Immunofluorescent staining of human leukemic cells with monoclonal antibody to phosphotyrosine

Peripheral blood cells and bone marrow cells from patients with various types of leukemia, but not those from healthy persons, were brightly immunofluorescent (IF) after staining with monoclonal antibody reactive to O-phosphotyrosine. All the IF-positive cells observed in peripheral blood were judged to be leukemic in morphology, and the IF-positive cells comprised 40-90% of total leukemic cells present in blood. Similar bright fluorescence was observed in the K562 human leukemic cell line. The results raise the possibility that leukemic cells can be distinguished from normal hematologic cells by their increased contents of phosphorylated tyrosine residues.