Rived T cells in these BIBS39 cost tissues (Table 2 and Figure 2C,D). Surprisingly, despite the extremely poor T cell repopulation in lymphoid tissues in RagKO MCs, the levels of donor T cells in the liver of these mice were comparable to those of WT MCs (Figure 2E). However, unlike the WT MCs, in which almost all T cells were donor BM-derived, T cells in the liver of RagKO MCs were all DLI-derived (Table 2) and presumably long-term surviving alloreactive T cells. The data correlated well with the pathological findings (Figure 1D) in RagKO MCs.Both Donor BM-derived CD4 and CD8 T Cells Mediate Protection Against GVHD Induced by DLI in Established Mixed ChimerasThe potential role of donor BM-derived CD4 and CD8 T cells in regulation of DLI T cell alloresponses was assessed by comparing GVHD development among WT MCs, RagKO MCs, and MCs that were FCCP prepared by injection of syngeneic plus CD4KO (CD4KO MCs) or CD8KO (CD8KO MCs) allogeneic BMCs. Although significant differences were detected in the levels of CD4 and CD8 T cell subsets (Table 3), the overall T cell levels were comparable among these MCs prior to DLI (Figure 3A). Consistent with the results in Figure 1, DLI given at week 8 induced significantly more severe GVHD in RagKO MCs than in WT MCs (Figure 3B). Although CD4KO MCs showed more profound body weight loss starting at 5 weeks than WT MCs (p,0.01), these MCs had less severe GVHD, as shown by lowerIncreased Expansion and Survival of Donor DLI-derived Allogeneic T Cells in RagKO Mixed ChimerasWe also assessed the kinetics of recipient and donor T cells in peripheral blood of WT vs. RagKO MCs after DLI. In order to distinguish between donor BM- and DLI-derived T cells, MCs were prepared by injecting mixed TCD BMCs from BALB/c plus WT (CD45.2+) or RagKO (CD45.2+) B6 mice into lethallyDe Novo Donor BM-Derived T Cells Inhibit GVHDFigure 3. Both donor BM-derived CD4 and CD8 T cells are protective against GVHD in mixed chimeras receiving delayed DLI. Lethally (8 Gy) irradiated BALB/c mice were reconstituted with a mixture of TCD BALB/c plus WT (WT MC; n = 7), RagKO (RagKO MC; n = 6), CD4KO (CD4KO MC; n = 7), or CD8KO (CD8KO MC; n = 8) B6 BMCs 8 weeks before DLI from WT B6 donors. (A) Hematopoietic chimerism in WBCs measI can hear Kazured one week prior to DLI. (B) Survival (left) and body weight changes (right). doi:10.1371/journal.pone.0047120.gmortality and significantly improved body weight recovery than CD8KO (p,0.001 starting at 5 weeks after DLI) and RagKO (p,0.05 for the entire period of 
observation) MCs (Figure 3B). The survival rates and body weight changes were, in general, comparable between CD8KO and RagKO MCs, with the exception that the latter group showed significantly more severe body weight loss starting at 5 weeks after DLI (p,0.05). These results 1531364 indicate that both BM-derived CD4 and CD8 T cells mediate protection against DLI-induced GVHD, but the latter cell population is more effective.Depletion of Donor BM-derived T Cells in Established Mixed Chimeras after DLI Provokes GVHDAlthough lymphopenia at the time of DLI may potentially promote GVHD [8], RagKO MCs did not show lymphopenia compared to WT MCs at the time of DLI (Figure 1A ; Table 1). However, lymphopenia was detected at the later times in RagKO MCs when recipient BM-derived cells were eliminated (Table 1; Figure 2), suggesting that the continuous presence of donor BMderived T cells might be required to inhibit GVHD. To address this question, we assessed the effect of post.Rived T cells in these tissues (Table 2 and Figure 2C,D). Surprisingly, despite the extremely poor T cell repopulation in lymphoid tissues in RagKO MCs, the levels of donor T cells in the liver of these mice were comparable to those of WT MCs (Figure 2E). However, unlike the WT MCs, in which almost all T cells were donor BM-derived, T cells in the liver of RagKO MCs were all DLI-derived (Table 2) and presumably long-term surviving alloreactive T cells. The data correlated well with the pathological findings (Figure 1D) in RagKO MCs.Both Donor BM-derived CD4 and CD8 T Cells Mediate Protection Against GVHD Induced by DLI in Established Mixed ChimerasThe potential role of donor BM-derived CD4 and CD8 T cells in regulation of DLI T cell alloresponses was 
assessed by comparing GVHD development among WT MCs, RagKO MCs, and MCs that were prepared by injection of syngeneic plus CD4KO (CD4KO MCs) or CD8KO (CD8KO MCs) allogeneic BMCs. Although significant differences were detected in the levels of CD4 and CD8 T cell subsets (Table 3), the overall T cell levels were comparable among these MCs prior to DLI (Figure 3A). Consistent with the results in Figure 1, DLI given at week 8 induced significantly more severe GVHD in RagKO MCs than in WT MCs (Figure 3B). Although CD4KO MCs showed more profound body weight loss starting at 5 weeks than WT MCs (p,0.01), these MCs had less severe GVHD, as shown by lowerIncreased Expansion and Survival of Donor DLI-derived Allogeneic T Cells in RagKO Mixed ChimerasWe also assessed the kinetics of recipient and donor T cells in peripheral blood of WT vs. RagKO MCs after DLI. In order to distinguish between donor BM- and DLI-derived T cells, MCs were prepared by injecting mixed TCD BMCs from BALB/c plus WT (CD45.2+) or RagKO (CD45.2+) B6 mice into lethallyDe Novo Donor BM-Derived T Cells Inhibit GVHDFigure 3. Both donor BM-derived CD4 and CD8 T cells are protective against GVHD in mixed chimeras receiving delayed DLI. Lethally (8 Gy) irradiated BALB/c mice were reconstituted with a mixture of TCD BALB/c plus WT (WT MC; n = 7), RagKO (RagKO MC; n = 6), CD4KO (CD4KO MC; n = 7), or CD8KO (CD8KO MC; n = 8) B6 BMCs 8 weeks before DLI from WT B6 donors. (A) Hematopoietic chimerism in WBCs measI can hear Kazured one week prior to DLI. (B) Survival (left) and body weight changes (right). doi:10.1371/journal.pone.0047120.gmortality and significantly improved body weight recovery than CD8KO (p,0.001 starting at 5 weeks after DLI) and RagKO (p,0.05 for the entire period of observation) MCs (Figure 3B). The survival rates and body weight changes were, in general, comparable between CD8KO and RagKO MCs, with the exception that the latter group showed significantly more severe body weight loss starting at 5 weeks after DLI (p,0.05). These results 1531364 indicate that both BM-derived CD4 and CD8 T cells mediate protection against DLI-induced GVHD, but the latter cell population is more effective.Depletion of Donor BM-derived T Cells in Established Mixed Chimeras after DLI Provokes GVHDAlthough lymphopenia at the time of DLI may potentially promote GVHD [8], RagKO MCs did not show lymphopenia compared to WT MCs at the time of DLI (Figure 1A ; Table 1). However, lymphopenia was detected at the later times in RagKO MCs when recipient BM-derived cells were eliminated (Table 1; Figure 2), suggesting that the continuous presence of donor BMderived T cells might be required to inhibit GVHD. To address this question, we assessed the effect of post.
