PDCD1 and neoplasm: As we all know, there were various phenotypes on the surface of MAIT cells, in addition to CD4, CD8, IL-12 receptors and IL-18 receptors, also includes chemokine receptors CCR5, CCR6 and CXCR6 [19, 24], and immune-related molecules NKG2D, PD-1 and CTLA-4 [19], etc. Some molecules are important in tumor immunity.