Fresh versus cryopreserved cultured allografts for the treatment of chronic skin ulcers

The added value of cultured cells in burn treatment: A systematic review

INTRODUCTION

Advancements in resuscitative care and burn surgery have improved survival rates after extensive burn injuries, shifting focus to enhancing the quality of survival. Conventional treatment with split-thickness skin grafts (STSG) presents limitations such as donor-site morbidity, limited availability in extensive burn injuries, and hypertrophic scarring. Tissue engineering aims to address these drawbacks by developing optimal skin substitutes. This systematic review aims to provide an overview of the current applications of cultured cells in burn surgery, encompassing diverse approaches and addressing existing challenges to enhance burn wound management and improve patient outcomes.

METHODS

Following PRISMA guidelines, a comprehensive search was performed across three databases (PubMed, Embase, Cochrane Library) for articles on cultured cell use in burn treatment. Only clinical studies were included. Articles were screened by two independent reviewers. Quality assessment was performed.

RESULTS

The search yielded 167 articles, of which 14 met the eligibility criteria. The selection included 8 randomized controlled trials, 5 prospective cohort trials, and 1 retrospective cohort study. Various tissue-engineered skin substitutes, from cultured epidermal autografts to dermal regeneration templates seeded with cultured cells, showed promising outcomes. Several substitutes exhibited take rates comparable to STSG with improved scar quality.

CONCLUSION

Results are promising, though standardization of cultured skin substitutes and robust clinical trials with larger populations and appropriate comparators are still lacking.

Cadaveric Skin Grafts May Greatly Increase the Healing Rate of Recalcitrant Ulcers When Used Both Alone and in Combination With Split-Thickness Skin Grafts

BACKGROUND

Leg ulcers that do not heal despite appropriate treatment are defined as recalcitrant ulcers. Large surface area, depth, and long duration represent some of most important factors impeding ulcer healing. After sharp debridement, dermal substitutes including skin from cadaver donors may increase the healing rate of recalcitrant ulcers reducing the risk of scar formation and recurrence.

OBJECTIVE

Assessing if, after sharp debridement, dermal substitutes including skin from cadaver donors may increase the healing rate of recalcitrant ulcers reducing the risk of scar formation and recurrence.

PATIENTS AND METHODS

Among patients admitted to our hospital for all types of chronic leg ulcers, we retrospectively reviewed the records of patients affected by recalcitrant ulcers (surface greater than 100 cm, tissue loss involving epidermis, dermis, and subcutaneous tissue, duration longer than 1 year, and showing no healing tendency). After sharp debridement, the ulcers were covered by allografts with strict follow-up after discharge. Multiple allografts were performed when necessary, and a final autograft was applied in case of incomplete healing.

RESULTS

The records of 414 patients were analyzed. Forty-three patients were lost at follow-up, and the remaining 371 healed after 765 grafting procedures. In 163 patients, the ulcers healed by means of a final autograft. In all the remaining cases, allograft led to ulcer healing.

CONCLUSION

Allografts represent an effective treatment option in case of recalcitrant, large, deep and long-lasting leg ulcers.

Skin-Derived Stem Cells for Wound Treatment Using Cultured Epidermal Autografts: Clinical Applications and Challenges

The human skin fulfills important barrier, sensory, and immune functions-all of which contribute significantly to health and organism integrity. Widespread skin damage requires immediate treatment and coverage because massive skin loss fosters the invasion of pathogens, causes critical fluid loss, and may ultimately lead to death. Since the skin is a highly immunocompetent organ, autologous transplants are the only viable approach to permanently close a widespread skin wound. Despite the development of tissue-saving autologous transplantation techniques such as mesh and Meek grafts, treatment options for extensive skin damage remain severely limited. Yet, the skin is also a rich source of stem and progenitor cells. These cells promote wound healing under physiological conditions and are potential sources for tissue engineering approaches aiming to augment transplantable tissue by generating cultured epidermal autografts (CEAs). Here, we review autologous tissue engineering strategies as well as transplantation products based on skin-derived stem cells. We further provide an overview of clinical trial activities in the field and discuss relevant translational and clinical challenges associated with the use of these products.

Using Living Skin Equivalents for Diabetic Foot Ulceration

Diabetic foot ulcers are a major clinical challenge with enormous socioeconomic consequence. All advances in the understanding and management of this problem are eagerly received by wound specialists. The development of bioengineered skin—living skin equivalent—is an interesting event that could be significant in the management of lower extremity wounds such as the diabetic foot ulcer.

A Prospective Multicenter Study of the Efficacy and Tolerability of Cryopreserved Allogenic Human Keratinocytes to Treat Venous Leg Ulcers

Allogeneic human keratinocyte cultures have been used to treat burn wounds, donor sites, and chronic skin ulcers with some success. Cryopreservation of these cultures allows for the production of large standardized batches that are readily available for use. The aim of the study presented in this report was to study effects of cryopreserved cultured allogenic human keratinocytes (Cryo Ceal) on chronic lower extremity wounds. Parameters were measured to study efficacy, tolerability, pain associated with chronic wounds, and quality of life of patients. Twenty-seven patients with hard-to-heal venous leg ulcers received a maximum of 9 applications of Cryo Ceal in a prospective, uncontrolled multicenter study lasting 48 weeks. Eleven out of 27 patients (41%; 95% CI: 22%-61%) had complete wound closure within 24 weeks (1 week). The time required for complete wound closure in these 11 patients ranged from 4.1 to 24.9weeks. Only 1 patient had recurrence of the ulcer at 48 weeks. Local (wound) pain scores decreased from a mean of 2.5 at baseline to 0.9 at week 24. Fifty percent of the patients attained a pain score of 0 after 12 weeks and remained stable at this score until the end of the study. Overall, the patient quality of life was better at week 24, compared to baseline values. The treatment was well tolerated, and wound infection was the most frequently occurring adverse event.

Cutaneous Tissue Engineering and Lower Extremity Wounds (Part 1)

Tissue-engineered skin is a novel therapeutic with which difficult-to-heal lower extremity wounds may be treated. Such skins are products of cutaneous tissue engineering that provide an alternative for autologous or allogeneic tissue transplantation, thereby avoiding problems associated with donor site availability, the risk of infection, and scarring. Recently developed tissue-engineered skin equivalents have shown to be superior in certain ways to compression therapy for refractory venous ulcers and acute wounds. These biologic products behave similarly to autografts.

Synergistic Effect of Regeneration and Inflammation via Ibuprofen-Loaded Electrospun Fibrous Scaffolds for Repairing Skeletal Muscle

Adult skeletal muscle regeneration involves serial steps among which inflammation in the wounded area is critical for the healing process. However, accelerated tissue regeneration and the inhibition of excessive inflammation are always the targets of tissue engineering, because excessive inflammation in the early stage can impede the regeneration in the following step. In this study, a feasible ibuprofen-loaded poly (L-lactide) (PLLA) fibrous scaffold was designed to evaluate the ability of preventing excessive inflammatory response and promoting regeneration using 35 Sprague-Dawley (SD) rats. The cytotoxicity assay of PLLA and ibuprofen-loaded PLLA fibrous scaffolds (IBU/PLLA) showed that there were no significant cell cytotoxicity on L6 cells. The histological results showed that the IBU/PLLA group had slighter inflammation than PLLA and control groups during the whole process. In the later stage, the regeneration process of the IBU/PLLA group took place on the 7th day, which was almost more than one week earlier than the PLLA and control groups. qRT-PCR analysis further displayed that the IBU/PLLA group had a lower level of inflammatory factors and higher expression of repair factors than the PLLA and control groups, especially from the 7th day, and lasted until the 21st day. Furthermore, there were no statistical differences between the PLLA group and the control group from histological results and qRT-PCR analysis. Taken together, through the muscle wound healing process, the results demonstrated that the ibuprofen-loaded PLLA fibrous scaffolds had better control of excessive inflammation and faster process of healing than non-ibuprofen-loaded groups.

Wound-healing potential of Cultured Epidermal Sheets is unaltered after lyophilization: a preclinical study in comparison to cryopreserved CES

Lyophilized Cultured Epidermal Sheets (L-CES) have been reported to be as effective as the cryopreserved CES (F-CES) in treating skin ulcers. However, unlike F-CES, no preclinical study assessing wound-healing effects has been conducted for L-CES. The present study was set out to investigate the microstructure, cytokine profile, and wound-healing effects of L-CES in comparison to those of F-CES. Keratinocytes were cultured to prepare CES, followed by cryopreservation at −70°C and lyophilization. Under microscopic observation, intact cells with apparent intracellular junctions were observed in L-CES. The L-CES, like fresh CES, consisted of three to four well-maintained epidermal layers, as shown by the expression of keratins, involucrin, and p63. There were no differences in the epidermal layer or protein expression between L-CES and F-CES, and both CES were comparable to fresh CES. TGF-α, EGF, VEGF, IL-1α, and MMPs were detected in L-CES at levels similar to those in F-CES. In a mouse study, wounds treated with L-CES or F-CES completely healed at least 4 days faster than untreated wounds. CES-treated wounds completely healed by day 10, while the untreated wounds did not heal by day 14. Masson's trichrome staining showed that collagen deposition in the CES-treated wounds was highly increased in the dermis of the wound center compared to that in the control wounds. Thus, this study demonstrates that L-CES is as clinically effective as F-CES for wound treatment.

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

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

MATERIALS AND METHODS

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

INCLUSION CRITERIA

all patients who received CAlloK.

EXCLUSION CRITERIA

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

RESULTS

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

CONCLUSION

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

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

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

Tissue Engineering for Cutaneous Wounds

Skin, the largest organ in the body, protects against toxins and microorganisms in the environment and serves to prevent dehydration of all non-aquatic animals. Immune surveillance, sensory detection, and self-healing are other critical functions of the skin. Loss of skin integrity because of injury or illness may result acutely in substantial physiologic imbalance and ultimately in significant disability or even death. It is estimated that, in 1992, there were 35.2 million cases of significant skin loss (US data) that required major therapeutic intervention. Of these, approximately 7 million wounds become chronic. Regardless of the specific advanced wound care product, the ideal goal would be to regenerate tissues such that both the structural and functional properties of the wounded tissue are restored to the levels before injury. The advent of tissue-engineered skin replacements revolutionized the therapeutic potential for recalcitrant wounds and for wounds that are not amenable to primary closure. This article will introduce the reader to the field of tissue engineering, briefly review tissue-engineered skin replacement from a historical perspective and then review current state-of-the-art concepts from our vantage point.

Evaluation of ApligrafR persistence and basement membrane restoration in donor site wounds: a pilot study

Apligraf is a bilayered tissue-engineered product consisting of a bovine collagen matrix with neonatal fibroblasts, overlaid by a stratified epithelium containing living keratinocytes. The United States Food and Drug Administration has approved its use for venous leg ulcers and neuropathic diabetic foot ulcers. Apligraf provides a dermal matrix and produces cytokines similar to the human skin. However, its mechanism of action and ultimate fate in host wounds are unclear. The aim of this study was to evaluate the persistence of Apligraf fibroblasts and keratinocytes in human acute partial-thickness wounds (split-thickness donor sites) treated with Apligraf. In an open-label, within-patient, three-centered, controlled pilot study, 10 patients were treated with Apligraf, Apligraf dermis only (without epidermis), and a polyurethane film for donor site wounds of the same size, depth, and anatomical location. Apligraf DNA persistence was the primary outcome measure. Basement membrane components, cosmetic outcome, time to wound healing, and safety parameters were secondary outcome measures. One week after the initial treatment, reverse transcription polymerase chain reaction analysis found that two Apligraf and two Apligraf dermis-only-treated sites had Apligraf DNA present. Four weeks posttreatment, only one Apligraf and one Apligraf dermis-only sites showed the presence of Apligraf DNA. There was no difference between the three treatment modalities in establishing basement membrane in donor site wounds. No differences in other secondary outcomes were found. Apligraf DNA persisted in a minority of patients at 4 weeks in acute partial-thickness wounds. Apligraf's success in speeding healing of acute wounds appears to be related to factors other than the persistence of donor DNA or effect on basement membrane restoration.

The possibility of long-term cryopreservation of cultured dermal substitute

Allogeneic cultured dermal substitute (CDS) was prepared by cultivating fibroblasts on a two-layered spongy matrix of hyaluronic acid (HA) and atelo-collagen (Col). CDS can be cryopreserved and transported to other hospitals in a frozen state. To evaluate cell viability, cell growth, and release of VEGF after long-term cryopreservation, the CDS was cryopreserved at -85 degrees C or -152 degrees C for a given period. We measured cell viability immediately after thawing and cell growth in CDS that was recultured for 1 week after thawing. In addition, the amount of vascular endothelial growth factor (VEGF) released from CDS that was recultured for 1 week after thawing was measured. The cell viability and cell growth of control CDS that was thawed within 3 weeks after freezing was 56.2% and 132.7%, respectively. The cell viability and cell growth of the CDS that was cryopreserved at -85 degrees C for 6 months was 43.4% and 119.7%, respectively. When cryopreserved at -152 degrees C for 1 year, the cell viability and cell growth was 52.0% and 110.8%, respectively. These values were comparable to those of the control. The amount of VEGF released from CDS cryopreserved at -85 degrees C for 6 months (491.0 pg/mL) or at -152 degrees C for 1 year (586.8 pg/mL) was comparable to that of the control CDS (587.3 pg/mL). In contrast, the amounts of VEGF released from CDS cryopreserved at -85 degrees C for 1 year (322.5 pg/mL) or at -152 degrees C for 2 years (210.8 pg/mL) were low, with a marked decrease in cell viability and cell growth. These findings suggest that CDS cryopreserved at -85 degrees C for 6 months or at -152 degrees C for 1 year maintains sufficient cell viability and the ability to proliferate and release a significant amount of VEGF. The release of VEGF from CDS after long-term cryopreservation is a useful therapeutic effect, and is important for clinical use.

Other uses of homologous skin grafts and skin bank bioproducts

The main use of homologous skin grafts or grafts of related bioproducts is in the treatment of severe burns. However, various new clinical and experimental sectors, in which this type of skin substitute can be useful, have recently emerged. The main new clinical indications for skin allografts include: skin loss, surgical wounds and bullous diseases. In these fields donor skin can be used for different purposes: as a physiological biological dressing to control pain and protect deep structures such as tendons, bones, cartilage and nerves, and to promote reepithelization with a significant reduction in healing time, and as skin substitute with dermal tissue to guide repair and make it as physiological as possible. In particular, skin bank bioproducts are currently used in the treatment of several conditions such venous and arterial leg ulcers, pressure ulcers, diabetic foot ulcers, pyoderma gangrenosum, post traumatic lesions, Mohs surgery, reconstructive surgery, wound cover in critical areas, aesthetic surgery, congenital epidermolysis bullosa and Lyell's syndrome. Skin bank bioproducts have also been used for experimental indications, to study in vitro toxicology and in vitro skin biology. Recently the demonstration that de-epidermized dermis (DED) has all the characteristics of an excellent dermal substitute into which various types of cells can be introduced and made to develop, opens exciting new possibilities of research in the field of wound healing and tissue engineering. Our preliminary observations seems to indicate that CD 34+ stem cells from umbilical cord blood can survive in DED and in a few weeks populate collagen bundles. The observation of tubular structures without lumina close to collagen bundles as well as clusters of epithelioid or fibroblast-shaped cells may represent aspects of differentiation of CD 34+ stem cells. More detailed and sophisticated studies are clearly needed to answer all the questions that these initial observations pose. Anyway the 3-dimensional model proposed seems to be suitable for the study of the behaviour of peripheral CD 34+ and perhaps also other types of stem cells in 3-dimensional dermal matrix.

Cultured human epithelium: human umbilical cord blood stem cells differentiate into keratinocytes under in vitro conditions

BACKGROUND

Stem cells have the capacity to renew or to give rise to a specialized cell types. Human umbilical cord blood (HUCB) has been explored as an alternative source of stem cells. However, its potential to differentiate into cells of other tissues is still under discussion. The aim of our study was to evaluate if HUCB stem cells could differentiate into epithelial cells under in vitro conditions.

METHODS

Human keratinocytes derived from adult female skin donors, were isolated and cultured on fibrin glue/fibroblast gels-control group. In the umbilical cord blood cell group, male umbilical cord blood cells were added at a 1:10 ratio to keratinocytes and co-cultured on the fibrin glue/fibroblasts gel. After 15 days of culture, the sheets were analyzed by use of histochemistry and FISH. DNA was extracted and evaluated by use of polymerase chain reaction (PCR) for detection of Y-chromosome-specific sequences.

RESULTS

In both groups a regular epithelial sheet consisting of three to four layers of cells was formed. Using PCR and FISH, in the umbilical cord blood cell group the presence of Y-chromosome-specific sequences in the cultured keratinocytes could be detected. In the control group, no Y-chromosome-specific sequences could be detected.

CONCLUSION

Our findings indicate that umbilical cord blood stem cells differentiate into epithelial cells under in vitro conditions and thereby, might serve as a starting material for isolation and expansion of cells for transplantation in patients with large skin defects.

Gene therapy in the treatment of lower extremity wounds

This article presents a brief overview of the etiology of chronic wounds of the lower extremities and their current medical and surgical treatment. Gene therapy as a potential tool for treating therapeutically challenging wounds is described in terms of the vectors employed in gene transfer, as well as the strategies used to promote wound healing. Results from animal model studies, as well as clinical trials, are presented.

Construction of skin equivalents for gene therapy of recessive dystrophic epidermolysis bullosa

We have shown that retroviral vectors efficiently transfer the 9-kb collagen type VII cDNA into keratinocytes of dogs with recessive dystrophic epidermolysis bullosa (RDEB) and achieve correction of the RDEB phenotype in vitro. As a next step toward gene therapy applications, we have assessed the suitability of retroviral vectors to transduce human collagen type VII cDNA into primary human RDEB keratinocytes and generate transplantable autologous skin equivalents. The transduced RDEB keratinocytes permanently express high levels of recombinant collagen type VII that assembles into functional homotrimers readily secreted into the extracellular matrix. The recombinant collagen type VII reverts the migration and invasion potential of the transduced RDEB keratinocytes in vitro and is efficiently deposited at the dermal epidermal junction of artificial skin prepared with the reverted cells and artificial dermis made of biomaterial sponges embedded with dermal RDEB fibroblasts. Transplantable fibrin-based skin equivalents made with the transduced RDEB keratinocytes and grafted onto SCID mice either orthotopically or in accordance with the flap method generated cohesive and orderly stratified epithelia with all the characteristics of normal human epidermis, including rapid formation of anchoring fibrils. Because transplantable epithelia are routinely used to cure patients suffering from large skin or mucosal defects, the full phenotypic reversion of primary RDEB epidermal clonogenic cells mediated by recombinant retroviral vectors opens new perspectives in the long-term treatment of genodermatoses.

The Viennese culture method: cultured human epithelium obtained on a dermal matrix based on fibroblast containing fibrin glue gels

The aim of this study was to develop a new keratinocyte culture system on a dermal equivalent suitable for skin wound closure. Our dermal matrix is based on a fibrin glue gel containing live human fibroblast (from human foreskin). Keratinocytes obtained from primary culture according to the Rheinwald and Green method, were seeded on to the gel. In all cases, the keratinocytes plated on the dermal equivalent grew to confluence and stratified epithelium was obtained. After 10 days an irregular multilayer could be observed. The cells showed active interaction with the fibrin support, presenting as cell formations projecting into the matrix. After 15 days a regular epithelial sheet consisting of three to four layers of cells was formed. A limiting membrane demarcating the keratinocytes from the fibrin matrix was discernible. Squamous differentiation similar to Strata reticulare and corneum found in vivo could be observed. Nuclei of basal cells were regularly spaced from each other and the chromatin was of homogeneous appearance without prominent nucleoli. The last time point (20 days) showed signs of disintegration of the epithelial sheet. A basement membrane-like structure could not be seen any more. Detachment of the basal cells was associated with subepithelial vacuoles. Basal cells contained irregular nuclei. Therefore, we conclude that 15 days of culture were optimal for the generation of a keratinocyte layers with signs of differentiation; this new culture system could be an important step forward in covering severely burned patients due to a number of advantages, as for example a large expansion factor, the shortening of the optimal culture time to 15 days, the usage of commercially available fibrin glue gels and the versatile manipulation of composite cultures.

Cryopreserved and lyophilized cultured epidermal allografts in the treatment of leg ulcers: a pilot study

BACKGROUND

In the conservative therapy of venous leg ulcers modern types of dressings are used most frequently. In the past 20 years 'active wound dressings' - cultured epidermal keratinocytes as autografts and allografts - were also introduced in the management of leg ulcers.

METHODS

The aim of our study was to compare the effect of cryopreserved and lyophilized cultured epidermal allografts in the treatment of venous leg ulcers. Evaluation of the therapy was documented as photodocumentation, planimetry, healing time and evaluation of pain relief over a 3-month period after application. Fifty patients with venous leg ulcers were selected. Twenty-five patients (group I) were treated with cryopreserved keratinocytes and 25 (group II) with lyophilized keratinocytes.

RESULTS

The final evaluation 3 months after the application of allografts showed 84% of healed ulcers in group I and 80% in group II. The number of healed ulcers and the healing rate both showed no statistically significant differences. The size of the ulcer was reduced by half during the first week in both groups. The size differences during the first week are statistically significant in both groups and they are comparable (P < 0.001). The intensity of the pain was statistically significantly reduced during the first week after application in both groups (P < 0.001).

CONCLUSIONS

The cryopreserved and lyophilized cultured allografts are comparable in healing rate, course of healing and relief of pain, and also in planimetric changes during the healing of venous leg ulcers. Lyophilized allografts are more convenient for routine use than cryopreserved allografts as they can be stored at room temperature. These results could give rise to the more frequent use of lyophilized allografts in slow-healing venous leg ulcers.

Organotypic cultures of autologous hair follicle keratinocytes for the treatment of recurrent leg ulcers

Our purpose was to evaluate, in an open study, the efficacy of epidermal equivalents (EEs), a tissue-engineered epidermis prepared from autologous hair follicle keratinocytes, for the treatment of recurrent leg ulcers (n = 50). To generate EEs, keratinocytes expanded from the outer root sheaths of plucked anagen hair follicles were seeded on cell culture inserts at air-liquid interface. The total culture time was 5 to 6 weeks. Three days after the procedure, 95% of EEs adhered to the wound bed. After 8 weeks, 70% of the total wound surface was re-epithelialized and 32% of the ulcers were healed. After applying the EEs, a major relief of wound pain was noticed by the patients. EEs were applied in ambulatory patients without surgical facilities. Because 92% of the cases included in this study presented a recurrence of their ulcers after a split-thickness skin graft, we consider these ulcers as difficult to treat and propose the EEs as an alternative effective treatment of recurrent leg ulcers.

Evaluation of tissue-engineered skin (human skin substitute) and secondary intention healing in the treatment of full thickness wounds after Mohs micrographic or excisional surgery

BACKGROUND

Human Skin Substitute (Apligraf, Organogenesis, Inc., Canton, MA) is a bi-layered tissue-engineered living biological dressing developed from neonatal foreskin. It consists of a bovine collagen matrix containing human fibroblasts with an overlying sheet of stratified human epithelium containing living human keratinocytes. Human Skin Substitute (HSS) appears to be immunologically inert, and has shown usefulness in the treatment of chronic and acute wounds.

OBJECTIVE

Primary objectives were to evaluate the safety and efficacy of HSS in the treatment of full-thickness wounds in a prospective case series. Secondary objectives were to determine the rate of complete wound reepithelialization, incidence of complete wound healing, pain at wound site, overall cosmetic outcome, and patient satisfaction.

METHODS

Fourteen patients were enrolled in the study, of which 12 were evaluable. HSS was applied in a blinded fashion to 6 of the patients immediately following Mohs or excisional surgery for skin cancer. The remaining 6 patients were allowed to heal by secondary intention. Both groups were evaluated at weekly appointments until complete reepithelialization occurred. During each evaluation, wound quality was assessed through the Vancouver Burn Scar Assessment Scale by the investigator and an independent blinded dermatologist. The investigator, blinded observer, and patient further evaluated the cosmetic outcome of the wound through the use of a Visual Analog Scale over a 6-month period.

RESULTS

HSS patients and secondary intention patients were equivalent in comorbid factors such as pain, erythema, edema, exudate, infection, or hematoma between the groups. The incidence of complete wound healing at 6 months was 100% for both groups. Both groups also appeared to heal at similar rates, as defined by the complete reepithelialization of the wound. HSS patients ultimately resulted in more pliable and less vascular wounds as defined by the Vancouver Burn Scar Assessment Scale. Patient satisfaction with cosmetic outcome in both groups was positive at 6 months.

CONCLUSIONS

HSS appears to be a safe, well-tolerated biological dressing with equivalent comorbid factors to secondary intention healing. HSS, however, seems to produce a more pliable and less vascular scar than those developed through healing by secondary intention. HSS also appears to produce more satisfactory cosmetic results when compared to secondary intention healing.

Low-intensity laser therapy/combined phototherapy in the management of chronic venous ulceration: a placebo-controlled study

OBJECTIVE

The current placebo-controlled study was undertaken to investigate the efficacy of combined phototherapy and low-intensity laser therapy (LILT) in the management of chronic venous ulceration when used in conjunction with standardized nursing intervention.

MATERIALS AND METHODS

Approval was granted by Research Ethical Committees at the University of Ulster and Altnagelvin Hospitals Health and Social Services Trust. Patients (n = 15; 10 female/5 male; age +/- SD = 69.9 +/- 13.8 years) were recruited from an outpatient "leg ulcer clinic," where they attended once per week for irradiation/sham treatments for 4 weeks. Treatment was withheld for a total of 8 weeks, and patients were reviewed during this time (weeks 8 and 12) for ulcer and pain assessment only. A multisource diode array (660-950 nm) was used for irradiation; parameters were kept constant for the duration of the study (532 mW; 5 kHz; 12 J/cm(2)). Wound and pain assessment were carried out by an independent investigator. Digitizing was used to quantify surface areas from wound tracings.

RESULTS

Although there was no statistically significant difference between Treatment and Placebo groups, an apparent clinical difference in wound healing rate was noted; at postirradiation, a continued reduction in wound size was evident for the treatment group. These effects were believed to be due to an apparent delayed effect. There was no statistically significant difference between groups for pain.

CONCLUSION

These findings provide only limited evidence for the use of this modality as an adjunctive therapy with current nursing intervention. Further group studies are indicated to investigate the apparent delayed effect reported here for various etiologies of ulceration.

Factors that influence healing in chronic venous ulcers treated with cryopreserved human epidermal cultures

BACKGROUND

Cryopreserved epidermal cultures (CEC) offer an "off the shelf" treatment for chronic wounds. These cultures are derived from neonatal foreskin and grow rapidly in vitro to form epidermal sheets. They do not require a biopsy from the patient, an advantage compared to autografts. They seem to act as a biological dressing, stimulating epithelialization from the wound edges and adnexae, probably through growth factor release.

OBJECTIVE

To summarize our recent experience with the use of CEC in chronic venous leg ulcers and to determine the factors that influence healing in chronic venous ulcers treated with CEC.

PATIENTS AND METHODS

A single arm, open label study including a total of 11 patients with documented venous ulcers was performed. The study involved the application of cryopreserved epidermal cultures every other week to nonhealing leg ulcers for a total of 12 weeks or until complete healing of the ulcer.

RESULTS

A total of 11 patients with one or more leg ulcers were treated. The average age was similar in healed and unhealed groups. Seven patients completely healed after an average of 4.14 CEC applications. Four patients did not heal after a total of 12 CEC applications.

CONCLUSION

Predictors for failure to heal after CEC application in our patients were long wound duration, wound size, presence of lipodermatosclerosis, and history of failed prior split-thickness skin grafts.

Artificial skin: past, present and future

The integrity of the skin should be restored as soon as possible whenever the skin gets wounded. Recent research has revealed some of the complex pathways in wound healing. Based on this knowledge, researchers have been looking for better skin substitutes to treat difficultly healing or large wounds. Some of these highly sophisticated wound dressings, also known as bio-dressings, contain material of human or animal origin, e.g. cultured skin cells. Although the ideal skin substitute has not been established yet, the currently available bio-dressings help clinicians close difficultly healing skin wounds.

Cryopreserved cultured epidermal allografts achieved early closure of wounds and reduced scar formation in deep partial-thickness burn wounds (DDB) and split-thickness skin donor sites of pediatric patients

Burn treatment in children is associated with several difficulties, e.g. available skin replacement is small, donor area could expand, and subsequent hypertrophic scar and contracture could become larger along with their physical growth. In order to have better clinical results, the authors prepared cryopreserved cultured epidermal allografts from excess epidermal cells of other patients, and applied the epidermal allografts to 55 children, i.e. 43 cases of deep partial-thickness burn wounds (DDB) due to scald burn and 12 cases with split-thickness skin donor sites. In the 43 DDB patients, epithelialization was confirmed 9.1+/-3.6 days (mean+/-S.D.) after treatment. In 10 of the 43 patients, epithelialization was comparable between the area which received the epidermal allografts (grafted area) and the area which did not receive the epidermal allografts but was covered with usual wound dressing (non-grafted area). As a result, epithelialization day was 7.9+/-1.7 in grafted areas and 20.5+/-2.3 in non-grafted areas. In the 12 patients with split-thickness skin donor sites, epithelialization was confirmed 6.3+/-0.9 days after treatment. Epithelialization of the grafted and non-grafted areas was comparable in 8 of the 12 patients, and it was 6.5+/-1.1 days and 14.1+/-1.6 days, respectively. In these 10 DDB patients and 8 split-thickness skin donor site patients, redness and scar formation were also milder in the grafted area. The 55 patients have been followed up for 1-8 years (mean, 4.75 years), and scar formation was suppressed in both DDB and split-thickness skin donor sites. These findings showed that cryopreserved cultured epidermal allografts achieve early closure of the wounds and good functional outcomes.

Tissue-engineered product: allogeneic cultured dermal substitute composed of spongy collagen with fibroblasts

Recently, various types of allogeneic skin substitutes including cultured epidermal substitute (CES), cultured dermal substitute (CDS), and cultured skin substitute (CSS), which are composed of keratinocytes and/or fibroblasts as the cellular component(s), have been used as biological wound dressings. In our study, the allogeneic CDS was prepared by plating fibroblasts on a spongy collagen. The clinical evaluation was conducted using fresh or cryopreserved allogeneic CDS. In 145 of our clinical cases, 95% (138/145) of various wounds were evaluated as achieving good or excellent results, including 96% (22/23) of deep dermal burns (DDB) and dermal burns (DB), 100% (53/53) of partial-thickness donor wounds, 91% (21/23) of traumatic skin defects, 100% (5/5) of pressure ulcers, 82% (9/11) of chronic skin ulcers, 100% (6/6) of coverage for debrided DB, and 92% (22/24) of coverage for autologous meshed graft. The results obtained in our study suggest that the allogeneic CDS is able to provide an effective therapy for patients with partial and/or full-thickness skin defects.

Can we produce a human corneal equivalent by tissue engineering?

Tissue engineering is progressing rapidly. Bioengineered substitutes are already available for experimental applications and some clinical purposes such as skin replacement. This review focuses on the development of reconstructed human cornea in vitro by tissue engineering. Key elements to consider in the corneal reconstruction, such as the source for epithelial cells and keratocytes, are discussed and the various steps of production are presented. Since one application of this human model is to obtain a better understanding of corneal wound healing, the mechanisms of this phenomenon as well as the function played both by membrane-bound integrins and components from the extracellular matrix have also been addressed. The analysis of integrins by immunohistofluorescence labelling of our reconstructed human cornea revealed that beta(1), alpha(3), alpha(5), and alpha(6) integrin subunits were expressed but alpha(4) was not. Laminin, type VII collagen and fibronectin were also detected. Finally, the future challenges of corneal reconstruction by tissue engineering are discussed and the tremendous applications of such tissue produced in vitro for experimental as well as clinical purposes are considered.

Long-term viability of cryopreserved cultured epithelial grafts

Human cultured epithelial grafts are frozen for long-term preservation. To assess the viability of these stored grafts, their cell survival rate and colony-forming efficiency of grafts cryopreserved at -135 degrees C and at -80 degrees C were followed over time. Flow cytometry showed that the cell survival rate of the grafts cryopreserved at -135 degrees C for 1 month, 6 months and 1 year averaged 89.3%, 61.7% and 61.6%. Cryopreservation at -80 degrees C maintained cell survival rate as well for 1 month, but after 6 months of cryopreservation survival was reduced at -80 degrees C (35.2%) compared with that of -135 degrees C. In histological examination, the cell structure and basal layer were very well preserved after 6 months of storage at -135 degrees C, but not at -80 degrees C. Cell survival rate at -135 degrees C was also assessed by colony-forming efficiency. Colony-forming efficiency of the grafts cryopreserved for 1 month, 6 months and 1 year averaged 66.1%, 58.5% and 55.1% of control (noncryopreserved) grafts. These findings suggest that, even when cultured epithelial grafts are subjected to long-term cryopreservation, cell viability remains sufficient, reculturing is possible, and that graft banking could be used for clinical applications.

Skin grafting

No longer an option of last resort, skin grafting has become a technique that is routinely and sometimes preferentially considered as skin replacement for burns, chronic ulcers, and skin defects after cutaneous surgical procedures. When selected as the best alternative for wound closure, autologous skin grafts are commonly considered the gold standard. Availability of autologous grafts is a major obstacle, however, and the search for a manufactured skin replacement has continued. In cases in which autologous grafts cannot be performed, skin substitutes have become an attractive alternative.

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

In 1975, serial subculture of human keratinocytes was first described. Clinical application of this discovery was made possible after the preparation of these cells into epithelial sheets. In 1981, the earliest application of cultured autologous epithelia was made for the treatment of extensive third-degree burns. Although the most important advantage is the large surface area obtained from a relatively small biopsy of healthy skin from the patient, a disadvantage is the delay, which is too long, especially for the treatment of extensive deep burns. This delay leads to denutrition and infection of the burn wounds, which in turn risks the life of the patient and jeopardizes the engraftment of the cultures. More recently, allogenic cultured epidermis, obtained more quickly from donor skin, has been described in the treatment of leg ulcers, repair of skin donor site harvested for split thickness autograft, dermatological diseases and in second-degree burns, although limited to certain areas. In this last case, grafted cells act by stimulation of epithelialisation from the adnexal appendages. To be able rapidly to treat patients suffering extensive and deep second-degree burns, a bank of allogenic keratinocytes has been created, with due attention to safety and security. The paper demonstrates the advantages of using allogenic keratinocytes in the first phase of treatment of a 97% deep second-degree burn patient awaiting autologous cultured keratinocytes. The time required for complete healing achieved using such a strategy is compared with the results obtained after treatment using autologous sheets of two patients burnt on 80% and 82% of their total body area. The treatment of these two latter patients is relatively long and complicated by potentially lethal problems. In the 97% burnt patient, however, the clinical course is shorter and without complication. Moreover, autologous and allogenic cultured epithelia give good aesthetic results, without the mesh aspect obtained with a split-thickness autograft, and also without the discomfort for the patient of removing a sample of skin. Deep second-degree burns are an application of choice for the cultured epithelia, as the presence of the dermis avoids retractions responsible for functional complications usually observed in third-degree burns where dermis is absent. Because of the safety of the bank of allogenic keratinocytes, the treatment of extensive and deep second-degree burns has become safer and faster, with better functional and aesthetic results.

Frozen allogeneic human epidermal cultured sheets for the cure of complicated leg ulcers

BACKGROUND

Skin ulcers due to venous stasis or diabetes are common among the elderly and are difficult to treat. Repeated applications of cell-based products have been reported to result in cure or improvement of leg ulcers of small size in a fraction of patients.

OBJECTIVE

To examine the effects of frozen human allogeneic epidermal cultures for the treatment of acute and chronic ulcers.

METHODS

We treated a series of 10 consecutive patients with leg ulcers of different etiology and duration with frozen human allogeneic epidermal cultures stored frozen and thawed for 5-10 minutes at room temperature before application. Three patients had ulcers with exposed Achilles or extensor tendon. The ulcers treated were as large as 160 cm2 in area and of up to 20-years' duration. After preliminary preparation of the wounds by debridement to remove necrotic tissue and application of silver sulfadiazine to control infection, thawed cultures were applied biweekly from 2 to 15 times depending on the size and complexity of the ulcer.

RESULTS

All ulcers healed, including those with tendon exposure. After the first few applications, granulation tissue formed in the ulcer bed and on exposed tendons, and epidermal healing took place through proliferation and migration of cells from the margins of the wound. The time required for complete healing ranged from 1 to 31 weeks after the first application.

CONCLUSION

The use of frozen human allogeneic epidermal cultures is a safe and effective treatment for venous or diabetic ulcers, even those with tendon exposure. It seems possible that any leg ulcer will be amenable to successful treatment by this method.

Clinical evaluation of an allogeneic cultured dermal substitute composed of fibroblasts within a spongy collagen matrix

We have developed an allogeneic cultured dermal substitute (CDS) that was prepared by plating fibroblasts on to a spongy collagen matrix and culturing them for 7 to 10 days. The matrix was freeze-dried from a 1% aqueous solution of bovine-hide atelocollagen. This study was designed to evaluate the efficacy of promoting epithelialisation clinically on 26 donor-site wounds for split-thickness skin grafts. One half of a wound was covered with an allogeneic CDS and the other half side was covered with a commercially-available freeze-dried porcine dermis (FPD). Both macroscopically and histologically the epithelialisation on the area of the donor site that was covered with allogeneic CDS was more rapid than that covered with FPD. In a representative donor-site wound covered with allogeneic CDS, there was a stratified structure of epithelial cells on the underlying connective tissue on day 5, and the epithelium had matured by day 12. When covered with FPD a stratified structure of epithelial cells was noted on day 8, and the epithelium had matured by day 15. We conclude that allogeneic CDS provides a good environment for epithelialisation.

Allogeneic cultured dermal substitute composed of spongy collagen containing fibroblasts: evaluation in animal test

The authors developed a cultured dermal substitute (CDS) composed of a spongy collagen containing cultured fibroblasts. The cultured fibroblasts derived from Sprague Dawley rat skin were seeded on a spongy collagen at a density of 5 x 10(5) cells cm(-2) and cultured for 7 days. This CDS was applied to the debrided wound of full-thickness burn which was inflicted experimentally on the dorsum of Wister rat, and then the wound conditions were observed over a period of 2 weeks. The comparative study was conducted using an acellular spongy collagen as well as a commercially available temporary wound dressing, Biobrane, since a different type of cultured dermal substitute, Dermagraft-TC, is composed of Biobrane, whose inner site is combined with cultured fibroblasts. Each covering material was applied on the debrided wound area and exchanged by new one 1 week later. When the debrided wound was covered with Biobrane, a small portion of necrotic tissue was observed 1 week after application, and the granulation tissue formation was greatly delayed. This wound area showed a poor granulation tissue even 2 weeks later. On the contrary, when covered with an acellular spongy collagen, no necrotic tissue was observed. This wound area showed a more or less irregular granulation tissue at 1 week and then a healthy granulation tissue 2 weeks later. This preliminary comparative study suggests that an acellular spongy collagen is able to function as a more suitable matrix for CDS, compared with Biobrane. The wound area covered with a CDS assumed a moist, shiny, and hyperaemic appearance 1 week after application showing a healthy granulation tissue. The macroscopic evaluations indicate that the CDS is able to prepare a healthy granulation tissue at an earlier stage, compared with the acellular spongy collagen. In addition, the histologic views demonstrate that the CDS is able to prepare a thicker and denser granulation tissue, compared with the acellular spongy collagen. Although the fate of cultured fibroblasts in the CDS on the wound surface within 1 week is not clear, these findings suggest that fibroblasts in CDS are able to provide excellent conditions for wound healing.

Cultivation and transplantation of epidermal keratinocytes

Transplantation of autologous cultured keratinocytes is the most advanced area of tissue engineering which has clinical application in restoration of skin lesions. In vitro, disaggregated keratinocytes undergo activation and after adhesion and histogenic aggregation form three-dimensional epithelial sheets suitable for grafting on prepared wounds that provide a reparative environment. Epidermal stem cells survive and proliferate in culture, retaining their potential to differentiate and to produce neoepidermis. Reconstructed skin is physiologically compatible to split-thickness autografts. Autotransplantation of cultured keratinocytes is a promising technique for gene therapy. In many cases allografting of cultured keratinocytes promotes wound healing by stimulation of epithelialization. Banking of cryopreserved keratinocytes is a significant improvement in usage of cultured keratinocytes for wound healing. Skin substitutes reconstructed in vitro that have morphological, biochemical, and functional features of the native tissue are of interest as model systems that enable extrapolation to situations in vivo.

Cultivation of human keratinocyte stem cells: current and future clinical applications

Cultured human keratinocytes have a wide spectrum of clinical applications. Clinical results reported by several investigators are, however, contradictory. In this review, the authors discuss the biological and surgical issues which play a key role in the clinical outcome of cultured epidermal autografts used for the treatment of massive full-thickness burns. The importance of cultivation of epidermal stem cells and of their transplantation onto a wound bed prepared with donor dermis is emphasised. The paper also reviews recent data showing that: (i) cultured epidermal autografts bearing melanocytes can be used for the treatment of stable vitiligo; (ii) keratinocytes isolated from other lining epithelia, such as oral, urethral and corneal epithelia, can be cultivated and grafted onto patients suffering from disabling epithelial defects; (iii) keratinocyte stem cells can be stably transduced with retroviral vectors and are therefore attractive targets for the gene therapy of genodermatoses.