[CTLA4-Ig prevents corneal allograft rejection in mice]

Selective inhibition of T cell activation using the B7 specific fusion protein CTLA4-Ig has been shown to block CD28/B7 signal pathway. In this study, the capacity of soluble CTLA4-Ig alone in the suppressing corneal allograft rejection is further tested in mice, and its mechanism of preventing the cornea from immune rejection in local eye is analyzed.

The mouse models of corneal allografts were established. In one group (25 mice), the corneal donors from C57BL/6 mice were incubated in corneal storage medium containing 10 microg/ml of CTLA4-Ig for 24 hours, and then transplanted orthotopically into the recipients cornea of BALB/c mice. In another group (25 mice), as a control, no treatment was conducted on the donor corneas before surgery. The condition of the allografts was monitored using slit lamp microscopy every 3 days and the cellar architecture of selected graft was examined by histological and immunohistochemical techniques weekly. Local corneal cytokines expressing in the rejected grafts were examined. Some mice, which were treated with CTLA4-Ig and their grafts survived beyond 6 weeks, were selected as recipients of skin grafts from C57BL/6 donors. Delayed type hypersensitivity (DTH) was measured after the skin grafts rejection.

All mice in the control group were rejected within 14 days after transplantation, while grafts incubated in CTLA4-Ig for 24 hours survived well beyond 100 days. The histopathology of surviving allografts had a normal cellular architecture, whereas the rejected allografts were heavily infiltrated with inflammatory cells and T lymphocytes (including CD4+, CD8+, and CD11+ cells). The cytokines including IL-10, TNF-alpha, IFN-gamma, B7-1 and CD40 were detected in the rejected corneas. Skin grafts from the C57BL/6 donor into the BALB/c mice after corneal transplantation were rejected with the expected median survival time of 11 days. DTH ear swelling challenge was induced after skin rejection, and a significant difference was found comparing with negative control mice.

The results indicate that CTLA4-Ig could competitively combine with B7, block CD28/B7 T-cell signals, and inhibit immune responses.