Human Vγ2Vδ2 T cells play important roles in microbial and tumor immunity by monitoring foreign- and self-prenyl pyrophosphate metabolites in isoprenoid biosynthesis. Accumulation of isoprenoid metabolites after bisphosphonate treatment allows Vγ2Vδ2 cells to recognize and kill tumors independently of their MHC expression or burden of non-synonymous mutations. Clinical trials with more than 400 patients show that adoptive immunotherapy with Vγ2Vδ2 T cells has few side effects but has resulted in only a few partial and complete remissions.
Ex vivo expansion for gamma delta T cells was done by pulsing with zoledronate in the presence of IL-2. Multicolor Flow Cytometry LSR II was used to assess the cell functionality by measuring cytokines expression (IFN-γ, and TNF-a). Human prostate cancer PC-3 cell line and NSG mice were used for the in vivo adoptive immunotherapy. PD-1 blockeds were used based on the approved clinical standards. Tumor size was assessed once weekly by external measurement of the longitudinal and transverse tumor diameter using a digital vernier caliper.
We have tested Vγ2Vδ2 T cells for expression of inhibitory receptors and determined whether adding PD-1 checkpoint blockade to adoptively transferred Vγ2Vδ2 T cells enhances immunity to human PC-3 prostate tumors in an NSG mouse model. We find that Vγ2Vδ2 cells express PD-1, CTLA-4, LAG-3, and TIM-3 inhibitory receptors during the 14-day ex vivo expansion period, and PD-1, LAG-3, and TIM-3 upon subsequent stimulation by pamidronate-treated tumor cells. Expression of PD-L1 on PC-3 prostate cancer cells was increased by co-culture with activated Vγ2Vδ2 T cells. Importantly, anti-PD-1 mAb treatment enhanced Vγ2Vδ2 T cell immunity to PC-3 tumors in immunodeficient NSG mice, reducing tumor volume nearly to zero after 5 weeks of treatment.
These results demonstrate that PD-1 checkpoint blockade can enhance the effectiveness of adoptive immunotherapy with human γδ T cells in treating prostate tumors in a preclinical model. Our findings should provide new insights and perspectives to further increase the responsiveness of solid and less immunogenic tumors to immunotherapies.
The authors.
VA Healthcare.
All authors have declared no conflicts of interest.