Protection of corneal allografts by CTLA4-Ig

Purpose. CTLA4, a high-affinity ligand of B7, can, in soluble form, prevent antigen-driven T-cell activation by blocking CD28-B7 interaction and can t hereby prevent immune graft rejection. In this study, we tested the capacit y of soluble CTLA4-Ig alone or in combination with UV-B irradiation to supp ress corneal allograft rejection in rabbits. Methods. Corneas from Dutch be lted rabbits were incubated in corneal storage medium containing 0, 1, 10, 25, or 250 mu g/ml of CTLA4-Ig for 18 h and were then transplanted into the vascularized or nonvascularized corneas of New Zealand White rabbit recipi ents. A series of donor corneas were exposed to UV-B irradiation alone or a combination of irradiation and CTLA4-Ig to determine if these two treatmen ts would have an additive effect in prolonging graft survival. The fate and clinical condition of the allografts were evaluated by slit-lamp photomicr oscopic observation and corneal-thickness measurements. Grafts that were re jected were processed for histopathologic and immunohistochemical analysis to determine the characteristics of cells infiltrating the grafts. Results. Grafts placed in nonvascularized corneas showed no differences in survival times, regardless of treatment. Among the grafts placed in vascularized co rneas, those incubated with CTLA4-Ig at a concentration of 250 mu g/ml fail ed within 7-14 days. Histopathologic and immunocytochemical examination rev ealed a dense accumulation of immune inflammatory cells, especially class I I major histocompatibility complex (MHC)-expressing, antigen-presenting cel ls, in the failed grafts. Grafts incubated with CTLA4-Ig at concentrations of 1 and 10 mu g/ml had mean survival times greater than the control, untre ated corneal allografts. Some of the grafts in these two treatment groups s urvived for the 100-day observation period, whereas none of the grafts in t he other treatment groups survived to this end point. UV-B irradiated graft s incubated with CTLA4-Ig at a concentration of 1 mu g/ml appeared to have longer survival times and fewer rejections compared with control, untreated grafts and grafts treated with UV-B or CTLA4-Ig alone. Conclusion. The res ults show that the CTLA4-Ig coreceptor blocking agent can prolong corneal a llograft survival in vascularized graft sites and that UV-B irradiation fol lowed by incubation in CTLA4-Ig may prolong graft survival better than eith er treatment alone. These results suggest that agents that prevent second-s ignal interaction between antigen-presenting cells and T lymphocytes may be useful for inhibiting corneal allograft rejection.