Negative immune regulation can result in the poor control of virus replication in chronic infections but is probably important to prevent tissue damage from chronic immune activation. Three recent studies have shown that programmed cell death (PD)-1 expression on T cells correlates with viral load in HIV infection, and that interrupting PD-1 signaling using an antagonistic antibody rejuvenates T-cell effector functions in vitro. These findings have important implications for potential therapies for chronic infection and, perhaps, for improved tumor immunity. Here, we discuss impending issues in the translation to clinical studies in light of recent adverse events with costimulatory antibody therapy.