Low affinity immunoglobulin gamma Fc receptor IIIa (FcγRIIIa) 158V variant (FcγRIIIa 158V)

Low affinity immunoglobulin gamma Fc receptor IIIa (FcγRIIIa), also known as CD16a, is a crucial activating receptor expressed on natural killer (NK) cells and macrophages that bridges the adaptive and innate immune systems [1, 5]. The 158V variant is a common functional polymorphism (rs396991) characterized by a valine substitution for phenylalanine at position 158, which significantly increases the receptor's binding affinity for the Fc portion of IgG1 and IgG3 antibodies [1, 13]. This high-affinity interaction enhances the potency of antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP), making the 158V variant a key determinant of therapeutic efficacy for monoclonal antibodies such as rituximab and trastuzumab [2, 5]. In clinical oncology, the presence of the 158V allele is often associated with improved outcomes in patients treated with IgG1-based therapies, serving as a valuable pharmacogenetic biomarker for patient stratification [5, 6]. However, the high-affinity nature of this variant can also lead to adverse outcomes, such as an increased risk of developing anti-drug antibodies in inflammatory diseases or contributing to the immunopathology of severe infections like COVID-19 through excessive cytokine production [8, 12]. Consequently, modern drug development frequently focuses on engineering antibody Fc regions to optimize binding across both 158V and 158F variants to ensure consistent clinical performance regardless of a patient's genotype [6, 14].

Other names

CD16a 158V variantFCGR3A V158Fc-gamma RIIIa 158VCD16A V158Low affinity immunoglobulin gamma Fc receptor III-A valine-158 variant

The FcγRIIIa 158V variant acts as a high-affinity trigger for antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) [1, 2]. Therapeutic monoclonal antibodies bind to target antigens via their Fab regions, while their Fc regions engage the 158V variant on effector cells like NK cells and macrophages [1, 14]. This high-affinity interaction leads to the release of cytotoxic granules and pro-inflammatory cytokines, resulting in the destruction of the opsonized target cell [1, 13].