Imaging of focal sites of inflammation in rhesus monkeys with ^99mTc-labeled human polyclonal IgG

The biological behavior of human polyclonal immunoglobulin G (IgG) radiolabeled with ^99mTc via a nicotinyl hydrazine derivative, was evaluated in Rhesus monkeys. ^99mTc-IgG and ¹¹¹In-MACROSCINT ® DTPA-IgG were co-administered to Rhesus monkeys with focal sites of sterile inflammation and scintillation camera images were acquired at 6 and 19 h after injection. The biodistribution of the two antibody preparations were similar, however, small differences were detected: ^99mTc-IgG > ¹¹¹In-IgG in spleen and lung; ^99mTc-IgG < ¹¹¹In-IgG in bone and skeletal muscle. A linear correlation of the tissue-to-blood ratios of ^99mTc- and ¹¹¹In-labeled IgG was observed at both times (r² > 0.98). The slopes of the regression lines were not significantly different from unity: 6 h-0.982 ± 0.018; 19 h 1.0334 ± 0.0226. Also, at both 6 and 19 h after injection, the target-to-background ratios ( T B) for the sites of inflammation were remarkably similar for ¹¹¹In and ^99mTc. These studies establish that human polyclonal IgG labeled with ^99mTc via a nicotinyl hydrazine modified intermediate is equivalent to ¹¹¹In-MACROSCINT^R DTPA IgG for imaging focal sites of inflammation in monkeys.