Intraindividual comparison of 99mTc-labelled anti-SSEA-1 antigranulocyte antibody and 99mTc-HMPAO labelled white blood cells for the imaging of infection

Technetium-99m labelled antigranulocyte antibodies are ready to use and an sensitive and specific in the diagnosis of infectious diseases. Tc-99m-SSEA antigranulocyte antibodies have a very high affinity constant (K-d 10(-12) M) for human neutrophils (PMNs), and excellent imaging qualities with high target/background ratios. The aim of this study was to compare the diagnostic accuracy of the Tc-99m-anti-SSEA-1 monoclonal antibody (Mab) with that of Tc-99m-hexamethylpropylene amine oxime (HMPAO)-labelled white blood cells (WBCs). To this end, 17 patients with 23 proven infectious foci were examined with 555 MBq Tc-99m-anti-SSEA-1 MAb and with 370 MBq Tc-99m-HMPAO labelled autologous leucocytes within a period of 7 days. All the infections were confirmed by culture, biopsy, surgery and followup. Whole-body images and planar spot views with the antibody were performed at 1-h, 4-h and 24-h post injection; the biodistribution of the antibody was quantified, absorbed radiation doses were calculated and the diagnostic results were compared with the Tc-99m-HMPAO WBC images. Human anti-mouse antibody (HAMA) evaluation was performed in all patients before and 3 months after antibody injection. Blood was drawn at different times after Tc-99m-anti-SSEA-1 MAb injection to determine the amount of granulocyte-associated radioactivity and to calculate recovery. Tc-99m-anti-SSEA-1 MAb scintigraphy detected all 23 lesions, while 21 were detected with Tc-99m-HMPAO WBC scan. In this small group of patients, the sensitivity and specificity of Tc-99m-anti-SSEA-1 MAb scintigraphy were 95% and 96% respectively, as compared with 91% and 82% respectively for Tc-99m-HMPAO WBC scan. An increasing uptake of the injected activity in the lesion at different time points was indicative of high affinity and of specific PMN binding. There was no HAMA formation. In four of five patients investigated, a transient mild leukopenia was found at 15 min p.i.. There was increased uptake of the antibody in liver and spleen and normal uptake in kidneys and bone marrow. The estimated radiation doses for the whale body and the red bone marrow were 1.1 x 10(-2) cGy/37 MBq and 5.3 x 10(-2) cGy/37 MBq, respectively. The activity associated to the PMNs in vivo was 33.5%, 30.6%, 21.3% and 9% at 5, 15, 30 and 45 min. post-injection, respectively. It is concluded that use of Tc-99m-anti-SSEB-1 antigranulocyte antibodies demonstrates promising results comparable to these obtained with Tc-99m-labelled autologous WBCs. The Tc-99m-labelled MAb is ready to use, has excellent image qualities and a high target/background ratio.