Prolonged Gene Expression in Muscle Is Achieved Without Active Immune Tolerance Using MicrorRNA 142.3p-Regulated rAAV Gene Transfer

Gene transfer efficacy is limited by unwanted immunization against transgene products. In some models, immunization may be avoided by regulating transgene expression with mir142.3p target sequences. Yet, it is unclear if such a strategy controls T-cell responses following recombinant adeno-associated viral vector (rAAV)-mediated gene transfer, particularly in muscle. In mice, intramuscular rAAV1 gene delivery of a tagged human sarcoglycan muscle protein is robustly immunogenic and leads to muscle destruction. In this model, the simple insertion of mir142.3p-target sequences in the transgene expression cassette modifies the outcome of gene transfer, providing high and persistent levels of muscle transduction in C57Bl/6 mice. Such regulated vector fails to prime specific CD4 and CD8 T cells; although, transgene tolerance seems to result from ignorance and could be broken by a robust antigenic challenge. While effective in normal mice, the mir142.3p-regulated transgene remains immunogenic in sarcoglycan-deficient dystrophic mice. In these mice, transgene expression is only prolonged but does not persist as effector CD4 and CD8 T-cell responses develop. Thus, using a mir142.3p-regulated transgene can improve rAAV muscle gene transfer results, but the level of efficacy depends on the context of application. In normal muscle, this strategy is sufficient to prevent immunization and functions even more effectively than tissue-specific promoters. In dystrophic models, additional strategies are required to fully control T-cell responses.