Anti-CD54 (ICAM-1) Has Antitumor Activity in SCID Mice with Human Myeloma Cells

Recent studies have suggested that ICAM-1 (CD54) is involved in the pathogenesis of human multiple myeloma. A monoclonal antihuman CD54 antibody has been generated by immunizing BALB/c mice with human myeloma cell lines. SCID mice injected with human ARH-77 myeloma cells develop disseminated myeloma which is similar in several respects to multiple myeloma in humans. The mice have monoclonal gammopathy and succumb to hind leg paralysis caused by infiltration of tumor cells into the thoracolumbar vertebrae, resulting in compression of the spinal cord. In the absence of treatment, the mean paralysis time of the SCID/ARH-77 mice is 29 days. When the SCID/ARH-77 mice received four consecutive daily i.V. injections of anti-CD54 mAb commencing 1 day after tumor inoculation, they survived for 150 days, at which time the experiment was terminated. Histopathological analyses indicated that prior to death all control SCID/ARH-77 mice had myeloma cells in the vertebrae and skull. At this time, the anti-CD54-treated mice had no evidence of tumor. High levels of human immunoglobulin were detected in the sera of control, but not treated mice. F(ab′)2 fragments of the anti-CD54 antibody also had similar, albeit, slightly less antitumor activity in vivo, suggesting that antibody effector function may account for some, but not all the antitumor activity of anti-CD54. In vitro studies indicate that anti-CD54 does not inhibit homotypic adhesion, the binding of myeloma cells to murine bone marrow stromal cells, or cell proliferation. By exclusion, we propose that the CD54-mediated homing of these ARH-77 cells to certain anatomical sites is crucial for their growth in vivo.