In Vivo Expansion of Regulatory T Cells by Low-Dose Interleukin-2 Treatment Increases Allograft Survival in Corneal Transplantation

Abstract

Background

Corneal allograft survival dramatically decreases in hosts with inflamed or vascularized recipient beds. We have previously shown that in rejected corneal allografts regulatory T cells (Tregs) demonstrate diminished Foxp3 expression and immunoregulatory function. Treatment with low doses of IL-2 selectively expands Tregs and has been proposed for the treatment of autoimmune diseases. In this study we investigated the effect of low-dose IL-2 administration on Treg function and corneal allograft survival.

Methods

Allogeneic corneal transplantation was performed on inflamed host beds. Low-dose systemic IL-2 was administered starting three days before grafting until six weeks after transplantation. Frequencies of Tregs as well as their immunosuppressive function and antigen specificity were assessed using flow cytometry, in vitro proliferation assays and adoptive transfer experiments. Frequencies of effector T cells (Teff) and graft infiltrating immune cells were measured at 2 weeks post-transplantation. Long-term allograft survival was evaluated for up to 9 weeks using Kaplan-Meier survival analysis.

Results

Treatment with low-dose IL-2 significantly increased frequencies of CD4+CD25+Foxp3+ Tregs and their immunosuppressive function. It also suppressed alloimmune response as shown by the decreased CD4+IFNγ+T cell frequencies and graft infiltration of CD45+ and CD4+ cells. Clinical evaluation of the grafts showed significant improvement in long-term corneal allograft survival in the IL-2 treated group compared to controls.

Conclusions

Our study is the first to report that treatment with low-dose IL-2 increases survival of corneal allografts. We propose that IL-2-mediated Treg expansion can be an effective tool to prevent alloimmunity and to improve long-term allograft survival in transplantation.