It has been reported that DCs expanded by Flt3L only express low levels of costimulatory molecules, and therefore, they are able to delay allograft rejection in transplantation settings [25, 26] . In contrast to Flt3L or Rapa alone, our data show that Flt3L combined with low-dose of Rapa are more potent to expand DCs with tolerogenic characteristics. Moreover, short-term of low-dose Rapa exerts the effect to expand Tregs while to avoid side effect due to high-dose of Rapa.