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Immune stress suppresses innate immune signaling in preleukemic precursor B cells to cause leukemia

ABSTRACT: We used microarrays to investigate gene expression changes in leukemic bone marrow from Pax5+/-;Myd88+/- mice compared with bone marrow precursor B cells from WT mice and to study the effect of Myd88 downregulation in healthy Pax5+/- proB cells. The initial steps of B-cell acute lymphoblastic leukemia (B-ALL) development usually pass unnoticed in children; germline or somatic alterations affecting transcription factor genes cause the appearance of preleukemic cells still compatible with normal hematopoiesis, and preclinical studies have shown that immune stressors can trigger the malignant transformation of these otherwise silent preleukemic precursors to full-blown B-ALL. Understanding how exposure to immune stressors drives this conversion is a longstanding and unsolved challenge. Here we unveiled a specific “gene/environmental factor” interaction triggering B-ALL development. Our data show that B-ALL development falls into the category of cancers associated with dysregulation of innate immunity, which plays a driving role in the clonal evolution of pre-malignant B-cell precursors toward B-ALL following exposure to an immune stress. Transcriptional profiling of B-ALL allowed the identification of an inflammation-dependent role for Myd88 as a key player in this process. A preleukemic B-cell-autonomous role was evidenced by a significant increase in B-ALL incidence upon Myd88 dowregulation in the leukemia-prone Pax5+/- model. Likewise, early innate immune response induction by Toll-like receptor (TLR) ligation during the preleukemic phase in Pax5+/- mice resulted in a significant delay of B-ALL development. These findings identify a central role for innate immunity dysregulation in B-ALL, with important implications for the understanding and potential therapeutic targeting of the preleukemic state in children.

ORGANISM(S): Mus musculus

PROVIDER: GSE221597 | GEO | 2023/08/10

REPOSITORIES: GEO

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Project description:ETV6-RUNX1 is associated with childhood B-cell acute lymphoblastic leukemia (B-ALL), but the consequence of ETV6-RUNX1 expression on cell lineage decision during B-cell leukemogenesis remains largely evasive. Clinically silent ETV6-RUNX1 preleukemic clones are frequently found in neonatal cord blood, but only a few carriers develop B-ALL as a result of the acquisition of secondary postnatal genetic hits, like KDM5C or PAX5 loss. However, understanding the mechanism involved in this transformation would advance the development of non-toxic prophylactic interventions to preleukemic carriers. Using genetic lineage tracing, we have examined the capacity of ETV6-RUNX1 in instructing a B-cell malignant phenotype. Restricted Cre-mediated activation of ETV6-RUNX1 from the endogenous Etv6 locus into B-cell precursors does not trigger B-ALL development. Similarly, concomitant transient ETV6-RUNX1 expression in hematopoietic progenitors close to restricted Cre-mediated introduction of second hit (Kdm5c loss) in B-cells fail to induce B-ALL. In contrast, targeting ETV6-RUNX1 in hematopoietic progenitors was required to induce leukemia. These mice develop either T-ALL or B-ALL, suggesting that the nature of the second hit may define tumor cell identity during ETV6-RUNX1 leukemogenesis. In order to uncover a potential exclusive effect of the second hit in establishing the leukemic phenotype, we next showed that the introduction of the second hit, either Kdm5c or Pax5 loss, to the ETV6-RUNX1 preleukemic clone confers the tumor B-cell identity without need of environmental infection exposure. The resulting B-ALLs clustered according to the second-hit by RNA sequencing (RNA-Seq) analysis. Together these results provide a novel paradigm for the generation of tumor B cells through ETV6-RUNX1 in vivo where the second hit confers the tumor cell-identity to the ETV6-RUNX1 preleukemic clone. These findings could be relevant to develop new therapeutic approaches to prevent disease development.

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Immune stress suppresses innate immune signaling in preleukemic precursor B cells to cause leukemia

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