Survival of cultured allogeneic keratinocytes transplanted to deep dermal bed assessed with probe specific for Y chromosome

The development of bioengineered skin

Driven by the need for donor tissue for patients suffering from extensive burns, alternatives to autologous and cadaver-derived tissue have been under development for the past 20 years. Unilayered and bilayered models representing the skin's epidermal and/or dermal components have been developed using both cells and matrix materials. In addition to their use in patients with extensive burns, trials using these products on refractory and challenging patients with both acute and chronic wounds have led to the commercial availability of some of these products.

Tissue engineering and the development of Apligraf, a human skin equivalent

In recent years, skin grafting has evolved from the initial autograft and allograft preparations to biosynthetic and tissue-engineered living skin replacements. This review details the pioneering work of numerous investigators that led to the following precursors of tissue-engineered skin replacement: cultured autologous keratinocyte grafts, cultured allogeneic keratinocyte grafts, autologous/allogeneic composites, acellular collagen matrices, and cellular matrices. It also discusses the rationale for the development of the newer products and describes the technical advances leading to the development of Apligraf, a tissue-engineered human skin product.

Treatment of burns and donor sites with human allogeneic keratinocytes grown on acellular pig dermis

The absence of a dermal component predisposes cultured epidermal sheets to instability, contractibility, and makes them difficult to handle. In order to overcome these drawbacks, we developed recombined human/pig skin (RHPS) composed of human keratinocytes cultured on cell-free pig dermis. The original intention to prepare a permanent skin substitute composed of xenodermis and autologous epidermis was not achieved, but it has been proved that RHPS can serve as an effective, ready to use keratinocyte delivery system when applied 'upside-down', i.e. with epidermal cells facing the wound surface. The keratinocyte layer establishes a direct contact with the wound bed, while the dermal layer mechanically protects the wound. Twenty deep dermal burns were grafted with RHPS: 13 (65%) healed completely in 4-14 days, three (15%) healed partially and four (20%) did not heal. Of five full thickness burn wounds only one healed after repeated RHPS grafting within 18 days. Thirty-one (100%) donor sites treated with any of the three forms of RHPS, subconfluent, confluent meshed or confluent unmeshed, healed within 6-8 days compared with 14-18 days in control sites. Seven donor sites (100%) of immunodeficient patients with prolonged wound healing epithelialized in 7-10 days under RHPS compared with 32-90 days in areas treated with tulle gras and dry gauze.

Retroviral marking identifies grafted autologous keratinocytes in porcine wounds receiving cultured epithelium

Cultured epithelial autografts are often applied to wounds with a capacity for regeneration from dermal appendages. It is unclear in these circumstances whether the cultured autografts act merely as a biologic dressing or whether they become incorporated into the new epithelium. We have used retroviral gene transfer techniques to identify autologous keratinocytes in an established porcine model of cultured epidermal (CE) grafting. Porcine keratinocytes were transduced with an MFG-lacZ nls vector produced by the amphotropic packaging line GP+EnvAm12. Transduction rates of 15.1%, in the absence of selection, were achieved by a single passage on gamma-irradiated retroviral producers as a feeder layer. Full-thickness wounds were created on Large White pigs and isolated from the surrounding skin by a polytetrafluoroethylene chamber. Wounds were grafted initially with autologous de-epidermized dermis (DED), followed 7 d later by sheets of retrovirally marked or unmarked CE autografts. Two weeks after grafting, the mean area of epithelium was 48.4% in wounds that received CE grafts and 32.3% in wounds that were left as DED alone. The epithelium on DED represents regeneration from dermal appendages. The contribution made by the autograft cells to the new epidermis was demonstrated unequivocally, however, by lacZ-positive areas visible macroscopically on the surface of the excised wound. In cryostat sections through the lacZ-positive areas, retrovirally marked cells were present at both superficial and basal positions in the new epithelium.

Clinical results of cultured epithelial cell grafting in the oral and maxillofacial region

Cultured epithelium has proven to be a good grafting material for skin defects. In our experience two kinds of epithelial cells, skin keratinocytes and mucosal cells, have been used to fabricate cultured epithelial sheets and autografted to the patients. Traumatic scars of the face were treated by cultured epidermal epithelium (CEE). The skin graft in the oral cavity was replaced by mucosa using cultured mucosal epithelium (CME). Also, the CME was applied to the skin defects at the donor sites of split-thickness skin grafts. Postsurgical follow-up showed good results. As a result, CME was useful in improving the biological environment around the abutments of dental implants, and it also promoted the re-epithelialization of skin defects. From our investigations, CEE/CME are promising treatment modalities which can reduce pain and speed up the healing process in burn patients. Therefore, cultured epithelium banks are worth establishing for auto- and allografting of skin/mucosal defects.

Split-thickness skin grafting for lower extremity ulcerations

BACKGROUND

Leg ulcers are often refractory to conservative treatment, often mandating the use of skin grafting.

OBJECTIVES

This review article discusses skin grafts, with special emphasis on split-thickness grafts for lower extremity ulcerations.

METHODS

Historical background, proposed mechanisms of action, biology of skin grafts, techniques for skin grafting, and results after grafting are discussed separately.

RESULTS

Skin grafting has been performed for centuries. However, how skin grafts work, whether solely as tissue replacement or, additionally, as a stimulus for healing, is still not fully known. After placement, the grafted skin proceeds through a series of phases by which nutrients are supplied and neovascularization occurs. Adherence to the ulcer bed through interactions between the graft and the ulcer bed appear critical. When meshed split-thickness skin grafts are properly performed, success rates from 50% to 75% have been reported for refractory venous ulcers.

CONCLUSIONS

Better understanding of the biologic and clinical aspects of skin grafting should lead to improved patient care.

LEARNING OBJECTIVES

After studying this article, participant should be able: 1. To understand the various types of skin grafts. 2. To learn the potential mechanisms of action of how skin grafts work. 3. To appreciate the benefit of skin grafts for lower extremity ulcerations.

What is new in clinical research in wound healing

Treating the underlying pathophysiology of the wound remains of utmost importance. Several new treatment modalities may soon be available as adjunctive treatments. The efficacy of some remains to be established in well-controlled clinical studies.

Genetically modified human epidermis overexpressing PDGF-A directs the development of a cellular and vascular connective tissue stroma when transplanted to athymic mice--implications for the use of genetically modified keratinocytes to modulate dermal regeneration

We investigated the hypothesis that keratinocyte-produced platelet-derived growth factor-AA (PDGF-AA) is involved in epidermal-dermal interactions and that PDGF-AA is an important mediator of the temporal and spatial events of tissue repair. Retroviral-mediated gene transfer was used to introduce the gene encoding human PDGF-A into cultures of human diploid keratinocytes. Genetic modification boosted the endogenous in vitro level of PDGF-AA secretion by over 300 fold. When PDGF-secreting cells were transplanted as epithelial sheets to athymic mice, modified keratinocytes underwent terminal differentiation and generated a stratified epithelium comparable to unmodified cells. Seven days after grafting the newly synthesized connective tissue layer subjacent to the PDGF-A-modified grafts was significantly thicker, was rich in mononuclear cells and fibroblasts, and had increased numbers of blood vessels when compared to control grafts of unmodified cells. These results suggest that PDGF-AA secreted by the epidermis is an important mediator of epithelial-mesenchymal interactions and helps to promote growth and vascularization of the underlying dermal tissue. Further, these data demonstrate the feasibility of using genetically modified cells to modulate tissue regeneration.

Epidermal differentiation and dermal changes in healing following treatment of surgical wounds with sheets of cultured allogeneic keratinocytes

AIMS

To establish the structural changes that occur in deep surgical wounds engrafted with allogeneic sheets, their time course and inter-relation.

METHODS

Deep surgical wounds following shave excision of tattoos (down to deep dermis/subcutaneous fat) were treated with sheets of sex mismatched allogeneic keratinocytes in 19 patients and then biopsied weekly until wound healing was complete. More superficial surgical wounds--that is, 20 standard skin graft donor sites, were biopsied at seven to 10 days (all healed) following application of keratinocyte allografts. All biopsy specimens were examined with a large panel of monoclonal antibodies to keratins, envelope proteins, basement membrane components, and to extracellular matrix components.

RESULTS

The hyperproliferative keratin pair K6/16 was expressed in all wounds, for up to six weeks in keratinocyte grafted deep wounds, and up to six months in split thickness skin grafted wounds.

CONCLUSIONS

Keratins 6 and 16 have not been detected in normal skin, although the relevant mRNA has. This raises the possibility of regulation at a post-transcriptional level allowing a rapid response to injury with cytoskeletal changes that may aid cell migration. This keratin pair offers the most sensitive marker for altered epidermis following wounding.

Transplantation of keratinocytes in the treatment of wounds

BACKGROUND

Keratinocyte grafting can be used to treat acute traumatic and chronic non-healing wounds. The keratinocyte sheets are fragile and clinical "take" is difficult to assess, especially as activated keratinocytes secrete many growth factors, which have effects on wound healing apart from take. We have developed animal models of grafting that allow us to examine factors influencing autologous keratinocyte graft take. Results show clearly that pretreatment of the wound bed with viable dermis greatly increases the take of keratinocyte grafts.

DATA SOURCES

International literature.

CONCLUSIONS

As a greater understanding of the complex interactions of cell and matrix evolve, so will potential therapeutic maneuvers, not just in the field of cultured keratinocyte grafts, but clearly in that of benign tumors, for example, keloids, and that of oncology. There is now overwhelming evidence of the requirement for a dermal substitute for cultured keratinocyte autografts, and the sheet complexity of the situation demands that this should approximate live human dermis as closely as possible. The stumbling blocks relate to avoiding the risks of viral transmission, tissue matching of host and donor, providing early epithelial cover, and improving delivery systems for fragile keratinocyte grafts.

Culturing skin in vitro for wound therapy

Current tissue-culture techniques enable keratinocytes from a small piece of skin to be grown into sheets of epithelium, or cultured keratinocyte grafts, that are suitable for treating wounds. Serial subculture enables rapid expansion of a cell population, such that grafts of a total area equivalent to that of the surface of an adult can be obtained from an initial skin biopsy of approximately 2 cm2 in under one month. In this article, the methods currently used for culturing keratinocytes, the search for a fully functional replacement for the dermal elements of skin, and the prospects for clinical development of these technologies in the near future are discussed.

Preliminary report of the clinical use of cultured allogeneic keratinocytes

Three case reports are used to show that the recently introduced skin culture technology has been mastered to the extent that three patients with deep burns covering 50 per cent and more of the body surface area survived.

TGF-beta 1 gene expression in cultured human keratinocytes does not decrease with biologic age

The biologic activity of cultured epithelial grafts is believed to diminish with increasing cellular age. Therefore, keratinocytes from young donors are used preferentially in the production of cultured allografts for wound treatment. However, the impact of biologic age on cytokine gene expression by human keratinocytes has not been previously investigated. In this study, transforming growth factor-beta 1 (TGF-beta 1) gene expression in human keratinocytes derived from normal foreskins of males ranging in age from 7 months to 82 years was analyzed. Keratinocytes were harvested from fresh specimens and cultivated in vitro on 3T3 fibroblast feeder layers through second passage. The cells were analyzed both qualitatively and semiquantitatively for TGF-beta 1 gene expression using three separate techniques: in situ hybridization, Northern hybridization, and competitive polymerase chain reaction. By in situ hybridization, the signal representing TGF-beta 1 transcript was detected in cells in all layers of the stratified cultures, and immunohistochemical staining for TGF-beta 1 protein was equally intense in all layers. Northern blots of total RNA extracted from the cultivated cells showed no decrease in band density with increasing biologic age. Likewise, no decrease in TGF-beta 1 mRNA levels with biologic age was observed using a semiquantitative polymerase chain reaction assay. These results indicate that the potential for TGF-beta 1 gene expression in cultured foreskin keratinocytes does not decline with increasing cellular age. The findings imply that the clinical performance of cultured grafts, at least as it relates to the elaboration of this growth factor, may not be significantly altered by the biologic age of the keratinocyte donor.

Treatment of skin defects using suspensions of in vitro cultured keratinocytes

The in vitro cultivation of keratinocytes and their application in the form of confluent sheets to cover various kinds of skin defects involves a number of problematical steps which could be improved by using single cell suspensions instead. Therefore we developed a method to apply keratinocytes suspended as single cells in a fibrin gel. By testing the feasibility of this method in different experimental animal models we found that it facilitates cultivation as well as application of the cells, moreover, this method allows a much more flexible use of the cells, i.e. it is easier to consider the clinical condition of the patient than by the conventional method.

Mid-term results with cultured epidermal autografts, allogenic skin transplants and cyclosporin A medication

Transplantation of allogenic split thickness skin grafts (STSG) and immunosuppression with cyclosporin A enable early and definitive skin replacement of extensive, deep partial and full thickness burns. Covering burn defects with definitely engrafted, allogenic dermis and cultivated epithelial autografts (CEA) permits the subsequent withdrawal of cyclosporin A medication. Light-microscopy examination of biopsies, taken 12 and 24 months postgrafting, and electron microscopy of biopsies taken 12 months postgrafting, demonstrates a re-established, but somewhat reduced anchoring of the CEA as compared with a normal epidermal-dermal junction. Clinical inspection, 20 months postgrafting, confirms the histological observations that epifascial transplantation is qualitatively inferior to placing the allogenic STSG on the subcutaneous tissue. In the first situation, the dermis is inelastic and collagen deposition is excessive, whereas in the second case collagen deposition is comparatively reduced and the dermis shows clinically some elasticity.

Randomized trial comparing cryopreserved cultured epidermal allografts with hydrocolloid dressings in healing chronic venous ulcers

BACKGROUND

Cultured epidermal allografts have been successfully used to treat a variety of wounds. Their postulated mechanism of action is through release of cytokines that stimulate epithelialization. On the basis of previous experience we expected ulcers treated with cryopreserved cultured allografts (CCAs) to be healed by 6 weeks. Hydrocolloid dressings (HCDs) have also been reported to be effective in the treatment of venous ulcers.

OBJECTIVE

Our purpose was to compare the effectiveness of CCAs with HCDs in healing chronic venous ulcers.

METHODS

Forty-three patients with 47 ulcers were enrolled in a randomized controlled trial. Ulcers not healed by 6 weeks were changed to the other treatment.

RESULTS

No difference in the number of healed ulcers between the two groups was observed at 6 weeks. Healing rate, percent reduction of initial ulcer size, and radial progression toward wound closure were significantly greater for CCAs than for HCDs. Pain relief was not significantly different.

CONCLUSION

CCAs achieve more rapid healing and greater reduction in ulcer size than HCDs.

Cryopreservation of cultured dermal fibroblast impregnated collagen gels

The survival of cultured dermal fibroblasts was evaluated following manufacture, freezing and disaggregation of fibroblast-impregnated collagen gels. The concentration which gave optimal cell survival was determined for three cryoprotectants (glycerol, dimethyl, sulphoxide (DMSO) and ethanediol) and their efficacy compared. DMSO led to the highest cell viability after freezing and thawing. The effect of rate of freezing was also compared and 0.5 degree C/min (within the range 20 degrees C to -70 degrees C) was found to result in a significant enhancement of cell viability in comparison with freezing at 1.0 degree C/min or rapid freezing.

Cultured keratinocyte allografts and wound healing in severe recessive dystrophic epidermolysis bullosa

BACKGROUND

Patients with recessive dystrophic epidermolysis bullosa (RDEB) frequently have painful erosions that are slow to heal. There is no definitive treatment; therefore any therapy that improves wound healing would be beneficial to these patients.

OBJECTIVE

Our purpose was to assess the effects of cultured allogeneic keratinocytes on wound healing in RDEB.

METHODS

Ten patients with RDEB and dermatome-induced superficial dermal wounds were studied. Cultured keratinocyte grafts were applied to part of the wound, with another part left ungrafted. Both sites were assessed clinically and microscopically, particularly with regard to basement membrane zone reconstitution.

RESULTS

Apart from minor differences in keratinocyte differentiation and a moderate analgesic effect induced by the graft, there were no other distinguishing findings in wound healing in the grafted and nongrafted sites.

CONCLUSION

There was little clinical benefit from cultured keratinocyte allografts in wound healing in RDEB. However, this study showed that RDEB keratinocytes have an inherent capacity to express some type VII collagen epitopes transiently during wound healing, although this was not associated with the detection of anchoring fibrils.

Biologic skin substitutes

BACKGROUND

The ideal skin substitute should closely approximate the skin in function. The substitute should be readily available, easily sterilized and stored, and relatively inexpensive.

OBJECTIVE

To describe recent developments in the area of biologic skin substitutes.

RESULTS

Considerable advances have been made in keratinocyte and fibroblast culturing when used in conjunction with a biodegradable material as a substrate.

CONCLUSION

There is no skin substitute that perfectly mimics autologous skin. However, recent developments show promise.

Specific cloning of DNA fragments unique to the dog Y chromosome

A novel technique that enabled the specific cloning of a DNA fragment unique to the dog Y chromosome is described. The method involves competitive hybridization of DNA prepared from male dog lymphocytes with biotin-labeled DNA prepared from female dog lymphocytes. The biotinylated female-female and male-female hybrid DNA fragments were removed by capture with streptavidin-coated paramagnetic particles. Full-length double-stranded DNA was generated from the remaining fragments by using the Klenow fragment of DNA polymerase I, followed by direct cloning using a low-background ligation technique. Analysis of putative recombinant clones derived by this method has led to the identification of a fragment that hybridizes specifically to male dog DNA. The clones were selected initially on the basis of a differential signal obtained when hybridized to dilutions of male and female dog DNA immobilized on neural nylon membrane. To evaluate its suitability as a probe for trans-sexually grafted cells in transplantation studies, the fragment was labeled with digoxigenin and hybridized in situ to male and female dog tissue sections. The clone designated number 6.2 hybridized strongly to male dog nuclei. The cloning strategy employed could be extended to other studies in which competitive reassociation can be used to identify unique DNA sequences.

Variable rejection patterns of cultured keratinocyte allografts in the rabbit

There are many conflicting reports on the survival of cultured keratinocyte allografts (CKAs). Studies were performed in the rabbit model to elucidate further the fate of CKAs. Of 24 CKAs, 7 were identified as technical failures, 13 displayed classical macroscopic evidence of rejection with a prolonged mean survival time of 2.8 days, compared to non-cultured allograft controls (p < 0.01), and 4 failed to display typical macroscopic evidence of rejection. Furthermore, the time to eventual wound healing of the classically rejected CKAs were delayed by 6.0 days (p < 0.0001), compared to identical non-grafted control wounds.

Chemiluminescent restriction fragment length polymorphism analysis (DNA fingerprinting) to identify keratinocytes from two donors in co-culture

The transplantation of allogeneic cells such as pancreatic islet cells, bone marrow, and keratinocytes for skin replacement is in growing use clinically. Present techniques which are used to distinguish transplanted allogeneic cells from phenotypically identical host cells in chimeric tissue have serious limitations. This study assesses the feasibility of using chemiluminescent restriction fragment length polymorphism (RFLP) analysis to distinguish between keratinocyte cell lines from 2 different donors grown in co-culture. We evaluated the sensitivity of this technique in tissue cultured cells in order to define its usefulness in clinical situations. RFLP analysis readily detects heterologous DNA comprising only 10% of a 5 micrograms sample. This was a detection threshold of 500 ng of high molecular weight DNA. With standard extraction methods, this represents the DNA obtained from 4000 cells. This new chemiluminescent technique is as sensitive as older techniques which employ radioactive probes, but avoids the hazards of handling radioactive material. Using this RFLP analysis, the presence of transplanted allogeneic cells can be readily detected in small biopsy specimens. This technique has wide potential application in allogeneic cellular transplantation investigations.

Burn wound healing: James Ellsworth Laing memorial essay for 1991

This essay has concentrated on the basic processes, clinical techniques involved in burn wound healing and how the two relate to each other. The achievement of early, sound, durable burn wound healing is one of the fundamental aims of burn care in order to minimize subsequent morbidity and mortality. It must be remembered that all patients with burns are individuals. There is no standard way to treat a burn and treatment must be tailored to suit the needs and requirements of both the patient and the burn wound. Burn wound healing is not the specific domain of any one specialist. It requires input from all disciplines and can be best achieved by the burn team approach.

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.

Clinical observations and methods for identifying the existence of cultured epidermal allografts

Thirty-two burned or plastic surgery patients were grafted with allogeneic cultured epidermis on autograft donor sites. Two techniques, the indirect enzyme conjugated Staphylococcus Protein A assay with monoclonal antibodies against A or B blood group antigens and the polymerase chain reaction to detect a Y chromosome-specific DNA sequence, were employed to identify the presence of cultured epidermal allograft based on different ABO blood grouping or sex between donor and recipient. The methods have the advantage of high sensitivity and specificity in identifying the existence of allogeneic skin cells in grafts. The results indicated that the survival time of cultured epidermal allograft was prolonged up to 35 days. In addition, the intact coverage on some grafting sites may be composed of both host and donor origin cells, after about 3 weeks postgrafting.

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.

Treatment of full skin thickness burn injury using cultured epithelial grafts

This report presents the experience gained from 26 patients treated with autogenic cultured epithelial grafts (auto-CEG). All auto-CEG were applied to wounds clinically defined as full skin thickness injury. In total 89 separate sites were grafted. The overall estimate of 'take' ranged from 0 to 98 per cent with a mean value of 15 per cent. The highest level of 'take' (43 per cent) was observed when auto-CEG were applied to wounds which had been previously covered with allogenic split-thickness skin grafts. An increased incidence of wound colonization with pathogenic species of bacteria corresponded with a decreased graft 'take'. Ps. aeruginosa and Staph. aureus were found to be present on 32.6 per cent and 60.5 per cent of wound swabs respectively, where 10 per cent or less 'take' of auto-CEG was seen, indicating that bacterial infection is in part responsible for graft failure. However, in 20.9 per cent of such instances, no growth of bacteria was detected, perhaps suggesting that certain wound beds may not present the correct physical environment necessary to support proliferating epithelial cells isolated from their underlying dermal component.

Leg ulcers

The treatment of leg ulcers is a common and sometimes difficult problem. They can be costly to treat and are associated with loss of working capacity and sometimes significant morbidity. In the western world, leg ulcers are most frequently caused by venous insufficiency, arterial insufficiency, neuropathy (usually diabetic), or a combination of these factors. The pathogenesis, clinical features, and management of these types of leg ulcers are emphasized in this review.

The use of intermingled autograft and parental allograft skin in the treatment of major burns in children

Large burns continue to pose the problem of providing sufficient autologous skin cover. The experience of this unit using cultured keratinocytes as a substitute for split-skin grafts has been disappointing; at the same time, we have been obliged to abandon human allograft skin from cadavers and other patients because of the possibility of infection with HIV. Our favoured method for resurfacing large-area burns in children is to use widely meshed autologous skin overlaid with meshed allograft from a parent (to minimise the risk of HIV transmission). We report our experience using this technique in 10 children. The fate of the intermingled grafts has been followed clinically, and in some cases histologically and by Y-chromosome identification. There has generally been long-term persistence of the parental skin without rejection, and allograft dermis appears to contribute to the final cover. Evidence suggests, however, that cellular elements of the parental skin do not survive.

Cryopreservation of cultured skin cells

Cryopreservation of human skin keratinocytes and fibroblast cells has been evaluated using three cryoprotectants at various concentrations, three cooling rates and two warming rates. Optimal combinations of factors were determined. Selection for tolerance to cryopreservation was not detected after repeated freeze/thaw cycles. A beneficial effect of serum was shown to be cooling rate dependent.

The differentiation and proliferation of newly formed epidermis on wounds treated with cultured epithelial allografts

Fifteen patients, eight with burn or scald wounds and seven with split-thickness donor sites, were treated with cultured epithelial allografts. Skin was obtained from HIV-negative donors undergoing circumcision and sheets of epithelium were cultured using the 3T3 feeder method. Multiple post-operative biopsies were performed at various time intervals and stained with a panel of monoclonal antibodies against cytokeratins, involucrin, transferrin receptor and epidermal growth factor receptor. Fresh cultured epithelial sheets, normal skin, standard treated donor sites and burns treated with autografts were also studied. Cytokeratin-10 expression was not observed at treated sites until 4 weeks post-grafting, when normal suprabasal levels were observed. Cytokeratins 13 and 16, usually observed in highly proliferative states such as psoriasis, were observed in epithelial-treated sites for up to 6 months. Other proliferation markers such as Ki67 and transferrin receptor were only expressed 2-3 weeks post-operatively. Involucrin, a marker of keratinocyte terminal differentiation, was expressed throughout newly formed epidermis until 15 weeks, when the normal pattern of granular expression was observed. These results indicate that although the cultured 'allograft' does not survive, it may modulate the proliferation and differentiation of spontaneously regenerating epithelium.

Epidermal allografts

The epidermis is the sheet of stratified epithelial cells covering the dermal connective tissues. In addition to the epithelial cells (known as keratinocytes) there exist within the epidermis two populations of migratory leukocytes: the class II-positive, dendritic Langerhans' cell, and gamma-delta receptor-positive T lymphocytes. Allografts consisting essentially of epidermis have been in use since the introduction of "pinch" grafts by L. Reverdin in 1872. However, the capacity to culture keratinocytes in vitro to produce sheets of stratified epithelial cells has opened new possibilities. Cultured keratinocyte layers are devoid of passenger leukocytes and were initially widely believed not to be susceptible to rejection. This, however, is clearly not the case, at least in rats and humans. Nevertheless, in spite of severe acute rejection, it is interesting that cultured keratinocyte allografts are very poor at evoking antibody responses in graft recipients. Where permanent survival of the keratinocyte is required, autografts must be used, since the administration of immunosuppression to protect allografts would not be justified. Clinical application of cultured keratinocyte allografts, without immunosuppression, is limited to their use as temporary dressings (e.g., in burns) or to stimulate the recipient's own skin cells to growth (e.g., on leg ulcers). Autografts have been used for patients with extensive burns and in the treatment of chronic mastoiditis.

Utilization of human cultured epidermal keratinocytes: irreversibility of the inhibition of proliferation induced in stored detached cultures

In order to look for the best conditions required for the utilization of cultured epithelium in the treatment of burn wounds, some experiments have been performed studying the storage of dispase-detached cultures. The viability of keratinocytes and, after trypsin dissociation of the cultures, the adhesion and proliferative potential of living keratinocytes were measured. Our laboratory investigations suggest that the storage period of detached cultures has to be kept as short as possible to preserve the keratinocytes' growth potential.

Use of a biotinylated DNA probe specific for the human Y chromosome in the evaluation of the allograft lung

A cloned 3.4 kilobase DNA probe derived from the heterochromatin of the Y chromosome was used to investigate the regeneration and reepithelialization of allograft lungs of nine recipients who received sex mismatched donor organs. Patients were monitored for varying periods of time, up to four years, by transbronchial biopsy. In situ hybridization on paraffin-embedded biopsies utilizing the Y probe revealed that bronchial and alveolar epithelium and arterial and venous endothelium of the peripheral lung retained a donor phenotype, irrespective of episodes of acute or chronic rejection (obliterative bronchiolitis) which are known to injure these cellular subsets. In contrast, migratory cells, lymphocytes and macrophages, gradually, at varying rates, infiltrated the allografted lungs, replacing preexisting donor elements. Cases of active OB were manifested by infiltration of bronchioles by sex-mismatched lymphocytes; however, in some instances, quiescent recipient lymphocytes colonized the allograft and were unassociated with histologic rejection. Macrophages of similar sex seemed to cluster together within air spaces. Use of a DNA probe for the Y chromosome and in situ hybridization techniques allow monitoring of cellular alterations over time in recipients with sex mismatched allografts.

The treatment of donor sites with cultured epithelial grafts

In a significant number of elderly patients, the healing of split skin donor sites can be delayed. The cultured allogenic epithelial graft (CAG) has been reported to heal leg ulcers. The mechanism of action may be to improve the healing environment and thus stimulate the host skin cells. A clinical trial was undertaken to compare the healing rate of the donor sites of elderly patients using CAGs and two commercially available dressings. Compared to Jelonet, CAGs (p = 0.008) and OpSite (p = 0.013) significantly reduced the number of patients with delayed healing. There was no significant difference between CAGs and the occlusive dressing, OpSite.

Grafting of venous leg ulcers. An intraindividual comparison between cultured skin equivalents and full-thickness skin punch grafts

Skin equivalents that consisted of a noncontracted collagen gel populated with allogeneic fibroblasts and covered with autologous cultured keratinocytes were used for grafting venous leg ulcers. The results were compared in the same patient with those obtained with a routinely used standard method of grafting with autologous full-thickness punch grafts. The skin equivalents and the punch grafts were grafted successfully in four of five patients. The median healing time of ulcers grafted with skin equivalents was 18 days whereas that of ulcers covered with punch grafts was 15 days. The cosmetic appearance of the skin equivalent-grafted ulcers was better than that of the punch-grafted ulcers.

Treatment of leg ulcers with an allogeneic cultured-keratinocyte-collagen dressing

A living cellular allogeneic dressing made up of cultured keratinocytes adhering to a collagen film was used to treat 20 leg ulcers of various aetiologies in 16 patients. A reduction in pain was noted in 80% of cases, and promotion of granulation tissue in the ulcer bed in 70% of cases. In 10 patients, epithelialization of 71 +/- 29% of the ulcer was noted at Day 30.

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.

Cultured epidermal autografts and allografts: a study of differentiation and allograft survival

Cultured epidermal sheets were examined before and at various times after grafting on skin ulcer beds. Before grafting, the sheet consisted of four to five layers of keratinocytes with incomplete differentiation. Ten days after grafting, graft recipient sites showed compact hyperkeratosis, a normal-appearing epidermis, and a flat dermoepidermal junction. At 6 months, the stratum corneum had a basket-weave appearance but the dermoepidermal junction remained flat. Monoclonal antibodies to keratins 14 and 10 showed normal basal and suprabasal localization, respectively. Electron microscopy showed a normal basement membrane with anchoring fibrils. LH7:2, a monoclonal antibody that binds to the type VII collagen molecule, stained the dermoepidermal junction in all biopsy specimens. AE-1, an antibody that stains suprabasal cells in hyperproliferative skin, was expressed suprabasally for up to 12 weeks after healing (16 weeks after grafting), but expression was confined to the basal layer at 18 weeks after healing (6 months after grafting). Anti-involucrin staining was found in the deeper layers of the epidermis up to 12 weeks after healing (16 weeks after grafting) but had receded to a normal distribution in upper spinous and granular layers at 18 weeks (6 months after grafting). Overall, the histologic patterns observed in recipient sites during the first 4 months after grafting resembled those observed for 10 to 14 days in newly healed epidermis and in hyperproliferative states such as psoriasis. In four sex-mismatched graft sites, specimens were reacted with a biotinylated probe to the Y chromosome by in situ hybridization. Lack of Y chromosome-positive cells suggested that host keratinocytes had replaced the allografts. Multilocus DNA analysis in one patient confirmed this observation. Our data suggest that an altered state of epithelial maturation persists for several months after culture grafting, with restoration of the normal pattern by 6 months. No differences were detected between autografted and allografted sites.

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.

Treatment of postoperative otorrhoea by grafting of mastoid cavities with cultured autologous epidermal cells

Autologous cultured keratinocyte layers were grafted onto the unepithelialised open mastoid cavities in 8 patients with otorrhoea for 2 to 32 years. All procedures were done on an outpatient basis without anaesthesia, except for local anaesthesia for skin biopsy. The cultured keratinocyte layers adhered well to the bed of granulation tissue lining the mastoid cavity and formed an excellent protective covering of stratified squamous epithelium. All 8 patients have been free from otorrhoea for the 2 to 6 months since grafting.