AN IMMUNOFLUORESCENT ASSAY FOR ACUTE PROMYELOCYTIC LEUKEMIA-CELLS

Sequential treatment with all-trans retinoic acid followed by chemothe rapy significantly improves the long-term survival of patients who hav e acute promyelocytic leukemia (APL). Consequently, a simple and accur ate test is needed to establish the diagnosis of APL and to identify t hose patients having a relapse of the disease. We describe an accurate , 2-hour indirect immunofluorescent assay for identifying APL cells in bone marrow specimens. The assay uses the PML (PG-M3) murine monoclon al antibody that is directed against the amino-terminal portion of the PML gene product We observed a distinctive, finely speckled pattern o f fluorescence in the NB4 cell line (a positive control), as well as i n 15 clinical specimens that were confirmed to have APL by cytogenetic , cytochemical, and immunophenotypic studies, including four cases of microgranular variant of APL. By contrast, a coarse globular pattern o f fluorescence was observed in 53 other clinical specimens that did no t contain APL. When we performed dilution studies using artificial mix tures of APL cells with normal bone marrow cells, we detected as few a s 5% APL cells in the mixture. Finally, there was complete concordance between the immunofluorescent assay and a polymerase chain reaction-b ased assay for the PML-retinoic acid receptor a chimeric gene in 12 ot her clinical specimens. We conclude that the immunofluorescent assay f or PML, protein is a rapid, sensitive, and accurate method for determi ning the presence of APL cells in clinical specimens. This assay there fore should be considered as a cost-effective alternative to other dia gnostic tests, such as karyotyping or polymerase chain reaction, for t he diagnostic evaluation of APL.