42. Differential Transduction Profiles of AAV Vectors in a Mouse Model of Human Glycosylation

Recent studies have demonstrated that AAV gene transfer efficiency and tropism, particularly with regard to the liver, can vary markedly across animal species. A mechanistic understanding of such host-specific AAV transduction profiles is essential for translating preclinical studies to the clinic. In this regard, virus-glycan interactions are key determinants of tissue tropism displayed by various AAV vectors. It is now known that AAV serotypes 1, 4, 5 and 6 utilize glycans terminating in sialic acid (Sia) as a primary receptor. Amongst various forms of Sia, N-glycolylneuraminic acid (Neu5Gc) is the most prevalent in most mammals; however humans are unable to synthesize Neu5GC from its precursor, N-acetylneuraminic acid (Neu5AC), due to a loss-of-function mutation. Consequently, Neu5AC is the predominant Sia in humans. In the current study, we first observed that metabolic incorporation of the nonhuman Sia, Neu5GC selectively reduces transduction efficiency of AAV1 and 6 in vitro. Utilizing a mouse model genetically engineered to express only the human-specific Sia, Neu5AC, we assessed the effects of sialic acid composition on the tropism and biodistribution of various AAV serotypes. Post systemic administration in humanized mice, modest differences in transduction were noted in case of serotypes 4 and 6, without changes to endogenous tissue tropism. Interestingly, AAV9, which utilizes galactose (Gal) showed an increase in transduction across multiple organs. Further, AAV9, which tends to transduce both neuronal and glial cell populations upon intracranial injection in normal mice, showed a transduction pattern restricted to neurons in humanized mice. These results suggest AAV vector biology may differ across species at both the cellular and tissue levels. These findings could have important implications towards the design and interpretation of pre-clinical studies/data leading to clinical translation.