Migration and imaging of 111Indium-labelled lymphocytes in cardiac allograft rejection

The diagnosis of cardiac allograft rejection is based on routine endomyocardial biopsy. To study an alternative method the authors evaluated the migration and scintigraphic imaging of 111Indium-labelled lymphocytes in a model of acute heart allograft rejection.

Cervical heterotopic heart transplantation was performed in 10 dogs. Blood samples were harvested at 24 and 48 h after surgery for labelling of 36 +/- 6 x 10(6) lymphocytes with 6.62 +/- 0.56 MBq of 111Indium. Daily blood samples and heart biopsies were obtained for nuclear counting on the next three days; animals were sacrificed and both donor and native hearts were studied. Between 20 and 31% of autologous labelled lymphocytes remained in circulation until 72 h after injection. Maximal plasma 111Indium activity was 315 +/- 90 compared with 5513 +/- 1483 cpm/mL in whole blood (P less than 0.05). An average of 10,176 +/- 3444 labelled lymphocytes per gram of tissue were present in allograft biopsies while histological evaluation showed mild to moderate acute rejection. The ratio of tissue biopsy to blood 111Indium counts varied from 0.7 +/- 0.2, 6 h after autologous injection to 8.5 +/- 3.8 48 h later (P less than 0.05). At autopsy, 298 +/- 66 labelled cells per gram of tissue were present in native hearts compared with 2686 +/- 711 in allografts (P less than 0.05). Scintigraphic imaging using holospectral acquisition was performed; six lateral projections showed an indium activity ratio (transplanted heart to background tissue) of 2.8, 24 to 72 h after autologous injection of labelled cells.

Labelling of a small number of lymphocytes with 111Indium gave a stable population of circulatory lymphocytes for studying migration of labelled cells into allografts and a noninvasive scintigraphic approach to diagnose cardiac allograft rejection.