| Recombinant adeno-associated virus (rAAV) vectors are considered promising for human gene replacement because they facilitate the stable expression of numerous therapeutic proteins in vivo. Whether the success of human gene therapy will be influenced by cellular immune responses to transgene-encoded proteins is largely unknown. Here we characterized CD8+ T cell activity against beta-galactosidase and enhanced green fluorescent protein, model antigens containing MHC class I epitopes that are constitutively produced in murine skeletal muscle after rAAV vector transduction. In mice receiving rAAV vectors encoding eGFP and beta-galactosidase, failure of CD8+ T cells to clear antigen-positive myocytes was associated with a loss of effector function occurring locally within vector-transduced muscle. Stable transgene expression was facilitated, in part, by the induction of programmed death for muscle-infiltrating CD8+ T cells. While a potential role for the PD-1/PD-L1 pathway in the local regulation of T cell responses was identified, this pathway was ruled out as the dominant mediator of apoptosis for the rAAV-primed cells. Importantly, through our investigation into the maintenance of failing CD8+ T cell responses, we have identified a potential role for dendritic cells in the propagation of cellular and humoral immune responses to rAAV-encoded transgene products. Together our data formally demonstrate that stable rAAV transgene expression is characterized by the coexistence of antigen and targeting CD8+ T cell responses. Such observations may prove beneficial for further understanding of immunity to rAAV gene therapy in humans where, in all likelihood, tolerance to the encoded gene product will be a necessity for therapeutic success. |
