Portal venous ultraviolet B-irradiated donor alloantigen prevents rejection in circumferential rat tracheal allografts

Chapter 8: Current techniques and concepts in peripheral nerve repair

Despite the progress in understanding the pathophysiology of peripheral nervous system injury and regeneration, as well as advancements in microsurgical techniques, peripheral nerve injuries are still a major challenge for reconstructive surgeons. Thorough knowledge of anatomy, pathophysiology, and surgical reconstruction is a prerequisite of proper peripheral nerve injury management. This chapter reviews the currently available surgical treatment options for different types of nerve injuries in clinical conditions. In overview of direct nerve repair, various end-to-end coaptation techniques and the role of end-to-side repair for proximal nerve injuries is described. When primary repair cannot be performed without undue tension, nerve grafting or tubulization techniques are required. Current gold standard for bridging nerve gaps is nerve autografting. However, disadvantages of this approach, such as donor site morbidity and limited length of available graft material encouraged the search for alternative means of nerve gap reconstruction. Nerve allografting was introduced for repair of extensive nerve injuries. Tubulization techniques with natural or artificial conduits are applicable as an alternative for bridging short nerve defects without the morbidities associated with harvesting of autologous nerve grafts. Achieving better outcomes depends both on the advancements in microsurgical techniques and introduction of molecular biology discoveries into clinical practice. The field of peripheral nerve research is dynamically developing and concentrates on more sophisticated approaches tested at the basic science level. Future directions in peripheral nerve reconstruction including, tolerance induction and minimal immunosuppression for nerve allografting, cell based supportive therapies and bioengineering of nerve conduits are also reviewed in this chapter.

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.

Laryngeal transplantation in 2005: a review

There is no good surgical, medical or prosthetic solution to the problems faced by those with a larynx whose function is irreversibly damaged by tumor or trauma. Over the past 10 years, the pace of research designed to establish laryngeal transplantation as a therapeutic option for these persons has increased steadily. The biggest milestone in this field was the world's first true laryngeal transplant performed in Cleveland, Ohio in 1998. The recipient's graft continues to function well, in many respects, even after 7 years. However, it has also highlighted the remaining barriers to full-scale clinical trials. Stimulated by these observations, several groups have accumulated data which point to answers to some of the outstanding questions surrounding functional reinnervation and immunomodulation. This review seeks to outline the progress achieved in this field by 2005 and to point the way forward for laryngeal transplantation research in the 21st century.

Animal models for tracheal research

Tracheal research covers two main areas of interest: tracheal reconstruction and tracheal fixation. Tracheal reconstructions are aimed at rearranging or replacing parts of the tracheal tissue using implantation and transplantation techniques. The indications for tracheal reconstruction are numerous: obstructing tracheal tumors, trauma, post-intubation tissue reactions, etc. Although in the past years much progress has been made, none of the new developed techniques have resulted in clinical application at large scale. Tissue engineering is believed to be the technique to provide a solution for reconstruction of tracheal defects. Although developing functional tracheal tissue from different cultured cell types is still a challenge. Tracheal fixation research is relatively new in the field and concentrates on solving fixation-related problems for laryngectomized patients. In prosthetic voice rehabilitation tracheo-esophageal silicon rubber speech valves and tracheostoma valves are used. This is often accompanied by many complications. The animal models used for tracheal research vary widely and in most publications proper scientific arguments for animal selection are never mentioned. It showed that the choice on animal models is a multi-factorial process in which non-scientific arguments tend to play a key role. The aim of this study is to provide biomaterials scientists with information about tracheal research and the animal models used.

Orthotopic tracheal transplantation in the murine model

BACKGROUND

Before tracheal transplantation can be clinically applied for the reconstruction of life-threatening airway defects, the immunobiology of this organ system must be better characterized. The availability of reagents and transgenic mice strains make the murine model ideal for this purpose. We have developed a reliable and reproducible method of orthotopic tracheal transplantation and characterized the kinetics of rejection.

METHODS

Balb/c donor tracheal segments (five tracheal rings), were orthotopically transplanted into either syngeneic Balb/c recipients or allogeneic C57BL/6 recipients. Tracheal graft rejection was monitored by daily clinical airway assessment, in vivo cilia motility, and histologic examination using hematoxylin and eosin staining and CD8/CD4 immunohistochemistry.

RESULTS

Two days after tracheal transplantation, allogenic recipients developed a persistent audible stridor that did not occur in the syngeneic experimental group. Whereas syngeneic tracheal autografts demonstrated normal mucociliary function after transplantation, allogeneic recipients failed to achieve normal mucociliary function. Normal histologic architecture persisted in the syngeneic grafts without evidence of lymphocytic infiltrate; however, the nonimmunosuppressed allogeneic grafts demonstrated a loss of normal ciliated respiratory epithelia and a CD8/CD4-positive lymphocytic infiltrate that peaked at 21 days after transplantation.

CONCLUSIONS

The Balb/c (donor) to C57BL/6 (recipient) murine orthotopic tracheal transplant model offers a reliable method for the study of tracheal transplantation.