Advantages of using a bank of allogenic keratinocytes for the rapid coverage of extensive and deep second-degree burns

The use of human-derived feeder layers for the cultivation of transplantable human epidermal cell sheet to repair second degree burn wounds

BACKGROUND AND OBJECTIVES

Human epidermal cell sheet (human-ECS) is a feasible treatment option for wound injury. Traditionally, researchers often use murine 3T3 fibroblast cells as feeder layer to support human epidermal cell sheet grafts, thus increase risk to deliver animal-borne infection. To overcome the potential risks involved with xenotransplantation, we develop human foreskin fibroblast cell as feeder layer culture system and investigate the effects of human-ECS on second-degree burn wound healing in mini-pig in order to develop more effective and safer therapies to enhance wound healing in human.

MATERIALS AND METHODS

Human epidermal keratinocytes and fibroblasts were isolated from foreskin tissue and were co-cultured to manufacture human-ECS. The cell morphology was monitored with phase-contrast microscopy, the stem cell markers were assessed by flow cytometry, and by colony-forming efficiency (CFE) assay. The structure of human-ECS was observed by hematoxylin and eosin staining. Expression of cytokines in human-ECS was confirmed by enzyme-linked immunosorbent assay. Second-degree burn wounds were created on the dorsal of miniature pig to evaluate the effect of oil gauze, oil gauze combined with commercial epidermal growth factor (EGF) cream, and oil gauze combined with human-ECS. Wound healing rate, histological examination, and Masson staining were measured to observe the wound repair efficacy. Real-time PCR and Western blot were utilized to detect the expression level of EGF and interleukin 6 (IL-6).

RESULTS

Stratified human-ECS with 6-7 layers of epidermal cells was successfully cultivated with human-derived feeder cells, in which epidermal cell highly expressed CD49f and CFE was 3% ± 0.45%. Application of human-ECS induced a higher wound healing rate than commerical EGF cream and oil gauze control. The expression of EGF in human-ECS group was higher than those in the other groups; however, the expression of IL-6 was significantly decreased at day 14 by human-ECS treatment group.

CONCLUSIONS

Human-derived feeder cells are suitable for cultivation of human-ECS, avoiding pathogen transmission. Human-ECS could enhance second-degree burn wound healing, and its promoting effect involved secreting a variety of cytokines to regulate tissue reparative process.

Understanding the mechanisms of spontaneous and skin-grafted wound repair: the path to engineered skin grafts

Spontaneous wound repair is a complex process that involves overlapping phases of inflammation, proliferation and remodelling, co-ordinated by growth factors and proteases. In extensive wounds such as burns, the repair process would not be achieved in a timely fashion unless grafted. Although spontaneous wound repair has been extensively described, the processes by which wound repair mechanisms mediate graft take are yet to be fully explored. This review describes engraftment stages and summarises current understanding of molecular mechanisms which regulate autologous skin graft healing, with the goal of directing innovation in permanent wound closure with skin substitutes. Graftability and vascularisation of various skin substitutes that are either in the market or in development phase are discussed. In doing so, we cast a spotlight on the paucity of scientific information available as to how skin grafts (both autologous and engineered) heal a wound bed. Better understanding of these processes may assist in developing novel methods of wound management and treatments.

In Situ Forming Nutritional and Temperature Sensitive Scaffold Improves the Esthetic Outcomes of Meshed Split-Thickness Skin Grafts in a Porcine Model

Objective: Full-thickness burn wounds require immediate coverage, and the primary clinical approaches comprise of skin allografts and autografts. The use of allografts is often temporary due to the antigenicity of allografts. In contrast, the availability of skin autografts may be limited in large burn injuries. In such cases, skin autografts can be expanded through the use of a skin mesher, creating meshed split-thickness skin grafts (MSTSGs). MSTSGs have revolutionized the treatment of large full-thickness burn injuries since the 1960s. However, contractures and poor esthetic outcomes remain a problem. We previously formulated and prepared an in situ forming skin substitute, called MeshFill (MF), which can conform to complex shapes and contours of wounds. The objective of this study was to assess the esthetic and wound healing outcomes in full-thickness wounds treated with a combination of MF and MSTSG in a porcine model. Approach: Either MSTSGs or MSTSG+MF was applied to full-thickness excisional wounds in Yorkshire pigs. Wound healing outcomes were assessed using histology, immunohistochemistry, and wound surface area analysis from day 10 to 60. Clinical evaluation of wounds were utilized to assess esthetic outcomes. Results: The results demonstrated that the combination of MSTSGs and MF improved wound healing and esthetic outcomes. Innovation: Effects of MSTSGs and reconstitutable liquid MF in a full-thickness porcine model were investigated for the first time. Conclusion: MF provides promise as a combination therapeutic regimen to improve wound healing and esthetic outcomes.

Novel pre-vascularized tissue-engineered dermis based on stem cell sheet technique used for dermis-defect healing

Insufficient donor dermis and the shortage of three-dimensional vascular networks are the main limitations in the tissue-engineered dermis (TED). To solve these problems, we initially constructed pre-vascularized bone marrow mesenchymal stem cell sheet (PBMCS) and pre-vascularized fibroblasts cell sheet (PFCS) by cell sheet technology, and then superimposed or folded them together to construct a pre-vascularized TED (PTED), aiming to mimic the real dermis structure. The constructed PTED was implanted in nude mice dorsal dermis-defect wound and the wound-healing effect was quantified at Days 1, 7 and 14 via the methods of histochemistry and immunohistochemistry. The results showed that PTED could rapidly promote the wound closure, especially at Day 14, and the wound-healing rate of three-layer PTED could reach 97.2% (P < 0.01), which was faster than the blank control group (89.1%), PBMCS (92.4%), PFCS (93.8%) and six-layer PTED (92.3%). In addition, the vessel density in the PTED group was higher than the other groups on the 14th day. Taken together, it is proved that the PTED, especially three-layer PTED, is more conducive to the full-thickness dermis-defect repair and the construction of the three-dimensional vascular networks, indicating its potential application in dermis-defect repair.

Amniotic Stem Cells Cultured on Thermoresponsive Polymers Allow Obtaining a Full Cell Sheet

Amniotic stem cells promote adhesion and migration of epithelial cells. Obtaining a full sheet containing amniotic stem cells seems to be the best solution for the treatment of burn wounds. The main advantage of this method is obtaining a full sheet of cells by lowering the temperature below the transition temperature, which does not affect extracellular matrix. The purpose of this work was to produce a skin substitute-a full sheet consisting of amniotic mesenchymal stem cells-and compare with well-known fibroblast sheet. Amniotic membrane cells revealed better tendency to full sheet detachment than fibroblasts. Confluence after 24 hours was always higher on polymer-coated dishes than on normal polypropylene dishes. Also viability was higher than on the control culture dish, while the number of apoptotic cells was always highest on polypropylene (control). Ile-Lys-Val-ala-Val (IKVAV) 0.28 addition to poly (poly [ethylene glycol] ethyl methacrylate) (PTEGMA) caused best cell confluence and highest percentage of cells in mitosis phase of cell cycle, but also worst cell detachment was observed in both cell types on PTEGMA IKVAV 0.28. Viability of cells transferred in cell sheet form onto a new culture dish was higher than when detached as suspension enzymatically. Additionally, percentage of apoptotic cells transferred in cell sheet form onto a new culture dish was always lower than when detached as suspension enzymatically. Culturing of PTEGMA, PTEGMA IKVAV 0.28 and PTEGMA IKVAV 0.14 have a stimulating effect on number of cells in mitosis in amniotic cell culture even after cell sheet transfer onto a new dish, whereas such effect with fibroblast was not observed.

Platelet-rich plasma with keratinocytes and fibroblasts enhance healing of full-thickness wounds

Advances in tissue engineering led to the development of various tissue-engineered skin substitutes (TESS) for the treatment of skin injuries. The majority of the autologous TESS required lengthy and costly cell expansion process to fabricate. In this study, we determine the possibility of using a low density of human skin cells suspended in platelet-rich plasma (PRP)-enriched medium to promote the healing of full-thickness skin wounds. To achieve this, full-thickness wounds of size 1.767 cm² were created at the dorsum part of nude mice and treated with keratinocytes (2 × 10⁴ cells/cm²) and fibroblasts (3 × 10⁴ cells/cm²) suspended in 10% PRP-enriched medium. Wound examination was conducted weekly and the animals were euthanized after 2 weeks. Gross examination showed that re-epithelialization was fastest in the PRP+cells group at both day 7 and 14, followed by the PRP group and NT group receiving no treatment. Only the PRP+cells group achieved complete wound closure by 2 weeks. Epidermal layer was presence in the central region of the wound of the PRP+cells and PRP groups but absence in the NT group. Comparison between the PRP+cells and PRP groups showed that the PRP+cells-treated wound was more mature as indicated by the presence of thinner epidermis with single cell layer thick basal keratinocytes and less cellular dermis. In summary, the combination of low cell density and diluted PRP creates a synergistic effect which expedites the healing of full-thickness wounds. This combination has the potential to be developed as a rapid wound therapy via the direct application of freshly harvested skin cells in diluted PRP.

A computational prediction for the effective drug and stem cell treatment of human airway burns

Burns in the airway from inhaling hot gases lead to one of the most common causes of death in the United States. In order to navigate tissues with large burn areas, the velocity, temperature, and heat flux distributions throughout the human airway system are computed for the inhalation of hot air using the finite-element method. From there, the depth of burned tissue is estimated for a range of exposure times. Additionally, the effectiveness of drug or stem cell delivery to the burned airway tissue is considered for a range of drug or cell sizes. Results showed that the highest temperature and lowest heat flux regions are observed near the pharynx and just upstream of the glottis. It was found that large particles such as stem cells (>20 μm) are effective for treatment of the upper airways, whereas small particles (<10 μm) such as drug nanoparticles are effective in the lower airways.

Outcome of Burns Treated With Autologous Cultured Proliferating Epidermal Cells: A Prospective Randomized Multicenter Intrapatient Comparative Trial

Standard treatment for large burns is transplantation with meshed split skin autografts (SSGs). A disadvantage of this treatment is that healing is accompanied by scar formation. Application of autologous epidermal cells (keratinocytes and melanocytes) may be a suitable therapeutic alternative, since this may enhance wound closure and improve scar quality. A prospective, multicenter randomized clinical trial was performed in 40 adult patients with acute full thickness burns. On two comparable wound areas, conventional treatment with SSGs was compared to an experimental treatment consisting of SSGs in combination with cultured autologous epidermal cells (ECs) seeded in a collagen carrier. The primary outcome measure was wound closure after 5-7 days. Secondary outcomes were safety aspects and scar quality measured by graft take, scar score (POSAS), skin colorimeter (DermaSpectrometer) and elasticity (Cutometer). Wound epithelialization after 5-7 days was significantly better for the experimental treatment (71%) compared to the standard treatment (67%) (p = 0.034, Wilcoxon), whereas the take rates of the grafts were similar. No related adverse events were recorded. Scar quality was evaluated at 3 (n = 33) and 12 (n = 28) months. The POSAS of the observer after 3 and 12 months and of the patient after 12 months were significantly better for the experimental area. Improvements between 12% and 23% (p ≤ 0.010, Wilcoxon) were detected for redness, pigmentation, thickness, relief, and pliability. Melanin index at 3 and 12 months and erythema index at 12 months were closer to normal skin for the experimental treatment than for conventional treatment (p ≤ 0.025 paired samples t-test). Skin elasticity showed significantly higher elasticity (p = 0.030) in the experimental area at 3 months follow-up. We showed a safe application and significant improvements of wound healing and scar quality in burn patients after treatment with ECs versus SSGs only. The relevance of cultured autologous cells in treatment of extensive burns is supported by our current findings.

Cultured autologous keratinocytes in the treatment of large and deep burns: a retrospective study over 15 years

AIM

The aim was to review the use and indications of cultured autologous epidermis (CAE) in extensive burns and to evaluate the efficiency of our strategy of burn treatment.

MATERIALS AND METHODS

This retrospective study comprised 15 years (1997-2012).

INCLUSION CRITERIA

all patients who received CAE.

EXCLUSION CRITERIA

patients who died before complete healing and patients who received exclusively cultured allogeneic keratinocytes. Evaluation criteria were clinical. Time and success of wound healing after CAE graft were evaluated.

RESULTS

A total of 63 patients were included with severity Baux score of 107 (from 70 to 140) and mean percentage of TBSA of 71% (from 40% to 97%). The CAE were used as Cuono method, in STSG donor sites and deep 2nd degree burns and in combination with large-meshed STSG (1:6-1:12) in extensively burned patients. Cuono method was used in 6 patients. The final take was 16% (0-30) because of the great fragility of the obtained epidermis. Nine patients with deep 2nd degree burns (mean TBSA 81%, from 60 to 97%) were successfully treated with only CAE without skin grafting. Combined technique (STSG meshed at 1:6-1:12 covered with CAE) was used in 27 patients (mean TBSA 69%, from 49% to 96%) with 85% success rate. Finally, donor sites treated with CAE in 49 patients could be harvested several times thanks to rapid epithelialization (time of wound healing was 7 days (from 5 to 10 days)).

CONCLUSION

The CAE allow rapid healing of STSG donor sites and deep 2nd second degree burns in extensively burned patients.

Cultured allogenic keratinocytes for extensive burns: a retrospective study over 15 years

The aim was to review the use and indications of cultured allogenic keratinocytes (CAlloK) in extensive burns and their efficiency.

MATERIALS AND METHODS

This retrospective study comprised 15 years (1997-2012).

INCLUSION CRITERIA

all patients who received CAlloK.

EXCLUSION CRITERIA

patients who died before complete healing. Evaluation criteria were clinical. Time and success of wound healing after CAlloK use were evaluated.

RESULTS

The CAlloK were used for 2 indications - STSG donor sites and deep 2nd degree burns in extensively burned patients. A total of 70 patients were included with severity Baux score of 99.2 (from 51 to 144) and mean percentage of TBSA of 63.49% (from 21 to 96%). Fifty nine patients received CAlloK for STSG donor sites with a mean number of applications of 4 and mean surface of 3800 cm(2) per patient. Treated donor sites were re-harvested 2.5 times. The mean time of complete epithelialization was 7 days. In 11 patients, CAlloK were used for deep 2nd degree burns. The mean percentage of burned surface was 73.7%. The mean surface of CAlloK per patient was 2545 cm(2). Complete healing was achieved in 6.4 days.

CONCLUSION

The CAlloK allow rapid healing of STSG donor-sites and deep 2nd second degree burns in extensively burned patients.

Keratinocytes in the treatment of severe burn injury: an update

Burns are among the most life-threatening physical injuries, in which fast wound closure is crucial. The surgical burn care has evolved considerably throughout the past decennia resulting in a shift of therapeutic goals. Therapies aiming to provide coverage of the burn have been replaced by treatments that have both functional as aesthetic outcomes. The standard in treating severe burns is still early excision followed by skin grafting. The use of cultured keratinocytes to cover extensive burn wounds appeared very promising at first, but the technique still has several limitations of which the long time to culture, the major costs, the risk of infection and the need for an adequate dermal layer limit clinical application. The introduction of dermal substitutes, composite grafts, tissue engineering based on stem cell application have been advocated. The aim of this review is to assess the use of cultured keratinocytes in terms of technical aspects, clinical application, limitations and future perspectives. Cultured keratinocytes are expected to keep playing a role in wound healing, especially in the field of chronic wounds. In severe burns, despite its limitations, keratinocytes can be beneficial if implemented as one of the elements in a broader wound management.

Feeder layer- and animal product-free culture of neonatal foreskin keratinocytes: improved performance, usability, quality and safety

Since 1987, keratinocytes have been cultured at the Queen Astrid Military Hospital. These keratinocytes have been used routinely as auto and allografts on more than 1,000 patients, primarily to accelerate the healing of burns and chronic wounds. Initially the method of Rheinwald and Green was used to prepare cultured epithelial autografts, starting from skin samples from burn patients and using animal-derived feeder layers and media containing animal-derived products. More recently we systematically optimised our production system to accommodate scientific advances and legal changes. An important step was the removal of the mouse fibroblast feeder layer from the cell culture system. Thereafter we introduced neonatal foreskin keratinocytes (NFK) as source of cultured epithelial allografts, which significantly increased the consistency and the reliability of our cell production. NFK master and working cell banks were established, which were extensively screened and characterised. An ISO 9001 certified Quality Management System (QMS) governs all aspects of testing, validation and traceability. Finally, as far as possible, animal components were systematically removed from the cell culture environment. Today, quality controlled allograft production batches are routine and, due to efficient cryopreservation, stocks are created for off-the-shelf use. These optimisations have significantly increased the performance, usability, quality and safety of our allografts. This paper describes, in detail, our current cryopreserved allograft production process.

The use of cultured allogenic keratinocyte grafting in a patient with epidermolysis bullosa simplex

Epidermolysis bullosa (EB) is a rare genetic disease that is known for continuous skin blistering caused by minor trauma. The skin blisters and bullae that develop often cause skin defects. There is no definitive treatment for EB, only symptomatic relief. We report our experience with cultured allogenic keratinocyte grafting in a newborn patient with EB simplex who had unhealed raw surfaces and was not a skin grafting candidate. The skin lesions of the patient were covered with cultured allogenic keratinocyte grafts and re-epithelialized quickly with no scarring. Allogenic keratinocyte grafting reduced pain and produced noticeable improvements in the unhealed wounds. We think that allogenic keratinocyte grafting can play an important role in the management of patients with EB simplex.

Suprathel®—An innovative, resorbable skin substitute for the treatment of burn victims

Autologous split skin grafts are the most reliable method for closing third degree burns. Under this scheme, donor sites as well as second degree burns under conservative treatment, however, would benefit from rapid wound closure. For this treatment, biological as well as synthetic materials are available. For the improvement of these materials, primary goals are pain reduction and easy handling in the absence of biological risk. From a synthetic copolymer mainly based on DL-lactic acid a new skin substitute was developed, marketed as Suprathel. Within the scope of a bicentric study Suprathel was compared versus paraffin gauze intraindividually applied on split skin donor sites. Wound pain was measured on the Visual Pain Analog Scale over a period of 10 days as the critical criterion. Accordingly Suprathel versus Omiderm were compared on second degree burns (degree 2a, partial thickness burns). In both study parts, Suprathel significantly reduced pain. Its easy handling was superior compared to other materials. The Suprathel membrane adhered rapidly to the wound thus protecting against infections and promoting wound healing. No allergic reactions were observed. The ability of the material to resorb ensured pain-free removal after complete healing of the wound.

New technologies for burn wound closure and healing--review of the literature

Methods for handling burn wounds have changed in recent decades. Increasingly, aggressive surgical approach with early tangential excision and wound closure is being applied leading to improvement in mortality rates of burn victims. Autografts from uninjured skin remain the mainstay of treatment. Autologous skin graft, however, has limited availability and is associated with additional morbidity and scarring. Severe burn patients invariably lack sufficient adequate skin donor sites requiring alternative methods of skin replacement. The present review summarizes available replacement technologies.

State of the Art in Burn Treatment

Optimal treatment of burn victims requires deep understanding of the profound pathophysiological changes occurring locally and systemically after injury. Accurate estimation of burn size and depth, as well as early resuscitation, is essential. Good burn care includes also cleansing, debridement, and prevention of sepsis. Wound healing, is of major importance to the survival and clinical outcome of burn patients. An ideal therapy would not only promote rapid healing but would also act as an antiscarring therapy. The present article is a literature review of the most up-to-date modalities applied to burn treatment without overlooking the numerous controversies that still persist.

Overexpression of vascular endothelial growth factor accelerates early vascularization and improves healing of genetically modified cultured skin substitutes

Cultured skin substitutes (CSS) lack a vascular plexus, leading to slower vascularization after grafting than split-thickness skin autograft. CSS containing keratinocytes genetically modified to overexpress vascular endothelial growth factor (VEGF) were previously shown to exhibit enhanced vascularization up to 2 weeks after grafting to athymic mice. The present study examines whether enhanced vascularization compared with controls persists after stable engraftment is achieved and analyzes VEGF expression, wound contraction, and engraftment. Control and VEGF-modified (VEGF+) CSS were grafted onto full-thickness wounds in athymic mice. VEGF expression was detected in VEGF+ CSS 14 weeks after grafting. Graft contraction was significantly lower in VEGF+ CSS compared with controls, suggesting more stable engraftment and better tissue development. Positive HLA-ABC staining, indicating persistence of human cells, was seen in 86.7% (13/15) of grafted VEGF+ CSS, compared with 58.3% (7/12) of controls. Differences in dermal vascularization between control and VEGF+ grafts were significant 1 week after surgery, but not at later times. However, the distribution of vessels was different, with more vessels in the upper dermis of VEGF+ grafts. These results suggest that VEGF overexpression in genetically modified CSS acts to accelerate early graft vascularization and can contribute to improved healing of full-thickness skin wounds.

[Cultured epidermis for the treatment of severe burns. A 2-year study (18 patients)]

AIM OF THE STUDY

For fifteen years, Edouard Herriot Burn Center has been using cultured epidermis provided by an hospital Laboratory. This means of production results in great freedom for their application compared with the centers who have to buy the cultured epidermis. In order to evaluate our clinical results, a two-year study has been performed.

MATERIAL AND METHODS

Eighteen patients suffering acute burns were concerned. The average burned area was 68% of the total body surface (range 49 to 88). The average age was 31.6 years, ranging from 1 to 58, including two children. Even autologous or allogenic epidermis was used. In our series cultured epidermis was grafted according four different strategies. It was the preparation of the wound bed by skin allografts, the association of widely meshed auto-graft with cultured epidermis, the stimulation of the healing of extensive deep second degree burns with allogenic epidermis, and the coverage of skin auto-graft donor sites.

RESULTS

Two patients died. For the survivors, the average hospital stay was 60 days (range 22 to 90), and on average 70 days over 70% TBSA burns. Cultured epidermis allowed the definitive coverage of 17% of the total body surface of the patients. This study supports the importance of a careful preparation of the patient for the engraftment of cultured epidermis.

CONCLUSION

In our opinion, in spite of the difficulties of handling of cultured epidermis, they represent a precious means of coverage for the rapid and definitive healing of extensive burns over 70% TBSA.