Allogeneic fibroblasts used to grow cultured epidermal autografts persist in vivo and sensitize the graft recipient for accelerated second-set rejection

Regenerative Medicine of Epithelia: Lessons From the Past and Future Goals

This article explores examples of successful and unsuccessful regenerative medicine on human epithelia. To evaluate the applications of the first regenerated tissues, the analysis of the past successes and failures addresses some pending issues and lay the groundwork for developing new therapies. Research should still be encouraged to fill the gap between pathologies, clinical applications and what regenerative medicine can attain with current knowledge.

Bioreactor Microcarrier Cell Culture System (Bio-MCCS) for Large-Scale Production of Autologous Melanocytes

Restoration of cutaneous pigmentation can be achieved in stable vitiligo by autologous cultured melanocyte transplantation. It was the goal of this study to construct a bioreactor microcarrier cell culture system (Bio-MCCS) to produce autologous melanocytes in large scale. In this Bio-MCCS, porcine gelatin microbeads were used as microcarriers, spinning bottle as fermented tank. Autologous melanocytes were able to attach to and proliferate on the gelatin microbeads in serum-free melanocyte medium in the Bio-MCCS, reaching up to 24-fold the cells seeded on day 15 (MTT assay). These autologous melanocytes cultured on gelatin microbeads could leave the microbeads and proliferate on the bottom of tissue culture flasks. Although Pluronic F68 has been widely used to protect animal cells from hydrodynamic stress in animal cell bioreactors, Pluronic F68 at a concentration of 0.25–1.0% showed no significant protective effects on the autologous melanocytes cultured on the microbeads and subjected to mechanical stress in the Bio-MCCS. This Bio-MCCS using porcine gelatin microbeads as microcarriers enabled large-scale production of autologous mela-nocytes, offering a potential treatment for large-area stable vitiligo by direct administration of the melanocytes cultured on the gelatin microbeads to the vitiliginous site.

A hyaluronan hydrogel scaffold-based xeno-free culture system for ex vivo expansion of human corneal epithelial stem cells

PurposeTo develop a hyaluronan hydrogel scaffold-based xeno-free culture system for ex vivo cultivation of human corneal epithelial stem cells (CESCs).Patients and MethodsCESCs were cultivated from donor limbal explants on the HyStem-C Hydrogel bio-scaffold in 12-well plates for 3 weeks. Group A used the traditional supplemented hormonal epidermal medium (SHEM) and group B used the defined SHEM (without fetal bovine serum and toxin A, adding 20% serum replacement). The growth and morphology of the cultured cells were assessed by phase contrast microscope. The expressions of specific cell markers were assessed by immunofluorescence staining and quantitative real-time PCR (qRT-PCR).ResultsSuccessful cultures of CESCs were obtained in both groups, resulting in multilayered stratified epithelia. Comparing to group A, the cells in group B was grown slightly slower and formed less cellular layers at the end of culture. The corneal specific cytokeratin (K) 12 and differentiation markers, involucrin, and connexin 43, were mainly expressed in the superficial cellular layers in both groups. Interestingly, certain basal cells were immune-positive to proposed stem cell markers such as K19, ABCG2, and integrin β1 in both groups. There was no significant difference between the two groups with regard to the gene expression levels of all these selected corneal markers (all P>0.05).ConclusionsThe hyaluronan hydrogel scaffold-based xeno-free culture system may support the expansion of regenerative CESCs without the risk of xeno component contamination. The regenerated epithelium maintains similar characteristics of native corneal epithelium.

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.

Tissue engineering in burn scar reconstruction

Nowadays, most patients with severe burns will survive their injury. This evolution is accompanied by the challenge to cover a large percentage of total body surface area burned. Consequently, more and more patients have to deal with the sequelae of burn scars and require (multiple) reconstructions. This review provides a gross overview of developments in the field of tissue engineering for permanent burn wound coverage and reconstructive burn surgery, focusing on usage and clinical effectiveness. Not only skin substitutes will be discussed but also the replacement of subcutaneous fat tissue and cartilage.

Occurrence and control of sporadic proliferation in growth arrested Swiss 3T3 feeder cells

Growth arrested Swiss mouse embryonic 3T3 cells are used as feeders to support the growth of epidermal keratinocytes and several other target cells. The 3T3 cells have been extensively subcultured owing to their popularity and wide distribution in the world and, as a consequence selective inclusion of variants is a strong possibility in them. Inadvertently selected variants expressing innate resistance to mitomycin C may continue to proliferate even after treatment with such growth arresting agents. The failure of growth arrest can lead to a serious risk of proliferative feeder contamination in target cell cultures. In this study, we passaged Swiss 3T3 cells (CCL-92, ATCC) by different seeding densities and incubation periods. We tested the resultant cultures for differences in anchorage-independent growth, resumption of proliferation after mitomycin C treatment and occurrence of proliferative feeder contaminants in an epidermal keratinocyte co-culture system. The study revealed subculture dependent differential responses. The cultures of a particular subculture procedure displayed unique cell size distribution and disintegrated completely in 6 weeks following mitomycin C treatment, but their repeated subculture resulted in feeder regrowth as late as 11 weeks after the growth arrest. In contrast, mitomycin C failed to inhibit cell proliferation in cultures of the other subculture schemes and also in a clone that was established from a transformation focus of super-confluent culture. The resultant proliferative feeder cells contaminated the keratinocyte cultures. The anchorage-independent growth appeared in late passages as compared with the expression of mitomycin C resistance in earlier passages. The feeder regrowth was prevented by identifying a safe subculture protocol that discouraged the inclusion of resistant variants. We advocate routine anchorage-independent growth assay and absolute confirmation of feeder disintegration to qualify feeder batches and caution on the use of fetal bovine serum.

Biological parameters determining the clinical outcome of autologous cultures of limbal stem cells

AIM

Limbal cultures restore the corneal epithelium in patients with ocular burns. We investigated the biological parameters instrumental for their clinical success.

METHODS

We report a long-term multicenter prospective study on 152 patients carrying corneal destruction due to severe ocular burns, treated with autologous limbal cells cultured on fibrin and clinical-grade 3T3-J2 feeder cells. Clinical results were statistically evaluated both by parametric and nonparametric methods.

RESULTS

Clinical outcomes were scored as full success, partial success and failure in 66.05, 19.14 and 14.81% of eyes, respectively. The total number of clonogenic cells, colony size, growth rate and presence of conjunctival cells could not predict clinical results. Instead, the clinical data provided conclusive evidence that graft quality and likelihood of a successful outcome rely on an accurate evaluation of the number of stem cells detected before transplantation as holoclones expressing high levels of the p63 transcription factor. No adverse effects related to the feeder layer have been observed and the regenerated epithelium was completely devoid of any 3T3-J2 contamination.

CONCLUSION

Cultures of limbal stem cells can be safely used to successfully treat massive destruction of the human cornea. We emphasize the importance of a discipline for defining the suitability and the quality of cultured epithelial grafts, which are relevant to the future clinical use of any cultured cell type.

Limbal epithelial cell therapy: past, present, and future

The cornea, the clear window at the front of the eye, transmits light to the retina to enable vision. The corneal surface is renewed by stem cells located at the peripheral limbal region. These cells can be destroyed by a number of factors, including chemical burns, infections, and autoimmune diseases, which result in limbal stem cell deficiency (LSCD), a condition that can lead to blindness. Established therapy for LSCD based on ex vivo expanded limbal epithelial cells is currently at a stage of refinement. Therapy for LSCD is also rapidly evolving to include alternative cell types and clinical approaches as treatment modalities. In the present perspectives chapter, strategies to treat LSCD are discussed and advances in this important field of regenerative medicine are highlighted.

Characterization of chitosan-gelatin scaffolds for dermal tissue engineering

Porous scaffolds for dermal tissue engineering were fabricated by freeze-drying a mixture of chitosan and gelatin (CG) solutions. Different crosslinking agents including glutaraldehyde, 1-(3-dimethylaminopropyl)-3-ethyl-carbodimide hydrochloride (EDC), and genipin were used to crosslink the scaffolds and improve their biostability. The porous structure and mechanical properties were determined for the scaffolds. The proliferation of human fibroblasts in the scaffolds was analyzed. It was found that EDC crosslinked scaffolds had the greatest amount of cells after four days. EDC crosslinked CG scaffolds had tensile modulus in a dry state and compressive modulus in a wet state similar to commercial collagen wound dressing. They also showed appropriate pore size, high water absorption, and good dimensional stability during cell culture. When human fibroblasts were seeded on acellular porcine dermis (APD), acellular human dermis (AHD), and CG scaffolds for 3D cell culture, they were well-distributed in the centre of the CG scaffolds but stayed only on the superficial layer of APD or AHD after seven days. A gelatin-based bioglue was applied to the CG scaffolds where the keratinocytes were seeded to mimic epidermal structure. After 14 days, the bioglue degraded and keratinocytes grew to form monolayers on the scaffolds. This study showed that CG scaffolds crosslinked by EDC and seeded with human fibroblasts could serve as dermal constructs, while the bioglue coating seeded with keratinocytes could serve as an epidermal construct. Such a combination could help regenerate skin with integrated dermal and epidermal layers and a have potential use in tissue-engineered skin.

Stem cells of the human cornea

INTRODUCTION

Blindness affects 50 million individuals worldwide; a significant proportion of them require a cell or tissue-based repair or replacement strategy to mend their damaged or diseased cornea. This review will focus on the epithelial stem cell (ESC) population of the cornea, where they reside, how they are identified and what alternative cells can be used as functional substitutes.

SOURCE OF DATA

Data for this review were collated after performing literature searches by inserting key words (cornea, limbal, stem cells (SCs), epithelium, stroma, and endothelium) into the search engine PubMed.

AREAS OF AGREEMENT

The prevailing notion is that corneal ESCs reside in an exclusive niche and their activation is dictated by niche-specific signals.

AREAS OF CONTROVERSY

Recent studies refute this hypothesis, as the central cornea of many animal species also possesses similar proliferative and clonogenic activity. The other area of controversy is in relation to the use of autologous and/or allogeneic cell therapies which are mostly contaminated with xenogeneic factors, potentially exposing the recipient to potentially harmful foreign infection.

GROWING POINTS

Due to the shortage of donor corneal biomaterial, alternative cellular sources are being sought, discovered and trialed.

AREAS TIMELY FOR DEVELOPING RESEARCH

With the exception of conjunctival and oral mucosal epithelium, no other cell type has been successfully used to treat patients with severe corneal epithelial defects. Embryonic and foetal SCs may have the greatest potential of all; however there are moral, legal, religious and scientific hurdles to overcome before they become routinely used in the clinic.

Adipocytes constitutively release factors that accelerate keratinocyte proliferation in vitro

Keratinocytes grown directly on adipose tissue have greater proliferation rates than keratinocytes grown alone. It is unknown if factors released by adipose tissue into culture media could increase keratinocyte proliferation without requiring incorporation of adipose tissue into skin graft models, or serve as a substitute for the fibroblast feeder layer.Human keratinocytes were grown with and without NIH 3T3 fibroblast feeder layer in the following conditions (12 cultures per group) adipose tissue coculture (AT), cultures supplemented with medium from whole adipose tissue referred to as adipose-conditioned medium (ACM), and control. Proliferation was measured with a colorimetric proliferation assay and digital calculations of percent confluence over time. Culture morphology was assessed by light microscopy.ACM cultures without 3T3s, AT cultures with and without 3T3s, and 3T3 control cultures demonstrated a similarly significant keratinocyte proliferation increase over non-3T3 control (P < 0.05) corresponding with a 2-fold increase in percent confluence by day 7. ACM cultures with 3T3s proliferated significantly faster than all other treatment groups (P < 0.05) resulting in complete confluence by day 5. ACM cultures with and without 3T3s produced a thick keratinized layer by day 7 whereas all other cultures including AT cultures did not.Engineered tissue replacement can be accelerated and simplified by ACM without requiring the addition of adipose tissue or a fibroblast feeder layer to keratinocyte culture systems. ACM supplementation provides an additive proliferation benefit when combined with a feeder layer producing mature grafts in approximately half the time as keratinocytes alone by accelerating proliferation and increasing keratinization.

Ex vivo cultivation of corneal limbal epithelial cells in a thermoreversible polymer (Mebiol Gel) and their transplantation in rabbits: an animal model

We evaluated the efficacy of autologous expanded corneal epithelial cell transplants derived from harvested limbal biopsy cultured on a thermoreversible polymer (Mebiol Gel) for the management of unilateral limbal stem cell deficiency (LSCD). Corneal limbal biopsies from 12 rabbits were cultured on a thermoreversible polymer Mebiol Gel at 37 degrees C. Cells were harvested from the dishes after 3 weeks by reducing temperature to 4 degrees C. Autologous transplantation was undertaken to reconstruct the experimentally induced limbal stem cell deficiency in the rabbit eyes. The corneas of both eyes of all rabbits were harvested later for molecular studies. Reparative surgery was a total success in seven rabbits, partial success in two, and failure in three eyes. Histology of the seven successful eyes showed the successful growth of the corneal epithelium. Immunohistochemistry and reverse transcriptase polymerase chain reaction showed the cornea phenotype and stem cell-associated markers in the limbus of the seven successful eyes, indicating the homing of these cells into limbus. In the three failure cases and in the two control rabbit eyes, used in the study, histology showed presence of goblet cells and vascularization in the stroma with abortive formation of corneal epithelium. Our results suggest that transplantation of autologous limbal epithelial cells grown in thermoreversible polymer Mebiol Gel may restore a nearly normal ocular epithelial surface in eyes with unilateral LSCD.

Transgene-specific host responses in cutaneous gene therapy: the role of cells expressing the transgene

A major issue in long-term gene therapy is host immune responses to therapeutic cells when transgene encodes a potential antigen. The nature of these responses depends on several factors including the type of cell and tissue expressing the transgene. Keratinocytes and fibroblasts, which are known to display distinct immunogenic profiles, are both potential targets for transgene expression in cutaneous gene therapy. However, whether there is an immunological advantage in targeting one cell type over the other is not known. To study the effect of cell type on transgene-specific host responses independent of antigen levels or methods of gene transfer and transplantation, we used a skin transplantation model in which transgene expression can be targeted transgene to either keratinocytes or fibroblasts. Although targeting an antigen to either cell type resulted in the induction of immune responses, these responses differed significantly. Transgenic keratinocytes were rejected acutely by a dominant Th2 response, while in the majority of grafted animals transgenic fibroblasts failed to induce acute rejection despite the induction of Th1 type inflammation in the graft. In a small number of mice, transgenic fibroblasts persisted for at least 20 weeks despite elicitation of antigen-specific responses. Therefore, fibroblasts may be an immunologically preferred target over keratinocytes for cutaneous gene therapy.

Human platelet lysate enhances the proliferative activity of cultured human fibroblast-like cells from different tissues

Several studies have shown the presence of fibroblast-like cells in the stromal fraction of different tissues with a high proliferative and differentiation potential. Platelet alpha granules contain growth factors released into the environment during activation. The effects of different supplements for culture medium (human serum, bovine serum and platelet lysate) on cultured human fibroblast-like cells from bone marrow, adipose tissue, trabecular bone and dental pulp have been compared. Expression of typical stromal and hematopoietic markers was analyzed and proliferative rates were determined. Flow cytofluorometry showed a homogenous pattern in serial-passaged cells, with a high level of stromal cell-associated markers (CD13, CD90, CD105). The presence of platelet lysate in culture media increased the number of cell generations obtained regardless of cell source. This effect was serum-dependent. Cell-based therapies can benefit by the use of products from human origin for "ex vivo" expansion of multipotent cells.

Preparation of Cultured Skin for Transplantation Using Insulin-like Growth Factor I in Conjunction with Insulin-like Growth Factor Binding Protein 5, Epidermal Growth Factor, and Vitronectin

BACKGROUND

Cultured skin for transplantation is routinely prepared by growing patient keratinocytes in the presence of semidefined sources of growth factors including serum and feeder cells, but these materials require substantial risk remediation and can contribute to transplant rejection.

METHODS

We have therefore investigated the potential of a novel combination of recombinant and purified growth factors to replace serum and feeder cells in cultures of human keratinocytes suitable for clinical application. Our technique was investigated with respect to culture establishment, serial propagation, colony-forming efficiency, immunocytochemistry, epidermal reconstruction, and suitability to support transplantation by aerosolization.

RESULTS

We demonstrate that insulin-like growth factor (IGF)-I--used in conjunction with epidermal growth factor (EGF), insulin-like growth factor binding protein (IGFBP)-5 and vitronectin--supports growth in the absence of serum. Moreover, a threefold greater number of cells are generated within 7 days compared to those grown under current best practice conditions using serum (P<0.05). The resulting test cultures are suitable for epidermal reconstruction and support the option for delivery in the form of an aerosolized cell suspension. Serial propagation, with the view to producing confluent sheets for extensive injuries, was achieved but with less consistency and this result correlated with a significant decline in colony-forming efficiency compared to controls.

CONCLUSIONS

IGF-I used in conjunction with IGFBP-5, EGF, and vitronectin provides a superior alternative to serum for the rapid expansion and transplantation of cultured keratinocytes within the first week of treatment. Nevertheless, further optimization is required with respect to elimination of feeder cells and serial expansion of cultures for treatment of extensive injuries.

Local expression of indoleamine 2,3-dioxygenase protects engraftment of xenogeneic skin substitute

The expression of indoleamine 2,3-dioxygenase (IDO), which metabolizes tryptophan, an essential amino acid, into kynurenine, has been identified as having a key role in the prevention of the immune rejection of the semi-allogeneic fetus during pregnancy. We have previously demonstrated that IDO expressed in fibroblasts causes bystander CD4(+) T cell damage as well as THP-1 cell damage by apoptosis. As T cells are primarily responsible for graft rejection, here, we asked the question of whether engraftment of IDO-expressing xenogeneic fibroblasts populated in a collagen matrix can be immuno-protected in an animal model. The results show a significant reduction in the number of infiltrated CD3(+) T lymphocytes on days 14 and 28 post-transplantation in the wounds receiving IDO-expressing fibroblasts relative to controls. IDO-expressing human fibroblasts embedded in bovine collagen on wounds in a rat model accelerates wound healing by promoting neovascularization during the early stages and providing protection of the xenograft fibroblasts. Using a co-culture system, we further confirm that IDO can induce angiogenesis through the depletion of tryptophan. These findings suggest that IDO may have an application in promoting the engraftment of skin substitutes and other transplanted organs.

Allogeneic fibroblasts in dermal substitutes induce inflammation and scar formation

In the present study, we compared the use of autologous versus allogeneic fibroblasts in dermal skin substitutes in a porcine wound model. The allogeneic fibroblast populations were isolated from female and a male pig (allo-1, - 2 and - 3) and the controls, autologous fibroblasts, from female graft-recipient pigs (control). The histocompatibility of the three donor pigs with the recipient pigs was determined with a mixed lymphocyte reaction. In two pigs, full-thickness wounds were treated with the fibroblast-seeded dermal substitutes (n = 5 per animal) and immediately overgrafted with meshed split-skin autografts. After 6 weeks, wound contraction was measured by planimetry and scar formation was scored. At 2, 4, and 6 weeks biopsies were taken and evaluated for the presence of inflammatory reactions, myofibroblasts, and scar formation. The mixed lymphocyte reaction of both recipient pigs showed the highest responses on peripheral blood mononuclear cells of the allo-3 donor pig, and was low or negative for allo-1 and allo-2. In all "allogeneic" wounds, more inflammatory cells were observed over time along with inflammatory foci consisting of a mix of lymphocytes and granulomatous cells. After 4 weeks, myofibroblasts were absent in the control wounds, whereas in "allogeneic" wounds, myofibroblasts colocalized with inflammation foci. The final scar tissue of the "allogeneic" wounds showed granulating areas with thin, immature collagen bundles. In contrast, the control wounds showed a dermal tissue with mature collagen bundles organized randomly like in normal skin. The wounds treated with allo-3 fibroblasts showed in both pigs a significant increase in scar formation and wound contraction when compared with control wounds. In conclusion, for optimal restoration of dermal skin function with minimal scar formation, skin substitutes containing autologous fibroblasts are preferred over skin substitutes with allogeneic fibroblasts.

Autologous keratinocyte suspensions accelerate epidermal wound healing in pigs

BACKGROUND

Tissue culture techniques enable in vitro expansion of keratinocytes that can be used to treat burns and chronic wounds. These keratinocytes are commonly grafted onto the wounds as differentiated sheets of mature epithelium. Less is however known about the effects of transplanting the cells as suspensions. This study evaluated epidermal regeneration in fluid-treated skin wounds treated with suspensions of cultured and noncultured autologous keratinocytes.

MATERIALS AND METHODS

Eighty-seven full-thickness excisional skin wounds were created on the back of 6 pigs and then transplanted with either cultured or noncultured autologous keratinocytes. The wounds were enclosed with liquid-tight chambers containing saline to provide a hydrated and standardized environment.

RESULTS

Keratinocyte transplantation resulted in several cell colonies within the granulation tissue of the wound. These colonies progressively coalesced and contributed to a new epithelium. The origin of the transplanted keratinocytes was confirmed by histochemical staining of wounds transplanted with transfected keratinocytes expressing beta-galactosidase. Transplantation of 0.125 x 10(6), 0.5 x 10(6), and 2.0 x 10(6) cultured keratinocytes, and 0.5 x 10(6) and 5.0 x 10(6) noncultured keratinocytes, increased reepithelialization dose dependently over saline-treated controls. The epithelial barrier function recovered faster in transplanted wounds as demonstrated by less protein leakage over the wound surface on Days 7-10 as compared to control wounds. Wound reepithelialization and the number of keratinocyte colonies observed in granulation tissue were significantly less in wounds transplanted with noncultured keratinocytes compared to wounds seeded with cultured keratinocytes.

CONCLUSION

Our study demonstrates successful transplantation of keratinocyte suspensions and their dose-dependent acceleration of wound repair. Selection of proliferative cells during culture and higher colony-forming efficiency may explain the greater effects observed with cultured keratinocytes.

Expansion and long-term culture of differentiated normal rat urothelial cells in vitro

The objective of this study is to establish a reliable cell culture system for the long-term culture of rat urothelial cells (RUC), in which the cells multiply in vitro and form stratified polarized urothelium. Urothelial cells were harvested by the enzymatic digestion of the urothelium exposed by the eversion of resected rat bladders. Primary cultures were initiated in keratinocyte serum-free medium (KSFM) for selective proliferation of urothelial cells. Subsequently, the cells were propagated in a mixture of conditioned medium (CM) derived from Swiss 3T3 cell culture supernatant and KSFM (CM-KSFM). Mean population doubling time was 13.8 +/- 0.9 h. RUC were successfully maintained for 18 passages over a period of 4-5 mo. Detailed investigations of culture conditions showed that CM-KSFM yielded a differentiated multilayer structure. The stratified urothelial sheets measuring 4 x 6 cm2 could be formed and then detached using dispase. Cytokeratin pattern in both the cultured urothelial monolayer and engineered stratified layers was similar to those seen in vivo, as assessed with monoclonal antibody against cytokeratin 17. Ultrastructural morphology showed microvilli, basal cell layer, and desmosomes between adjacent cells in the stratified urothelium.

Development and evaluation of a new composite Laserskin graft

BACKGROUND

Tremendous effort has been made to improve the graft take rate of cultured epidermal autograph. The purpose of this study is to develop and evaluate a new composite Laserskin graft (CLSG) as a human skin substitute for wound resurfacing.

METHODS

The seeding efficacy of cultured keratinocytes on plain Laserskin was compared with the 3T3 cell-seeded Laserskin and allogenic fibroblast-populated Laserskin. Three different types of CLSG, 2 cm in diameter each, were prepared and tested in rats. Type A CLSG consisted of proliferative allogenic rat fibroblasts on both sides of the Laserskin with autologous keratinocytes also on the upper side. Fibroblasts and keratinocytes were seeded only on the upper side of the Laserskin in type B CLSG. Keratinocytes alone were seeded on plain Laserskin in type C CLSG. Type B CLSG consisting of autologous keratinocytes and autologous dermal fibroblasts was tested on five selected wounds (5x5 cm each) of a patient with full-thickness burn. In another burn patient, type B CLSG consisting of autologous keratinocytes and allogenic dermal fibroblasts was grafted onto three wounds (5x5 cm each).

RESULTS

The seeding efficacy of human keratinocytes on plain Laserskin increased from 75% to 95% when proliferative allogenic fibroblasts were grown as a feeder layer on the Laserskin. The seeding efficacy of rat keratinocytes increased from 36% to 88% in the presence of a proliferative allogenic fibroblast feeder layer, whereas human/rat keratinocytes had respective seeding efficacy of 98%/91% on Laserskin preseeded with mitomycin C-treated 3T3 cells. Skin biopsies of grafted type A CLSG on day 14 after grafting showed complete epithelialization without severe inflammation in 16 of 20 (80%) grafted surgical wounds in rats. There were eight (40%) and seven (35%) "takes" of the CLSG in types B and C, respectively. The infection rate in type B CLSG was two (10%). There was one (5%) infection in types A and C. The respective take rates on the two patients grafted with type B CLSG were 60% and 100%.

CONCLUSION

The animal experiment and the preliminary clinical data showed that the CSLGs consisting of autologous keratinocytes and of autologous/allogenic fibroblasts are good human skin substitutes in terms of durability, biocompatibility, high seeding efficacy for keratinocytes, high graft take rate, and low infection rate.

Living skin substitutes: survival and function of fibroblasts seeded in a dermal substitute in experimental wounds

The healing of full-thickness skin defects requires extensive synthesis and remodeling of dermal and epidermal components. Fibroblasts play an important role in this process and are being incorporated in the latest generation of artificial dermal substitutes. We studied the fate of fibroblasts seeded in our artificial elastin/collagen dermal substitute and the influence of the seeded fibroblasts on cell migration and dermal substitute degradation after transplantation to experimental full-thickness wounds in pigs. Wounds were treated with either dermal substitutes seeded with autologous fibroblasts or acellular substitutes. Seeded fibroblasts, labeled with a PKH-26 fluorescent cell marker, were detected in the wounds with fluorescence microscopy and quantitated with flow cytofluorometric analysis of single-cell suspensions of wound tissue. The cellular infiltrate was characterized for the presence of mesenchymal cells (vimentin), monocytes/macrophages, and vascular cells. Dermal substitute degradation was quantitated by image analysis of wound sections stained with Herovici's staining. In the wounds treated with the seeded dermal substitute, fluorescent PKH-26-labeled cells were detectable up to 6 d and were positive for vimentin but not for the macrophage antibody. After 5 d, flow cytofluorometry showed the presence of 3.1 (+/-0.9) x 10(6) (mean +/- SD, n = 7) PKH-26-positive cells in these wounds, whereas initially only 1 x 10(6) fluorescent fibroblasts had been seeded. In total, the percentage of mesenchymal cells minus the macrophages was similar after 5 d between wounds treated with the seeded and the acellular substitutes. In the wounds treated with the seeded substitute, however, 19.5% of the mesenchymal cells were of seeded origin. Furthermore, the rate of substitute degradation in the seeded wounds was significantly lower at 2-4 wk after wounding than in wounds treated with the acellular substitute. Vascular in-growth and the number of infiltrated macrophages were not different. In conclusion, cultured dermal fibroblasts seeded in an artificial dermal substitute and transplanted onto full-thickness wounds in pigs survived and proliferated. The observed effects of seeded fibroblasts on dermal regeneration appeared to be mediated by reducing subcutaneous fibroblastic cell migration and/or proliferation into the wounds without impairing migration of monocytes/macrophages and endothelial cells. Moreover, the degradation of the implanted dermal substitute was retarded, indicating a protective activity of the seeded fibroblasts.

Large surface of cultured human epithelium obtained on a dermal matrix based on live fibroblast-containing fibrin 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 gel from plasma cryoprecipitate containing live human fibroblast (from human foreskin). Keratinocytes obtained from primary culture according to the Rheinwald and Green method, were seeded on the gel at different seeding ratios. In all cases, the keratinocytes plated on the dermal equivalent grew to confluence and stratified epithelium was obtained within 10-15 days in culture. Early expression of basal membrane proteins was detected by immunostaining with laminin and type IV collagen antibodies. Cell proliferation was detected both in the epidermal layer and in the fibroblast embedded in the gel as assessed by BrdU incorporation. Detachment of composite cultures from dishes or flasks is a simple and quick procedure without the need for dispase treatment. Grafting of composite cultures to nude mice gave rise to an orderly stratified, orthokeratinized epithelium resembling human epidermis. A number of advantages including a large expansion factor without the need of 3T3 feeder layer, the availability of fibrin/plasma cryoprecipitate from blood banks and the versatile manipulation of composite cultures suggest that this system could be suitable for the definitive coverage of severely burned patients.

Autologous transplantation of urothelium into demucosalized gastrointestinal segments: evidence for epithelialization and differentiation of in vitro expanded and transplanted urothelial cells

PURPOSE

Our study established a technique for in vitro expansion and subsequent transplantation of autologous urothelial cells into vascularized seromuscular segments from stomach and colon in sheep. The proof of proliferation and differentiation of the transplanted urothelium in the absence of resident urothelium is considered to be a prerequisite for use of this technique in bladder augmentation.

MATERIALS AND METHODS

Autologous sheep urothelial cells were expanded in vitro and grown on collagen membranes for sheet grafting. Using a vital stain, viability and confluency status of the urothelial graft were determined before transplantation into demucosalized segments isolated from the sheep stomach and colon gastrointestinal pouches. The gastrointestinal segments were sewn up and remained in the abdomen as small pouches stiched to the abdominal wall. Take and differentiation of transplanted cells within the pouch were assessed two and three weeks later using histological and immunohistological means.

RESULTS

Urothelial cells grew well on collagen membranes. A confluency status > 40% and co-culturing with 3T3 feeder cells favored successful transplantation. Two weeks after transplantation a multilayered urothelial-like epithelium was found to line the lumen of the pouch. The epithelium was characterized by a distinct urothelium-typical distribution of basal and luminal keratins and the expression of the umbrella cell-specific marker uroplakin III. Moreover, the epithelium had an underlying basal lamina which focally contained collagen type IV.

CONCLUSIONS

The data indicate that in vitro expanded urothelial cells are capable of epithelializing demucosalized gastrointestinal segments forming a genuine, differentiated "neo" urothelium.