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Publication Abstract from PubMed

The Fc variant of IgG2, designated as IgG2sigma, was engineered with V234A/G237A /P238S/H268A/V309L/A330S/P331S substitutions to eliminate affinity for Fcgamma receptors and C1q complement protein and consequently, immune effector functions. IgG2sigma was compared to other previously well-characterized Fc 'muted' variants, including aglycosylated IgG1, IgG2m4 (H268Q/V309L/A330S/P331S, changes to IgG4), and IgG4 ProAlaAla (S228P/L234A/L235A) in its capacity to bind FcgammaRs and activate various immune-stimulatory responses. In contrast to the previously characterized muted Fc variants, which retain selective FcgammaR binding and effector functions, IgG2sigma shows no detectable binding to the Fcgamma receptors in affinity and avidity measurements, nor any detectable antibody-dependent cytotoxicity, phagocytosis, complement activity, or Fc-mediated cytokine release. Moreover, IgG2sigma shows minimal immunogenic potential by T-cell epitope analysis. The circulating half-life of IgG2sigma in monkeys is extended relative to IgG1 and IgG2, in spite of similar in vitro binding to recombinant FcRn. The three-dimensional structure of the Fc, needed for assessing the basis for the absence of effector function, was compared with that of IgG2 revealing a number of conformational differences near the hinge region of the CH2 domain that result from the amino acid substitutions. Modeling reveals that at least one of the key interactions with FcgammaRs is disrupted by a conformational change that reorients P329 to a position that prevents it from interacting with conserved W90 and W113 residues of the FcgammaRs. Inspection of the structure also indicated significant changes to the conformations of D270 and P329 in the CH2 domain that could negatively impact C1q binding. Thus, structural perturbations of the Fc provide a rationale for the loss of function. In toto, these properties of IgG2sigma suggest that it is a superior alternative to previously described IgG variants of minimal effector function, for future therapeutic applications of non-immunostimulatory mAb and Fc-fusion platforms.

An engineered Fc variant of an IgG eliminates all immune effector functions via structural perturbations.,Vafa O, Gilliland GL, Brezski RJ, Strake B, Wilkinson T, Lacy ER, Scallon B, Teplyakov A, Malia TJ, Strohl WR Methods. 2013 Jul 17. pii: S1046-2023(13)00247-8. doi:, 10.1016/j.ymeth.2013.06.035. PMID:23872058^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.