Treg-Therapy Allows Mixed Chimerism and Transplantation Tolerance Without Cytoreductive Conditioning

Abstract

Establishment of mixed chimerism through transplantation of allogeneic donor bone marrow (BM) into sufficiently conditioned recipients is an effective experimental approach for the induction of transplantation tolerance. Clinical translation, however, is impeded by the lack of feasible protocols devoid of cytoreductive conditioning (i.e. irradiation and cytotoxic drugs/mAbs). The therapeutic application of regulatory T cells (Tregs) prolongs allograft survival in experimental models, but appears insufficient to induce robust tolerance on its own. We thus investigated whether mixed chimerism and tolerance could be realized without the need for cytoreductive treatment by combining Treg therapy with BM transplantation (BMT). Polyclonal recipient Tregs were cotransplanted with a moderate dose of fully mismatched allogeneic donor BM into recipients conditioned solely with short-course costimulation blockade and rapamycin. This combination treatment led to long-term multilineage chimerism and donor-specific skin graft tolerance. Chimeras also developed humoral and in vitro tolerance. Both deletional and nondeletional mechanisms contributed to maintenance of tolerance. All tested populations of polyclonal Tregs (FoxP3-transduced Tregs, natural Tregs and TGF-β induced Tregs) were effective in this setting. Thus, Treg therapy achieves mixed chimerism and tolerance without cytoreductive recipient treatment, thereby eliminating a major toxic element impeding clinical translation of this approach.

Alloreactive regulatory T cells generated with retinoic acid prevent skin allograft rejection

“…Our results show that allogeneic stimulation of naive T cells in the presence of RA consistently induced the de novo differentiation of Treg cells with an unbiased homing potential, presenting effective in vivo suppressive abilities in a skin allograft model. Several protocols have been developed to generate Treg cells; some are designed to produce polyclonal Treg cells by stimulating naive T cells with anti-CD3 in anti-inflammatory conditions [55,56], while others have expanded selected thymus-derived Treg cells [29,30]. Although these Treg cells can be used to produce tolerance to a transplanted tissue, they cannot be used for cellular therapy in humans due to the lack of specificity.…”

Immunological Considerations for Inducing Skin Graft Tolerance

“…Skin graft (Chai et al, 2005) Foxp3 transduced expression in naïve CD4 + CD25 _ Skin graft (Banuelos et al, 2004) DST and anti-CD154 in CD4, CD8, or CD25 depleted skin and islet graft recipients Skin graft (Sanchez-Fueyo et al, 2007) Wt or Class II -mice Skin graft Mixed chimerism (Pilat et al, 2010) Rapamyacin and costimulation blockade;…”

Deletional and regulatory mechanisms coalesce to drive transplantation tolerance through mixed chimerism

“…Recently, two methods have been reported to successfully eliminate myelosuppression from recipient conditioning. One involves the coupling of Treg-cell therapy with the mixed chimerism strategy [40]. Studies from our group established that the administration of polyclonal recipient Treg cells at the time of transplantation of a conventional dose of fully allogeneic donor BM induces multilineage mixed chimerism in murine recipients conditioned solely with a short course of costimulation blockers (CTLA4Ig, anti-CD40L) and an mTOR inhibitor (rapamycin) ( Fig.…”

“…Along these lines, regulation is critical in the NHP setting and in clinical trials (see below) in which permanent mixed chimerism (which is a prerequisite for maintaining continuous central deletion) is not achieved [69]. Combining Treg-cell therapy with noncytoreductive BMT actively has been shown to potentiate regulatory mechanisms [40,41]. Clonal deletion has been shown with such a Treg-cell chimerism regimen, but is less pronounced, while regulation is predominant throughout follow up.…”

“…Studies from our group established that the administration of polyclonal recipient Treg cells at the time of transplantation of a conventional dose of fully allogeneic donor BM induces multilineage mixed chimerism in murine recipients conditioned solely with a short course of costimulation blockers (CTLA4Ig, anti-CD40L) and an mTOR inhibitor (rapamycin) ( Fig. 1) [40]. Relatively low chimerism levels were observed with this protocol, but transplantation of BM retrieved from chimeras into secondary BMT recipients demonstrated that HSC engraftment had been achieved in the primary BMT recipients [40].…”