LONG-TERM COMPOSITE TISSUE ALLOGRAFT SURVIVAL IN A NOVEL PORCINE MODEL WITH CYCLOSPORINE (CSA)/MYCOPHENOLATE MOFETIL (MMF) THERAPY

Abstract

77 Effective antirejection therapy with minimal systemic morbidity is required if composite tissue allografts (CTAs) are to become a clinical reality. Low-dose, combination CSA/MMF therapy has significantly reduced the incidence of rejection and drug-induced side-effects in rat hindlimb allograft recipients. With an eye toward direct clinical application, we developed a porcine, brachial-artery based, radial forearm osteomyocutaneous flap allograft model to assess the ability of CSA/MMF treatment to delay rejection without antilymphocyte antibody induction. Transplants were performed between size-matched (17-24 kg), female, outbred, mixed-lymphocyte culture-reactive, donor-recipient pairs assigned to one of two groups: 5 control pigs received no immunosuppression; and 5 animals received a once-daily oral CSA/MMF/prednisone regimen. CSA dose was 35 mg/kg/d, adjusted to maintain 24 hr whole-blood trough levels between 100-200 ng/ml by the EMIT 2000 specific assay; MMF dose was 1 g/d; and prednisone was tapered from 2.0 to 0.1 mg/kg/d over 30 days. Drug doses were not adjusted based on clinical course. Electrolytes and complete blood count were obtained thrice weekly for 1 week, and then weekly. Graft skin biopsies were performed at 0, 2, 4, 7, 14, 21, and 30 days posttransplant. Rejection was assessed clinically by visual inspection of the flap skin through a cast window by two examiners. In all control pigs, the skin became erythematous on day 3, with blister formation on day 5, and cyanosis/sloughing on day 7, at which point the flap was considered to be completely rejected and the animal sacrificed. An acute rejection grading schema (I-IV) was established for the treatment group based on the severity of each of four distinct histopathologic changes noted to occur in control skin (vasculitis, dermal inflammation, folliculitis, and epidermal degeneration), with the control animals designated as having grade IV (severe) rejection. Among the pigs receiving treatment, one animal died from pneumonia on day 19 with no evidence of rejection; one graft was lost on day 27 from grade IV rejection; and the remaining 3 animals are still rejection-free at 35, 37, and 43 days posttransplant (p < 0.009 by Mann-Whitney U test). There were no technical failures nor morbidity from the surgical procedure in either group. White blood cell and platelet counts as well as serum creatinine and liver function tests remained normal in all pigs receiving CSA/MMF, with animals demonstrating normal weight gain and no evidence of drug-induced toxicity. We conclude that our model is technically feasible and useful for the preclinical study of CTA rejection, and is without the surgical morbidity of a whole-limb transplant. Our preliminary study demonstrates for the first time that rejection can be significantly delayed in a large-animal CTA model including skin using only orally-administered agents dosed according to clinically-relevant strategies without detectable systemic side-effects.