Pilot Project Grant Program Awardees

2009-2010 Pilot and Feasibility Grant Winners

• Stephanie Halene, M.D.
  Instructor/Attending Physician
  Department of Internal Medicine—Section of Hematology
  The role of C/EBPα in acute megakaryoblastic leukemia

• Ruslan Medzhitov, Ph.D.
  Professor of Immunobiology
  Howard Hughes Medical Institute Investigator
  Analysis of cell competition among hematopoietic stem cells

• Warren Shlomchik, M.D.
  Associate Professor of Medicine and Immunobiology
  Understanding GVL-resistance by 2 photon microscopy of leukemia stem cells and effector T cells in vivo

Previous Grant Awardees:

• 2008-2009
• 2007-2008
• 2006-2007
• 2005-2006
  

Stephanie Halene, M.D.
Instructor/Attending Physician
Department of Internal Medicine—Section of Hematology

The role of C/EBPα in acute megakaryoblastic leukemia
Acute megakaryoblastic leukemia (AMKL) with the translocation t (1;22) is a subset of AMKL in children with poor outcome.  The t (1; 22) generates the OTT-MKL1 fusion gene product.  The mechanism by which the fusion protein promotes leukemogenesis is largely unknown.  Studies have been hampered by the rarity of primary samples and the lack of transforming activity.  My preliminary data indicate that the fusion protein leads to aberrant transcriptional activity and that it may inappropriately activate SRF-dependent gene expression.  The generally accepted mechanism of leukemogenesis involves two steps: Deregulation of transcription and proliferation. OTT-MKL1 affects expression of key hematologic transcription factors in hematopoietic cells. In a tet-inducible HEL cell system, I identified CEBPα as one of the most differentially deregulated transcription factors.

C/EBPα, a member of the CCAAT/enhancer binding protein family, is located on chromosome 19 q and is essential in myeloid differentiation.  Many reports have implicated C/EBPα mutations and transcriptional deregulation in acute myeloid leukemia and have confirmed its prognostic relevance.

C/EBPα mutational status in AMKL is not known and has rarely been analyzed in other non-myeloid leukemias.  However, chromosome 19 abnormalities in AMKLs are a recurrent abnormality.  Here I propose to study the effects of deregulated expression of C/EBPα on megakaryocytic differentiation and to analyze CEBP expression and mutation status in primary AMKLs.

Ruslan Medzhitov, Ph.D.
Professor of Immunobiology
Howard Hughes Medical Institute Investigator

Analysis of cell competition among hematopoietic stem cells
Elimination of stressed, damaged or otherwise suboptimal cells is important for tissue f unction and maintenance.  However, cell-autonomous mechanisms may not be sufficient for the efficient elimination of unfit cells.  Cell competition has been described in Drosophila as an active process that promotes selection of the fittest cells.  Thus, under certain conditions, cell fate may depend on the relative status of other cells in the same tissue.  This may be particularly important for long lived stem or progentitor cells.  However, little is known about cell competition in mammals.  We have recently described a novel type of cell competition in the hematopoietic system of mice.  This competition is induced by stress and controlled by p53.  Unlike the classical p53-mediated response, it depends on relative rather than absolute levels of p53 activity in competitors, and is restricted to stem cells.  Other types of cell competition, mediated by other tumor suppressors such as PTEN, likely play an important role in normal physiology of HSCs, as well as cancer initiation.  We are proposing a simple approach to develop and characterize mosaic mouse models to study non-cell-autonomous roles of PTEN and other tumor suppressors in cell competition among HSCs.

Warren Shlomchik, M.D.
Associate Professor of Medicine and Immunobiology

Understanding GVL-resistance by 2 photon microscopy of leukemia stem cells and effector T cells in vivo
Much of the efficacy of allogeneic stem cell transplantation in treating hematologic malignancies is due to the T cell-mediated graft-vs-leukemia (GVL) effect.  Chronic phase CML (CP-CML) is the most GVL-sensitive leukemia whereas most other neoplasms are relatively GVL-resistant.

The basis for differential susceptibility, even between such closely related leukemias as CP-CML and GVL-resistant blast crisis CML (BC-CML) is unknown.  A detailed understanding of the mechanisms underlying GVL-resistance is essential to develop approaches to make GVL-resistant cancers more GVL-sensitive.  To address this we have been dissecting GVL responses against mouse models of GVL-sensitive chronic phase and GVL-resistant blast crisis CML.

Mouse chronic phase CML (mCP-CML) is induced by the retroviral transduction of mouse bone marrow with bcr-abl.  Mouse blast crisis CML (mBC-CML) is created by transducing bone marrow with bcr-abl and a fusion between NUP98 and HOXA9.  We hypothesize that leukemia stem cells (LSCs) are the key GVL targets and have sort-purified both mCP-CML and mBC-CML LSCs.  We hypothesize that LSCs are the key targets of GVL and that GVL resistance is manifest in the interaction between effector T cells and mBC-CML LSCs.  We will characterize these interactions in vivo at the cellular level with two photon microscopy.