Development and characterization of a first-in-class adjustable-dose gene therapy system

•We report the development of the first adjustable-dose gene therapy system.•The vector is non-antigenic and produces durable and adjustable gene expression.•The system is localized to the subQ injection site and is specific for adipocytes.•Delivered DNA cassettes enable gene expression of secreted therapeutic proteins.•Exenatide, delivered in vivo, achieves clinically relevant levels in circulation. Despite significant potential, gene therapy has been relegated to the treatment of rare diseases, due in part to an inability to adjust dosage following initial administration. Other significant constraints include cost, specificity, antigenicity, and systemic toxicity of current generation technologies. To overcome these challenges, we developed a first-in-class adjustable-dose gene therapy system, with optimized biocompatibility, localization, durability, and cost. A lipid nanoparticle (LNP) delivery system was developed and characterized by dynamic light scattering for size, zeta potential, and polydispersity. Cytocompatibility and transfection efficiency were optimized in vitro using primary human adipocytes and preadipocytes. Durability, immunogenicity, and adjustment of expression were evaluated in C57BL/6 and B6 albino mice using in vivo bioluminescence imaging. Biodistribution was assessed by qPCR and immunohistochemistry; therapeutic protein expression was quantified by ELISA. Following LNP optimization, in vitro transfection efficiency of primary human adipocytes reached 81.3 % ± 8.3 % without compromising cytocompatibility. Critical physico-chemical properties of the system (size, zeta potential, polydispersity) remained stable over a broad range of genetic cassette sizes (1,871–6,203 bp). Durable expression was observed in vivo over 6 months, localizing to subcutaneous adipose tissues at the injection site with no detectable transgene in the liver, heart, spleen, or kidney. Gene expression was adjustable using several physical and pharmacological approaches, including cryolipolysis, focused ultrasound, and pharmacologically inducible apoptosis. The ability of transfected adipocytes to express therapeutic transgenes ranging from peptides to antibodies, at potentially clinically relevant levels, was confirmed in vitro and in vivo. We report the development of a novel, low-cost therapeutic platform, designed to enable the replacement of subcutaneously administered protein treatments with a single-injection, adjustable-dose gene therapy.