Unraveling the Crucial Roles of FoxP3+ Regulatory T Cells in Vascularized Composite Allograft Tolerance Induction and Maintenance

Abstract

Background: The role of regulatory T cells (Treg) in tolerance induction of vascularized composite allotransplantation (VCA) remains unclear. This study was designed to examine characteristics of Treg after VCA, and their capacity to rescue allografts from rejection. Methods: Osteomyocutaneous allografts were transplanted from Balb/c to C57BL/6 mice. All mice received costimulatory blockade and a short course of rapamycin. To elucidate the role of Treg for tolerance induction, Treg depletion was performed at postoperative day (POD) 0, 30 or 90. To assess capacity of Treg to rescue allografts from rejection, injection of 2x10⁶ Treg isolated from tolerant mice was applied. Results: 80% of VCA recipient mice using costimulatory blockade and RPM regimen developed tolerance. The tolerant recipients had higher ratio of circulating Treg to effector T cells and elevated IL-10 at POD 30. A significantly higher rejection rate was observed when Treg were depleted at POD 30. But Treg depletion at POD 90 had no effect on tolerance. Treg from tolerant recipients showed stronger suppressive potential, and the ability to rescue allografts from rejection. Furthermore, transplanted Treg-containing skin grafts from tolerant mice delayed rejection elicited by adoptively transferred Teff to Rag2^-/^- mice. Conclusion: Circulating Treg are crucial for inducing VCA tolerance in early posttransplant phase and allograft-residing Treg may maintain the tolerance. Treg may therefore serve as a potential cellular therapeutic to improve VCA outcomes.