01). To further validate the in vivo findings in our aGvHD model, we also tested the functional capacity of our aTreg cells to prolong allogeneic skin graft survival. As depicted in Figure 5, 1 day prior to transplantation,

C57BL/6Rag–/– mice were reconstituted with 2 × 105 CD4+CD25+ aTreg cells isolated from primary cultures together with 1 × 105 CD8+ and 1 × 105 CD4+CD45RBhigh T cells. As a control, we included a group receiving Teff cells only. aCD4+TGF-β+RA aTreg cells prolonged graft survival compared to mice reconstituted with aTreg cells from untreated or aCD4-only treated cultures (*p ≤ 0.5) (Fig. 5B). In contrast, DAPT purchase aCD4+Rapa aTreg cells did not perform better than aTreg cells obtained from aCD4-only treated cultures. Interestingly, animals receiving aCD4+TGF-β+RA aTreg cells showed also an improved recovery and weight gain after transplantation compared with mice receiving aTreg cells from all other groups (Fig. 5C). Here, we present an optimised protocol for in vitro generation of murine aTreg cells with improved in vivo function in two independent models of transplantation tolerance. This could be accomplished by addition of TGF-β+RA or Rapa Erlotinib purchase to our previously described aCD4-mAb Treg-cell expansion protocol [16]. Notably, the optimised aTreg-cell expansion

protocol increased aTreg-cell frequencies and absolute aTreg-cell counts while reducing the number of undesired Teff cells. The aTreg cells were predominantly generated by an expansion of nTreg cells. Helios and Neuropilin-1 expression levels,

stability of the aTreg phenotype, and the suppressive in vitro and in vivo function exceeded in our novel aCD4+TGF-β+RA Treg protocol over all other protocols including addition of Rapa. Several protocols for the generation alloreactive T cells with regulatory function, shown to suppress anti-donor immune responses, have been described in addition to our anti-CD4mAb-based enough protocol. These include IL-10-mediated induction of Tr1 cells [28, 29], stimulation with allogeneic APCs or peptide-pulsed APCs in the presence of TGF-β [30-32], ex vivo costimulatory blockade [33] or IFN-γ-conditioned stimulation with alloantigen [34, 35]. In addition, vitamin D or Rapa-conditioned tolerogenic DCs have been used to generate T cells with alloreactive regulatory functions [36-38]. It will be of importance in future investigations which of these strategies is the most superior one. It was also shown that Rapa induces human Treg cells from conventional CD4+ T cells in vitro [39] as well as in vivo [40, 41]. In our experiment, Rapa increased the generation of murine aTreg cells only in combination with aCD4. The ability of TGF-β to induce Treg cells has been known for a long time [42]. Wan and Flavell showed that TGF-β is essential to keep the functionality of CD4+CD25+Foxp3+ in the periphery and that TGF-β has the potential to induce Foxp3 in naïve cells [43].