Engineered aglycosylated full-length IgG Fc variants exhibiting improved FcγRIIIa binding and tumor cell clearance

FcγRIIIa, which is predominantly expressed on the surface of natural killer cells, plays a key role in antibody-dependent cell-mediated cytotoxicity (ADCC), a major effector function of therapeutic IgG antibodies that results in the death of aberrant cells. Despite the potential uses of aglycosylated IgG antibodies, which can be easily produced in bacteria and do not have complicated glycan heterogeneity issues, they show negligible binding to FcγRIIIa and abolish the activation of immune leukocytes for tumor cell clearance, in sharp contrast to most glycosylated IgG antibodies used in the clinical setting. For directed evolution of aglycosylated Fc variants that bind to FcγRIIIa and, in turn, exert potent ADCC effector function, we randomized the aglycosylated Fc region of full-length IgG expressed on the inner membrane of Escherichia coli. Multiple rounds of high-throughput screening u…