Vectors based on adeno-associated viruses (AAVs) show promise for the treatment of genetic diseases. This study evaluates the biology of AAV-mediated gene transfer to liver in nonhuman primates (NHPs) using vectors based on AAV serotypes 2, 7, and 8. Transgenes encoding self-proteins were selected to minimize the confounding development of transgene-specific immune responses. These included the beta subunit of choriogonadotropic hormone (bCG) and erythropoietin (Epo), both derived from cDNAs from rhesus macaques. Experiments were performed with bCG in rhesus macaques and Epo in cynomolgus macaques. We demonstrated the previously untested hypothesis that preexisting immunity to a natural infection does substantially diminish the efficacy of gene transfer with a vector derived from an endogenous virus. Route of vector administration clearly has an impact on the development of immune responses to self-antigens. In general, efficiency of gene transfer to liver with AAV7 and 8 vectors was higher than what was achieved with AAV2, although a variety of host factors may influence this important parameter, such as preexisting immunity, gender, and transgene immunity.