-Author name in bold denotes the presenting author
-Asterisk * with author name denotes a Non-ASH member
Clinically Relevant Abstract denotes an abstract that is clinically relevant.

PhD Trainee denotes that this is a recommended PHD Trainee Session.

Ticketed Session denotes that this is a ticketed session.

664 Distinct Bone Marrow Blood Vessels Differentially Regulate Normal and Malignant Hematopoietic Stem and Progenitor Cells

Hematopoiesis and Stem Cells: Microenvironment, Cell Adhesion and Stromal Stem Cells
Program: Oral and Poster Abstracts
Type: Oral
Session: 506. Hematopoiesis and Stem Cells: Microenvironment, Cell Adhesion and Stromal Stem Cells: Hematopoietic Stem Cell Niche
Monday, December 7, 2015: 3:30 PM
W304EFGH, Level 3 (Orange County Convention Center)

Tomer Itkin, PhD1*, Shiri Gur Cohen, PhD1*, Joel A. Spencer, PhD2*, Amir Schajnovitz3*, Saravana K. Ramasamy, PhD4*, Anjali P. Kusumbe, PhD4*, Yookyung Jung, PhD5*, Guy Ledergor, MD1*, Idan Milo, PhD1*, Michael Gustave Poulos, PhD6*, Maria Garcia Fernandez, PhD7*, Alexander Kalinkovich, MD PhD1*, Aya Ludin1*, Orit Kollet, Ph.D1, Guy Shakhar, PhD8*, Simon Mendez-Ferrer, PhD9,10, Jason M. Butler, PhD11, Shahin Rafii, MD12, Ralf H. Adams, PhD4*, David T. Scadden, MD3,13,14, Charles P. Lin5* and Tsvee Lapidot, PhD1

1Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel
2Center for Systems Biology and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA
3Center for Regenerative Medicine, Massachusetts General Hospital, Boston, MA
4Max Planck Institute for Molecular Biomedicine, Munster, Germany
5Massachusetts General Hospital, Boston
6Ansary Stem Cell Institute/Genetic Medicine, Weill Cornell Medical College, New York, NY
7Centro Nacional de Investigaciones Cardiovasculares Carlos III, Madrid, Spain
8The Weizmann Institute of Science, Rehovot, Israel
9Stem Cell Institute and Department of Haematology, University of Cambridge, and National Health Service Blood and Transplant, Cambridge, United Kingdom
10Centro Nacional de Investigaciones Cardiovasculares (CNIC), Madrid, Spain
11Ansary Stem Cell Institute, Weill Cornell Medical College, New York, NY
12Department of Medicine, Weill Cornell Medical College, New York, NY
13Harvard Stem Cell Institute, Cambridge, MA
14Stem Cell and Regenerative Biology, Harvard University, Cambridge, MA

Bone marrow (BM) endothelial cells (BMECs) form a network of blood vessels (BVs) that regulate both leukocyte trafficking and hematopoietic stem and progenitor cell (HSPC) maintenance. However, it is not clear how BMECs balance between these dual regulatory roles and if these events occur at the same vascular site. We define the BM architecture of functionally distinct BVs, their spatial localization and association with specific stromal precursors, which cooperatively regulate HSPC fate. BM stem and progenitor cell maintenance in a metabolically non-active state and leukocyte trafficking occur at separate sites and are differentially regulated by specific BVs with distinct permeability properties. BM arteries were found to be mostly encircled by aSMA+ pericytes whereas the ensuing small-diameter endosteal and trabecular arterioles were predominantly surrounded by stem cell-niche supporting stromal precursor cells. Live imaging and flow analysis revealed that endosteal arteriole BVs exhibited high flow rate, low permeability to external plasma from the peripheral blood, and high levels of adhesion- and tight-junction molecules. Primitive HSPCs located in peri-arteriole regions were found in a non-activated, low reactive oxygen species (ROS) state. Exposure of BM HSPCs to peripheral blood plasma, enhanced their metabolic activity, exhibited by enhanced intracellular ROS levels, and glucose uptake. The same was also evident for circulating HSPCs in the blood. Plasma-exposed HSPCs displayed enhanced motility alongside with reduced long-term repopulation potential. Live imaging showed that all immature and mature leukocyte bi-directional trafficking occurred exclusively at the more permeable sinusoids, located downstream to the endosteal arterioles. Of note, BM sinusoids contained a higher prevalence of ROShigh cells in their microenvironment, including HSPCs. Rapid AMD3100-induced HSPC mobilization preferentially affected sinusoidal but not arterial BVs permeability and CXCL12 chemokine release. Endothelial specific in vivo interference with CXCL12-CXCR4 interactions, via conditional CXCR4 genetic deletion, hampered BM barrier integrity resulting in enhanced HSPC egress. In line with these results we found that during conditions favoring BM stem and progenitor cells expansion, endothelial integrity was enhanced along with reduced HSPC bi-directional trafficking. Conversely, conditional endothelial specific induced genetic or pharmacologic disruption of barrier integrity augmented ROS levels in HSPCs, enhancing their bi-directional trafficking and differentiation while reducing their BM pool size and maintenance in a metabolically non-active state. Of note, humanized mice engrafted with pre-B ALL cells exhibited reduced BM barrier permeability most probably due to BM endothelium modification via FGF-2 secretion by the leukemic clone. Interestingly, human pre-B ALL cells displayed hypersensitivity to plasmatic exposure. We hypothesize that malignant cells modify BM endothelium to provide themselves with a supportive and protective microenvironment composed of undifferentiated BM stromal progenitors and tightly sealed endothelial barrier. In conclusion, our study identifies anatomically distinct BM BVs with different barrier functions serving as systemic leukocyte trafficking or HSPC BM maintenance sites with clinical therapeutic relevance.

Disclosures: Rafii: Angiocrine Bioscience: Consultancy , Equity Ownership .

*signifies non-member of ASH