dMMR/MSI-H tumors are also largely infiltrated by immune cells, in particular CD8+ and T-helper 1 (Th1) CD4+ lymphocytes expressing high levels of CTLA-4 and PD-1, whereas myeloid cells expressing the immune checkpoint ligands (PD-L1) are mainly located at the tumor-stroma interface [183,184,185]. The gene discussed is PDCD1; the disease is neoplasm.