Introducing new effector function to IgG via protein engineering of an IgA-IgG hybrid antibody
Antibody therapeutics are becoming more prevalent in the clinic as pharmaceutical companies increase their efforts to develop biologic drugs. Currently all FDA-approved antibody therapeutics are of the IgG isotype due to the strong activation of the human immune system by this class of antibody upon engagement of FcγRs on innate effector cells. Cellular activation via FcγR binding can stimulate potent ADCC and ADCP responses to neutralize a wide variety of targets including cancer cells and bacteria. However, it may be possible to increase the therapeutic effect by recruiting more effector cells through interaction with Fc receptors characteristic of other antibody classes. Specifically, the IgA isotype can activate an ADCC response by binding to FcαRI present on neutrophils, the most abundant white blood cells in humans. We have engineered an IgG Fc domain with affinity for FcαRI that retains binding to certain FcγRs to allow for synergistic action. Introducing de novo binding to an IgG backbone obviates the problems associated with IgA production such as low expression yields and problematic assembly while creating new function as demonstrated by in vitro cell killing assays of Her2+ tumor cells.