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Enhancement of the Antibody-Dependent Cellular Cytotoxicity of Low-Fucose IgG1 Is Independent of FcγRIIIa Functional Polymorphism

Purpose: The most common polymorphic variant of Fcγ receptor type IIIa (FcγRIIIa), FcγRIIIa-158F, has been associated with inferior clinical responses to anti-CD20 chimeric IgG1 rituximab compared with FcγRIIIa-158V. As we previously found that removal of fucose residues from the oligosaccharides of human IgG1 results in enhanced antibody-dependent cellular cytotoxicity, we compared the effects of the FcγRIIIa gene (FCGR3A) polymorphism on normal and low-fucose versions of rituximab on antibody-dependent cellular cytotoxicity. Experimental Design: The polymorphism at position 158 of FcγRIIIa was determined for the peripheral blood mononuclear cells (PBMCs) of 20 healthy donors. The PBMCs were then used as effector cells to compare the antibody-dependent cellular cytotoxicity of rituximab and a low-fucose version, KM3065. The contributions of the different cell types within the PBMC to antibody-dependent cellular cytotoxicity were examined. Results: We found KM3065-mediated antibody-dependent cellular cytotoxicity was increased 10 to 100-fold compared with rituximab for each of the 20 donors. In contrast to rituximab, KM3065 antibody-dependent cellular cytotoxicity enhancement was similar for both FCGR3A alleles and thus independent of genotype. In addition, antibody-dependent cellular cytotoxicity of both KM3065 and rituximab requires natural killer cells but not monocytes nor polymorphonuclear cells. The antibody-dependent cellular cytotoxicity (ADCC) of each of the 20 donors correlated with the natural killer cell numbers present in the PBMCs. Importantly, using KM3065, the ADCC mediated by effector cells bearing the lower affinity variant FcγRIIIa-158F was significantly increased compared with rituximab-mediated ADCC using effector cells bearing the higher affinity FcγRIIIa-158V receptors. Conclusions: The use of low-fucose antibodies might improve the therapeutic effects of anti-CD20 therapy for all patients independent of FcγRIIIa phenotype beyond that currently seen with even the most responsive patients.