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Abstract
Antibodies have become a popular treatment for a wide variety of diseases. Within the body, certain immune cells express Fcγ receptors (FcγRs), that bind to the Fc region of antibodies, and initiate cell activation. In response, the immune cells will release cytotoxic granules that destroy the opsonized target. This process, antibody-dependent cell-mediated cytotoxicity (ADCC), is primarily mediated by natural killer, although macrophages, neutrophils and monocytes may also perform ADCC to an extent. ADCC response is triggered by antibody binding and subsequent signaling through a single receptor, CD16a. Several recent immunotherapies have investigated the potential of CD16a-expressing NK cells as a new disease treatment. Additionally, the most common therapeutic antibody class IgG1, binds to CD16a. Despite the significance of CD16a connecting antibody binding to cytotoxic response, relatively little is known about its structure and function. Herein, we detail the structure and function of CD16a as well as propose a model for its binding to Fc. We show how CD16a glycosylation changes its structure and regulates ADCC. The role of glycans is often overlooked. Even the concept that glycosylation had any impact on CD16a affinity was a recent discovery. The deep level of involvement that glycosylation has on CD16a highlights the importance of these modifications on protein function. The tools we used to study them, including our novel NMR labeling approach, provide researchers with techniques that will allow them to study glycans in-depth. Another significant discovery is the CD16a affinity directly correlates with ADCC. Several clinical trials are investigating “high affinity” NK cells as a treatment for multiple different diseases. Although, the high affinity is referring to the cells being V158 homozygotes. We have achieved higher affinity than V158, and provide evidence to suggest that further improving CD16a affinity will lead to higher ADCC. The contents of this work provide a compelling case for CD16a engineering for therapeutic use.