An immunological method for the detection of BCR-ABL fusion protein and monitoring its activation.

We have developed a simplified sandwich immunoassay to measure free circulating total and phosphorylated fusion BCR-ABL protein in patients with the t(9;22)(q34;q11) chromosomal translocation. The assay is based on immunoprecipitating BCR-ABL protein using beads coated with anti-BCR antibody and detecting the fusion protein with anti-ABL antibody and flow cytometry. We show that this method allows the quantification of this protein in the plasma and may allow the measurement of tumor load. This method also allows the measurement of the level of phosphorylation of the immunoprecipitated BCR-ABL using antibodies against phosphorylated ABL protein, which can be used for monitoring of therapy with kinase inhibitors. The sensitivity of this immunoassay was comparable to the sensitivity of reverse transcription-polymerase chain reaction (RT-PCR) assay. This technique is useful in monitoring patients with chronic myeloid leukemia (CML) or acute lymphoblastic leukemia (ALL), but the same approach can be used in other translocations and has the potential of multiplexing.