We have shown previously that cardiac allograft rejection can be detected noninvasively with gamma scin-tigraphy after administration of indium-111 (111In)-la beled lymphocytes. To determine whether this technique could be used to monitor salvage immunosuppressive therapy in reversing rejection, 5 dogs were studied after thoracic heterotopic cardiac transplantation. Initial postoperative immunosuppression was maintained with cyclosporine (10—20 mg/kg/day) and prednisone (1 mg/ kg/day) for 7 days after transplantation and then dis-continued. Scintigraphy after administration of labeled lymphocytes was performed during initial immuno-suppression and every 3 days after its termination. Endomyocardial biopsies were obtained on each day scin-tigraphy was performed. Once scintigraphic criteria for rejection were met (111In-lymphocyte uptake > mean ± 2SD of normal myocardium), animals were treated with high dose methylprednisolone and cyclosporine. Myocardial 111In-lymphocyte activity compared with that in blood was 0.7±0.8 during initial immunosuppression, increased to 5.7±3.5 after termination of therapy (P<0.01), and diminished with salvage immunosuppressive therapy to 0.5±0.8 (P=NS compared with native hearts or allografts during initial immunosuppression). Scintigraphy accurately predicted all but one episode of biopsy-documented rejection and accurately detected reversal of rejection during salvage. Thus, scintigraphy with 111In-labeled lymphocytes should facilitate noninvasive monitoring of antirejection therapy in patients.
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