Although the elderly represents a rapidly growing population among transplant recipients, age-specific aspects have not been considered sufficiently in clinical trials. Moreover, age-specific effects of immunosuppressive therapies remain poorly understood.Methods
Here, we assessed the impact of rapamycin on alloimmune responses in old recipients using a fully major histocompatibility complex–mismatched murine transplantation model.Results
Old untreated recipients displayed a prolonged skin graft survival compared to their young counterparts, an observation that confirmed data of our previous experiments. Rapamycin led to a significant prolongation of graft survival in both young and old recipients. However, graft survival was age-dependent and extended in old versus young recipients (19 days vs 12 days, P = 0.004). This age-specific effect was not linked to changes in frequencies or subset composition of either cluster of differentiation (CD)8+ or CD4+ T cells. Moreover, antiproliferative effects of rapamycin on CD8+ and CD4+ T cells as assessed by in vivo bromdesoxyuridine incorporation were comparable and age-independent. In contrast, the systemic production of IL-10 was markedly elevated in old recipients treated with rapamycin. In parallel to this shift in cytokine balance, IFN-γ/IL-10 double-positive regulatory type 1 cells emerged during T helper type 1 differentiation of old T helper cells in presence of rapamycin. Similarly, CD4+IFN-γ+IL-10+ cells expanded among Foxp3-negative cells after in vivo treatment of old recipients with rapamycin.Conclusions
Our results highlight novel aspects of age-dependent immunosuppressive effects of rapamycin, with relevance for age-specific immunosuppressive regimens.