Reconstitution of structure and cell function in human skin grafts derived from cryopreserved allogeneic dermis and autologous cultured keratinocytes

Use of a porcine dermis template to enhance widely expanded mesh autologous split-thickness skin graft growth: preliminary report

To answer the question whether a xenograft dermal substitute could enhance skin grafting, we used porcine dermis as a template for a widely expanded mesh autologous split-thickness skin (ASTS) graft in a rat model. Four groups of rats had received widely expanded meshed skin autografts to cover an excised back wound. Group 1 had a bed of autologous dermis, group 2 had porcine xenograft dermis, group 3 had widely expanded meshed autograft alone, and group 4 had no graft with the wound healing by contraction alone. Wounds were studied by clinical inspection for texture and contraction, and by histologic and immunofluorescent techniques. At 2 weeks, there was acceptable ASTS graft take, and most of the wound healed completely by 3 weeks. The integrity of this complex skin graft was maintained for 4 months but wound contraction gradually decreased overall wound size. Size was maintained better in the ASTS-autodermis and ASTS-xenodermis groups at postgraft 4, 5, and 6 weeks when compared with the ASTS graft, and there was no difference between the ASTS-autodermis and ASTS-xenodermis groups. Thus both allodermis and xenodermis provided a similar template to enhance widely expanded mesh skin growth and delay wound contraction. The pathologic studies indicate that the xenodermis collagen was replaced either by fibrosis or by biodegradation to rat collagen. The immunofluorescent study also reflected that anti-porcine antibody activity was hugely diminished in the ASTS-xenodermis graft wound after long-term follow-up. In conclusion, either autodermis or xenodermis enhances widely expanded mesh ASTS survival in a rat model, and could significantly maintain the original wound size better than ASTS graft without a template. In a long-term follow-up study, the porcine dermis was replaced either by fibrosis or biodegradation to rat dermis.

Grafting on nude mice of living skin equivalents produced using human collagens

Autologous epidermal transplantation for human burn management is an example of a significant breakthrough in tissue engineering. However, the main drawback with this treatment remains the fragility of these grafts during and after surgery. A new human bilayered skin equivalent (hSE) was produced in our laboratory to overcome this problem. The aim of the present work was to study skin regeneration after hSE grafting onto nude mice. A comparative study was carried out over a period of 90 days, between anchored bovine skin equivalent, hSE and hSE+, the latter containing additional matrix components included at concentrations similar to those in human skin in vivo. The addition of a dermal layer to the epidermal sheet led to successful graft take, enhanced healing, and provided mechanical resistance to the grafts after transplantation. In situ analysis of the grafts showed good ultrastructural organization, including the deposition of a continuous basement membrane 1 week after surgery.

Evaluation of human skin reconstituted from composite grafts of cultured keratinocytes and human acellular dermis transplanted to athymic mice

This study evaluates the use of composite grafts of cultured human keratinocytes and de-epidermalized, acellular human dermis to close full-thickness wounds in athymic mice. Grafts were transplanted onto athymic mice and studied up to 8 wk. Graft take was excellent, with no instances of infection or graft loss. By 1 wk, the human keratinocytes had formed a stratified epidermis that was fused with mouse epithelium, and by 8 wk the grafts resembled human skin and could be freely moved over the mouse dorsum. Immunostaining for keratins 10 and 16 and for involucrin revealed an initial pattern of epithelial immaturity, which by 8 wk had normalized to that of mature unwounded epithelium. Mouse fibroblasts began to infiltrate the acellular dermis as early as 1 wk. By 8 wk fibroblasts had completely repopulated the dermis, and blood vessels were evident in the most superficial papillary projections. Dermal elements, such as rete ridges and elastin fibers, which were present in the starting dermis, persisted for the duration of the experiment. Grafts using keratinocytes from dark-skinned donors as opposed to light-skin donors had foci of pigmentation as early as 1 wk that progressed to homogenous pigmentation of the graft by 6 wk. These results indicate that melanocytes that persist in vitro are able to resume normal function in vivo. Our study demonstrates that composite grafts of cultured keratinocytes combined with acellular dermis are a useful approach for the closure of full-thickness wounds.

Human skin histology as demonstrated by Herovici's stain: a guide for the improvement of dermal substitutes for use with cultured keratinocytes?

The potential for the widespread use of cultured keratinocytes for burns treatment is handicapped by practical problems such as fragility, poor take and, often, unsatisfactory cosmesis. Although dermal equivalents reduce these problems there remains a lack of consensus on what is the best structure of such equivalents. At present the commonest support is type I collagen. This histological study, however, using Herovici's stain, clearly shows that in human skin from a variety of anatomical sites the epidermis is not in direct contact with type I collagen but rather with a distinct layer of type III collagen. We suggest that dermal equivalents may have to be constructed so as to include a layer of type III collagen at the interface between the keratinocytes and a type I collagen neo-dermis, so mimicking normal skin structure more closely.

Histological evaluation of skin reconstruction using artificial dermis

An artificial dermis, composed of a collagen matrix, was applied to a full-thickness skin defect prepared on the back of rats. Two weeks later, a thin split-thickness skin autograft was overlaid on the matrix at each recipient site. The dermal layer at the recipient sites was 1.02 mm thick with prior application of artificial dermis, as compared with the 0.46 mm thickness observed without such pretreatment. Histologically, the split-thickness skin graft normally lies with no gap on the artificial dermis, which looks like natural dermis. Six days after grafting, the epithelial basal cells in the grafts showed an active uptake of bromodeoxyuridine (a thymidine analogue), indicating high activity of cell proliferation. About 50 and 20% respectively of the artificial dermis remained at each recipient site at 12 and 20 weeks after its application (after the skin defect). This finding indicates that bovine collagen, which is a constituent of the artificial dermis, is gradually replaced by the host tissue.

Cultured epithelial autograft: five years of clinical experience with twenty-eight patients

Cultured epithelial autograft (CEA) has been used as an adjunct in burn wound coverage at the Vancouver Hospital and Health Sciences Centre since 1988, and has been available to all patients admitted with significant burn injuries. During the 5-year period from 1988 to 1992 inclusive, 28 patients treated with CEA survived long enough for assessment. The mean age was 35.3 years with a mean total body surface area burn of 52.2% and a mean total full thickness injury of 42.4%. CEA was applied to wounds covering between 2% and 35% body surface area (BSA; mean 10.4%) after excision to fat or fascia. Most wounds had interim homograft coverage. Preservation of homograft dermis was attempted in three patients at the time of removal without effect. The mean CEA "take" was 26.9% of the grafted area. Eight patients had 50% or greater take and were discharged with between 1 and 19% BSA covered with CEA. Thirteen patients had no take on wounds between 2 and 16% BSA. Overall mortality in burn patients treated at the Vancouver Hospital and Health Sciences Centre from 1988 to 1992 was not significantly different from 1983 to 1987 with the populations being similar in terms of total BSA burns, age, inhalation injury, and homograft availability. When compared to a matched control population from the preceding 5 years, when CEA was not available, there was no significant difference in duration of hospital stay or number of autograft harvests. However, approximately one more debridement without autograft harvest per CEA patient occurred. Timing and depth of wound excision, interim coverage, type of dressing, and wound microbiology were not found to influence good versus poor take. The anterior trunk and thighs were the best recipient sites. Subjective differences between CEA and meshed autograft were noted. The results show that after 5 years of use, CEA engraftment continues to be unpredictable and inconsistent, and hence, it should be used as only a biologic dressing and experimental adjunct to conventional burn wound coverage with split thickness autograft.

Reduced wound contraction and scar formation in punch biopsy wounds. Native collagen dermal substitutes. A clinical study

In full-thickness skin wounds dermal regeneration usually fails, resulting in scar formation and wound contraction. We studied dermal regeneration by implantation of collagenous matrices in a human punch biopsy wound model. Matrices were made of native bovine collagen I fibres, and either hyaluronic acid, fibronectin, or elastin was added. Matrices were placed in 6-mm punch biopsy holes in seven patients (biopsies were used for the grafting of leg ulcers), and covered with a protective semi-permeable polyether urethane membrane. Histology, wound contraction and dermal architecture were studied. Dermal architecture was evaluated using a recently developed laser scatter technique. All collagen matrices showed a tendency to reduce wound contraction, compared with control wounds; elastin- and fibronectin-treated matrices showed significantly less contraction than control wounds. Only the addition of elastin had a clear beneficial effect on dermal architecture; collagen bundles were more randomly organized, compared with control wounds, and wounds treated with collagen matrices coated with fibronectin or hyaluronic acid, or without coating. We conclude that the punch biopsy wound model provides important information on dermal regeneration in humans. Native collagen matrices with elastin contributed to dermal regeneration and reduced wound contraction, in contrast with matrices coated with fibronectin or hyaluronic acid, or without coating. Future clinical studies of large-area, full-thickness wounds will be required to establish their clinical relevance for leg ulcer and burn treatment.

An investigation into the mechanisms by which human dermis does not significantly contribute to the rejection of allo-skin grafts

The dermis is an important element in skin substitutes and in allo- or xeno-skin grafts. However, the reason(s) why dermis does not significantly induce the immune rejection reaction in vivo remain(s) hitherto unknown. To clarify the mechanisms underlying this phenomenon, we undertook the evaluation of: (i) the response of the peripheral blood mononuclear cells (PBM) to isolated allo-dermal cells or to pieces of or to whole allo-dermis, (ii) the migration and homing of the PBM inside allo-dermis or split thickness allo-skin, (iii) the distribution of the ICAM-1 protein within skin, and (iv) the features expressed by the PBM that migrate into allo-skin. The results herein presented show that (1) the isolated allo-dermal cells had the highest and the whole allo-dermis the lowest capacity to initiate the reactive proliferation of the PBM in vitro; (2) in an allo-skin/PBM co-culture model, most of the PBM slowly, yet preferentially, migrated to and homed inside the allo-epidermal compartment, instead of staying in the allo-dermis; (3) under the conditions employed, rather little ICAM-1 could be immunohistochemically detected within the epidermis, conversely, both the dermal cells and the dermal matrix were ICAM-1 positive; and (4) most of the PBM migrating into the allo-skin pieces expressed either the CD18 or the CD19 or the CD8 molecule, yet very few of them exhibited the LFA-1-antigen, and none of them were found to be CD4 positive.2+Therefore, we conclude that because

Genetically modified skin to treat disease: potential and limitations

Molecular definition of disease at the level of the gene and advances in recombinant DNA technology suggest that many diseases are amenable to correction by genes not bearing the defective elements that result in disease. Many questions must be answered before this therapy can be used to correct chronic diseases. These questions fall into safety and efficacy categories. Experience with transplanting cellular elements of skin or skin substitutes (defined as skin that possess the cell types and a dermal structure to develop into a functioning skin) to athymic rodents is considerable and is seen as a system where these questions can be answered. This paper reviews these questions and presents our early analysis of genetically modified cells in skin substitutes in vivo and in vitro. Experimental data demonstrate that both a matrix of woven nylon, housing a fibroblast generated collage, and dead dermis can be utilized to shuttle genetically modified human fibroblasts from the laboratory to an in vivo setting. Genetically modified fibroblasts do not migrate from the shuttle to the surrounding tissue. The survival of significant numbers, approximately 70%, of genetically modified fibroblasts for at least 6 weeks in these shuttles, supports this general approach as having clinical utility. It is also concluded that skin substitute systems can be used to generate a genetically modified skin in vitro that has the capacity to develop into functional skin in vivo. Further, as genetically modified keratinocytes differentiate there is increased production by the transgene, supporting the concept that keratinocytes have true potential as shuttles for therapeutic genes. This work demonstrates that transplantation of systems containing genetically modified cells of the skin can be used to experimentally define many aspects of gene therapy using skin before this technology is taken to the clinic. Examples include determining the effect of gene transduction and expression on structure and function of the genetically modified skin as well as on distant skin and an assessment of the translational capacity of the transgene as function of time and cell number.

Normalization of essential-fatty-acid-deficient keratinocytes requires palmitic acid

Cultured adult human keratinocytes show accelerated growth rates in medium that is essential fatty acid deficient. The cells also show decreased amounts of the essential fatty acids 18:2, 20:3, and 20:4 and contain increased amounts of the monounsaturated fatty acids 16:1 and 18:1. These lower levels of polyunsaturated fatty acids were only partially restored by supplementing the medium with 18:2 and 20:4 fatty acid. The addition of the non-essential fatty acid 16:0 (5 microM), along with the essential fatty acids, resulted in the successful normalization of the major fatty acids in the deficient keratinocytes. Normalized cells showed a constant total fatty acid/mg of protein in the phospholipid fraction, as the total cell fatty acid content per cell increased with augmenting fatty acid supplementation. Supplementation of the medium with 16:0 and essential fatty acids decreased the growth and passage potential of the cells. Use of 18:1 in lieu of 18:2 fatty acid yielded essential-fatty-acid-deficient keratinocyte growth values. Likewise the least supplemented medium (5 microM 18:2 + 5 microM 16:0) also gave the accelerated cell growth rates. This study shows that manipulation of the essential fatty acid levels, if accompanied by 5 microM 16:0 in the growth medium, alters the growth properties of adult human primary keratinocytes.

Cultured autologous keratinocytes in fibrin glue suspension, exclusively and combined with STS-allograft (preliminary clinical and histological report of a new technique)

The use of cultured epidermal cell sheets has become a recognized method for the coverage of extensive burns. The disadvantages are a long time-lag until the cells are available, the fragility and difficult handling of the grafts, an unpredictable 'take' and extremely high costs. In three patients with deep partial and full skin thickness burns we have applied cultured autologous keratinocytes suspended in fibrin glue. In two of these patients the keratinocyte culture in the fibrin matrix (KFGS) was overgrafted with allogeneic, glycerine-preserved split thickness cadaver skin. The area thus covered ranged from 3 to 15 per cent TBSA. Cultured grafts were available between 2.5 and 3 weeks. The non-confluent cells developed a continuous epithelial layer within the 4 days until the first dressing change. Histological examination showed a stratified neoepidermis. Clinically the new skin had satisfactory stability and mechanical quality. The epidermis of the allogeneic overgrafts desquamated within a few days without signs of inflammation, but there are indications that the STS-allograft dermis is at least partly integrated into the new skin and may serve as a scaffold for the grafted cell culture. The fibrin glue matrix seems to give sufficient adherence stability to keratinocytes that are grafted in an actively proliferating state. Further advantages are the easy repetition and application, as well as a reduction in operating time and costs in these severely injured patients.

Cologne Burn Centre experience with glycerol-preserved allogeneic skin: Part II: Combination with autologous cultured keratinocytes

Autologous keratinocytes cultured in vitro from skin biopsies of patients with deep partial and full skin thickness burns were grafted onto nine necrectomized wound surfaces between 17 and 25 days after injury. The cells were applied as nonconfluent single cells suspended in fibrin glue. In four wounds, this cell-fibrin suspension was used to attach an additional glycerolized allogeneic split thickness skin graft (STSG). Re-epithelialization was very rapid as demonstrated clinically and histologically. Keratinocyte grafted areas without cadaver skin overgraft showed less mechanical stability than when the keratinocyte-fibrin glue suspension was combined with allogeneic STSG. There is clinical and histological evidence that the allodermis may be partially integrated into the new skin.

Euro Skin Bank: large scale skin-banking in Europe based on glycerol-preservation of donor skin

Although skin banking has been well developed through the years as a means of providing sufficient skin which is instantly accessible to the burn patient, the methods of preservation and the scale on which various institutions bank skin vary considerably. In 1984, the Dutch National Skin Bank started using glycerol as a preservant for skin allografts. Since then there has been a marked increase in both the volume of glycerol skin grafts applied and the area over which these have been distributed. The procedure and organizational aspects of the Euro Skin Bank, as our own institution is now called, and its current method of skin preservation are described.

What role does the extracellular matrix serve in skin grafting and wound healing?

Recent research on the structure and composition of the extracellular matrix (ECM) now strongly indicates that the major role of this matrix is in regulating cell/cell communication rather than in passively supporting cells. A wealth of structural data on the ECM suggests that there are specific arrangements of sequences within these proteins which profoundly influence the behaviour of the cells moving in that area, with respect to attachment, migration, differentiation and proliferation. In the skin, the ECM can be argued to promote 'appropriate' communication between the keratinocyte and the fibroblast. Skin ECM can be considered to consist both of the large insoluble proteins produced primarily by the fibroblasts, and soluble proteins which may be produced by fibroblasts or keratinocytes and become attached to the ECM. Both the large insoluble and the smaller soluble proteins may constitute signals which influence the behaviour of the keratinocytes. The clinical awareness of the need for a dermal component in skin grafting highlights the need for further research into the way in which the ECM influences keratinocyte/fibroblast biology. Such research will prove relevant to understanding the problems of graft take, graft contracture and scarring.

Management of burn wounds with prompt excision and immediate closure

The past 30 years have been witness to significant improvements in the overall care and prognosis of those suffering burn trauma. At the heart of this success is an aggressive approach to burn wounds. This approach, which is detailed in this review, involves early operative removal of devitalized tissue and biological coverage of resultant wounds, with particular attention to wounds in specialized areas.

Studies of tissue cultured sliced dermis as a skin substitute

A dermis slicer designed by the authors enabled us to prepare about 10 sheets of sliced dermal grafts (SDG), 300 micron(s) thick, from the dermis harvested from the back or buttocks of adult patients during operations. Such a sliced dermal sheet was stretched with one surface stuck on the base of a culture dish. It was then incubated in Dulbecco's essential medium for tissue culture, to which epidermal growth factor had been added. By the first week only its upper side was epithelialized from epithelial components in sliced dermis. The formation of basement membrane with anchoring fibrils was confirmed by electron microscopy. The appearance of type IV collagen and laminin was observed between epithelialized basal cells and the dermal layer. Thus, it is thought that the SDG is useful not only for immediate grafting, when epithelialization follows, but also as a substitute for free split thickness skin grafts following tissue culture.

Restoration of basement membrane structure in pigs following keratinocyte autografting

The attachment of grafts of keratinocyte sheets is mediated in part by the presence and organisation of basement membrane components. The reappearance of basement membrane following keratinocyte autografting was examined in pigs. These studies showed that there was rapid expression of anchoring fibrils and hemidesmosomes, which reached normal numbers at 10 days. However, the length of hemidesmosomes did not reach normal size during the period of study. Weakness of attachment of keratinocyte autografted epidermis was found to lie between the basement membrane and the granulation tissue. This suggests that reported clinical problems with keratinocyte graft attachment may be mediated not only by delay in maturation of the basement membrane but also by its poor integration with collagen of the wound bed.

Kerato-dermal grafts: the importance of dermis for the in vivo growth of cultured keratinocytes

In a porcine model, we studied the benefit of dermis for the growth of cultured autologous keratinocytes (CAK) on full-thickness wounds isolated within skin graft chambers. Kerato-dermal grafts were prepared in a two stage process using autologous de-epidermalised dermis (DED) and CAK (Group 1). Control wounds were prepared by grafting either CAK only (Group 2) or DED only (Group 3). The median epidermal cover of 34 wounds in Group 1 was 47% and was significantly greater (p < 0.001) than the epidermal cover of 12 wounds in Group 2 (4%) and 14 wounds in Group 3 (12%). The epidermis in Group 1 was durable whereas it was fragile in the control wounds. Histologically rête ridges were present at 2 weeks in Group 1, but not in the control wounds. These data indicate that a dermal wound bed significantly improves the in vivo growth of cultured keratinocytes.

A recombined skin composed of human keratinocytes cultured on cell-free pig dermis

Treatment of full skin thickness burns requires replacement of both the dermal and the epidermal components of the skin. We describe a method of preparing recombined human/pig skin (RHPS) by cultivating human keratinocytes on dried cell-free pig dermis (CFPD). CFPD dried on a tissue culture dish forms a thin collagen film which behaves like a firm substrate for cell cultures. HK were grown on the epidermal side of the CFPD using lethally irradiated 3T3 cells as feeders. After reaching confluency of human keratinocytes, human fibroblasts can be cultured on the dermal side of the RHPS. It was possible to obtain approximately 500 cm2 of the RHPS from 1 cm2 human split-skin graft in 3 weeks. RHPS is easy to handle, is similar in structural, mechanical and adhesive properties to the normal skin, and can be meshed. This RHPS might be advantageous for permanent covering of wounds in major burns.

Expression of basement membrane components in skin equivalents--influence of dermal fibroblasts

We have made a skin equivalent constructed of fibroblasts embedded in a type I collagen, with an overlying stratified keratinocyte epithelium to examine formation of the basement membrane. We assessed the influence of the existence and species of fibroblasts in the collagen gel. Cultured human keratinocytes were well attached to the dermal equivalent. Plating efficiency was not clearly different among several types of gel. On the control and mouse fibroblast gel, sheet formation was delayed and epithelial stratification on the human fibroblast gel was more remarkable than on the control gel. On the human fibroblast gel, we observed the expression of basement membrane components (bulbous phemphigoid antigen, laminin, type IV collagen and fibronectin) between the sheet of cultured keratinocytes and the human fibroblast gel earlier than those on the control gel and mouse fibroblast gel. Type VIII collagen was not observed in any of the models at 4 weeks.

Treatment of burns with skin substitutes

More than 2 million persons sustain thermal injuries in the United States annually (Monafo and Crabtree, 1985) and more than 10,000 burn victims die (Collini and Kealey, 1989). The principal factors affecting mortality are the total area burned and the area of third degree (full thickness) burns (Tompkins et al., 1985) with wound sepsis being the leading cause of mortality. Early aggressive excision and immediate covering of the wounds improve survival (Herndon and Parks, 1986). Various biological and synthetic substrates have been employed to replace the injured skin. Most of these provide a permeability barrier which substitutes for the epidermal function of the lost skin. An ideal skin replacement should also provide a substitute for dermis, which provides both support and stability for the epidermal replacement and prevents wound contraction. The dermal and epidermal replacement should be firmly integrated by a complete basement membrane zone (BMZ).

Epidermal keratinocyte self-renewal is dependent upon dermal integrity

The epidermis is a major site of self-renewal in which there is constant replacement by cell division in the basal layers of cells lost by desquamation in the superficial layers. Such a tissue is therefore likely to contain stem cells and in this study we have examined the role of the dermis in the maintenance of epidermal self-renewal. We have developed a mouse model to address the question of whether the maintenance of epidermal self-renewal is dependent, as in the hemopoietic system, upon a heterologous cell type. Intact epidermis separated from dermis at the dermo-epidermal junction or epidermis derived from disaggregated epidermal cells, can reconstitute a stratified squamous epithelium when grafted onto the lumbo-dermal fascia of the mouse or onto an experimentally induced granulation tissue bed. However, we have shown that, after grafting, the clonogenic capacity of the keratinocytes declines sharply and the colonies that are produced are incapable of self-renewal in vitro. Although initially hyperplastic, these epidermal grafts assume an atrophic appearance after 40-70 d and this may be related to the loss of self-renewal observed in vitro. With both experimental murine grafts and clinical grafts the failure of keratinocytes to self-renew can be alleviated, partially, by the presence of the dermis in full-thickness or split-thickness grafts, which implies that the dermis has a functional role in epidermal stem cell maintenance. The relevance of these observations to the clinical experience with cultured autologous keratinocyte sheets as wound dressings to patients is discussed.

New grafts for old? A review of alternatives to autologous skin

Immediate resurfacing of skin defects is a challenging prospect, especially in patients with extensive full-thickness burns. Currently, split-thickness autografts offer the best form of wound coverage, but limited donor sites and their associated morbidity have prompted the search for alternatives. The application of allogeneic skin is restricted by availability and the risk of transmission of infection, whilst synthetic skin substitutes are simply expensive dressings. The problems of limited expansion may be overcome by culturing keratinocytes in vitro. Unlike autologous cells, allogeneic keratinocytes are available immediately, although they survive for less than a week when applied to full-thickness skin defects. Moreover, the absence of a dermal component in these grafts predisposes to instability and contracture. A cross-linked collagen and glycosaminoglycan dermal substitute, covered with thin split-skin grafts or cultured autologous keratinocytes, shows promise in burns patients. An alternative is a collagen matrix populated by allogeneic fibroblasts and overlaid with cultured autologous or allogeneic keratinocytes. The clinical application of cultured grafts remains imperfect but offers the prospect of immediate coverage and massive expansion.

Burn wound closure using permanent skin replacement materials

Over the past decade, very significant advances in the development of clinically useful, permanent skin replacement materials have taken place. The most prominent and successful approaches to the physiological closure of an open wound have been either by creating a totally artificial dermal matrix material, by using culture techniques to expand cell populations for autologous transplantation, or by using a combination of these methods. As a result of substantial early progress in this field, permanent skin replacement materials as a treatment modality promise significant contributions to improved wound management and increased survival rates for patients with devastating soft tissue destruction such as massive burn injuries.

In vitro reconstitution of skin: fibroblasts facilitate keratinocyte growth and differentiation on acellular reticular dermis

Extensive full-thickness burns require replacement of both epidermis and dermis. We have described a method in which allogeneic dermis from engrafted cryopreserved cadaver skin was combined with cultured autologous keratinocytes. In the present study we combined human keratinocytes and fibroblasts, and acellular human dermis in vitro and transplanted this "reconstituted skin" into athymic mice. Both human papillary dermis in which the basement membrane zone has been retained and human reticular dermis that has been repopulated with human dermal fibroblasts are good substrates for keratinocyte attachment, stratification, growth, and differentiation. Both of these dermal preparations can be lyophilized and stored at room temperature without losing their ability to support keratinocyte growth. In contrast, human papillary dermis that has been treated with trypsin lacks laminin and collagen type IV in the BMZ and supports keratinocyte attachment and differentiation less well.

Epidermis generated in vitro: practical considerations and applications

The technology for culture of epidermis is one of the most advanced to date for generation of a tissue in vitro. Cultured epidermis is already used for a number of applications ranging from use as a permanent skin replacement to use as an organotypic culture model for toxicity testing and basic research. While simple epidermal sheets have been grafted successfully, more advanced models for skin replacement consisting of both dermal and epidermal components are in development and being tested in a number of laboratories. One of the most advanced in vitro models is the living skin equivalent, an organotypic model consisting of a collagen lattice contracted and nourished by dermal fibroblasts overlaid with a fully formed epidermis.

Synthetic membranes and cultured keratinocyte grafts

Significant progress has been made in skin replacement options in the past several decades. Although initially various materials have been used mainly for burn coverage, their application to dermatologic practice has increased significantly. We review the research, progress, and other aspects of wound coverage with synthetic membranes and cultured epithelial sheets in both burn and nonburn wound management.

Allografted keratinocytes used to accelerate the treatment of burn wounds are replaced by recipient cells

Cultured keratinocytes were used as allografts on burn wounds in two patients. In both patients successful covering of the wounds was obtained. DNA fingerprinting of the epidermis covering the wounds 21 days later showed that the cultured keratinocytes were replaced by the patients' cells.

Dispase, a neutral protease from Bacillus polymyxa, is a powerful fibronectinase and type IV collagenase

Dispase, a neutral protease isolated from culture filtrates of Bacillus polymyxa, has proven to be a rapid, effective, but gentle agent for separating intact epidermis from the dermis and intact epithelial sheets in culture from the substratum. In both cases it effects separation by cleaving the basement membrane zone region while preserving the viability of the epithelial cells. Because it is not known what or where in the basement membrane zone Dispase cleaves, we set up studies to define its substrate specificity. Using purified basement membrane components and sodium dodecyl sulfate-polyacrylamide gel electrophoresis we show that Dispase cleaves fibronectin and type IV collagen, but not laminin, type V collagen, serum albumin, or transferrin. The action of Dispase on collagen appears to be selective for type IV collagen in that several stable degradation products are formed, whereas the enzyme degrades type I collagen only minimally. In newborn human skin, as seen by electron microscopy, Dispase removes the lamina densa, rich in type IV collagen, but preserves the anchoring fibrils (structures known to contain type VII collagen) and the epidermal cells. Because its action is so selective, it suggests that Dispase can serve as a powerful tool for dissecting epithelial-mesenchymal interactions.