Benzene-induced myelosuppression confers a survival advantage to hematopoietic progenitors: Single-cell analysis of malignant transformation dynamics in a murine model.

Benzene is a well-established environmental leukemogen, but how benzene-induced myelosuppression evolves into rapid malignant transformation remains unclear. To deconstruct this progression, Mll-Af9 chimeric mice were subjected to chronic benzene inhalation. Following exposure, mice exhibited prolonged hematotoxicity, but the initially suppressed white blood cells and CD45.2⁺ pre-leukemic cells progressively rebounded, significantly exceeding control levels by week 10. Serial colony-forming assays revealed suppressed clonogenic capacity at week 8, followed by a robust enhancement at week 10 that was predominantly driven by sustained colony-forming unit-granulocyte-macrophage progenitor (CFU-GM) expansion. These phenotypic shifts pinpointed the 8-10-week interval as the critical tipping point for the suppression-to-proliferation switch. Single-cell RNA sequencing identified granulocyte-macrophage progenitors (GMPs) as the principal cellular drivers of this transformation. During the suppressive phase, a distinct GMP subset displayed cell cycle arrest yet aberrantly co-activated myeloid differentiation (CEBPA) and pro-leukemic self-renewal (HOXA9/MEIS1) programs, accompanied by marked S100a8/S100a9 upregulation. This stress-adapted phenotype transcriptional state was associated with subsequent transcriptional reversal and clonal outgrowth that ultimately shortened overall survival. Clinical relevance was further supported by The Cancer Genome Atlas cohort, where elevated S100A8/S100A9 expression correlated with poorer survival in acute myeloid leukemia patients. Collectively, these findings delineate a stress-driven evolutionary pathway linking benzene-induced marrow suppression to early pre-leukemic adaptation and highlight S100a8/S100a9-associated transcriptional programs as potential early molecular features of benzene-related leukemogenic progression.