Vγ9Vδ2 T cells expanded from human PBMCs and adoptively transferred into a murine xenograft model of human lymphomagenesis have potent antitumor effects, even without coadministration of checkpoint inhibitors, likely due to consistently low PD-1 expression on the γδ T cells. Recruitment of γδ T cells to the tumor was followed by decreased expression of PD-L1 and PD-L2 on lymphoma cells.
A central issue for adoptive cellular immunotherapy is overcoming immunosuppressive signals to achieve tumor clearance. While gammadelta T cells are known to be potent cytolytic effectors that can kill a variety of cancers, it is not clear whether they are inhibited by suppressive ligands expressed in tumor microenvironments. Here, we have used a powerful preclinical model where EBV infection drives the de novo generation of human B cell lymphomas in vivo, and autologous T lymphocytes are held in check by PD-1/CTLA-4-mediated inhibition. We show that a single dose of adoptively transferred Vdelta2+ T cells has potent antitumor effects, even in the absence of checkpoint blockade or activating compounds. Vdelta2+ T cell immunotherapy given within the first 5 days of EBV infection almost completely prevented the outgrowth of tumors. Vdelta2+ T cell immunotherapy given more than 3 weeks after infection (after neoplastic transformation is evident) resulted in a dramatic reduction in tumor burden. The immunotherapeutic Vdelta2+ T cells maintained low cell surface expression of PD-1 in vivo, and their recruitment to tumors was followed by a decrease in B cells expressing PD-L1 and PD-L2 inhibitory ligands. These results suggest that adoptively transferred PD-1lo Vdelta2+ T cells circumvent the tumor checkpoint environment in vivo.