Mesenchymal stem cells in combination with low-dose rapamycin significantly prolong islet allograft survival through induction of regulatory T cells.

We previously demonstrated the protective effect of MSCs in an adaptive transfer mouse model. However, their therapeutic potential in an allogeneic immunocompetent setting mimicking clinical context of islet transplantation remained unknown. The aim of this study was to determine whether MSCs therapy, either by itself, or combined with Rapamycin could benefit the allograft survival of fully MHC-mismatched mouse islet transplant. Combination therapy of MSCs and low-dose Rapamycin significantly prolonged the survival of islet allografts, whereas treatment of MSCs, or Rapamycin alone, had no impact. Interestingly, this protective effect was associated with an induced expansion of regulatory T cells in islet grafts and draining lymph nodes, a skewed T-cell differentiation toward immunotolerance, and a profound suppression of alloreactivity against donor antigen. Our study suggests that a combination therapy of MSCs and low-dose Rapamycin can prolong the survival and preserve the function of islet allograft in the MHC-mismatched mouse model of islet transplantation.