CD4 and infection: CD4 CTL developed in response to cytomegalovirus (CMV) (7, 8), human immunodeficiency virus (HIV) (9, 10), and Epstein–Barr virus (EBV) (11, 12) infection in humans as well as lymphocytic choriomeningitis virus (LCMV) (13, 14) and mouse gammaherpes virus (15, 16) in mice.