University of California - San Diego Jan 3 2025 Since its discovery in the 1990s, "programmed cell death protein 1," or PD-1, has been regarded as a leading target in cancer treatments. A "checkpoint" receptor that often resides on the surface of immune system cells, the PD-1 molecule works as a type of off switch that keeps immune cells from attacking other cells. After its discovery, which revolutionized oncology and earned a 2018 Nobel Prize, researchers developed new drugs to block PD-1 and