PDCD1 and cancer: γδT cells, distinct from αβT cells, can detect changes during the transformation of healthy cells into cancer cells to monitor cancer development and eliminate them in time.163 With the development of a tumor, γδT cells in the tumor change from a PD-1–IFNγ+ antitumor phenotype to a PD–1+IL17+ IFNγ− protumor phenotype.164 Exosomes secreted by γδT cells (γδ-T-Exos) can upregulate the expression of CCR5 on T cells to promote T cell migration.