Detection of cardiac transplant rejection with radiolabeled lymphocytes

To determine whether rejections of cardiac transplants could be detected specifically and non-invasively by lymphocytes labeled with indium-111 (111In), we studied 36 allogeneic and 14 isogeneic heterotopic cardiac transplants in rats. Allogeneic grafts accumulated autologous 111In-lymphocytes, detectable scintigraphically 24 hours after i.v. injection of the labeled cells. At the time of peak histologic rejection, the allogeneic grafts accumulated 92. +/- 4.8 times more activity than the native hearts (determined by well counting). The tissue-to-blood ratio in the rejecting transplants was 3.7 +/- 2.2; total uptake by the graft was 2.9 +/- 2.1% of the injected dose. Autoradiography confirmed that graft radioactivity was associated with labeled lymphocytes. In contrast, isogeneic grafts showed no signs of rejection and did not accumulate radioactivity. Because conventionally isolated and labeled lymphocytes are often contaminated with platelets, we prepared both 111In-platelets and purified 111In-lymphocytes for use in additional experiments. Allogeneic grafts accumulated platelets and purified lymphocytes independently. Thus, deposition of immunologically active cells in the rejecting graft representing specific pathophysiologic events can be detected. The results suggest that rejection of cardiac transplants can be detected noninvasively, potentially facilitating objective early clinical detection of rejection and titration of antirejection therapy.