Immunomodulation Of Rat Composite Tissue Allotransplantation By Adenoviral-mediated OX40-Ig Topical Gene Therapy

Objective: To investigate adenoviral-mediated OX40-Ig topical gene therapy for OX40/OX40 ligand (OX40L) costimulatory pathway blockade to inhibit T cells mediated acute composite tissue allograft rejection in rats.Methods: We constructed AdOX40Ig, a replication-defective adenovirus carrying genes encoding human OX40 and IgG1Fc portion. In this study, a novel ex vivo gene transfer technique was used to genetically modify allograft to deliver OX40-immunoglobulin(Ig) locally. The ablility of adenoviral vector mediated local production of OX40-Ig, blocking the OX40/OX40 ligand(OX40L) costimulatory pathway, from genetically modified allograft to facilitate long-term engraftment was examined in BN-to-LEW rat allogeneic superficial inferior epigastric artery (SIEA) flap transplantation model. Recipients were randomly divided into 5 groups, which were treated with topical OX40-Ig gene transfer, a single low dose of rapamycin alone, or in combination. Graft survival was assessed using histopathology classification of clinical skin rejection.Results: The ex vivo OX40-Ig gene transfer into isolated flaps resulted in high regional expression of OX40-Ig protein. All animals in untreated or AdEGFP-treated groups developed gradeⅢclinical rejection by postoperative day 7. Unexpectedly, no significant difference in allograft survival between the local AdOX40Ig-treated groups (8.3±0.8 days) and the untreated groups (7.8±1.2 days) could be observed (t test: p>0.05). The allograft survival in the local AdOX40Ig-treated groups was extended to 18.6±1.3 days when transduction was combined with a low dose of rapamycin, a significant improvement over survival with rapamycin treatment alone (13.5±0.5 days, p<0.01).Conclusion: These results demonstrated that local immunomodulation by allograft itself and low-dose rapamycin treatment synergistically promote composite tissue allograft acceptance. This protocol may be a way to reduce the immunosuppressive dosage needed for the successful inhibition of acute rejection in the early postoperative period.