In particular, studies in transplantation patients (Sester et al., 2001; Einsele et al., 2002; Peggs et al., 2003; Gratama et al., 2008) and in adults with primary human CMV (HCMV) infections (Rentenaar et al., 2000; Gamadia et al., 2003; Lilleri et al., 2008b) have confirmed the vital role that HCMV specific CD4+ T cells play in controlling symptomatic disease. Here, CD4 is linked to infection.