Protein depleting pre-existing antibodies for viral gene therapy

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Project Summary: This is a fast-track SBIR grant proposal. As effective gene therapy (GT) products using adeno-associated viral (AAV) vectors advance to clinical applications, the translation faces critical challenge of high prevalence of αAA) antibodies (Abs) in humans. Currently, only individuals negative of αAAV-Abs are eligible for AAV GT treatment. The goal of this SBIR project is to develop a therapeutic product capable of effectively depleting Abs towards clinical application and commercialization, in order to make potentially life-saving AAV GT products available to all patients in need of administration and re-administration. To address the challenge of pre-existing αAAV-Abs, we have developed a new effective Ab-depleting protein product, antibody cleaver (AbC), based on the demonstrated IgG degrading enzymes of Streptococci (IdeS). IdeS specifically cleaves IgG of humans, primate, sheep and rabbit (but not mouse) origin. Numerous studies demonstrate effective transient IgG degradation by IdeS in animals and humans, with no detectable dose limiting toxicity. Our preliminary studies showed effective Ab depletion by an IV AbC infusion, leading to the transient clearance of pre-existing αAAV9-Abs and allowing effective transduction in rabbitized αAAV9-Abs- positive MPS IIIA mice after an IV scAAV9-hSGSH delivery. We believe that IV AbC administration offers a great tool to overcome the pre-existing αAAV-Abs for the translation of rAAV GT to treat diseases in humans. This proposal is to further develop and establish an optimal AbC Ab-depletion regimen for systemic rAAV9 gene delivery. In Phase I studies, we will identify optimal AbC product. Once validated, in Phase II, the optimal Ab-C product will be evaluated in pre-clinical studies in animal models (Aim #2, 3), to assess the efficacy and therapeutic potential of transient Ab-depletion by AbC. In Phase II, we will also optimize the AbC production procedures for scale-up manufacture towards clinical application and commercialization (Aim #4). Notably, The Phase II studies will lead to an IND and subsequent clinical trials to bridge the AbC administration with systemic scAAV9-hSGSH gene replacement therapy clinical trials in patients with MPS IIIA, for which an IND were recently submitted. More importantly, the AbC Ab depletion may offer the answer to the challenge posed by pre-existing Abs to gene therapy products using AAV and other viral vectors in general.