Abstract
The clinical trial using adeno-associated virus (AAV) vector delivery of mini-dystrophin in patients with Duchenne Muscular Dystrophy (DMD) demonstrated a cytotoxic lymphocyte (CTL) response targeting the transgene product. These mini-dystrophin-specific T-cells have the potential to clear all transduced muscle, presenting the general gene therapy concern of overcoming the CTL response to foreign proteins that provide therapeutic benefit. In this study, we exploited a natural immunosuppression strategy employed by some viruses that results in CTL evasion only in transduced cells. After transfection of the plasmids encoding viral peptides and ovalbumin, which includes the immune-domain epitope SIINFEKL, several viral small peptides (ICP47 and US6) inhibited the SIINFEKL peptide presentation. A single AAV vector genome that consisted of either transgene AAT fused with SIINFEKL epitope and, separately, ICP47 expressed from different promoters or a single fusion protein with ICP47 linked by a furin cleavage peptide (AATOVA-ICP47) decreased antigen presentation. Compared with AAV/AATOVA in which decreased AAT expression was observed at late time points, persistent transgene expression was obtained after systemic administration of AAV/AATOVA-ICP47 vectors in mice. We extended this strategy to DMD gene therapy. After administration of AAV vector encoding human mini-dystrophin fusion protein with ICP47 into mdx mice, a lower mini-dystrophin-specific CTL response was induced. Importantly, the ICP47 fusion to mini-dystrophin inhibited CTLs mediated cytotoxicity. Although demonstrated herein using AAT and mini-dystrophin transgenes in an AAV context, the collective results have implications for all gene therapy applications resulting in foreign peptides by immune suppression in only genetically modified cells.