PD-1 (programmed death-1 receptor): Unabbreviated, it sounds like an Xbox villain. But PD-1 is hardly a fantasy scoundrel. During any bodily infection, this protein keeps the immune system from attacking healthy cells while targeting infected ones. Recently, however, scientists found that PD-1 can sometimes play the heavy with HIV: It may hamper immune cells from tackling the virus. Can researchers crack the PD process and ignite cells into HIV action? We need the answer—and we need it PDQ.