Haematopoietic stem cells, niches
and differentiation pathways
Thomas Graf and Andreas Trumpp
Haematopoietic stem cells (HSCs) continuously replenish blood cells that are lost by
attrition or tissue damage. They are capable of self-renewal and are currently the only
adult stem-cell type routinely used in clinical settings to replace lost cells. HSCs are mostly
quiescent but can be mobilized from their niche to proliferate and differentiate intolineages of the innate and adaptive immune system, as well as into red blood cells andplatelets. Cell-fate decisions are initiated and maintained by specific combinations oftranscription factors, the activity of which is orchestrated by extrinsic and intrinsic signals.
The study of changes in regulatory networks during haematopoietic differentiation has
long served as a paradigm for basic processes of cell-fate specification and its aberrations,such as those that occur in leukaemia. The easy accessibility and transplantability of normal
and leukaemic haematopoietic cells has led to the discovery of cytokines, oncogenes andcancer stem cells and to some of the most celebrated successes of targeted drug design.

Guide through the poster
Placenta

HSC niches

Yolk sac

Bone marrow

Sinusoid
Mesenchymal HSC precursors

HSCs are transiently present
in the placenta (E11–E15)

Bone marrow

Thymic rudiment
Mouse embryo

Endothelial cell

CXCL12-expressing
reticular cell

From E10 onwards, AGM-derived
HSCs colonize the fetal liver,where they expand and mature.
Approximately at birth, HSCs start
to migrate to the bone marrow,
which becomes the main site ofhaematopoiesis in the adult.

HSCs are generated in theAGM between E8.5 and E.11.5

TPO
GATA1
FOG1ETS1

Vascular niche

Eosinophil

Erythrocyte

Megakaryocyte

EPO
GATA1
FOG1
EKLF

IL-5
GATA2
C/EBPαFetal liver
F-HSC

ST-HSCLT-HSC

IL-3

MPP

ECM

MBT

ID2SPIB
IL-7
SCF
FLT3L

Low O2MTNK

Neutrophil

CXCL12expressing
reticular cell

Macrophage Megakaryocyte

T-cell developmentin the thymus

Sonic
hedgehog

Phenotypes of HSCs
Mouse: Lin–Sca1+Kit+CD34–CD48–CD150+
Human: LIN–CD34+CD38–THY1lowKIT+

PatchedNotchligand
DLL4producing
corticalepithelial
cellEffect on self-renewal capacity+ (Promote HSC maintenance and/or quiescence): BMI1, FOXO, GFI1, STAT5, ATM, p57, HOXB4– (Promote HSC proliferation and/or differentiation): cMYC, cMYB, JUNB, β-catenin, p18, p27

Adhesion

Self-renewal,
Survival

Dormancy,
adhesion

Self-renewal

Lodging

CXCL12Migration

RAC
KIT

CD44

IgM+NK cell
Immature
B cell (T1)
Fetal precursor

IL-7
RAG
SOX13

B-1a/b cell
(In peritoneum
as well as in spleen)γδ T cell

DN3
TCRβ GATA3
Notch1 RAG

IgMhi
IgDlow
Antigenstimulation,
helper T-cells

OPNBMP
ECM

Migration
TCF
E2A?

Calciumreceptor

β-catenin

Hyaluronicacid

Abcam Stem Cell antibodies you can rely on!
Abcam supplies primary and secondary antibodies and reagentsto researchers worldwide. We ship direct to over 60 countries
and have offices in the UK, US and Japan, as well as offering
customer support in English, French, German and Japanese.
We are rapidly developing and expanding our range, looking for
new targets and improving our existing antibodies. To help us with
this, we actively attend, support and help organise conferences on
Stem Cell research. Find out more on our Stem Cells resource page:

GATA3
RAG

Marginal-zone
B cellICAM1 orVCAM1DPFrizzled

IL-15
TCRα

SCA1TCRαGATA3ThPOKTCRαRUNX3TReg cell
TGFβ
FOXP3
RUNX1IgMlow
IgDhi

Short-lived
plasma cell

Follicular B cell

LRP5or LRP6Ca2+

NKT cellAntigenstimulation,
helper T-cells
APRIL/BAFF

SP CD4+

SP CD8+WNT
PTH

Membranebound SCF

JaggedWe have over 30,000 antibodies in our catalogue.
Our Stem Cell Markers range includes over 2000 antibodies to:• Embryonic Stem Cells• Embryonic Germ Cells• Endothelial progenitors• Hematopoietic progenitors• Mesenchymal Stem Cells• Neural Stem Cells• Neural Crest Stem Cells• Ectoderm, Mesoderm and Endoderm lineages• Wnt, TGF-β, Hedgehog and Notch signaling pathways

T-cell developmentin the periphery(spleen andlymph node)

IFNγ
IL-12
T-bet
STAT4
RUNX3

SP CD8+SP CD4+HSC synapse

Quality and honesty are our top priorities. Our Abpromise
guarantees full technical support from our experienced team.
If an antibody doesn’t work as it says on our datasheet we will
give you a full refund or replacement if you tell us within
90 days. We publish everything we know about every producton our datasheets and our catalogue is web-based. This allows
daily updates and far more information than in any printed
catalogue, including customer reviews, technical enquiries andlinks to publication references. Visit our website today and see
for yourself:

Memory T cell

Effector T cellAbbreviations
AGM, aorta–gonad–mesonephros; ANG1, angiopoietin 1;
APRIL, a proliferation-inducing ligand; ATM, ataxia-telangiectasia
mutated; BAFF, B-cell-activating factor; BCL, B-cell lymphoma;
BCR, B-cell receptor; BLIMP1, B-lymphocyte-induced
maturation protein 1; BMP, bone morphogenetic protein;
BMPR1A, bone morphogenetic protein receptor, type 1 A;
C/EBPα, CCAAT/enhancer-binding protein α; CLP, commonlymphoid progenitor; CMP, common myeloid progenitor;CXCL12, CXC-chemokine ligand 12; CXCR4, CXC-chemokine
receptor 4; DC, dendritic cell; DLL4, delta-like ligand 4;
DN, double negative; DP, double positive; E2A, transcription
factor E2A; EBF, early B-cell factor; ECM, extracellular matrix;
EGR1, early-growth response; EKLF, erythroid Kruppel-likefactor; EPO, erythropoietin; ETP, early T-cell-lineage progenitor;

TH1 cell

IL-6
BLIMP1
STAT3
NF-κB

IL-6
TGFβ
RORγt
Plasma
cell

IL-4
GATA3
STAT6

PTHR

www.abcam.com/stemcells

BAFF
Strong BCR
signal?
?

ANG1

BMPR1A

IgMlow
IgD+Mature
B cell (T2)

Notch2BAFF
Weak BCR
signalVLA4
CadherinsCXCL12

CD44

Notch

Cadherins

VLA5

TIE2Self-renewal
Non-canonical
WNT signalling

?

CXCR4

www.abcam.com/stemcells

Ikaros
ETS1
PU.1

DN4
MPL

Osteoblast

IL-15
IL-2
ID2

TCRβ
GATA3
RAG

Survival
MCL1

Self-renewal
Dormancy

Immature B cell

DN2

Smoothened

TPO

Pre-B cell

CXCL12-expressing
reticular cell

IL-7
TCF
FLT3L PU.1
E2A
GATA3

Nucleus

Dormant HSC

Pro-B cell

IgM

BCR
RAG

B-cell developmentin the spleen

Notch1
IkarosETP/
DN1

B cellCXCL12expressing
reticular cell

Pre/proB cell

preBCR
RAG

TSP

Osteoblast

Bone
Macrophage/neutrophil

DCCXCL12
PAX5

NK cellOsteocyte

T cell

DCFLT3L E2A
CXCL12 EBF

Differentiation,
migration andexpansion

Dormant
LT-HSCMBGM-CSF
IL-4

DCCLP

LMPP

MPP

Monocyte/macrophage

ID2
SPIB

Fibroblast

Endosteal niche

M-CSF PU.1hi
EGR1/2 IRF8
MAFB C/EBPα
GMP

Mast cell

Dividing HSC

Neutrophil

PU.1hi
C/EBPα

CMP

FLT3L
SCF
PU.1

Homeostasis (rare)
Injury (frequent)

Erythrocyte

IL-3
GATA2
C/EBPαMEP
Activated
LT-HSC

G-CSF
C/EBPαGFI1Basophil

PAX5
BCL6

IgG+Memory B cell

TH2 cell

TH17 cellETS1, v-ets erythroblastosis virus E26 oncogene homologue 1;
F-HSC, fetal HSC; FLT3L, FMS-related-tyrosine-kinase-3 ligand;
FOG1, friend of GATA 1; FOX, forkhead box; GATA1, GATAbinding protein 1; G-CSF, granulocyte colony-stimulating factor;
GFI1, growth-factor independent 1; GM-CSF, granulocyte/macrophage CSF; GMP, granulocyte/macrophage progenitor;
HOXB4, homeobox B4; HSC, haematopoietic stem cell; ICAM1,intercellular adhesion molecule 1; ID2, inhibitor of DNAbinding 2; IFNγ, interferon-γ; IL, interleukin; IRF8, interferonregulatory factor 8; LIN, lineage; LMPP, lymphoid primed MPP;
LRP5, low-density-lipoprotein-receptor-related protein 5;
LT-HSC, long-term repopulating HSC; MB, myeloid/B-cell
precursor; MBT, myeloid, T- and B-cell precursor; MCL1,myeloid-cell leukaemia sequence 1; M-CSF, macrophagecolony-stimulating factor; MEP, megakaryocyte/erythroid
progenitor; MPL, myeloproliferative leukaemia virus oncogene;

MPP, multipotent progenitor; MT, myeloid/T-cell precursor;
NF-κB, nuclear factor-κB; NK, natural killer; OPN, osteopontin;
PAX5, paired box gene/protein 5; PTH, parathyroid hormone;
PTHR, parathyroid hormone receptor; PU.1, transcription factor
PU.1; RAG, recombination-activating gene 1; RORγt, retinoicacid-receptor-related orphan receptor-γt; RUNX, runt-relatedtranscription factor; SCA1, stem-cell antigen 1; SCF, stemcell factor; SOX13, SRY box 13; SPIB, Spi-B transcription
factor; STAT, signal transducer and activator of transcription;
ST-HSC, short-term repopulating HSC; T1, transitional B cell 1;
TCF, T-cell factor; TCR, T-cell receptor; TGFβ, transforming
growth factor-β; TH, T helper; ThPOK, T helper-inducing
POZ/Kruppel factor; TIE2, tyrosine kinase receptor 2;
TPO, thrombopoietin; TReg, T regulatory; TSP, thymus-seedingprogenitor; VCAM1; vascular cell-adhesion molecule 1;
VLA, very late antigen.

The upper left region of the poster shows a mouseembryo with its haematopoietic anlagen. Although theextent of yolk-sac contribution to the formation of adult
HSCs is controversial, most HSCs are probably formed inthe aorta–gonad–mesonephros (AGM) region. From here,
stem cells seed the fetal liver, where they expand anddifferentiate into myeloid and lymphoid lineages.
Subsequently, HSCs exit the liver and populate
specialized bone-marrow microenvironments (niches) inwhich they gradually become quiescent. As shown in thelower left panel, dormant HSCs are mostly located close
to the lining of the trabecular bone, the endosteal niche.
This niche contains osteoblasts and CXC-chemokine
ligand 12 (CXCL12)-expressing reticular (CAR) cells.
Several cell adhesion molecules, together with shortrange signalling molecules, control HSC lodging andmaintenance (lower left panel). In response to specificsignals, it is thought that HSCs are recruited to vascularniches — that are comprised of CAR cells andfenestrated sinusoidal endothelial cells — where they
begin to divide, differentiate and enter the circulation.
Bone-marrow-derived thymus-seeding progenitors(TSPs) seed the thymus and become committed to theT-cell lineage (lower right panel). In the thymus, the cells
travel from the cortex through the subcapsular zone tothe medulla, encountering different epithelial niches
that guide them through several developmental stages.
Finally, CD4+ and CD8+ T cells enter the circulation anddifferentiate into mature effector and helper T cells inthe spleen and lymph nodes. B-lineage cells become
committed in the bone marrow and, after immature
B cells enter the circulation and home to the spleen,
they mature into antibody-secreting memory B cells andplasma cells (lower right panel).
The differentiation pathways are shown beginningwith HSCs and ending with mature cells. Dotted lines
represent transitions in which the origin of the moremature cell is not clear. Arrows indicate points ofmigration of circulating cells (with the exception of theHSC synapse panel). It is likely that the early stages of
HSC development represent a continuum. There are still
uncertainties about several parts of the pathways. The
poster shows multipotent progenitors (MPPs) branching
into megakaryocyte/erythroid progenitors (MEPs) andlymphoid-primed multipotent progenitors (LMPPs).
LMPPs either become common lymphoid progenitors(CLPs) or common myeloid progenitors (CMPs) andgranulocyte/macrophage progenitors (GMPs). However,
GMPs can also generate eosinophils, basophils and mast
cells and it is possible that more than one pathway togranulocytes and macrophages exists. Finally, there arecontroversies about the developmental origin of thedifferent types of dendritic cells and B cells. The poster
also shows lineage-instructive signals such as chemokines,
cytokines and transcription factors at the points where
they are required. The definition of a lineage-instructive
factor is complex and is ideally based on gene ablation,
cell-type-specific gene inactivation and gain-of-function
experiments. Since this applies only to a fraction of thefactors shown here, the information provided issomewhat speculative. Also, only transcription factorsthat act dominantly during lineage commitment arelisted, but not those that need to be silenced.
Thomas Graf is an ICREA investigator at the Centre for Genomic Regulation,
Dr Aiguader 88, E08003 Barcelona, Spain. e-mail: thomas.graf@crg.esAndreas Trumpp is at the Swiss Institute for Experimental Cancer Research (ISREC)
and the Ecole Polytechnique Fédérale de Lausanne (EPFL), Chemin des Boveresses155, 1066 Epalinges, Lausanne, Switzerland. e-mail: Andreas.Trumpp@isrec.ch
Supplementary information (glossary terms and background reading) is associatedwith the online version of this poster. www.nature.com/nri/posters/hsc
Edited by Elaine Bell; copy edited by Marta Tufet; designed by Neil Smith andSimon Fenwick. © 2007 Nature Publishing Group.

Glossary
Haematopoietic stem cells(HSCs). Cells that are capable of reconstituting all lineages of thehaematopoietic system after transplantation into lethally irradiatedmice. Long-term repopulating HSCs (LT-HSCs) do this life-long andafter secondary transplantations into irradiated hosts, whereas
short-term repopulating HSCs (ST-HSCs) only show multilineage
repopulation for a few weeks. LT- and ST-HSCs can be identified
and isolated by flow cytometry on the basis of their expression of
specific cell-surface antigens.
Lineage commitment
Also known as cell-fate determination; a process whereby HSCs
become specialized while losing their self-renewal capacity.
Progenitor cells
Also known as precursor cells; are intermediates between HSCs anddifferentiated cells with restricted differentiation potential, highproliferative capacity, but little or no self-renewal capacity. They
are probably equivalent to the transit amplifying cells of other adultstem-cell systems.
Myeloid cells
A term variously used to define non-lymphoid cells or cells of themonocyte–macrophage compartment (known as myelomonocyticcells).
Granulocytes
A group of cells including neutrophils, eosinophils, and basophils,
but the term is often used for neutrophils only.

Bone-marrow and/or HSC transplantation
A procedure involving injection of HSCs or bone marrow into
irradiated hosts to determine the cell’s biological potential. In theclinic it is a life-saving procedure after chemotherapy or radiation
therapy that destroys the haematopoietic system. Bone-marrowtransplantation typically requires immunosuppression to prevent
graft rejection due to tissue mismatch.
Cord-blood stem cells
These are fetal HSCs present in the umbilical cord of newborns.
They are used clinically as an alternative to bone-marrow-derived
HSCs. If stored frozen and thawed years later, they can be useful forregenerating the haematopoietic system of the donor, obviating thedanger of tissue rejection of mismatched transplants.
Dormancy and mobilization
Although HSCs self-renew, they are mostly quiescent, dividing
approximately once a month. Proliferation can be activated inresponse to injury or injection of cytokines, such as granulocytecolony-stimulating factor (G-CSF). G-CSF also induces the exitof HSCs from their niches and mobilization of the cells into thecirculation, a procedure that is used clinically to obtain HSCs from apatient’s blood.
Cytokines and chemokines
Secreted proteins that stimulate cell growth, survival anddifferentiation.

Stem-cell niches
Specialized microenvironments that control stem-cell dormancy
and the balance between stem-cell self-renewal and differentiation.

Colony-forming assay
If seeded in semi-solid medium, blood-cell precursors form colonies
in the presence of appropriate cytokines. This assay is widelyused to define a cell’s differentiation potential and to identify
biologically active molecules.

Plasticity
The capacity of defined cell types to acquire new identities. Theextent of plasticity of HSCs and haematopoietic progenitors underphysiological conditions is controversial and probably quite limited.
However, re-specification of cell fate can be induced by enforced
transcription factor expression, cell fusion or nuclear transfer.

Cancer and/or leukaemia stem cells
These are self-renewing cells capable of generating leukaemia
after transplantation. They can give rise to more differentiatedcells comprising the bulk of the leukaemia. Cancer stem cells,
first identified in acute myeloid leukaemia, are critical targets forintervention.

Self-renewal
The ability of cells to repeatedly generate at least one identicaldaughter cell.

Lineage priming
The promiscuous expression of myeloid–erythroid lineage
associated markers in HSCs.

Background reading
Wilson, A. & Trumpp, A. Bone-marrow haematopoietic-stem-cellniches. Nature Rev. Immunol. 6, 93–106 (2006).

Takahama Y. Journey through the thymus: stromal guides for T-celldevelopment and selection. Nature Rev. Immunol. 6, 127–135 (2006).

Rothenberg E.V. Cell lineage regulators in B and T cell development.
Nature Immunol. 8, 441–444 (2007).

Cumano, A. & Godin, I. Ontogeny of the hematopoietic system.
Annu Rev. Immunol. 25, 745–785 (2007).

Laiosa C.V., Stadtfeld, M. & Graf, T. Determinants of lymphoidmyeloid lineage diversification. Annu. Rev. Immunol. 24, 705–738(2006).

Nagasawa T. Microenvironmental niches in the bone marrow
required for B-cell development. Nature Rev. Immunol. 6, 107–116(2006).