Liver transplantation remains the only treatment for terminal liver diseases. However, immunosuppressive drugs required for allograft acceptance are toxic and may be responsible for severe side effects. Modulating the immune system to induce tolerance is a promising approach to reduce immunosuppressive regimen. More particularly, promoting natural CD4⁺ CD25⁺ FoxP3⁺ Tregs could be crucial in achieving tolerance. Contrary to calcineurin inhibitors, reports indicate that mTOR inhibitors may have a positive impact on Tregs.

Here we present the first randomized prospective clinical study where Tregs levels from liver transplanted patients receiving either tacrolimus or everolimus were monitored for 6 months, starting from the day of transplantation. A total of 30 patients from four centers were monitored. Blood samples were obtained at day 0, day 14, one month, three months and six months post-transplantation. Flow-cytometry immunophenotyping of Tregs (CD4⁺ CD25⁺ CD127⁻ FoxP3⁺) and functional assays with Tregs were performed to assess their immunosuppressive capacity. Levels of Tregs were significantly reduced after one month of standard tacrolimus-based immunosuppressive regimen (p<0.05). Four months after conversion, levels of Tregs from patients treated with everolimus was significantly higher than patients under tacrolimus (p<0.02). Functional assays demonstrated that Tregs conserved their capacity to suppress the proliferation of activated PBMC.