Our study aimed to evaluate the levels of MDSCs and Tregs in pediatric B-cell acute lymphoblastic
leukemia (B-ALL), their relation to patients’ clinical and laboratory features, and the impact of these
cells on the induction response. This study included 31 pediatric B-ALL patients and 27 healthy
controls. All patients were treated according to the protocols of the modified St. Jude Children’s
Research Hospital total therapy study XIIIB for ALL. Levels of MDSCs and Tregs were analyzed using
flow cytometry. We observed a reduction in the levels of CD4 + T-cells and an increase in both the
polymorphonuclear MDSCs (PMN-MDSCs) and Tregs. The frequencies of PMN-MDSCs and Tregs were
directly related to the levels of peripheral and bone marrow blast cells and CD34 + cells. Complete
postinduction remission was associated with reduced percentages of PMN-MDSCs and Tregs, with
the level of PMN-MDCs in this subpopulation approaching that of healthy controls. PMN-MDSCs and
Tregs jointly play a critical role in maintaining an immune-suppressive state suitable for B-ALL tumor
progression. Thereby, they could be independent predictors of B-ALL progress, and finely targeting
both PMN-MDSCs and Tregs may be a promising approach for the treatment of B-ALL.