Anti-BTN3A1 monoclonal antibody, clone fCjpCU4.2

The mechanistic requirements of antigen recognition by T cells expressing a gamma delta TCR has revealed important differences with those of alpha beta TCR cells and, despite impressive new data generated in the very recent years, they remain poorly understood. Based on the structure of the TCR chains and the tissue distribution, gamma delta cells are represented in a variety of populations. The major subset of human peripheral blood gamma delta cells express V gamma 9V gamma delta TCR heterodimers and are all stimulated by phosphorylated metabolites (commonly called phosphoantigens). Phosphoantigens are molecules with a very small mass and only stimulate V gamma 9V gamma delta cells in the presence of antigen-presenting cells, suggesting a strict requirement for dedicated antigen-presenting molecules. Recent studies have identified butyrophilin (BIN) 3A1 as the molecule necessary to stimulate V gamma 9V gamma delta cells. BTN3A1 extracellular, transmembrane, and cytoplasmic domains have different functions, including cognate interaction with the V gamma 9V gamma delta TCR, binding of the phosphoantigens, and interaction with cytoplasmic proteins. This review mainly discusses the known molecular mechanisms of BTN3A1-mediated antigen presentation to gamma delta cells and proposes a model of phosphoantigen presentation, which integrates past and recent studies. Keywords: antigen presentation, gamma delta TCR, butyrophilin 3A1, infection control, tumor surveillance

Human V gamma 9/V delta 2 T-cells detect tumor cells and microbial infections by recognizing small phosphorylated prenyl metabolites termed phosphoantigens (P-Ag). The type-1 transmembrane protein Butyrophilin 3A1 (BTN3A1) is critical to the P-Ag-mediated activation of V gamma 9/V delta 2 T-cells; however, the molecular mechanisms involved in BTN3A1-mediated metabolite sensing are unclear, including how P-Ag's are discriminated from nonantigenic small molecules. Here, we utilized NMR and X-ray crystallography to probe P-Ag sensing by BTN3A1. Whereas the BTN3A1 immunoglobulin variable domain failed to bind P-Ag, the intracellular B30.2 domain bound a range of negatively charged small molecules, including P-Ag, in a positively charged surface pocket. However, NMR chemical shift perturbations indicated BTN3A1 discriminated P-Ag from nonantigenic small molecules by their ability to induce a specific conformational change in the B30.2 domain that propagated from the P-Ag binding site to distal parts of the domain. These results suggest BTN3A1 selectively detects P-Ag intracellularly via a conformational antigenic sensor in its B30.2 domain and have implications for rational design of antigens for V gamma 9/V delta 2-based T-cell immunotherapies.