In vitro keratinocyte expansion for cell transplantation therapy is associated with differentiation and loss of basal layer derived progenitor population

Towards propagation of epidermal cells for wound repair: glass, as cell culture substrate, enhances proliferation and migration of human keratinocytes

Introduction

Human keratinocytes require relatively long propagation time which impedes their availability as autologous cell transplantation within a clinically reasonable timeframe. There is an unmet need for efficient xeno-free cell expansion approaches to propagate human keratinocytes as regenerative therapy.

Methods

Primary human keratinocytes and HaCaT cells were cultured on glass, plastic, and animal-derived collagen I matrix for 10 days. Proliferation, migration, DNA methylation, as well as gene and protein expression were assessed to characterize the effect of the tested culture substrates on keratinocytes at the molecular and functional levels.

Results

Keratinocytes cultured on glass exhibited faster proliferation, global DNA demethylation and upregulation of epidermal differentiation markers. Scratch wound assay revealed that keratinocytes cultured on glass demonstrated enhanced cell migration compared to those on plastic or collagen I. Multiplex immunoassays identified temporal and substrate-dependent variations in a panel of keratinocyte-specific secreted factors, encompassing immunomodulatory cytokines, growth factors, and angiogenic factors.

Discussion

Glass, as a culture substrate, promotes epidermal differentiation and enhances keratinocyte migration. The latter is a critical factor in re-epithelialization and wound healing. Functional properties suggest that glass may optimize the inflammatory response and promote efficient wound repair, making it a promising candidate for the short-term expansion of keratinocytes for transplantation purposes. Further in-vivo validation is required to definitively establish the efficacy of keratinocytes cultured on glass for clinical applications.

A novel method for the establishment of autologous skin cell suspensions: characterisation of cellular sub-populations, epidermal stem cell content and wound response-enhancing biological properties

Introduction: Autologous cell suspension (ACS)-based therapy represents a highly promising approach for burns and chronic wounds. However, existing technologies have not achieved the desired clinical success due to several limitations. To overcome practical and cost-associated obstacles of existing ACS methods, we have established a novel methodology for rapid, enzymatic disaggregation of human skin cells and their isolation using a procedure that requires no specialist laboratory instrumentation and is performed at room temperature. Methods: Cells were isolated using enzymatic disaggregation of split-thickness human skin followed by several filtration steps for isolation of cell populations, and cell viability was determined. Individual population recovery was confirmed in appropriate culture medium types, and the presence of epidermal stem cells (EpSCs) within keratinocyte sub-populations was defined by flow cytometry via detection of CD49 and CD71. Positive mediators of wound healing secreted by ACS-derived cultures established on a collagen-based wound-bed mimic were detected by proteome arrays and quantified by ELISA, and the role of such mediators was determined by cell proliferation assays. The effect of ACS-derived conditioned-medium on myofibroblasts was investigated using an in-vitro model of myofibroblast differentiation via detection of α-SMA using immunoblotting and immunofluorescence microscopy. Results: Our methodology permitted efficient recovery of keratinocytes, fibroblasts and melanocytes, which remained viable upon long-term culture. ACS-derivatives comprised sub-populations with the CD49-high/CD71-low expression profile known to demarcate EpSCs. Via secretion of mitogenic factors and wound healing-enhancing mediators, the ACS secretome accelerated keratinocyte proliferation and markedly curtailed cytodifferentiation of myofibroblasts, the latter being key mediators of fibrosis and scarring. Discussion: The systematic characterisation of the cell types within our ACS isolates provided evidence for their superior cell viability and the presence of EpSCs that are critical drivers of wound healing. We defined the biological properties of ACS-derived keratinocytes, which include ability to secrete positive mediators of wound healing as well as suppression of myofibroblast cytodifferentiation. Thus, our study provides several lines of evidence that the established ACS isolates comprise highly-viable cell populations which can physically support wound healing and possess biological properties that have the potential to enhance not only the speed but also the quality of wound healing.

Wound Healing after Acellular Dermal Substitute Positioning in Dermato-Oncological Surgery: A Prospective Comparative Study

BACKGROUND

MatriDerm and Integra are both widely used collagenic acellular dermal matrices (ADMs) in the surgical setting, with similar characteristics in terms of healing time and clinical indication. The aim of the present study is to compare the two ADMs in terms of clinical and histological results in the setting of dermato-oncological surgery.

METHODS

Ten consecutive patients with medical indications to undergo surgical excision of skin cancers were treated with a 2-step procedure at our Dermatologic Surgery Unit. Immediately after tumor removal, both ADMs were positioned on the wound bed, one adjacent to the other. Closure through split-thickness skin grafting was performed after approximately 3 weeks. Conventional histology, immunostaining and ELISA assay were performed on cutaneous samples at different timepoints.

RESULTS

No significant differences were detected in terms of either final clinical outcomes or in extracellular matrix content of the neoformed dermis. However, Matriderm was observed to induce scar retraction more frequently. In contrast, Integra was shown to carry higher infectious risk and to be more slowly reabsorbed into the wound bed. Sometimes foreign body-like granulomatous reactions were also observed, especially in Integra samples.

CONCLUSIONS

Even in the presence of subtle differences between the ADMs, comparable global outcomes were demonstrated after dermato-oncological surgery.

Ex vivo gene modification therapy for genetic skin diseases-recent advances in gene modification technologies and delivery

Genetic skin diseases, also known as genodermatoses, are inherited disorders affecting skin and constitute a large and heterogeneous group of diseases. While genodermatoses are rare with the prevalence rate of less than 1 in 50,000 - 200,000, they frequently occur at birth or early in life and are generally chronic, severe, and could be life-threatening. The quality of life of patients and their families are severely compromised by the negative psychosocial impact of disease, physical manifestations, and the lack or loss of autonomy. Currently, there are no curative treatments for these conditions. Ex vivo gene modification therapy that involves modification or correction of mutant genes in patients' cells in vitro and then transplanted back to patients to restore functional gene expression has being developed for genodermatoses. In this review, the ex vivo gene modification therapy strategies for genodermatoses are reviewed, focusing on current advances in gene modification and correction in patients' cells and delivery of genetically modified cells to patients with discussions on gene therapy trials which have been performed in this area.

Cutaneous Radiation Injuries: Models, Assessment and Treatments

Many cases of human exposures to high-dose radiation have been documented, including individuals exposed during the detonation of atomic bombs in Hiroshima and Nagasaki, nuclear power plant disasters (e.g., Chernobyl), as well as industrial and medical accidents. For many of these exposures, injuries to the skin have been present and have played a significant role in the progression of the injuries and survivability from the radiation exposure. There are also instances of radiation-induced skin complications in routine clinical radiotherapy and radiation diagnostic imaging procedures. In response to the threat of a radiological or nuclear mass casualty incident, the U.S. Department of Health and Human Services tasked the National Institute of Allergy and Infectious Diseases (NIAID) with identifying and funding early- to mid-stage medical countermeasure (MCM) development to treat radiation-induced injuries, including those to the skin. To appropriately assess the severity of radiation-induced skin injuries and determine efficacy of different approaches to mitigate/treat them, it is necessary to develop animal models that appropriately simulate what is seen in humans who have been exposed. In addition, it is important to understand the techniques that are used in other clinical indications (e.g., thermal burns, diabetic ulcers, etc.) to accurately assess the extent of skin injury and progression of healing. For these reasons, the NIAID partnered with two other U.S. Government funding and regulatory agencies, the Biomedical Advanced Research and Development Authority (BARDA) and the Food and Drug Administration (FDA), to identify state-of-the-art methods in assessment of skin injuries, explore animal models to better understand radiation-induced cutaneous damage and investigate treatment approaches. A two-day workshop was convened in May 2019 highlighting talks from 28 subject matter experts across five scientific sessions. This report provides an overview of information that was presented and the subsequent guided discussions.

In Vitro Expansion of Keratinocytes on Human Dermal Fibroblast-Derived Matrix Retains Their Stem-Like Characteristics

The long-term expansion of keratinocytes under conditions that avoid xenogeneic components (i.e. animal serum- and feeder cell-free) generally causes diminished proliferation and increased terminal differentiation. Here we present a culture system free of xenogeneic components that retains the self-renewal capacity of primary human keratinocytes. In vivo the extracellular matrix (ECM) of the tissue microenvironment has a major influence on a cell's fate. We used ECM from human dermal fibroblasts, cultured under macromolecular crowding conditions to facilitate matrix deposition and organisation, in a xenogeneic-free keratinocyte expansion protocol. Phospholipase A2 decellularisation produced ECM whose components resembled the core matrix composition of natural dermis by proteome analyses. Keratinocytes proliferated rapidly on these matrices, retained their small size, expressed p63, lacked keratin 10 and rarely expressed keratin 16. The colony forming efficiency of these keratinocytes was enhanced over that of keratinocytes grown on collagen I, indicating that dermal fibroblast-derived matrices maintain the in vitro expansion of keratinocytes in a stem-like state. Keratinocyte sheets formed on such matrices were multi-layered with superior strength and stability compared to the single-layered sheets formed on collagen I. Thus, keratinocytes expanded using our xenogeneic-free protocol retained a stem-like state, but when triggered by confluence and calcium concentration, they stratified to produce epidermal sheets with a potential clinical use.

Extracellular matrix deposition by adipose-derived stem cells and fibroblasts: a comparative study

Cell-based strategies are today widely studied as possible therapies for wound healing. In this setting, fibroblasts play a key role since they are the main dermal cellular component and are responsible for extracellular matrix secretion. Several works report on the possibility of using fibroblast-derived extracellular matrix scaffolds for wound healing in skin injuries. While fibroblast-based substitutes have already been intensively studied by other groups, we focused our attention on the possibility of creating an adipose-derived stem cell (ADSC)-induced dermal scaffold for wound healing. ADSCs are a particular subset of mesenchymal stem cells present in the stromal vascular fraction of the adipose tissue. The aim of our work was to compare the ability of ADSCs and fibroblast to produce in vitro a scaffolding material, both in terms of collagen and fibronectin production. ADSCs turned out to be capable of efficiently producing a collagen and fibronectin-containing dermal matrix upon stimulation with ascorbic acid. We observed fibronectin and collagen production by ADSCs to be even more abundant when compared to fibroblasts'. Our results support the use of ADSC-induced sheets instead of fibroblast-based dermal substitutes as wound-healing strategies in full-thickness skin injuries.

An in vitro feasibility investigation considering primary human melanocytes for spray- grafting of freshly isolated autologous skin cells for burn treatment and a clinical case report

A skin cell-spray grafting technique that enables the on-site application of freshly isolated autologous single cell suspensions was already applied in many cases on caucasian patients with low skin coloration. Our project hypothesis is that these suspensions contain keratinocytes and vital melanocytes, that are of particular interest for the treatment of patients of darker skin color. To test this, we applied an in vitro model, wherein the feasibility of i) isolating and ii) spraying of freshly isolated autologous melanocyte-keratinocyte cell suspensions was investigated. Primary human epidermal keratinocytes (HEKs) and melanocytes (MCs) were isolated from skin biopsies (n=8). Biochemical parameter, cell counts, cell morphology, growth behavior and immunofluorescence results were compared in two groups using MC cultures and co-cultures of MCs with HEKs. Case information on using the method clinically with one patient is included. The sprayed mixed cell suspensions proliferated in all groups without measurable loss of viability, and MCs exhibited a regular cell morphology in monoculture up to passage 4°. The sprayed MCs and HEKs demonstrated in vitro glucose and lactate metabolism that was comparable to the pipetted controls. In co-culture, well distributed CK14+ HEKs and NKI/beteb+ MCs could be demonstrated, which interacted in the in vitro model. The ratio of HEKs : MCs in our primary cultures were microscopically counted (n=8 each) as mean +/- SD 1,211,000 (+/- 574,343) HEK : 99,625 (+/- 59,025) MC; i.e., a ratio of approx. 12 : 1. Using the isolation method clinically for a patient with dark skin coloration after suffering severe second-degree burns shows a satisfying re-pigmentation of the resulting wound post healing. Freshly isolated spray-on melanocyte/keratinocyte suspensions provide for a considerable amount of viable HEKs and MCs. Using MCs in spray-grafting suspensions could represent a promising approach for treating severe partial-thickness burns and innovative therapy developments that also aim to address cosmetic aspects.

Spontaneous evolution of human skin fibroblasts into wound-healing keratinocyte-like cells

Producing keratinocyte cells (KCs) in large scale is difficult due to their slow proliferation, disabling their use as seed cells for skin regeneration and wound healing. Cell reprogramming is a promising inducer-based approach to KC production but only reaches very low cellular conversion. Here we reported a unique cellular conversion phenomenon, where human skin fibroblasts (FBs) were spontaneously converted into keratinocyte-like cells (KLCs) over the time without using any inducers.

Methods: FBs were routinely cultured for more than 120 days in regular culture medium. Characteristics of KLCs were checked at the molecular and cellular level. Then the functionality and safety of the KLCs were verified by wound healing and tumorigenicity assay, respectively. To identify the mechanism of the cell conversion phenomenon, high-throughput RNA sequencing was also performed.

Results: The global conversion started on day 90 and reached 90% on day 110. The KLCs were as functional and effective as KCs in wound healing without causing oncogenicity. The conversion was regulated via a PI3K-AKT signaling pathway mediated by a long non-coding RNA, LINC00672. Modulating the pathway could shorten the conversion time to 14 days.

Conclusion: The discovered FBs-KLCs conversion in the study might open a new avenue to the scalable production of cell sources needed for regenerating skins and healing large-area wounds.

In vitro Engineering of a Skin Substitute Based on Adipose-Derived Stem Cells

In the field of wound healing, stem cell-based strategies are gaining importance for their regenerative potential. Adipose-derived stem cells (ADSCs) are a particular subset of mesenchymal stem cells present in the stromal-vascular fraction of the adipose tissue, today considered very attractive for their relative abundance and accessibility in the human body. However, ADSCs are still not routinely used in normal clinical practice. Several studies have also reported ADSC transplantation in association with biomaterials in an attempt to enhance the local retention and growth rate of the cells. The aim of our study was to evaluate the ability of ADSCs to build a dermal scaffold to be potentially used as a dermal substitute in the field of wound healing, with optimal biocompatibility and mechanical properties. ADSCs were defined as CD90-, CD73-, and CD105-positive cells. ADSCs turned out to be capable of secreting all the main components of the extracellular matrix (ECM) upon stimulation, thus efficiently producing a collagen and fibronectin-containing dermal matrix. We also checked whether the ADSC-produced dermal scaffold could be seeded with keratinocytes. The scaffolding material directly produced by ADSCs has several advantages when compared to the commercially available ones: it is easily obtained from the patients and it is 100% biocompatible and supports cell-ECM interaction. Moreover, it represents a possible powerful therapeutic tool for patients with chronic ulcers since it appears to be potentially grafted with keratinocytes layers, thus bypassing the classical two-step grafting procedure.

Using paracrine effects of Ad-MSCs on keratinocyte cultivation and fabrication of epidermal sheets for improving clinical applications

Recent advances in wound healing have made cell therapy a potential approach for the treatment of various types of skin defects such as trauma, burns, scars and diabetic leg ulcers. Cultured keratinocytes have been applied to burn patients since 1981. Patients with acute and chronic wounds can be treated with autologous/allograft cultured keratinocytes. There are various methods for cultivation of epidermal keratinocytes used in cell therapy. One of the important properties of an efficient cell therapy is the preservation of epidermal stem cells. Mesenchymal Stem Cells (MSCs) are major regulatory cells involved in the acceleration of wound healing via induction of cell proliferation, angiogenesis and stimulating the release of paracrine signaling molecules. Considering the beneficial effects of MSCs on wound healing, the main aim of the present study is investigating paracrine effects of Adipose-derived Mesenchymal Stem Cell (Ad-MSCs) on cultivation of keratinocytes with focusing on preservation of stem cells and their differentiation process. We further introduced a new approach for culturing isolated keratinocytes in vitro in order to generate epidermal keratinocyte sheets without using a feeder layer. To do so, Ad-MSC conditioned medium was applied as an alternative to commercial media for keratinocyte cultivation. In this study, the expression of several stem/progenitor cell (P63, K19 and K14) and differentition (K10, IVL and FLG) markers was examined using real time PCR on days 7, 14 and 21 of culture in keratinocytes in Ad-MSC conditioned medium. P63 and α6 integrin expression was also evaluated via flow cytometry. The results were compared with control group including keratinocytes cultured in EpiLife medium and our data indicated that this Ad-MSC conditioned medium is a good alternative for keratinocyte cultivation and producing epidermal sheets for therapeutic and clinical purposes. The reasons are the expression of stem cell and differentiation markers and overcoming the requirement for feeder layer which leads to a xenograft-free transplantation. Besides, this approach has low cost and is easier to perform. However, more in vitro and in vivo experiments as well as safety evaluation required before clinical applications.

Delivery systems of current biologicals for the treatment of chronic cutaneous wounds and severe burns

While wound therapy remains a clinical challenge in current medical practice, much effort has focused on developing biological therapeutic approaches. This paper presents a comprehensive review of delivery systems for current biologicals for the treatment of chronic wounds and severe burns. The biologicals discussed here include proteins such as growth factors and gene modifying molecules, which may be delivered to wounds free, encapsulated, or released from living systems (cells, skin grafts or skin equivalents) or biomaterials. Advances in biomaterial science and technologies have enabled the synthesis of delivery systems such as scaffolds, hydrogels and nanoparticles, designed to not only allow spatially and temporally controlled release of biologicals, but to also emulate the natural extracellular matrix microenvironment. These technologies represent an attractive field for regenerative wound therapy, by offering more personalised and effective treatments.