Treatment of skin ulcers with cultured epidermal allografts

Successful treatment of chronic leg ulcers with epidermal equivalents generated from cultured autologous outer root sheath cells

The outer root sheath cells of hair follicles can substitute for interfollicular epidermal keratinocytes, as during healing of skin wounds when these cells migrate onto the denuded area and contribute to epidermal regeneration. Using improved culture techniques, we generated epidermal equivalents from cultured outer root sheath cells of patients suffering from recalcitrant chronic leg ulcers, primarily of vascular origin. In such epidermal equivalents, tissue organization as well as immunolocalization of epidermal differentiation products (keratin 10, involucrin, filaggrin) and integrins were indistinguishable from normal epidermis. As determined by the number of bromodeoxyuridine-incorporating cells, the basal layer contained a large compartment of proliferative cells irrespective of donor age. FACS analysis of the outer root sheath cells, used to prepare the epidermal equivalents, disclosed a fraction of small cells with enhanced expression of beta1-integrin, a potential stem cell marker. in contrast to acute wounds, a major definitive take of grafted cultured autologous keratinocytes has not been convincingly demonstrated in chronic wounds. In a pilot study, grafting of epidermal equivalents generated in vitro from autologous outer root sheath cells on 11 ulcers in five patients resulted in a definitive take rate of about 80%, with subsequent complete healing within 2 to 3 wk of five out of seven ulcers grafted with densely arranged cultures. This improvement in the treatment of chronic leg ulcers with cultured autologous keratinocytes probably depends on the large compartment of proliferative cells as well as on a well-developed horny layer which prevents disintegration of the grafts. Practical advantages of the new technique are its noninvasiveness, the lack of need for surgical facilities or anesthesia, and a short immobilization period after grafting.

Expression of interleukin-1alpha, interleukin-6, and basic fibroblast growth factor by cultured skin substitutes before and after grafting to full-thickness wounds in athymic mice

OBJECTIVES

Cultured skin substitutes (CSSs), consisting of human keratinocytes and human fibroblasts attached to collagen-glycosaminoglycan substrates, have been demonstrated to cover wounds, and may release detectable quantities of growth factors that promote wound healing.

MATERIALS AND METHODS

Basic fibroblast growth factor (bFGF), interleukin-1alpha (IL-1alpha), and interleukin-6 (IL-6) were assayed by enzyme linked immunosorbent assay and immunohistochemistry in CSSs in vitro and at days 1, 3, 7, 14, and 21 after grafting to full-thickness wounds in athymic mice.

MEASUREMENTS AND MAIN RESULTS

When isolated cells were tested, IL-1alpha was found to come primarily from the keratinocytes, whereas bFGF was from the fibroblasts. Combinations of both cell types in the CSSs resulted in a synergistic enhancement of IL-6 expression. Quantities of all three cytokines from CSSs were greater in vitro compared with in vivo levels at all time points after grafting. bFGF increased from day 1 to day 7, and then remained relatively constant until day 21. At day 3 maximal levels of IL-1alpha were observed. By day 7, IL-1alpha decreased to approximately 40% of maximal levels, and subsequently increased until day 21. IL-6 levels were highest at day 7 after grafting. All cytokines had reached elevated levels during the time of wound revascularization (days 3-7).

CONCLUSIONS

The sequence of cytokine synthesis in the wounds (i.e., rapid IL-1alpha increase followed by IL-6 expression) parallels serum levels reported after a septic challenge. These findings support the hypothesis that the wound is a source of systemic cytokines.

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.

Comparative assessment of cultured skin substitutes and native skin autograft for treatment of full-thickness burns

OBJECTIVE

Comparison of cultured skin substitutes (CSSs) and split-thickness autograft (STAG) was performed to assess whether the requirement for autologous skin grafts may be reduced in the treatment of massive burns.

SUMMARY BACKGROUND DATA

Cultured skin substitutes consisting of collagen-glycosaminoglycan substrates populated with autologous fibroblasts and keratinocytes have been demonstrated to close full-thickness skin wounds in athymic mice and to express normal skin antigens after closure of excised wounds in burn patients.

METHODS

Data were collected from 17 patients between days 2 and 14 to determine incidence of exudate, incidence of regrafting, coloration, keratinization, and percentage of site covered by graft (n = 17). Outcome was evaluated on an ordinal scale (0 = worst; 10 = best) beginning at day 14, with primary analyses at 28 days (n = 10) and 1 year (n = 4) for erythema, pigmentation, epithelial blistering, surface roughness, skin suppleness, and raised scar.

RESULTS

Sites treated with CSSs had increased incidence of exudate (p = 0.06) and decreased percentage of engraftment (p < 0.05) compared with STAG. Outcome parameters during the first year showed no differences in erythema, blistering, or suppleness. Pigmentation was greater, scar was less raised, but regrafting was more frequent in CSS sites than STAG. No differences in qualitative outcomes were found after 1 year, and antibodies to bovine collagen were not detected in patient sera.

CONCLUSIONS

These results suggest that outcome of engrafted CSSs is not different from STAG and that increased incidence of regrafting is related to decreased percentage of initial engraftment. Increased rates of engraftment of CSSs may lead to improved outcome for closure of burn wounds, allow greater availability of materials for grafting, and reduce requirements for donor skin autograft.

Early basement membrane formation following the grafting of cultured epidermal sheets detached with thermolysin or Dispase

The basement membrane zone is important for graft adhesion and stability. The aim of the present study was to visualize the regeneration of the basement membrane and determine the sequential appearance of its constituents in the early postgrafting period of cultured human epidermal sheets. A keratinocyte single cell suspension, devoid of dermal fibroblast contamination, was obtained from human skin by a two-step tissue digestion method with thermolysin and trypsin. After culturing, epidermal sheets were generated, detached enzymatically by incubating with thermolysin (for 20-30 min) or Dispase (for 45-60 min), and deposited on a muscular graft bed of athymic mice. Immunohistochemistry and ultrastructural analyses were performed on biopsies harvested 2, 4 and 21 days postgrafting. Bullous pemphigoid antigens and laminin were detected at the dermo-epidermal junction, showing an almost continuous line 2 days postgrafting. Type IV collagen was generally absent at this time, but it was detected 4 days postgrafting. Type VII collagen was labelled as a discontinuous line of increasing intensity from 2 to 21 days postgrafting. Ultrastructural analysis revealed hemidesmosomes and a discontinuous lamina densa 2 days postgrafting, and a complete basement membrane with a continuous lamina densa, hemidesmosomes and anchoring fibrils 21 days postgrafting. The sequence of appearance of major basement membrane components was similar for cultured sheets detached with thermolysin or Dispase. However, it differed from that of other wound healing models. Results are discussed in terms of the variable keratinocyte migration requirement between various wound healing models.

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.

Treatment of non-healing skin ulcers with autologous activated mononuclear cells

The aim of this study was to investigate whether cultured autologous mononuclear cells (MNC) effectively initiate, accelerate and improve granulation and epithelialisation of skin ulcers. Thirty-three patients with chronic arterial occlusive disease (CAOD; n = 21) or venous post-thrombotic syndrome (PTS; n = 12) were treated with autologous MNC and compared with a control group of 30 patients who received tissue culture medium alone. Previous treatments had been unsuccessful for a mean of 9.23 (3-19) months. MNC were harvested from the peripheral blood of each patient by standard techniques, cultured for three days and applied to the ulcer twice a week. After 4.6 +/- 1.9 weeks, 29/33 ulcers were closed in the MNC group. Patients in the control group took 8.1 +/- 1.2 weeks for 17/30 ulcers. Thus ulcer healing was significantly speedier with MNC seeding; 48% of all ulcers were closed after 30 days of MNC treatment and 92% after 60 days. Patients with PTS responded significantly faster than patients with CAOD. In 90% of patients with painful ulcers MNC treatment resulted in pain relief, whereas in the control group only 50% of patients became pain-free.

What is infection?

Wound colonization by bacteria is not always the same as invasive infection. Furthermore, the classic definition of infection does not always aid the clinician in determining whether a patient is in the process of developing life-threatening sepsis. Although research efforts have focused on identification and quantification of organisms involved, the predictive value of this variable is limited. Other variables, such as the nature of the organism, nature of the wound, and nature of the host's defense mechanisms must also be considered. For instance, large acute wounds have been found to react differently to skin flora organisms than small, chronic, ulcerative wounds. Careful and frequent patient and wound assessment is still required to predict if and when offending organisms, their toxins, or both reach sufficient concentrations to overwhelm their local host defenses.

Immunohistochemical studies on regeneration in cultured epidermal autografts used to treat full-thickness burn wounds

The normal pattern of healing following culture grafting is not well-established. The present study describes the immunohistochemical expression of differentiation markers during various stages of wound healing after resurfacing full-thickness burn wounds with cultured epidermal autografts. For this purpose, biopsy specimens were obtained from six patients 6 days to 4.5 years after transplantation. A panel of monoclonal antibodies was used against various differentiation-specific protein markers, including cytokeratins, involucrin, transglutaminase and filaggrin. Findings from early and late biopsies were compared with site-matched normal skin and cultured epidermal sheets. The persistence of cytokeratins 6 and 16, and to a lesser extent, the abnormal distribution of involucrin up to 4.5 years after resurfacing burns with cultured autografts was observed. These findings confirm previous studies--that the newly formed epidermis after culture grafting remains in a hyperproliferative state for a long time, which may be caused by the absence of a modulating dermal factor. Our results suggest that keratinocyte maturation following culture autografting does not return to normal for at least 4.5 years after healing of full-thickness burn wounds.

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.

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.

Delivery of growth factor to wounds using a genetically engineered biological bandage

Increasing the rate of wound healing of acute wounds and promoting the closure of chronic ulcers is an important goal in wound therapy. Growth factors have been shown to facilitate this process; however, the systems described for growth factor delivery are not ideal. In the present report we demonstrate the feasibility of a new method of delivering growth factors to the wound site using a genetically engineered biological bandage. The bandage consists of keratinocytes (SCC-13 cells) that are engineered by gene transfer to produce high levels of bovine growth hormone (bGH). bGH was selected for these studies because it can be easily distinguished from rat and human growth hormone in wound fluids and culture medium. The bGH-producing cells are contained and maintained in serum-free medium inside an envelope composed of a low protein binding, 0.2 micron pore size, polysulfone membrane. The genetically engineered cells cannot escape from the bandage, but the bGH is freely released into the surrounding culture medium. When placed onto a full-thickness, surgically generated wound on rats, the cells within the bandage continue to produce and release bGH into the wound for at least 3 days. This system is a safe and reliable way of providing real-time delivery of any desired biomolecule into the wound site.

Use of autografts for the treatment of leg ulcers in elderly patients

Human keratinocytes obtained from seven elderly patients who had long-standing leg ulcers of venous or rheumatoid origin were grown into sheets for autografting on to their ulcers on at least one and, in some cases, two occasions. Following the application of the autografts on to the ulcers the appearance of the ulcer base improved with an increase in the vascularity of the granulation tissue and decrease in the amount of exudate. An 'edge effect' was also noted in five cases, with the previously indolent-looking edge of the ulcer appearing healthier and more active. However, over a 4-month follow-up period there was no complete re-epithelialization in any of the ulcers despite these initial improvements.

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.

Improvement of human keratinocyte isolation and culture using thermolysin

We propose a modification of the conventional keratinocyte isolation method which has shown a significant improvement in the purity, colony forming efficiency (c.f.e.) and growth capacity of the isolated epidermal cell population. This method utilized thermolysin since it selectively digests the dermo-epidermal junction. Following separation from the dermis, the epidermis was digested with trypsin to obtain a single cell suspension. Compared with the conventional procedure, this isolation method was shorter and resulted in (i) cells displaying a higher colony forming efficiency, (ii) cells reaching confluence 1-3 days earlier, (iii) cells not contaminated by fibroblasts, (iv) a cell population containing all the basal layer keratinocytes. These cells were suitable for the establishment of primary cultures and could be subcultured. Such cell populations should be advantageous in studies of epithelial-mesenchymal interactions in which keratinocyte populations, free of fibroblasts, are desirable. In the treatment of extensively burned patients using cultured epidermal sheets, the main problem remains the time required for their production. Thus, the absence of fibroblast overgrowth of the keratinocyte cultures and the significantly reduced time to obtain confluent cultures and epidermal sheets with our method have very important implications for the treatment of large burn wounds.

Ontogenesis of the basement membrane zone after grafting cultured human epithelium: a morphologic and immunoelectron microscopic study

Sheets of cultured epithelial cells have been successfully used as autografts for the permanent coverage of patients with full-thickness burns and as allografts to stimulate the healing of chronic skin ulcers. The basement membrane zone (BMZ), composed of lamina lucida, lamina densa, and anchoring fibrils, plays a pivotal role in the firm adherence of the epidermis to the dermis. The present study describes the ultrastructural development during various stages of wound healing after resurfacing different wound areas by cultured epithelial grafts. For this purpose, biopsies were obtained from five patients 5 d to 4.5 years after resurfacing full-thickness burns with cultured autografts, and from five patients at various stages after treatment of excised tattoos and chronic skin ulcers with cultured allografts. One biopsy was taken from a spontaneously healed burn wound 30 years post-injury. Ultrathin sections were prepared for transmission and immunoelectron microscopy, using monoclonal antibodies against type IV and VII collagen. Findings were compared to controls of age- and site-matched normal skin. Eleven days after grafting, the first BMZ features had regenerated, including lamina lucida, a discontinuous lamina densa, hemidesmosomes, and sparse anchoring fibrils. The process of de novo synthesis of BMZ components had begun, and within 4 to 5 weeks complete reformation of BMZ was observed, including normal distribution of anchoring fibrils. Immunolabeling of type VII collagen was first observed upon the lower part of lamina densa at day 11 and steadily increased, reaching normal values 5 weeks after grafting. In contrast, gold deposition of type IV collagen upon lamina densa was strongly increased at day 19 compared to normal. This high expression reduced a little at 5 weeks, but remained high up to 30 years after injury. Long-term burn scars exhibited pseudopodia-like extensions of all basal cells, abundant anchoring fibrils, and an increased amount of arching anchoring fibrils. These features might compensate for the lack of proper rete ridges.

Treatment of chronic erosions of junctional epidermolysis bullosa with human epidermal allografts

We have successfully treated chronic central facial erosions of a patient with junctional epidermolysis bullosa using cultured epidermal allografts. Keratinocytes isolated from a skin biopsy of the patient's biological mother were used to generate the epidermal allografts. Significant re-epithelialization occurred during the course of four grafting procedures. Cultured epidermal allografts appear to be a promising method for treatment of chronic erosions of junctional epidermolysis bullosa.

Treatment of refractory and stable vitiligo by transplantation of in vitro cultured epidermal autografts bearing melanocytes

BACKGROUND

Previous reports demonstrated the usefulness of in vitro cultured epidermis for repigmenting vitiligo.

OBJECTIVE

Our purpose was to determine the potential of in vitro cultured epidermal sheets to treat extensive areas of intractable vitiligo.

METHODS

In nine patients with long-standing, stable, and refractory vitiligo, autologous epidermis was cultured in vitro in H-MEM but without growth enhancers or hormones and transplanted onto previously denuded achromic lesions.

RESULTS

Repigmentation was achieved to almost 100% in three subjects, 60% improvement was seen in two patients, and 30% to 40% in three additional cases. Only one patient had almost no response. Long-term observations in these patients indicate that repigmentation obtained by this method is permanent.

CONCLUSION

Transplantation of in vitro cultured epidermis bearing melanocytes is potentially effective to treat extensive areas of vitiligo, but this method is presently at an experimental stage.

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.

Grafting of leg ulcers with undifferentiated keratinocytes

A procedure for transplanting cultured human keratinocytes has been developed and used successfully to treat patients with persistent leg ulcers. Shave excisions of donor skin of 1 cm2 or less were expanded in culture in 1 week to cover wounds as large as 90 cm2. The uniqueness of this system is the use of a biochemically modified surgical dressing that permits the transplantation of undifferentiated cells. Several hours after inoculation, trypsinized single cells become attached to the dressing and are ready for grafting. Seven of eight persistent stasis ulcers completely reepithelialized after application of the modified surgical dressing with undifferentiated keratinocytes.

Therapeutic use of cytokines in dermatology

Cytokines are glycoproteins produced by many different cells. Via binding to specific receptors on target cells they regulate the activation, differentiation, and proliferation of immune and nonimmune cells. After injury keratinocytes synthesize and release cytokines such as interleukins, colony stimulating factors, and growth factors. In addition, a network of interacting cytokines appears to be crucial to maintain proper balance. Dysregulation may contribute to certain diseases, particularly those of infectious and autoimmune origin. Therefore many of these mediators appear to be promising candidates to treat infectious and malignant diseases. This article briefly discusses the most important cytokines. Newly developed regimens with cytokines to treat cutaneous disorders will be reviewed.

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 keratinocyte sheets enhance spontaneous re-epithelialization in a dermal explant model of partial-thickness wound healing

An in vitro model for partial-thickness cutaneous wound healing is described in which the influence of variables present in vivo, such as blood-borne factors and inflammatory cells, is eliminated. Dermal sheets of porcine skin are maintained in culture at the air-liquid interface in serum-free medium, and re-epithelialization from the keratinocytes of the hair infundibula can be studied. Dermal sheets of different thicknesses harvested from various depths were first evaluated for viability and regenerative potential in serum-supplemented medium. Mid-dermal explants, 20/1000 inch thick, showed the greatest epithelial outgrowth from the appendigeal keratinocytes and the longest viability in vitro. Explants of this type were used in all subsequent experiments. The effects of growth factors on re-epithelialization of the explants were studied in a serum-free environment. Epidermal growth factor, cholera toxin, bombesin, and insulin-like growth factor alone and in various combinations were applied to the explant surface in aqueous solutions by micropipette. Outgrowth was assessed by computerized morphometric analysis (RS/1 program by BBN) at days four and eight. Among all factors tested, cholera toxin alone and in combination with insulin-like growth factor produced the greatest epithelial outgrowth. Nevertheless, topical applications of growth factors failed to induce complete re-epithelialization within the experimental time frame. In contrast, explants to which cultured human keratinocyte sheets were topically applied regenerated a confluent and regularly stratified epidermis within 6 d.

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.

Cultured allogenic keratinocyte grafts in the management of wound healing: prognostic factors

Cultured allografts derived from neonatal foreskin provide a potent stimulus to wound healing in a wide variety of wounds. Their application is a simple outpatient procedure involving no discomfort for the patient. In contrast to autografting, no biopsy is necessary, and growth of newborn keratinocytes in cultures is more rapid than that of adult cells. Use of cultured allogeneic cells offers immediate graft availability and the possibility of stockpiling and preserving the graft for future use. Cultured epidermal allografts may be valuable in accelerating healing by second intention in surgical wounds, as well as being a helpful addition to chronic ulcer management. In venous disease, the outcome is at least comparable to other forms of skin grafting. Ulcers due to connective tissue disorders fared less well and deep chronic ulcers (down to fascia or tendon) were not significantly improved by cultured allograft application. Surprisingly, patient age did not influence outcome.