Fc engineering for the reprogramming the effector functions of antibodies for improved therapeutic potency
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Monoclonal antibodies (mAb) are very important for cancer therapy, as they target cancerous cells without side effects. mAbsrecognize cell-surface proteins on cancerous cells and mediate the killing of these targeted cells by multiple mechanisms, including antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cell-mediated phagocytosis (ADCP), both of which are dependent upon a fragment crystallizable (Fc) domain interacting with effector Fc gamma receptors (Fc[gamma]Rs). mAb can induce productive synapse formation between tumor and immune effector cells by recruiting Fc[gamma]Rs on the effector cells. N-linked carbohydrate chains on the Fc domain of an immunoglobulin (Ig)G1 antibodies are so critical for binding to Fc[gamma]Rs that the antibodies cannot measurably bind to the receptors without the glycans. However, we have recently isolated an engineered aglycosylated Fc variant with selectivity towards Fc[gamma]RI with nanomolar K[subscript D] but no detectable binding to other Fc[gamma]Rs. This Fc-engineered aglycosylated antibody shows novel effector functions which do not show in glycosylated counterparts. The novel property of the engineered antibody is derived from selective binding to one or more of the activating Fc[gamma]Rs but not to the inhibitory Fc[gamma]RIIb, which mediates potent inhibition of cellular immune activity. This unique effector function indicates that aglycosylated IgGs can be reprogrammed to display unique Fc[gamma]R selectivity profiles. These Fc-engineered aglycosylated antibodies have advantages over glycosylated antibodies because they can be produced in bacteria at a low cost through rapid bioprocessing while circumventing the problem of glycan heterogeneity. This dissertationdescribes engineering of aglycosylated antibodies that selectively binds to i) Fc[gamma]RIIIa and also Fc[gamma]RI (Chapter 2) and ii) bind to Fc[gamma]RIIIa but show decreased or no detectable binding to the inhibitory receptor Fc[gamma]RIIb (Chapter 3). BIACore analysis of the binding of the engineered Fc domains to recombinant Fc[gamma]Rs is described in detail. This dissertation also describes a screening strategy for pH-dependent FcRn binding (Chapter 4). In separate studies, binding properties of Fc5 to Fc[gamma]RI using Fc-III peptideand its implication on structure as well as affinities of Fc1000 serieswere evaluated (Appendices A and B, respectively).