2027 – DEVELOPMENTAL STAGE SHAPES LINEAGE FATE AND REVEALS A TARGETABLE PRELEUKEMIC STATE IN BCR::ABL1-DRIVEN LEUKEMIA

Abstract

Clonal hematopoiesis, predominantly linked to myeloid malignancies, has established that premalignant stem cell states can precede overt disease; analogous lymphoid preleukemic states remain poorly defined. BCR::ABL1 offers a unique model to dissect how a shared lesion drives distinct phenotypes: its two major isoforms (p190, p210) preferentially associate with B-cell acute lymphoblastic leukemia (B-ALL) and chronic myeloid leukemia (CML), respectively. We generated humanized xenograft models by CRISPR/Cas9 engineering of human primary hematopoietic stem cells (HSCs) across four developmental states and performed integrated single-cell RNA-seq and ATAC-seq across >200,000 cells. BCR::ABL1-driven transformation was strikingly isoform- and developmental state-dependent: in adult HSCs, p210 induced a CML-like myeloid disease, whereas p190 promoted lymphoid-biased output. Early developmental HSCs did not support CML-like transformation, indicating that CML fate requires adults-stage HSCs and p210 signaling. Mechanistically, adult HSCs exhibited higher baseline chromatin accessibility at CEBP-family motifs than early development HSCs, further amplified by p210, supporting a model in which developmentally-defined epigenetic priming cooperates with oncogenic signaling to dictate lineage fate. Across developmental states, both isoforms expanded a distinct ProB_VDJ transcriptional state consistent with a lymphoid preleukemic maturation arrest marked by inflammatory activation (TNF-α, IFN-γ). BCR::ABL1⁺ HSCs also showed reduced quiescence and increased oxidative phosphorylation (OXPHOS); OXPHOS inhibition with metformin significantly reduced lymphoid preleukemic expansion in vivo. Together, developmental state constrains BCR::ABL1 lineage fate through chromatin accessibility and defines a conserved metabolic vulnerability of a lymphoid preleukemic stem cell state.

Clonal hematopoiesis, predominantly linked to myeloid malignancies, has established that premalignant stem cell states can precede overt disease; analogous lymphoid preleukemic states remain poorly defined. BCR::ABL1 offers a unique model to dissect how a shared lesion drives distinct phenotypes: its two major isoforms (p190, p210) preferentially associate with B-cell acute lymphoblastic leukemia (B-ALL) and chronic myeloid leukemia (CML), respectively. We generated humanized xenograft models by CRISPR/Cas9 engineering of human primary hematopoietic stem cells (HSCs) across four developmental states and performed integrated single-cell RNA-seq and ATAC-seq across >200,000 cells. BCR::ABL1-driven transformation was strikingly isoform- and developmental state-dependent: in adult HSCs, p210 induced a CML-like myeloid disease, whereas p190 promoted lymphoid-biased output. Early developmental HSCs did not support CML-like transformation, indicating that CML fate requires adults-stage HSCs and p210 signaling. Mechanistically, adult HSCs exhibited higher baseline chromatin accessibility at CEBP-family motifs than early development HSCs, further amplified by p210, supporting a model in which developmentally-defined epigenetic priming cooperates with oncogenic signaling to dictate lineage fate. Across developmental states, both isoforms expanded a distinct ProB_VDJ transcriptional state consistent with a lymphoid preleukemic maturation arrest marked by inflammatory activation (TNF-α, IFN-γ). BCR::ABL1⁺ HSCs also showed reduced quiescence and increased oxidative phosphorylation (OXPHOS); OXPHOS inhibition with metformin significantly reduced lymphoid preleukemic expansion in vivo. Together, developmental state constrains BCR::ABL1 lineage fate through chromatin accessibility and defines a conserved metabolic vulnerability of a lymphoid preleukemic stem cell state.