PDCD1 and neoplasm: I-E TIMEs are filled with immune cells but lack cytotoxic lymphocytes (CTLs) in the tumor core, while I-I TIMEs are significantly infiltrated with CTLs expressing programmed cell death 1 (PD-1), and leukocytes and tumor cells within I-I TIMEs are characterized by the expression of immune-dampening PD-1 ligand (PD-L1).