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Susan CHAN
Tel. : +33 (0)3 88 65 34 31
Tel. : +33 (0)3 88 65 34 61
Philippe KASTNER
Tel. : +33 (0)3 88 65 34 72

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Function Of The Ikaros Transcription Factor In The Homeostasis And Transformation Of B1 Progenitors

Reference : PhD Philippe KASTNER

Offer publication : April 5, 2016

B lymphocytes, the cells that produce antibodies, exist as several subtypes. Among these, B1 lymphocytes are considered as part of the innate immune system, as they produce natural polyreactive antibodies. These B cells are mostly generated during fetal life, but B1 specific progenitors also exist in the adult bone marrow. However, the mechanism that regulate their development remain poorly understood. In addition, since many pediatric B-cell acute lymphoblastic leukemias (B-ALL) are initiated in utero, fetal B1 progenitors may be at the origin of a subset of B-ALL, but this has not been investigated. It is therefore important to better understand the mechanisms that govern B1 cell diferentiation, and their possible
implication in leukemias.

Our team has recently identified the transcription factor Ikaros as a negative regulator of B1 cell development (Macias-Garcia et al., J Biol Chem 2016). Notably, the deletion of Ikaros in adult mice leads to an increase of B1 progenitors in the bone marrow. Since Ikaros is also a tumor suppressor which exhibits loss of function in 20% of B-ALL (notably in the majority of cases that express the BCR-ABL fusion oncoprotein), our hypothesis is that
the loss of Ikaros could contribute to the development of "B1" cell leukemias.

The project aims at studying the role of Ikaros in B1 progenitors, and at understanding if the loss of its function favors their transformation. Specifically:

1) How does Ikaros regulate B1 cell differentiation ? To better understand the biological pathways important in WT B1 and B2 progenitors, he/she will first characterize their gene expression program and identify specific sets of genes or pathways in each type of progenitor. The transcriptome of Ikaros
deficient progenitors will also be determined to identify Ikaros dependent genes in these populations. In addition, he/she will study if the response to TLSP, a cytokine important for the expansion of B1 progenitors, is altered. These studies should allow to better understand the biology of B1 progenitors, and how it is controlled by Ikaros.

2) Does Ikaros loss favor the emergence of B1 leukemias ? This question will be studied in the mouse. B1 and B2 WT or Ikaros-deficient progenitors will be amplified in vitro, and transduced with a retrovirus that expresses BCR-ABL.The frequency of transformation will be evaluated in clonogenic cultures, and by transplantation to immunodeficient mice under limiting dilution condition. The transcriptome of the B1 or B2-derived leukemias will be determined, in order to identify a molecular signature of B1 cell leukemias, and to evaluate if Ikaros loss impacts on this signature. We will also determine if this signature characterizes murine leukemias that arise in mice that are transgenic for BCR-ABL and haploinsufficient for Ikaros (collab.
Jacques Ghysdael, Institut Curie).

3) Do leukemias with a B1 phenotype exist among human B-ALL ? If yes, are Ikaros mutations frequent in these leukemias ? Human B1 cells have been shown to harbor distinct rearrangements of the immunoglobulin heavy chain. In collaboration with clinicians from Strasbourg and Paris, we will
study if these rearrangements characterize a subset of B-ALL, and if these cases exhibit an increased frequency of IKZF1 mutations.

These studies will be completed with the analysis of the expression of gene or markers specific for B1 cells. Notably, if specific markers for murine B1 leukemias are identified in (2), we will determine if these markers can also distinguish subsets of human B-ALL.

- WISHED SKILLS : Immunology and hematology. Medical knowledge of human leukemias

- EXPERTISES WHICH WILL BE ACQUIRED DURING THE TRAINING : Genomic analyses, mouse work, molecular biology, cancer biology

Your application

Application Deadline : Dec. 31, 2016

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