Overexpression of wild type IL-7Ra promotes T-cell acute lymphoblastic leukemia/lymphoma

Tight regulation of IL-7Ra expression is essential for normal T-cell development. IL-7Ra 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-7Ra overexpression, rather than mutational activation, on leukemogenesis remains unclear. Here, we show that overexpression of IL-7Ra in tetracycline-inducible Il7r transgenic and Rosa26 IL7R knock-in mice drives 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-7Ra can promote T-cell tumorigenesis even in the absence if IL-7Ra mutational activation.