Antiproliferative activity of a humanized anti-CD74 monoclonal antibody, hLL1, on B-cell malignancies

The humanized anti-CD74 monoclonal antibody (mAb) hLL1 is under evaluation as a therapeutic agent. The effects of hLL1-at times in comparison with the CD20 mAb rituximab-were assessed on non-Hodgkin lymphoma (NHL) and multiple myeloma (MM) cell lines and in tumor-bearing SCID mice. In vitro, hLL1 caused growth inhibition and induction of apoptosis in B-cell lines when cross-linked with an antihuman immunoglobulin G (IgG) second antibody. The sensitivity profile of the cell lines was different for hLL1 and rituximab, and antiproliferative activity was augmented when the 2 mAbs were combined. Unlike rituximab, hLL1 did not induce antibody-dependent cellular cytotoxicity or complement-mediated cytotoxicity. In xenograft models of NHL and MM, treatment with hLL1 yielded significant survival benefits without cross-linking agents. Efficacy was greater in the MM model, in which median survival time was increased more than 4.5-fold. Thus, hLL1 has therapeutic potential as a naked mAb for B-cell malignancies because of high antigen expression on malignant cells, specifically MM, with limited expression on normal tissue, and because of its antiproliferative activity. Further, hLL1 may be a therapeutic candidate for rituximab-resistant disease because the 2 antibodies apparently act through distinct mechanisms and exhibit different expression and sensitivity profiles, and activity can be augmented when the mAbs are combined.