Rat model for a vascularized laryngeal allograft

Laryngeal graft after total laryngectomy in humans: A SWiM analysis

Evaluation of the results of laryngeal transplantation (LT) in humans. Analysis of 3 bibliographic databases with the keywords "larynx, transplantation, autograft". In total, 626 abstracts were read and 25 articles selected. The main objective was to analyze the characteristics of laryngeal transplant patients. The accessory objectives comprised analysis of operative technique, immunosuppressive treatment and results. Four articles were selected for analysis. Two patients were transplanted after total laryngectomy for laryngeal carcinoma and 2 after laryngeal trauma. Three of the 4 patients had true transplantation with arterial, venous and neural microanastomosis. Two patients were decannulated and the tracheostomy tube was maintained in the other 2. Three of the 4 patients had good-quality phonation and could feed without a gastric tube. One patient died of carcinoma progression and 1 patient had to be explanted 14 years after transplantation. The number of LTs reported is too small for scientific determination of the place of this intervention in laryngology. The published results could, at first sight, suggest that the future of LT is uncertain. However, several elements, also suggest that otolaryngologists should continue to take an interest in this technique.

A New Animal Model of Laryngeal Transplantation

Only three laryngeal transplants have been described in the literature to date, and none of the techniques has enabled a completely satisfactory functional result to be obtained. This article presents a new model of laryngeal transplantation, with quality of revascularisation of the transplant being the principal objective and optimisation of the various steps of the procedure, with the integration of a new reinnervation technique as a secondary objective. We present a preclinical animal study. Three pig larynges removed in vivo underwent allotransplantation according to the same protocol. The quality of the revascularisation was examined immediately after the surgery as well as by endoscopy for one animal on the fourth day after the operation. The mean time of cold ischaemia was 3 h 15 min. The anaesthetic tolerance of the pigs was excellent. Revascularisation was achieved and judged to be excellent for the three transplants immediately after the operation and the endoscopy performed for one pig on the fourth day after the operation confirmed this result. The anatomical similarities also enabled the application and integration of an innovative technique of laryngeal reinnervation into the various phases of the operation. We describe a reliable and reproducible animal model for laryngeal transplantation. Its application in humans can be envisaged.

Perfusion-Decellularized Larynx as a Natural 3D Scaffold in a Rabbit Model

INTRODUCTION

Decellularized larynges could be used as scaffolds to regenerate the larynx. The purpose of this study was to establish a perfusion decellularization protocol to produce a 3-dimensional whole laryngeal extracellular matrix (ECM) scaffold in a rabbit model.

METHODS

The larynges of 20 rabbits assigned to the study group were harvested and decellularized using a perfusion decellularization protocol, while the larynges of 10 rabbits in the control group were harvested and untreated. Macroscopic and microscopic morphological analyses, a molecular analysis, a cellular content analysis, and scanning electron microscopy were performed.

RESULTS

A histological analysis showed the absence of cellular components, the presence of the ECM, and an intact cartilage structure filled with chondrocytes. The mean total DNA amounts of the native larynx, decellularized larynx, and decellularized cartilage-free larynx were 1,826.40, 434.70, and 41.40 μg/µL, respectively; those for the decellularized larynx and decellularized cartilage-free larynx were significantly lower (p < 0.001 and p < 0.001, respectively). The total amount of DNA in the decellularized sample was significantly lower compared to that in the native sample, at 57.2% in cartilage (p < 0.001), 2.4% in the thyroid gland (p < 0.001), 2.7% in muscle (p < 0.001), 1.6% in vessels (p < 0.001), and 4.8% in the vocal cords (p < 0.001).

CONCLUSION

Our perfusion decellularization protocol is feasible and reproducible to produce a 3-dimensional whole laryngeal ECM scaffold in a rabbit.

Animal models for basic and translational research in reconstructive transplantation

Reconstructive transplantation represents a bona fide option for select patients with devastating tissue loss, which could better restore the appearance, anatomy, and function than any other conventional treatment currently available. Despite favorable outcomes, broad clinical application of reconstructive transplantation is limited by the potential side effects of chronic multidrug immunosuppression. Thus, any reconstructive measures to improve these non-life-threatening conditions must address a delicate balance of risks and benefits. Today, several exciting novel therapeutic strategies, such as the implementation of cellular therapies including bone marrow or stem cells that integrate the concepts of immune regulation with those of nerve regeneration, are on the horizon. The development of reliable and reproducible small and large animal models is essential for the study of the unique immunological and biological aspects of vascularized composite allografts and to translate such novel immunoregulatory and tolerance-inducing strategies and therapeutic concepts from the bench to bedside. This review provides an overview of the multitude of small and large animal models that have been particularly designed for basic and translational research related to reconstructive transplantation.

Experimental models of composite tissue allograft transplants

Composite tissue allotransplantation has been recently introduced as a potential clinical treatment for complex reconstructive procedures including traumatic injuries, cancer ablative surgeries, or extensive tissue loss secondary to burns. Composite tissue allografts (CTAs) consist of heterogeneous tissues including skin, fat, muscle, nerves, lymph nodes, bone, cartilage, ligaments, and bone marrow with different antigenicities. Thus, composite tissue structure is considered to be more immunogenic than solid organ transplants. In this article, we present the experimental applications of CTA transplantation. To study the mechanisms of CTA acceptance and rejection, different experimental models, strategies, and different immunosuppressive protocols were used.

Laryngeal transplantation: research, clinical experience, and future goals

The loss of a functional voice because of trauma or laryngectomy can have a devastating impact on a patient's self-esteem and overall quality of life. Unfortunately, even with advances in organ preservation therapy, total laryngectomy is frequently necessary in the treatment of laryngeal carcinoma. Over the past several years, the senior author initiated research into laryngeal transplantation with the goal of restoring lung-powered speech for these patients. The research led to the development of an animal model and several groundbreaking studies in this area. Investigations into the use of irradiation, single-drug and multidrug immunosuppression, and the effects of mammalian target of rapamycin (mTOR) inhibitors have produced significant insight into laryngeal allograft preservation. The laboratory research culminated in the first successful total laryngeal transplant in 1998. The patient had suffered significant laryngeal trauma and strongly desired return of laryngeal phonation. The patient has been maintained on multidrug immunosuppression with minimal difficulties. Now more than 8 years after the procedure, the patient continues to have an excellent voice and dramatically improved quality of life. Recent data suggest that altered immunosuppression schedules and the use of mTOR inhibitors may allow patients to minimize immunosuppression-related adverse effects and ameliorate the risk of developing recurrent or de novo carcinoma. These data, when considered in combination with the progress made over the past 14 years, lead us to believe that the future of laryngeal transplantation is bright.

Réalités et perspectives des allotransplantations laryngées

Laryngeal stenosis or amputation for tumor definitely impairs laryngeal functions with negative impact on quality of life. Experimental laryngeal transplantation has been carried out for nearly 40 years hoping that human transplantation would become feasible in the near future. Nearly 10 years ago, a 40 years old man with a long-standing history of recalcitrant laryngeal stenosis, benefited from a vascularized laryngeal allotransplantation. Speech and deglutition resumed quickly making of this first attempt a success. Although a tracheostomy canula and immunosuppressive regimen are still necessary, this man enjoyed a tremendous improvement in this quality of life. Cumulated experiences tend to demonstrate that laryngeal transplantation in human is not only feasible, but may represents the only chance for rehabilitation of number of laryngeal cripple. Induction of a functional tolerance may allow the necessary evaluation of laryngeal allotransplantation in humans.

Laryngeal Sensation Recovery by Reinnervation in Rabbits

OBJECTIVES/HYPOTHESIS

To assess the possibilities of restoring laryngeal sensation in an animal model by way of the internal branch of the superior laryngeal nerve (ibSLN) bilateral section and anastomosis to itself or to transposition nerves (i.e., lingual, glossopharyngeal, and great auricular nerves).

STUDY DESIGN

Prospective study using New Zealand rabbits.

METHODS

Six groups of rabbits were operated on and evaluated: healthy controls (n = 6); section without reinnervation (denervated group, n = 7); section and reinnervation with ibSLN (SLN-SLN group, n = 9); and section and anastomosis with the lingual nerve (lingual group, n = 7), the glossopharyngeal nerve (glossopharyngeal group, n = 6), and the great auricular nerve (GA group, n = 7). After 9 months, recovery of a laryngeal closure reflex was assessed by stimulation of the epiglottis and nerve anastomosis.

RESULTS

Laryngeal sensation was restored in 14.3% in the denervated group, 66.6% in the SLN-SLN group, 71.4% in the lingual group, 100% in the GA group (P < .001), 50% in glossopharyngeal group. Some anastomoses were severed. When anastomosis was intact, a laryngeal closure reflex was observed in 91.7% of the rabbits of the SLN-SLN group (P < .001), 80% in the lingual group (P < .001), 100% in the GA group (P < .05) and 100% of the glossopharyngeal group.

CONCLUSIONS

Rehabilitation of supraglottic laryngeal sensation is feasible by way of anastomosis of the ibSLN to itself, but also to the lingual, glossopharyngeal, and great auricular nerves. These results suggest that this type of procedure may be useful in humans to prevent aspiration and subsequent pneumonia as related to lesions of the laryngeal reflex pathway. It could also be considered one stage toward the functional rehabilitation of a transplanted larynx.

Early immunological changes associated with laryngeal transplantation in a major histocompatibility complex-matched pig model

Laryngeal transplantation is an increasingly viable proposition for patients with irreversible diseases of the larynx. One human transplant has been performed successfully, but many questions remain before routine transplantation can begin. In order to measure the immunological changes in mismatched transplants, it is first necessary to know the immediate combined effects of ischaemia-reperfusion injury (IRI) plus the added insult of major surgery in a fully matched setting. We measured the changes in immunologically active mucosal cells following 3 h of cold ischaemia and 8 h of in situ reperfusion in a major histocompatibility complex (MHC)-matched minipig model (n = 4). Biopsies were prepared for quantitative, multiple-colour immunofluorescence histology. The number of immunologically active cells was significantly altered above (supraglottis) and below (subglottis) the vocal cords following transplantation and reperfusion (P < 0.05, P < 0.001, respectively). However, the direction of the change differed between the two subsites: cell numbers decreased post-transplant in the supraglottis and increased in the subglottis. Despite the statistical evidence for IRI, these changes were less than the large normal inter- and intrapig variation in cell counts. Therefore, the significance of IRI in exacerbating loss of function or rejection of a laryngeal allograft is open to question. Longer-term studies are required.

The effect of donor-specific transfusion upon rejection in a rat model of laryngeal transplantation

Lifelong immunosuppression carries significant morbidity, and techniques to reduce or eliminate such immunosuppression might expand laryngeal transplantation. This study investigates the ability of donor-specific transfusion to establish tolerance in a rat model of laryngeal transplantation. A total of 289 transplants were performed from Lewis-Brown-Norway donors to Lewis recipients. Donor-specific transfusion was provided as single intravenous injections of donor splenocytes 1 hour before transplantation. Different combinations of in vitro irradiation of donor larynges and postoperative cyclosporine doses provided additional immunomodulation. Allograft rejection was scored histologically at sacrifice 15 or 30 days posttransplant. Multivariate analysis was performed across all groups, and paired analyses compared groups with and without donor-specific transfusion. Donor-specific transfusion did not improve rejection score, although increased cyclosporine dose did (P < .001). Donor splenocyte injection on the day of transplantation does not establish tolerance to laryngeal allografts or permit reduction of other immunosuppression. Other immunomodulatory strategies to establish tolerance in rat laryngeal transplantation require further investigation.

An ex vivo model for reperfusion of laryngotracheal grafts

OBJECTIVE

To describe the development of an ex vivo model to facilitate the study of ischemia-reperfusion injury in laryngotracheal grafts taken from Minnesota minipigs.

STUDY DESIGN

This is a descriptive study.

METHODS

Laryngotracheal grafts from Minnesota minipigs were harvested and placed in cold storage for 3 hours. Autologous blood was used to reperfuse the graft for up to 8 hours using the described reperfusion model.

RESULTS

By altering retrieval technique and pressures within the graft, we demonstrated healthy grafts after 8 hours of reperfusion.

CONCLUSIONS

Ex vivo reperfusion offers a range of experimental advantages over in vivo reperfusion including close control of interventions, ease of outcome measurement, and reduction in animal use. This model is now ready to be used for further studies of interventions to reduce ischemia-reperfusion injury in these grafts.

Direct Revascularization is Superior for Rat Parathyroid Allotransplantation with Fk506

Parathyroid gland allotransplantation has been a challenging goal for decades. Our objective was to optimize a parathyroid allotransplantation model for analysis of short-term or low-dose immunosuppressive regimens. Rats that had undergone parathyroidectomy received parathyroid allografts either by direct microvascular anastomoses as part of a composite laryngotracheal graft or by direct implantation into hind limb muscle. All rats were maintained on daily low-dose FK506 (tacrolimus). Intact serum parathyroid hormone (PTH) levels for both groups were recorded over a period of at least 45 days and compared with a repeated-measures mixed model. We found that microvascular anastomosis was superior to implantation for parathyroid gland survival, as all revascularized grafts immediately produced normal levels of PTH, whereas implanted grafts had a significantly slower recovery of function (p < .001). Four of the 11 implanted grafts (36%) never produced detectable PTH levels. Using this model, we are developing innovative strategies that will lead to successful parathyroid allotransplantation without the need for chronic immunosuppression.

Evaluation of parathyroid hormone as a functional biological marker of rat laryngeal transplant rejection

OBJECTIVES/HYPOTHESIS

Short-term immunosuppressive protocols in a preclinical rat model that have led to prolonged survival of the graft in preliminary trials were investigated. Rat allografts, by their heterotopic nature, do not allow direct examination or functional interpretation. The primary objective of the study was to identify a reliable functional biological marker allowing monitoring of graft status. A secondary goal was to use this marker to indicate onset of rejection.

STUDY DESIGN

The authors elected to study rat parathyroid hormone as a functional marker of laryngotracheal complex rejection. Theoretically, a pulsed immunosuppressive regimen that is administered when parathyroid hormone levels begin to fall could prevent rejection.

METHODS

Eleven Lewis recipient rats underwent parathyroidectomy one week before laryngeal transplantation. Parathyroid hormone levels were obtained on various days following transplantation, then analyzed with an intact rat parathyroid hormone assay. Animals were killed on different days to allow for comparison of parathyroid hormone levels with histopathological signs of rejection.

RESULTS

All animals had undetectable levels of parathyroid hormone before transplantation. By 24 hours after transplantation, parathyroid hormone levels were within normal range. At 72 hours, the parathyroid hormone levels dropped precipitously. Rejection of parathyroid glands paralleled the early histological changes of rejection seen in the other anatomical areas of interest in the laryngotracheal graft.

CONCLUSION

The study represents the first time a hematological marker has been identified that has predictive value for rejection of transplanted rat larynges. As such, it not only enables a 3-month experimental window with reasonable numbers of animals, but also opens the door for novel sequencing of immunosuppressive modalities.

Rat model of laryngeal transplantation with normal circulation maintained by combination with the tongue

Recent research on laryngeal transplantation used a rat model with physiologically abnormal circulation, because the common carotid artery was used for venous drainage. Since a model with normal circulation is better for accurate assessment, we developed a vascularized laryngeal graft, using the common carotid artery as the arterial supply and the external jugular vein as the venous drainage. The transplant included other tributaries from the tongue and the pharynx by combination with the tongue, because the tributaries from the larynx were very small. Ten transplants were performed. The transplanted organs were examined daily. Seven days after transplantation, the composite grafts were evaluated histologically. The mortality rate was 10%. All composite grafts were fully viable, and their structure was maintained in the remaining nine rats. Our model is appropriate for experiments on laryngeal transplantation.

Tacrolimus and mycophenolate mofetil provide effective immunosuppression in rat laryngeal transplantation

OBJECTIVES/HYPOTHESIS

Tacrolimus is efficacious in several transplantation settings. Some studies have demonstrated improved results using combination therapy with mycophenolate mofetil. Our primary objective was to evaluate the efficacy and optimal dosing of tacrolimus in preventing rejection, using an established rat model of laryngeal transplantation. Further, the ability of mycophenolate to allow lower dosing of tacrolimus while achieving equivalent immunosuppression was investigated.

STUDY DESIGN

A dosage efficacy study with 10 experimental arms was conducted.

METHODS

Dosage groups were 0.1, 0.2, 0.3, and 0.6 mg/kg tacrolimus alone and 0.1 mg/kg tacrolimus combined with 15 mg/kg mycophenolate mofetil, 0.1 mg/kg tacrolimus combined with 30 mg/kg mycophenolate mofetil, 0.1 mg/kg tacrolimus combined with 40 mg/kg mycophenolate mofetil, 0.2 mg/kg tacrolimus combined with 15 mg/kg mycophenolate mofetil, 0.2 mg/kg tacrolimus combined with 30 mg/kg mycophenolate mofetil (30 d only), and 0.2 mg/kg tacrolimus combined with 40 mg/kg mycophenolate mofetil. Each group contained 8 to 10 rats. Grafts were harvested for histopathological analysis on day 15 or 30 after transplantation. Histopathological appearance of the graft was blindly graded according to an established scale. Dosage groups were compared on rejection score using Wilcoxon's rank sum test and the Jonckheere-Terpstra test for trend.

RESULTS

There was a significant association between increasing dose of tacrolimus and decreasing rejection score at both 15 and 30 days (P <.001). In the groups treated with 0.1 mg/kg T, an increasing dose of mycophenolate was associated with lower rejection scores at both 15 and 30 days (P =.001). In the group treated with 0.2 mg/kg T, there was no evidence that the addition of mycophenolate resulted in lower rejection at 15 days. However, at 30 days, combination therapy with increasing doses of mycophenolate was associated with decreasing rejection score (P =.002).

CONCLUSIONS

Tacrolimus is an effective immunosuppressive agent for laryngeal transplantation. Mycophenolate mofetil allows lower doses of tacrolimus to be used while preserving graft viability in the early post-transplantation period.

Immunosuppressive effect of irradiation in the murine laryngeal transplantation model: a controlled trial

Since the first successful human laryngeal transplantation in 1998, research continues toward developing less-morbid immunosuppressive protocols. Although irradiation of donor organs is known to decrease acute rejection, the most advantageous method of radiation delivery is still unknown. Using a rat laryngeal transplant model, we sought to determine the most beneficial timing and delivery method of irradiation. A prospective study was undertaken including 16 treatment arms of 10 to 30 animals each (189 transplantations). The animals received 800 cGy before transplantation to the donor larynx in vivo, the donor larynx in vitro, or the recipient animal's neck. The transplantation occurred at 24 hours, 5 days, or 10 days after irradiation. The transplanted larynges were harvested 15 days after transplantation and histologically scored for rejection. Irradiation of allogeneic transplantations demonstrated a strongly protective effect from rejection as compared to no irradiation (p < .001), regardless of the method of radiation delivery or the amount of time between irradiation and transplantation (p = .78). Irradiation of donor larynges between allogeneic rats has a protective effect, reducing the degree of acute rejection when irradiation is used as the single mode of immunosuppression, and is unrelated to either the timing or the mode of delivery of the irradiation.

Rat laryngeal transplant model: technical advancements and a redefined rejection grading system

The rat laryngeal transplant model, introduced in 1992, laid the basic science foundation that contributed to the first successful human larynx transplant in 1998. Over 1,500 rat transplants later, numerous modifications have improved the model, increasing the initially reported evaluability rate of 50% to almost 100%. The observed histologic rejection process has been altered, as well. We report the technique modifications, as well as the results of a new study using nonimmunosuppressed, allogenic transplantations, in order to define a new rejection grading system. Using the updated model, we performed 50 transplantations between LBN(f1) donor rats and Lewis recipients. Larynges from 8 groups of 5 to 10 animals were harvested at intervals between 1 and 20 days after transplantation. The larynges were examined grossly and microscopically in a blinded manner for evidence of rejection. A multivariable linear regression model was used to define a new rejection grading scale. All 50 animals survived their assigned posttransplantation period. No animals exhibited vascular thromboses, for an evaluability rate of 100%. Histologic criteria in 7 categories and gross criteria in 5 categories demonstrated increased rejection proportional to the amount of time after transplantation. The equation [Group = -2.209 + 0.465 x (Size) + 0.901 x (VA Flow) + 0.613 x (Muscle) + 1.040 x (Thyroid)] reproducibly grades rejection on the basis of gross and histologic findings. New modifications to the rat laryngeal transplant model have conferred greatly improved animal survival rates and anastomotic patency rates. Additionally, the observed rates of rejection have been reduced in comparison to those of initial studies. This updated rejection staging system will be used to compare immunosuppressive regimens in future rat laryngeal transplant studies.

Model for experimental revascularized laryngeal allotransplantation

BACKGROUND

Although a human laryngeal transplant has been undertaken successfully, important questions remain that require a suitable animal model.

METHODS

A pig model for allotransplantation has been developed. Organ perfusion was studied in nine animals before four transplants were performed in congenic (unrecovered) animals and eight in unmatched (recovered) animals. Larynges were regularly examined endoscopically until death at 14 days. Immunosuppression included the use of tacrolimus. Revascularization was achieved by anastomosing the donor right cervical vascular tree to the recipient common carotid. In recovered animals, four allografts were placed orthotopically and four heterotopically.

RESULTS

The pig larynx was perfused adequately via the right cervical vascular tree and congenic grafts were well tolerated. Of eight allografts, seven were well tolerated and remained healthy for the duration of the study (14 days). One allograft became infected between days 4 and 7 after operation. Median operating time was 6 h, with a median cold ischaemia time of 3 h.

CONCLUSION

Revascularized allotransplants of the larynx can be undertaken reliably in pigs and this provides a preclinical model for studies of laryngeal transplantation.

Effects of adding steroids, in vitro irradiation, or both to cyclosporine immunosuppression in the murine laryngeal transplantation model

Adding oral prednisone or in vitro organ irradiation to an immunosuppressive regimen for laryngeal transplantation may allow cyclosporine dosage to be decreased without compromising organ rejection rates. Using an established rat laryngeal transplant model, we sought to determine whether combined immunosuppressive regimens decreased rejection rates. Twenty-two treatment groups of 10 animals each were studied. Cyclosporine was administered at 2 different historically low dosages (1.5 and 2 mg/kg per day) alone, in combination with prednisone, and with in vitro irradiation of the harvested larynx. At 15 days after transplantation, cyclosporine combined with prednisone did not significantly alter the mean severity of rejection. At 30 days after transplantation, rats treated with a combination of cyclosporine 2 mg/kg and prednisone 1 mg/kg showed the least amount of rejection. Rejection rates were significantly higher with 2 mg/kg cyclosporine alone (p < .00024). Irradiation did not significantly decrease the severity of rejection. These results demonstrate that at 1 month after transplantation, a combined steroid and cyclosporine regimen reduces the severity of rejection after laryngeal transplantation in an animal model. Our findings suggest that laryngeal transplant patients may be treated with low cyclosporine doses without experiencing organ rejection if steroids are added to the immunosuppressive regimen.

Effect of in vitro irradiation of donor larynges on cyclosporine requirements and rejection rates in rat laryngeal transplantation

Total lymphoid irradiation is an acknowledged adjunctive immunosuppressant in whole organ transplantation in humans and animals. Local irradiation administered for a similar purpose is at best controversial. We evaluated in vitro donor larynx irradiation immediately preceding laryngeal transplantation as an immunomodulator. Each donor larynx was pretreated with 7.34 Gy of radiation in vitro. After transplantation, cyclosporine was administered in doses of 5 mg/kg per day, 2.5 mg/kg per day, and 1 mg/kg per day for trial lengths of 15 days and 30 days. Each of these 6 groups consisted of 10 rats per group. Earlier data have shown cyclosporine dosed at 5 mg/kg per day, without irradiation, administered for 1 month to have varied efficacy. Established histologic criteria were used to determine rejection patterns. All recipient rats survived the 15-day and 30-day trials. In all 10 rats receiving 5 mg/kg per day of cyclosporine for 15 days, the harvested transplanted larynges were viable without evidence of meaningful rejection (mild rejection). In 9 of the 10 rats receiving 5 mg/kg per day of cyclosporine for 30 days, the transplanted larynges displayed no meaningful rejection (mild rejection). In 9 of the 10 rats receiving 2.5 mg/kg per day of cyclosporine for 15 days, the transplanted larynges displayed no meaningful rejection (mild rejection). One rat receiving 2.5 mg/kg per day of cyclosporine for 15 days had a transplanted larynx that displayed moderate rejection. In all 10 rats receiving 2.5 mg/kg per day of cyclosporine for 30 days, the transplanted larynges displayed no meaningful rejection (mild rejection). At 15 days, 5 rats treated with 1 mg/kg per day of cyclosporine displayed mild rejection, 2 displayed moderate rejection, 2 displayed advanced to moderate rejection, and 1 displayed severe rejection. At 30 days, 4 rats treated with 1 mg/kg per day of cyclosporine displayed moderate rejection, 2 displayed advanced to moderate rejection, and 4 displayed severe rejection. We conclude that pretransplantation in vitro irradiation of donor larynges has immunomodulatory effects, allowing reduced cyclosporine immunosuppression with less rejection.

An anatomic study of the rat larynx: establishing the rat model for neuromuscular function

The gross and microscopic anatomy of the rat larynx was studied with particular attention to myology and neuromuscular structures to further validate it as a model to evaluate morphologic and functional changes induced by botulinum injection. A laryngeal alar cartilage (LAIC), alar cricoarytenoid (ACA) muscle, and a superior cricoarytenoid muscle (SCA) were identified as anatomic structures not previously described. Two portions (medial and lateral) of the thyroarytenoid muscle (TA) were distinguished. The function of the ACA was suggested to be similar to the aryepiglottis muscle in humans and the function of the SCA was suggested to be similar to the human interarytenoid muscle. The predominant pattern of motor endplate (MEP) distribution in rat laryngeal muscles (posterior cricoarytenoid, lateral cricoarytenoid, cricothyroid, and SCA) was to have MEPs concentrated mostly at the midbelly of muscle where they were distributed throughout the cross-sectional area of the midbelly. The TA and ACA differed from this pattern. The lateral TA had MEPs concentrated at the anterior third of its belly and those of the medial TA were located at the midbelly. Motor endplates in the ACA were located mostly at the posterior portion of muscle. Muscle fiber-typing showed subtle differences between the intrinsic laryngeal muscles. Fast fibers were predominant in the rat laryngeal muscles. This study supports the expanded use of rats in studies of laryngeal neuromuscular function and disease in humans.

Reinnervation of the allograft larynx in the rat laryngeal transplant model

The rat model for a vascularized laryngeal allograft is duplicated with significant technical modifications. We report the addition of unilateral host-to-allograft recurrent laryngeal nerve anastomosis to this model. Long-term survival experiments determine the feasibility of reinnervation studies of the allograft larynx with this new mode. A total of 59 transplants have been performed on histocompatible Munich Wistar rats, 36 with attempted unilateral allograft reinnervation. Because of the initially high operative mortality rates, additions and modifications of the original technique resulting in reproducibly enhanced survival are detailed. Factors critical to the functional study of this model with regard to reinnervation are elucidated. Preliminary data on allograft reinnervation are reported as confirmed by videodocumentation of vocal fold mobility, evoked and spontaneous electromyography, and glycogen-depletion studies.

Laryngeal transplantation: a program for investigating new parameters

Laryngeal transplantation was actively investigated in the late 1960s and early 1970s using a dog model. An expanded knowledge base in immunobiology, pharmacology, and deglutition makes reassessment timely after an approximately 20-year hiatus. The basic parameters to be evaluated include varied methods of preservation, optimal immunosuppressive drug regimens, and the role of radiation therapy. Our current research protocol addressing the latter considerations is outlined, including a brief introduction of a new animal model developed specifically for this purpose. We will ultimately attempt to answer the question: Is laryngeal transplantation feasible?

The effects of cyclosporin A on transplanted rat allografts

Since 1983, Cyclosporin A (CsA) has been the most successful primary drug in preventing rejection of organ transplants. This study was designed to determine the efficacy and dose response of CsA in preventing rejection of LBNF-1 rat allografts to Lewis recipients. Four groups of animals were studied. Group I served as the control, and groups II, III, and IV were given daily intramuscular doses of CsA for 1 month. The groups were given doses of 5 mg/kg, 7.5 mg/kg, and 10 mg/kg, respectively. Sixty-eight animals were transplanted to get eight viable transplanted animals at 1 month in each CsA group. Laryngeal viability was assessed with both clinical and histological parameters. Groups II, III, and IV had representative clinically viable larynges. The histology varied and had some correlation with CsA dosage. Group II evidenced changes ranging from mild to severe rejection. Group III was more homogeneous with the most severe change being characterized as mild-to-moderate rejection. Group IV was the most uniform with all representative specimens showing only limited infiltration of inflammatory cells with intact mucosa and submucosal glands (mild rejection). None of the CsA groups evidenced the squamous metaplasia characteristic of the control group. CsA can prevent rejection of laryngeal allografts from LBNF-1 donors to Lewis recipients.