Chronic wound healing by fetal cell therapy may be explained by differential gene profiling observed in fetal versus old skin cells

Fetal Skin Wound Healing: Key Extracellular Matrix Components and Regulators in Scarless Healing

Fetal skin at early gestational stage is able to regenerate and heal rapidly after wounding. The exact mechanisms and molecular pathways involved in this process are however still largely unknown. The numerous differences in the skin of the early fetus versus skin in later developmental stages might provide clues for the mechanisms of scarless healing. This review summarizes the differences between mammalian fetal skin and the skin at later developmental phases in healthy and wounded conditions, focusing on extracellular matrix components, which are crucial factors in the microenvironment that direct cells and tissue functions and hence the wound healing process.

Establishing a Xenograft Model with CD-1 Nude Mice to Study Human Skin Wound Repair

BACKGROUND

A significant gap exists in the translatability of small-animal models to human subjects. One important factor is poor laboratory models involving human tissue. Thus, the authors have created a viable postnatal human skin xenograft model using athymic mice.

METHODS

Discarded human foreskins were collected following circumcision. All subcutaneous tissue was removed from these samples sterilely. Host CD-1 nude mice were then anesthetized, and dorsal skin was sterilized. A 1.2-cm-diameter, full-thickness section of dorsal skin was excised. The foreskin sample was then placed into the full-thickness defect in the host mice and sutured into place. Xenografts underwent dermal wounding using a 4-mm punch biopsy after engraftment. Xenografts were monitored for 14 days after wounding and then harvested.

RESULTS

At 14 days postoperatively, all mice survived the procedure. Grossly, the xenograft wounds showed formation of a human scar at postoperative day 14. Hematoxylin and eosin and Masson trichome staining confirmed scar formation in the wounded human skin. Using a novel artificial intelligence algorithm using picrosirius red staining, scar formation was confirmed in human wounded skin compared with the unwounded skin. Histologically, CD31 + immunostaining confirmed vascularization of the xenograft. The xenograft exclusively showed human collagen type I, CD26 + , and human nuclear antigen in the human scar without any staining of these human markers in the murine skin.

CONCLUSION

The proposed model demonstrates wound healing to be a local response from tissue resident human fibroblasts and allows for reproducible evaluation of human skin wound repair in a preclinical model.

CLINICAL RELEVANCE STATEMENT

Radiation-induced fibrosis is a widely prevalent clinical phenomenon without a well-defined treatment at this time. This study will help establish a small-animal model to better understand and develop novel therapeutics to treat irradiated human skin.

Retrospectives on Three Decades of Safe Clinical Experience with Allogeneic Dermal Progenitor Fibroblasts: High Versatility in Topical Cytotherapeutic Care

Allogeneic dermal progenitor fibroblasts constitute cytotherapeutic contenders for modern cutaneous regenerative medicine. Based on advancements in the relevant scientific, technical, and regulatory fields, translational developments have slowly yet steadily led to the clinical application of such biologicals and derivatives. To set the appropriate general context, the first aim of this study was to provide a current global overview of approved cell and gene therapy products, with an emphasis on cytotherapies for cutaneous application. Notable advances were shown for North America, Europe, Iran, Japan, and Korea. Then, the second and main aim of this study was to perform a retrospective analysis on the various applications of dermal progenitor fibroblasts and derivatives, as clinically used under the Swiss progenitor cell transplantation program for the past three decades. Therein, the focus was set on the extent and versatility of use of the therapies under consideration, their safety parameters, as well as formulation options for topical application. Quantitative and illustrative data were summarized and reported for over 300 patients treated with various cell-based or cell-derived preparations (e.g., progenitor biological bandages or semi-solid emulsions) in Lausanne since 1992. Overall, this study shows the strong current interest in biological-based approaches to cutaneous regenerative medicine from a global developmental perspective, as well as the consolidated local clinical experience gathered with a specific and safe allogeneic cytotherapeutic approach. Taken together, these current and historical elements may serve as tangible working bases for the further optimization of local and modern translational pathways for the provision of topical cytotherapeutic care.

miR-124- and let-7-Mediated Reprogram of Human Fibroblasts into SST Interneurons

Many neurological disorders stem from defects in or the loss of specific neurons. Dysfunction of γ-aminobutyric acid (GABA)ergic interneurons may cause a variety of neurological and psychiatric disorders such as epilepsy, autism, Alzheimer's disease, and depression. Unlike other types of neurons, which can be generated relatively easily by direct reprogramming, it is difficult to generate GABAergic neurons by traditional methods. Neuronal transdifferentiation of fibroblasts mediated by nongenomic-integrated adenovirus has many advantages, but the efficiency is low, and there is a lack of studies using human cells as the initial materials. In this study, we explored the feasibility of the conversion of human fibroblasts into neurons through adenovirus-mediated gene expression and found that by introducing two microRNAs, miR-124 and let-7, together with several small chemical compounds, they can effectively generate GABAergic neuron-like cells from human neonatal fibroblasts without reverting to a progenitor cell stage. Most of these cells expressed neuronal markers and were all somatostatin (SST)-positive cells. Therefore, our study provides a relatively safe and efficient method to generate SST interneurons.

Back to the Cradle of Cytotherapy: Integrating a Century of Clinical Research and Biotechnology-Based Manufacturing for Modern Tissue-Specific Cellular Treatments in Switzerland

Empirically studied by Dr. Brown-Séquard in the late 1800s, cytotherapies were later democratized by Dr. Niehans during the twentieth century in Western Switzerland. Many local cultural landmarks around the Léman Riviera are reminiscent of the inception of such cell-based treatments. Despite the discreet extravagance of the remaining heirs of "living cell therapy" and specific enforcements by Swiss health authorities, current interest in modern and scientifically sound cell-based regenerative medicine has never been stronger. Respective progress made in bioengineering and in biotechnology have enabled the clinical implementation of modern cell-based therapeutic treatments within updated medical and regulatory frameworks. Notably, the Swiss progenitor cell transplantation program has enabled the gathering of two decades of clinical experience in Lausanne for the therapeutic management of cutaneous and musculoskeletal affections, using homologous allogeneic cell-based approaches. While striking conceptual similarities exist between the respective works of the fathers of cytotherapy and of modern highly specialized clinicians, major and important iterative updates have been implemented, centered on product quality and risk-analysis-based patient safety insurance. This perspective article highlights some historical similarities and major evolutive differences, particularly regarding product safety and quality issues, characterizing the use of cell-based therapies in Switzerland over the past century. We outline the vast therapeutic potential to be harnessed for the benefit of overall patient health and the importance of specific scientific methodological aspects.

Evolution of Diploid Progenitor Lung Cell Applications: From Optimized Biotechnological Substrates to Potential Active Pharmaceutical Ingredients in Respiratory Tract Regenerative Medicine

The objective of this review is to describe the evolution of lung tissue-derived diploid progenitor cell applications, ranging from historical biotechnological substrate functions for vaccine production and testing to current investigations around potential therapeutic use in respiratory tract regenerative medicine. Such cell types (e.g., MRC-5 or WI-38 sources) were extensively studied since the 1960s and have been continuously used over five decades as safe and sustainable industrial vaccine substrates. Recent research and development efforts around diploid progenitor lung cells (e.g., FE002-Lu or Walvax-2 sources) consist in qualification for potential use as optimal and renewed vaccine production substrates and, alternatively, for potential therapeutic applications in respiratory tract regenerative medicine. Potentially effective, safe, and sustainable cell therapy approaches for the management of inflammatory lung diseases or affections and related symptoms (e.g., COVID-19 patients and burn patient severe inhalation syndrome) using local homologous allogeneic cell-based or cell-derived product administrations are considered. Overall, lung tissue-derived progenitor cells isolated and produced under good manufacturing practices (GMP) may be used with high versatility. They can either act as key industrial platforms optimally conforming to specific pharmacopoeial requirements or as active pharmaceutical ingredients (API) for potentially effective promotion of lung tissue repair or regeneration.

Optimized Manufacture of Lyophilized Dermal Fibroblasts for Next-Generation Off-the-Shelf Progenitor Biological Bandages in Topical Post-Burn Regenerative Medicine

Cultured fibroblast progenitor cells (FPC) have been studied in Swiss translational regenerative medicine for over two decades, wherein clinical experience was gathered for safely managing burns and refractory cutaneous ulcers. Inherent FPC advantages include high robustness, optimal adaptability to industrial manufacture, and potential for effective repair stimulation of wounded tissues. Major technical bottlenecks in cell therapy development comprise sustainability, stability, and logistics of biological material sources. Herein, we report stringently optimized and up-scaled processing (i.e., cell biobanking and stabilization by lyophilization) of dermal FPCs, with the objective of addressing potential cell source sustainability and stability issues with regard to active substance manufacturing in cutaneous regenerative medicine. Firstly, multi-tiered FPC banking was optimized in terms of overall quality and efficiency by benchmarking key reagents (e.g., medium supplement source, dissociation reagent), consumables (e.g., culture vessels), and technical specifications. Therein, fetal bovine serum batch identity and culture vessel surface were confirmed, among other parameters, to largely impact harvest cell yields. Secondly, FPC stabilization by lyophilization was undertaken and shown to maintain critical functions for devitalized cells in vitro, potentially enabling high logistical gains. Overall, this study provides the technical basis for the elaboration of next-generation off-the-shelf topical regenerative medicine therapeutic products for wound healing and post-burn care.

Surgical Management Evolution Between 2 Massive Burn Cases at 17-Year Interval: Contribution of Cell Therapies in Improving the Surgical Care

We report the cases of 2 patients admitted to our hospital at a 17-year interval, both with 90% total body surface area (TBSA) burns. These two young patients were in good health before their accident, but major differences in time of intensive care and hospitalization were observed: 162 versus 76 days in intensive care unit and 18 versus 9.5 months for hospitalization, respectively. We have analyzed the different parameters side-by-side during their medical care and we have identified that the overall improved outcomes are mainly due to a better adapted fluid reanimation in combination with the evolution of the surgical management to encompass allogenic cellular therapy (Biological Bandages). Indeed, autologous cell therapy using keratinocytes has been used for over 30 years in our hospital with the same technical specifications; however, we have integrated the Biological Bandages and routinely used them for burn patients to replace cadaver skin since the past 15 years. Thus, patient 1 versus patient 2 had, respectively, 83% versus 80% TBSA for autologous cells, and 0% versus 189% for allogenic cells. Notably, it was possible that patient 2 was able to recover ∼6% TBSA with the use of Biological Bandages, by stimulating intermediate burn zones toward a spontaneous healing without requiring further skin grafting (on abdomen and thighs). The body zones where Biological Bandages were not applied, such as the buttocks, progressed to deeper-stage burns. Despite inherent differences to patients at their admission and the complexity of severe burn care, the results of these two case reports suggest that integration of innovative allogenic cell therapies in the surgical care of burn patients could have major implications in the final outcome.

Antimicrobial Peptide Dendrimers and Quorum-Sensing Inhibitors in Formulating Next-Generation Anti-Infection Cell Therapy Dressings for Burns

Multidrug resistance infections are the main cause of failure in the pro-regenerative cell-mediated therapy of burn wounds. The collagen-based matrices for delivery of cells could be potential substrates to support bacterial growth and subsequent lysis of the collagen leading to a cell therapy loss. In this article, we report the development of a new generation of cell therapy formulations with the capacity to resist infections through the bactericidal effect of antimicrobial peptide dendrimers and the anti-virulence effect of anti-quorum sensing MvfR (PqsR) system compounds, which are incorporated into their formulation. Anti-quorum sensing compounds limit the pathogenicity and antibiotic tolerance of pathogenic bacteria involved in the burn wound infections, by inhibiting their virulence pathways. For the first time, we report a biological cell therapy dressing incorporating live progenitor cells, antimicrobial peptide dendrimers, and anti-MvfR compounds, which exhibit bactericidal and anti-virulence properties without compromising the viability of the progenitor cells.

GMP Tiered Cell Banking of Non-enzymatically Isolated Dermal Progenitor Fibroblasts for Allogenic Regenerative Medicine

Non-enzymatically isolated primary dermal progenitor fibroblasts derived from fetal organ donations are ideal cell types for allogenic musculoskeletal regenerative therapeutic applications. These cell types are differentiated, highly proliferative in standard in vitro culture conditions and extremely stable throughout their defined lifespans. Technical simplicity, robustness of bioprocessing and relatively small therapeutic dose requirements enable pragmatic and efficient production of clinical progenitor fibroblast lots under cGMP standards. Herein we describe optimized and standardized monolayer culture expansion protocols using dermal progenitor fibroblasts isolated under a Fetal Transplantation Program for the establishment of GMP tiered Master, Working and End of Production cryopreserved Cell Banks. Safety, stability and quality parameters are assessed through stringent testing of progeny biological materials, in view of clinical application to human patients suffering from diverse cutaneous chronic and acute affections. These methods and approaches, coupled to adequate cell source optimization, enable the obtention of a virtually limitless source of highly consistent and safe biological therapeutic material to be used for innovative regenerative medicine applications.

Industrial Development of Standardized Fetal Progenitor Cell Therapy for Tendon Regenerative Medicine: Preliminary Safety in Xenogeneic Transplantation

Tendon defects require multimodal therapeutic management over extensive periods and incur high collateral burden with frequent functional losses. Specific cell therapies have recently been developed in parallel to surgical techniques for managing acute and degenerative tendon tissue affections, to optimally stimulate resurgence of structure and function. Cultured primary human fetal progenitor tenocytes (hFPT) have been preliminarily considered for allogeneic homologous cell therapies, and have been characterized as stable, consistent, and sustainable cell sources in vitro. Herein, optimized therapeutic cell sourcing from a single organ donation, industrial transposition of multi-tiered progenitor cell banking, and preliminary preclinical safety of an established hFPT cell source (i.e., FE002-Ten cell type) were investigated. Results underlined high robustness of FE002-Ten hFPTs and suitability for sustainable manufacturing upscaling within optimized biobanking workflows. Absence of toxicity or tumorigenicity of hFPTs was demonstrated in ovo and in vitro, respectively. Furthermore, a 6-week pilot good laboratory practice (GLP) safety study using a rabbit patellar tendon partial-thickness defect model preliminarily confirmed preclinical safety of hFPT-based standardized transplants, wherein no immune reactions, product rejection, or tumour formation were observed. Such results strengthen the rationale of the multimodal Swiss fetal progenitor cell transplantation program and prompt further investigation around such cell sources in preclinical and clinical settings for musculoskeletal regenerative medicine.

Retrospective Evaluation of Progenitor Biological Bandage Use: A Complementary and Safe Therapeutic Management Option for Prevention of Hypertrophic Scarring in Pediatric Burn Care

Progenitor Biological Bandages (PBB) have been continuously applied clinically in the Lausanne Burn Center for over two decades. Vast translational experience and hindsight have been gathered, specifically for cutaneous healing promotion of donor-site grafts and second-degree pediatric burns. PBBs constitute combined Advanced Therapy Medicinal Products, containing viable cultured allogeneic fetal dermal progenitor fibroblasts. Such constructs may partly favor repair and regeneration of functional cutaneous tissues by releasing cytokines and growth factors, potentially negating the need for subsequent skin grafting, while reducing the formation of hypertrophic scar tissues. This retrospective case-control study (2010-2018) of pediatric second-degree burn patients comprehensively compared two initial wound treatment options (i.e., PBBs versus Aquacel® Ag, applied during ten to twelve days post-trauma). Results confirmed clinical safety of PBBs with regard to morbidity, mortality, and overall complications. No difference was detected between groups for length of hospitalization or initial relative burn surface decreasing rates. Nevertheless, a trend was observed in younger patients treated with PBBs, requiring fewer corrective interventions or subsequent skin grafting. Importantly, significant improvements were observed in the PBB group regarding hypertrophic scarring (i.e., reduced number of scar complications and related corrective interventions). Such results establish evidence of clinical benefits yielded by the Swiss fetal progenitor cell transplantation program and favor further implementation of specific cell therapies in highly specialized regenerative medicine.

Development of Standardized Fetal Progenitor Cell Therapy for Cartilage Regenerative Medicine: Industrial Transposition and Preliminary Safety in Xenogeneic Transplantation

Diverse cell therapy approaches constitute prime developmental prospects for managing acute or degenerative cartilaginous tissue affections, synergistically complementing specific surgical solutions. Bone marrow stimulation (i.e., microfracture) remains a standard technique for cartilage repair promotion, despite incurring the adverse generation of fibrocartilagenous scar tissue, while matrix-induced autologous chondrocyte implantation (MACI) and alternative autologous cell-based approaches may partly circumvent this effect. Autologous chondrocytes remain standard cell sources, yet arrays of alternative therapeutic biologicals present great potential for regenerative medicine. Cultured human epiphyseal chondro-progenitors (hECP) were proposed as sustainable, safe, and stable candidates for chaperoning cartilage repair or regeneration. This study describes the development and industrial transposition of hECP multi-tiered cell banking following a single organ donation, as well as preliminary preclinical hECP safety. Optimized cell banking workflows were proposed, potentially generating millions of safe and sustainable therapeutic products. Furthermore, clinical hECP doses were characterized as non-toxic in a standardized chorioallantoic membrane model. Lastly, a MACI-like protocol, including hECPs, was applied in a three-month GLP pilot safety evaluation in a caprine model of full-thickness articular cartilage defect. The safety of hECP transplantation was highlighted in xenogeneic settings, along with confirmed needs for optimal cell delivery vehicles and implantation techniques favoring effective cartilage repair or regeneration.

Use of ovine acellular peritoneal matrix combined with honey and ovine fetal skin extract in the healing of full-thickness infected burn wounds in a rat model

Treatment of infected burn wounds remains a challenge in burn units. Silver-sulfadiazine (SSD) is the most commonly used topical antimicrobial agent in managing these wounds. We aimed to accelerate the healing of burn wounds by combined application of ovine acellular peritoneal matrix (OAPM), honey (H), and ovine fetal skin extract (OFSE). Sixty-four standardized burn wounds were created on the dorsum of 16 rats and were subsequently inoculated with Staphyloccocus aureus and Pseudomonas aeruginosa. After 48 hr, the wounds were surgically debrided and received either physiologic saline (control group) or SSD, OAPM+SSD, OAPM+H+SSD, and OAPM+H+OFSE+SSD. The healing wounds were evaluated for size, bacterial counts, histopathology, and biomechanical properties on days 3, 7, 14, 21, and 28 after surgery. All treatments had effectively reduced the level of S. aureus and P. aeruginosa on wounds compared to the control group by day 3 and 7. The wounds treated with combined application of OAPM+H+OFSE+SSD demonstrated considerable inflammation reduction, fibroplasia, complete re-epithelialization, and wound contraction together with significantly lesser scar tissue formation. Treatment with OAPM+H+OFSE+SSD showed superior biomechanical properties of the healing wounds. The findings suggested that the synergistic effect of dressing the wounds with OAPM, H, and OFSE was a very effective approach in accelerating the healing process of the experimentally induced infected full-thickness burn wounds in rats.

Holistic Approach of Swiss Fetal Progenitor Cell Banking: Optimizing Safe and Sustainable Substrates for Regenerative Medicine and Biotechnology

Safety, quality, and regulatory-driven iterative optimization of therapeutic cell source selection has constituted the core developmental bedrock for primary fetal progenitor cell (FPC) therapy in Switzerland throughout three decades. Customized Fetal Transplantation Programs were pragmatically devised as straightforward workflows for tissue procurement, traceability maximization, safety, consistency, and robustness of cultured progeny cellular materials. Whole-cell bioprocessing standardization has provided plethoric insights into the adequate conjugation of modern biotechnological advances with current restraining legislative, ethical, and regulatory frameworks. Pioneer translational advances in cutaneous and musculoskeletal regenerative medicine continuously demonstrate the therapeutic potential of FPCs. Extensive technical and clinical hindsight was gathered by managing pediatric burns and geriatric ulcers in Switzerland. Concomitant industrial transposition of dermal FPC banking, following good manufacturing practices, demonstrated the extensive potential of their therapeutic value. Furthermore, in extenso, exponential revalorization of Swiss FPC technology may be achieved via the renewal of integrative model frameworks. Consideration of both longitudinal and transversal aspects of simultaneous fetal tissue differential processing allows for a better understanding of the quasi-infinite expansion potential within multi-tiered primary FPC banking. Multiple fetal tissues (e.g., skin, cartilage, tendon, muscle, bone, lung) may be simultaneously harvested and processed for adherent cell cultures, establishing a unique model for sustainable therapeutic cellular material supply chains. Here, we integrated fundamental, preclinical, clinical, and industrial developments embodying the scientific advances supported by Swiss FPC banking and we focused on advances made to date for FPCs that may be derived from a single organ donation. A renewed model of single organ donation bioprocessing is proposed, achieving sustained standards and potential production of billions of affordable and efficient therapeutic doses. Thereby, the aim is to validate the core therapeutic value proposition, to increase awareness and use of standardized protocols for translational regenerative medicine, potentially impacting millions of patients suffering from cutaneous and musculoskeletal diseases. Alternative applications of FPC banking include biopharmaceutical therapeutic product manufacturing, thereby indirectly and synergistically enhancing the power of modern therapeutic armamentariums. It is hypothesized that a single qualifying fetal organ donation is sufficient to sustain decades of scientific, medical, and industrial developments, as technological optimization and standardization enable high efficiency.

Small Extracellular Vesicles from Human Fetal Dermal Cells and Their MicroRNA Cargo: KEGG Signaling Pathways Associated with Angiogenesis and Wound Healing

The use of cell secreted factors in clinical settings could be an alternative to conventional cell therapy, with the advantage of limiting concerns generally associated with traditional cell transplantation, such as tumorigenicity, immunoreactivity, and carrying of infections. Based on our published data, we predict a potential role for extracellular vesicles (EVs) in contributing to the proangiogenic activity of human fetal dermal cell secretome. Depletion of nanosized EVs from secretome significantly impaired its ability to induce formation of mesh-like structures in vitro. The isolated EVs were characterized for size and concentration by nanoparticle tracking analysis, and for protein markers (Rab5⁺, Alix⁺, CD63⁺, and calnexin⁻). The microRNA profile of EVs revealed 87 microRNAs significantly upregulated (≥15-fold increase) in fetal compared to adult dermal cell-derived EVs. Interestingly, these upregulated microRNAs included microRNAs with a validated role in angiogenesis according to literature. Moreover, the DIANA-TarBase v7.0 analysis confirmed enrichment in the KEGG signaling pathways associated with angiogenesis and wound healing, with the identification of putative target genes including thrombospondin 1. To validate the in silico data, EVs were also characterized for total protein contents. When tested in in vitro angiogenesis, fetal dermal cell-derived EVs were more effective than their adult counterpart in inducing formation of complete mesh-like structures. Furthermore, treatment of fibroblasts with fetal dermal-derived EVs determined a 4-fold increase of thrombospondin 1 protein amounts compared with the untreated fibroblasts. Finally, visualization of CSFE-labeled EVs in the cytosol of target cells suggested a successful uptake of these particles at 4-8 hours of incubation. We conclude that EVs are important contributors of the proangiogenic effect of fetal dermal cell secretome. Hence, EVs could also serve as vehicle for a successful delivery of microRNAs or other molecules of therapeutic interest to target cells.

Bringing Safe and Standardized Cell Therapies to Industrialized Processing for Burns and Wounds

Cultured primary progenitor cell types are worthy therapeutic candidates for regenerative medicine. Clinical translation, industrial transposition, and commercial implementation of products based on such cell sources are mainly hindered by economic or technical barriers and stringent regulatory requirements. Applied research in allogenic cellular therapies in the Lausanne University Hospital focuses on cell source selection technique optimization. Use of fetal progenitor cell sources in Switzerland is regulated through Federal Transplantation Programs and associated Fetal Biobanks. Clinical applications of cultured primary progenitor dermal fibroblasts have been optimized since the 1990s as “Progenitor Biological Bandages” for pediatric burn patients and adults presenting chronic wounds. A single organ donation procured in 2009 enabled the establishment of a standardized cell source for clinical and industrial developments to date. Non-enzymatically isolated primary dermal progenitor fibroblasts (FE002-SK2 cell type) served for the establishment of a clinical-grade Parental Cell Bank, based on a patented method. Optimized bioprocessing methodology for the FE002-SK2 cell type has demonstrated that extensive and consistent progenitor cell banks can be established. In vitro mechanistic characterization and in vivo preclinical studies have confirmed potency, preliminary safety and efficacy of therapeutic progenitor cells. Most importantly, highly successful industrial transposition and up-scaling of biobanking enabled the establishment of tiered Master and Working Cell Banks using Good Manufacturing Practices. Successive and successful transfers of technology, know-how and materials to different countries around the world have been performed. Extensive developments based on the FE002-SK2 cell source have led to clinical trials for burns and wound dressing. Said trials were approved in Japan, Taiwan, USA and are continuing in Switzerland. The Swiss Fetal Transplantation Program and pioneer clinical experience in the Lausanne Burn Center over three decades constitute concrete indicators that primary progenitor dermal fibroblasts should be considered as therapeutic flagships in the domain of wound healing and for regenerative medicine in general. Indeed, one single organ donation potentially enables millions of patients to benefit from high-quality, safe and effective regenerative therapies. This work presents a technical and translational overview of the described progenitor cell technology harnessed in Switzerland as cellular therapies for treatment of burns and wounds around the globe.

Severe Burn Injury Progression and Phasic Changes of Gene Expression in Mouse Model

Patients with severe burns are susceptible to infectious complications including burn-site infections and sepsis. The purpose of this study was to explore the pathologic development of burn injury in a mouse model and to screen genes dysregulated at different time points on the basis of gene expression microarrays. Differential expression analysis identified a total 223 genes that related to only time progression independent of burn injury and 214 genes with aberrant expression due to burn injury. Weighted gene co-expression network analysis (WGCNA) of the 214 genes obtained seven gene modules which named as red, blue, turquoise, green, brown, yellow, and gray module, and the blue module was found to be significantly associated with severe burn injury progression, and in which several genes were previously reported being associated with inflammation and immune response, such as interleukin IL-6, IL-8, and IL-1b. Functional enrichment analysis indicated significant enrichment of biological processes that related to metabolism and catabolism, and pathways of proteasome, notch signaling and cell cycle. This result supports a phase progression of severe burn with gene expression changes and interpretation of biological processes in mouse.

Evolution of Biological Bandages as First Cover for Burn Patients

Significance: Cutaneous wound regeneration is vital to keep skin functions and for large wounds, to maintain human survival. In a deep burn, the ability of the skin to heal is compromised due to the damage of vasculature and resident cells, hindering a coordinated response in the regeneration process. Temporal skin substitutes used as first cover can play a major role in skin regeneration as they allow a rapid wound covering that, in turn, can significantly reduce infection risk, rate of secondary corrective surgeries, and indirectly hospitalization time and costs. Recent Advances: Skin was one of the first tissues to be bioengineered providing thus a skin equivalent; however, what is the current status subsequent to 40 years of tissue engineering? We review the classic paradigms of biological skin substitutes used as first cover and evaluate recent discoveries and clinical approaches adapted for burn injuries cover, with an emphasis on innovative cell-based approaches. Critical Issues: Cell-based first covers offer promising perspectives as they can have an active function in wound healing, such as faster healing minimizing scar formation and prepared wound bed for subsequent grafting. However, cell-based therapies encounter some limitations due to regulatory hurdles, as they are considered as "Advanced Therapy Medicinal Products," which imposes the same industry-destined good manufacturing practices as for pharmaceutical products and biological drug development. Future Directions: Further improvements in clinical outcome can be expected principally with the use of cell-based therapies; however, hospital exemptions are necessary to assure accessibility to the patient and safety without hindering advances in therapies.

Skin tissue engineering: wound healing based on stem-cell-based therapeutic strategies

Normal wound healing is a dynamic and complex multiple phase process involving coordinated interactions between growth factors, cytokines, chemokines, and various cells. Any failure in these phases may lead wounds to become chronic and have abnormal scar formation. Chronic wounds affect patients' quality of life, since they require repetitive treatments and incur considerable medical costs. Thus, much effort has been focused on developing novel therapeutic approaches for wound treatment. Stem-cell-based therapeutic strategies have been proposed to treat these wounds. They have shown considerable potential for improving the rate and quality of wound healing and regenerating the skin. However, there are many challenges for using stem cells in skin regeneration. In this review, we present some sets of the data published on using embryonic stem cells, induced pluripotent stem cells, and adult stem cells in healing wounds. Additionally, we will discuss the different angles whereby these cells can contribute to their unique features and show the current drawbacks.

A randomized, double-blind, phase I clinical trial of fetal cell-based skin substitutes on healing of donor sites in burn patients

BACKGROUND

Due to limited graft donor sites in extensive burns, re-harvesting of a single donor area is very common. Given the importance of fetal fibroblasts in accelerating fetal wound healing, fetal cell-based skin substitutes have emerged as a novel therapeutic modality for regenerating damaged skin. In this trial, we aimed to evaluate the safety, feasibility and potential efficacy of application of amniotic membranes seeded with fetal fibroblasts for accelerating donor sites healing in burn patients.

METHODS

In this randomized, double-blind, phase I clinical trial, 10 patients with total burn surface area of 10-55% were enrolled. Three equal parts (10×10cm) were selected in donor site of each patient and covered by Vaseline gauze (control group), amniotic membrane (AM group), or amniotic membrane seeded with fetal fibroblasts (AM-F group). Adverse events, pain intensity scores, and wound sizes were recorded on days 4, 8, 11, 14, and 20 post-treatment. Also, histological assessments were done on days 0 and 14 after the surgery.

RESULTS

All patients underwent surgery, and no adverse events occurred during the procedure and follow-up period. Significantly lower pain intensity and higher healing rates were observed in AM-F and AM groups compared to the control group. Moreover, mean complete re-epithelializatin in AM-F and AM groups were 10.1±2.4 and 11.3±2.9 days, showing that the healing process was significantly accelerated compared to the control group with mean closure time of 14.8±1.6 days. Histological assessment showed lower inflammatory cells infiltration in AM-F and AM groups compared to control group.

CONCLUSIONS

This study indicated the safety of transplantation of amniotic membrane seeded with fetal fibroblasts for treatment of donor sites in burn patients; however, preliminary assessments showed no benefits for this therapeutic modality over amniotic membrane alone. Thus, to draw accurate conclusions, further trials in larger populations should be conducted.

LEVEL OF EVIDENCE

This study is assigned as level I.

Cell-based skin substitutes accelerate regeneration of extensive burn wounds in rats

BACKGROUND

This study investigated the effects of amniotic membrane combined with adipose-derived stem cells or fetal fibroblasts on regenerating extensive burns in rats.

METHODS

Third degree burns of 1100-1800 mm² were induced on 32 Sprague-Dawley rats. Burned sites were excised and randomly covered with Vaseline gauze (control), human amniotic membrane (HAM), human fetal fibroblasts seeded on HAM (HAM-FF), or human adipose-derived stem cells seeded on HAM (HAM-ASC), and followed by wound closure and histological assessments.

RESULTS

Wound closure rates of HAM-FF, HAM-ASC, HAM and control groups at seven and 14 days after the treatment were 42.2% and 81.9%, 41.9% and 81.7%, 33.5% and 74.2%, and 16.5% and 69.7%, respectively. Wounds of HAM-FF, HAM-ASC, HAM and control groups were closed on 40, 40, 50 and 60 days after the treatment, respectively (P < 0.05). Histological assessments revealed lower inflammatory cell infiltration in HAM-ASC and HAM-FF groups.

CONCLUSIONS

Cell-based engineered skin substitutes seem to accelerate wound regeneration, especially within the first 14 days.

Biomaterials and tissue engineering for scar management in wound care

Scars are a natural and unavoidable result from most wound repair procedures and the body's physiological healing response. However, they scars can cause considerable functional impairment and emotional and social distress. There are different forms of treatments that have been adopted to manage or eliminate scar formation. This review covers the latest research in the past decade on using either natural agents or synthetic biomaterials in treatments for scar reduction.

Anti-Microbial Dendrimers against Multidrug-Resistant P. aeruginosa Enhance the Angiogenic Effect of Biological Burn-wound Bandages

Multi-drug resistant Pseudomonas aeruginosa has increased progressively and impedes further regression in mortality in burn patients. Such wound infections serve as bacterial reservoir for nosocomial infections and are associated with significant morbidity and costs. Anti-microbial polycationic dendrimers G3KL and G3RL, able to kill multi-drug resistant P. aeruginosa, have been previously developed. The combination of these dendrimers with a class of biological bandages made of progenitor skin cells, which secrete growth factors, could positively impact wound-healing processes. However, polycations are known to be used as anti-angiogenic agents for tumor suppression. Since, neovascularization is pivotal in the healing of deep burn-wounds, the use of anti-microbial dendrimers may thus hinder the healing processes. Surprisingly, we have seen in this study that G3KL and G3RL dendrimers can have angiogenic effects. Moreover, we have shown that a dendrimer concentration ranging between 50 and 100 μg/mL in combination with the biological bandages can suppress bacterial growth without altering cell viability up to 5 days. These results show that antimicrobial dendrimers can be used in combination with biological bandages and could potentially improve the healing process with an enhanced angiogenesis.

Microchimeric fetal cells play a role in maternal wound healing after pregnancy

Fetal cells persist in mothers for decades after delivery: in a phenomenon called fetal microchimerism. While persistent fetal cells were first implicated in autoimmune disease, parallel studies in animal and human pregnancy now suggest that microchimeric fetal cells play a role in the response to tissue injury. The aim of this study was to investigate the impact of fetal microchimeric cells in the adult wound, using caesarean section (CS) as a model of wound healing in pregnancy. XY-FISH (fluorescence in situ hybridization) and immunostaining was used in multiple tissue sections from CS skin biopsies from 70 women, to locate, quantitate and characterize microchimeric male presumed-fetal cells. Y-FISH and Nested PCR was used to confirm XY-FISH results. XY-FISH demonstrated the presence of isolated 0-9 male fetal cells per section in the epidermis of the healed CS scars from only those women who had their first male child by CS. Both Y-FISH and Y-PCR confirmed the presence of fetal cells in CS scars. Combined FISH and immunostaining showed all male fetal cells present were keratinocytes, as they expressed cytokeratin, and were almost exclusively located in epidermis. Microchimeric fetal cells also expressed Collagen I, III, and TGF-β3 in healed maternal scars. Identification of male-presumed fetal cells in healed maternal CS scars after pregnancy suggests that, possibly in response to signals produced by maternal skin injury at CS, fetal cells migrate to the site of damage to become involved in maternal tissue repair, or proliferate locally.

Strategies for improving the repair of focal cartilage defects

Articular cartilage, together with skin, was predicted to be one of the first tissues to be successfully engineered. However cartilage repair remains nowadays still elusive, as we are still not able to overcome the hurdles of creating biomaterials corresponding to the native properties of the tissue, and which operate in joints environment that is not favorable for regeneration. In this review, we give an overview of the outcome of current cartilage treatment techniques. Furthermore we present current research strategies for improving cartilage tissue engineering.

Human Fetal Progenitor Tenocytes for Regenerative Medicine

Tendon injuries are very frequent and affect a wide and heterogeneous population. Unfortunately, the healing process is long with outcomes that are not often satisfactory due to fibrotic tissue appearance, which leads to scar and adhesion development. Tissue engineering and cell therapies emerge as interesting alternatives to classical treatments. In this study, we evaluated human fetal progenitor tenocytes (hFPTs) as a potential cell source for treatment of tendon afflictions, as fetal cells are known to promote healing in a scarless regenerative process. hFPTs presented a rapid and stable growth up to passage 9, allowing to create a large cell bank for off-the-shelf availability. hFPTs showed a strong tenogenic phenotype with an excellent stability, even when placed in conditions normally inducing cells to differentiate. The karyotype also indicated a good stability up to passage 12, which is far beyond that necessary for clinical application (passage 6). When placed in coculture, hFPTs had the capacity to stimulate human adult tenocytes (hATs), which are responsible for the deposition of a new extracellular matrix during tendon healing. Finally, it was possible to distribute cells in porous or gel scaffolds with an excellent survival, thus permitting a large variety of applications (from simple injections to grafts acting as filling material). All of these results are encouraging in the development of an off-the-shelf cell source capable of stimulating tendon regeneration for the treatment of tendon injuries.

Key regulatory role of dermal fibroblasts in pigmentation as demonstrated using a reconstructed skin model: impact of photo-aging

To study cutaneous pigmentation in a physiological context, we have previously developed a functional pigmented reconstructed skin model composed of a melanocyte-containing epidermis grown on a dermal equivalent comprising living fibroblasts. The present studies, using the same model, aimed to demonstrate that dermal fibroblasts influence skin pigmentation up to the macroscopic level. The proof of principle was performed with pigmented skins differing only in the fibroblast component. First, the in vitro system was reconstructed with or without fibroblasts in order to test the global influence of the presence of this cell type. We then assessed the impact of the origin of the fibroblast strain on the degree of pigmentation using fetal versus adult fibroblasts. In both experiments, impressive variation in skin pigmentation at the macroscopic level was observed and confirmed by quantitative parameters related to skin color, melanin content and melanocyte numbers. These data confirmed the responsiveness of the model and demonstrated that dermal fibroblasts do indeed impact the degree of skin pigmentation. We then hypothesized that a physiological state associated with pigmentary alterations such as photo-aging could be linked to dermal fibroblasts modifications that accumulate over time. Pigmentation of skin reconstructed using young unexposed fibroblasts (n = 3) was compared to that of tissues containing natural photo-aged fibroblasts (n = 3) which express a senescent phenotype. A stimulation of pigmentation in the presence of the natural photo-aged fibroblasts was revealed by a significant increase in the skin color (decrease in Luminance) and an increase in both epidermal melanin content and melanogenic gene expression, thus confirming our hypothesis. Altogether, these data demonstrate that the level of pigmentation of the skin model is influenced by dermal fibroblasts and that natural photo-aged fibroblasts can contribute to the hyperpigmentation that is associated with photo-aging.

Fetal stem cell transplantation: Past, present, and future

Since 1928, human fetal tissues and stem cells have been used worldwide to treat various conditions. Although the transplantation of the fetal midbrain substantia nigra and dopaminergic neurons in patients suffering from Parkinson’s disease is particularly noteworthy, the history of other types of grafts, such as those of the fetal liver, thymus, and pancreas, should be addressed as there are many lessons to be learnt for future stem cell transplantation. This report describes previous practices and complications that led to current clinical trials of isolated fetal stem cells and embryonic stem (ES) cells. Moreover, strategies for transplantation are considered, with a particular focus on donor cells, cell processing, and the therapeutic cell niche, in addition to ethical issues associated with fetal origin. With the advent of autologous induced pluripotent stem cells and ES cells, clinical dependence on fetal transplantation is expected to gradually decline due to lasting ethical controversies, despite landmark achievements.

Fetal fibroblasts and keratinocytes with immunosuppressive properties for allogeneic cell-based wound therapy

Fetal skin heals rapidly without scar formation early in gestation, conferring to fetal skin cells a high and unique potential for tissue regeneration and scar management. In this study, we investigated the possibility of using fetal fibroblasts and keratinocytes to stimulate wound repair and regeneration for further allogeneic cell-based therapy development. From a single fetal skin sample, two clinical batches of keratinocytes and fibroblasts were manufactured and characterized. Tolerogenic properties of the fetal cells were investigated by allogeneic PBMC proliferation tests. In addition, the potential advantage of fibroblasts/keratinocytes co-application for wound healing stimulation has been examined in co-culture experiments with in vitro scratch assays and a multiplex cytokines array system. Based on keratin 14 and prolyl-4-hydroxylase expression analyses, purity of both clinical batches was found to be above 98% and neither melanocytes nor Langerhans cells could be detected. Both cell types demonstrated strong immunosuppressive properties as shown by the dramatic decrease in allogeneic PBMC proliferation when co-cultured with fibroblasts and/or keratinocytes. We further showed that the indoleamine 2,3 dioxygenase (IDO) activity is required for the immunoregulatory activity of fetal skin cells. Co-cultures experiments have also revealed that fibroblasts-keratinocytes interactions strongly enhanced fetal cells secretion of HGF, GM-CSF, IL-8 and to a lesser extent VEGF-A. Accordingly, in the in vitro scratch assays the fetal fibroblasts and keratinocytes co-culture accelerated the scratch closure compared to fibroblast or keratinocyte mono-cultures. In conclusion, our data suggest that the combination of fetal keratinocytes and fibroblasts could be of particular interest for the development of a new allogeneic skin substitute with immunomodulatory activity, acting as a reservoir for wound healing growth factors.

Elastin signaling in wound repair

Skin is an important organ to the human body as it functions as an interface between the body and environment. Cutaneous injury elicits a complex wound healing process, which is an orchestration of cells, matrix components, and signaling factors that re-establishes the barrier function of skin. In adults, an unavoidable consequence of wound healing is scar formation. However, in early fetal development, wound healing is scarless. This phenomenon is characterized by an attenuated inflammatory response, differential expression of signaling factors, and regeneration of normal skin architecture. Elastin endows a range of mechanical and cell interactive properties to skin. In adult wound healing, elastin is severely lacking and only a disorganized elastic fiber network is present after scar formation. The inherent properties of elastin make it a desirable inclusion to adult wound healing. Elastin imparts recoil and resistance and induces a range of cell activities, including cell migration and proliferation, matrix synthesis, and protease production. The effects of elastin align with the hallmarks of fetal scarless wound healing. Elastin synthesis is substantial in late stage in utero and drops to a trickle in adults. The physical and cell signaling advantages of elastin in a wound healing context creates a parallel with the innate features of fetal skin that can allow for scarless healing.

Novel differences in the expression of inflammation-associated genes between mid- and late-gestational dermal fibroblasts

While cutaneous wounds of late-gestational fetuses and on through adulthood result in scar formation, wounds incurred early in gestation have been shown to heal scarlessly. Unique properties of fetal fibroblasts are believed to mediate this scarless healing process. In this study, microarray analysis was used to identify differences in the gene expression profiles of cultured fibroblasts from embryonic day 15 (E15; midgestation) and embryonic day 18 (E18; late-gestation) skin. Sixty-two genes were differentially expressed and 12 of those genes are associated with inflammation, a process that correlates with scar formation in fetal wounds. One of the differentially expressed inflammatory genes was cyclooxygenase-1 (COX-1). COX-1 was more highly expressed in E18 fibroblasts than in E15 fibroblasts, and these differences were confirmed at the gene and protein level. Differences in COX-1 protein expression were also observed in fetal skin by immunohistochemical and immunofluorescence staining. The baseline differences in gene expression found in mid- and late-gestational fetal fibroblasts suggest that developmental alterations in fibroblasts could be involved in the transition from scarless to fibrotic fetal wound healing. Furthermore, baseline differences in the expression of inflammatory genes by fibroblasts in E15 and E18 skin may contribute to inflammation and scar formation late in gestation.

Common threads in cardiac fibrosis, infarct scar formation, and wound healing

Wound healing, cardiac fibrosis, and infarct scar development, while possessing distinct features, share a number of key functional similarities, including extracellular matrix synthesis and remodeling by fibroblasts and myofibroblasts. Understanding the underlying mechanisms that are common to these processes may suggest novel therapeutic approaches for pathologic situations such as fibrosis, or defective wound healing such as hypertrophic scarring or keloid formation. This manuscript will briefly review the major steps of wound healing, and will contrast this process with how cardiac infarct scar formation or interstitial fibrosis occurs. The feasibility of targeting common pro-fibrotic growth factor signaling pathways will be discussed. Finally, the potential exploitation of novel regulators of wound healing and fibrosis (ski and scleraxis), will be examined.

Tissue-engineered fetal dermal matrices

In the early to mid-gestation fetus, skin wounds heal with no scar formation and perfect restoration of dermal architecture. This phenomenon is intrinsic to fetal skin. The intrinsic phenotypic properties of the fetal fibroblast are believed to be "the effector of scarless repair". We sought to prepare dermal matrices with high similarity to the mid-gestation fetal dermis using the technology of "self-assembly" with fetal dermal cells of 18, 20, and 22 wk gestation. Comparison of these dermal constructs to those prepared with neonatal dermal cells, adult skin, neonatal foreskin, and mid-gestation fetal skin demonstrates that these fetal dermal matrices bear marked morphological and biochemical resemblance to the mid-gestation fetal dermis. In order to shed further light on the genes involved in scarless wound healing, we conducted a differential gene array analysis of the neonatal and fetal dermal matrices. Using a gene chip (GLYCOv4 gene chip) of approximately 1,260 human genes, we observed differential expression of 67 genes. A number of fibrotic genes were observed to be downregulated and anti-fibrotic genes upregulated.

Epiphyseal Chondroprogenitors Provide a Stable Cell Source for Cartilage Cell Therapy

Articular cartilage regeneration poses particularly tough challenges for implementing cell-based therapies. Many cell types have been investigated looking for a balanced combination of responsiveness and stability, yet techniques are still far from defining a gold standard. The work presented focuses on the reliable expansion and characterization of a clinical grade human epiphyseal chondroprogenitor (ECP) cell bank from a single tissue donation. A parental human ECP cell bank was established, which provides the seed material for master and working cell banks. ECPs were investigated at both low and high cumulative population doublings looking at morphology, monolayer expansion kinetics, resistance to cryogenic shock, colony-forming efficiency, and cell surface markers. Three-dimensional micropellet assays were used to determine spontaneous extracellular matrix deposition at varying population doublings and monolayer 2D differentiation studies were undertaken to assess the propensity for commitment into other lineages and their stability. ECPs exhibited remarkable homogeneity in expansion with a steady proliferative potential averaging three population doublings over 8 days. Surface marker analysis revealed no detectable contaminating subpopulations or population enrichment during prolonged culture periods. Despite a slight reduction in Sox9 expression levels at higher population doublings in monolayer, nuclear localization was equivalent both in monolayer and in micropellet format. Equally, ECPs were capable of depositing glycosaminoglycans and producing aggrecan, collagen I, and collagen II in 3D pellets both at low and high population doublings indicating a stable spontaneous chondrogenic potential. Osteogenic induction was differentially restricted in low and high population doublings as observed by Von Kossa staining of calcified matrix, with a notable collagen X, MMP13, and ADAMTS5 downregulation. Rare adipogenic induction was seen as evidenced by cytoplasmic lipid accumulation detectable by Oil Red O staining. These findings highlight the reliability, stability, and responsiveness of ECPs over prolonged culture, making them ideal candidates in defining novel strategies for cartilage regeneration.

Biologicals and fetal cell therapy for wound and scar management

Few biopharmaceutical preparations developed from biologicals are available for tissue regeneration and scar management. When developing biological treatments with cellular therapy, selection of cell types and establishment of consistent cell banks are crucial steps in whole-cell bioprocessing. Various cell types have been used in treatment of wounds to reduce scar to date including autolog and allogenic skin cells, platelets, placenta, and amniotic extracts. Experience with fetal cells show that they may provide an interesting cell choice due to facility of outscaling and known properties for wound healing without scar. Differential gene profiling has helped to point to potential indicators of repair which include cell adhesion, extracellular matrix, cytokines, growth factors, and development. Safety has been evidenced in Phase I and II clinical fetal cell use for burn and wound treatments with different cell delivery systems. We present herein that fetal cells present technical and therapeutic advantages compared to other cell types for effective cell-based therapy for wound and scar management.

Human fetal bone cells in delivery systems for bone engineering

The aim of this study was to culture human fetal bone cells (dedicated cell banks of fetal bone derived from 14 week gestation femurs) within both hyaluronic acid gel and collagen foam, to compare the biocompatibility of both matrices as potential delivery systems for bone engineering and particularly for oral application. Fetal bone cell banks were prepared from one organ donation and cells were cultured for up to 4 weeks within hyaluronic acid (Mesolis®) and collagen foams (TissueFleece®). Cell survival and differentiation were assessed by cell proliferation assays and histology of frozen sections stained with Giemsa, von Kossa and ALP at 1, 2 and 4 weeks of culture. Within both materials, fetal bone cells could proliferate in three-dimensional structure at ∼70% capacity compared to monolayer culture. In addition, these cells were positive for ALP and von Kossa staining, indicating cellular differentiation and matrix production. Collagen foam provides a better structure for fetal bone cell delivery if cavity filling is necessary and hydrogels would permit an injectable technique for difficult to treat areas. In all, there was high biocompatibility, cellular differentiation and matrix deposition seen in both matrices by fetal bone cells, allowing for easy cell delivery for bone stimulation in vivo.

The wound healing process: an overview of the cellular and molecular mechanisms

Wound healing remains a challenging clinical problem and correct, efficient wound management is essential. Much effort has been focused on wound care with an emphasis on new therapeutic approaches and the development of technologies for acute and chronic wound management. Wound healing involves multiple cell populations, the extracellular matrix and the action of soluble mediators such as growth factors and cytokines. Although the process of healing is continuous, it may be arbitrarily divided into four phases: (i) coagulation and haemostasis; (ii) inflammation; (iii) proliferation; and (iv) wound remodelling with scar tissue formation. The correct approach to wound management may effectively influence the clinical outcome. This review discusses wound classification, the physiology of the wound healing process and the methods used in wound management.