Immune modulation by butyrophilin 1A1 (BTN1A1)

Abstract The butyrophilins are B7-like T cell co-regulatory molecules. These molecules are of increasing interest in cancer immunotherapy as they may represent a novel subset of immune check-point regulators. In this study, we expressed the recombinant human butyrophilin 1A1 extracellular domain with a C terminal 6-His tag (BTN1A1) in NSO mouse myeloma cell line, and investigated the biological functions of the purified recombinant BTN1A1 protein in vitro. Human T cells were treated with plate-bound anti-CD3 and BTN1A1. The levels of multiple cytokines were measured in cell culture supernatants using R&D Systems Proteome Profiler™ Human Cytokine Array and confirmed by measuring individual cytokines using cytokine-specific Quantikine® ELISA kits. BTN1A1 significantly decreased T-cell derived cytokines such as IL-2, IL-21, IL-25, CD40L, and C5a, but not IFN-gamma. BTN1A1 also markedly inhibited anti-CD3-induced human T cell proliferation in a dose dependent manner. Furthermore, BTN1A1 showed binding to anti-CD3 activated, but not rest T cells. Moreover, recombinant human BTN1A1 inhibited p38 MAPK, CREB, and TOR Phosphorylation, suggesting BTN1A1 modulates TCR signaling through the p38 MAP kinase, CREB, and TOR pathways. Taken together, our data suggests that BTN1A1 acts as a co-inhibitory molecule to modulate T cells through an unknown receptor on the surface of T cells. BTN1A1 may be a potential target of immune check-point molecules for therapeutic purposes.