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

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.

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.

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.

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.