Targeting the PD-1/PD-L1 axis in multiple myeloma: a dream or a reality?

The programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway is a negative regulator of immune activation that is upregulated in multiple myeloma and is a critical component of the immunosuppressive tumor microenvironment. Expression is increased in advanced disease and in the presence of bone marrow stromal cells. PD-1/PD-L1 blockade is associated with tumor regression in several malignancies, but single-agent activity is limited in myeloma patients. Combination therapy involving strategies to expand myeloma-specific T cells and T-cell activation via PD-1/PD-L1 blockade are currently being explored.