Successful AAV8 readministration: Suppression of capsid‐specific neutralizing antibodies by a combination treatment of bortezomib and CD20 mAb in a mouse model of Pompe disease.

Background: A major challenge to adeno‐associated virus (AAV)‐mediated gene therapy is the presence of anti‐AAV capsid neutralizing antibodies (NAbs), which can block viral vector transduction even at very low titers. In the present study, we examined the ability of a combination immunosuppression (IS) treatment with bortezomib and a mouse‐specific CD20 monoclonal antibody to suppress anti‐AAV NAbs and enable readministration of AAV vectors of the same capsid in mice. Methods: An AAV8 vector (AAV8‐CB‐hGAA) that ubiquitously expresses human α‐glucosidase was used for initial gene therapy and a second AAV8 vector (AAV8‐LSP‐hSEAP) that contains a liver‐specific promoter to express human secreted embryonic alkaline phosphatase (hSEAP) was used for AAV readministration. Plasma samples were used for determination of anti‐AAV8 NAb titers. Cells isolated from whole blood, spleen, and bone marrow were analyzed for B‐cell depletion by flow cytometry. The efficiency of AAV readministration was determined by the secretion of hSEAP in blood. Results: In näive mice, an 8‐week IS treatment along with AAV8‐CB‐hGAA injection effectively depleted CD19+B220+ B cells from blood, spleen, and bone marrow and prevented the formation of anti‐AAV8 NAbs. Following administration of AAV8‐LSP‐hSEAP, increasing levels of hSEAP were detected in blood for up to 6 weeks, indicating successful AAV readministration. In mice pre‐immunized with AAV8‐CB‐hGAA, comparison of IS treatment for 8, 12, 16, and 20 weeks revealed that the 16‐week IS treatment demonstrated the highest plasma hSEAP level following AAV8‐LSP‐hSEAP readministration. Conclusions: Our data suggest that this combination treatment is an effective IS approach that will allow retreatment of patients with AAV‐mediated gene therapy. A combination IS treatment with bortezomib and a mouse‐specific CD20 monoclonal antibody effectively suppressed anti‐AAV NAbs in naïve mice and in mice with pre‐existing antibodies, allowing successful readministration of the same AAV capsid vector. [ABSTRACT FROM AUTHOR]