Human laryngeal allograft: shift of emphasis in transplantation

Immunosuppressive protocols after laryngeal transplantation: a systematic review

BACKGROUNDS

Larynx transplantation has been successfully performed four times, in 1998, 2010, 2015 and 2023 remained the ultimate goal of voice, feeding and breathing rehabilitation.

OBJECTIVE

Immunosuppressive protocols used during the previous successful larynx allotransplantation are detailed.

MATERIAL AND METHODS

A systematic review of the literature on PUBMED/Medline, Cochrane and Embase was conducted. Articles relating to actual human larynx transplantations were included.

RESULTS

Bibliography search gathered N = 10 publications related to the performance and follow-up of human laryngeal transplantations. N = 8 publications were included corresponding to N = 3 actual human larynx transplantations performed in 1998 and 2010 in the USA and in 2015 in Poland. Immunosuppression protocols, induction and maintenance strategies, rejection monitoring and history of all the three previous laryngeal grafts were detailed.

CONCLUSIONS

Beyond the surgical prowess, larynx transplantation is feasible and associated with a reasonably successful outcome when compared to other solid organ transplants. Immunosuppressive regimen protocols and technologies for the monitoring of the organ viability have evolved.

SIGNIFICANCE

The reevaluation of this surgical option serves as the reminder of the critical necessity to implement a meticulous immunosuppression protocol when transplanting this inherently immunogenic composite organ, the larynx.

Tissue-engineering the larynx: Effect of decellularization on human laryngeal framework and the cricoarytenoid joint

Decellularization approaches have been commonly used as alternative techniques to reconstruct tissues. However, due to the complex tissue compartmentation of the larynx, the decellularization process may not retain the characteristics necessary for the successful recreation of the larynx. The aim of this study was to assess the effect of the decellularization process on the framework of the human cadaveric larynx generally and the cricoarytenoid joint specifically. In this work, five freshly frozen human cadaveric larynges were decellularized utilizing a protocol that was previously demonstrated to be effective in decellularizing a porcine larynx. The decellularization protocol included: biological, chemical, and physical decellularization methods. Each specimen served as its own control to assess changes after decellularization. Studies and measurements included: histological, using Hematoxylin and Eosin (H&E) and Live/Dead™ stains; DNA quantification; micro-computed tomography (μ-CT) imaging; and biomechanical testing of the cricoarytenoid joints. The decellularization protocol took 12 days for each specimen. Microscopy of H&E stained samples demonstrated substantial removal of cells with preservation of the extracellular matrix that was more evident in cartilage than muscle specimens. Confocal microscope images of Live/Dead™ stained specimens also demonstrated almost complete removal of cells. Pre-decellularization cartilage-DNA quantity range was 27.0 to 336.8 ng/mg while post-decellularization DNA quantity range was 0 to 30.4 ng/mg (p = 0.031). For muscles, pre-decellularization DNA quantity range was 150.0 to 3,384.6 ng/mg, while post-decellularization DNA quantity range was 0 to 45.5 ng/mg (p = 0.031). μ-CT demonstrated preservation of the cartilaginous framework with a slight reduction of cricoarytenoid joint space. Furthermore, μ-CT demonstrated no significant reduction in the Housefield unit (p = 0.25) and mineral density (p = 0.25) after decellularization. Biomechanical testing demonstrated a non-significant reduction of forces required for anterior displacement of the arytenoid (mean reduction of forces, 0.1 ± 0.2 N, p = 0.16) and forces required for posterior displacement of the arytenoid (mean reduction of forces, 0.2 ± 0.3 N, p = 0.05). This study demonstrates effective decellularization of human larynges as evidenced by significant DNA depletion and preservation of extracellular matrix, which are outcomes that are required for a biological scaffold to regenerate a non-immunogenic larynx. The decellularization process caused minimal weakness in the cricoarytenoid joints due to treatment with multiple detergents and enzymes in the decellularization protocol.

Applied Bioengineering in Tissue Reconstruction, Replacement, and Regeneration

IMPACT STATEMENT

The use of autologous tissue in the reconstruction of tissue defects has been the gold standard. However, current standards still face many limitations and complications. Improving patient outcomes and quality of life by addressing these barriers remain imperative. This article provides historical perspective, covers the major limitations of current standards of care, and reviews recent advances and future prospects in applied bioengineering in the context of tissue reconstruction, replacement, and regeneration.

In vivo implantation of a tissue engineered stem cell seeded hemi-laryngeal replacement maintains airway, phonation, and swallowing in pigs

Laryngeal functional impairment relating to swallowing, vocalisation, and respiration can be life changing and devastating for patients. A tissue engineering approach to regenerating vocal folds would represent a significant advantage over current clinical practice. Porcine hemi-larynx were de-cellularised under negative pressure. The resultant acellular scaffold was seeded with human bone marrow derived mesenchymal stem cells and primary human epithelial cells. Seeded scaffolds were implanted orthotopically into a defect created in the thyroid cartilage in 8 pigs and monitored in vivo for 2 months. In vivo assessments consisted of mucosal brushing and bronchoscopy at 1, 2, 4, and 8 weeks post implantation followed by histological evaluation post termination. The implanted graft had no adverse effect on respiratory function in 6 of the 8 pigs; none of the pigs had problems with swallowing or vocalisation. Six out of the 8 animals survived to the planned termination date; 2 animals were terminated due to mild stenosis and deep tissue abscess formation, respectively. Human epithelial cells from mucosal brushings could only be identified at Weeks 1 and 4. The explanted tissue showed complete epithelialisation of the mucosal surface and the development of rudimentary vocal folds. However, there was no evidence of cartilage remodelling at the relatively early censor point. Single stage partial laryngeal replacement is a safe surgical procedure. Replacement with a tissue engineered laryngeal graft as a single procedure is surgically feasible and results in appropriate mucosal coverage and rudimentary vocal fold development.

Airway tissue engineering: an update

INTRODUCTION

Prosthetic materials, autologous tissues, cryopreserved homografts and allogeneic tissues have thus far proven unsuccessful in providing long-term functional solutions to extensive upper airway disease and damage. Research is therefore focusing on the rapidly expanding fields of regenerative medicine and tissue engineering in order to provide stem cell-based constructs for airway reconstruction, substitution and/or regeneration.

AREAS COVERED

Advances in stem cell technology, biomaterials and growth factor interactions have been instrumental in guiding optimization of tissue-engineered airways, leading to several first-in-man studies investigating stem cell-based tissue-engineered tracheal transplants in patients. Here, we summarize current progress, outstanding research questions, as well as future directions within the field.

EXPERT OPINION

The complex immune interaction between the transplant and host in vivo is only beginning to be untangled. Recent progress in our understanding of stem cell biology, decellularization techniques, biomaterials and transplantation immunobiology offers the prospect of transplanting airways without the need for lifelong immunosuppression. In addition, progress in airway revascularization, reinnervation and ever-increasingly sophisticated bioreactor design is opening up new avenues for the construction of a tissue-engineered larynx. Finally, 3D printing is a novel technique with the potential to render microscopic control over how cells are incorporated and grown onto the tissue-engineered airway.

Stem cell-based organ replacements-airway and lung tissue engineering

Tissue engineering requires the use of cells seeded onto scaffolds, often in conjunction with bioactive molecules, to regenerate or replace tissues. Significant advances have been made in recent years within the fields of stem cell biology and biomaterials, leading to some exciting developments in airway tissue engineering, including the first use of stem cell-based tissue-engineered tracheal replacements in humans. In addition, recent advances within the fields of scaffold biology and decellularization offer the potential to transplant patients without the use of immunosuppression.

Clinical applications of mesenchymal stem cells in laryngotracheal reconstruction

During the past several years, mesenchymal stem cells (MSCs) derived from adult tissue have rapidly moved from in vitro and animal studies into clinical trials as a therapeutic modality for a diverse group of clinical applications, including head and neck reconstruction. For many diseases, cell therapy could affect the underlying pathophysiologic processes through multiple pathways providing an advantage over current treatment modalities. There is an emerging body of evidence that MSCs have unique immunomodulatory properties in addition to the ability to differentiate into multiple tissue lineages which make them even more attractive for regenerative medicine. A variety of pre-clinical and clinical studies have shown that MSCs may have a useful role in tissue repair as well as engineering strategies in head and neck reconstructive surgery. Clinically, this has ranged from injection laryngoplasty to the implantation of a tracheal construct seeded with MSC-derived chondrocytes. Recent advances in stem cell immunobiology can offer insight to the multiple mechanisms through which MSCs could affect underlying pathophysiologic processes ranging from vocal fold scarring to composite tissue defects. Thorough evaluation of the current literature is necessary in understanding how MSCs could potentially revolutionize our approach to head and neck defects. The purpose of this review is to highlight the advances in MSC-based therapies in head and neck surgery, specifically laryngotracheal reconstruction. The clinical role of tissue-derived MSCs, though not well understood, holds promise for many therapeutic applications in regenerative medicine and reconstruction.

Complete traumatic laryngotracheal disruption--a case report and review

Blunt neck trauma is an infrequent cause of injury in the pediatric population; however, significant injury is possible even with minor trauma to the neck. The authors present the previously unreported case of a combined laryngotracheal and esophageal disruption as well as a severe laryngeal crush injury in a pediatric patient following a blunt, clothesline neck injury. Immediate management of laryngotracheal or esophageal separation is frequently discussed, but little information exists concerning long-term treatment and management of total laryngotracheal disruption and crush injuries in pediatric patients. A review of the literature is presented to address these concerns.

A survey of north american hand surgeons on their current attitudes toward hand transplantation

PURPOSE

Although composite tissue allotransplantation (CTA) is unparalleled in its potential to reconstruct "like with like," the risk-benefit ratio and clinical indications are difficult to determine. We examined current attitudes regarding the emerging field of CTA from those who treat complex hand injuries.

METHODS

A web-based survey regarding CTA was sent to members of the American Society for Surgery of the Hand, which identified their demographic data and practice profiles. Respondents' support for CTA and their assessment of the level of risk associated with these procedures were addressed. Additional questions focused on the clinical application of CTA with current immunosuppression, ethical issues surrounding CTA, and the indications for hand transplantation. Finally, 2 clinical situations that closely mirrored past hand transplantations were presented, and members evaluated their suitability for allotransplantation.

RESULTS

A total of 474 surgeons responded to the survey (22% response rate), who were divided in their opinion of hand transplantation with 24% in favor, 45% against, and 31% undecided. The majority (69%) consider this surgery to be a high-risk endeavor; however, a large percentage (71%) still believe it to be an ethical procedure when performed on properly selected patients. The most accepted indications for hand transplantation were loss of bilateral hands (78%) and amputation of a dominant hand (32%). Only 16% were in favor of performing transplants with the immunosuppression available today. In response to the clinical situation, 66% would offer transplantation to a bilateral hand amputee, whereas only 9% would offer transplantation to a patient with diabetes who had lost his or her dominant hand.

CONCLUSIONS

This survey demonstrates support for hand allotransplantation as a solution for dominant-hand and bilateral hand amputees. However, surgeons continue to be concerned about the adverse effects of immunosuppression and the risks of acute and chronic rejection, and many want to wait for the development of better immunologic treatment options.

Science of composite tissue allotransplantation

The science of composite tissue allotransplantation (CTA) is rooted in progressive thinking by surgeons, fueled by innovative solutions, and aided by understanding the immunology of tolerance and rejection. These three factors have allowed CTA to progress from science fiction to science fact. Research using preclinical animal models has allowed an understanding of the antigenicity of complex tissue transplants and mechanisms to promote graft acceptance. As a result, translation to the clinic has shown that CTA is a viable treatment option well on the way of becoming a standard of care for those who have lost extremities and suffered large tissue defects. The field of CTA has been progressing exponentially over the past decade. Transplantation of hands, larynx, vascularized knee, trachea, face, and abdominal wall has been performed. Several important observations have emerged from translation to the clinic. Although it was predicted that rejection would pose a major limitation, this has not proven true. In fact, steroid-sparing protocols for immunosuppression that have been successfully used in renal transplantation are sufficient to prevent rejection of limbs. Although skin is highly antigenic when transplanted alone in animal models, when part of a CTA, it has not proven to be. Chronic rejection has not been conclusively demonstrated in hand transplant recipients and is difficult to induce in rodent models of CTA. This review focuses on the science of CTA, provides a snapshot of where we are in the clinic, and discusses prospects for the future to make the procedures even more widely available.

Composite tissue transplantation: a rapidly advancing field

Composite tissue allotransplantation (CTA) is emerging as a potential treatment for complex tissue defects. It is currently being performed with increasing frequency in the clinic. The feasibility of the procedure has been confirmed through 30 hand transplantation, 3 facial reconstructions, and vascularized knee, esophageal, and tracheal allografts. A major drawback for CTA is the requirement for lifelong immunosuppression. The toxicity of these agents has limited the widespread application of CTA. Methods to reduce or eliminate the requirement for immunosuppression and promote CTA acceptance would represent a significant step forward in the field. Multiple studies suggest that mixed chimerism established by bone marrow transplantation promotes tolerance resulting in allograft acceptance. This overview focuses on the history and the exponentially expanding applications of the new frontier in CTA transplantation: immunology associated with CTA; preclinical animal models of CTA; clinical experience with CTA; and advances in mixed chimerism-induced tolerance in CTA. Additionally, some important hurdles that must be overcome in using bone marrow chimerism to induce tolerance to CTA are also discussed.

Management of Larynx and Trachea Donors

INTRODUCTION

Laryngeal transplantation is a possibility for patients with irreversible laryngeal disease, such as complex trauma and larynx cancer. The objective of performing this procedure was to solve problems that these patients face with a laryngectomy. The medical literature has reviews about larynx transplantations, but almost nothing about the larynx donor. The following is our experience on management of these donors.

MATERIALS AND METHODS

Selection criteria was as follows: (1) 18-50 years old; (2) gender and ABO blood type matched between donor and recipient; (3) No abuse of tobacco, cocaine, and marijuana, (4) tracheal intubation time <3 days; and (5) time in the intensive care unit <7 days. The preservation was simple hypothermia with larynx infusion via the carotid artery with University of Wisconsin solution.

RESULTS

Between 2001 and 2006, we managed 25 donors, among whom 12 grafts were discarded. The 13 larynx donors were of average age 27.2 +- 7.9 years and their cause of death was head trauma. Each was of male and 12 were multiorgan donors. Three donors had previous consumption of tobacco and 2 donors of marijuana. There were 2 cases of acute rejection episodes. Graft survival rate at 2 years was 90%.

DISCUSSION

These donors may have differences from other multiorgan donors: (1) they do not require strict fluid management; (2) vasoactive agents may be used in higher doses than in organ donors, and (3) the larynx tolerates hemodynamic instability. It was necessary to use some donors who had used addictive substances, showing that some selection criteria may be flexible. There was no conflict between thoracic surgeons and larynx surgeons. The priority always was for life-saving organs. Family consent was sometimes difficult because of the retrieval times and body donor reconstruction. The larynx surgery retrieval demanded an additional 2-5 hours during routine multiorgan donor surgery, and always the family asked about body reconstruction. The body appearance was always preserved.

The larynx as an immunological organ: immunological architecture in the pig as a large animal model

The larynx is a mucosal organ positioned at the divergence of the respiratory and digestive tracts. It is exposed to a wide variety of environmental components, including foreign antigens, tobacco smoke, laryngopharyngeal reflux and pollutants. The mucosal immune system generates either active immune responses or tolerance, depending on the nature of the antigen and we hypothesize that the larynx is important organ for immunological decision-making in the airway. Because the pig is an ideal large animal model in which to explore laryngological research questions, such as those relating to laryngeal transplantation, we investigated the normal mucosal immunology of the porcine larynx. Pig larynges and tracheae were processed and prepared for bright-field microscopy and quantitative, multiple-colour immunofluorescence histology using pig-specific monoclonal antibodies. There was an abundance of immunologically active cells within the mucosa of the larynx and trachea of both the newborn and adult animal. Specifically, major histocompatibility complex class II (MHC class II+) cells, CD4+ and CD8+ cells were identified, although regional differences in numbers were apparent: specifically, the supraglottis contained fewer immunologically relevant cells than other sites sampled. There was a significant correlation between the numbers of MHC class II+ and CD4+ cells indicating co-ordinate regulation and therefore functional local interactions. The presence of such an immunological structure suggests that the larynx may have important functions in respiratory immunology and that it may trigger strong alloresponses after laryngeal transplantation.

Heterotopic en bloc tracheobronchial transplantation with direct revascularization in pigs

OBJECTIVE

This article describes the application of a novel aortic tube technique for directly revascularized tracheobronchial transplantation with dual blood supply in pigs.

METHODS

Eleven adult Large White pigs underwent heterotopic tracheal transplantation with a dual revascularization technique (inferior thyroid artery and bronchial artery). Seven tracheobronchial grafts were perfused ex vivo, and hemodynamic data were collected.

RESULTS

At the last evaluation, 6 pigs had normally epithelialized mucus-producing allografts with correct morphologic conformation and cartilage viability. The histopathologic examination revealed homogeneous tissue regardless of biopsy site (trachea, carina, or bronchi), demonstrating the efficacy of the revascularization procedure. Four animals had early ischemic necrosis develop, 2 from acute rejection and 2 from technical mishap. One additional pig had acute rejection starting on the 14th postoperative day. The CD4(+)/CD8(+) ratio was maintained close to or above 0.8 in the subgroup with rejection and below 0.6 in the animals that were correctly immunosuppressed. Pressure-flow curves in 7 ex vivo tracheobronchial grafts showed a nonsignificant difference (P <.12) in vascular resistance between the bronchial artery territory (lower resistance) and the inferior thyroid artery territory.

CONCLUSIONS

For the first time, a transplantation technique encompassing the entire trachea, carina, and stem bronchi has been made possible. By means of the dual inferior thyroid and bronchial artery axis, we were able to obtain a structurally healthy and functional graft to replace the main airway.

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.

Past, present, and future research in the field of composite tissue allotransplantation

In September 1998, a surgical team in Lyon, France, performed the first successful hand transplant. After this historic event, in January 1999, the University of Louisville performed the first hand transplant in the United States. These events sparked interest and debate concerning the justification of performing limb allotransplantation. The field of composite tissue allotransplantation (CTA) has made significant advances in the past two decades, yet advancement of the applications of CTA into the clinical arena had been fairly limited to this point. The most inherent controversy in CTA involves the fact that the clinical applications for the most part involve restoration of function and/or structural integrity. These procedures are done essentially for quality-of-life concerns, not life-saving issues. Present concern involves subjecting CTA recipients to a lifetime of postoperative immunosuppressive therapy. We cannot fully understand where we stand at present and in what future directions the field is heading unless we have an understanding of where we have been in composite tissue transplantation. This article reviews the historical aspects of CTA, discusses the present state of CTA, and speculates on potential future applications of CTA.

Experimental model of anorectal transplantation

BACKGROUND

Anorectal transplantation with pudendal nerve anastomosis after rectal excision is a possible strategy that would avoid a colostomy and recreate potentially normal anorectal function. This study investigates the technical feasibility of anorectal transplantation with pudendal nerve and inferior mesenteric artery and vein anastomosis in a porcine model.

METHODS

Four female pigs (22-42 kg) provided donor anorectum for four male recipients (29-39 kg) under standard general anaesthesia. The donor operation involved abdominoperineal excision of rectum (APR) taking the anal sphincter, pudendal neurovascular bundle and inferior mesenteric vessels. The recipient underwent APR, transperineal introduction of the donor graft, anastomoses of the rectum, inferior mesenteric vessels and pudendal neurovascular bundle, and perineal closure. Recorded variables were duration of each step of transplantation, ischaemic time, dimensions of anastomosed structures and postoperative graft viability. Animals were killed at 24 h, the state of the graft was noted and tissue was taken for confirmatory histology.

RESULTS

Mean operation time was 372 (range 303-435)min. Mean ischaemic time was 118 (100-130)min. Before death, observation at laparotomy revealed two pink grafts, one slightly dusky but healthy graft and one outright failure, reflecting the state of the mesenteric vessels, which were patent in three and thrombosed in one. Histological examination showed no difference between control biopsies and the three cases with satisfactory mesenteric flow. Gross ischaemia was present histologically in the failed case.

CONCLUSION

Anorectal transplantation is technically feasible in a pig model. Longer-term studies are now needed to assess return of function and overcome rejection issues.

Sensory nerve supply of the human oro- and laryngopharynx: a preliminary study

To date, the details of human sensory innervation to the pharynx and upper airway have not been demonstrated. In this study, a single human oro- and laryngopharynx obtained from autopsy was processed with a whole-mount nerve staining technique, Sihler's stain, to determine its entire sensory nerve supply. The Sihler's stain rendered all mucosa and soft tissue translucent while counterstaining nerves. The stained specimen was then dissected and the nerves were traced from their origins to the terminal branches. It was found that the sensory innervation of the human pharynx is organized into discrete primary branches that innervate specific areas, although these areas are often connected by small neural anastomoses. The density of innervation varied, with some areas receiving almost no identifiable nerve supply (e.g., posterior wall of the hypopharynx) and certain areas contained much higher density of sensory nerves: the posterior tonsillar pillars; the laryngeal surface of the epiglottis; and the postcricoid and arytenoid regions. The posterior tonsillar pillar was innervated by a dense plexus formed by the pharyngeal branches of the IX and X nerves. The epiglottis was densely innervated by the internal superior laryngeal nerve (ISLN) and IX nerve. Finally, the arytenoid and postcricoid regions were innervated by the ISLN. The postcricoid region had higher density of innervation than the arytenoid area. The use of the Sihler's stain allowed the entire sensory nerve supply of the pharyngeal areas in a human to be demonstrated for the first time. The areas of dense sensory innervation are the same areas that are known to be the most sensitive for triggering reflex swallowing or glottic protection. The data would be useful for further understanding swallowing reflex and guiding sensory reinnervation of the pharynx to treat neurogenic dysphagia and aspiration disorders.

A preclinical model for laryngeal transplantation: anatomy and mucosal immunology of the porcine larynx

BACKGROUND

A major step in translating work on laryngeal transplantation into clinical practice is the establishment of a preclinical model. We have investigated the anatomy and mucosal immunology of the porcine larynx in eight Minnesota Minipigs (12-37 weeks).

METHODS

Neck dissections were carried out and the vascular tree was mapped. Snap-frozen biopsies from epiglottis, supraglottis, glottis, and subglottis were prepared for conventional histology, immunohistochemistry (CD45), and single and two-color immunofluorescence (CD3, MHC-II, CD45).

RESULTS

The anatomy of the laryngeal skeleton was broadly similar to that of the human larynx. The blood supply is predominantly via the caudal thyroid vessels, with assistance from the cranial laryngeal artery. The porcine larynx is clearly highly immunologically active. Structured collections of leukocytes were found in the mucosal epithelium, around tubuloacinar glands, and occasionally in the submucosa. MHC-II and CD 3 cells were predominantly found within the epithelium. The highest densities of all cell types were observed in the epiglottis, tailing off caudally. The lowest densities were seen in the vocal cords.

CONCLUSIONS

The porcine larynx is both anatomically and immunologically similar to the human larynx and contains a high level of immunological organization. It presents an ideal preclinical model for laryngeal transplantation.

Anatomy of the human internal superior laryngeal nerve

The mucosa of the larynx contains one of the most dense concentrations of sensory receptors in the human body. This sensitivity is used for reflexes that protect the lungs, and even momentary loss of this function is followed rapidly by life-threatening pneumonia. The internal superior laryngeal nerve (ISLN) supplies the innervation to this area, and, to date, the distribution and branching pattern of this nerve is unknown. Five adult human larynges were processed by using Sihler's stain, a technique that clears soft tissue while counterstaining nerves. The whole-mount specimens were then dissected to demonstrate the branching of the ISLN from its main trunk down to the level of terminal axons. The human ISLN is divided into three divisions: The superior division supplies mainly the mucosa of the laryngeal surface of the epiglottis; the middle division supplies the mucosa of the true and false vocal folds and the aryepiglottic fold; and the inferior division supplies the mucosa of the arytenoid region, subglottis, anterior wall of the hypopharynx, and upper esophageal sphincter. Several dense sensory plexi that cross the midline were seen on the laryngeal surface of the epiglottis and arytenoid region. The human ISLN also appears to supply motor innervation to the interarytenoid (IA) muscle. A detailed map is presented of the distribution of the ISLN within the human larynx. The areas seen to receive the greatest innervation are the same areas that have been shown by physiological experiments to be the most sensate: the laryngeal surface of the epiglottis, the false and true vocal folds, and the arytenoid region. The observation that the human ISLN appears to supply motor innervation to the IA muscle is contrary to current concepts of the ISLN as a purely sensory nerve. These findings are relevant to understanding how the laryngeal protective reflexes work during activities like swallowing. The nerve maps can be used to guide surgical attempts to reinnervate the laryngeal mucosa when sensation is lost due to neurological disease.