PDCD1 and neoplasm: PD-1, a PD-L1 receptor, has been known to be expressed at the surface of a number of immune cells including activated T cells, natural killer (NK) cells, B cells, macrophages, dendritic cells, and lymphocytes (T cells and B cells) with regulatory phenotypes (Tregs and Bregs) 71-73; therefore, the tumor microenvironment consisting of these PD-1-expressing immune cells in the syngeneic mouse model may be beyond the capacity of NCT-80 to enhance antitumor immunity by suppressing PD-L1 expression.