A sensitive immunoradiometric assay for the quantification of murine monoclonal antibodies in human serum

The clinical investigation of murine monoclonal antibodies (MoAbs) as potential immunotherapeutic agents necessitates their quantification in human serum. The present paper reports the development of a sensitive, non-competitive "sandwich" immunoradiometric assay specifically optimized for measurement of murine IgG in human serum. Affinity-purified goat anti-mouse IgG antibody covalently bound to acrylic microspheres serves as the solid-phase antibody and 125I-labelled goat anti-mouse IgG antibody functions as tracer. All assay reagents were obtained from commercial sources. The assay is sensitive (capable of detecting 20 ng ml-1 of murine IgG), specific (less than 0.0001% cross-reactivity with human IgG), reproducible (intra-assay % RSD less than 6.3%), and rapid (a 100-tube assay can routinely be processed in 3 h). The assay has a working concentration range of 20-2000 ng ml-1 and is suitable for measuring MoAbs of any antigenic specificity. The assay was validated for use with human serum and cell culture media by comparison studies with flow cytometric and immunonephelometric methods and by high-performance size-exclusion chromatographic studies. Application of this assay should facilitate further investigation of murine MoAbs as potential immunotherapeutic agents.