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 × 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 × 10−4 white blood cells. © 2011 International Clinical Cytometry Society