CMV-specific T-cell expansion may constrict the T-cell repertoire. (A) Healthy individuals have diverse repertoire of T cells. In CMV-seropositive healthy individuals, there is a disproportionate accumulation of CMV-specific T cells compared with those of other specificities in young but especially in older subjects.⁶  (B) CMV-seropositive CLL patients have significantly increased proportions of CMV-specific T cells compared with age-matched controls which is even more striking in those who have received chemotherapy.¹  One hypothesis for the increased incidence of infections and decreased survival in both CMV-seropositive CLL patients and older humans is that T cells of other specificities (eg, VZV) may be lost through competition for growth factors and or survival niches in tissues.^6-8