B-acute lymphoblastic leukaemia (B-ALL) is the most common cancer in children, with 20% of patients relapsing. CD9, a transmembrane protein, is linked to the migratory and adhesion capacities of leukaemia cells and could be associated with relapses. The aim of this project is to understand how CD9 regulation can be a marker of potential relapses, using bone and blood sampling of newly diagnosed patients at 3 crucial moments of therapy.

B-acute lymphoblastic leukaemia (B-ALL) is the most common cancer in children, with 20% of patients relapsing despite major therapeutic advances. A research team of the Development and Genetic Institute in Rennes has identified that the expression of CD9, a transmembrane protein, is linked to the migratory and adhesion capacities of leukaemia cells, enabling them to persist in niches such as the testis. CD9-associated relapses often arise from these niches. Understanding the regulation of CD9 expression is therefore essential.

The hypothesis on which this project is based is that CD9 expression could be orchestrated by ncRNAs. Due to the complexity of deciphering circRNA-miRNA-mRNA networks, an exploration of patient blasts is envisaged in order to delineate a specific non-coding RNA network regulating CD9 expression from bone marrow and blood samples of paediatric-aged patients with B-ALL. If this hypothesis is confirmed, the ncRNAs identified could constitute new specific diagnostic and prognostic markers, or even therapeutic targets.

To confirm this hypothesis, bone and blood sampling of newly diagnosed patients will be collected at the diagnosis, after first phase of treatment and at the relapse, if it occurs.

Inclusion Criteria:

• Under 18 years
• With established diagnosis of B-ALL
• Initial diagnosis made in the investigating centre
• Having received oral and written information about the protocol, or oral only if the patient is unable to read.
• Having signed a consent form if the patient is capable of giving informed written consent.
• Whose legal guardians have received oral and written information about the protocol, and have signed a free, informed and written consent.
• Beneficiary of a social security scheme

Exclusion Criteria:

• Isolated extramedullary involvement at inclusion
• Patient of childbearing age without effective contraception.
• Adult subject to legal protection (safeguard of justice, curatorship, guardianship), person deprived of liberty.