Complement Activation by Adeno-Associated Virus-Neutralizing Antibody Complexes.

Treatment of monogenetic disorders using vectors based on adeno-associated virus (AAV) is an area of intense interest. AAV is non-pathogenic human virus, and preexisting capsid antibodies are prevalent in the population posing a challenge to the safety and efficacy of AAV-mediated gene therapies. In this study, we investigated the risk of AAV-mediated complement activation when sera from a cohort of human donors were exposed to AAV9 capsid. Seropositive donor sera carrying neutralizing antibodies from a previous environmental exposure activated complement when admixed with AAV9 capsids and complement activation was associated with donors who had higher levels of anti-AAV IgG1 antibodies. These findings were consistent with mass spectrometry analysis that identified increased binding of immunoglobulins and complement factors when AAV9 capsids were admixed with seropositive sera. Finally, complement activation was abrogated after IgG-depletion using affinity columns or serum pretreatment with an IgG degrading enzyme. Overall, these results demonstrate an important role of preexisting neutralizing antibodies in activating complement; a risk that can be mitigated by using adequate immunosuppression strategies when dosing seropositive patients with vector.

Higher Seroprevalence of Anti-Adeno-Associated Viral Vector Neutralizing Antibodies Among Racial Minorities in the United States.

Anti-adeno-associated viral vector (AAV) neutralizing antibodies (NAbs) can ablate efficacy of transgene expression following intravenous vector administration. This observation in both preclinical and clinical trials has led to exclusion of NAb-positive patients from receiving AAV gene therapy. AAV drug development includes selection of capsids with lower NAb seroprevalence that also possess other favorable traits. Often a limited number of healthy volunteers are screened to gauge NAb seroprevalence. However, limited data sets can be biased leading to inaccurate estimates of NAb incidence. In this study, we evaluated AAV NAbs against a panel of vectors among healthy donors within the United States. While the overall seroprevalence against most AAVs was lower, we did observe increased NAb incidence among black and Hispanic donors. These findings of increased NAb seroprevalence among the minority races were confirmed in a second set of donors who also demonstrated higher seroprevalence among these races. Interracial- and intraracial differences within genders were also observed among donors. The increased incidence of AAV NAb among racial minorities was unexpected. Our findings underscore the need for removing bias in sample data sets and evaluating seroprevalence within the patient population while selecting capsids.