Cytomegalovirus seropositivity has an impact on the differentiation state of CD8+ T cells during ageing (Fig.1) and a previous report showed that chronic CMV infection also reduced the telomere length of the CD8+ T-cell pool.26 We therefore stratified young and old individuals on the basis of their CMV status and investigated telomere length in the four CD45RA/CD27 defined subsets. Here, CD8A is linked to cytomegalovirus infection.