Novel strategy to block AAV neutralizing antibody activity

Adeno-associated virus (AAV) vectors have been successfully applied in clinical trials in patients with different genetic disorders. However, the high prevalence of neutralizing antibodies (Nabs) is one of major concerns to limit the broad AAV application in clinics. In humans, approximately 50% of the population has Nabs. Several approaches have been investigated to evade or overcome AAV Nabs, including virion surface masking, application of different AAV serotypes, capsid engineering, as well as Nab depletion with biological methods (empty capsid utilization, B cell depletion, plasma-apheresis and IgG cleavage enzymes). Generally, these approaches have low efficiency for Nab evasion or induce unwanted side effects or change AAV tropism. Therefore, it is imperative to develop ideal strategies to block Nab activity, but without tissue tropism alternation from capsid modifications or negative side effects from pharmacological treatment. Recently, we have developed an effective approach to universally block Nabs using a unique Protein-M, which is derived from mycoplasma. Protein-M can bind to all immunoglobulin from any species. Our preliminary studies have demonstrated that protein M inhibited AAV Nab activity over 100-fold in vitro and 1000-fold in mice, which indicates that protein M approach is the most effective one to evade AAV Nabs so far. The wild type of protein M is structurally unstable at body temperature (37°C), which may decrease its potency for Nab blockade when using in vivo. To improve PM stability, we have rationally engineered 150 individual protein mutants and found that one mutant NG101 specifically had high thermal stability and biological activity, like wild type protein M. In this STTR Phase II application, we will study the efficacy and safety of NG101 from large scale to block Nabs in AAV-based therapies in mice primates. The long-term objective is to apply this effective strategy with NG101 to evade Nab activity in future AAV gene therapy and extend the technology to broad applications for any therapeutic molecule delivery (using adenovirus vector, nanoparticle, etc) in cancer treatment and vaccination.