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

Effects of cryopreservation on tracheal allograft antigenicity in dogs

BACKGROUND

Prolonged cryopreservation (~8-10 months) has been shown to reduce the antigenicity of tracheal allografts due to subsequent denuding of epithelium. In the present study, tracheal epithelium was assessed after variable periods of cryopreservation. Immunosuppressant-free allotransplantation was then undertaken to evaluate the impact of cryopreservation on tracheal antigenicity in dogs.

METHODS

Tracheal rings [7-8] were removed from mongrel adult dogs for cryopreservation (1-10 months, -85 °C) and grafting. Before transplantation, one ring was sectioned from each end for histologic examination. The residual five-ring segments of mediastinal trachea were then transplanted into recipient dogs after 1-7 months (group 1, n=9) or 8-10 months (group 2, n=6) of cryopreservation. Anastomotic sites and allografts were covered by omental pedicles. No immunosuppressants whatsoever were administered.

RESULTS

In microscopic views, the ciliated tracheal epithelium of most grafts showed variable loss but was generally intact after cryopreservation, still demonstrating major histocompatibility complex (MHC)-II positivity. By postoperative bronchoscopy, allografts in both groups had largely developed lethal strictures. In group 1, eight dogs were sacrificed or died within 50 days post-transplantation, whereas survival times in group 2 were somewhat longer, with three dogs surviving for >60 days. Upon sacrifice, histologic preparations of grafted tissue in both groups were typically denuded of epithelium, with marked lymphocytic/monocytic submucosal infiltrates. Tracheal cartilage had been absorbed or destroyed.

CONCLUSIONS

After cryopreservation, some degree of tracheal epithelium loss maybe expected, but complete denudation is not obligatory. Retained epithelial antigenicity is thus capable of triggering rejection, resulting in transplant failures. Although prolonging transplant survival to an extent, fatal rejection of tracheal allografts was not preventable by prior cryopreservation.

Reconstruction of Anterior Tracheal Defects Using a Bioengineered Graft in a Porcine Model

BACKGROUND

Reconstruction of long-segment tracheal defects can be challenging and a suitable tracheal substitute remains lacking. We sought to create a bioengineered tracheal graft to repair such lesions using acellullar bovine dermis extracellular matrix (ECM) and male human mesenchymal stem cells (hMSCs) and implant it in a porcine model.

METHODS

hMSCs were seeded on the ECM and incubated for 1 week with chondrogenic factors. An anterior 4 cm × 3 cm defect was surgically created in the trachea of 4-week-old female Yorkshire pigs. The defect was reconstructed using the bioengineered graft (n = 7) or control (n = 3, ECM only). The study duration was 3 months.

RESULTS

Survival ranged from 7 days (n = 3) to 3 months (n = 7). Early death was due to graft malacia (n = 1, control), graft infection (n = 1, bioengineered), and pneumonia (n = 1, bioengineered). There was substantial animal growth at 3 months (>200% weight). Surveillance bronchoscopy showed patent airway, mild stenosis, and integration of the graft with the native trachea. On histology, luminal epithelialization and neovascularization with scant submucosa were observed in both the bioengineered graft and control groups. Chondrogenesis was seen only in the bioengineered graft. The neocartilage was less mature and organized compared to native cartilage. SRY immunostain was positive in the neocartilage but not control or native trachea.

CONCLUSIONS

We demonstrate the feasibility of the bioengineered graft for reconstruction of long anterior tracheal defects with favorable short-term outcomes. Furthermore, we show its ability to facilitate chondrogenesis, neovascularization, and epithelialization. Importantly, it supported rapid animal growth offering potential solutions for both pediatric and adult applications.

Visual observation of African trypanosomes during cryopreservation

Protozoa have been widely used for the study of cryopreservation. The survival rate after cryopreservation has always received the most attention, while the cell viability during the process of freezing and thawing has been much less studied. In the present study, we report successful cryopreservation of Trypanosoma brucei, a parasitic protozoa of human and animals, using controlled-rate freezing at 5°C/min, and real-time observation of activity using a microscope differential scanning calorimeter system during the freezing and thawing process. Trehalose used as a cryoprotective agent at a concentration of 0.4 M allowed the trypanosomes to endure freezing and thawing with >89% survival rate. Results from mechanisms analysis indicate that vitrification by trehalose contributes significantly to the protection of the trypanosomes from damage at low temperature.

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.

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.

Current concepts in tracheal reconstruction

PURPOSE OF REVIEW

Many patients require tracheal reconstruction either for tracheal stenosis/malacia or following tumor extirpation. However, such patients can be debilitated following failed conventional treatments. Recent advances in tissue engineering and vascularized composite grafts are accelerating the field of tracheal reconstruction. This article reviews new clinical concepts for tracheal reconstruction.

RECENT FINDINGS

Novel treatments include composite autografts, allografts, chimeric autografts and allografts, tissue-engineered grafts, prosthetic scaffolds, and the use of free-tissue vascularized carriers.

SUMMARY

New procedures for tracheal reconstruction hold much promise for treating difficult tracheal disorders and improving the quality of life for affected patients. Many of the techniques reviewed herein are single case series and require further investigation and validation.

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.

Successful circumferential free tracheal transplantation in a large animal model

BACKGROUND

Long segment tracheobronchial stenoses are associated with high morbi-mortality rates and difficult treatment. Transplantation hasn't proved to be useful yet. Currently, the successful results achieved in small animal models couldn't be satisfactorily accomplished or extrapolated in large mammals. We aimed to evaluate the viability of orthotopic tracheal autoimplantation in an ovine model.

METHODS

All animals underwent tracheal transplantation of 4 cm (5-7 rings) of the cervical trachea and were divided randomly in two groups: isolated autoimplantation (Group A/6) and autoimplantation with omental wrapping (Group B/6). Clinical follow up and weekly bronchoscopical examinations were performed. The grafts were macroscopically, histologically, and bacteriologically analyzed.

RESULTS

In group A, four animals achieved their planed survival and were sacrificed up to 60 days after transplantation with viable grafts. In group B, only two sheep had successful results. Graft failure with infection, necrosis and severe stenosis was observed in the rest of the animals from both groups. Pseudomonas aeruginose was isolated in all cases. The main complication of the omental pedicle was vascular congestion and peritracheal hemorrhage.

CONCLUSIONS

Contrary to the data reported to date, we found that tracheal transplantation is viable in a large mammal like the sheep. The main complication observed in this animal model was graft infection. The use of an omental pedicle with the technique applied worsened the grafts survival. The encouraging results obtained in this investigation justify further research in order to manage graft infection, leading us to establish a suitable large animal model for allotransplantation.

Ultrastructural changes in cryopreserved tracheal grafts of sprague-dawley rats

It has been reported that immunosuppressant-free tracheal transplantation can be achieved by using cryopreserved grafts. However, the ultrastructural changes of cryopreserved tracheal tissue remain unclear. This study investigated this issue in cryopreserved tracheal grafts of 30 Sprague-Dawley (SD) rats, divided into five groups (n = 6 rats/group). Tracheal rings removed from them were stored in a deep freezer at -85 degrees C for 1 week, 1 month, 3 months, or 6 months. Never frozen tracheal tissues were obtained from the control group. Ultrastructural changes in the cryopreserved tracheas of each group were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). As the duration of cryopreservation lengthened, tracheal grafts were observed by SEM to develop an obviously speckled depletion of epithelium, accompanied by a loss of cilia in the remaining epithelium. TEM examination of chondrocytes that had been cryopreserved for 3 months revealed obvious injury. Cell membranes and nuclei were frequently observed to be ruptured, and fibrils appeared disorganized and randomly oriented. As the time of cryopreservation increased, ultrastructural injury to tracheal chondrocytes became more severe. The data indicated that the optimal maximum time for cryopreservation of tracheal grafts of SD rats might be <3 months with our methods.

Tracheal replacement with cryopreserved allogenic aorta

BACKGROUND

Radical resection of primary tracheal tumors may be challenging when more than one-half of the tracheal length is concerned. The present study evaluated the use of cryopreserved aortic allografts (CAAs) to replace long tracheal segments.

METHODS

Sixteen adult minipigs underwent tracheal replacement with a CAA. A silicone stent was used to splint the CAA for the first 12 months. Animals were followed-up using bronchoscopic evaluation and killed at predetermined times, for a period up to 18 months long.

RESULTS

Intense inflammation and progressive disappearance of typical histologic structures of the aorta were seen within the first 3 months. All animals studied for more than 3 months showed progressive transformation of the graft into a chimerical conduit sharing aortic and tracheal histologic patterns (eg, islands of disorganized elastic fibers/mature respiratory ciliated epithelium, respiratory glands, islets of cartilage). Stent removal was attempted after 12 months in 10 animals, and critical tracheal stenosis was found in six animals and moderate asymptomatic stenosis in four. Clinical course in these latter animals was uneventful until they were killed at 15 to 18 months. In situ hybridization showed that collagen2a1 mRNA was expressed in the cartilage islets at 1 year. Polymerase chain reaction analysis of the SRY gene demonstrated that the newly formed cartilage cells derived from the host.

CONCLUSIONS

CAA may be considered as a valuable tracheal substitute for patients with extensive tracheal tumors. Prolonged stenting will be probably mandatory for the clinical application of the procedure in humans.

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.

Tracheal replacement with cryopreserved, decellularized, or glutaraldehyde-treated aortic allografts

BACKGROUND

Seven years of experimental research provided a valuable tracheal substitute, the aortic allograft, which can promote the regeneration of epithelium and cartilage. In human application, both fresh and preserved aortic allografts could be used. The optimal method of aortic allograft preservation remains to be evaluated. This study assessed the use of cryopreserved, decellularized, or glutaraldehyde-treated aortic allografts as tracheal substitutes.

METHODS

Twenty-two sheep underwent tracheal replacement using cryopreserved (n = 10), decellularized (n = 7) or glutaraldehyde-treated (n = 5) allografts, supported by a temporary stent to prevent airway collapse. Aortic segments were retrieved at regular intervals up to 12 months after implantation to analyze the regenerative process.

RESULTS

All animals survived the operation. Major complications such as infection, stent migration, or obstruction were predominantly encountered in the decellularized group. The lack of major inflammatory response within the aortic graft observed in the glutaraldehyde group was associated with the absence of tracheal regeneration. Histologic examinations showed a progressive transformation of the aorta into a tracheal tissue comprising respiratory epithelium and cartilage only in the cryopreserved group.

CONCLUSIONS

This study demonstrated that regeneration of a functional tissue could be obtained after tracheal replacement with a cryopreserved aortic allograft. The regenerative process followed the same pattern as previously described for fresh allografts. Cryopreserved aortic allografts present major advantages: availability in tissue banks, permanent storage, and no need for immunosuppression. This offers a new field of perspectives for clinical application in patients with extensive tracheal cancer.

Endocrine function and lymphocyte infiltration of newborn rat ovaries after ultrarapid freezing and allotransplantation

OBJECTIVE

To evaluate the endocrine function and lymphocyte infiltration of ultrarapidly frozen newborn rat ovaries in adult recipients.

DESIGN

Animal study.

SETTING

Reproductive Medicine Laboratory of Ningxia Medical College.

ANIMAL(S)

Newborn rats within 24 hours after birth and Sprague-Dawley female adult rats.

INTERVENTION(S)

Newborn or adult rat ovary tissues were cryopreserved with ultrarapid freezing method, using 1.5 M propylene glycol and 0.1 M sucrose as a cryoprotectant agent. After thawing, they were allotransplanted under the kidney capsule of ovariectomized adult female rats to assess the function and the microstructure.

MAIN OUTCOME MEASURE(S)

Vaginal smear, serum E2 level in recipients, grafts histologic observation, 3beta-hydroxy steroid dehydrogenase histochemistry staining, and CD4(+)/CD8(+) T cell immunohistochemistry staining.

RESULT(S)

Frozen-thawed newborn rat ovaries survived and established a vascular network with the kidney of recipients. More growing follicles were found in these survival grafts. No significant differences were found in both resumption rates, the day of initiating estrous cycles, and E2 level between the frozen adult and frozen newborn rat ovaries transplant group. Among all the groups, the number of lymphocyte in the frozen newborn rat ovary transplant group is the lowest.

CONCLUSION(S)

This is the first report for ultrarapid cryopreservation that can preserve the development potential of immature ovaries in ovariectomized adult recipients and further reduce their immunogenicity successfully.

Tracheal replacement by allogenic aorta in the pig

BACKGROUND

To assess whether fresh aortic allografts (AAs) can be used for tracheal replacement.

METHODS

Twenty-one male minipigs underwent tracheal replacement using AAs harvested from female pigs. The length of replaced segments exceeded 50% of the trachea. A stent was implanted into the lumen of the AA to prevent collapse. The animals were killed at 3-month intervals, and AAs were assessed for ingrowth of respiratory epithelium and cartilage formation and tested for type II collagen formation and the presence of the SRY gene.

RESULTS

A high stent migration rate was observed. Only 10 pigs and 4 pigs made it to follow-up periods exceeding 3 months and 9 months, respectively. Neither rejection nor ischemia were observed. At 3 months, a metaplastic epithelium lined the graft. At 10 months, a posterior membrane could be seen with immature cartilage and disorganized elastic fibers. SRY gene assay showed that the cells engrafted in the AAs, particularly at the level of the newly formed cartilage, were of male origin and thus originated from the recipient.

CONCLUSION

This study confirms that a fresh AA, replacing more than half of the trachea of the pig, transforms into a conduit containing the major tracheal components. These components are relatively immature and do not as of yet replicate the form and function of the native trachea. Questions remain concerning the exact mechanisms of this process. Further research on the role of tracheal replacement is recommended.

Transplantation of the cryopreserved tracheal allograft in growing rabbits: effect of immunosuppressant

Transplantation of a cryopreserved tracheal allograft is considered to be a useful strategy in treating congenital tracheal stenosis. Recent reports of tracheal transplant experiments have shown that the antigenicity of the trachea is decreased by cryopreservation, making transplantation of the trachea possible. However, we reported that cryopreserved tracheal allografts exhibited favorable patency, but no significant growth in an animal model. In this study, we hypothesize that an immune reaction may play a role in the failure of an allograft's growth. Each allograft was harvested from 90- to 120-day-old Japanese rabbits, immersed in preservation solution, stored in a programmable freezer until it reached -80 C, and then kept for 1 month. Orthotopic tracheal transplantation of four tracheal rings in an end-to-end fashion was performed in age-matched young rabbits. Ten recipients were classified into three groups: a group provided with tacrolimus (FK-506) as an immunosuppressant (n = 6), a group receiving a graft irradiated before transplantation (n = 2), and a control group (n = 2). All grafts were evaluated 4-8 weeks after transplantation (tacrolimus group: 3-13 weeks). Body weight gain of the tacrolimus group was less than that of the other two groups. All grafts were well incorporated with the recipients macroscopically, but the grafts showed no growth in diameter. Microscopic examination showed inflammation in the tacrolimus and control groups temporarily. The irradiated allografts had marked fibrosis in the subepithelium. Although calcification of the tracheal cartilage was present in all transplanted allografts, the difference between groups was not significant. Patency of the cryopreserved tracheal allografts was favorable but no growth occurred even with an immunosuppressant. Further studies are required to address the growth of the tracheal allograft.

Carinal Replacement With an Aortic Allograft

BACKGROUND

Carinal replacement after extensive resection remains a tremendous challenge in thoracic surgery. In previous studies, we demonstrated that an aortic graft could be a valuable tracheal substitute. The goal of this new study was to evaluate the reconstruction of the carina using a stent supported bifurcated aortic allograft.

METHODS

In 15 sheep the replacement of the tracheobronchial bifurcation with an aortic allograft was performed under cardiopulmonary bypass. A temporary stent prevented airway collapse. No immunosuppression was used. Aortic segments were retrieved at regular intervals up to 24 months after implantation.

RESULTS

All animals survived the initial aortic allograft operation. Six animals died postoperatively (1 of graft necrosis, 2 of pneumonia, and 3 of bronchial fistula). The remaining 9 animals were in good condition until they were euthanized. Stent removal was tolerated after 9 months in 3 animals. Progressive transformation of the arterial graft initially into extensive inflammatory tissue, and after 3 to 6 months into a tracheal tissue comprising a well-differentiated epithelium and cartilage was confirmed by histology.

CONCLUSIONS

This study showed that regeneration of a functional tissue can be obtained after replacement of the carina with an aortic allograft. The origin and mechanisms of this regenerative process remains to be discovered. These results represent an important hope for the reconstruction of the carina after extensive resection, especially for cancer lesions. In human application, the systemic use of omentoplasty or myoplasty should further reduce its risk of complication.

Experimental study of replacing circumferential tracheal defects with new prosthesis

PURPOSE

To investigate the feasibility of using a new tracheal prosthesis made of biomaterials to replace extensive circumferential tracheal defects.

DESCRIPTION

Three types of tracheal prostheses were developed and studied. Type I prosthesis was used in 8 mongrel dogs (group A), type II in 4 dogs (group B), and type III in 4 dogs (group C).

EVALUATION

In group A, one died from prosthetic dehiscence, another from anastomotic leakage, and the others had uneventful postoperative courses. The implanted prosthesis was completely incorporated with the recipient trachea, where different lengths of reepithelialization occurred on the luminal surface of the reconstructed trachea. Macroscopic examination showed scattered and different sizes of neo-ossification surrounding the implanted prosthesis. The prosthesis was radioopaque when exposed to routine x rays. In contrast, a relatively high number of complications occurred postoperatively in groups B and C.

CONCLUSIONS

Type I tracheal prosthesis, with further improvements, may be the optimal tracheal graft to replace circumferential tracheal defects, and appears very promising for clinical application.

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.

Transplantation of the cryopreserved tracheal allograft in growing rabbits

BACKGROUND

Surgical treatment of the congenital tracheal stenosis is challenging, and the long-term fate of transplanted tracheal allograft remains unclear. The authors evaluated the morphologic changes of the cryopreserved tracheal allograft after transplantation in a growing rabbit model.

METHODS

Each allograft (n = 7) was harvested from 90- to 120-day-old Japanese rabbits, immersed in the preservation solution, and stored in a programmable freezer until reaching -80 degrees c and then kept in liquid nitrogen for 1 week. Orthotopic tracheal transplantation of 7 tracheal rings in an end-to-end fashion was performed in age-matched young rabbits without immunosuppression. The grafts were assessed at 1 week, 1 month, and 3 months after transplantation. As controls, fresh autografts also were evaluated after the same procedure.

RESULTS

Two animals died of pneumonia. The body weight gain was similar in both groups. All grafts were patent, but no allografts showed normal growth in length or diameter. Microscopic findings of the allograft showed calcification of the tracheal cartilage without infiltration of inflammatory cells and marked lymphocyte proliferation in the subepithelium.

CONCLUSIONS

Cryopreserved tracheal allografts without immunosuppressant showed favorable patency of the trachea at 3 months; however, no growth of the allograft occurred in this animal model. The problem of calcification of the allograft remains to be solved.