Quantitation of human anti-mouse antibody in serum by flow cytometry

Clinical investigations utilizing murine monoclonal antibodies require techniques for the detection of the human anti-mouse antibody (HAMA) response in patient serum. We report here a flow cytometric assay for the quantitation of HAMA. Commercially available beads conjugated with goat anti-mouse antibody provide a solid phase matrix for a triple bridge immunoassay. The measurement of fluorescein labeled antibodies by flow cytometry allows accurate quantitation of the HAMA. The assay will detect antibody levels of approximately 1.0 ng/ml. Antibody recovery in serum samples with known amounts of antibody added was greater than 90% at levels greater than or equal to 10 micrograms/ml. Serum samples obtained from 41 patients prior to and after single or multidose infusions of KS1/4-Desacetyl-vinblastine were analyzed. These results were compared with HAMA titers previously determined by ELISA. With few exceptions, patients with low titers as determined by ELISA demonstrated low HAMA potencies by flow cytometry and those with highest titers the highest potencies. Patients with no detectable HAMA by ELISA were also negative by flow analysis. The results of our studies demonstrate that HAMA levels can be accurately and quantitatively determined by flow cytometry.