Synthesis of Pyrophosphate-Containing Compounds that Stimulate VγVδ2 T Cells: Application to Cancer Immunotherapy

Human Vγ2Vδ2 T cells recognize nonpeptide antigens, such as isoprenoid pyrophosphomonoester intermediates, alkylamine compounds, and bisphosphonate drugs, as well as some tumor cells. Although attempts have been made to derive novel cancer immunotherapies based on the discovery of these unconventional antigens, effective therapies remain to be developed. Here, we synthesized a series of pyrophosphate-containing compounds and examined the chemical requirements for the recognition of pyrophosphomonoester antigens by γδ T cells. The structural analysis clearly demonstrated that a proximal methylene moiety plays a crucial role in the stimulatory activity of the antigens. For optimal γδ T cell proliferation, we find that the use of human serum albumin was preferred and that pyrophosphomonoesters were superior to nitrogen-containing bisphosphonate compounds. Using these techniques, we have successfully expanded γδ T cells from healthy donors as well as from cancer patients using one of the most active compounds, 2-methyl-3-butenyl-1- pyrophosphate (2M3B1PP). The resulting expanded γδ T cells exhibited potent, cytotoxic activity against a wide variety of tumor cell lines. Even γδ T cells from a patient with advanced liver carcinoma efficiently responded to 2M3B1PP and exhibited strong cytotoxic activity against tumor cells. The pretreatment of tumor cells with nonpeptide antigens was essential for efficient cytotoxicity via TCR-γδ.The present study suggests a novel strategy for cancer immunotherapy using synthetic small pyrophosphate-containing compounds and nitrogen-containing bisphosphonates.