Complement activation by AAV-neutralizing antibody complexes.

Abstract

Treatment of monogenetic disorders using adeno-associated viral vectors (AAV) is an area of intense interest. AAV is a human pathogen and pre-existing capsid antibodies are prevalent in the population posing a challenge to safety and efficacy of AAV-mediated gene therapies. Here we investigated the risk of AAV-mediated complement activation when sera from a cohort of human donors was 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 ant-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 pre-treatment with an IgG degrading enzyme. Overall, these results demonstrate an important role of pre-existing neutralizing antibodies in activating complement; a risk that can be mitigated by employing adequate immunosuppression strategies when dosing seropositive patients with vector.