Fcγ Receptor II (CD32) on Malignant B Cells Influences Modulation Induced by Anti-CD19 Monoclonal Antibody

Abstract

AbstractAntigenic modulation is one of many factors determining the effectiveness of monoclonal antibody (MoAb)-mediated therapy. To select the isotype of a CD 19 MoAb most suitable for radioimmunotherapy of patients with B-cell malignancies, we studied the influence of MoAb isotype on modulation, after binding of the MoAb to different cell-line cells. The CD19-IgG1 MoAb was found to induce modulation of CD19 antigens on Daudi cell line cells more rapidly than did its IgG2a switch variant. We provide evidence that this difference in modulation rate is caused by the expression of Fcγ receptor II (FcγRII) on these cells. Experiments aimed at elucidating the mechanism of FcγRII involvement in modulation induction by COI 9-IgG1 showed that FcγRII did not comodulate with CD19 MoAbs. However, cocross-linking of CD19 and FcγRII with CD19-IgG1 MoAb resulted in enhanced calcium mobilization in Daudi cells. This increased signal induction accompanies the enhanced capping and subsequent modulation of CD19 antigens. Because FcγRII is expressed in varying densities on malignant B cells in all differentiation stages, our results have implications for the MoAb isotype most suitable for use in MoAb-based therapy of patients with B-cell malignancies.