Donor Specific Regulatory T-Cell Expansion Is Associated With the Maintenance of Allograft Tolerance Induced By Transient Mixed Chimerism.

Abstract

Listen

Translate article

Background: We have previously reported successful induction of solid organ allograft tolerance in nonhuman primates (NHP) via a mixed chimerism approach. Since these recipients achieved tolerance after only transient hematopoietic chimerism, peripheral mechanisms are considered to be operative in the maintenance of tolerance. In the current study, we evaluated the role of donor specific regulatory T cells (Treg) in NHP that achieved long-term allograft survival. Method:Nine cynomolgus monkeys that achieved long-term (>360 days) allograft survival without maintenance immunosuppression [kidney (n=6), kidney/heart (n=2), and lung (n=1)] were investigated. Three recipients [heart alone (n=2) and kidney (n=1)] that received the same conditioning regimen but rejected their allografts after discontinuation of immunosuppression were evaluated as controls. Anti-donor and anti-third party responses in these recipients were evaluated by ELISPOT (INF-g) and expansion of donor specific Tregs was evaluated by MLR against donor and third party cells with CFSE/Foxp3 staining. Expanded T cells were sorted and their suppressive function was evaluated by inhibition of T cell activation by CD3/CD28 beads. Results: Donor-specific hyporesponsiveness was observed with ELISPOT in long-term survivors, but substantial anti-donor responses in recipients with rejection. (Fig.1) Foxp3+ cells proliferated significantly more after MLR with donor PBMC than when stimulated with self or third party PBMC in 5/7 long-term survivors. (Fig.2 representative flow cytometric analysis).Figure: No Caption available.Sorted Treg dominant cells expanded after MLR with donor cells showed suppressive effects in T cell activation. In contrast, there was no proliferation of FoxP3+ cells observed after MLR with donor cells in recipients with rejection. Conclusion: These data suggested that Tregs play a critical role in the maintenance of long-term allograft tolerance following induction of transient mixed chimerism.