Ex Vivo Expanded Human Non-Cytotoxic CD8(+)CD45RC(low/−) Tregs Efficiently Delay Skin Graft Rejection and GVHD in Humanized Mice

Both CD4(+) and CD8(+) Tregs play a critical role in the control of immune responses and immune tolerance; however, our understanding of CD8(+) Tregs is limited while they are particularly promising for therapeutic application. We report here existence of highly suppressive human CD8(+)CD45RC(low/−) Tregs expressing Foxp3 and producing IFNγ, IL-10, IL-34, and TGFβ to mediate their suppressive activity. We demonstrate that total CD8(+)CD45RC(low/−) Tregs can be efficiently expanded in the presence of anti-CD3/28 mAbs, high-dose IL-2 and IL-15 and that such expanded Tregs efficiently delay GVHD and human skin transplantation rejection in immune humanized mice. Robustly expanded CD8(+) Tregs displayed a specific gene signature, upregulated cytokines and expansion in the presence of rapamycin greatly improved proliferation and suppression. We show that CD8(+)CD45RC(low/−) Tregs are equivalent to canonical CD4(+)CD25(high)CD127(low/−) Tregs for suppression of allogeneic immune responses in vitro. Altogether, our results open new perspectives to tolerogenic strategies in human solid organ transplantation and GVHD.