Background: Vitamin C-treated induced-regulatory T cells (V-iTreg) have superior in-vitro suppressive activity and stability of Foxp3 expression to conventional iTregs (C-iTreg); however, the role of V-iTreg in allograft rejection in either wild type (WT) or vitamin C-deficient (Gulo knockout, Gulo-KO) mice has not been shown.
Methods: Tregs were induced from non-Tregs using TGF-β and IL-2 in the presence or absence of Vitamin C. In-vitro suppression assays for T cell proliferation were performed using C- and V-iTreg under polyclonal or alloantigen stimulation. Heterotrophic heart transplantation was performed from BALB/C mice to WT or Gulo-KO C57BL/6J mice after adoptive transfer of C- or V-iTregs with or without Vitamin C supplementation.
Results: Efficiency of conversion to iTregs was similar between C- and V-iTregs in both WT and Gulo-KO mice. V-iTregs from both WT and Gulo-KO mice showed better in-vitro stability of Foxp3 expression than C-iTregs, although there was no difference between WT V-iTregs and Gulo-KO V-iTregs. Furthermore, V-iTregs from WT or Gulo-KO mice suppressed in-vitro proliferation of T cells to greater extent than C-iTregs. Following adoptive transfer of iTregs to WT or Gulo-KO mice, V-iTregs maintained higher expression of Foxp3 than C-iTregs. Adoptive transfer of either C- or V-iTregs prolonged heart allograft survival in WT mice; however, there was no significant difference between C- and V-iTreg groups. Similarly, both C- and V-iTreg prolonged heart allograft survival in Gulo-KO mice to similar extent. Supplementation of low- or high-dose Vitamin C did not induce significant change in heart allograft survival in Gulo-KO recipients that had received either C-iTregs or V-iTregs.
Conclusions: V-iTreg do not have significantly better suppressive effects on heart allograft survival than C-iTregs in either WT or Vitamin C-deficient recipients despite their better in-vitro suppressive activity.