Programmed death 1 immune checkpoint inhibitors.

Programmed death 1 (PD-1) is an immune checkpoint that provides inhibitory signals to the immune system in order to modulate the activity of T cells in peripheral tissues and maintain self-tolerance in the setting of infection and inflammation. In cancer, the immune checkpoints are exploited so that the tumor cells are able to evade the immune system. Immune checkpoint inhibitors are a type of cancer immunotherapy that targets pathways such as PD-1 in order to reinvigorate and enhance the immune response against tumor cells. The US Food and Drug Administration (FDA) has approved 2 PD-1 inhibitors, nivolumab and pembrolizumab, and several others are under investigation. Although PD-1 inhibitors have demonstrated activity in many different types of malignancies, FDA approval has been granted only in melanoma and in non-small cell lung cancer (NSCLC). Identifying biomarkers that can predict response to PD-1 inhibitors is critical to maximizing the benefit of these agents. Future directions for PD-1 inhibitors include investigation of combination therapies, use in malignancies other than melanoma and NSCLC, and refinement of biomarkers.