Total and Neutralizing Antibody Seroprevalence of Hepatotropic Adeno-Associated Virus Among Healthy and Hemophilia A or B Population from India

The natural tissue tropism of adeno-associated viruses (AAVs) is being widely exploited in their use as vectors for transgene delivery for gene therapy of human diseases. A major limitation of this approach is the prevalence of antibodies to AAV capsid antigens, which can neutralize the infused vector and thus affect expression of the transgene. There are limited data on the prevalence of such antibodies, total (TAb) and neutralizing (NAb), to determine the eligibility of patients for gene therapy using specific AAV vectors. Using whole capsid ELISA for TAb and transduction inhibition assay (mCherry-based flow cytometry method for AAV5 and luciferase-based assay for AAV8) for NAb, in this study, we have evaluated the seroprevalence of anti-AAV5 and anti-AAV8 antibodies in three groups: healthy individuals (AAV5 <i>n</i> = 130, AAV8 <i>n</i> = 75), individuals with hemophilia A (AAV5 <i>n</i> = 62, AAV8 <i>n</i> = 88), and individuals with hemophilia B (AAV5 <i>n</i> = 42, AAV8 <i>n</i> = 55). The TAb prevalence for AAV5 in the three groups was 77.7%, 90.3%, and 95.2%, respectively, and that for AAV8 was 89.3%, 93.2%, and 92.7%, respectively. The AAV5 NAb seropositivity in the three groups was 89.2%, 100%, and 100% and that against AAV8 was 45.3%, 46.6%, and 45.5%, respectively. To check endpoint titer for AAV5 NAb, 21 out of the 42 hemophilia B samples were screened, using a dilution of 1 in 80 and 1 in 160. Among the AAV5 hemophilia B samples with higher dilutions, 81% of the individuals had a titer of ≤80. Age-stratified AAV5 and 8 TAb and NAb seroprevalence showed high prevalence across all age groups in all three groups of samples screened. High positivity among AAV5 NAb at lower dilutions should be further evaluated for cross-reactivity.