Chronic rejection of concordant aortic xenografts in the hamster-to-rat model.

Several groups have demonstrated that it is possible to obtain long-term graft survival of concordant xenografts. One of the important questions that remains is whether xenografts are susceptible to chronic rejection. To answer this question we used the aorta transplantation model. One centimetre of hamster aorta was interposed in the abdominal aorta of Lewis rat recipients. The recipients were either untreated (group 1), or treated with 10 mg/kg cyclosporine (CsA), given intramuscularly three times a week (group 2). Rats were sacrificed at day 7, 14, 21, 28, 56 and 84 and the thickness of the intima, the media and the adventitia was measured. Furthermore, the cellularity of the media and the adventitia was assessed by counting the number of nuclei per 0.05 mm2 and immunohistochemistry of the aortic grafts was performed. Graft arteriosclerosis developed in aortic xenografts of both group 1 and group 2. In group 1, intimal lesions were already present from day 21 onwards in all rats, whereas in group 2 they were present only in 33% (2/6) of the rats. At day 84 all the grafts in group 1 were totally occluded, while those in group 2 were still open. The thickness of the media was slightly increased in both groups during the whole observation period, mainly due to edema. Although a few infiltrating macrophages could be seen, the number of nuclei per 0.05 mm2 of the media remained constant during the first 21 days, but declined sharply from day 21 onwards, as a consequence of disappearing myocytes. Thickness of the adventitia in both groups increased after transplantation due to infiltrating macrophages and T cells, reaching a peak at day 14. After day 14 the adventitial thickness in group 1 decreased rapidly to reach values comparable to group 2 from day 28 onwards. In conclusion, graft arteriosclerosis, as a sign of chronic rejection, occurs in concordant aortic xenografts. The lesions in the xenografts develop extremely rapidly, and compared to data from the literature, faster than in aortic allografts. The process of chronic rejection in aortic xenografts can be reduced by CsA.

Ketanserin reduces graft arteriosclerosis after allogeneic aorta transplantation in rats.

The serotonin-2 receptor antagonist ketanserin has been suggested to diminish arteriosclerotic development by its effect on platelet function and on vascular smooth muscle cells. We investigated the ability of ketanserin in reducing immune-mediated arteriosclerosis using the BN-WAG and WAG-BN rat aortic transplantation models. Ketanserin (10 mg/kg/day) administered in drinking water significantly reduced posttransplant arteriosclerotic thickening of the intima in the BN-WAG rat model to 102 +/- 23 mu m as compared with 171 +/- 60 mu m in untreated BN-WAG allografts 8 weeks posttransplantation (p < 0.05). In the opposite WAG-BN combination, at 4 weeks posttransplantation, no significant reduction in intimal thickening was attained (112 +/- 42 vs. 152 +/- 49 mu m). Platelet aggregation to increasing amounts of collagen did not show a correlation between the effect of ketanserin on platelet function and reduction in intimal thickening. Ketanserin had no effect on systolic blood pressure or mononuclear cell infiltration. We conclude that ketanserin reduces graft arteriosclerosis by a mechanism other than by inhibition of platelet function, decrease in blood pressure, or immunosuppression. Because of this antiarteriosclerotic effect, ketanserin therapy might be beneficial to the long-term survival of vascular allografts.

Suppression of acute rejection prevents graft arteriosclerosis after allogeneic aorta transplantation in the rat.

Rat aortic allografts develop arteriosclerotic alterations in the vascular wall that are histologically similar to those observed in chronic rejecting vascular allografts. We used cyclosporine and rapamycin (RAPA) in two different rat strain aorta transplantation models to investigate the effect of immunosuppression on posttransplant graft arteriosclerosis. High dose CsA (25 mg/kg, 3 times/week) treatment significantly inhibited intimal proliferation in the "strong" WAG-BN model (P < 0.01) as well as in the "weak" BN-WAG combination (P < 0.001), compared with untreated allogeneic controls. In the latter combination, even fewer intimal lesions were present than in WAG autotransplants, suggesting that CsA may also inhibit the arteriosclerotic response to mechanical injury. RAPA (3 mg/kg, 3 times/week) was as effective as CsA in reducing intimal lesions (P < 0.01 and P < 0.001 in the BN-WAG and WAG-BN models, respectively). Low dose CsA (5 mg/kg, 3 times/week) was only partially effective in preventing intimal lesions. Histology of the nontreated allografts showed ongoing acute rejection in the adventitial layer. The degree of cellular infiltration correlated with the severity of arteriosclerotic lesions. High dose CsA and RAPA treatment prevented adventitial infiltration in both models, while low dose CsA was only moderately effective. In conclusion, in the present study, the degree of arteriosclerotic involvement after allogeneic aorta transplantation was related to the severity of cellular adventitial infiltration. The myointimal thickening was inhibited by effective immunosuppressive treatment. These observations may imply that chronic rejection develops after ineffective immunosuppression.

Injection of recombinant tumor necrosis factor directly into liver metastases: an experimental and clinical approach.

Systemic treatment with tumor necrosis factor (TNF) is associated with side-effects, limiting its clinical use in the treatment of malignancies. To investigate the feasibility of other routes of administration experimental and clinical studies were started to establish the toxicity and antitumor activity of TNF after intratumoral (i.t.) injection. In a rat model for colon adenocarcinoma, tumor fragments, implanted subcutaneously or under the hepatic capsule, were treated with TNF injected i.v. or i.t. A dosage of 40 micrograms/kg was lethal when given i.v., but not i.t. Injection of TNF (40 micrograms/kg) directly into the tumor resulted in inhibition of tumor growth in the subcutaneous as well as subhepatic tumor model. A phase I study was started in patients with advanced malignancies to determine the toxicity of TNF injected into liver metastases. Injection of TNF into liver metastases was accomplished by ultrasonography. A 50 microgram-dose escalating schedule (3 patients/dosage) was chosen, starting at a dose of 100 micrograms TNF/injection. Up to now, 12 patients have been treated, the highest dosage of TNF injected being 250 micrograms. Chills, fever, nausea and vomiting were the main side-effects. No significant changes were found in circulatory, hematologic, renal and liver parameters. In summary, i.t. administration of TNF is associated with antitumor efficacy in experimental models and well-tolerated in man. The antitumor efficacy of TNF i.t. in man awaits evaluation in a phase II study.