Chimeric B72.3 mouse/human (IgG1) antibody directs the lysis of tumor cells by lymphokine-activated killer cells

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Abstract
Chimeric mouse/human B72.3 (cB72.3) antibodies having a human IgG1 (γ1) or IgG4 (γ4) constant region were compared to the native murine IgG1 B72.3 (nB72.3) monoclonal antibody (mAb) for their ability to participate with human effector cells in antibody-dependent cellular cytotoxicity (ADCC). Because the TAG-72 antigen recognized by B72.3 is poorly expressed on tissuecultured tumor cell lines, the xenografted OVCAR-3 human ovarian carcinoma ascites was used as a cytotoxicity target. The lytic activity of the cB72.3(γ1) mAb with peripheral blood lymphocytes was 1.5- to 50-fold greater than that of the nB72.3 mAb and usually the cB72.3(γ4) mAb. However, lymphocytes from some donors had similar ADCC activity with either the cB72.3(γ1) or cB72.3(γ4) mAb. The cB72.3(γ1) and the murine anti-colon carcinoma CO17-1A mAb had comparable activity in mediating ADCC against the OVCAR-3 tumor. Exposure of lymphoid cells to interleukin-2 (IL-2) (100–500 U/ml) for 24 h to generate lymphokine-activated killer (LAK) cells augmented ADCC mediated by the cB72.3(γ1) mAb 2- to 22-fold. By contrast, LAK cells from most donors expressed weak non-specific cytotoxicity against OVCAR-3 ascites tumor cells. The cB72.3(γ1), and to a lesser extent, the cB72.3(γ4) chimera also participated with monocytes in mediating ADCC, but the antibody-dependent lytic potency of monocytic effectors was much weaker than that of IL-2-activated lymphoid cells. These studies show that the cB72.3(γ1) mAb has appreciable ADCC-mediating properties, suggesting a potential role for its incorporation into treatment strategies utilizing adoptive killer cell and/or lymphokine therapy.