The emergence of cancer immunotherapies, drugs that activate and enlist the immune system to fight cancer, has emerged as a promising approach to combat the disease in its many forms. Lawrence Fong, co-leader for the Cancer Immunotherapy Program at the University of California, San Francisco, stands at the intersection of several initiatives involving UCSF to better understand the immune system’s response to cancer and develop more effective drugs in the battle against it. We spoke to Fong about the potential of immunotherapies, the various efforts underway at UCSF, and what we known and don’t know about the immune system.