Identification of a long-term surviving human mesenchymal stromal cell subpopulation and implications for recessive dystrophic epidermolysis bullosa treatment

BACKGROUND: Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin disease caused by loss-of-function pathogenic variants in COL7A1 encoding type VII collagen (C7). Patients with RDEB suffer since birth from skin and mucosal blistering and develop severe local and systemic complications resulting in poor prognosis. Mesenchymal stromal cells (MSCs) have demonstrated their potential to enhance wound healing and reduce skin inflammation in RDEB patients due to their anti-inflammatory properties and capacity to express C7. We aim to optimize in vitro conditioning of human bone marrow-derived MSCs (BM-MSCs) to improve their limited survival following local injection in a murine model. METHODS: ). These cells were subsequently injected intradermally (ID) in immunodeficient mice and their survival was assessed by in vivo imaging. BM-MSCs populations were analyzed prior to injection by single-cell RNA sequencing (scRNAseq). Murine skin injected with BM-MSCs were sampled two months post-injection and the surviving subpopulations were characterized by spatial transcriptomic. RESULTS: scRNAseq analysis revealed marked variations between monolayer and spheroid conditions, which were significantly impacted by oxygen level. Although most injected cells gradually died within the first 2 months in all tested conditions, 1% of live bioluminescent cells persisted for 54 up to 61 weeks post-injection. Spatial transcriptomics data analysis demonstrated that all surviving cells, regardless of their in vitro preconditioning, retained the expression of the MSC markers THY1, ENG, and NT5E, shared features with fibroblasts, and exhibited enriched expression in genes related to extracellular matrix and collagen fibril organization, which are key processes in wound healing. Spatial transcriptomic and scRNAseq data integration suggested that surviving BM-MSCs were initially present in the injected population, regardless of their culture condition. Remarkably, none of the in vitro preconditioning strategies appeared to affect their survival capacity or functional properties following local injection. CONCLUSIONS: The identification and characterization of a BM-MSC subpopulation capable of long-term survival following ID injection hold promise for the development of improved cell therapy protocols for RDEB.