EVALUATION OF NEW MARKERS FOR FLOW CYTOMETRIC MONITORING OF MINIMAL RESIDUAL DISEASE IN CHILDHOOD B-CELL PRECURSOR ACUTE LYMPHOBLASTIC LEUKEMIA

ABSSUB-5537

Background: B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is the most common cancer of childhood. Initial diagnostics of this disease is currently established with multiparametric flow cytometry, e.g. using EuroFlow Consortium approach. Flow cytometry is also successfully applied for treatment monitoring, through the detection of minimal residual disease (MRD) at different treatment timepoints. The initial response to the induction treatment, ie. degree of reduction of leukemic cell burden during the first 4-6 weeks of chemotherapy as measured by MRD is particularly crucial for stratification of patients into risk groups.

Aims: The aim of the study was to assess the expression of newly identified markers of blast cells in childhood BCP-ALL, CD304 and CD86 which are not expressed by normal B-cell precursor cells. The stability of expression of these markers was assessed in terms of usefulness for MRD monitoring.

Methods: Bone marrow samples of 99 consecutive children with BCP-ALL were stained at initial diagnosis with four 8-color combinations of monoclonal antibodies, including the new markers CD304 and CD86. In 53 patients, bone marrow samples were analysed at day 15 of the induction treatment and in 25 patients also at day 33.

Results: The expression of CD304 was observed in 56.4% of patients at diagnosis. High expression of CD304 was observed in 27.4% of patients whereas in 29.0% of patients the expression of CD304 was weak. The expression of CD86 was found in 32.7% of patients at diagnosis. High expression of CD86 was observed in 12.7% of patients while in 20.0% of patients the expression of CD86 was low. The examination of bone marrow samples at day 15 and 33 of the induction treatment revealed that the level of expression of both CD304 and CD86 during treatment was similar as compared to the diagnosis. No cases of disappearance of either of the two examined antigens were found.

Summary/Conclusion: Both tested markers appeared to be useful for MRD monitoring, particularly CD304. More accurate definition of the phenotype of leukemic blasts enables more precise assessmet of leukemic blasts numbers during early treatment timepoints, which is important for proper stratification of BCP-ALL patients into risk groups.

This work was supported by funding from ERA-NET PRIOMEDCHILD (grant 40-41800-98-027) and Internal Grant from the Medical University of Silesia.

Keywords: Acute lymphoblastic leukemia, Flow cytometry, Minimal residual disease (MRD)

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