Experimental study of tracheal allotransplantation with cryopreserved grafts

Current Strategies for Tracheal Replacement: A Review

Airway cancers have been increasing in recent years. Tracheal resection is commonly performed during surgery and is burdened from post-operative complications severely affecting quality of life. Tracheal resection is usually carried out in primary tracheal tumors or other neoplasms of the neck region. Regenerative medicine for tracheal replacement using bio-prosthesis is under current research. In recent years, attempts were made to replace and transplant human cadaver trachea. An effective vascular supply is fundamental for a successful tracheal transplantation. The use of biological scaffolds derived from decellularized tissues has the advantage of a three-dimensional structure based on the native extracellular matrix promoting the perfusion, vascularization, and differentiation of the seeded cell typologies. By appropriately modulating some experimental parameters, it is possible to change the characteristics of the surface. The obtained membranes could theoretically be affixed to a decellularized tissue, but, in practice, it needs to ensure adhesion to the biological substrate and/or glue adhesion with biocompatible glues. It is also known that many of the biocompatible glues can be toxic or poorly tolerated and induce inflammatory phenomena or rejection. In tissue and organ transplants, decellularized tissues must not produce adverse immunological reactions and lead to rejection phenomena; at the same time, the transplant tissue must retain the mechanical properties of the original tissue. This review describes the attempts so far developed and the current lines of research in the field of tracheal replacement.

Large animal models for long-segment tracheal reconstruction: a systematic review

BACKGROUND

The reconstruction of extensive tracheal defects is an unresolved problem. Despite decades of research, a reliable and practical substitute remains to be found. While there have been clinical reports of successful long-segment tracheal reconstruction, reproducibility and widespread applicability of these techniques have yet to be achieved. Large animals such as the dog, pig, sheep, and goat have comparable tracheal morphology and physiology to humans making them useful preclinical models to screen potential therapeutic strategies.

MATERIALS AND METHODS

The literature was reviewed to identify large animal models commonly used for tracheal reconstruction. A systematic search of PubMed and EMBASE was performed for large animal studies reporting on the reconstruction of long-segment tracheal and carinal defects. Fifty-seven studies were identified for analysis.

RESULTS

There is no standard large animal model available for tracheal research. In recent years, livestock species have gained favor over dogs as animal models in this field. The minimum requirements for successful tracheal replacement are rigidity, vascularity, and epithelial lining. Early attempts with synthetic prostheses were met with disappointing results. An autologous tracheal substitute is ideal but hindered by limited donor site availability and the lack of a dominant vascular pedicle for microsurgical reconstruction. Although tracheal allotransplantation enables like-for-like replacement, there are unresolved issues relating to graft vascularity, immunosuppression, and graft preservation. Tissue engineering holds great promise; however, the optimal combination of scaffold, cells, and culture conditions is still indeterminate.

CONCLUSIONS

Despite impressive advances in tracheal reconstruction, a durable substitute for extended tracheal defects continues to be elusive.

Successful immunosuppressant-free heterotopic transplantation of tracheal allografts in the pig

OBJECTIVES

It has been demonstrated that both heterotopic and orthotopic transplants of epithelium-denuded cryopreserved tracheal allografts are feasible in immunosuppressant-free rabbits. Validation of these results in large animals is required before considering clinical applications. We evaluated the viability, immune tolerance and strain properties of such tracheal allografts heterotopically transplanted in a pig model.

METHODS

Ten tracheal segments, 5 short (5 rings) and 5 long (10 rings), were obtained from male Landrace pigs. The tracheal segments were surgically denuded of their epithelium, then cryopreserved and stored in a tissue bank for 33 to 232 days. After thawing, tracheal segments stented with a silicone tube were wrapped in the omentum in 2 groups of 5 female recipients. The animals did not receive any immunosuppressive drugs. The animals were euthanized from Day 6 to Day 90 in both groups.

RESULTS

An effective revascularization of allografts regardless of length was observed. Lymphocyte infiltrate was shown in the early postoperative period and became non-significant after 30 days. Allografts displayed high levels of neoangiogenesis and viable cartilage rings with islets of calcification. Biomechanical measurements demonstrated strain properties similar to those of a fresh tracheal segment from Day 58.

CONCLUSIONS

Our results demonstrate the acceptability and satisfactory stiffness of epithelium-denuded cryopreserved tracheal allografts implanted in the omentum, despite the absence of immunosuppressive drugs. Since the omentum has the capability to reach the tracheal region, this approach should be investigated in the setting of orthotopic transplants in a pig model before considering clinical applications.

Current Solutions for Long-Segment Tracheal Reconstruction

This article is a continuation of previous reviews about the appropriate method for long-segment tracheal reconstruction. We attempted to cover the most recent, successful and promising results of the different solutions for reconstruction that are rather innovative and suitable for imminent clinical application. Latest efforts to minimize the limitations associated with each method have been covered as well. In summary, autologous and allogenic tissue reconstruction of the trachea have been successful methods for reconstruction experimentally and clinically. Autologous tissues were best utilized clinically to enhance revascularization, whether as a definitive airway or as an adjunct to allografts or tissue-engineered trachea (TET). Allogenic tissue transplantation is, currently, the most suitable for clinical application, especially after elimination of the need for immunosuppressive therapy with unlimited supply of tissues. Similar results have been reported in many studies that used TET. However, clinical application of this method was limited to use as a salvage treatment in a few studies with promising results. These results still need to be solidified by further clinical and long-term follow-up reports. Combining different methods of reconstruction was often required to establish a physiological rather than an anatomical trachea and have shown superior outcomes.

Vitrification transiently alters Oct-4, Bcl2 and P53 expression in mouse morulae but does not affect embryo development in vitro

This study was conducted to determine the impact of vitrification on the expression of genes regulating pluripotency and apoptosis in mouse morulae. The morulae were randomly allocated into three groups: (1) untreated (control), (2) exposed to vitrification solution without freezing (toxicity), or (3) vitrified by open-pulled straw method (vitrification). In vitro development was evaluated by morphology and assessed by the blastocyst rate and the blastocyst total cell number. Gene expression in morulae and blastocysts was assessed by quantitative Real Time-PCR (qRT-PCR) and western blot. The results showed that at morulae stage, the POU class 5 homeobox1 (Oct-4) and B-cell lymphoma2 (Bcl2) mRNA levels of vitrification group were significantly lower (P < 0.05) than those of control. Strikingly, the p53 mRNA level was significantly higher in vitrification group. However, the Oct-4, Bcl2 and p53 mRNA levels in mouse blastocysts were not statistically different. Furthermore, western blot results showed that there was no significant difference in Oct-4, Bcl2 and p53 expression at protein level in mouse morulae among three groups. Additionally, the blastocyst rate (96.67%-100.00%) and the average cell number of blastocysts (89.67-92.33) were similar between all groups. The data demonstrate that vitrification transiently changes the mRNA expression of several key genes in mouse morulae regulating early embryo development but does not affect embryo developmental potential in vitro.

Is Tracheal Transplantation Possible With Cryopreserved Tracheal Allograft and Hyperbaric Oxygen Therapy? An Experimental Study

BACKGROUND

Allografts have achieved prominence for tracheal reconstruction because of their natural physiologic and anatomic structure, which preserves respiratory tract flexibility and lumen patency. The immunomodulatory effects of cryopreservation prevent tracheal allograft rejection. In addition, hyperbaric oxygen therapy (HBOT) accelerates wound healing by promoting epithelization and neovascularization. This experimental study investigated the early and late effects of HBOT on cryopreserved tracheal allografts (CTAs).

METHODS

The study used 33 outbred Wistar rats weighing 300 to 350 g as allograft transplantation donors and recipients. Among these, 22 recipient rats were randomly assigned to the HBOT (n = 11) and control (n = 11) groups. Rats in the HBOT group were treated with 100% oxygen for 60 minutes at 2.5 atmospheres of absolute pressure for 7 days. Recipient rats in both groups were euthanized at 1 week (n = 5) and 4 weeks (n = 6) after transplantation, defined as the early and late periods, respectively.

RESULTS

In the early period, no significant histopathologic differences were observed between groups (p > 0.05). However, microscopic evaluation of the control group during the late period showed low epithelization of the CTA. In contrast, microscopic evaluation of the HBOT group during this same period revealed epithelium covering the transplanted CTA lumen. Significant epithelization and vascularization and significantly reduced inflammation and fibrosis were found in the HBOT group compared with the control group (p < 0.05).

CONCLUSIONS

HBOT may be effective in tracheal reconstruction by increasing epithelization and neovascularization after extended tracheal resection. HBOT, therefore, should be considered in CTA transplantation.

Advances in tracheal reconstruction

SUMMARY

A recent revival of global interest for reconstruction of long-segment tracheal defects, which represents one of the most interesting and complex problems in head and neck and thoracic reconstructive surgery, has been witnessed. The trachea functions as a conduit for air, and its subunits including the epithelial layer, hyaline cartilage, and segmental blood supply make it particularly challenging to reconstruct. A myriad of attempts at replacing the trachea have been described. These along with the anatomy, indications, and approaches including microsurgical tracheal reconstruction will be reviewed. Novel techniques such as tissue-engineering approaches will also be discussed. Multiple attempts at replacing the trachea with synthetic scaffolds have been met with failure. The main lesson learned from such failures is that the trachea must not be treated as a "simple tube." Understanding the anatomy, developmental biology, physiology, and diseases affecting the trachea are required for solving this problem.

Advances in tracheal reconstruction

Summary:

A recent revival of global interest for reconstruction of long-segment tracheal defects, which represents one of the most interesting and complex problems in head and neck and thoracic reconstructive surgery, has been witnessed. The trachea functions as a conduit for air, and its subunits including the epithelial layer, hyaline cartilage, and segmental blood supply make it particularly challenging to reconstruct. A myriad of attempts at replacing the trachea have been described. These along with the anatomy, indications, and approaches including microsurgical tracheal reconstruction will be reviewed. Novel techniques such as tissue-engineering approaches will also be discussed. Multiple attempts at replacing the trachea with synthetic scaffolds have been met with failure. The main lesson learned from such failures is that the trachea must not be treated as a “simple tube.” Understanding the anatomy, developmental biology, physiology, and diseases affecting the trachea are required for solving this problem.

Immune tolerance of epithelium-denuded-cryopreserved tracheal allograft

OBJECTIVES

Animal and clinical studies have demonstrated the feasibility of tracheal allograft transplantation after a revascularization period in heterotopy, thus requiring immunosuppressive therapy. Given the key role of the respiratory epithelium in the immune rejection, we investigated the consequence of both epithelium denudation and cryopreservation in immune tolerance of tracheal allograft in a novel rabbit model.

METHODS

Five adult female New Zealand rabbits served as donors of tracheas that were denuded of their epithelium and then cryopreserved, and 13 males were used as recipients. Following graft wrap using a lateral thoracic fascial flap, allograft segments 20 mm in length with (n = 9) or without (n = 4) insertion of an endoluminal tube were implanted under the skin of the chest wall. The animals did not receive any immunosuppressive drugs. Sacrifices were scheduled up to 91 days. Macroscopic and microscopic examinations and detection of apoptotic cells by immunohistochemical staining (Apostain) were used to study the morphology, stiffness, viability and immune rejection of allografts.

RESULTS

There were no postoperative complications. Grafted composite allografts displayed satisfactory tubular morphology provided that an endoluminal tube was inserted. All rabbits were found to have an effective revascularization of their allograft and a mild non-specific inflammatory infiltrate with no significant lymphocyte infiltration. Cartilage rings showed early central calcification deposit, which increased over time, ensuring graft stiffness. Apoptosis events observed into the allograft cells were suggestive of minimal chronic rejection.

CONCLUSIONS

Our results demonstrated that the epithelium-denuded-cryopreserved tracheal allograft implanted in heterotopy displayed satisfactory morphology, stiffness and immune tolerance despite the absence of immunosuppressive drugs. This allograft with a fascial flap transferable to the neck should be investigated in the setting of tracheal replacement in rabbits. Similar studies need to be conducted in bigger mammals before considering clinical applications.

Double-chamber rotating bioreactor for dynamic perfusion cell seeding of large-segment tracheal allografts: comparison to conventional static methods

Tracheal transplantation with a long-segment recellularized tracheal allograft has previously been performed without the need for immunosuppressive therapy. Recipients' mesenchymal stromal cells (MSC) and tracheal epithelial cells (TEC) were harvested, cultured, expanded, and seeded on a donor trachea within a bioreactor. Prior techniques used for cellular seeding have involved only static-seeding methods. Here, we describe a novel bioreactor for recellularization of long-segment tracheae. Tracheae were recellularized with epithelial cells on the luminal surface and bone marrow-derived MSC on the external surface. We used dynamic perfusion seeding for both cell types and demonstrate an increase in both cellular counts and homogeneity scores compared with traditional methods. Despite these improvements, orthotopic transplantation of these scaffolds revealed no labeled cells at postoperative day 3 and lack of re-epithelialization within the first 2 weeks. The animals in this study had postoperative respiratory distress and tracheal collapse that was incompatible with life.

Influence of mesenchymal stem cells on cryopreserved tracheal allografts in rabbits

Background

Ischemic injury and the rejection process are the main reasons for graft failure in tracheal transplantation models. To enhance the acceptance, we investigated the influence of mesenchymal stem cells (MSCs) on tracheal allografts.

Methods

Extracted tracheal grafts from New Zealand white rabbits were cryopreserved for 4 weeks and orthotopically transplanted (control group A, n=8). In group B (n=8), cyclosporin A (CsA, 10 mg/kg) was injected daily into the peritoneal cavity. In group C (n=8), MSCs (1.0×10⁷ cells/kg) from the same donor of the tracheal allograft, which had been pre-cultured for 4 weeks, were infused intravenously after transplantation. In group D (n=8), MSCs were infused and CsA was injected daily. Four weeks after transplantation, gross and histomorphological assessments were conducted for graft necrosis, measuring the cross-sectional area of the allograft, determining the degree of epithelization, lymphocytic infiltration, and vascular regeneration.

Results

The morphologic integrity of the trachea was retained completely in all cases. The cross-sectional areas were decreased significantly in group A (p=0.018) and B (p=0.045). The degree of epithelization was enhanced (p=0.012) and the lymphocytic infiltration was decreased (p=0.048) significantly in group D compared to group A. The degree of vascular regeneration did not differ significantly in any of the groups. There were no significant correlations among epithelization, lymphocytic infiltration, and vascular regeneration.

Conclusion

The administration of MSCs with concurrent injections of CsA enhanced and promoted epithelization and prevented lymphocytic infiltration in tracheal allografts, allowing for better acceptance of the allograft.

Cryopreservation of the tracheal grafts: Review and perspective

Transplantation of the trachea may become the preferred method for the reconstruction of extensive tracheal defects, however, several unresolved problems must be addressed, such as immunosuppression, preservation and donor shortage. In this manuscript, the cryopreservation of tracheal grafts is reviewed, which potentially is associated with a lessened immunological response. Cryopreservation may be used clinically for long-term preservation and may solve the donor shortage. It is very important to confirm the immunomodulatory effect of cryopreservation on tracheal allografts in order to expand the potential clinical application of tracheal transplantation in the future. The cartilage as well as the epithelium and lamina propria serve as targets for rejection. However, the effect of cryopreservation on chondrocytes could be associated with reduced allogenicity of the trachea. The long-term cryopreservation of cartilage must be investigated in basic research models of chondrocyte viability. Growth of cryopreserved tracheal allografts is less well understood. Further studies are needed to elucidate the mechanism of synergistic effects of both cryopreservation and adequate immunosuppression for tracheal xenografts.

Bone marrow-derived mesenchymal stem cells enhance cryopreserved trachea allograft epithelium regeneration and vascular endothelial growth factor expression

BACKGROUND

Epithelium regeneration and revascularization of tracheal implants are challenging issues to be solved in tracheal transplantation research. Bone marrow-derived mesenchymal stem cells (BMSCs) can migrate to the damaged tissue and promote functional restoration. Here, we applied intravenous transplantation of BMSCs combined with a cryopreserved allograft to investigate the role of BMSCs in enhancing implant survival, tracheal epithelium regeneration and revascularization.

METHODS

After transplantation with cryopreserved allografts, PKH-26 labeled 3 to 5 passage BMSCs were injected into recipient rats through the tail vein. Rats in the control groups were injected with a comparable amount of phosphate-buffered saline. We observed the histology of the tracheal allograft and measured vascular endothelial growth factor (VEGF) protein levels in the epithelium to evaluate the effect of BMSCs on epithelium regeneration and revascularization.

RESULTS

Histologic observation of the rats from the BMSCs injection groups showed that the tracheal lumen was covered by pseudostriated ciliated columnar epithelium. The cartilage structure was intact. There were no signs of denaturation or necrosis. PKH-26 labeled BMSCs migrated to the implant site and exhibited red fluorescence, with the brightest red fluorescence at the anastomotic site. VEGF protein levels in the allograft epithelium of the BMSCs injection group were higher than the levels in the phosphate-buffered saline injection group.

CONCLUSIONS

Our results indicate that given systemic administration, BMSCs may enhance epithelium regeneration and revascularization by upregulating VEGF expression.

Airway tissue engineering

INTRODUCTION

Prosthetic replacements, autologous tissue transfer and allografts have so far failed to offer functional solutions for the treatment of long circumferential tracheal defects and loss of a functioning larynx. Interest has therefore turned increasingly to the field of tissue-engineering which applies the principles and methods of bioengineering, material science, cell transplantation and life sciences in an effort to develop in vitro biological substitutes able to restore, maintain or improve tissue and organ function.

AREAS COVERED

This article gives an overview of the tissue-engineering approach to airway replacement and will describe the encouraging results obtained so far in tracheal regeneration. The recent advances in the field of tissue-engineering have provided a new attractive approach towards the concept of functional substitutes and may represent an alternative to the shortage of suitable grafts for reconstructive airway surgery. We summarize fundamental questions, as well as future directions in airway tissue engineering.

EXPERT OPINION

The replacement of active movement, as would be necessary to replace an entire larynx introduces another order of magnitude of complexity, although progress in this area is starting to bear fruit. In addition, the stem cell field is advancing rapidly, opening new avenues for this type of therapy.

Long-term outcomes of microsurgical reconstruction for large tracheal defects

BACKGROUND

Reconstruction of large tracheal defects has been largely unsuccessful. The purpose of this study was to review the authors' experience with microsurgical reconstruction of these defects.

METHODS

Seven cases of microsurgical tracheal reconstruction were performed between May 2002 and April 2008. All but 1 patient had recurrent thyroid cancer; the other patient had primary adenocystic carcinoma of the trachea. The radial forearm free flap was used for lining in all cases. Rigid support was provided with a variety of prosthetic materials.

RESULTS

All defects involved the cervical trachea, with an average length of 5.8 cm ± 1.0 cm (range, 5 cm-7.5 cm). The width of defects ranged from half of the tracheal circumference to the entire circumference. Major complications included air leak in 4 patients, exposure and removal of prosthesis in 2 patients, and cardiopulmonary complications in 2 patients. One patient with postoperative retroperitoneal hematoma, abdominal compartment syndrome, and multiple organ failure died 2 months after surgery. Two patients died of other causes 1 year and 4 years, respectively, after surgery. The other 4 patients were alive and disease free, with follow-up ranging from 1 to 4.5 years. Four patients are asymptomatic, with normal speech and swallowing functions. Two patients remained tracheostomy dependent, but vocal ability was intact. All patients tolerated a regular diet.

CONCLUSIONS

Microsurgical reconstruction is a viable option in selected patients with large cervical tracheal defects that are beyond primary repair.

Moving towards in situ tracheal regeneration: the bionic tissue engineered transplantation approach

In June 2008, the world's first whole tissue-engineered organ - the windpipe - was successfully transplanted into a 31-year-old lady, and about 18 months following surgery she is leading a near normal life without immunosuppression. This outcome has been achieved by employing three groundbreaking technologies of regenerative medicine: (i) a donor trachea first decellularized using a detergent (without denaturing the collagenous matrix), (ii) the two main autologous tracheal cells, namely mesenchymal stem cell derived cartilage-like cells and epithelial respiratory cells and (iii) a specifically designed bioreactor that reseed, before implantation, the in vitro pre-expanded and pre-differentiated autologous cells on the desired surfaces of the decellularized matrix. Given the long-term safety, efficacy and efforts using such a conventional approach and the potential advantages of regenerative implants to make them available for anyone, we have investigated a novel alternative concept how to fully avoid in vitro cell replication, expansion and differentiation, use the human native site as micro-niche, potentiate the human body's site-specific response by adding boosting, permissive and recruitment impulses in full respect of sociological and regulatory prerequisites. This tissue-engineered approach and ongoing research in airway transplantation is reviewed and presented here.

Cryopreserved Tracheal Grafts: A Review of the Literature

Cryopreserved tracheal grafts have been used in several experimental models of long segment replacement. The clinical application of the procedure has been limited due to the fact that contradictory results have been reported. The purpose of this article is to present a review of the literature on tracheal cryopreservation. Despite the fact that most authors indicate that cryopreserved tracheal allografts retain viability and have a low immunological response, though they continue to function after transplantation with good epithelialization and patency, cryopreservation leads to significant damage to cartilage, the degree of which is based on the freezing-storage methods that affect the function and durability of a graft. The long-term storage of cartilage must therefore be investigated in more detail in basic research models of cartilage viability: the evaluation of chondrocyte apoptosis, and the use of different solutions for tracheal cryopreservation other than RPMI-1640, Dulbecco's modified Eagle's, Eurocollins, and TC-199. Furthermore, problems that involve improving the blood supply to the graft after extensive resection and immunosuppression must be resolved before tracheal cryopreservation can become a clinically established method for tracheal grafts.

The cryopreservation of composite tissues: Principles and recent advancement on cryopreservation of different type of tissues

Cryopreservation of human cells and tissue has generated great interest in the scientific community since 1949, when the cryoprotective activity of glycerol was discovered. Nowadays, it is possible to reach the optimal conditions for the cryopreservation of a homogeneous cell population or a one cell-layer tissue with the preservation of a high pourcentage of the initial cells. Success is attained when there is a high recovery rate of cell structures and tissue components after thawing. It is more delicate to obtain cryopreservation of composite tissues and much more a whole organ. The present work deals with fundamental principles of the cryobiology of biological structures, with special attention to the transfer of liquids between intra and extracellular compartments and the initiation of the formation and aggregation of ice during freezing. The consequences of various physical and chemical reactions on biological tissue are described for different cryoprotective agents. Finally, we report a review of results on cyropreservation of various tissues, on the one hand, and various organs, on the other. We also report immunomodulation of antigenic responses to cryopreserved cells and organs.

The fate of homograft tracheal transplants in sheep

OBJECTIVE

An established method of tracheal substitution is not yet available, but homograft tracheal transplantation might provide a realistic tracheal replacement. With the objective of sequentially examining the healing of tracheal homografts, we have established a suitable large-animal model.

METHODS

Five sheep received orthotopic tracheal transplantation of a 4-cm cervical tracheal homograft. The trachea was supported for 6 weeks with a self-expanding polyester stent. The plan was to euthanize the animals after 2, 4, 8, 12 and 16 weeks, or whenever complications occurred.

RESULTS

The implantation itself was performed without complications. After 2 weeks the homograft was firmly encapsulated by connective tissue, without signs of necrosis or abscess. The original mucous membrane no longer existed; the cartilage rings were exposed. In all animals that were euthanized at the later dates, the homografts were completely absorbed and replaced by inflammatory scar tissue. This, in turn, was covered with a shiny cellular surface layer.

CONCLUSIONS

The results from this animal experiment reveal-contrary to data published to date-that tracheal homografts are not incorporated but absorbed. They are replaced by scar/granulation tissue that cannot secure the stability of the trachea. Therefore, further experiments with respect to the biocompatability of homografts appear to be necessary.

La cryopréservation de tissus composites: principe, revue de la littérature et expérience de l'équipe bordelaise

The cryopreservation of cells and human tissues has generated a great interest from the scientific community since 1949 when the cryoprotective activity of glycerol was discovered. For a homogeneous cellular group or a one-layer cellular tissue it is easy to define the optimal technique conditions of its cryopreservation (cryoprotective agents, speed and steps of freezing, speed of warming). It is considered successful when a high recovery of the cellular structures and tissue components after warming is achieved. The cryopreservation of a whole composite tissue is less easy to obtain. Each tissue presents its own parameters and its own reactivity during the cryopreservation process. The challenge consists in, on the one hand, the selection of the ideal cryoprotective agents'combination which can fit the needs of the different tissues and on the other hand, the definition of adequate technical parameters. The aim of this work is to demonstrate the feasability to cryopreserve a composite tissue in order to carry out surgical reconstructive procedures of particular anatomical and functionnal units (metacarpo-phalangeal and proximal interphalangeal joints, flexor system apparatus, extensor system, median nerve, etc.) with complete revitalization of the allograft using vascular microsurgical procedures. To do so, our present work is divided into three different parts. The first chapter deals with the fundamental principles of the cryobiology of biological structures with special interest in the liquid transfer process between the extracellular and intracellular compartments and ice initiation and agregation during the freezing process. The different physical and chemical reactions and their consequences on the biological tissues are described according to the different cryoprotective agents used, should they belong to the extracellular or intracellular cryoprotective groups. The second chapter makes a review of the litterature concerning the results of all experiments made on the cryopreservation of the different tissue structures as skin, vessels, bones, cartilage, periosteum, nerves, cornea, on the one hand, and the different organs as kidneys, liver, heart, trachea, lung, parathyroid glands and ovaries, on the other hand. We are reporting the results of these experiments focusing on the immunomodulation effect of cryopreservation on the antigenic response of biological structures. These experiments were made either on organs or on the cells involved in the immunogenic process. In the third chapter, we are reporting the results of our experiments carried out in the Aquitaine Hand Institute in the field of the cryopreservation of the xenografts of digital segments on the rabbit. These digital segments were cryopreserved, then warmed and revitalized through vascular microsurgical techniques. The preliminary results are very encouraging and pave the way to the allotransplantation of cryopreserved composite organs in our common surgical activity.

Tracheal replacements: part 1

In this review, we summarize the history of tracheal reconstruction and replacement as well as progress in current tracheal substitutes. In Part 1, we cover the historical highlights of grafts, flaps, tube construction, and tissue transplants and address the progress made in tracheal stenting as a means of temporary tracheal support. This is followed in Part 2 by an analysis of solid and porous tracheal prostheses in experimental and clinical trials. We conclude Part 2 with a summary of recent efforts toward generating a bioengineered trachea. Finally, we provide an algorithm on the spectrum of options available for tracheal replacement.

Histological examination of cryopreserved rat tracheal grafts

It has been reported that tracheal tissue treated by cryopreservation can be used for tracheal replacement in the absence of immunosuppressants. However, the mechanism of reduced antigenicity is unclear. We investigated this issue in cryopreserved rat trachea using detailed histologic evaluation. Rat tracheal segments were preserved in a cryopreservative solution at -85 degrees C. The epithelium of tracheal segments (n = 6 in each group) was subjected to light microscopic and scanning electron microscopic examination before freezing and after cryopreservation for 1 week, 1 month, 3 months, and 6 months. The expression of major histocompatibility complex II (MHC-II) was determined using frozen sections. Ultrastructure of dendritic cells (DCs) was observed by transmission electron microscopy. Tracheal epithelium was partially intact even after 6 months in cryopreservation, although cellularity decreased with time. MHC-II antigen expression was detected even at 6 months, although expression was lower than that measured on fresh tissue. Tracheal tissue DCs displayed dilatations of perinuclear cisterna and degeneration of vacuoles. Density of the mitochondrial matrix was increased. These results suggest that damage to the epithelium and DCs during cryopreservation and concomitant loss of MHC-II expression might explain the reduction of antigenicity.

Engineering a Composite Neotrachea in a Rat Model

BACKGROUND

Attempts to reconstruct the trachea have been largely unsuccessful because of its rigidity and opening to the outside environment. Materials that impart rigidity are usually alloplastic, so they cannot be exposed to the open environment without an unacceptably high risk of infection and rejection. The authors hypothesized that tissue engineering principles can be employed to construct a well-integrated neotrachea with rigid support and an epithelial lining to mimic the structure and function of the native trachea.

METHODS

A 30-mm-long segment of polytetrafluoroethylene vascular graft with a diameter of 10 mm was lined with a fascial flap based on the superficial inferior epigastric artery with full-thickness skin grafts on its luminal surface. The composite unit was then buried under the abdominal skin of 20 rats and harvested 3 weeks later. Microfil and methylene blue dye were injected into the superficial inferior epigastric arteries and histologic analyses were performed to assess microcirculation and polytetrafluoroethylene-tissue integration.

RESULTS

Two composite neotracheas experienced minor damage due to chewing by the rats, but all other neotracheas were viable and without infection. Injection studies demonstrated excellent circulation throughout the fascial flaps and skin grafts and across the polytetrafluoroethylene grafts to the overlying abdominal skin. Histologic analyses revealed abundant muscle-walled blood vessel ingrowth within the polytetrafluoroethylene grafts and all layers of the neotracheas with minimal inflammatory reactions.

CONCLUSION

The authors successfully have engineered a well-integrated neotrachea in rats that possesses rigid support, an epithelial lining, and reliable coverage-the prerequisites for successful trachea reconstruction.

Tracheal regeneration following tracheal replacement with an allogenic aorta

BACKGROUND

Tracheal replacement remains an unsolved surgical problem. Attempts to use tracheal substitutes have failed to achieve reliable results. In this study, tracheal regeneration was obtained after tracheal replacement with an allogenic aorta.

METHODS

Twenty female sheep underwent a 8-cm tracheal replacement with a fresh aortic allograft. In the six last animals, aortic grafts came from male sheep. A stent prevented airway collapse. No immunosuppressive therapy was used. Aortic segments were retrieved at regular intervals up to 16 months. A polymerase chain reaction for the SRY gene was performed in specimens with aortic grafts from male sheep.

RESULTS

All animals but one survived the operation without complications. Clearly identified between the suture lines, the aortic segments were completely transformed into a tracheal structure. Histology showed initially an inflammatory reaction with proliferation of a squamous epithelium followed by mucociliary epithelium and newly formed cartilage rings. SRY gene was not found in newly formed cartilage rings showing that the regeneration originated from recipient cells.

CONCLUSIONS

This study presents a new type of tissue regeneration and brings hopes to the treatment of extensive tracheal lesions.

Heterotopic tracheal transplantation with omentum wrapping in the abdominal position preserves functional and structural integrity of a human tracheal allograft

OBJECTIVES

Transplantation of a human trachea has been reported only twice in the literature with limited documentation of the functional and structural properties of the allograft.

PATIENTS AND METHODS

A 57-year-old patient with chronic obstructive pulmonary disease with low segment tracheal stenosis was accepted for lung transplantation and 2-stage tracheal allotransplantation. Standard bilateral sequential lung transplantation was performed with the transfer of the donor trachea into the recipient's abdomen, which was wrapped in the greater omentum and sutured into the abdominal wall, similar to a stoma. The patient received immunosuppression consisting of cyclosporine A, mycophenolate mofetil, and cortisone. Sixty days later, the tracheal allograft presented with macroscopically normal appearance with maintained elasticity and rigidity. The patient underwent a cricotracheal resection 6 months after lung transplantation. However, reconstruction with direct end-to-end anastomosis was achievable. The tracheal allograft, therefore not needed for reconstruction, was harvested and underwent complete investigations.

RESULTS

Cross-section of the graft revealed a mechanically stable and macroscopically intact trachea. Hematoxylin-eosin staining demonstrated vital cartilage covered by respiratory epithelium. Angiography, followed by corrosion studies and electromicroscopy, demonstrated excellent vascularization of the tracheal wall.

CONCLUSION

The patient is alive 31 months posttransplantation and remains in bronchiolitis obliterans syndrome stage 0. Human trachea wrapped in omentum maintains its functional and structural integrity and may be used for 2-stage allotransplantation.

Allowable warm ischemic time to tracheal extraction for allotransplantation of cryopreserved trachea

OBJECTIVE

The allowable warm ischemic time from circulatory arrest to tracheal extraction for allotransplantation of cryopreserved tracheal grafts from cadaveric donors was examined in adult mongrel dogs.

SUBJECTS AND METHODS

The animals were divided into 4 groups (n = 28) according to the warm ischemic time of less than 1 hour, 3 hours, 6 hours, and 12 hours, after transplantation, and comparisons were made. The grafts were cryopreserved for at least 2 months and were evaluated by extraction from the recipients generally 2 months after transplantation.

RESULTS

All the grafts with a warm ischemic time of less than 1 hour were viable and did not show stenosis. This group did not differ significantly from the groups with a warm ischemic time of 3 and 6 hours in terms of viability. However, all of the grafts with a warm ischemic time of 12 hours showed stenosis, and there was a significantly lower viability rate. Histological examination of the grafts showed that warm ischemia caused necrosis of the tracheal cartilage.

CONCLUSION

Based on these results, it was concluded that 6 hours was the maximum allowable warm ischemic time for cryopreserved tracheal transplantation, and that necrosis of the tracheal cartilage due to warm ischemia reduced the viability of the grafts.

Experimental study of a new tracheal prosthesis: Pored Dacron tube

OBJECTIVE

This study was designed to evaluate how various sizes and densities of pores in Dacron tubing might enhance its utility as a tracheal prosthesis.

METHODS

A vascular prosthesis made of knitted external velour polyester was prepared for pore formation with a laser. The first set compared different pore sizes (300, 500, and 700 microm) and pore densities (25/cm(2) or 100/cm(2)). Grafts were reinforced with an externally heat-sealed silicone ring. The second set tested grafts with a pore density of 64/cm(2) and a pore size of 500 microm internally reinforced with a stainless-steel spiral stent. In all experiments, a canine mediastinal trachea 10 cartilage rings in length was resected, and the prosthesis was then implanted with an omental flap.

RESULTS

Lower pore size and density (300 microm, 25 pores/cm(2)) led to essentially no tissue ingrowth. Larger pore size (700 microm) and low density (25 pores/cm(2)) led to rapid and excessive ingrowth of granulation. Midrange pore size (500 microm) and high density (100 pores/cm(2)) invited steady tissue ingrowth, but marked luminal stenosis eventually developed. Stent-reinforced prostheses with 500-microm pores at 64 pores/cm(2), as used in the second set, maintained an average patency rate of 60% or more (range, 20%-100%) at least 12 months after implantation.

CONCLUSION

Our data show that porosity is a key factor for tissue growth through our Dacron tracheal prostheses. This artificial trachea model has led to long-term survivors up to 27 months after the operation and seems promising as a basic model for clinical tracheal repair.

Chronic subglottic and tracheal stenosis: endoscopic management vs. surgical reconstruction

Laryngotracheal stenosis has been and remains one of the most vexing problems in the field of head and neck surgery. Two treatment modalities prevail, endoscopic and external. The indication for each modality is not yet clearly defined. This undefined situation motivated our current work, and we decided to assess laser-assisted endoscopy (with or without stenting) vs. open surgery for treating chronic laryngotracheal stenosis. Our study included 28 cases of chronic laryngotracheal stenosis that were classified according to treatment in two main groups: group I included 13 patients who were endoscopically treated and group II included 15 patients with surgical reconstruction. The mean follow-up period was 12.58 months for group I and 27.43 months for group II. Respiratory function tests (RFT) were carried out preoperatively, 1-month postoperatively and on completion of follow-up. Except for age, which was significantly higher in group I (P<0.001), there was no significant difference between both groups. Although the incidence of complications was higher in group I (69%) than in group II (47%), it was nonsignificant. The postoperative RFT improved significantly in both groups. Although the improvement was higher in group I than group II, the difference was nonsignificant. The correlation between preoperative stridor and all other variables demonstrated that preoperative stridor correlated with the diameter of the stenosed segment (rs=-0.631, P<0.001) and the peak expiratory flow rate (PEFR) (rs=-0.488, P=0.030). Our results indicate that open surgery is the treatment of choice. Compared with endoscopic treatment, it provides a higher success rate and better functional results, especially long term. However, if contraindications to open surgery exist, whether local or general, laser-assisted endoscopy with stenting can offer good palliative results.

Segmental tracheal replacement in mongrel dogs

OBJECTIVE

To evaluate the use of alcohol- and detergent-preserved tracheal allografts in dogs.

MATERIAL AND METHODS

Experimental segmental tracheal replacement was performed in 18 adult mongrel dogs. Three different techniques were tried in three groups of dogs. In the first group, a four-ring cervical tracheal segment was dissected out and implanted in the trachea of another dog. In the second group, the procedure was performed using a tracheal allograft that had been preserved in 70% ethyl alcohol for 20 days. In the third group, tracheal grafts were previously impregnated in 10% povidone iodine for 72 h before being implanted. Allografts were harvested 60 days after transplantation and assessed both histologically and in terms of the percentage patency. Dogs that died within 60 days were also included in the analysis.

RESULTS

The best results were found in the group in which the tracheal allograft had been preserved in ethyl alcohol and this was explained by the reduced antigenicity of the graft in this group.

CONCLUSIONS

The use of alcohol-preserved allografts is a practical method of tracheal transplantation, and the alcohol-preservation technique markedly reduces the immunogenicity of the grafts.

The immunomodulatory effect of cryopreservation in rat tracheal allotransplantation

BACKGROUND

Cryopreservation is one solution to the problem of donor organ deficit. To investigate the effect of cryopreservation on tracheal allografts, we performed 2 experiments in rats.

METHODS

In Experiment 1, we assessed second-set graft rejection. Two weeks after primary heterotopic transplantation (Group 1, fresh isografts; Group 2, fresh allografts from Lewis rats; and Group 3, cryopreserved allografts from Lewis rats; n = 5, respectively), each animal underwent secondary heterotopic grafting with isografts and allografts from Lewis and Wistar Furth rats (n = 5, respectively). Four weeks after the secondary transplantation, all grafts were retrieved for histologic analysis. In Experiment 2, we assessed the long-term results of allograft cryopreservation, without immunosuppression therapy. Six months after transplantation of fresh (Group 4) and cryopreserved (Group 5) allografts, the tracheal segments (each group, n = 5) were histologically evaluated.

RESULTS

In Experiment 1, only the secondary allografts from Lewis rats in Group 2 did not maintain lumen structure and often showed dislocated or destroyed cartilage. Second-set graft rejection was specifically recognized in Group 2, but not in Group 1 or 3. In Experiment 2, the cryopreserved allografts appeared almost normal and lumen rigidity was preserved 6 months after transplantation. These allografts were superior to the fresh allografts in patency and in cartilage dislocation and mononuclear cell infiltration scores, but not in the viable chondrocyte ratio.

CONCLUSIONS

We conclude that cryopreservation may produce successful long-term results because of its immunomodulatory effect on tracheal allografts.

Failure of airway healing in an ovine autotransplantation model that includes basic fibroblast growth factor

OBJECTIVE

Basic fibroblast growth factor is among the most potent promoters of angiogenesis. Its ability to enhance the blood supply to ischemic airways or nonvascularized tracheal autograft has been demonstrated. Its cumulative effect with muscular wrapping and its efficacy in a noncanine large animal model remain unknown. Treatment with basic fibroblast growth factor and muscular wrapping were compared with no special treatment and with muscular wrapping alone in an ovine tracheal autotransplantation model.

METHODS

All sheep underwent orthotopic tracheal transplantation with 5 to 8 ring autografts in the cervical trachea. Fifteen sheep were classified randomly into the following three groups: no treatment (group A, n = 5), muscular wrapping with the right sternomastoid muscle (group B, n = 5), and topical administration of fibrin glue enriched with 2 microg/cm(2) basic fibroblast growth factor (group C, n = 5).

RESULTS

Devascularized tracheal autografts were unable to maintain their structural integrity without other treatment (group A). However, the grafts were surrounded by well-vascularized connective tissue. In the muscular wrapping group (group B), infections occurred around the grafts, and the muscular wrapping was subject to necrosis. No neovascularization of the grafts occurred. Therapy with basic fibroblast growth factor (group C) led to improved muscular wrapping circulation and to adherence to the tracheal stumps. However, no success was achieved in validating the circulation in the grafts.

CONCLUSIONS

In contrast to the results achieved by other authors with canine models, the neovascularization of tracheal autografts was not achieved in sheep with the topical administration of basic fibroblast growth factor. Cranially pediculated muscular wrapping led to poorer circulation in the tissue around the graft than did no therapy at all.

Tracheal replacement: a critical review

This review discusses the need for tracheal replacement, distinct from resection with primary anastomosis, the requirements for replacement, and the many efforts over the past century to accomplish this goal experimentally and clinically. Approaches have included use of foreign materials, nonviable tissue, autogenous tissue, tissue engineering, and transplantation. Biological problems in each category are noted.

Successful allotransplantation of cryopreserved tracheal grafts with preservation of the pars membranacea in nonhuman primates

OBJECTIVE

This study was performed to confirm the feasibility of cryopreserved tracheal allotransplantation in primates, the anatomy and immunology of which are considered to be more closely related to those of humans than those of other animals.

METHODS

Cryopreserved tracheal allotransplantations were performed in 3 recipient primates. In the control group fresh tracheal allotransplantations were performed in 2 primates (control A), and a tracheal allotransplantation with a simply frozen tracheal graft was performed in 1 primate (control B). Monthly bronchoscopic examinations, histologic examinations, electron microscopic examinations, and immunohistochemical investigations were performed in each of the primates.

RESULTS

In the cryopreserved tracheal allotransplantation group, 3 recipient monkeys were killed on the 35th, 144th, and 387th postoperative days, respectively. All grafts were incorporated by the recipient trachea without stenosis in the cryopreserved group. In the control group 2 recipient monkeys were killed on the 93rd postoperative day (control A), and one was killed on the 84th postoperative day (control B). Severe stenosis was observed after the transplantation in all of the control monkeys. Immunologic reactions appeared to be attenuated by the cryopreservation, whereas T cell-mediated immunologic rejection (control A) and loss of cartilage viability (control B) were considered to be the causes of graft failure in the control group.

CONCLUSION

The immunogenicity of the tracheal allografts was reduced by cryopreservation, and cryopreserved tracheal allotransplantation was successful in our primate model. Further investigation of cryopreserved tracheal allotransplantation with regard to proper clinical applications and the limitations of the procedure should be performed.

Tracheal allotransplantation in beagle dogs without immunosuppressants

BACKGROUND

The antigenicity of tracheal grafts is still unclear. We investigated the possibility of performing tracheal allotransplantation without immunosuppressants.

METHODS

Intrathoracic five-ring tracheal replacements were performed in beagle dogs without immunosuppressants (n = 18). The dogs were divided into 9 pairs, and grafts were exchanged within the pairs. In group 1 (n = 6), the paired dogs were blood relatives, whereas in group 2 (n = 12), the paired dogs were not related. Full-thickness skin transplantation was also performed in both groups.

RESULTS

In group 1, 5 animals survived uneventfully for more than 3 months. No stenosis was observed in any of the dogs. In group 2, the grafts were incorporated by the host trachea in 2 dogs. Four animals died of airway obstruction within 3 months. Moderate or slight airway stenosis was observed in 6 dogs. Rejection was confirmed by histologic examination. In both groups, all of the skin allografts were destroyed within 2 weeks.

CONCLUSIONS

After tracheal allotransplantation, long-term survival was achieved, especially in recipient dogs that were blood relatives of donors. We conclude that it is possible to perform tracheal allotransplantation using histocompatible matched grafts without immunosuppressants.

Effect of cryopreservation period on rat tracheal allografts

BACKGROUND

The effect of cryopreservation on tracheal allogenicity is still unclear. Therefore, in this study, we assessed the effect of cryopreservation period on tracheal allografts in 62 rats.

METHODS

Each transplant consisted of a 3-ring segment of the trachea harvested from 8 Lewis rats, immersed in preservation solution, and cryopreserved and stored in a Bicell biofreezing vessel in a deep freezer at -80 degrees C. Six tracheal grafts without cryopreservation that underwent a heterotopically syngeneic transplantation into the omentum served as controls. Forty-eight tracheal segments were randomly assigned to 8 groups according to period of cryopreservation, which ranged from 0 to 12 months (0, 0.5 [2 weeks], 1, 2, 3, 6, 9 and 12 months). The cryopreserved grafts were then thawed and heterotopically implanted into the omentum of recipient Brown-Norway rats. After 28 days, the tracheal segments were then evaluated histologically.

RESULTS

All isografts in Group 1 were intact, whereas the allografts undergoing a particularly shorter period of cryopreservation showed a more stenotic lumen. Prolonged periods of cryopreservation tended to show decreasing tendencies of viability of chondrocytes, mononuclear cell infiltration and sub-epithelial thickness, whereas all allografts showed a uniformly denuded epithelium, irrespective of the length of cryopreservation.

CONCLUSIONS

A longer period of cryopreservation may help to maintain a better patency of tracheal allografts by preventing an allogeneic response. Reduced tracheal allogenicity may be associated with a decreased viability of chondrocytes by cryopreservation.

Tracheal allotransplantation maintaining cartilage viability with long-term cryopreserved allografts

BACKGROUND

Cartilage viability of a cryopreserved tracheal allograft seems to affect graft function and durability. We previously reported the influence of warm ischemia and cryopreservation on cartilage viability of tracheal allografts. For the clinical application of tracheal allotransplantation, it is essential to preserve grafts for a long time. In this study, we assessed cartilage viability of tracheal allografts after long-term cryopreservation in transplantation models.

METHODS

The tracheas were harvested from Lewis rats. The grafts were frozen to -80 degrees C in a programmable freezer immediately after being harvested and were then stored in liquid nitrogen (-196 degrees C) for different lengths of preservation (1, 2, 6, 9, 12, 18, and 24 months; n for each group = 8). Cartilage viability was evaluated by estimating proteoglycan synthesis. After harvest or thawing of the tracheas, the cartilage was labeled with 4 muCi/mL of Na2 35SO4. Specimens were then hydrolyzed in 0.5 mol/L NaOH, and a solution of the extracts was then counted by a liquid scintillation counter. 35Sulfur incorporation before and after cryopreservation was examined in each group. Tracheal allotransplantation was performed using Lewis rats as donors and Brown Norway rats as recipients.

RESULTS

The average 35S incorporation in the cartilage before cryopreservation was 224 +/- 17 disintegrations per minute per milligram of tissue protein. The average 35S incorporation in the cartilage after cryopreservation decreased to 67% to 76% compared with that before cryopreservation. There were no significant differences among the groups in 35S incorporations after cryopreservation. Histologic examination after transplantation revealed normal tracheal cartilage in all groups.

CONCLUSIONS

The viability of tracheal cartilage after cryopreservation decreased to 67% to 76%. There were no significant differences in viability of cartilage among the tracheas after different lengths of cryopreservation. Tracheal allotransplantation after long-term cryopreservation can be safely performed in the rat model.

Effects of warm ischemia and cryopreservation on cartilage viability of tracheal allografts

BACKGROUND

For clinical use of a cryopreserved tracheal allograft, it is important to evaluate cartilage viability. We assessed cell viability of the cartilage in a cryopreserved tracheal allograft by measurement of Na2 35SO4 incorporation. We also investigated the effects of warm ischemic time on tracheal cartilage viability.

METHODS

The tracheas from Lewis rats were harvested and preserved at different warm ischemic times from cardiac death to preservation (0, 1, 2, 4, 6, 9, and 12 hours, each group n = 8). The cartilage was labeled with 4 muCi/mL of Na2 35SO4. The specimen was hydrolyzed in 0.5 mol/L NaOH, and a solution of the extracts was then counted by liquid scintillation counter. Tracheas were transplanted into Brown Norway rats.

RESULTS

35Sulfur incorporation in the cartilage decreased as warm ischemic time increased. In addition, 35Sulfur incorporation decreased from 76% to 67% after cryopreservation. Histologic examinations of the normal tracheal cartilage before preservation and after thawing were done in all the groups. After transplantation, the cartilage had severe fibrous changes, and its layer was almost nonobservable in the 9- and 12-hour groups.

CONCLUSIONS

The viability of the tracheal cartilage decreased with warm ischemic time and from 76% to 67% after cryopreservation. In the rat tracheal transplantation model, a cryopreserved tracheal allotransplant could be done safely with a graft that was cryopreserved within 6 hours of warm ischemic time.

Allogenicity of cryopreserved human fibroblasts: cryopreservation does not downregulate the allogenicity of fibroblasts making up the matrices of allografts

BACKGROUND

Although cryopreserved tissue allografts are being widely used, long-term degeneration of implanted cryopreserved allografts has become a problem. Although immunologic rejection has been suggested to play a part in this degeneration, cryopreserved allografts are considered to be less immunogenic than fresh allografts.

OBJECTIVE

We investigated the effect of cryopreservation on the allogenicity of the fibroblasts that make up the matrices of allografts.

METHODS

Fibroblast cell strains obtained from surgically resected lung specimens were used. Allogenicity-related antigens expressed on the cell surface (human leukocyte antigen 1, human leukocyte antigen 2, and intercellular adhesion molecule 1), stimulation indices during 1-way mixed lymphocyte-fibroblast cell culture, and proliferation indices of freshly passaged fibroblasts and cryopreserved fibroblasts stored for 1, 4, and 24 weeks were examined. Flow cytometric analysis with monoclonal antibodies was used to test for cell surface antigens, and a colorimetric methyl-thiazol-diphenyl-tetrazolium assay was used to assess stimulation indices and fibroblast proliferation indices. The effect of exogenous interferon-gamma on the degree of expression of human leukocyte antigen 1, human leukocyte antigen 2, and intercellular adhesion molecule 1 was examined simultaneously.

RESULTS

The proliferation indices of fibroblasts were well maintained by cryopreservation. Expression of human leukocyte antigen 1, human leukocyte antigen 2, and intercellular adhesion molecule 1 by fibroblasts was significantly upregulated by interferon-gamma, and cryopreservation did not downregulate this expression.

CONCLUSION

Our study suggests that although the fibroblast cell component may be beneficial in restoring allograft function properties initially, it may render the implanted allograft more immunogenic, ultimately resulting in greater rejection and inflammatory responses by the host and, in turn, degeneration of the graft.

Epithelial re-growth is associated with inhibition of obliterative airway disease in orthotopic tracheal allografts in non-immunosuppressed rats

BACKGROUND

Because epithelial cells are targets of alloimmune injury leading ultimately to airway obliteration, we tested whether epithelial re-growth could prevent obliterative airway disease (OAD) in orthotopic tracheal allografts.

METHODS

Brown Norway tracheal segments were orthotopically transplanted into nonimmunosuppressed Lewis rats. Allografts were removed on days 2-10 (n=13), 30 (n=4), and 60 (n=5) for histology, computerized morphometry (obliteration), and immunohistochemical detection of mononuclear cells, smooth muscle alpha-actin, and tissue phenotype. Normal tracheas, host tracheas, and heterotopically transplanted allografts served as controls.

RESULTS

Orthotopic allografts removed on days 2-10 exhibited epithelial damage and re-growth and mononuclear cell infiltration. On days 30 and 60, partially ciliated cuboidal or attenuated epithelium completely covered the lumen. Although mononuclear cells declined, numerous T cells with a high CD4/CD8 ratio were found in the epithelium till day 60. Orthotopic allograft epithelium expressed donor phenotype on day 7, but recipient phenotype on days 30 and 60. Despite subepithelial alpha-actin positive myofibroblast proliferation, obliteration did not progress from day 7 to 30 and 60 (35, 30, and 33%, respectively). Although more than in normal or host tracheas, the obliteration in orthotopic allografts on days 30 and 60 was significantly less (P<0.001) than in heterotopic allografts.

CONCLUSIONS

We describe, for the first time, longterm patency of fully histoincompatible orthotopic tracheal allografts in nonimmunosuppressed rats. Despite acute alloimmune injury and induction of myofibroblast proliferation, epithelial re-growth from the host limited the progression of OAD, thus emphasizing the role of epithelium in the control of airway obliteration.

A new tracheal bioartificial organ: evaluation of a tracheal allograft with minimal antigenicity after treatment by detergent

The aim of this study was to reduce the antigenicity of tracheal allografts by detergent treatment. We attempted to apply these grafts to tracheal immunosuppressant-free allotransplantation. Fresh tracheal grafts were harvested from donor beagle dogs and treated with a detergent at 4 degrees C for 48 hours. By using treated grafts, we have performed tracheal immunosuppressant-free transplantation in six dogs at an intrathoracic five-ring defect. Implanted grafts were covered with an omental pedicle. In five of the six grafts, complete removal of the epithelium and mixed glands was recognized with both light microscopy and scanning electron microscopy. The appearance of the cartilage cells in the grafts was similar to those in fresh trachea. Five dogs that received detergent treated grafts survived uneventfully. The grafts had been incorporated by the host trachea without stenosis. On the one tracheal graft in which removal of the epithelium was incomplete (noted after implantation), moderate stenosis occurred 1 month after placement. These results suggest that removal of the tracheal epithelium and mixed glands can remarkably reduce tracheal antigenicity. A tracheal graft that has its epithelium and mixed glands removed can be used in tracheal immunosuppressant-free allotransplantation.

Immunosuppressant-free allotransplantation of the trachea: the antigenicity of tracheal grafts can be reduced by removing the epithelium and mixed glands from the graft by detergent treatment

OBJECTIVE

To develop a method for eliminating the epithelium and mixed glands from tracheal grafts by detergent treatment and evaluate these grafts for immunosuppressant-free allotransplantation in dogs.

METHODS

Fresh canine tracheal grafts were treated with a detergent (1% Triton X-100 t-octylphenoxypolyethoxyethanol; T-9284; Sigma Chemical Co, St Louis, Mo) at 4 degrees C for 48 hours. The grafts were then used for intrathoracic 5-ring tracheal replacement in other dogs without immunosuppressant treatment (n = 6, detergent treatment group). In the control group (n = 6) fresh untreated canine tracheal segments were implanted as allografts. All the implanted grafts were covered with an omental pedicle.

RESULTS

In the detergent treatment group the chondrocytes in the graft had a similar appearance to those in the fresh trachea, indicating that the chondrocytes remained viable after the detergent treatment. In 5 of the 6 grafts, the epithelium and mixed glands had been removed completely. After transplantation, these 5 grafts were incorporated by the host trachea without stenosis. In the remaining treated tracheal graft, in which removal of the epithelium was incomplete, moderate stenosis was observed at the fourth week after implantation, although this was not progressive. In the control group, granulation tissue of the graft and significant stenosis were observed after transplantation.

CONCLUSION

The antigenicity of tracheal grafts can be greatly reduced by removing the epithelium and mixed glands by the use of detergent treatment. The epithelium and mixed glands of the graft appear to be the determining elements involved in rejection after tracheal allotransplantation.

Revascularization of canine cryopreserved tracheal allografts

BACKGROUND

We examined the blood supply of a cryopreserved tracheal allograft and its morphohistologic changes after transplantation.

METHODS

In each of 22 dogs, a five-ring tracheal segment was replaced by one of the following tracheal grafts: fresh autografts (n = 8), cryopreserved tracheal allografts (n = 8), or fresh allografts (n = 6). The cryopreserved tracheal allografts were preserved at -196 degrees C for 60 days. No immunosuppressant was given to any of the animals. All grafts were retrieved at 1 and 12 weeks and assessed by microangiography and histology.

RESULTS

The epithelial denudation and the revascularization of the transverse intercartilaginous arteries were recognized within 7 days as common to each of the three types of grafts. In the cryopreserved tracheal allografts, neither cartilage degradation nor graft shrinkage occurred at 7 days. However, the recanalized transverse intercartilaginous arteries completely disappeared at 12 weeks, and marked shrinkage occurred; the cartilage cells were accompanied by karyolysis and were significantly decreased in number (p < 0.05). Recanalization of the transverse intercartilaginous arteries was also demonstrated in the fresh allografts; however, necrosis abruptly occurred as a result of acute rejection responses.

CONCLUSIONS

Cryopreservation of a tracheal allograft provided sufficient reduction of the acute rejection responses, and blood supply to the cryopreserved tracheal allograft was established through the recanalized transverse intercartilaginous arteries within 7 days; however, subsequent chronic rejection responses resulted in occlusion of the transverse intercartilaginous arteries and atrophy.