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Leukemia. 2014 Mar;28(3):666-74. doi: 10.1038/leu.2013.346. Epub 2013 Nov 18.

Ligand-independent FLT3 activation does not cooperate with MLL-AF4 to immortalize/transform cord blood CD34+ cells.

Author information

1
GENYO, Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain.
2
1] GENYO, Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain [2] Faculty of Medicine, Department of Stem Cells, Development and Cancer, Cell Therapy Program of the University of Barcelona, Josep Carreras Leukemia Research Institute, Barcelona, Spain.
3
Institute of Pharmaceutical Biology/ZAFES/DCAL, Goethe-University of Frankfurt, Biocenter, Frankfurt, Germany.
4
Hospital Universitario de Salamanca, Servicio de Hematología, Salamanca, Spain.
5
1] GENYO, Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain [2] Faculty of Medicine, Department of Stem Cells, Development and Cancer, Cell Therapy Program of the University of Barcelona, Josep Carreras Leukemia Research Institute, Barcelona, Spain [3] Instituciò Catalana de Reserca i Estudis Avançats (ICREA).

Abstract

MLL-AF4 fusion is hallmark in high-risk infant pro-B-acute lymphoblastic leukemia (pro-B-ALL). Our limited understanding of MLL-AF4-mediated transformation reflects the absence of human models reproducing this leukemia. Hematopoietic stem/progenitor cells (HSPCs) constitute likely targets for transformation. We previously reported that MLL-AF4 enhanced hematopoietic engraftment and clonogenic potential in cord blood (CB)-derived CD34+ HSPCs but was not sufficient for leukemogenesis, suggesting that additional oncogenic lesions are required for MLL-AF4-mediated transformation. MLL-AF4+ pro-B-ALL display enormous levels of FLT3, and occasionally FLT3-activating mutations, thus representing a candidate cooperating event in MLL-AF4+ pro-B-ALL. We have explored whether FLT3.TKD (tyrosine kinase domain) mutation or increased expression of FLT3.WT (wild type) cooperates with MLL-AF4 to immortalize/transform CB-CD34+ HSPCs. In vivo, FLT3.TKD/FLT3.WT alone, or in combination with MLL-AF4, enhances hematopoietic repopulating function of CB-CD34+ HSPCs without impairing migration or hematopoietic differentiation. None of the animals transplanted with MLL-AF4+FLT3.TKD/WT-CD34+ HSPCs showed any sign of disease after 16 weeks. In vitro, enforced expression of FLT3.TKD/FLT3.WT conveys a transient overexpansion of MLL-AF4-expressing CD34+ HSPCs associated to higher proportion of cycling cells coupled to lower apoptotic levels, but does not augment clonogenic potential nor confer stable replating. Together, FLT3 activation does not suffice to immortalize/transform MLL-AF4-expressing CB-CD34+ HSPCs, suggesting the need of alternative (epi)-genetic cooperating oncogenic lesions.

PMID:
24240202
DOI:
10.1038/leu.2013.346
[Indexed for MEDLINE]

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