Normal levels of peripheral CD19(+) CD5(+) CLL-like cells: toward a defined threshold for CLL follow-up -- a GEIL-GOELAMS study.

Background: The development of flow cytometry as a useful tool for the detection of minimal residual disease (MRD) in chronic lymphocytic leukemia (CLL) is potentially hampered by the fact that a normal subset of B-cells with a similar immunophenotype is present in the peripheral blood. This subset of CLL-like cells is not well defined in terms of frequency. Methods: Here, we performed a multicenter study with a panel of four-color antibody combinations possibly useful for the detection of MRD in CLL, to establish the levels of normal CLL-like cells in 49 healthy controls. ROC curves established the upper level of such cells at 4 x 10(-4). The two best combinations were further applied to 419 samples from 117 treated CLL patients. Results: The combinations CD19/CD5/CD43/CD79b and CD19/CD5/CD81/CD22 appeared very robust and well correlated to enumerate normal CLL-like cells in a lysis no-wash approach. In follow-up samples from CLL patients, they disclosed only 9.8% of the samples within the normal range. In more than 90% of the cases, it was thus possible to report confidently on the absence or presence of MRD in these patients. Conclusions: This manuscript reports on the frequency of CD19(+)CD5(+) B-cells in normal peripheral blood and confirms the combinations recommended by the European research initiative on CLL as being performing to assess remaining CLL cells above a threshold of 4 x 10(-4) white blood cells. (C) 2011 International Clinical Cytometry Society