The investigators aimed to study the effect of chemotherapy on regulatory T cells (Tregs) in children with precursor B (PreB) acute lymphoblastic leukemia (ALL) at 15 and 33 days of malignity directed therapy. The investigators will analyze peripheral and bone marrow blood samples of the participants, obtained at diagnosis, 15 and 33 days of treatment, about Treg / non Treg cells and interleukin (IL)-2, IL-6, IL-10, and transforming growth factor (TGF) beta levels. By this means, investigators will search response to chemotherapy. Also, investigators will analyze correlation between Treg population-Treg related cytokines with demographic, clinical and laboratory findings of the participants with ALL at these certain time points. Additionally, the investigators will compare Treg population and minimal residual disease at 15-33 days of malignity directed therapy. Also investigators will compare these Treg-Treg related cytokines obtained from the participants with ALL and a healthy children control group whom are voluntary donors for bone marrow transplantation.

Inclusion Criteria:

• Children between 1-18 years
• Recent PreB ALL diagnosis

Exclusion Criteria:

• Children under 1 or over 18 years
• Underlying disease e.g. immune deficiency, germline mutations or diseases
• Tcell ALL or acute myeloid leukemia (AML) patients

The patients diagnosed with PreB ALL in a hematology clinic. Healthy children whom are volunraty bone marrow donors.