Safety of adeno-associated virus as cochlear gene transfer vector: analysis of distant spread beyond injected cochleae.

The adeno-associated virus (AAV), inoculated into the perilymph, has been shown to be an effective vector for mediating intracochlear transgene expression. The unexpected finding of transgene expression in the contralateral cochlea in previous work raised concern about dissemination of the virus from the target tissue. The current study was undertaken to assess the extent of AAV dissemination following its introduction into the inner ear. Adult male guinea pigs were injected with recombinant AAV into their left ears and sacrificed at 2 or 4 weeks. Various organs including the cochleae were harvested to characterize the presence and expression of the viral DNA. Virus DNA was detected via polymerase chain reaction in the infused and contralateral cochlea and in the cerebellum but not in any other organs, including cortex, heart, lung, liver, spleen, and kidney. Although the viral presence was established in the cerebellum, transgene expression in this organ was undetectable with either Western blot or immunohistochemistry. Transgene expression was demonstrated via immunohistochemistry in multinucleated giant cells in the bone marrow spaces adjacent to the infused and contralateral cochleae. Collectively, these results suggest potential routes for AAV dissemination from the infused cochlea via the cochlear aqueduct or by extension through the temporal bone marrow spaces. This study reinforces the need to investigate factors that mitigate viral leakage.