PD-1 blockade markedly enhances immunity to prostate tumors by adoptively transferred human Vγ2Vδ2 T cells in an NSG mouse model

Abstract

Abstract Human γδ T cells expressing Vγ2Vδ2 TCRs monitor foreign- and self-prenyl pyrophosphate metabolites in isoprenoid biosynthesis to mediate immunity to microbes and tumors. Bisphosphonate treatment of tumors results in increases in isopentenyl pyrophosphate that is sensed by butyrophilin 3A1. This allows Vγ2Vδ2 T cells to recognize and kill all tumor types independent of MHC expression or the number of tumor mutations. In clinical trials, adoptive immunotherapy with Vγ2Vδ2 cells has few side effects but has only resulted in a few partial and complete remissions with the most common response being stable disease. To improve effectiveness, we have now tested the combination of PD-1 blockade with Vγ2Vδ2 T cells and the bisphosphonate, pamidronate. Vγ2Vδ2 T cells were found to express PD-1, CTLA-4, LAG-3, and TIM-3 inhibitory receptors during the 14 day ex vivo expansion. Moreover, tumor expression of PD-L1 was increased by co-culture with activated Vγ2Vδ2 cells and by exogenous IFN-γ. To assess the in vivo effect of PD-1 blockade, immunodeficient NSG mice were inoculated with human PC-3 prostate cancer cells that naturally express PD-L1. After 13 days, the mice were treated with pamidronate followed 1 day later by purified Vγ2Vδ2 cells combined with either an anti-PD-1 or a control IgG1 mAb. This regimen was repeated weekly for 5 weeks. Anti-PD-1 mAb treatment markedly enhanced Vγ2Vδ2 immunity to PC-3 tumors, reducing tumor volume nearly to zero after 5 weeks. These results demonstrate that PD-1 checkpoint blockade can enhance the effectiveness of adoptive immunotherapy with γδ T cells in treating prostate tumors in a preclinical model and suggests that this combination should be tested in patients.