We focus here on the CMV-specific CD8+ T-cell response, since firstly, T-cell immunity plays an important role in controlling CMV infection [7] and preventing symptomatic, disseminated CMV disease [8–10] and secondly, the frequency of CMV-specific T-cell responses is unusually high, on average 10% of the CD4+ and CD8+ T-cell memory compartments in adult peripheral blood [11]. The gene discussed is CD4; the disease is cytomegalovirus infection.