PD-1 signaling and inhibition in AML and MDS.

Acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) are clinically and molecularly heterogeneous clonal myeloid disorders with a poor prognosis especially in the relapsed refractory setting and in patients above the age of 60. While allogeneic hematopoietic stem cell transplantation (ASCT) is a potentially curative approach, high relapse, morbidity, and mortality rates necessitate the development of alternative therapies. Immune checkpoint inhibitors unmask tumoral immune tolerance and have demonstrated efficacy in the treatment of chemotherapy-resistant hematologic and solid malignancies. The rationale for the investigation of those agents in AML and MDS is supported by an observed increased expression of programmed cell death 1 protein (PD-1) and ligand 1 (PD-L1) in the hematopoietic microenvironment of AML and MDS, and its association with low TP53 and a poor prognosis. Early clinical experience in combination with a hypomethylating agent has shown encouraging responses; however, larger clinical trials are needed to determine the role of checkpoint inhibition in myeloid malignancies.