755. One-time Gene Therapy for Hereditary Angioedema

Abstract

Hereditary angioedema (HAE) is a potentially life-threatening autosomal dominant deficiency affecting 1 in 50,000 individuals from all ethnic groups worldwide. More than 99% of HAE cases are caused by a deficiency in functional plasma C1 esterase inhibitor (C1E-INH, a serine protease inhibitor) due to mutations in the SERPING1 gene. Low plasma C1E-INH activity dysregulates the contact, complement, and fibrinolytic systems, resulting in unpredictable, recurrent submucosal edema of cutaneous tissues, gastrointestinal and respiratory tracts. If not treated in a timely manner, laryngeal edema can result in death by asphyxiation. Current HAE treatments consist of management of acute attacks, repeated prophylactic therapy with C1E-INH or long term prophylaxis with attenuated androgens, each complicated by a high economic burden, limited compliance, drug side effects and contraindications. To circumvent this challenge, we hypothesized that a one-time administration of an adeno-associated virus (AAV) gene transfer vector expressing the genetic sequence of C1 esterase-inhibitor (serotype 10 expressing the human CIE-INH coding sequence, AAVrh.10hC1EI) would provide sustained C1E-INH activity levels in plasma, sufficient to prevent angioedema episodes. To study the efficacy of AAVrh.10hC1EI, using CRISPR/Cas9 technology we created a novel C1E-INH deficient mouse model analogous to human HAE disease, and characterized the resulting SERPING1 gene mutations by genome sequencing. The heterozygous mouse model shares characteristics associated with HAE in humans including decreased C1E-INH and C4 levels in plasma and increased vascular permeability. Administration of AAVrh.10hC1EI to the heterozygous mice resulted in sustained human C1E levels above the predicted therapeutic levels. In order to demonstrate that the increased vascular permeability observed in heterozygote C1E-INH+/- mice was a direct result of C1E-INH deficiency, Evans blue dye was injected intravenously and extravasation of dye from the vasculature evaluated. Compared to wild type mice under baseline conditions, the C1EINH+/- mice had increased extravasation of the dye into the hind paws quantitated by optical absorbance at 600 nm. Strikingly, AAVrh10.hC1EI-treated (1011 gc) mice displayed a marked decrease in dye extravasation, whereas non-treated C1E-INH +/- mice had markedly increased dye extravasation. These results demonstrate that a single treatment with AAVrh.10hC1EI has the potential to provide long term protection from angioedema attacks in the affected population, representing a paradigm shift in current therapeutic approaches.