Developmental interplay between transcriptional alterations and a targetable cytokine signaling dependency in pediatric ETO2::GLIS2 leukemia

Background: Several fusion oncogenes showing a higher incidence in pediatric acute myeloid leukemia (AML) are associated with heterogeneous megakaryoblastic and other myeloid features. Here we addressed how developmental mechanisms influence human leukemogenesis by ETO2::GLIS2, associated with dismal prognosis. Methods: We created novel ETO2::GLIS2 models of leukemogenesis through lentiviral transduction and CRISPR-Cas9 gene editing of human fetal and post-natal hematopoietic stem/progenitor cells (HSPCs), performed in-depth characterization of ETO2::GLIS2 transformed cells through multiple omics and compared them to patient samples. This led to a preclinical assay using patient-derived-xenograft models to test a combination of two clinically-relevant molecules. Results: We showed that ETO2::GLIS2 expression in primary human fetal CD34⁺ hematopoietic cells led to more efficient in vivo leukemia development than expression in post-natal cells. Moreover, cord blood-derived leukemogenesis has a major dependency on the presence of human cytokines, including IL3 and SCF. Single cell transcriptomes revealed that this cytokine environment controlled two ETO2::GLIS2-transformed states that were also observed in primary patient cells. Importantly, this cytokine sensitivity may be therapeutically-exploited as combined MEK and BCL2 inhibition showed higher efficiency than individual molecules to reduce leukemia progression in vivo. Conclusions: Our study uncovers an interplay between the cytokine milieu and transcriptional programs that extends a developmental window of permissiveness to transformation by the ETO2::GLIS2 AML fusion oncogene, controls the intratumoral cellular heterogeneity, and offers a ground-breaking therapeutical opportunity by a targeted combination strategy.