Interferences with Two-site Immunoassays by Human Anti-mouse Antibodies Formed by Patients Treated with Monoclonal Antibodies: Comparison of Different Blocking Reagents

The most widely used approach for reducing interferences with two-site immunoassays by human anti-mouse antibodies (HAMAs) developed by many patients after exposure to murine immunoglobulins is to include high amounts of nonspecific mouse IgG within the assay buffer (1)(2). Recently, Mossner et al. (3) have developed a polymerized form of murine IgG (MAK33), which they found to be superior to normal mouse IgG for blocking HAMA interferences. In contrast, we observed false-positive values for the cancer antigen 125 (CA 125), because of HAMA interferences in samples from ovarian cancer patients treated with the anti-CA-125 antibody OC125, which could be corrected by preincubation with mouse IgG but not with MAK33 (4). The aim of the present study was to examine whether treatment with other monoclonal antibodies gives rise to additional HAMAs that are insensitive to MAK33 and to further characterize this specific HAMA response. Sixty-four serum samples were obtained from 51 ovarian cancer patients who, in the course of several clinical studies (5)(6)(7)(8), had received multiple infusions of one of four murine monoclonal antibodies: OC125 (16 patients), B43.13 (8 patients), ACA125 (18 patients), and B72.3 (9 patients). The procedures followed in this study were in accordance with the standards of the ethical committee of our faculty. The interfering HAMA activity of the samples was quantified with a bridging HAMA assay (HAMA-ELISA medac, Medac) involving polyclonal murine IgG in both capture and detection steps before and after preincubation (30 min at room temperature) with the following: (a) polyMAK-33 (MAK33), a polymerized murine IgG1,κ preparation (gift of Boehringer Mannheim, Mannheim, Germany); (b) Immunoglobulin Inhibiting Reagent (IIR) a formulation of immunoglobulins targeted against HAMAs (gift of Bioreclamation, East Meadow, NY); (c) polyclonal mouse IgG (reagent grade, Sigma Chemical Co.); and (d) mouse IgG of different …