Interleukin-7 receptor α (encoded by IL7R) is essential for lymphoid development. Whether acute lymphoblastic leukemia (ALL)-related IL7R gain-of-function mutations can trigger leukemogenesis remains unclear. Here, we demonstrate that lymphoid-restricted mutant IL7R, expressed at physiological levels in conditional knock-in mice, establishes a pre-leukemic stage in which B-cell precursors display self-renewal ability, initiating leukemia resembling PAX5 P80R or Ph-like human B-ALL. Full transformation associates with transcriptional upregulation of oncogenes such as Myc or Bcl2, downregulation of tumor suppressors such as Ikzf1 or Arid2, and major IL-7R signaling upregulation (involving JAK/STAT5 and PI3K/mTOR), required for leukemia cell viability. Accordingly, maximal signaling drives full penetrance and early leukemia onset in homozygous IL7R mutant animals. Notably, we identify 2 transcriptional subgroups in mouse and human Ph-like ALL, and show that dactolisib and sphingosine-kinase inhibitors are potential treatment avenues for IL-7R-related cases. Our model, a resource to explore the pathophysiology and therapeutic vulnerabilities of B-ALL, demonstrates that IL7R can initiate this malignancy.
Tight regulation of IL-7Rα expression is essential for normal T-cell development. IL-7Rα gain-of-function mutations are known drivers of T-cell acute lymphoblastic leukemia (T-ALL). Although a subset of T-ALL patients display very high IL7R mRNA levels and cases with IL7R gains have been reported, the impact of IL-7Rα overexpression, rather than mutational activation, on leukemogenesis remains unclear. Here, we show that overexpression of IL-7Rα in tetracycline-inducible Il7r transgenic and Rosa26 IL7R knock-in mice drives potential thymocyte self-renewal, and thymus hyperplasia due to increased proliferation of T-cell precursors, which subsequently infiltrate lymph nodes, spleen and bone marrow, ultimately leading to fatal leukemia. The tumors mimic key features of human T-ALL, including heterogeneity in immunophenotype and genetic subtype between cases, frequent hyperactivation of PI3K/Akt pathway that is paralleled by downregulation of p27Kip1 and upregulation of Bcl-2, and gene expression signatures evidencing JAK/STAT, PI3K/Akt/mTOR and Notch signaling activation. Notably, we also find that established tumors may no longer require high levels of IL-7R expression upon secondary transplantation and can progress in the absence of IL-7, but remain sensitive to inhibitors of IL-7R-mediated signaling Ruxolitinib (Jak1), AZD1208 (Pim), Dactolisib (PI3K/mTOR), Palbociclib (Cdk4/6), and Venetoclax (Bcl-2). The relevance of these findings for human disease are highlighted by the fact that T-ALL patient samples with high wild type IL7R expression display a transcriptional signature resembling that from IL-7-stimulated pro-T cells and, critically, from IL7R mutant T-ALL cases. Overall, our studies demonstrate that high expression of IL-7Rα can promote T-cell tumorigenesis even in the absence of IL-7Rα mutational activation.
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