A very low thymus function identifies patients with substantial increased risk for long-term mortality after kidney transplantation

BACKGROUND: End-stage renal disease is associated with premature ageing of the T cell immune system but inter-individual variation is substantial. The hypothesis was tested that advanced immunological T cell ageing assessed by peripheral T cell differentiation increases the long-term mortality risk after renal transplantation. RESULTS: Circulating T cells of 211 recipients of a kidney from a living donor were analyzed before and in the first year after transplantation. The number of CD31-positive naive T cells (as a marker for recent thymic emigrants) and the differentiation status of the memory T cells was assessed. Thirty recipients died during follow-up of at least 5 years. Absolute numbers of naive CD4(+) (living:258 cells/μl vs. deceased:101 cells/μl, p < 0.001) and naive CD8(+) T cells (living:97 cells/μl vs. deceased:37 cells/μl, p < 0.001) were significantly lower in the deceased group prior to transplantation. In a multivariate proportional hazard analysis the number of naive CD4(+) T cells remained associated with all-cause mortality (HR 0.98, CI 0.98–0.99, p < 0.001). The low number of naive T cells in the deceased patient group was primarily caused by a decrease in recent thymic emigrants (i.e. less CD31(+) naive T cells) indicating a lowered thymus function. In addition, the physiological age-related compensatory increase in CD31(−) naïve T cells was not observed. Within the first year after transplantation, the number and characteristics of naive T cells remained stable. CONCLUSIONS: A severe reduction in circulating naïve T cells because of a decrease in recent thymic emigrants is highly associated with all-cause mortality after renal transplantation.