Effective Gene Therapy for Hemophilia a: Novel Re-Dosable Non-Viral Formulation That Provides Stable, and Durable FVIII Expression with Improved Tolerability

Abstract

Current first-line treatments for Hemophilia A patients are clotting factor replacement or bi-specific antibodies. These treatments require continuous, lifelong infusions, yet many patients have breakthrough bleeds. There remains a high unmet need for safe, effective, and durable therapies. We have developed a liver-directed non-viral in vivo gene insertion approach using the piggyBac® DNA insertion system. Unlike conventional AAV-based gene therapy, our platform enables delivery of large transgenes, the ability to stably and efficiently integrate the therapeutic transgene into the genome, and the potential for re-dosing to titrate to target FVIII activity levels. A key challenge for all gene insertion systems relates to the need to safely and efficiently deliver the transgene DNA. In the current study we evaluated a novel hepatocyte-targeted non-viral platform able to co-deliver both DNA and mRNA with superior safety and specificity relative to the traditional liver-directed LNP concept. We first evaluated a two nanoparticle system using conventional 4-component liver-directed LNPs, with one lipid nanoparticle (LNP) encapsulating the mRNA for the super piggyBac (SPB) transposase (LNP-SPB), and a second LNP encapsulating a plasmid containing the hFVIII transposon DNA (LNP-hFVIII). We subsequently developed a novel co-encapsulated LNP formulation, comprising both SPB mRNA and transposon plasmid DNA (LNP-SPB-hFVIII). In juvenile WT mice we observed a 50% increase in hFVIII antigen expression compared to the dual nanoparticle approach. This was further validated in a severe hemophilia A mouse model (FVIII knock-out). Following a single dose of the co-encapsulated LNP-SPB-hFVIII to adult hemophilia A mice tolerized to human FVIII, we observed ~30% of normal hFVIII expression sustained over the duration of the 7 month study. To further support the concept of re-dosing, we treated immunocompetent adult hemophilia A mice tolerized to human FVIII with repeated administrations every 3 weeks. We observed a dose-proportionate increase in FVIII activity after each administration, reaching an average hFVIII activity of 96% of normal, following 3 repeated doses. Traditional LNPs use several lipid components that typically include an ionizable lipid, cholesterol, a polyethylene glycol (PEG) lipid, and a structural lipid, each with a unique function to effectively encapsulate and deliver the DNA and mRNA required for the piggyBac platform. Cellular transfection of these traditional LNPs has been demonstrated to occur by passive mechanisms such as micropinocytosis or Apolipoprotein E (ApoE)-mediated endocytosis by the low-density lipoprotein receptor (LDLR). However, this can also result in delivery to unwanted cell-types, particularly tissue-resident immune cells. To address this potential failure mode, we explored the addition of a N-Acetylgalactosamine (GalNac)-based targeting ligand to our co-encapsulated LNP formulation (LNP-SPB-hFVIII-G). In immunocompetent animals, targeted LNPs yielded a ~2-3-log reduction in pro-inflammatory serum cytokines (IL-6, IFNɣ) while maintaining high hFVIII expression and no elevation in transaminases (ALT, AST). In conclusion, our results demonstrate the capabilities of the piggyBac DNA insertion system and non-viral approach in providing stable FVIII transgene expression through genomic integration, along with the potential for redosing. Additionally, we have highlighted the tolerability profile of our current generation of liver-targeted non-viral delivery platform. Altogether, these data provide proof-of-principle toward developing an effective and durable therapy for Hemophilia A.