Rapamycin has been shown to inhibit the up-regulation of maturation markers expressed by DCs [15] , while immature DCs have been demonstrated with capability to prolong allograft survival [16, 17] . In line with this notion, Flt3L combined with Rapa significantly blocked CD11c + DC maturation as manifested by the decreased CD40, CD80 expression (Fig. 2B ). Since CCR9 + pDCs had previously been reported to be potent inducers for Tregs [18] , we then investigated whether CCR9 + pDCs are implicated in the induction of allograft tolerance. Indeed, recipients treated with Flt3L and low-dose of Rapa displayed a significant increase for CCR9 + pDCs as compared with those recipients treated with Flt3L or Rapa alone or other groups (Fig. 2C ).