Abstract
We report the clinical usefulness of a sensitive triple-color flow cytometric assay (FCM) to detect residual leukemic cells. For this study, 23 cases of CD45-negative B-precursor acute lymphoblastic leukemia (ALL) were included, because the absence of CD45 expression provided a marker for the leukemic cells in addition to the positive expression of CD 10 and CD22 antigens. Leukemic cells in patients' bone marrow (BM) consistently showed CD 10+/CD22+/CD45- or dim phenotype. FCM analysis could detect leukemic cells at a level of 1 per 104 cells. The CD 10+/CD22+/CD45- or dim cell population was absent in normal BM, regenerating BM, and BM collected from leukemic patients in long-term complete remission. This assay could identify residual leukemic cells up to 50 days after starting induction chemotherapy. Furthermore, a gradual increase of leukemic cell population could be monitored by this assay before morphological confirmation of BM relapse. Taken together, a triple-color FCM was a sensitive method of detecting leukemic cells in BM. This assay could be an additional component of testing to monitor MRD in ALL patients.