Clades of Adeno-Associated Viruses Are Widely Disseminated in Human Tissues

Abstract

The potential for using Adeno-associated virus (AAV) as a vector for human gene therapy has stimulated interest in the Dependovirus genus. Serologic data suggest that AAV infections are prevalent in humans, although analyses of viruses and viral sequences from clinical samples are extremely limited. Molecular techniques were used in this study to successfully detect endogenous AAV sequences in 18% of all human tissues screened, with the liver and bone marrow being the most predominant sites. Sequence characterization of rescued AAV DNAs indicated a diverse array of molecular forms which segregate into clades whose members share functional and serologic similarities. One of the most predominant human clades is a hybrid of two previously described AAV serotypes, while another clade was found in humans and several species of nonhuman primates, suggesting a cross-species transmission of this virus. These data provide important information regarding the biology of parvoviruses in humans and their use as gene therapy vectors. Adeno-associated virus (AAV) is a member of the genusDependovirus, which lies within the Parvoviridae family (17). An interest in this family of viruses has been stimulated because of their potential use as gene transfer vectors (14).Little is known about the biology of AAV infections, although a significant proportion of humans and nonhuman primates have antibodies in their blood that react to some of the six existing serotypes of AAV (5, 7). This suggests that primates are hosts for infection with AAV, although the clinical sequelae of these infections have yet to be identified.The study of AAV has been limited to the previously described six serotypes, of which five were isolated as contaminants in laboratory preparations of adenoviruses (1,3,16). Our lack of understanding of AAV clinical infections has complicated the search for clinical isolates of the virus. Members of our laboratory recently described a strategy for evaluating latent or persistent AAV genomes from tissues of asymptomatic nonhuman primates through the use of PCR. These studies led to the discovery of two novel AAV serotypes, called AAV7 and AAV8, that have improved properties as vectors for gene therapy (10). In nonhuman primates, AAV sequences were quite prevalent and heterogenous (9).The goal of this study was to determine if latent AAVs exist in humans, and if so, to characterize their structural, serologic, and functional properties. MATERIALS AND METHODSCollection of primate tissues. Our sources of nonhuman primate tissues were described previously (9). Human tissues were collected under two independent IRB protocols approved by the Institutional Review Board of the University of Pennsylvania from either surgical procedures, postmortem examinations, or organ donors through two major national human tissue providers, the Cooperative Human Tissue Network and the National Disease Research Interchange. The human tissues used for this study were comprised of 18 different tissue types that included the colon, liver, lung, spl...

Heart-targeted adeno-associated viral vectors selected by in vivo biopanning of a random viral display peptide library

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