Treatment of postoperative otorrhoea by grafting of mastoid cavities with cultured autologous epidermal cells

Clinical Indications of Cultured Epithelial Autografts

ABSTRACT

Cultured epithelial autografts (CEAs) have been used for decades as a treatment for massive burn injuries. Cultured epithelial autografts allow for wounds to heal by taking a small sample and growing a patient's own epithelium in culture to create large, graftable sheets. This technique is especially useful in large wounds where donor sites are limited compared with conventional skin grafting. However, CEAs have a variety of uses in wound healing and reconstruction and have the potential to aid in the closure of several types of defects. Cultured epithelial autografts have shown applicability in large burns, chronic nonhealing wounds, ulcerating wounds of various etiologies, congenital defects, wounds requiring specialized epithelium to replace like by like, and wounds in critically ill patients. Several factors must be considered when using CEAs, such as time, cost, and outcomes. In this article, we detail the various clinical applications of CEAs and how they can be situationally advantageous outside of their original purpose.

Epithelial defect repair in the auricle and auditory meatus by grafting with cultured adipose-derived mesenchymal stem cell aggregate-extracellular matrix

Background:

Several patients experience persistent otorrhea after a flawless surgical procedure because of insufficient epithelial healing. Several efforts, such as autologous tissue allograft and xenograft, have been made to halt otorrhea. However, a stable technology to induce temporal epithelial repair is yet to be established. Therefore, this study aims to investigate whether implantation of seeding adipose-derived mesenchymal stem cell (ADMSC) aggregates on extracellular matrix (ECM; herein, ADMSC aggregate-ECM) into damaged skin wound promotes skin regeneration.

Methods:

ADMSC aggregate-ECM was prepared using a previously described procedure that isolated ADMSCs from rabbits and applied to the auricle and auditory meatus wound beds of New Zealand white rabbits. Wound healing was assessed by general observation and hematoxylin and eosin (H&E) staining. Secretion of growth factor of the tissue was evaluated by western blotting. Two other groups, namely, ECM and control, were used. Comparisons of three groups were conducted by one-way analysis of variance analysis.

Results:

ADMSCs adhered tightly to the ECM and quickly formed cell sheets. At 2 weeks, general observation and H&E staining indicated that the wound healing rates in the ADMSC aggregate-ECM (69.02 ± 6.36%) and ECM (59.32 ± 4.10%) groups were higher than that in the control group (43.74 ± 12.15%; P = 0.005, P < 0.001, respectively) in ear auricle excisional wounds. At 7 weeks, The scar elevation index was evidently reduced in the ADMSC aggregate-ECM (2.08 ± 0.87) and ECM (2.31 ± 0.33) groups compared with the control group (4.06 ± 0.45; P < 0.001, P < 0.001, respectively). In addition, the scar elevation index of the ADMSC aggregate-ECM group reached the lowest rate 4 weeks in advance. In auditory meatus excisional wounds, the ADMSC aggregate-ECM group had the largest range of normal skin-like structure at 4 weeks. The ADMSC aggregate–ECM and ECM groups secreted increased amounts of growth factors that contributed to skin regeneration at weeks 1 and 2, respectively.

Conclusions:

ADMSC aggregate-ECM and ECM are effective repair materials for wound healing, especially ADMSC aggregate-ECM. This approach will provide a meaningful experimental basis for mastoid epithelium repair in subsequent clinical trials.

Clinical application of cultured epithelial autografts on acellular dermal matrices in the treatment of extended burn injuries

Achieving permanent replacement of skin in extensive full-thickness and deep partial-thickness burn injuries and chronic wounds remains one of the fundamental surgical problems. Presently, split-thickness skin grafts are still considered the best material for surgical repair of an excised burn wound. However, in burns that affect greater than 50% of total body surface area, the patient has insufficient areas of unaffected skin from which split-thickness skin grafts can be harvested. The use of cultured epithelial (or epidermal) autografts (CEAs) has achieved satisfactory results. But the take rate of CEAs is poor in full-thickness bed or in chronically infected area. Providing temporary cover with allograft skin, or a more permanent allodermis, may increase clinical take. This review aims to (1) describe the use of CEAs in the regeneration of the epidermis, (2) introduce the application of the acellular dermal matrices (ADMs) in the clinics, and (3) enhance understanding of the CEAs applied with ADM as an appropriate strategy to treat the extended burn injuries. The current evidence regarding the cultured epithelial cell or keratinocyte autograft and dermal grafts applied in the treatment of burn injuries was investigated with an extensive electronic and manual search (MEDLINE and EMBASE). The included literature (N=136 publications) was critically evaluated focusing on the efficacy and safety of this technique in improving the healing of the deep dermal and full-thickness burn injuries. This review concluded that the use of ADM with CEAs is becoming increasingly routine, particularly as a life-saving tool after acute thermal trauma.

Keratinocytes in the treatment of severe burn injury: an update

Burns are among the most life-threatening physical injuries, in which fast wound closure is crucial. The surgical burn care has evolved considerably throughout the past decennia resulting in a shift of therapeutic goals. Therapies aiming to provide coverage of the burn have been replaced by treatments that have both functional as aesthetic outcomes. The standard in treating severe burns is still early excision followed by skin grafting. The use of cultured keratinocytes to cover extensive burn wounds appeared very promising at first, but the technique still has several limitations of which the long time to culture, the major costs, the risk of infection and the need for an adequate dermal layer limit clinical application. The introduction of dermal substitutes, composite grafts, tissue engineering based on stem cell application have been advocated. The aim of this review is to assess the use of cultured keratinocytes in terms of technical aspects, clinical application, limitations and future perspectives. Cultured keratinocytes are expected to keep playing a role in wound healing, especially in the field of chronic wounds. In severe burns, despite its limitations, keratinocytes can be beneficial if implemented as one of the elements in a broader wound management.

Tissue-engineered skin. Current status in wound healing

Tissue-engineered skin is a significant advance in the field of wound healing and was developed due to limitations associated with the use of autografts. These limitations include the creation of a donor site which is at risk of developing pain, scarring, infection and/or slow healing. A number of products are commercially available and many others are in development. Cultured epidermal autografts can provide permanent coverage of large area from a skin biopsy. However, 3 weeks are needed for graft cultivation. Cultured epidermal allografts are available immediately and no biopsy is necessary. They can be cryopreserved and banked, but are not currently commercially available. A nonliving allogeneic acellular dermal matrix with intact basement membrane complex (Alloderm) is immunologically inert. It prepares the wound bed for grafting allowing improved cultured allograft 'take' and provides an intact basement membrane. A nonliving extracellular matrix of collagen and chondroitin-6-sulfate with silicone backing (Integra) serves to generate neodermis. A collagen and glycosaminoglycan dermal matrix inoculated with autologous fibroblasts and keratinocytes has been investigated but is not commercially available. It requires 3 to 4 weeks for cultivation. Dermagraft consists of living allogeneic dermal fibroblasts grown on degradable scaffold. It has good resistance to tearing. An extracellular matrix generated by allogeneic human dermal fibroblasts (TransCyte) serves as a matrix for neodermis generation. Apligraf is a living allogeneic bilayered construct containing keratinocytes, fibroblasts and bovine type I collagen. It can be used on an outpatient basis and avoids the need for a donor site wound. Another living skin equivalent, composite cultured skin (OrCel), consists of allogeneic fibroblasts and keratinocytes seeded on opposite sides of bilayered matrix of bovine collagen. There are limited clinical data available for this product, but large clinical trials are ongoing. Limited data are also available for 2 types of dressing material derived from pigs: porcine small intestinal submucosa acellular collagen matrix (Oasis) and an acellular xenogeneic collagen matrix (E-Z-Derm). Both products have a long shelf life. Other novel skin substitutes are being investigated. The potential risks and benefits of using tissue-engineered skin need to be further evaluated in clinical trials but it is obvious that they offer a new option for the treatment of wounds.

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.

The development of bioengineered skin

Driven by the need for donor tissue for patients suffering from extensive burns, alternatives to autologous and cadaver-derived tissue have been under development for the past 20 years. Unilayered and bilayered models representing the skin's epidermal and/or dermal components have been developed using both cells and matrix materials. In addition to their use in patients with extensive burns, trials using these products on refractory and challenging patients with both acute and chronic wounds have led to the commercial availability of some of these products.

Split-thickness skin grafting for lower extremity ulcerations

BACKGROUND

Leg ulcers are often refractory to conservative treatment, often mandating the use of skin grafting.

OBJECTIVES

This review article discusses skin grafts, with special emphasis on split-thickness grafts for lower extremity ulcerations.

METHODS

Historical background, proposed mechanisms of action, biology of skin grafts, techniques for skin grafting, and results after grafting are discussed separately.

RESULTS

Skin grafting has been performed for centuries. However, how skin grafts work, whether solely as tissue replacement or, additionally, as a stimulus for healing, is still not fully known. After placement, the grafted skin proceeds through a series of phases by which nutrients are supplied and neovascularization occurs. Adherence to the ulcer bed through interactions between the graft and the ulcer bed appear critical. When meshed split-thickness skin grafts are properly performed, success rates from 50% to 75% have been reported for refractory venous ulcers.

CONCLUSIONS

Better understanding of the biologic and clinical aspects of skin grafting should lead to improved patient care.

LEARNING OBJECTIVES

After studying this article, participant should be able: 1. To understand the various types of skin grafts. 2. To learn the potential mechanisms of action of how skin grafts work. 3. To appreciate the benefit of skin grafts for lower extremity ulcerations.

Living epithelial-mesenchymal compounds formed in vitro suitable for autografting

Three different, human epithelial-mesenchymal compounds (EMC) were generated in vitro for prospective grafting in epithelial defects. All compounds consisted of a fibroblast-populated collagen lattice as a mesenchymal component seeded with different types of cultured epithelial cells isolated from biopsies of healthy skin, oral mucosa and respiratory mucosa. Maturation of the epithelial cells was enabled by the presence of a high calcium concentration (1.8 mM) when cultures were lifted to the air-liquid interface. Light and electron microscopy revealed moderate differentiation of the multilayered epithelium in all compounds as well as basement membrane development at the epithelial-mesenchymal junction after 2-3 weeks. A coherent, tissue-like consistency of the collagen lattice and the presence of a basement membrane preventing detachment of the epithelium permitted easy handling and even loose suturing of the compounds produced.

Long-term results of the use of cultured autologous epithelial cell grafting to mastoid cavities

Thirty-nine patients (42 ears) who have had a cultured autologous epithelial cell graft technique to a continuously discharging mastoid cavity have been evaluated to determine the continued effectiveness of this procedure. A postal questionnaire indicated a 58% improvement in both the smell and quantity of discharge, and our conclusion is that this is a very effective measure to provide extended symptomatic improvement in this troublesome condition.

Use of cultured mucosal grafts to cover defects caused by vestibuloplasty: an in vivo study

PURPOSE

In oral and maxillofacial surgery palatal mucosal grafts are routinely used to cover mucosal defects caused by vestibuloplasty. However, the quantity of palatal mucosa is a limiting factor in more extensive operations. This study investigated whether autologous cultured sheets of mucosa can serve as a dressing for these wounds.

MATERIALS AND METHODS

Punch biopsies (diameter, 4 mm) were taken from the hard palate of eight patients (five men, three women; mean age 43 years). Epithelial cells were enzymatically dissociated from these tissue specimens and grown in vitro in the presence of a fibroblast feeder layer. Within 3 weeks, a transplantable epithelial sheet of about 20 cm2 was obtained. The sheet was detached from the culture flask by enzyme treatment and fixed to a carrier of Vaseline (Cheeseborough Ponds Inc, Greenwich, CT) gauze. Using a split-mouth technique, the sheet was placed on half of a mucosal defect created by vestibuloplasty, while the other half of the defect was covered by a conventional split-thickness palatal graft. Both the cultured and conventional graft were held in place by the patient's relined denture fixed with perimandibular sutures. One week postsurgery, the denture and Vaseline gauze were removed. Three months after vestibuloplasty, biopsy specimens of each grafted site were taken and processed for light and transmission electron microscopy (LM, TEM).

RESULTS

Three months postsurgery, the grafted mucosa of both sites bore close resemblance to palatal mucosa. Both the cultured and split-thickness grafts were vascularized, did not evoke a homograft reaction, and showed a smooth graft/lip mucosal junction and minimal wound contraction. LM and TEM revealed that both types of grafts formed a fully differentiated keratinizing mucosa with a well-developed basement membrane and rete ridges, comparable with the histology and ultrastructure of palatal mucosa in situ.

CONCLUSION

It was concluded from this study that cultured mucosa can serve as a proper dressing for mucosal defects after vestibuloplasty.

Transplantation of keratinocytes in the treatment of wounds

BACKGROUND

Keratinocyte grafting can be used to treat acute traumatic and chronic non-healing wounds. The keratinocyte sheets are fragile and clinical "take" is difficult to assess, especially as activated keratinocytes secrete many growth factors, which have effects on wound healing apart from take. We have developed animal models of grafting that allow us to examine factors influencing autologous keratinocyte graft take. Results show clearly that pretreatment of the wound bed with viable dermis greatly increases the take of keratinocyte grafts.

DATA SOURCES

International literature.

CONCLUSIONS

As a greater understanding of the complex interactions of cell and matrix evolve, so will potential therapeutic maneuvers, not just in the field of cultured keratinocyte grafts, but clearly in that of benign tumors, for example, keloids, and that of oncology. There is now overwhelming evidence of the requirement for a dermal substitute for cultured keratinocyte autografts, and the sheet complexity of the situation demands that this should approximate live human dermis as closely as possible. The stumbling blocks relate to avoiding the risks of viral transmission, tissue matching of host and donor, providing early epithelial cover, and improving delivery systems for fragile keratinocyte grafts.

Culturing skin in vitro for wound therapy

Current tissue-culture techniques enable keratinocytes from a small piece of skin to be grown into sheets of epithelium, or cultured keratinocyte grafts, that are suitable for treating wounds. Serial subculture enables rapid expansion of a cell population, such that grafts of a total area equivalent to that of the surface of an adult can be obtained from an initial skin biopsy of approximately 2 cm2 in under one month. In this article, the methods currently used for culturing keratinocytes, the search for a fully functional replacement for the dermal elements of skin, and the prospects for clinical development of these technologies in the near future are discussed.

Treatment of skin defects using suspensions of in vitro cultured keratinocytes

The in vitro cultivation of keratinocytes and their application in the form of confluent sheets to cover various kinds of skin defects involves a number of problematical steps which could be improved by using single cell suspensions instead. Therefore we developed a method to apply keratinocytes suspended as single cells in a fibrin gel. By testing the feasibility of this method in different experimental animal models we found that it facilitates cultivation as well as application of the cells, moreover, this method allows a much more flexible use of the cells, i.e. it is easier to consider the clinical condition of the patient than by the conventional method.

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

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

Biologic skin substitutes

BACKGROUND

The ideal skin substitute should closely approximate the skin in function. The substitute should be readily available, easily sterilized and stored, and relatively inexpensive.

OBJECTIVE

To describe recent developments in the area of biologic skin substitutes.

RESULTS

Considerable advances have been made in keratinocyte and fibroblast culturing when used in conjunction with a biodegradable material as a substrate.

CONCLUSION

There is no skin substitute that perfectly mimics autologous skin. However, recent developments show promise.

Temporal bone histopathology of open mastoidectomy cavities

Open cavity mastoidectomy remains the principle surgical treatment of middle ear cholesteatoma in the United Kingdom. A significant proportion of mastoid cavities are prone to intermittent or continuous discharge. In this study the temporal bone histopathology of four patients who had undergone open cavity mastoidectomy is presented. Cavities were predominantly lined with stratified keratinizing squamous epithelium. Residual air cells were obliterated by fibrous tissue, with no evidence of persistent respiratory epithelium. Where inflammatory changes were found, these consisted of areas of granulation tissue in association with epithelial ulceration. Residual cholesteatoma pearls (epidermoids) were not associated with significant inflammatory changes.

A new technique using cultured epithelial sheets for the management of epistaxis associated with hereditary haemorrhagic telangiectasia

A new technique for the treatment of severe epistaxis associated with hereditary haemorrhagic telangiectasia is described. The nasal septum and inferior turbinates, surgically denuded of respiratory epithelium, were grafted using autografts of cultured epithelial sheets derived from buccal epithelium. All patients upon whom this technique has been used have shown considerable lessening in the frequency and severity of their epistaxes although two patients received grafts on two occasions, in each case approximately three months apart. It is postulated that a nasal lining of stratified squamous epithelium is likely to be more resistant to trauma than the normal respiratory type, and this is supported by the observation that bleeds very seldom occur from the oral cavity in this syndrome.

The histopathology of mastoidectomy cavities, with particular reference to persistent disease leading to chronic otorrhoea

Open cavity mastoidectomy remains the principal surgical treatment of middle ear cholesteatoma in the United Kingdom. A significant proportion of mastoid cavities are prone to intermittent or continuous discharge. In this study the histopathological features of material removed from 159 mastoid cavities at revision surgery were reviewed. Findings included squamous epithelium with acute and chronic inflammation, foreign body granuloma and aural polyps. Of particular note was the very infrequent finding of discharging cavities lined with respiratory epithelium, suggesting that retained mucosa in mastoid air cells is not a common cause of persistent otorrhoea.

In VitroReconstitution of Differentiated Human Epithelia

Human keratinocytes obtained from skin biopsies can be serially cultured in vitro. When plated on lethally irradiated 3T3 fibroblasts, keratinocyte colonies reconstitute a stratified squamous epithelium devoid of stratum corneum. The expression of a mature cornified epidermis, expressing all the morphological and biochemical markers of the in vivo epidermis, can be obtained by the “emerged dermal equivalent” culture system. Melanocytes grown under the same culture conditions, maintain a physiological melanocyte/keratinocyte ratio, are organised in the basal layer of the cultured epidermis, and maintain differentiated functions such as dendritic arborisation, melanin synthesis and melanosome transfer. This allows the reconstitution of an epidermis physiologically populated by functionally active melanocytes. Epithelial cells from different mucosal body sites, namely palate, urethra, conjunctiva, cornea and vagina, can also be cultured and maintain the characteristics of the original donor sites. The in vitro reconstituted human epithelia, permanently transplanted onto patients presenting large epidermal or mucosal defects, retain the characteristics of the original donor site, suggesting an intrinsic site-specific differentiation programme. These three-dimensional human epithelium models could prove useful in standard cytotoxicity assays and could be used as a tool to study the effects of a variety of compounds on normal human epithelia in vitro.

Epidermal allografts

The epidermis is the sheet of stratified epithelial cells covering the dermal connective tissues. In addition to the epithelial cells (known as keratinocytes) there exist within the epidermis two populations of migratory leukocytes: the class II-positive, dendritic Langerhans' cell, and gamma-delta receptor-positive T lymphocytes. Allografts consisting essentially of epidermis have been in use since the introduction of "pinch" grafts by L. Reverdin in 1872. However, the capacity to culture keratinocytes in vitro to produce sheets of stratified epithelial cells has opened new possibilities. Cultured keratinocyte layers are devoid of passenger leukocytes and were initially widely believed not to be susceptible to rejection. This, however, is clearly not the case, at least in rats and humans. Nevertheless, in spite of severe acute rejection, it is interesting that cultured keratinocyte allografts are very poor at evoking antibody responses in graft recipients. Where permanent survival of the keratinocyte is required, autografts must be used, since the administration of immunosuppression to protect allografts would not be justified. Clinical application of cultured keratinocyte allografts, without immunosuppression, is limited to their use as temporary dressings (e.g., in burns) or to stimulate the recipient's own skin cells to growth (e.g., on leg ulcers). Autografts have been used for patients with extensive burns and in the treatment of chronic mastoiditis.

Treatment of chronic mastoiditis by grafting of mastoid cavities with autologous epithelial layers generated by in vitro culture of buccal epithelium

Autologous cultured epithelial layers were established from biopsies from the mucosa of the cheek, a non-keratinizing region of the oral cavity. These were grafted to the unepithelialized mastoid cavities of nine patients with chronic mastoiditis and severe otorrhoea varying from two to 30 years' duration. All procedures were performed on an out-patient basis, with no anaesthesia except for topical anaesthesia for the mucosal biopsy. In seven of the patients the grafts took well, with complete resolution of the otorrhoea for a minimum follow-up period of eight months. In one patient there was a partial take of the graft with substantial improvement in the rate of discharge. The mastoid cavities of two patients were biopsied five months after grafting, and demonstrated a stratified squamous epithelium, with keratinization of the epithelium clearly evident.