Time course localization of immunoglobulin M monoclonal antibody and its fragments in leukemic tumor-bearing mice

In vivo localization of a mouse monoclonal antibody (F2-10.23 IgM) binding leukemic L 1210 cells was studied in DBA/2 mice bearing an L 1210 tumor. F(ab')2 fragments were prepared and their specific binding to L 1210 cells was analyzed by flow cytofluorometry. Radio-localization studies were performed by using 125I- or 131I-labeled IgM monoclonal antibody or its F(ab')2 fragments to ascertain their capacity to visualize the L 1210 tumor. F(ab')2 fragments were cleared more rapidly than the whole IgM; the clearance was as fast in healthy as in tumor-bearing mice. The tumor-to-muscle ratio observed 24 h after injection of 125I-radiolabeled F(ab')2 fragments and 125I-radiolabeled IgM was 10; the radioactivity level in the blood with F(ab')2 fragments was lower than with IgM, and so gamma-camera imaging was workable with F(ab')2 fragments without background subtraction. The tumor localization was studied over a period of 5 days by recording the distribution of the iodinated fragments in the tumor-bearing leg compared with that in the normal leg, and by computer analysis of the region of interest. F(ab')2 fragments gave better results than intact IgM in tumor visualization. Nevertheless, the rapid clearance of this antibody or its F(ab')2 fragments make them hardly suitable as carriers of toxic drugs.