PDCD1 and neoplasm: Having established the effects of tumor-derived factors on Vγ4+ and Vγ6+ cells as well as the differential expression of the T cell checkpoint molecules, PD-1 and TIM-3, on these cells, we set out to determine how inhibition of these checkpoint molecules may influence Vγ4+ and Vγ6+ cells in the pre-metastatic niche.