Florence Armstrong

NKX3.1 is a direct TAL1 target gene that mediates proliferation of TAL1-expressing human T cell acute lymphoblastic leukemia

TAL1 (also known as SCL) is expressed in >40% of human T cell acute lymphoblastic leukemias (T-ALLs). TAL1 encodes a basic helix-loop-helix transcription factor that can interfere with the transcriptional activity of E2A and HEB during T cell leukemogenesis; however, the oncogenic pathways directly activated by TAL1 are not characterized. In this study, we show that, in human TAL1–expressing T-ALL cell lines, TAL1 directly activates NKX3.1, a tumor suppressor gene required for prostate stem cell maintenance. In human T-ALL cell lines, NKX3.1 gene activation is mediated by a TAL1–LMO–Ldb1 complex that is recruited by GATA-3 bound to an NKX3.1 gene promoter regulatory sequence. TAL1-induced NKX3.1 activation is associated with suppression of HP1-α (heterochromatin protein 1 α) binding and opening of chromatin on the NKX3.1 gene promoter. NKX3.1 is necessary for T-ALL proliferation, can partially restore proliferation in TAL1 knockdown cells, and directly regulates miR-17-92. In primary human TAL1-expressing leukemic cells, the NKX3.1 gene is expressed independently of the Notch pathway, and its inactivation impairs proliferation. Finally, TAL1 or NKX3.1 knockdown abrogates the ability of human T-ALL cells to efficiently induce leukemia development in mice. These results suggest that tumor suppressor or oncogenic activity of NKX3.1 depends on tissue expression.

Expression of CD34 and CD7 on human T-cell acute lymphoblastic leukemia discriminates functionally heterogeneous cell populations.

Leukemia-initiating/repopulating cells (LICs), also named leukemic stem cells, are responsible for propagating human acute leukemia. Although they have been characterized in various leukemias, their role in T-cell acute lymphoblastic leukemia (T-ALL) is unclear. To identify and characterize LICs in T-ALL (T-LIC), we fractionated peripheral blood cell populations from patient samples by flow cytometry into three cell fractions by using two markers: CD34 (a marker of immature cells and LICs) and CD7 (a marker of early T-cell differentiation). We tested these populations in both in vitro culture assays and in vivo for growth and leukemia development in immune-deficient mice. We found LIC activity in CD7+ cells only as CD34+CD7− cells contained normal human progenitors and hematopoietic stem cells that differentiated into T, B lymphoid and myeloid cells. In contrast, CD34+CD7+ cells were enriched in LICs, when compared with CD34−CD7+ cells. These CD34+CD7+ cells also proliferated more upon NOTCH activation than CD34−CD7+ cells and were sensitive to dexamethasone and NOTCH inhibitors. These data show that CD34 and CD7 expression in human T-ALL samples help in discriminating heterogeneous cell populations endowed with different LIC activity, proliferation capacity and responses to drugs.

Interleukin-18 produced by bone marrow- derived stromal cells supports T-cell acute leukaemia progression

Development of novel therapies is critical for T‐cell acute leukaemia (T‐ALL). Here, we investigated the effect of inhibiting the MAPK/MEK/ERK pathway on T‐ALL cell growth. Unexpectedly, MEK inhibitors (MEKi) enhanced growth of 70% of human T‐ALL cell samples cultured on stromal cells independently of NOTCH activation and maintained their ability to propagate in vivo. Similar results were obtained when T‐ALL cells were cultured with ERK1/2‐knockdown stromal cells or with conditioned medium from MEKi‐treated stromal cells. Microarray analysis identified interleukin 18 (IL‐18) as transcriptionally up‐regulated in MEKi‐treated MS5 cells. Recombinant IL‐18 promoted T‐ALL growth in vitro, whereas the loss of function of IL‐18 receptor in T‐ALL blast cells decreased blast proliferation in vitro and in NSG mice. The NFKB pathway that is downstream to IL‐18R was activated by IL‐18 in blast cells. IL‐18 circulating levels were increased in T‐ALL‐xenografted mice and also in T‐ALL patients in comparison with controls. This study uncovers a novel role of the pro‐inflammatory cytokine IL‐18 and outlines the microenvironment involvement in human T‐ALL development.

Optimized gene transfer into human primary leukemic T cell with NOD-SCID/leukemia-initiating cell activity

Optimized gene transfer into human primary leukemic T cell with NOD-SCID/leukemia-initiating cell activity