Relevance of anti-alpha-fetoprotein antibody for radioimmunodetection: analysis with alpha-fetoprotein-secreting rat hepatoma and antigen-bound acrylic beads.

Using AFP-secreting AH66 rat hepatoma cells and AFP-bound acrylic beads (AFP-B), artificial cells expressing surface antigen, the effect of blood AFP level on the accumulation of radiolabeled rabbit anti-AFP antibody in the site of tumor and beads implanted in rats was examined. Scintigrams of hepatoma-bearing rats with implanted AFP-B showed a marked localization in AFP-B site, but not in the tumor site on day 5 after the injection of radiolabeled antibody. The imaging of AFP-B was most satisfactory in normal rats with extremely low blood AFP. Tissue/blood radioactivity ratio in AFP-B on day 5 was found to be significantly higher in normal rats (17.43 +/- 5.55), compared with 6.66 +/- 1.67 in the tumor-bearing rats (p less than 0.01), while the ratio of AFP-B in tumor-bearing rats remarkably recovered to 11.20 +/- 0.25 (p less than 0.01) after whole blood exchange to reduce an elevated serum AFP level. The accumulation of anti-AFP antibody in the tumor was not observed irrespective of AFP-B. Microautoradiography of tissue sections showed the specific localization of radioactivity on the surface of AFP-B but not on the surface or the inside of the tumor cells. Immune complexes were detected in plasma of tumor-bearing rats 1 min to 7 days after the administration of the radiolabeled antibody. In conclusion, the application of anti-AFP antibody for the diagnosis and treatment of tumors is limited to the case of the expression of AFP on the surface of tumor cells and lower AFP level in circulation.