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Abstract:
IgA antibodies play an important role in bridging adaptive and innate immunity. There is increasing evidence that FcαRI-dependent engagement of myeloid cells appears to be crucial to activate mechanisms like phagocytosis or antibody-dependent cell-mediated cytotoxicity and that myeloid cells constitute important effector cells in cancer and cancer immunotherapy. Here, we describe an Fc engineering approach to further improve the immunotherapeutic potential of IgA antibodies. Methods: Recombinant IgA antibodies against the epidermal growth factor receptor (EGFR) were produced by co-transfecting CHO-K1 cells with vectors encoding the 225 variable and Igα heavy and κ light chain constant regions, respectively. An Fc engineered IgA2 antibody was generated by mutating two N-glycosylation sites and by removing two free cysteines. The resulting antibody was compared to wild type IgA2 regarding biochemical characteristics as well as Fab and Fc-mediated effector functions. Additionally, serum half-life and in vivo efficacy in a xenogeneic FcαRI-transgenic tumor model were evaluated. Results: Rational engineering of an IgA2 antibody resulted in monomeric molecules with improved biochemical characteristics, identical Fab- and Fc- mediated effector functions, but with significantly lower levels of terminal galactose. This molecule demonstrated lower asialoglycoprotein-receptor (ASGPR) binding and subsequently improved pharmacokinetics in mice. Compared to wild type IgA, this novel molecule displayed enhanced therapeutic efficacy against A431 tumor cells in vivo, which required human FcαRI-dependent myeloid effector cell engagement. Conclusions: These results demonstrate that an Fc engineered IgA antibody against EGFR displayed improved immunotherapeutic efficacy, which may overcome limitations (stability, pharmacokinetics, in vivo efficacy) of wild type IgA antibodies. Thus, these results promote the concept of FcαRI-dependent engagement of myeloid effector cells as a promising approach for antibody-based tumor immunotherapy.
