PDCD1 and malignant colon neoplasm: As shown in Figure 1(A,B), the single-cell RNA sequencing of tumor tissues derived from 23 patients with colon cancer demonstrated that NKG2A was predominantly expressed in CD8+ T cells (93%), CD4+ T cells (3.7%), and NK cells (1.7%), whereas PD-1 was expressed in CD4+ T cells (46.3%), CD8+ T cells (39.5%), Tregs (8.2%), and NK cells (2.9%).