A protein called PD-1, which is found on immune cells called CD8+ T cells, plays a key role in controlling infection with the Epstein-Barr virus, according to a study published May 30 in the open-access journal PLOS Pathogens by Christian Münz of the University of Zurich, and colleagues. The results from this study indicate that monitoring PD-1 signaling during future vaccination and immunotherapy studies may inform patient outcomes.