CD4 and cytomegalovirus infection: To determine the effect of CMV infection on the magnitude of the circulating CD4+CD27-CD28- T cells, we compared PBMC from 8 CMV-seronegative (CMV-neg) HIV-seronegative (HIV-neg) blood donors, 14 CMV-seropositive (CMV-pos) HIV-neg blood donors or young adult volunteers and 14 CMV-pos HIV-seropositive (HIV-pos) individuals (Fig 1).