Host and vector-dependent effects on the risk of germline transmission of AAV vectors

The assessment of the risk of germline transmission of vector-coded sequences is critical for clinical translation of gene transfer strategies. We used rabbit models to analyze the risk of germline transmission of adeno-associated viral (AAV) vectors. Intravenous injection of AAV-2 or AAV-8 resulted in liver-mediated, long-term expression of therapeutic levels of human factor IX (hFIX) in a dose-dependent manner. In high-dose cohorts, AAV-8 resulted in twofold higher levels of circulating hFIX and of vector DNA in liver compared to AAV-2. Vector sequences were found in the semen of all rabbits. The kinetics of vector clearance from semen was dose- and time-dependent but serotype-independent. No late recurrence of AAV-8 sequences was found in the semen over several consecutive cycles of spermatogenesis. In a novel rabbit model, AAV-2 or AAV-8 sequences were detected in the semen of vasectomized animals that lack germ cells. Therefore, structures of the genitourinary (GU) tract, as well as the testis, contribute significantly to vector shedding in the semen. Collectively, data from these two models suggest that the risk of inadvertent germline transmission in males by AAV-8 vectors is low, similar to that of AAV-2, and that AAV dissemination to the semen is in part modulated by host-dependent factors.