Development of models of graft vascular disease in nonhuman primates: evaluation of GVD by intravascular ultrasound in a new cynomolgus model with arterial allograft exchange

Treatment by mycophenolate mofetil of advanced graft vascular disease in non-human primate recipients of orthotopic aortic allografts

Failure to control chronic graft dysfunction [e.g. graft vascular disease (GVD)] is the primary cause of immunologic graft failure. This is the first study of mycophenolate mofetil (MMF) for the treatment of GVD in non-human primate recipients of aortic allografts. Abdominal aortic allografts were exchanged between mixed leukocyte reaction (MLR) -mismatched, blood-group-compatible cynomolgus monkeys. Six control recipients were untreated. Individualized treatment with frequent dose adjustments of MMF insured that treatment was close to the maximum tolerated dose (mean 99.2 mg/kg/day). Immune-mediated injury proceeded unhindered until day 45, after which MMF treatment began. Changes in intimal volume (IV) were quantified by intravascular ultrasound (IVUS) and compared to histology on day 105. Serial IVUS measurements of IV (mm(3)) in controls showed progressive GVD. In four out of six animals, MMF was well tolerated, thus enabling optimum treatment; in all these animals, IV was significantly less than in the control animals (p = 0.02). In the two remaining animals, high doses were not tolerated; at day 105, there was no significant difference in IV between them and the controls. We found a significant correlation between the mean MMF tolerated dose and the inhibition of progression of IV (r = -0.88, p = 0.015). When high MMF doses were tolerated, MMF slowed progression of GVD.

Sirolimus (rapamycin) halts and reverses progression of allograft vascular disease in non-human primates

BACKGROUND

Current immunosuppressive protocols fail to prevent chronic rejection often manifested as graft vascular disease (GVD) in solid organ transplant recipients. Several new immunosuppressants including sirolimus, a dual function growth factor antagonist, have been discovered, but studies of drug efficacy have been hampered by the lack of a model of GVD in primates, as a prelude to clinical trials. As described earlier, we have developed a novel non-human primate model of GVD where progression of GVD is quantified by intravascular ultrasound (IVUS).

METHODS

Twelve cynomolgus monkeys underwent aortic transplantation from blood group compatible but mixed lymphocyte reaction-mismatched donors. To allow the development of GVD in the allograft, no treatment was administered for the first 6 weeks. Six monkeys were treated orally with sirolimus from day 45 after transplantation to day 105.

RESULTS

Progression of GVD measured as change in intimal area from day 42 to 105 was halted in sirolimus-treated monkeys compared to untreated monkeys (P<0.001, general linear model). On day 105, the intimal area +/- SEM was 3.7+/-1.0 and 6.4+/-0.5 mm2, respectively (P<0.05, t test). The magnitude of allograft intimal area on day 105 correlated inversely with sirolimus trough levels (R2=0.67, P<0.05). Regression of the intimal area was seen in four of six sirolimus-treated monkeys, which was significantly different from the untreated monkeys (P<0.05).

CONCLUSIONS

Our results in the first non-human primate model of GVD showed that treatment with sirolimus not only halted the progression of preexisting GVD but also was associated with partial regression. Sirolimus trough blood levels were correlated with efficacy. Therefore, sirolimus has the potential to control clinical chronic allograft rejection.