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

StrataGraft skin substitute is well-tolerated and is not acutely immunogenic in patients with traumatic wounds: results from a prospective, randomized, controlled dose escalation trial

OBJECTIVE

The goal of this study was to assess the immunogenicity and antigenicity of StrataGraft skin tissue in a randomized phase I/II clinical trial for the temporary management of full-thickness skin loss.

BACKGROUND

StrataGraft skin tissue consists of a dermal equivalent containing human dermal fibroblasts and a fully stratified, biologically active epidermis derived from Near-diploid Immortalized Keratinocyte S (NIKS) cells, a pathogen-free, long-lived, consistent, human keratinocyte progenitor.

METHODS

Traumatic skin wounds often require temporary allograft coverage to stabilize the wound bed until autografting is possible. StrataGraft and cadaveric allograft were placed side by side on 15 patients with full-thickness skin defects for 1 week before autografting. Allografts were removed from the wound bed and examined for allogeneic immune responses. Immunohistochemistry and indirect immunofluorescence were used to assess tissue structure and cellular composition of allografts. In vitro lymphocyte proliferation assays, chromium-release assays, and development of antibodies were used to examine allogeneic responses.

RESULTS

One week after patient exposure to allografts, there were no differences in the numbers of T or B lymphocytes or Langerhans cells present in StrataGraft skin substitute compared to cadaver allograft, the standard of care. Importantly, exposure to StrataGraft skin substitute did not induce the proliferation of patient peripheral blood mononuclear cells to NIKS keratinocytes or enhance cell-mediated lysis of NIKS keratinocytes in vitro. Similarly, no evidence of antibody generation targeted to the NIKS keratinocytes was seen.

CONCLUSIONS

These findings indicate that StrataGraft tissue is well-tolerated and not acutely immunogenic in patients with traumatic skin wounds. Notably, exposure to StrataGraft did not increase patient sensitivity toward or elicit immune responses against the NIKS keratinocytes. We envision that this novel skin tissue technology will be widely used to facilitate the healing of traumatic cutaneous wounds.This study was registered at www.clinicaltrials.gov (NCT00618839).

Long-term followup of dermal substitution with acellular dermal implant in burns and postburn scar corrections

Full-thickness burn and other types of deep skin loss will result in scar formation. For at least partial replacement of the lost dermal layer, there are several options to use biotechnologically derived extracellular matrix components or tissue scaffolds of cadaver skin origin. In a survey, we have collected data on 18 pts who have previously received acellular dermal implant Alloderm. The age of these patients at the injury varied between 16 months and 84 years. The average area of the implants was 185 cm². Among those, 15 implant sites of 14 patients were assessed at an average of 50 months after surgery. The scar function was assessed by using the modified Vancouver Scar Scale. We have found that the overall scar quality and function was significantly better over the implanted areas than over the surrounding skin. Also these areas received a better score for scar height and pliability. Our findings suggest that acellular dermal implants are especially useful tools in the treatment of full-thickness burns as well as postburn scar contractures.

Bioengineered skin in diabetic foot ulcers

OBJECTIVE

Bioengineered skin (BS) has been shown to play an important role in the treatment of diabetic foot ulcers (DFUs). Whether BS in the therapy of DFU can improve the outcomes still remains uncertain. We performed a quantitative meta-analysis of available randomized controlled trials to determine the effectiveness and safety of BS in the treatment of patients with DFUs.

DESIGN AND METHODS

Comprehensive search strategies of various electronic databases were used for this study to evaluate the effectiveness and safety between BS and conventional treatment (CT) in patients with DFU, and only randomized controlled trials were adopted in our review. Search terms included 'bioengineered skin', 'tissue-engineering skin', 'human-tissue graft', 'human-skin device', 'living-skin equivalent' and 'diabetic foot', 'diabetic ulcer', 'diabetic wound'. Analysis outcomes included complete wound closure, complications, ulcer recurrence and adverse severe events (ASEs).

RESULTS

Seven randomized controlled trials on BS vs. CT were included, and 880 participants met inclusion criteria. Pooled analysis showed a significant effectiveness and safety advantages for BS treatment compared to CT for patients with DFUs. In analysis of complications, only statistically significant difference of infection was noted. And no included trials reported ASEs related to these treatments.

CONCLUSIONS

Based on the meta-analysis, patients with DFUs may benefit from the BS because of its high effectiveness and safety and reduced risk for infections in comparison to CT.

Chimeric composite skin substitutes for delivery of autologous keratinocytes to promote tissue regeneration

OBJECTIVE

We hypothesize that the pathogen-free NIKS human keratinocyte progenitor cell line cultured in a chimeric fashion with patient's primary keratinocytes would produce a fully stratified engineered skin substitute tissue and serve to deliver autologous keratinocytes to a cutaneous wound.

SUMMARY OF BACKGROUND DATA

Chimeric autologous/allogeneic bioengineered skin substitutes offer an innovative regenerative medicine approach for providing wound coverage and restoring cutaneous barrier function while delivering autologous keratinocytes to the wound site. NIKS keratinocytes are an attractive allogeneic cell source for this application.

METHODS

Mixed populations of green fluorescent protein (GFP)-labeled NIKS and unlabeled primary keratinocytes were used to model the allogeneic and autologous components in chimeric monolayer and organotypic cultures.

RESULTS

In monolayer coculture, GFP-labeled NIKS had no effect on the growth rate of primary keratinocytes and cell-cell junction formation between labeled and unlabeled keratinocytes was observed. In organotypic culture employing dermal and epidermal compartments, chimeric composite skin substitutes generated using up to 90% GFP-labeled NIKS exhibited normal tissue architecture and possessed substantial regions attributable to the primary keratinocytes. Tissues expressed proteins essential for the structure and function of a contiguous, fully-stratified squamous epithelia and exhibited barrier function similar to that of native skin. Furthermore, chimeric human skin substitutes stably engrafted in an in vivo mouse model, with long-term retention of primary keratinocytes but loss of the GFP-labeled NIKS population by 28 days after surgical application.

CONCLUSIONS

This study provides proof of concept for the use of NIKS keratinocytes as an allogeneic cell source for the formation of bioengineered chimeric skin substitute tissues, providing immediate formal wound coverage while simultaneously supplying autologous cells for tissue regeneration.

Cultured bilayered skin allograft for vaginal construction

OBJECTIVE

This is the first report of live human cultured bilayered skin allograft (taken from another person) (LHCBSA) to line a dissected space to create a vagina.

CASE

A 19-year-old with Mayer-Rokitansky-Küster-Hauser syndrome (MRKH syndrome) of vaginal and uterine agenesis had a space dissected and lined with LHCBSA. Although the lining devitalized within 2 weeks, there was a rapid ingrowth of vaginal mucosal cells from the vaginal dimple with an excellent long-term result.

CONCLUSION

This is the first report that LHCBSA is able to stimulate vaginal mucosal cell growth for a neovagina. It is possible that it might stimulate other surface tissue lining to cover adjacent raw areas such as bladder or esophagus.

Tissue-engineered skin substitutes in regenerative medicine

Recent advance in cellular tissue-engineered skin constructs have refined the applications already commercially available, in particular, by the use of genetically modified cells to enhance their properties on the treatment of wounds and to ease the application of epidermis using sprayed keratinocytes. This approach lends itself to use of chimeric epidermis, cultured allogeneic cells, to provide short-term coverage, together with minimally cultured autologous cells for long-term repair. Experimental models of skin include pathological conditions, phenomena such as aging and organogenesis, as in the hair follicle grown from isolated cells in vitro. The recent development of induced pluripotent stem cells raises the possibility of realizing the dream of skin and even limb regeneration shown by animals such as the salamander.

Apligraf in the treatment of neuropathic diabetic foot ulcers

This study compared the efficacy and safety of Apligraf (Organogenesis, Inc., Canton, MA) in combination with standard therapy versus standard therapy alone in the treatment of neuropathic diabetic foot ulcers. Efficacy was assessed by time to complete wound healing (by 12 weeks) and incidence of complete wound closure (at 12 weeks). This was an international multi-center, randomized, controlled study. Patients were eligible for entry into the study if the following criteria were met: type 1 or type 2 diabetes mellitus, age 18 to 80 years, adequate glycemic control, and the presence of a full-thickness neuropathic ulcer for at least 2 weeks prior to the initial screening visit. Following the 2-week screening period, the 2 treatment groups received standard ulcer care consistent with international treatment guidelines that comprised sharp debridement, saline-moistened dressings, and a non-weight bearing regimen. There were 106 subjects screened for enrollment, 82 randomized to the treatment groups, and 72 treated (33 Apligraf subjects and 39 standard therapy subjects) before the study was terminated. Kaplan-Meier curves indicated a trend for shorter time to complete wound healing in the Apligraf group compared with the standard therapy group (p = .059; log-rank test). The median time to healing was 84 days in the Apligraf group, whereas no median time to healing could be determined for the standard therapy group because <50% of the standard therapy subjects healed. By 12 weeks, 51.5% (17/33) Apligraf subjects had achieved complete wound closure compared with 26.3% (10/38) of standard therapy subjects (p = .049; Fisher's exact test). Even though the study was halted prematurely, this study suggested that the use of Apligraf resulted in a higher incidence of wound closure by 12 weeks.

Stem cells for skin tissue engineering and wound healing

The tremendous ability of the skin's epidermis to regenerate is due to the presence of epidermal stem cells that continuously produce keratinocytes, which undergo terminal differentiation to a keratinized layer that provides the skin's barrier properties. The ability to control this process in vitro has made it possible to develop various types of tissue-engineered skin grafts, some of which are among the first tissue-engineered products to ever reach the market. In the past 30 years, these products have been applied with some success to the treatment of chronic skin wounds such as diabetic and venous ulcers and deep, acute wounds such as burns. Current technologies remain partially effective in their ability to restore other skin structures, for example, the dermis, which is critical to the overall long-term appearance and function of the skin. As yet, none of these approaches can regenerate skin appendages (e.g. hair follicles and sweat glands). The use of earlier progenitor and stem cells, including embryonic stem cells, is gaining interest in the attempt to overcome such limitations. Furthermore, recent evidence suggests that "adult" stem cells, which are present in the circulation, target areas of injury and likely participate in the wound-healing process. In this paper, we start with an overview of the wound-healing process and current methods used for wound treatment, both conventional and tissue-engineering based. We then review current research on the various types of stem cells used for skin tissue engineering and wound healing, and provide future directions.

Skin tissue engineering

The major applications of tissue-engineered skin substitutes are in promoting the healing of acute and chronic wounds. Several approaches have been taken by commercial companies to develop products to address these conditions. Skin substitutes include both acellular and cellular devices. While acellular skin substitutes act as a template for dermal formation, this discussion mainly covers cellular devices. In addressing therapeutic applications in tissue engineering generally, a valuable precursor is an understanding of the mechanism of the underlying pathology. While this is straightforward in many cases, it has not been available for wound healing. Investigation of the mode of action of the tissue-engineered skin substitutes has led to considerable insight into the mechanism of formation, maintenance and treatment of chronic wounds. Four aspects mediating healing are considered here for their mechanism of action: (i) colonization of the wound bed by live fibroblasts in the implant, (ii) the secretion of growth factors, (iii) provision of a suitable substrate for cell migration, particularly keratinocytes and immune cells, and (iv) modification of the immune system by secretion of neutrophil recruiting chemokines. An early event in acute wound healing is an influx of neutrophils that destroy planktonic bacteria. However, if the bacteria are able to form biofilm, they become resistant to neutrophil action and prevent reepithelialization. In this situation the wound becomes chronic. In chronic wounds, fibroblasts show a senescence-like phenotype with decreased secretion of neutrophil chemoattractants that make it more likely that biofilms become established. Treatment of the chronic wounds involves debridement to eliminate biofilm, and the use of antimicrobials. A role of skin substitutes is to provide non-senescent fibroblasts that attract and activate neutrophils to prevent biofilm re-establishment. The emphasis of the conclusion is the importance of preventing contaminating bacteria becoming established and forming biofilms.

A review of a bi-layered living cell treatment (Apligraf) in the treatment of venous leg ulcers and diabetic foot ulcers

Apligraf^® (Organogenesis, Canton, MA) is a bi-layered bioengineered skin substitute and was the first engineered skin US Food and Drug Administration (FDA)-approved to promote the healing of ulcers that have failed standard wound care. Constructed by culturing human foreskin-derived neonatal fibroblasts in a bovine type I collagen matrix over which human foreskin-derived neonatal epidermal keratinocytes are then cultured and allowed to stratify, Apligraf provides both cells and matrix for the nonhealing wound. Its exact mechanism of action is not known, but it is known to produce cytokines and growth factors similar to healthy human skin. Initially approved by the FDA in 1998 for the treatment of venous ulcers greater than one-month duration that have not adequately responded to conventional therapy, Apligraf later received approval in 2000 for treatment of diabetic foot ulcers of greater than three weeks duration. Herein, we review the use of Apligraf in the treatment of chronic venous leg ulcers and diabetic foot ulcers. Our goal is to provide a working understanding of appropriate patient selection and proper use of the product for any physician treating this segment of the aging population.

Production of a novel fibroblast-populated platelet matrix cocultured with keratinocytes

We have developed a new method for the production of a dermal matrix equivalent. Human platelets were used to dilute human fibroblasts. The platelet mix was placed in a cell culture well. Addition of 200 microL of a thrombin solution caused gel formation. Gels were overlaid with standard Iscove's growth medium supplemented with 10% fetal bovine serum, insulin, and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer. Medium was exchanged regularly. Keratinocytes were plated on top of selected gels and elevated to the air-liquid interface. The gels were harvested weekly, fixed, cut, and stained with hematoxylin and eosin stains and immunostains for collagens I, III, and IV and cytokeratins. Digital image analysis was used to quantitate collagen production. Growth factors, including transforming growth factor-beta (TGF-beta), platelet-derived growth factor, and vitamin C were added. Staining identified fibroblasts within the gels with a surrounding fibrous matrix. Immunostaining for cytokeratin identified keratinocytes on the gel surface. Immunostaining revealed the fibrous matrix to be composed of collagen I and III and some collagen IV. Digital image analysis demonstrated that greater TGF-beta concentration resulted in greater collagen production. These differences were statistically significant. With development of this construct, a viable dermal/epidermal replacement may be possible. TGF-beta enhances collagen production by fibroblasts in this matrix.