Adoptive transfer of polyclonal CD4+CD25+ regulatory T cells (Tregs) can tolerize transplantation alloresponses and prevent lethal acute graft-versus-host disease (GVHD). For optimal suppressive function, Tregs need to be activated via their T-cell receptors (TCR), but the antigen specificity of wild type Tregs remains elusive, and therefore controlling potency and duration of Treg activity in the transplantation setting remains not feasible. In this study, we used a murine lethal acute GVHD model system to test the hypothesis that specifically activated, antigen-specific Tregs induced by foxp3 transduction could suppress the response of T effector cells to alloantigens in vitro and prevent GVHD in vivo more effectively than polyclonal Tregs.
We found that the suppressive potential of TCR transgenic (Tg), antigen-specific CD4+CD25+ Tregs was much greater than that of polyclonal Tregs in vitro and in vivo. When activated by their specific peptide antigen, Tg Tregs protected 95% of recipients from lethal GVHD even at ten times lower doses than polyclonal Tregs. To facilitate the acquisition of larger numbers of antigen-specific Tregs, we transduced naive CD4+CD25- cells with foxp3, and observed that these foxp3-induced Tregs also suppressed alloresponses in vitro and prevented GVHD in vivo as effectively as naturally derived CD4+CD25+ Tregs. To enhance translational feasibility, we then used an antigen-specific CD4 Th1 T-cell clone as a source of Tregs after transduction with foxp3, and found those Tregs to effectively prevent GVHD in 90% of recipients. We further found that prevention of GVHD via foxp3-induced Tregs was also dependent on their activation by either a specific alloantigen expressed on recipient cells or by immunization with a specific peptide antigen.
The findings of this study provide a basis for the concept that the onset and potency of alloresponse suppression in GVHD can be regulated by using Tregs with known antigen specificity. The novel evidence that antigen-specific T cell clones can be used as the cell source for foxp3-induced Tregs further improves the feasibility of using Tregs for modulating immune responses in vivo. These data suggest a novel approach to control induction of tolerance using Tregs as an adoptive immunotherapy in allogeneic transplantation.