Low affinity immunoglobulin gamma Fc receptor IIIa (CD16a) (FcγRIIIa)

Low affinity immunoglobulin gamma Fc receptor IIIa, commonly known as CD16a, is a transmembrane glycoprotein expressed primarily on natural killer (NK) cells and certain subsets of monocytes and macrophages. It serves as a critical link between the adaptive and innate immune systems by binding the Fc portion of IgG1 and IgG3 antibodies. Upon binding to antibody-coated targets, FcγRIIIa triggers antibody-dependent cellular cytotoxicity (ADCC), leading to the direct lysis of the target cell and the secretion of pro-inflammatory cytokines like IFN-gamma. In the context of oncology, FcγRIIIa is the primary mediator of the therapeutic efficacy of many blockbuster monoclonal antibodies, such as Rituximab and Trastuzumab. A common genetic polymorphism (V158F) in the FCGR3A gene dictates the binding affinity of the receptor, where the 158V variant exhibits higher affinity and is often associated with better clinical outcomes in patients receiving antibody therapies. Modern drug development efforts include Fc-engineering of antibodies to increase their affinity for FcγRIIIa and the creation of bispecific engagers that specifically recruit NK cells to tumor sites.

Other names

CD16aFCGR3AFc-gamma RIIIaIgG Fc receptor III-2FcRIIIa

Therapeutic monoclonal antibodies bind to target antigens on diseased cells via their Fab domains, while their Fc domains bind to FcγRIIIa on NK cells. This cross-linking triggers the activation of NK cells, leading to the release of cytotoxic granules (perforin and granzymes) and the induction of apoptosis in the target cell, a process known as antibody-dependent cellular cytotoxicity (ADCC).