Presence of large progenitor cell populations in pz-cel autologous gene-corrected epidermal sheets

Summary: Background: Recessive Dystrophic Epidermolysis Bullosa (RDEB) is a rare genetic disorder caused by biallelic mutations in the COL7A1 gene, resulting in deficient or absent collagen VII (Col7) protein, leading to fragile skin and chronic wound formation under mechanical stress. Pz-cel (prademagene zamikeracel) was developed to address large, chronic wounds in RDEB patients. Epidermal cells isolated from patient skin biopsies are expanded <i>ex vivo</i> and genetically corrected by retroviral vector transduction to restore Col7 expression. The corrected cells are cultured and differentiated into epidermal sheets. A long-term follow-up study from a Phase 1/2a clinical trial demonstrated sustained wound closure for some wounds up to eight years. Additionally, a two-year follow-up on Col7 expression at the grafted sites revealed detectable Col7 in treated areas at 24 months. Methods: Pz-cel sheets dissociated and analyzed by flow cytometry. Cells were assessed using antibodies against key markers associated with progenitor cell populations, including K14, integrin α6, CD71, CD29 and K15. Results: Analysis confirmed that the cell sheets are primarily composed of basal keratinocytes (K14<i>+:</i>82%± 19% SD, N=10), which serve <i>in vivo</i> as a reservoir of epidermal stem cells and progenitors. Integrin α6<i>bright</i> expression was observed at a mean of 75.5% ± 22% SD, while K15 expression was detected at a mean of 32% ± 25% SD (N=6) in the epidermal sheets. Additionally, analysis showed 85.9% ± 15% SD of the cells were CD29<i>+</i>, and 88% ± 13% SD exhibited an CD28+/CD71<i>dim/- </i>phenotype. The Integrinα 6<i>bright</i>/CD29<i>+</i>/CD71<i>dim/- </i>subpopulation was estimated at 67% ± 21% SD. Conclusions: These results confirm the presence of a significant population of progenitor cells within the graft. The large proportion of these cells in the drug product may increase the likelihood of wound site repopulation by long-lasting, genetically corrected cells, consistent with the detection of Col7 at grafted sites at 24 months. Clarisse Rogat¹, Brian Kevany¹ 1. Abeona Therapeutics Inc, Cleveland, OH, United States. Stem Cell Biology, Tissue Regeneration and Wound Healing