PDCD1 and neoplasm: Besides, Wu et al. have demonstrated that TIGIT can be overexpressed in tumor-infiltrating CD8+ and CD4+ T-cells, and there is a remarkable relationship between TIGIT with PD-1, LAG-3, and TIM-3 in the tumor-infiltrating CD4+ and CD8+ T-cells in animal models of head and neck squamous cell carcinomas [15].