Spark Therapeutics announced the publication of new research in the journal Nature Medicine demonstrating that treatment with immunoglobulin G-degrading (IgG) enzyme of Streptococcus pyogenes (IdeS) resulted in rapid and transient reduction of neutralizing anti-adeno-associated virus (AAV) antibodies and restored gene therapy efficacy in controlled laboratory tests of animal models. The study was conducted by an international collaboration of researchers from Spark Therapeutics in the U.S., and Genethon, the Centre de Recherche des Cordeliers (Inserm, Sorbonne Université, Université de Paris) and the National Centre for Scientific Research (CNRS) in France. AAV-mediated gene therapy allows for the treatment of a growing number of diseases in patients, however the presence of neutralizing anti-AAV antibodies can lead to limitations of this technology. Specifically, neutralizing anti-AAV IgG pre-exist in up to 70% of the population and block the entry of viral vector particles in a given target tissue. Furthermore, high-titer anti-AAV antibody levels usually develop following vector administration and persist long-term thereafter, preventing vector re-administration. To date, researchers have been limited in their ability to bypass the neutralizing activity of anti-AAV IgG. The study demonstrated that treatment with the IgG-degrading enzyme IdeS, an endopeptidase from Streptococcus pyogenes that specifically hydrolyses human IgG, resulted in a rapid and transient elimination of neutralizing anti-AAV IgG and restored gene therapy efficacy. IdeS is an endopeptidase able to degrade circulating IgG that is currently being tested in transplant patients. Researchers demonstrated efficacy in vivo using animal models of liver gene transfer, including hemophilia A and B. Hemophilia is a rare genetic bleeding disorder that causes a delay in clot formation as a result of a deficiency in coagulation factor VIII or IX for hemophilia A or B, respectively. In both mice and non-human primates with neutralizing anti-AAV IgG, IdeS treatment prior to the injection of AAV vectors eliminated neutralizing IgG and rescued the expression of the factor VIII or IX in hepatocytes. Furthermore, administration of AAV vectors systematically induces a neutralizing anti-AAV immune response, making gene therapy inefficient upon subsequent injections of AAV vectors. The study also demonstrated that treatment with IdeS restores the efficacy of the re-administration of AAV vectors, allowing for efficient transgene expression in non-human primates. The research shows that IdeS allows the repeated administration of AAV vectors by blocking the neutralizing activity of anti-AAV IgG in small and large animal models. Additional studies in the field of gene therapy have the potential to translate these findings to human trials, with the goal of opening a therapeutic window for patients with neutralizing anti-AAV antibodies. Spark will assess and investigate the potential impact of the IdeS technology on its current gene therapy programs and potential applications in the future.