EXTRACORPOREAL IMMUNOADSORPTION OF RADIOLABELED MONOCLONAL-ANTIBODY -A METHOD FOR REDUCTION OF BACKGROUND RADIOACTIVITY AND ITS POTENTIAL ROLE DURING THE RADIOIMMUNOTHERAPY OF CANCER

To determine the ability of an on-line extracorporeal immunoadsorption (ECIA) procedure to remove non-tumor bound radiolabeled antibody afte r intravenous administration of In-111-KC4-G3, we performed pharmacoki netic, dosimetric, and imaging evaluations in 7 patients with KC4-G3-r eactive lung and breast cancers. We administered 0.4 to 5 mg KC4-G3 la beled with approximately 5 mCi In-111, with a mean immunoreactivity of 74 %. Immunoadsorption was begun 6.5 to 22 hours after In-111-KC4-G3 infusion, and lasted for 3 to 5 hours so that 5.4 to 9.7 liters of pla sma were processed. The procedure removed 54.6 to 75.8 % circulating I n-111-KC4-G3; which closely approximated modeled predictions of antibo dy removal. The rate of In-111-KC4-G3 clearance during immunoadsorptio n (Cl-IA) exceeded physiologic patient plasma clearance (CL(tot)) by g reater than 12 fold. Dosimetric predictions of bone marrow dose projec ted decreases of 29 to 56 % from the immunoadsorption procedure, with small changes in predicted tumor dose. Whole body gamma camera imaging performed before and after immunoadsorption demonstrated rapid blood pool clearance of radioactivity in all patients which led to earlier t umor visualization in those with tumors. This study directly supports the utility of ECIA in patient radioimmunodetection, and its potential in radioimmunotherapy.