PDCD1 and neoplasm: Since the development of lymph-node like vasculature within tumors is induced by activated T cells and NK cells via secretion of lymphotoxin alpha 3 and interferon gamma [43], PD-1/CTLA-4 blockade may increase the number of HEV structures within tumors by enhancing T cell activation, provided that some T cells are already infiltrating the tumor prior to treatment.