Several DC subsets have been reported to promote tolerance induction [4, 27] . The CD11c + CD8a + DC subset could promote peripheral self-tolerance and prolong the survival of cardiac allografts in rodents [28, 29] . More recently, pDC precursors have been identified and are implicated in the induction of allogeneic Tcell hyporesponsiveness [9, 30] . In line with these findings, our phenotypic analysis of splenic DCs in the recipient mice revealed that Flt3L/Rapa treatment increased the proportion of DC subsets with regulatory effect such as CD11c + CD8a + DCs and pDCs. It is known that immature DCs not only fail to prime T cells effectively, but also serve to promote tolerance induction [31] . Our studies show that Flt3L combined with Rapa could block DC maturation and increase the ratio of CCR9 + pDCs, while CCR9 + pDCs are immature pDCs with potency to suppress antigen-specific immune responses both in vitro and in vivo [18] .