PDCD1 and cancer: To quantify and visualize the differences in the killing of CRC cell lines by PD-1+ and PD-1– γδ T cells, we co-cultured the γδ T cell populations with three CRC cell lines (HCT-15, LoVo, HT-29) in the presence of a fluorescent cleaved-caspase-3/7 reporter to measure cancer cell apoptosis over time (Fig. 3d,e).