Splenic CD4+ T cells isolated 7 weeks post-cGVHD induction were stimulated with APCs from B6Kd or BALB/c mice, and also an irrelevant 3rd party stimulator (CBA strain, H-2k). The percentage of proliferating cells within both donor and recipient

cells was measured by CFSE dilution and counterstaining for H-2Kd as described in Figure 5A. As auto-Treg cells completely prevented engraftment of donor T cells, it was not possible to perform this analysis. Application of indirect and direct allospecific Treg cells were able to significantly inhibit recipient T-cell hyperactivation associated with cGVHD (Fig. 5B). Although not statistically significant, higher recipient T-cell responses to allostimulation with Talazoparib 3rd party APCs compared with self-MHC or recipient allo-MHC APCs were detected in animals treated with Treg cells. Co-administration of Treg cells was also significantly effective at inhibiting donor T-cell hyperactivity (Fig. 5C). More importantly, analysis of donor T cells indicated that Treg cells were able to mediate allospecific regulation of transferred donor T cells, as a significantly higher donor T-cell proliferative response was detected upon challenge with 3rd Party APCs, compared HKI 272 with self-MHC or recipient allo-MHC APCs (Fig. 5C). Recipient T-cell hyperproliferation

correlated with hyperactivity as detected by the production of high levels of Type 1 and Type 2 cytokines IFN-γ, TNF-α, IL-6 and IL-10 (IL-1β and IL-12 were not elevated by cGVHD), which were all significantly inhibited by each Treg-cell line (Fig. 5D). In this study, we have explored the capacity of allospecific Treg cells to prevent cGVHD disease pathology and found that donor Treg cells with defined specificities for autologous-MHC antigen or alloantigen are equally effective at preventing Amylase cGVHD, but differ in mechanism. Disease prevention was effected through a combination of modulation of

donor cell engraftment and regulation of donor T-cell auto and alloreactivity. These mechanisms acted to block recipient B-cell and T-cell hyperactivity and restrict productive T-cell help to prevent generation of pathogenic autoantibodies. Amelioration of disease pathology by Treg cells also correlated with an inhibition of proinflammatory cytokine production associated with this model of SLE-cGVHD [33]. While cGVHD prevention by auto-Treg cells was mediated by inhibition of donor T-cell engraftment, allospecific Treg cells inhibited the proliferation and activity of alloreactive and autoreactive T-cell clones to mediate complete protection against cGVHD pathology, despite the sustained long-term engraftment of donor-derived T cells.