Tolerogenic dendritic cells suppress murine corneal allograft rejection by modulating CD28/CTLA-4 expression on regulatory T cells.

Anterior chamber-associated immune deviation (ACAID) is initiated when dendritic cells (DCs) capture intraocular antigen and induce regulatory T cells (Tregs) in the spleen. We investigated whether DCs could be used as an immunotherapy to prevent murine corneal allograft rejection by inducing Tregs. Bone marrow-derived DCs (BMDCs) were differentiated with transforming growth factor-β2 (TGF-β2) in the presence of donor-derived allopeptide in vitro (TGFβ2-DCs), and adoptively transferred to BALB/c mice. Three days later a corneal allograft transplant was carried out. Graft rejection, as well as the number and the phenotype of splenic Tregs, were determined after transplant. CD86, CD80, CD40 were present, and MHC class II expression were significantly reduced on TGFβ2-DCs compared to BMDCs not exposed to TGF-β2. TGFβ2-DCs increased the number of splenic Tregs (CD4(+)CD25(+)) in recipient mice prior to transplant by modulating CD28/CTLA-4 expression. These induced Tregs suppressed proliferation of CD4(+)CD25(-) T cells ex vivo. TGFβ2-DCs delayed corneal allograft rejection and TGFβ2-DC recipient mice had significantly more splenic Tregs expressing Foxp3 and CTLA-4, but fewer CD28+ Tregs. Expression of GITR, CD69, and CD45RB were similar in TGFβ2-DC and control mice. Therefore, the phenotype of TGFβ2-DCs suggests they are tolerogenic DCs (tolDCs). In vivo, these cells increased the number and function of Tregs by modulating CD28/CTLA-4 expression. The suppressor Tregs induced by TGFβ2-DCs may be involved in the induction of ACAID, which helps to suppress corneal allograft rejection. Our results provide proof of principle for the use of tolDCs as immunotherapy during transplant.