379 KB105: An HSV-based gene therapy vector engineered to deliver functional TGM1 to Autosomal Recessive Congenital Ichthyosis (ARCI) keratinocytes

Abstract

ARCI, a heterogenous group of rare disorders affecting skin cornification, is most commonly caused by mutations in the TGM1 (transglutaminase 1) gene. Current therapeutic options for ARCI are inadequate, providing limited symptomatic relief without restoration of epidermal barrier function or molecular correction of the underlying disease. We have engineered KB105, a novel replication-defective HSV-1 gene therapy vector encoding an optimized TGM1 transgene, amenable to topical treatment, for the molecular correction of ARCI. Here we show that KB105 demonstrates robust efficacy, safety, and functionality in a surrogate in vitro model of ARCI. KB105 efficiently transduced TGM1-deficient ARCI patient-derived keratinocytes, producing physiological levels of functional TGM1 with no impact on cell morphology or viability. The keratinocytes were infected by KB105 at increasing multiplicities of infection (MOIs), and TGM1 expression was evaluated by qPCR, qRT-PCR, western blot, and immunofluorescence (IF). A dose-dependent increase in TGM1 gene/transcript copy number was detected; likewise, a dose-dependent increase in TGM1 protein level was observed by western blotting and IF between an MOI of 0.3 and 1. Interestingly, TGM1 protein concentration was not further increased between MOIs of 1 and 3, potentially due to regulation of TGM1 at the post-transcriptional/translational level. Importantly, the KB105-expressed human TGM1 was shown to be functional in ARCI keratinocytes as assessed by an in situ fluorescent synthetic peptide reporter assay measuring TGM1-mediated glutamine conjugation, indicating successful molecular correction of the underlying TGM1 deficiency in these cells. Taken together, these data, along with in vivo efficacy and safety seen in surrogate disease models, support application of KB105 for treatment of ARCI. A Phase 1 study is planned for the first half of 2019.