Expression of CD73 on leukemic blasts increases during follow-up - a promising candidate marker for minimal residual disease detection in pediatric B-cell precursor acute lymphoblastic leukemia.

Flow cytometry (FCM) is a precise and well-established tool to assess the minimal residual disease (MRD) level in childhood acute lymphoblastic leukemia (ALL). It is crucial to distinguish leukemic cells from their normal counterparts; thus new markers should be evaluated, to increase the accuracy of the analysis. The expression of CD73 on blast cells was measured and compared at the day of diagnosis and at days 15 and 33 of treatment. To determine antigen expression levels, a normalized scale based on median fluorescence intensity (nMFI) was used. The study group consisted of 188 patients from the Polish Pediatric Leukemia and Lymphoma Study Group. From 177 patients with positive MRD at day 15 of treatment, in 147 (83.1%) cases an increase of CD73 expression was observed (mean increase of +17 nMFI units). In addition, an increase of CD73 expression was noted in 26 of 31 (83.9%) patients at day 33 of treatment. In turn, a decrease of CD73 expression was observed only in 13/177 (7.3%) and 1/31 (3.2%) cases at days 15 and 33 of treatment, respectively. In 17 (9.6%) patients no change in expression of CD73 between diagnosis and day 15 of treatment was observed. In the great majority of cases the expression of CD73 is not only stable but increases during the early stages of treatment, which makes it a very useful marker to be used for MRD monitoring in childhood B-cell precursor (BCP)-ALL patients.