Expansion of an HSV-1-based gene therapy platform to treat Hailey-Hailey and Darier diseases

Summary: Abstract Body: The herpes simplex virus type 1 (HSV-1)-based gene therapy beremagene geperpavec (B-VEC) has been successful in treating the rare genetic skin blistering disease dystrophic epidermolysis bullosa (DEB). The underlying platform technology is being developed to treat additional rare skin diseases, including Hailey-Hailey disease (HHD) and Darier disease (DD). HHD and DD are inherited genodermatoses caused by pathogenic variants in the calcium ATPases ATP2C1 and ATP2A2, respectively, for which Krystal Biotech, Inc. is developing KB111 and KB112. Here, we sought to determine if these vectors are capable of transducing keratinocytes both in culture and in wild-type mice in order to express their encoded ATPases with minimal toxicity. Quantitative PCR (qPCR) and reverse-transcription PCR (RT-qPCR) were used to quantify vector genomes and transcripts, respectively, in clinically relevant immortalized human keratinocytes after transduction; western blotting (WB) was used to verify the production of full-length protein. To evaluate tolerability, Mosmann’s Tetrazolium Toxicity (MTT) assay and flow cytometry were used to assess cell viability at multiple timepoints post-dose. Immunofluorescent (IF) staining was employed to observe proper localization of ATP2C1 and ATP2A2 to the Golgi and endoplasmic reticulum, respectively. Experiments were also performed with mice administered either KB111 or KB112 topically or via intradermal injection. Twenty-four hours after administration, skin punches were taken for DNA and RNA quantification, IF, and hematoxylin and eosin staining. In vitro and in vivo analyses indicated that both KB111 and KB112 are capable of transducing keratinocytes and expressing their encoded ATPases with minimal toxicity both in culture and in murine skin, demonstrating that Krystal’s HSV-1-based platform is well-suited for the treatment of both HHD and DD. Bruce Nmezi¹, Mary Jane Duermeyer¹, Jorge Guzman-Lepe¹, Trevor Parry¹, Suma Krishnan¹ 1. Krystal Biotech Inc, Pittsburgh, PA, United States. Genetic Disease, Gene Regulation, Gene Therapy & Epigenetics