RADIOIMMUNODETECTION OF HUMAN MYELOMA XENOGRAFTS WITH A MONOCLONAL-ANTIBODY DIRECTED AGAINST A PLASMA-CELL SPECIFIC ANTIGEN, HM1.24

BACKGROUND. To develop a new immunologic approach to multiple myeloma, the authors generated a monoclonal antibody against a human plasma ce ll specific antigen, HM1.24. Their previous study showed the antitumor effect of this antibody in severe combined immunodeficiency (SCID) mi ce bearing human myeloma xenografts. In the current study, the efficac y of anti-HM1.24 immunoglobulin (Ig) G and its F(ab')(2) fragment were evaluated for radioimmunologic detection of the myeloma xenografts. M ETHODS. SCID mice bearing subcutaneous RPMI 8226 tumors were injected with I-125-labeled antibodies, and radioactivity in the tumor and norm al tissues was measured. Radioimmunoscintigraphy and autoradiography w ere performed to investigate the distribution of the antibodies. RESUL TS. In comparative biodistribution studies, the maximum tumor localiza tion index of anti-HM1.24 F(ab')(2) fragment was significantly higher than that of anti-HM1.24 IgG. Anti-HM1.24 F(ab')(2) consistently had h igher tumor-to-tissue ratio than anti-HM1.24 IgG and gave distinct tum or images by radioimmunoscintigraphy. Autoradiographic study showed th at anti-HM1.24 F(ab')(2) penetrated the tumor mass more uniformly than whole IgG antibody. CONCLUSIONS. These results indicate that anti-HM1 .24 antibody has the potential to provide a new approach to the immuno detection and immunotherapy of multiple myeloma and related plasma cel l dyscrasias. (C) 1998 American Cancer Society.