A simplified flow cytometric assay identifies children with acute lymphoblastic leukemia who have a superior clinical outcome

Abstract

Bone marrow normal lymphoid progenitors (CD19+, CD10+, and/or CD34+) are exquisitely sensitive to corticosteroids and other antileukemic drugs. We hypothesized that, in patients with B-lineage acute lymphoblastic leukemia (ALL), cells with this phenotype detected early in treatment should be leukemic rather than normal. We therefore developed a simple and inexpensive flow cytometric assay for such cells and prospectively applied it to bone marrow samples collected on day 19 from 380 children with B-lineage ALL. In 211 patients (55.5%), these cells represented 0.01% or more of the mononuclear cells; results correlated remarkably well with those of more complex flow cytometric and molecular minimal residual disease (MRD) evaluations. Among 84 uniformly treated children, the 10-year incidence of relapse or remission failure was 28.8% +/- 7.1% (SE) for the 42 patients with 0.01% or more leukemic cells on day 19 detected by the simplified assay versus 4.8% +/- 3.3% for the 42 patients with lower levels (P = .003). These assay results were the strongest predictor of outcome, even after adjustment for competing clinicobiologic variables. Thus, this new assay would enable most treatment centers to identify a high proportion of children with ALL who have an excellent early treatment response and a high likelihood of cure.

Figure 1.

A simplified flow cytometric assay to measure early treatment response in childhood B-lineage ALL. Bone marrow samples from 4 patients were obtained on day 19 of remission induction therapy and stained with anti-CD19, anti-CD10, and anti-CD34 antibodies. Flow cytometric dot plots show CD19 and CD10 expression among mononuclear cells. In patients 1 and 3 (left panels), CD19⁺ coexpressing CD10 (and CD34; not shown) were undetectable, whereas in patients 2 and 4 (right panels) they constituted 0.01% and 0.28%, respectively, of mononuclear cells.

Figure 2.

Relation between results of the simplified flow cytometric assays with those of more complex MRD assays. Bone marrow samples collected on day 19 of remission induction therapy from children with B-lineage ALL were examined for the presence of CD19⁺ cells coexpressing CD10 and/or CD34. Results were compared with those obtained with several sets of 4-antibody combinations in 376 patients (A), and with those of PCR amplification of immunoglobulin and T-cell receptor genes in 149 patients (B). Results of Spearman rank correlations are shown.

Figure 3.

Prognostic significance of detecting CD19⁺ cells coexpressing CD10 and/or CD34 on day-19 bone marrow. Cumulative incidence of remission failure or ALL relapse according to the presence or absence (< 0.01%) of CD19⁺ cells coexpressing CD10 and/or CD34 in 84 children with B-lineage ALL enrolled in a single chemotherapy program.