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

Overview

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 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 DTPA-IgG for imaging focal sites of inflammation in monkeys.