Gr-1^intCD11b⁺, not Gr1+CD11b+, cells, are myeloid-derived suppressor cells(MDSCs) in murine corneal allograft and induced by high dose IFN-γ

Abstract

Purpose : Although corneal allotransplantation is performed in the immune-privileged cornea,many grafts are still rejected after transplantation.The purpose of this study was to examine the characteristics of myeloid-derived immunosuppressive cells(MDSCs) and investigate their mechanism of induction and functional role in corneal allotransplantation using murine corneal allograft model.

Methods : C57BL/6 mice cornea was used for donor and was sutured onto recipient graft beds in central cornea of BALB/c, resulting in an allogeneic graft. Microscopic evaluation was done weekly for 8 weeks.To generate in-vitro MDSCs, mouse femur BM cells were treated with granulocyte macrophage-colony stimulating factor (GM-CSF) and different cytokines as transforming growth factor(TGF)-β, interleukin(IL)-10, IL-13, and interferon(IFN)-γ with different concentrations ranging from 10 ng to 10 μg.Gr-1 and CD11b double expressing cells were defined as mouse MDSCs.

Results : Gr-1⁺CD11b⁺ MDSCs were infiltrated to allografted area in murine corneal allograft model from the early phase of allograft.Distribution of Gr-1⁺CD11b⁺ cells were equal between accepted and rejected corneas, peripheral blood and bone marrow.However the ratio of Gr-1^intCD11b⁺/Gr-1⁺CD11b⁺ cells were higher in accepted corneal grafts compared to rejected grafts(p<0.001).Gr-1^intCD11b⁺ cells were found to dominantly infiltrate into the accepted corneal graft and expressed high levels of immunosuppressive cytokines,including TGF-β, IL-10, and tumor necrosis factor-related apoptosis-inducing ligand(TRAIL).We found that high dose, not low dose, of IFN-γ and GM-CSF could induce immunosuppressive cytokine expressing Gr-1^intCD11b⁺ cells with in vitro cell culture.Also, Gr1^intCD11b⁺ cells, generated by high dose IFN-γ and GM-CSF in vitro were injected to the peripheral blood and were confirmed to infiltrate into peri-graft area and reduce graft rejection.

Conclusions : Gr-1^intCD11b⁺, not Gr1⁺CD11b⁺, cells can be MDSCs in murine corneal allograft model and secrete immune suppressive molecules like IL-10, TGF-β, and TRAIL which, results in improvement of allograft survival.With the in vitro condition, high-dose IFN-γ in allograft area is needed for development of Gr-1^intCD11b⁺ MDSCs.This may indicate that certain cytokine milieu changes during the early period of allografts may result in differences of graft survival and rejection.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.