Effect of Ex Vivo–Expanded Recipient Regulatory T Cells on Hematopoietic Chimerism and Kidney Allograft Tolerance Across MHC Barriers in Cynomolgus Macaques

Abstract

Background Infusion of recipient regulatory T cells (Treg) promotes durable mixed hematopoietic chimerism and allograft tolerance in mice receiving allogeneic BMT with minimal conditioning. We applied this strategy in a Cynomolgus macaque model. Methods CD4+CD25high Treg that were polyclonally expanded in culture were highly suppressive in vitro and maintained high expression of FoxP3. Eight monkeys underwent nonmyeloablative conditioning and MHC-mismatched BMT with or without Treg infusion. Renal transplantation (from the same BMT donor) was performed 4 months post-BMT without immunosuppression to assess for robust donor-specific tolerance. Results Transient mixed chimerism, without significant T cell chimerism, was achieved in the animals that received BMT without Treg (N=3). In contrast, the 2 of 5 recipients of Treg + BMT that were evaluable displayed chimerism in all lineages, including T cells, for up to 335 days post-BMT. Importantly, in the animal that survived long-term, >90% of donor T cells were CD45RA+CD31+, suggesting they were new thymic emigrants. In this animal, the delayed (to 4 months) donor kidney graft was accepted >294 days without immunosuppression, whereas non-Treg BMT recipients rejected delayed donor kidneys within 3-4 weeks. Early cytomegalovirus reactivation and treatment was associated with early failure of chimerism, regardless of Treg administration. Conclusions Our studies provide proof-of-principle that, in the absence of early CMV reactivation (and BM-toxic antiviral therapy), co-transplantation of host Treg can promote prolonged and high levels of multilineage allogeneic chimerism and robust tolerance to the donor.

Characterization, biology, and expansion of regulatory T cells in the Cynomolgus macaque for preclinical studies

“…One Treg line with high FoxP3 expression (80%) showed a low percentage of TSDR demethylation, possibly reflecting two peaks of FoxP3 expression (Table 2; Line 2). 14 In addition, in two cell lines that were studied over time, we observed a decrease in the TSDR demethylation in association with a decrease in FoxP3 expression and suppressive capacity ( Figure 6C).…”

Mechanisms of Mixed Chimerism-Based Transplant Tolerance

“…In efforts to convert a transient chimerism protocol to durable chimerism without relying on GVH reactivity in a preclinical model, we are exploring the addition of expanded polyclonal recipient Treg infusion in NHP and have indeed observed prolongation of mixed chimerism in association with more robust allograft tolerance. Whereas the original NHP transient chimerism CKHCT protocol relies on the presence of a donor kidney in the early post-transplant period to promote tolerance, the prolonged chimerism achieved by the addition of expanded recipient Tregs allows acceptance of a donor kidney grafted as late as 4 months after the BMT, indicating a more robust form of tolerance than that induced by BMT alone [97]. The addition of donor-reactive Treg-enriched recipient cells to liver transplants dramatically increased the success rate of immunosuppressive drug weaning in a pilot study (clinical trial registration number: UMIN-000015789) [98].…”

Operational tolerance in kidney transplantation and associated biomarkers

“…As a result, they have not entered routine clinical practice to date. As detailed by Lombardi et al in the same issue of CEI, growing efforts are being undertaken by different groups to develop cellular therapies that may contribute to the achievement of more sustainable allograft tolerance [16].…”