HAVCR2 and neoplasm: Tumor cells can escape the killing of tumor cells by T cells through downregulating MHC and upregulating the expression of inhibitory receptors such as PD-L1, CTLA-4, LAG-3, TIM-3 and TIGIT (32–34), and blocking the binding of these inhibitory receptors to ligands can restore T-cell anti-tumor activity (35).