Cancer Immunotherapy: Beyond Checkpoint Blockade.

Blocking antibodies to the immune checkpoint receptors or their ligands have revolutionized the treatment of diverse malignancies. Many tumors are recognized by adaptive immunity, but these adaptive responses can be inhibited by immunosuppressive mechanisms within the tumor, often through pathways outside of the currently targeted checkpoints. For this reason, only a minority of cancer patients achieve durable responses to current immunotherapies. Multiple novel approaches strive to expand immunotherapy's reach. These may include targeting alternative immune checkpoints. However, many investigational strategies look beyond checkpoint blockade. These include cellular therapies to bypass endogenous immunity and efforts to stimulate new adaptive antitumor responses using vaccines, adjuvants, and combinations with cytotoxic therapy, as well as strategies to inhibit innate immune suppression and modulate metabolism within the tumor microenvironment. The challenge for immunotherapy going forward will be to select rational strategies for overcoming barriers to effective antitumor responses from the myriad possible targets.