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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.

Project description:MyD88 is an adaptor protein in Toll-like receptor and interleukin 1 receptor mediated signaling pathways that plays an essential role in activation of immune responses following pathogen recognition. We investigate that role in the zebrafish embryo model by using a zebrafish mutant line that contains a premature stop condon in the gene encoding MyD88, leading to a truncated protein that lacks domains important for its normal function. We infected these MyD88 mutants and wildtype individuals with Mycobacterium marinum to compare the resulting immune response by transcriptome profiling on total RNA isolated from single embryos. Autophagy regulator dram1 was identified as one of the MyD88-dependent genes. This RNAseq analysis was used to determine the effect of a truncation of the MyD88 protein on the innate immune response of zebrafish embryos during infection with Mycobacterium marinum. Myd88 mutant and wild type embryos were derived by incrossing homozygous myd88 mutant parents (allele hu3568, van der Vaart et al., 2013, Disease models & mechanisms 6, 841-854) or their wildtype siblings. RNA was isolated from pools of 20 embryos at 4 days post infection (4 dpi). The following treatment groups were used: homozygous mutants mock-injected with PBS/2%PVP 4 dpi, (2) wildtype siblings mock-injected with PBS/2%PVP 4dpi, (3) M. marinum-infected homozygous mutants 4dpi, (4) M. marinum-infected wildtype siblings 4dpi. Embryos were grown at 28.5M-bM-^@M-^S30M-BM-0C in egg water and manually dechorionated at 24 hours post fertilization (hpf). Subsequently, embryos were infected at 28 hpf by micro-injecting 200 colony forming units (CFU) of Mycobacterium marinum Mma20 bacteria into the caudal vein, or were mock-injected with buffer (PBS/2%PVP) as a control. After injections embryos were transferred into fresh egg water and incubated for 4 days at 28M-BM-0C. After the incubation period, single embryos were snap-frozen in liquid nitrogen and RNA was isolated for RNAseq analysis.

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

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