Local overexpression of nerve growth factor in rat corneal transplants improves allograft survival

PURPOSE. To investigate the effect and mechanisms of nerve growth factor (NGF) gene therapy to promote allograft survival in experimental rat corneal transplantation. METHODS. A rat major histocompatibility complex (MHC) class I/II disparate corneal transplant model was used. Recipients were randomly assigned to receive either local Ad (Ad)-mediated gene transfer of NGF or a single intraperitoneal injection of AdNGF 1 day before transplantation. Moreover, immunosuppressive therapy was introduced by systemic coapplication of an Ad expressing CTLA4Ig. The efficacy of this treatment was examined by intracorneal mRNA expression analysis of cytokines and cytoprotective molecules by quantitative RT-PCR at day 12 after transplant. Further graft integrity and immune response against adenoviral vectors were investigated. RESULTS. Local AdNGF-gene transfer significantly prolonged the mean survival time (MST) of rat corneal grafts (16.8 +/- 1.4 days) compared with control grafts (MST, 13.1 +/- 0.3 days; P < 0.03). In contrast, systemic AdNGF gene transfer did not result in improved corneal graft survival (MST, 15.2 +/- 1.0 days). RT-PCR analysis of cornea explants revealed diminished expression of proinflammatory cytokines (IFN-gamma, TNF-alpha) and increased expression of antiapoptotic molecules. In addition, graft endothetial integrity was improved, as measured by the detection of apoptotic cells. Moreover, coapplication of CTLA4Ig further significantly improved graft survival and protective effects of local NGF gene therapy. CONCLUSIONS. This is the first report showing the successful application of a neurotrophin gene therapy to prolong corneal graft survival in an experimental rat transplantation model. Moreover, immunomodulatory therapy further improves graft survival and demonstrates that both anti-inflammatory and cytoprotective mechanisms are involved in the prevention of corneal allograft rejection.