Enhanced Effector Functions Due to Antibody Defucosylation Depend on the Effector Cell Fcγ Receptor Profile

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 Fc gamma RIII, resulting in enhanced Fc gamma RIII-mediated effector functions. Normal plasma IgG contains similar to 94% fucosylated Abs, but alloantibodies against, for example, Rhesus D (RhD) and platelet Ags frequently have reduced fucosylation that enhances their pathogenicity. The increased FcgRIII-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 Fc gamma R 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 FcgRIII isoforms, without affecting binding affinity to other Fc gamma Rs. In contrast, when testing hypofucosylated anti-RhD Abs with Fc gamma RIIIaexpressing 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 FcgRs, including Fc gamma RIIIa. Our data suggest that the beneficial effects of afucosylated biologicals for clinical use can be anticipated when there is a substantial involvement of Fc gamma RIIIa-expressing cells, such as NK cells.