What is new in clinical research in wound healing

Comparison of the Application of Allogeneic Fibroblast and Autologous Mesh Grafting With the Conventional Method in the Treatment of Third-Degree Burns

Wound healing is a multipart process involving different cell types and growth factors. Third-degree burns are usually treated by early excision and skin grafting. Tissue engineering has been developed in this field in response to limitations associated with autografts. Allogeneic fibroblasts on meshed split thickness skin grafts (STSGs) are known to have useful properties in wound healing and can be used to construct a new model of living skin substitute. Fourteen patients were chosen from June 2009 until December 2010 as the sample for this study. After debridement and wound excision, meshed STSG was used to cover the entire wound. Alloskin (allofibroblasts cultured on a combination of silicone and glycosaminoglycan) was applied on one side and petroleum jelly-impregnated gauze (Iran Polymer and Petrochemical Institute) was applied on the other. The healing time, scar formation, and pigmentation score were assessed for the patients. All analyses were undertaken with SPSS 17 software. Alloskin demonstrated good properties compared to petroleum jelly-impregnated gauze. The average healing time and hypertrophic scar formation were significantly different between the two groups. In addition, the skin pigmentation score in the alloskin group was closer to normal. Alloskin grafting, including fibroblasts on meshed STSG, may be a useful method to reduce healing time and scar size and may require less autologous STSG in extensive burns where a high percentage of skin is burned and there is a lack of available donor sites.

Ex vivo expansion of corneal limbal epithelial/stem cells for corneal surface reconstruction

PURPOSE

The management of severe ocular surface disease due to limbal stem cell deficiency has changed dramatically. The concept of limbal stem cells, as the source of corneal epithelium revolutionised the therapeutic approach of ocular surface reconstruction. Deficiency of limbal stem cells results in blinding ocular surface diseases. Grafting viable limbal tissue, from either fellow healthy eye or a donor eye, with the resident stem cell population may replenish limbal stem cells and can restore the corneal surface to normality. Transplanting the limbal tissue can be achieved through a variety of procedures that include cadaveric keratolimbal allograft (KLAL), live or living related conjunctival limbal allograft (Ir-CLAL) and limbal autograft. Advances in tissue engineering techniques have offered a viable alternative to overcome the limitation of limbal tissue available for transplantation. Epithelial stem cells harvested from a small limbal biopsy can be expanded in vitro on a suitable carrier and then transplanted to the diseased cornea to successfully restore the corneal surface. This article is a chronological review of the important steps that brought ex vivo expanded stem cell transplantation in ocular, particularly corneal surface reconstruction.

METHODS

The MEDLINE data base was searched for the years 1966-2002, using key words cornea, cell culture, ex-vivo expansion, limbus, stem cell, ocular surface and transplantation. Several articles that were not found by MEDLINE search were taken from references from other articles. Inclusion or exclusion of article was based on the relevance to the subject.

CONCLUSIONS

Corneal epithelial reconstruction with ex vivo expanded limbal cells is a potential tool in ocular surface reconstruction, although the technique is currently investigational. Strategies to achieve conjunctival epithelial restoration and tear film replenishment will allow ophthalmic surgeons to truly reconstruct the ocular surface.

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.

The control of epidermal stem cells (holoclones) in the treatment of massive full-thickness burns with autologous keratinocytes cultured on fibrin

BACKGROUND

Cell therapy is an emerging therapeutic strategy aimed at replacing or repairing severely damaged tissues with cultured cells. Epidermal regeneration obtained with autologous cultured keratinocytes (cultured autografts) can be life-saving for patients suffering from massive full-thickness burns. However, the widespread use of cultured autografts has been hampered by poor clinical results that have been consistently reported by different burn units, even when cells were applied on properly prepared wound beds. This might arise from the depletion of epidermal stem cells (holoclones) in culture. Depletion of holoclones can occur because of (i) incorrect culture conditions, (ii) environmental damage of the exposed basal layer of cultured grafts, or (iii) use of new substrates or culture technologies not pretested for holoclone preservation. The aim of this study was to show that, if new keratinocyte culture technologies and/or "delivery systems" are proposed, a careful evaluation of epidermal stem cell preservation is essential for the clinical performance of this life-saving technology.

METHODS

Fibrin was chosen as a potential substrate for keratinocyte cultivation. Stem cells were monitored by clonal analysis using the culture system originally described by Rheinwald and Green as a reference. Massive full-thickness burns were treated with the composite allodermis/cultured autograft technique.

RESULTS

We show that: (i) the relative percentage of holoclones, meroclones, and paraclones is maintained when keratinocytes are cultivated on fibrin, proving that fibrin does not induce clonal conversion and consequent loss of epidermal stem cells; (ii) the clonogenic ability, growth rate, and long-term proliferative potential are not affected by the new culture system; (iii) when fibrin-cultured autografts bearing stem cells are applied on massive full-thickness burns, the "take" of keratinocytes is high, reproducible, and permanent; and (iv) fibrin allows a significant reduction of the cost of cultured autografts and eliminates problems related to their handling and transportation.

CONCLUSION

Our data demonstrate that: (i) cultured autografts bearing stem cells can indeed rapidly and permanently cover a large body surface; and (ii) fibrin is a suitable substrate for keratinocyte cultivation and transplantation. These data lend strength to the concept that the success of cell therapy at a clinical level requires cultivation and transplantation of stem cells. We therefore suggest that the proposal of a culture system aimed at the replacement of any severely damaged self-renewing tissue should be preceded by a careful evaluation of its stem cell population.

Transplanted fetal fibroblasts: survival and distribution over time in normal adult dermis compared with autogenic, allogenic, and xenogenic adult fibroblasts

Cell therapy is a widely applicable therapeutic approach using cells and cell elements, frequently from fetal or young animals, for their beneficial effects. This study evaluated the host response to and tolerance of transplanted fetal skin fibroblasts. Cultured fibroblasts from adult rabbit skin (autogenic and allogenic), 21-day fetal rabbit skin (allogenic), and adult pig skin (xenogenic) were labeled with a fluorescent vital dye CM-DiI, injected intradermally into the dorsal skin of adult rabbits at multiple sites and then biopsied over an 8-week period. Each cell type showed a biphasic distribution curve with an early phase (0 to 28 days) and a late phase (28 to 56 days). In the early phase, cells showed a rise and fall in total cell density (reflecting an increase and then a decrease in total cell number), followed by a slow decrease in cell density with cells still detectable at 56 days. Fetal cells showed the highest survival at the end of the study. None of the groups showed clinical or histologic signs of acute inflammation or rejection. This study demonstrated that (1) transplanted fibroblasts are well tolerated by an immunologically competent host, (2) CM-DiI-labeled cells are detectable in vivo for at least 8 weeks, and (3) fetal fibroblasts have a distribution and survival profile that is distinct from that of adult fibroblasts.