Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. According to modern concepts, leukemia develops from the precursor lymphatic cells, which, by accumulating mutations, are transformed into leukemia cells that affect the patient's bone marrow and then other organs. Depending on the individual characteristics of ALL progression, both a single leukemic clone and several subclones may form in the bone marrow. Initial clonal heterogeneity may be a key factor in ensuring the survival of leukemic cells during therapy, ultimately leading to relapse. The main objective of the project is the complex study of characteristics of clonal diversity formation and evolution of leukemic cells in B- and T-lineage acute lymphatic leukemia in children. In the course of the project implementation a high-performance multiplex method will be developed, which will allow to reconstruct clonal architecture of leukemic cells simultaneously for hundreds of patients with unprecedented low costs. Using the developed method a large-scale complex analysis of clonal structures of children's T- and B-ALL at the single-cell level will be performed for the first time. To analyze the clonal architecture of leukemic cells, genomic rearrangements of all existing T- and B-cell receptor genes, including previously unanalyzed TRA loci, will be analyzed simultaneously for the first time, which will allow obtaining previously inaccessible accuracy in determining clonal structures of leukemia cells. In addition, the analysis of leukemic cells transcriptomes will be performed to find genetic factors underlying the formation of ALL clonal diversity.