.....In this study T cell function and the composition of the T cell repertoire were analyzed in immunosuppressed renal transplant recipients of different age and CMV status in comparison to age- and CMV-matched controls. Independent of age and CMV status, the production of IL-2 and IFN-γ by T cells was decreased in the patient groups and autologous serum from patients was capable of inhibiting the proliferation of CD3+ T cells. CXCR5 expression on T cells was increased in patients versus controls reflecting reduced endogenous IL-2 signaling under immunosuppressive therapy. In CMV seronegative patients kidney transplantation and immunosuppressive therapy did not induce changes in the CD8+ T cell pool, but there was a moderate increase in CD4+ CD28- effector T cells when compared to age-matched controls. In contrast, latent CMV infection triggered a shift from early to late differentiated CD4+ and CD8+ T cells in patients and controls. This shift was most pronounced in elderly transplant patients under immunosuppressive therapy. In conclusion, our results demonstrate that immunosuppressive therapy following kidney transplantation is effective in patients older than 65 years. Latent CMV infection does, however, accelerate age-related changes in the T cell repertoire in elderly persons under immunosuppressive therapy. These patients should therefore be monitored with special care.