A dystrophic muscle broadens the contribution and activation of immune cells reacting to rAAV gene transfer

Recombinant adeno-associated viral vectors (rAAVs) are used for therapeutic gene transfer in skeletal muscle, but it is unclear if immune reactivity to gene transfer and persistence of transgene are affected by pathologic conditions such as muscular dystrophy. Thus, we compared dystrophic mice devoid of α-sarcoglycan with healthy mice to characterize immune cell activation and cellular populations contributing to the loss of gene-modified myofibers. Following rAAV2/1 delivery of an immunogenic α-sarcoglycan reporter transgene in the muscle, both strains developed strong CD4 and CD8 T-cell-mediated immune responses in lymphoid organs associated with muscle CD3+ T and CD11b+ mononuclear cell infiltrates. Selective cell subset depletion models revealed that CD4+ T cells were essential for transgene rejection in both healthy and pathologic mice, but macrophages and CD8+ T cells additionally contributed as effector cells of transgene rejection only in dystrophic mice. Vectors restricting transgene expression in antigen-presenting cells showed that endogenous presentation of transgene products was the sole mechanism responsible for T-cell priming in normal mice, whereas additional and protracted antigenic presentation occurred in dystrophic animals, leading to secondary CD4+ T-cell activation and failure to maintain transgene expression. Therefore, the dystrophic environment diversifies cellular immune response mechanisms induced by gene transfer, with a negative outcome.