Rapamycin promotes the expansion of CD4(+) Foxp3(+) regulatory T cells after liver transplantation.

Rapamycin can promote the generation and homeostasis of CD4(+)Foxp3(+) regulatory T cells (Tregs) both in vitro and in vivo. The mechanisms by which rapamycin mediates this effect are poorly defined. In this study, we characterized CD4(+)Foxp3(+) Tregs in liver grafts and peripheral blood following rapamycin treatment using a syngeneic liver transplant model. Orthotopic liver transplantation was performed from Lewis (LEW) to LEW rats. In the first 2 weeks the percentage of CD4(+)Foxp3(+) Tregs was increased in the liver grafts and blood only among the rapamycin group compared with control group. Conversely, the percentage of CD4(+)Foxp3(+) Tregs in the liver graft and blood decreased in the cyclosporine group. In normal rats, rapamycin did not impact the generation of CD4(+)Foxp3(+) Tregs in the thymus. Thus, rapamycin can significantly enhance the percentages of CD4(+)Foxp3(+) Tregs in the thymus and periphery, indicating that rapamycin favors Tregs expansion and may suppress other CD4(+) T cells.