Keratinocytes and Adipose-derived mesenchymal stem cells : The heir and the spare to regenerative cellular therapies for difficult-to-heal skin wounds

Abstract: Cell-based therapy is considered as Advanced Therapy Medicinal Product, (ATMP), which had increasingly stricter regulations in the last decade. The cells must be produced according to the ‘Guidelines on Good Manufacturing Practice (GMP) specific to Advanced Therapy Medicinal Products’, adopted by the European Medicines Agency (EMA). A fully compliant autologous keratinocyte-based ATMP certified for clinical use remains an unmet challenge in Europe. This necessitates the development of a comprehensive bio-production workflow to tackle key technical bottlenecks along this procedure. On the other hand, adipose-derived mesenchymal stem cells (AD-MSCs) hold promise as an effective alternative to primary keratinocytes in treating difficult-to-heal wounds, particularly for patients with extensive skin wounds. The overall aim of this thesis is to provide a bio-production workflow addressing the challenges associated with developing an autologous keratinocyte-based ATMP. Additionally, the thesis aims to elucidate the molecular and functional mechanisms that modulate the wound healing capabilities of keratinocytes and AD-MSCs. In papers I-III the bio-production procedure for an autologous keratinocyte-based ATMP to treat difficult-to-heal wounds was divided into 3 main stages; keratinocytes extraction, expansion, and transportation. Paper I validated the use of an animal-origin-free enzymatic workflow for the extraction of keratinocytes from the epidermis, compared to the classical workflow containing animal-derived products. Both workflows proved comparable in efficiency in terms of the final cell yield from skin samples, in addition to the purity and functionality of the keratinocytes following cultivation. This report confirms the feasibility of an entirely xeno-free workflow for acquiring GMP-compliant epidermal cells suitable for clinical application without altering key features of keratinocytes. Paper II evaluates an expansion approach for keratinocytes on three culture substrates (1) glass (2) conventional polystyrene (plastic) and (3) animal-derived collagen I ECM matrix. Keratinocytes cultured on glass showed better colonization and survival during the first 3 days of culture. Further molecular characterization revealed evidence of accelerated epidermal differentiation in keratinocytes cultured on glass. Henceforth, functional characterization revealed that glass enhanced the temporal angiogenic and migratory capabilities of keratinocytes. Our findings provided evidence that glass can be a promising substrate capable of supporting keratinocyte cultures, with enhanced wound repair characteristics favourable for transplantation applications. In paper III, we evaluated four candidate solutions for transporting keratinocytes in suspension at 4°C for 24h, namely (1) normal saline; (2) saline with 2.5% human serum albumin; (3) chemically defined, xenofree keratinocyte media; and (4) keratinocyte media with bovine pituitary extract. The tested conditions showed that 2.5% HSA preserved keratinocyte viability, colonization as well as phenotype. This study helped the research team to implement the use of human serum albumin as transportation solution for the proposed keratinocyte-ATMP approach. In paper IV, a direct co-culture model for human keratinocytes and AD-MSCs was proposed to investigate the ability of keratinocytes to enhance AD-MSCs’ differentiation toward the epidermal lineage. Furthermore, miRNA and protein content of human keratinocytes and AD-MSCs were analysed and bioinformatically analysed to identify possible regulations between differentially expressed miRNAs and proteins. This study predicted two potential miRNA-mediated gene regulations with strong implications in AD-MSCs-to-epidermal differentiation; the first was centred on epidermal growth factor (EGF) through miR-485-5p, miR-6765-5p and miR-4459. The second was the regulation of interleukin 1 alpha (IL-1α) by four isomers of miR-30-5p and miR-181a-5p. Paper V evaluates the regenerative potential of autologous AD-MSCs in-vivo using an excisional full-thickness porcine wound model. The data generated from miRNA and protein screening of AD-MSCs was re-analysed with a focus on possible regulations of AD-MCSs in wound healing. Our computational analyses predicted that miR-155 mediates multiple gene regulations of fibroblast growth factor 2 and 7, C-C motif chemokine ligand 2 and vascular cell adhesion molecule 1. The predicted model was verified experimentally and revealed a positive regulation between miR-155 and the identified four factors. Each of these factors carries out key functions within the wound healing process including vascularization, inflammation, proliferation, and remodelling. In summary, the core of the work presented in this thesis provides a complete, in-vitro validated, and EMA-compliant bio-production procedure for autologous keratinocyte as an ATMP. We also presented novel miRNA-mediated epigenetic regulations in human keratinocytes and AD-MSCs. These models can serve as a valuable tool to develop novel hypotheses aiming to elucidate the biology of stem cell differentiation and wound healing.