Recombinant adeno-associated virus (rAAV)-mediated gene transfer has shown promise for treating diseases in various animal models including the mdx mouse model of Duchenne muscular dystrophy (DMD). In many cases, however, preclinical studies in inbred mice have not successfully predicted human clinical responses. To assess the potential clinical utility of treating human DMD patients by AAV-mediated gene delivery, we performed a series of direct intramuscular injections in random-bred wild-type dogs. AAV serotypes 2 and 6 carrying different promoter-transgene cassettes were produced as previously described for murine studies and administered intramuscularly. The injection sites were biopsied at various time points and analyzed for transgene expression and immunohistochemical analysis. In contrast to the generally nonimmunogenic nature of these vectors in murine studies, both AAV2 and AAV6 vectors elicited robust cellular immune responses regardless of the transgene expressed, the cellular specificity of the promoter, and the muscle type injected. Viral purification by various methods did not diminish T cell-mediated infiltration. Our data indicate that AAV2 and AAV6 capsid proteins can elicit primary cellular immune responses when injected into the skeletal muscle of random-bred dogs, and suggest the possibility of cellular immunity to AAV vectors in humans.