PD-1 is among key receptors conveying an inhibitory signal to T cells. Over last decade, PD-1 and its ligand PD-L1 draw much attention, due to high efficiency of therapy with PD-1/PD-L1 inhibitors in a number of malignant disorders. In this review article, we aimed to summarize current data on the PD-1 receptor expression in different immune cell subpopulations, like as its potential role in cellular antitumor response. Along with molecular structure and receptor-ligand interactions, the main attention is drawn to special features of PD-1 expression on the СD8+ T cell population which plays a key role in antitumor immune response. Some common changes of PD-1 expression levels during the cell activation and differentiation are considered, mainly, for the CD8+ T cells. Moreover, we discuss PD-1 expression on the surface of regulatory T cells, NK cells, invariant NKT cells, myeloid suppressor cells which may play an important role for anticancer immune response. When performing current therapy with PD-1/PD-L1 inhibitors, the mentioned populations may influence development of resistance to this mode of immune treatment. Therefore, a number of recent studies are directed for studying the PD-1/PD-L1 involvement into the immune regulation and to test prospects of their usage as biomarkers for clinical immune checkpoint therapy.