[The limited possibility of using a simplified approach to detect minimal residual disease by the flow cytometry technique in children with precursor B-lineage acute lymphoblastic leukemia].

Minimal residue disease (MRD) is a state in which the tumor cells remain in the patient in the amounts unrecognizable with the standard cytological techniques. Flow cytometry is one of the basic methods for evaluation of MRD in precursor B-lineage acute lymphoblastic leukemia (PBLALL). The so-called simplified three-color analysis using the combination of CD19/CD10/CD34 antibodies has been proposed to detect MRD in the midcourse of induction therapy. Four-to-nine-color is presently used to identify MRD. One hundred and thirty-four bone marrow samples taken at different stages of therapy in 55 children with PBLALL were examined to estimate the possibility of using the flow cytometry technique using the 3-color simplified approach to determining MRD. The results of the simplified and standard approaches were compared in the samples stained with 6-8 monoclonal antibodies in the combinations that always included CD19, Cd10 and CD34. The comparison revealed that MRD had been incorrectly identified by the simplified method in 8.0, 17.6, and 75.8% of the patients on therapy days 15, 36, and 85, respectively. In addition, the content of residual tumor cells with respect to the threshold values more frequently proposed to stratify patients was found to be incorrectly calculated in some true positive samples. Thus, when the simplified approach was applied using the results of MRD detection to stratify the patients into risk groups, 16.0, 27.4, and 81.8% of the samples would yield incorrect information on therapy days 15, 36, and 85, respectively. Thus, the simplified approach to identifying MRD is most applicable on day 15 of therapy; however, there may be mistakes in this point of observation. This method used on day 36 more frequently yields incorrect results and is inapplicable on day 85.

[Minimal residual disease monitoring by flow cytometry in children with acute lymphoblastic leukemia].

The cells that have avoided the action of antitumor drugs may be retained after remission achievement during induction therapy and consolidation. A combination of these cells is given the name minimal residual disease (MRD). Multicolor flow cytometry has recently attracted considerable interest as the most promising method for measuring the content of residual tumor blasts. This technique is based on the detection of the so-called leukemia-associated immunophenotype (LAIP), i.e., a tumor-specific combination of the expression of membrane and cytoplasmic markers. Flow cytometry may be successfully used to monitor MRD in 90-95% cases of acute lymphoblastic leukemia (ALL) and in 80-85% of patients with acute myelocytic leukemia. The sensitivity of flow cytometry, which is real for routine flow techniques, is a possibility of identifying one cell among 10(4)-10(5) cells. Multicolor flow cytometry (that involves the simultaneous analysis of the expression of a few markers) is the most reasonable tool for MRD monitoring. The monoclonal antibody panels recommended by different groups of investigators for MRD monitoring in B-lineage ALL include antibodies to the pan-B-cell antigen CD19, markers of different stages of differentiation of B-lineage precursors of CD10, CD34, and CD20 and leukemia-associated markers different for each panel, such as CD22, CD38, CD58, CD45, TdT, CD13, CD33. The hyperexpression of CD10, CD34, CD19, TdT, the decreased expression of CD38, CD45, CD22, CD19, the simultaneous expression of markers of different stages of differentiation of B lymphocytes, such as CD10 and CD20, and the lymphoblast coexpression of myeloid markers of CD13, CD33, CDS15 are the most frequently described immunophenotype aberrations in B-lineage ALL. The selection of combinations of markers for MRD monitoring in children with T-ALL is based on the simultaneous expression of combinations of the antigens characteristic for early stages of differentiation of normal T lymphocytes, namely TdT and cytoplasmic CD3. Some authors consider the use of CD99 versus TdT to be most appropriate. There is recent evidence that MRD-positive patients have a higher cumulative risk for recurrences as compared with those without residual blasts. Moreover, the longer the tumor cells are retained during therapy, the worse the prognosis is. Thus, for choice of the adequate intensity of antitumor therapy, it is necessary to qualitatively and quantitatively assess MRD by multicolor flow cytometry at different stages of therapy.