Adeno-associated virus-mediated transduction of PD-L1 in a rodent lung transplant model

Acute cellular rejection is a key contributor to chronic lung allograft dysfunction following transplantation; while treatable, traditional immunosuppressive therapies are associated with significant side effects. Gene therapy offers an approach to modulate recipient immune responses while minimizing the toxicity of conventional immunosuppressive therapy. In this study, we evaluated adenoassociated virus (AAV)-mediated programmed death-ligand (PD-L)1 overexpression, an inhibitory ligand of T cells, in a rat single-lung transplant model. Allogeneic Brown Norway lungs were transplanted into Fischer F344 recipients and assigned to 3 groups: (1) AAV9-PD-L1 via the bronchus during static cold storage, (2) no-virus control, or (3) AAV9-luciferase control. All animals received cytotoxic T lymphocyte-associated protein 4 immunoglobulin on postoperative day (POD)1, and killed on POD14. Rejection was evaluated by a blinded lung transplant pathologist, and PD-L1 expression and CD8⁺ T cell infiltration assessed via immunohistochemistry. By POD14, the AAV9-PD-L1 group displayed significantly reduced rejection severity (mean score 1.40) compared to controls (mean 3.60; p=0.005). The AAV9-luciferase group exhibited comparable rejection scores to no-virus controls (mean 3.5). Immunohistochemistry confirmed exogenous PD-L1 expression, however no significant difference in CD8+ T cell count was observed between groups. These findings demonstrate that AAV-PD-L1 gene delivery can attenuate acute cellular rejection in lung transplants, offering a potential strategy to improve outcomes.