heavy Full Light Engineering KD FcRn mAb Avg Variants Sequence Chain Chain (nM) species / pH KD (nM) S S 0 8 .3 .3 0 .1 .8 .6 .8 .9 Example 3: Endothelial Recycling of Designed Fc Domain Variants This example assesses endothelial recycling of IgG Fc domain variants (see Table 3 below) as a direct measure of their in vivo half-life. Plasma half-life dramatically affects the therapeutic potential of a monoclonal antibody. Among many plasma proteins, immunoglobulins and human serum albumin (HSA) exhibit some of the longest half-lives. The recycling of immunoglobulins and HSA by endothelial cells through interaction with the neonatal fragment crystallizable receptor (FcRn) is a key process that mediates the long half-life of these proteins. the degree of an antibody's recycling in an in vitro assay using immortalized human endothelial cells correlates well with the in vivo half-life of antibodies in FcRn transgenic mice. To assess endothelial recycling, an immortalized human microvascular endothelial cell Attorney Docket: 064802-505001WO line, HMEC-1 (ATCC), was transduced with the human FcRn receptor using a lentiviral vector. The resulting cell line overexpressed the human FcRn receptor, as confirmed by qRT- PCR. Cells were plated in a standard tissue culture-treated 96-well plate at a density of 100,000 cells per well in 100 µL of growth medium and incubated overnight at 37°C with 5% CO2. The following morning, the growth medium was aspirated, and 400 nM of test antibodies were added in a volume of 100 µL of HSBS per well for 4 hours. After incubation, the cells were washed four times with 100 µL of HSBS, and 100 µL of growth medium without FBS was added to each well. The cells were then incubated for 18 hours at 37°C with 5% CO2. After overnight incubation, the supernatant from the culture was collected, the cells were washed twice with HSBS, and lysed in 60 µL of RIPA buffer. Supernatants (recycled antibody) and cell lysates (residual antibody) were serially diluted and assayed using a sandwich ELISA. Statistical analysis of the data was performed using Prism (GraphPad) software. The raw data were fitted to four-parameter logistic curves, and antibody concentrations were extrapolated from standard curves. Table 3 below shows the absolute concentration of the recycled antibodies. The Fc domains in the tested antibodies are shown in Table 3. Structural information of the whole antibodies can be found in Example 2 above. Table 3: Absolute Concentration of Recycled Antibodies Fc Variants Absolute Concentration of Recycled Antibodies (pM) Attorney Docket: 064802-505001WO The results suggest that certain IgG Fc variants lead to enhanced half-life of antibodies comprising such as relative to the antibody counterpart comprising either the wildtype IgG Fc domain or the YTE or LS variant. SEQUENCE TABLE SEQ ID Description Sequence NO. 1 WT I 1 H A TK P VFPLAP K T TAAL LVKDYFPEPVTV WNS K A L F S S K A L F S S K A L F S G N K T S IS Q K V M T L P I E Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. QFNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPSSIEKTIS N M T L P I E IS N D Q F S K P F S S A L K S A L K S Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. Region 004 Fc HKPSNTKVDKKVEPKSSDKTHTCPPCPAPELLGGPSVFLFPPK K P F S S A L K S K P F S S A L K S K P F S S K L F S Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. 17 IgG1 Heavy ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNS K A L F S S K A L G K S K A L F S S K A L G K S K A L F S S K A L F Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. M428L YPSDIAVEWESNGQPETNYKTTPPVLDSDGSFFLYSKLTVDKS S K A L F S S K A L F S S D T R K I E S D T P E D Q S D T P E D Q S D T R Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. M428L EEQFNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPSSIEK I E S D T P E D Q S D T R K I E S D T P E D Q S D T R K I E S D T R K I E S D Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. Region 010 Fc HKPSNTKVDKRVESKYGPPCPSCPAPEFLGGPSVFLFPPKPKDT P E D Q S D T P E D Q S D T P E D S D T P E D S D T P E D Q S D T P E D Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. 40 IgG4 Heavy ASTKGPSVFPLAPCSRSTSESTAALGCLVKDYFPEPVTVSWNS P S T S Y S S Y S T S Y S T Y Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. PSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSRLTVDKS S S Y S T S Y S S Y S T S Y Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. Fc Variant MNSLKTEDTAVYYCGSSFGSNYVFAWFTYWGQGTLVTVSS S S Y S S Y S T S Y S T S S T Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. KPREEQFNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKGLPS Y S T S S T S Y S T S Y S P Attorney Docket: 064802-505001WO SEQ ID Description Sequence NO. S T S Y S T S Y S T S Y S T S Y OTHER EMBODIMENTS All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features. From the above description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope Attorney Docket: 064802-505001WO thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, other embodiments are also within the claims. EQUIVALENTS While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the inventive teachings is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms. All references, patents and patent applications disclosed herein are incorporated by reference with respect to the subject matter for which each is cited, which in some cases may encompass the entirety of the document. The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the Attorney Docket: 064802-505001WO elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law. The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within an acceptable standard deviation, per the practice in the art. Alternatively, “about” can mean a range of up to ± 20 %, preferably up to ± 10 %, more preferably up to ± 5 %, and more preferably still up to ± 1 % of a given value. Alternatively, particularly with respect to biological systems or processes, the term can mean within an order of magnitude, preferably within 2-fold, of a value. Where particular values are described in the application and claims, unless otherwise stated, the term “about” is implicit and in this context means within an acceptable error range for the particular value. In some embodiments, the hinge domain is a hinge domain of a naturally occurring protein. As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also Attorney Docket: 064802-505001WO allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

Claims

Attorney Docket: 064802-505001WO WHAT IS CLAIMED IS:

1. A polypeptide comprising an IgG Fc domain variant, wherein relative to a wild- type counterpart, the IgG Fc domain variant comprises: (i) an amino acid residue substitution at position M428, position N434, or a combination thereof; and (ii) an amino acid residue substitution at one or more of positions M252, T256, V259, E269, L309, Q311, D312, N315, T359, N361, and N389, optionally V259, E269, L309, N361, and N389; wherein residue numbering is based on EU numbering of human IgG Fc domain; and wherein the IgG Fc domain variant has an increased binding affinity to a human neonatal Fc receptor (FcRn) at an acidic pH as compared with the wild-type counterpart.

2. The polypeptide of claim 1, wherein: the amino acid residue substitution at position M428 is M428V, M428L, or M428I, optionally M428L; and / or the amino acid residue substitution at position N434 is N434Q, N434S, N434T, or N434Y, optionally N434S or N434Y.

3. The polypeptide of claim 1 or claim 2, wherein: the amino acid residue substitution at position M252 is M252V, M252I, M252V, M252F, M252Y, or M252W; optionally M252I or M252Y; the amino acid residue substitution at position T256 is T256D or T256E, optionally T256E; the amino acid residue substitution at position V259 is V259I, V259L or V259M, optionally V259I; the amino acid residue substitution at position E269 is E269E or E269D, optionally E269D; the amino acid residue substitution at position L309 is L309A or L309G; optionally L309G; the amino acid residue substitution at position Q311 is D311H, D311K, or D311R, optionally Q311R; the amino acid residue substitution at position D312 is D312H, D312K, D312R, D312S, D312T, optionally D312R or D312S;Attorney Docket: 064802-505001WO the amino acid residue substitution at position N315 is N315D or N315E, optionally N315D; the amino acid residue substitution at position T359 is T359A or T359G, optionally T359A; the amino acid residue substitution at position N361 is N361E or N361D, optionally N361D; and / or the amino acid residue substitution at position N389 is N389S or N389T, optionally N389T.

4. The polypeptide of any one of claims 1-3, wherein the IgG Fc domain variant comprises: (i) the amino acid residue substitution at position M428, position N434, or a combination thereof; and (ii) the amino acid residue substitution(s) at the following position(s): (a) V259, (b) L309 and N361, (c) E269 and N389, (d) M252 and D312, (e) Q311, (f) D312, (g) L309, (h) T256 and V259 (i) T256, V259, and Q311, (j) M252 and Q311, (k) T359, (l) N361 and N389, (m) T359 and N389, (n) N361, (o) N315 and N389, or (p) Q311, N315, and N389.

5. The polypeptide of claim 4, wherein the IgG Fc domain variant comprises amino acid residue substitutions at the following positions:Attorney Docket: 064802-505001WO (a) V259, M428, and N434, (b) L309, N361, and N434, (c) E269, N389, M428, and N434, (d) M252, D312, M428, and N434, (e) Q311, M428, and N434, (f) D312, M428, and N434, (g) L309, M428, and N434, (h) T256, V259, M428, and N434, (i) T256, V259, Q311, M428, and N434, (j) M252, Q311, and N434, (k) T359, M428, and N434, (l) N361, N389, M428, and N434, (m) T359, N389, M428, and N434, (n) N361, M428, and N434, (o) N315, N389, M428, and N434, or (p) Q311, N315, N389, and M428.

6. The polypeptide of claim 1, wherein the IgG Fc domain variant comprises the following amino acid residue substitutions: (a) V259I, M428L, and N434S, (b) L309G, N361D, and N434Y, (c) E269D, N389T, M428L, and N434S, (d) M252I, D312R, M428L, and N434T, (e) Q311R, M428L, and N434S, (f) D312S, M428L, and N434S, (g) L309G, M428L, and N434S, (h) T256E, V259I, M428L, and N434S, (i) L309G, M428L, and N434T, (j) T256E, V259I, Q311R, M428L, and N434S, (k) M252Y, Q311R, and N434Y, (l) T359A, M428L, and N434S, (m) N361D, N389T, M428L, and N434S, (n) T359A, N389T, M428L, and N434S, (o) N361D, M428L, and N434S,Attorney Docket: 064802-505001WO (p) N315D, N389T, M428L, and N434S, or (q) Q311R, N315D, N389T, and M428L.

7. The polypeptide of any one of claims 1-6, wherein the IgG Fc domain variant does not comprise further amino acid residue substitutions in a binding site for the human fcRn; and wherein the binding site comprises amino acid residues T250-T254, T307-Q311 and H433-Y436.

8. The polypeptide of claim 7, wherein the IgG Fc domain variant comprises residue K286, N288, H310, L314, E345, H429, E430, and / or K439.

9. The polypeptide of any one of claims 1-8, wherein the acidic pH is about 6.

10. The polypeptide of any one of claims 1-9, wherein the IgG Fc domain variant has a reduced binding affinity to the human FcRn relative to the wild-type counterpart at a physiological condition, which optionally comprises a neutral pH.

11. The polypeptide of claim 10, wherein the IgG Fc domain variant has a reduced binding affinity to the human FcRn relative to the wild-type counterpart at a pH of about 7 to about 7.

5.

12. The polypeptide of any one of claims 1-11, wherein the IgG Fc domain variant further comprises: (i) at least one amino acid substitution that alters Fc effector function; optionally wherein the at least one amino acid substitution that alters Fc effector function is at position D265, optionally D265S or D265T; (ii) at least one amino acid substitution that alters binding to a human FcγR, optionally wherein the at least one amino acid substitution that alters binding to a human FcγR is at position L234, optionally L234A or L234G, and / or L235, optionally L235A or L235G; (iii) at least one amino acid substitution that alters binding to human C1q; and / or (iv) at least one amino acid substitution that alters antibody-dependent cellular cytotoxicity (ADCC).Attorney Docket: 064802-505001WO 13. The polypeptide of any one of claims 1-12, wherein the IgG Fc domain variant is a human IgG1 or human IgG4 Fc domain variant.

14. The polypeptide of claim 13, wherein the IgG Fc domain variant is a human IgG1 Fc domain variant, which comprise an amino acid sequence at least 85% identical to SEQ ID NO: 1 and the amino acid residue substitutions set forth in any one of claims 1-6.

15. The polypeptide of claim 14, wherein the IgG Fc domain variant comprises an amino acid sequence of any one of SEQ ID NOs: 8-24, optionally SEQ ID NO: 11, 17, or 23.

16. The polypeptide of claim 13, wherein the IgG Fc domain variant is a human IgG4 Fc domain variant, which comprise an amino acid sequence at least 85% identical to SEQ ID NO: 59 and the amino acid residue substitutions set forth in any one of claims 1-6.

17. The polypeptide of claim 16, wherein the IgG Fc domain variant comprises an amino acid sequence of any one of SEQ ID NOs: 25-41, optionally SEQ ID NO: 28, 34, or 40.

18. The polypeptide of any one of claims 1-17, which further comprises a heavy chain variable region or a cytokine linked to the IgG Fc domain variant.

19. An antibody comprising a heavy chain and a light chain, wherein the heavy chain comprises the IgG Fc domain variant set forth in any one of claims 1-17.

20. A nucleic acid comprising a nucleotide sequence encoding a polypeptide set forth in any one of claims 1-18.

21. The nucleic acid of claim 20, which is a vector, optionally an expression vector.

22. A host cell comprising the nucleic acid of claim 20 or claim 21.

23. A method for producing a polypeptide, comprising culturing the host cell of claim 22 under conditions allowing for expression of the polypeptide.Attorney Docket: 064802-505001WO 24. A composition comprising the polypeptide of any one of claims 1-18, the antibody of claim 19, or the nucleic acid of claim 20 or claim 21 and a pharmaceutically acceptable carrier.

25. A method for enhancing half-life of an Fc-containing protein in a subject, the method comprising introducing into the Fc domain in the Fc-containing protein the amino acid residue substitutions set forth in any one of claims 1-8 to produce a protein comprising a variant Fc domain; wherein the protein comprising the variant Fc domain has an increased half-life in a subject as compared with the Fc-containing protein.

26. The method of claim 25, wherein the Fc-containing protein is an antibody or an Fc-fusion polypeptide.

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