CD4+CD25+ Regulatory T Cells Contribute to the Immune Privilege of Corneal Allografts

Abstract

Purpose: : Recipients of orthotopic corneal allografts experiencing prolonged graft survival develop regulatory T cells that suppress immune responses to donor alloantigens. CD4⁺CD25⁺ regulatory T cells (T_reg) play an important role in maintaining immune privilege in the eye, in part, by producing IL-10. Recent studies in liver, skin and cardiac transplantation demonstrate that CD4⁺CD25⁺ T_reg cells play an important role in the long-term allograft survival. We hypothesize that CD4⁺CD25⁺ T_reg contribute to the immune privilege exhibited by corneal allografts.

Methods: : Corneal allografts were performed by surgically removing 2mm cornea buttons from donor mice and were sewn into place on the recipient mice with 11-0 running suture. Depletion of CD4⁺CD25⁺ T_reg cells was performed by administering anti-CD25 antibody weekly. IL-10 was depleted by administering weekly doses of anti-IL-10 antibody. Balb/c mice were adoptively transferred with either CD4⁺CD25⁺ T_reg cells or CD4⁺CD25^- T cells isolated by MACS bead separation from naïve Balb/c mice prior to receiving B6 corneal allografts.

Results: : Splenectomy of recipient CB6F1 mice exacerbated rejection of NZB donor corneal allografts compared to normal controls. Depletion of CD4⁺CD25⁺ T_reg cells with anti-CD25 antibody in CB6F1 or Balb/c recipients significantly increased the incidence and tempo of NZB or B6 donor corneal allograft rejection compared to the isotype control group. IL-10 depleted recipient mice exhibited accelerated and universal corneal allograft graft rejection. Adoptive transfer of CD4⁺CD25⁺ T_reg cells into Balb/c recipient mice decreased the incidence of B6 corneal allograft rejection compared to recipient mice adoptively transferred with CD4⁺CD25^- T cells (20% rejection vs. 50% rejection).

Conclusions: : Immune privilege experienced by corneal allografts is due, in part, to the generation of CD4⁺CD25⁺ regulatory T cells in the eye and implies that IL-10 production by T_reg cells and NKT cells is critical for corneal allograft survival. Augmenting CD4⁺CD25⁺ T_reg cells in corneal allograft recipients may be a feasible strategy to blunt immune rejection of corneal allografts and improve long-term graft survival.

Keywords: immune tolerance/privilege • cornea: basic science • immunomodulation/immunoregulation