THE UPTAKE OF A MONOCLONAL-ANTIBODY (PO66) IN LUNG-TUMOR CELL AGGREGATES INVOLVES A PHAGOCYTOSE-LIKE PHENOMENON

The efficacy of radioimmunotherapy with radiolabelled monoclonal antib ody (Mab) depends on the amount of antibody taken up by the tumour and on its intratumoral distribution. Multicellular spheroids (MTS) of lu ng cell carcinoma was investigated to study cellular and subcellular d istribution of a Mab Po66 labelled with I-125. We have shown that the incorporation of Po66 in MTS regularly increases during 3 days while P y, a non specific Mab, remains low. The distribution of radiolabelled studied by light and electron microscopy autoradiography have demonstr ated that Po66 first localized on extra cellular debris, is then phago cyted and observed in the cytoplasm of viable cells. This mechanism of penetration and distribution of Mab Po66 is a new and interesting phe nomenon, and emphasizes contribution of transmission electron microsco py in nuclear medicine.