Highly sensitive and specific solid-phase competitive assay utilizing a

Abstract

An in vitro solid-phase, competitive assay for detecting the presence of a peptide analyte in a biological sample, comprising contacting a fusion protein made of a first peptide and a second peptide to a solid supported first antibody which specifically binds to the first peptide, adding thereto a biological sample containing a peptide analyte, adding a second antibody specifically binding to the analyte and the second peptide, and allowing the second antibody to bind any free analyte present in the sample and the solid supported fusion protein to form analyte-second antibody and solid supported fusion protein-second antibody complexes, and determining the amount of solid supported second antibody present and comparing it to a control. When the amount of peptide analyte in the sample increases the amount of a second antibody bound to the solid support decreases. An optional final addition of an antibody-binding molecule helps detect the antibody-fusion protein complex bound to the solid support. The assay may be utilized for detecting neoplastic antigens from tumors or their metastases by utilizing a fusion protein containing an antigen of an epithelial mammary cell. A kit for detecting the presence of a neoplastic tissue comprises the fusion protein along with a first antibody specifically binding to the first peptide, and a second antibody specifically binding to the second peptide, and optionally a means for detecting the second antibody or fragment thereof, such as an antibody-binding molecule.