Donor-specific cytotoxic hyporesponsiveness associated with high interleukin-10 messenger RNA expression in cardiac allograft patients

Background: After transplantation, CD4(+)CD25(+)FOXP3(+) and interleukin (IL) 10-producing regulatory cells might regulate immune responses toward donor antigens. In this study, we determined whether cardiac allograft recipients show donor-specific hyporesponsiveness and studied the underlying mechanisms. Methods: We analyzed the donor-specific T-cell responses by mixed lymphocyte reactions and limiting dilution assays to define whether cardiac allograft recipients (n = 21) show proliferative and cytotoxic hyporesponsiveness to donor antigens long after transplantation (range, 1.5-7 years). The mechanisms controlling immune responses, that is, FOXP3(+)/GITR(+) T cells, and IL-10-producing cells, were studied by quantitative real-time polymerase chain reaction. Results: In the presence of a proliferative response to donor antigens, no cytotoxic responsiveness could be measured in a number of patients in the absence (73%) and presence of exogenous IL-2 (29%), IL-15 (31%), and IL-15 plus IL2R alpha blockade (88%). Overall, the cytotoxic response to donor cells was significantly lower than the reactivity to third-party cells after the addition of IL-2 (p = 0.004) and IL-15 plus IL2R alpha blockade (p < 0.001). After donor stimulation, the peripheral blood mononuclear cells expressed higher messenger RNA (mRNA) levels of IL-10, but not of FOXP3 or GITR, than after third-party stimulation (p = 0.003). Moreover, the IL-10 mRNA expression was inversely correlated with the donor-specific cytotoxic responsiveness (p = 0.01). Conclusions: A significant proportion of patients showed donor-specific cytotoxic hyporesponsiveness long after heart transplantation, which was associated with high mRNA levels of IL-10 but not of FOXP3 or GITR. This observation suggests that IL-10-producing cells participate in the donor-specific cytotoxic hyporeactivity.