Enhanced Effector Functions Due to Antibody Defucosylation Depend on the Effector Cell Fc{gamma} Receptor Profile [IMMUNOTHERAPY AND VACCINES]

Abs of the IgG isotype are glycosylated in their Fc domain at a conserved asparagine at position 297. Removal of the core fucose of this glycan greatly increases the affinity for FcRIII, resulting in enhanced FcRIII-mediated effector functions. Normal plasma IgG contains ~94% fucosylated Abs, but alloantibodies against, for example, Rhesus D (RhD) and platelet Ags frequently have reduced fucosylation that enhances their pathogenicity. The increased FcRIII-mediated effector functions have been put to use in various afucosylated therapeutic Abs in anticancer treatment. To test the functional consequences of Ab fucosylation, we produced V-gene–matched recombinant anti-RhD IgG Abs of the four different subclasses (IgG1–4) with and without core fucose (i.e., 20% fucose remaining). Binding to all human FcR types and their functional isoforms was assessed with surface plasmon resonance. All hypofucosylated anti-RhD IgGs of all IgG subclasses indeed showed enhanced binding affinity for isolated FcRIII isoforms, without affecting binding affinity to other FcRs. In contrast, when testing hypofucosylated anti-RhD Abs with FcRIIIa-expressing NK cells, a 12- and 7-fold increased erythrocyte lysis was observed with the IgG1 and IgG3, respectively, but no increase with IgG2 and IgG4 anti-RhD Abs. Notably, none of the hypofucosylated IgGs enhanced effector function of macrophages, which, in contrast to NK cells, express a complex set of FcRs, including FcRIIIa. Our data suggest that the beneficial effects of afucosylated biologicals for clinical use can be particularly anticipated when there is a substantial involvement of FcRIIIa-expressing cells, such as NK cells.

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