The FcγRIIIA (CD16) L48-H/R Polymorphism Enhances NK Cell-Mediated Antibody-Dependent Cellular Cytotoxicity by Promoting Serial Killing.

Many tumor-specific monoclonal antibody therapies stimulate antibody-dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells through FcγRIIIa (CD16). The efficacy of these ADCC-based immunotherapies is potentiated in patients with the common CD16 polymorphic variant F158-V that increases the binding affinity between the receptor and the IgG Fc domain. However, other CD16 variants are less well characterized. Here, we report that CD16 L48-H and L48-R variants both significantly enhance in vitro ADCC responses in primary NK cells and NK-92 cells. During ADCC responses, NK cells expressing CD16 48-H killed and disengaged from target cells faster than those expressing CD16 48-L, resulting in improved serial killing of tumor cells. We found that CD16 48-H also formed an immunologic synapse with a more compact interface, as well as more robust intracellular calcium signaling and quicker polarization of cytolytic vesicles. The ADCC response observed occurs due to increased cytolytic signaling and target cell disengagement, which drives NK cell-mediated serial killing of tumor cells. The L48-H/R polymorphism has potential to benefit patient responses to cancer antibody therapies and may also potentiate antitumor ADCC responses if incorporated into adoptive NK cell therapeutic platforms.