Rat Laryngeal Transplant Model: Technical Advancements and a Redefined Rejection Grading System

Abstract

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.

A new mouse laryngeal transplantation rejection grading system

“…3 Degradation of the allograft occurred in a predictable fashion over time in both models. Muscle, perichondrium, and cartilage all degraded in the same manner and over the same time frame as the rat.…”

“…Mice were euthanized at six separate time points (1,3,5,7,9, and 15 days post-transplant). Six mice were euthanized on post-transplant day 1.…”

“…Comparison of the level of allograft rejection for different regimens has been guided by a reliable rejection grading system, most recently refined in 2002. 3 Continued efforts to explore the full potential of human laryngeal transplantation have led our lab to investigate new cell-based immunosuppressive techniques. Recently, immunosuppression based on the modification of dendritic cells has been utilized with success in mouse cardiac and liver models.…”

Laryngeal Transplantation

“…Berke et al [10,11] continued similar work, and used microvascular techniques to develop a canine model for laryngeal transplantation. Strome and coworkers [12][13][14][15][16][17] performed considerable investigations after introducing the rat model of laryngeal transplantation in 1992, having since published voluminous work detailing technical modifications and immunosuppression regimens contributing to allograft success. Birchall's group [18 • , 19 • ] studied the histopathology of rejection in minipigs, concluding that the lack of strong immune response was encouraging to support future trials of laryngeal transplantation.…”

Induction of tolerance in a rat model of laryngeal transplantation

“…Previous studies have examined the effects of cyclosporine, steroids, and in vitro irradiation of the donor larynx in an existing rat model of laryngeal transplantation (2)(3)(4). No studies have yet demonstrated tolerance after laryngeal transplantation.…”