PD-1/PD-L1 as a prognostic factor in leukemia

PD-1 receptor is a component of the immune system that is recognized as a negative regulator of immune responses together with its ligand (PD-L1). In this study, we review the role of the immune system in leukemia cells through PD-1 and its ligand. Relevant literature was identified by a Pubmed search (1994-2017) of English-language papers using the terms PD-1, PD-L1, leukemia, and prognosis. PD-1 is an inhibitory receptor of CD28 family. Although initially introduced as a driving factor of apoptosis in the activated T cells, pre-clinical studies revealed the importance of this molecule as a checkpoint in ambient tolerance of the immune system. The ligand of this molecule is widely expressed on malignant cells in leukemia and inhibits the cytotoxic T cells. Therefore, targeting PD-1/PD-L1 can sensitize the malignant cells to chemotherapy and increase patient's survival as a therapeutic approach. Recently, immunotherapy has shown promising results in pre-clinical studies using antibodies against PD-1/PD-L1 in different cancers, and it is hoped that the application of these antibodies in combination with other treatments (including chemotherapy) could inhibit leukemia cells and improve the patient's conditions.