Phase I/II Clinical Trial of Ex Vivo Gene Therapy Using COL7A1-Encoding SIN Retroviral Vector in Recessive Dystrophic Epidermolysis Bullosa

The primary objective of this phase I/II clinical trial is to evaluate the **safety** of grafting SIN RV-mediated COL7A1 gene-modified autologous skin equivalents (SE) in adults with **recessive dystrophic epidermolysis bullosa (RDEB)**. This evaluation will be conducted at months 1, 2, 3, 6, and 12 post-grafting, with a continued regulatory follow-up at months 18, 24, 30, 36, 42, 48, 54, and 60. The clinical relevance of this objective lies in ensuring the safety of this novel gene therapy approach, which aims to provide a therapeutic option for individuals with RDEB, a condition characterized by severe skin fragility.

Secondary objectives include: - Assessing the **efficacy** of SIN RV-mediated COL7A1 gene-modified autologous SE in adults with RDEB at weeks 2, and months 1, 3, 6, 12, 24, 36, 48, and 60 post-grafting. - Evaluating the **immune response** against the recombinant type VII collagen (C7) at months 1, 3, 12, 18, 24, 30, 36, 42, 48, 54, and 60 post-grafting. These secondary objectives are crucial for understanding the therapeutic potential and immunogenicity of the treatment, which are essential for its clinical application.

The clinical trial involves participants diagnosed with **recessive dystrophic epidermolysis bullosa (RDEB)**, a rare genetic skin disorder. The study population includes both male and female adults aged 18 years and older. Participants are required to have a clinical and molecular diagnosis of RDEB with confirmed bi-allelic COL7A1 mutations. The trial does not involve a vulnerable population. The sponsor has not provided information regarding the total number of participants. Participants must have significantly reduced staining of C7 on skin biopsy, as measured by immunofluorescence microscopy, and a reduced number of or morphologically abnormal anchoring fibrils confirmed by transmission electron microscopy. Additionally, they should have at least 100 cm² of blistered and/or erosive skin areas, including chronic wounds suitable for skin grafting. The ability to undergo anesthesia for grafting procedures is also a requirement. The selection process ensures that participants are willing and able to give informed consent, highlighting the importance of understanding and agreeing to the trial's procedures and objectives.

The clinical trial is a **Phase I/II** study designed to evaluate the safety of a **skin equivalent graft** genetically corrected with a **COL7A1-encoding SIN retroviral vector** in adults with **recessive dystrophic epidermolysis bullosa (RDEB)**. This trial employs a randomized, double-blind, controlled design to ensure the reliability and validity of the results. The trial is expected to span a total duration of approximately seven years, with an estimated recruitment start date in January 2020 and an anticipated end date in June 2027.

Participants will undergo a series of study visits, beginning with an inclusion (screening) visit to confirm eligibility based on criteria such as age (≥18 years), clinical and molecular diagnosis of RDEB, and the presence of suitable skin areas for grafting. Following the initial grafting procedure, participants will attend follow-up visits at months 1, 2, 3, 6, and 12 to monitor safety and efficacy outcomes. Long-term follow-up visits will occur at months 18, 24, 30, 36, 42, 48, 54, and 60 to continue safety assessments and evaluate the durability of the treatment effects.

The primary endpoint focuses on the occurrence of adverse events (AEs), serious adverse events (SAEs), adverse reactions (ARs), and serious adverse reactions (SARs) over a 12-month period post-grafting and throughout the five-year follow-up. Secondary endpoints include skin biopsy analysis for **C7 protein** expression and anchoring fibril morphology, serum analysis for anti-C7 antibodies and T-cell responses, and clinical assessments of scar quality, blister numbers, and quality of life.

Participant involvement is expected to last for the entire duration of the trial, with conditions for early termination including the occurrence of significant adverse events or withdrawal of consent. The trial aims to provide valuable insights into the safety and potential therapeutic benefits of this innovative gene therapy approach for individuals with RDEB.

The clinical trial involves the use of an **experimental medication** known as the "Skin equivalent graft genetically corrected with a COL7A1-encoding SIN retroviral vector." This product is classified as a **living tissue equivalent** and is designed for the treatment of Recessive Dystrophic Epidermolysis Bullosa (RDEB). The active substance in this treatment consists of **autologous keratinocytes and fibroblasts** that have been transduced with a retroviral vector encoding the **COL7A1 cDNA**. The pharmaceutical form of this product is a living tissue equivalent, and it is administered through a route categorized as "other use," which typically involves direct application to the affected skin areas. The frequency and dosage of administration are determined based on the specific requirements of the trial protocol, and the treatment is not formulated for pediatric use.

In this clinical trial, there are no non-experimental treatments such as standard-of-care therapy, placebo, or comparator treatments explicitly mentioned. The focus is solely on evaluating the safety and efficacy of the genetically corrected skin equivalent graft. Participant compliance with the treatment regimen is monitored throughout the study to ensure adherence to the dosing schedule and to assess the safety profile of the experimental medication. The trial includes a follow-up period extending up to five years to monitor long-term safety and outcomes.

The efficacy of the clinical trial will be assessed through a series of primary and secondary endpoints. The primary endpoints focus on the evaluation of **adverse events (AEs)**, **serious adverse events (SAEs)**, **adverse reactions (ARs)**, and **serious adverse reactions (SARs)** at each visit over a 12-month period following grafting, as well as during a long-term follow-up period totaling five years. Secondary endpoints include detailed skin biopsy analyses of grafted skin at specified intervals (M3, M6, M12, M24, M36, M48, and M60) compared to baseline. These analyses will assess **C7 protein expression** using immunofluorescence microscopy (IF) and the morphology of anchoring fibrils at the dermal-epidermal junction (DEJ) via transmission electron microscopy (TEM).

Serum analysis will be conducted at multiple timepoints (M1, M6, M12, M18, M24, M30, M36, M42, M48, M54, and M60) to detect anti-C7 antibodies using enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence (IIF), and/or Western blot (WB), as well as T-cell responses to the full-length C7 by enzyme-linked immunosorbent spot (ELISPOT) assay. Clinical assessments will be performed at the same intervals to evaluate scar quality using the Vancouver Scar Scale (VSS), changes in blister numbers over the grafted skin, clinical appearance changes of grafted skin through photographs, pruritus changes measured by the Leuven Itch Scale (LIS), and changes in Quality of Life Score measured by the QOLEB. These comprehensive assessments will provide a robust evaluation of the treatment's efficacy in patients with **recessive dystrophic epidermolysis bullosa (RDEB)**.