Given that Flt3L/Rapa therapy resulted in reproducible longterm allograft survival in about 20% of recipients without immunosuppression ( Fig. 1A) , we thus employed adoptive transfer studies to characterize the cell subpopulations for sustained allograft survival. For this purpose, CD4 + T cells, CD8 + T cells, pDCs and total splenocytes were first isolated from long-term survival recipients, and then adoptively transferred into naive recipients. The mice were next transplanted with cardiac allografts as described. As shown in Figure 5 , transferred CD8 + T cells and pDCs exhibited the ability to prolong allograft survival. Unexpectedly, compared with CD8 + T cells and pDCs, adoptive transfer of CD4 + T cells failed to provide protection against allograft rejection.