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 Previous Article | Table of Contents | Next Article 
Blood, Vol. 93 No. 6 (March 15), 1999:
pp. 1916-1921
Hematopoietic Stem Cell Tracking In Vivo: A Comparison of
Short-Term and Long-Term Repopulating Cells
By
Sophie M. Lanzkron,
Michael I. Collector, and
Saul J. Sharkis
From the Johns Hopkins Oncology Center, Baltimore, MD.
 |
ABSTRACT |
We have previously demonstrated that we could separate long-term
repopulating stem cells from cells that provided radioprotection (short-term repopulating cells) on the basis of size and suggested that
this might be due to the quiescent nature of long-term repopulating cells. To further define the activity of these populations, we used a
dye (PKH26), which incorporates into the membrane of cells and is
equally distributed to daughter cells when they divide. We developed an
assay, which allowed us to retrieve PKH26+ long-term and
short-term repopulating cells in the hematopoietic tissues of the
recipients posttransplant. We were able to recover the labeled cells
and determine their cell cycle activity, as well as their ability to
reconstitute secondary lethally irradiated hosts in limiting dilution.
The results of our assay suggest that long-term repopulating cells are
quiescent in the bone marrow (BM) 48 hours after transplant. We were
able to detect only a few labeled cells in the peripheral blood
posttransplant and even though cells homed to both the spleen and BM,
more long-term repopulating cells homed to the marrow and only these
cells, which homed to the marrow, were capable of reconstituting
lethally irradiated secondary hosts long-term.
© 1999 by The American Society of Hematology.
| |
INTRODUCTION |
LITTLE IS UNDERSTOOD about the biology of
hematopoietic stem cell (HSC) homing after bone marrow (BM) transplant.
We have demonstrated that several populations of hematopoietic
reconstituting cells exist.1 Cells that provide
radioprotection (30-day survival) can be separated on the basis of size
from cells that engraft lethally irradiated hosts
long-term. Thus, small-sized cells obtained by counter
flow-elutriation (flow rate 25, FR25) will long-term reconstitute
lethally irradiated mice, but large cells (R/O) only provide for
short-term repopulation. By limited dilution FR25 cells, which are
further purified by removal of lineage positive cells
(Lin ), can reconstitute the mouse for its
lifetime.2 Because very few cells are injected (as low as
10 cells per recipient), it suggests that the homing mechanism is
exquisitely sensitive. It is thought that homing is mediated by contact
of stem cells with cells of the microenvironment through specific
receptors.3 The homing receptor has been described as a
110-kD glycoprotein, which requires galactosyl and mannosyl residues to
bind hematopoietic progenitors.4 That the process of
receptor recognition within hematopoietic environments is a necessity
for normal hematopoiesis has been demonstrated by blocking studies.
When neoglycoprotein probes have been used that block the binding of
the galactosyl or mannose residues to the receptor in long-term marrow
culture, the production of colony-forming unit-spleen (CFU-S) is
halted.3 Whether there is a difference in homing of
progenitors to the spleen versus the BM remains unclear.
Neoglycoprotein probes have been shown to block homing of CFU-S to the
BM, but do not have a similar effect on homing to the spleen. Whereas
treatment of donor cells before transplant with antibodies to very late
activation antigen-4 (VLA-4), a  1 integrin that binds
to fibronectin and vascular cell adhesion molecule  1
(VCAM-1) causes CFU-S to home more to the spleen and less
to the BM.5 These experiments suggest that the mechanism of
homing and the receptors involved are likely different for both the
spleen and the BM. However, others have shown that the seeding
efficiencies from normal donor marrow cells to the spleen and the femur
are similar.6
The rarity of stem cells in vivo makes them difficult to track.
Hendrikx et al7 have used the dye PKH26 to follow CFU-S localization in mice. PKH26 is a fluorescent marker that stains the
cell membrane, the intensity of the stain decreases in linear fashion
with each cell division. In this study, we have used PKH26 as a tool to
both track and describe the biology of stem cells in vivo. We will
demonstrate at 48 hours in the primary recipient we recover a maximum
number of PKH26 bright cells from the marrow, which allows us to
further study the biology of short-term and long-term repopulating cells.
| |
MATERIALS AND METHODS |
Animals.
Male and female C57 BL/6Jx DBA/2 F1 (B6D2F1)
mice (National Cancer Institute, Frederick, MD) 6 to 12 weeks of age,
were used for all studies. Mice were housed in sterile microisolator
cages. They were fed acidified water and sterilized lab chow ad libitum.
Isolating and staining HSC.
For each isolation experiment, 20 male mice were killed by cervical
dislocation and the hind legs removed. BM was flushed with medium from
the medullary cavities of both the femurs and tibias using a 25-gauge
needle. Single cell suspensions were produced by repeated passage
through the needle. Approximately 30 million whole bone marrow (WBM)
cells were set aside before counterflow centrifugal elutriation (CCE).
These served as control cells for recovery and cell cycle analyses (see
below). The cells were elutriated as previously
described.1,2 Cells were collected at a flow rate of 25 mL/minute (FR25, long-term repopulating cells) and from the rotor off
(R/O) fraction (short-term repopulating cells). The FR25 cells were
then lineage depleted by placing 107 cells on petri dishes
absorbed with a cocktail of 60 µg each rat antimouse AA4.1, B220,
CD5, GR-1, MAC-1, and TER119 as described.2 After
incubating at 4°C for 90 minutes, the nonadherent cells (Lin) were removed by gentle rocking and aspiration.
PKH26 staining.
The cells from each group (FR25Lin, R/O) were washed
in alpha-minimal essential media (MEM) without bovine serum albumin
(BSA) or serum. Samples were then resuspended in PKH diluent and added to the PKH26 dye at 10-µmol/L concentration. The cells were incubated at room temperature for 2 to 5 minutes with gentle agitation. To stop
the reaction, 2 mL of 100% serum was added, and the cells incubated
for 1 minute at room temperature with gentle agitation. A total of 4 mL
of alpha-MEM with 10% fetal calf serum (FCS) was added. The samples
were centrifuged and washed twice with 10 mL alpha-MEM with 10% FCS.
Male PKH26-stained cells from each group were then injected into
irradiated female mice at a dose of 2.5 million cells per animal. A
small number of cells were kept from each group to use as a control for
staining efficiency. A single mouse was injected with 2.5 million
stained WBM as a control.
Preparation of mice for transplant.
Female primary and secondary recipients received 105 cGy whole body
irradiation from a dual-cesium source (Atomic Energy of Canada, Kanata,
Ontario, Canada; 8.9 cGy per minute).
Tracking of PKH+ cells.
At 3, 24, 48, and 96 hours posttransplant, primary recipient mice were
killed. For the initial studies, peripheral blood was obtained by
retro-orbital bleed before recipient animals were killed, but as the
yield of PKH26+ cells from these samples was very low, the
remainder of experiments was limited to the spleen and BM. The spleen
was harvested and ground over wire mesh into media. The spleen samples
were then layered over Ficoll Hypaque and centrifuged at 1,200 rpm for
45 minutes. The upper layer was extracted and washed. BM samples were
harvested as described above. We obtained 1.43 × 106 ± 4.2 × 105 cells/hind limb (n = 7 mice, 14 hind
limbs) and 8.6 × 106 ± 1.5 × 105 cells/spleen (n = 5 mice) at 48 hours posttransplant.
BM cells for transplant were treated with ammonium chloride and then
layered over a FCS gradient to remove excess red blood cells and red
blood cell ghosts. PKH26 fluorescence intensity was then measured on a
Epics 740 flow cytometer (Counter Electronics, Hialeah, FL).
Cell cycle analysis.
BM and spleen samples (PKH26+ cells) collected by cell
sorting were washed with phosphate-buffered saline (PBS) containing 0.2% BSA and then resuspended in 100 µL of sucrose (250 mmol/L) trisodium citrate (40 mmol/L) buffer. They were treated with 0.9 mL
trypsin (30 µg/mL) and incubated for 10 minutes at room temperature. They were then incubated with 0.75 mL trypsin inhibitor (500 µg/mL) with ribonuclease A (100 µg/mL) for 10 minutes, stained with 0.75 mL
propidium iodide (416 µg/mL) with spermine tetra-hydrochloride (1.16 µg/mL, all staining reagents from Sigma, St Louis, MO) at 4°C and
analyzed by flow cytometry for percentage of cells in different phases
of the cell cycle.
Short-term and long-term reconstitution assays.
Mice that had been injected with PKH26-stained
FR25Lin or R/O cells as described above were killed
at 48 hours. The PKH26+ cells from BM or spleen were
collected by flow cytometry. The male PKH+ BM or spleen
cells from each group were injected at doses to include
101, 102, 103, or 104
cells along with 2 × 104 fresh female unstained R/O
cells into irradiated secondary female mice. Mice were observed for
30-day survival (short-term reconstitution). In addition, at 6, 12, and
24 weeks, mice receiving 102 PKH+ cells
underwent retro-orbital bleeds for donor engraftment. Fluorescent in
situ hybridization (FISH) for the Y chromosome was done as previously described2,8 to evaluate over time long-term
donor reconstitution.
| |
RESULTS |
We first examined the frequency of PKH26 bright cells at various times
posttransplant (Fig 1). The highest frequency of labeled cells was found at 48 hours posttransplant in recipient marrow from
both FR25Lin and R/O populations (Fig 1A and B,
respectively). This frequency allowed us to obtain sufficient cells for
further study of the biology of these cells. Staining
FR25Lin BM with PKH26 at time 0 results in 90.6%
PKH+ cells. At 48 hours postprimary transplant of
FR25Lin cells, we can recover 1.02% ± 0.04%
labeled cells from the donor within the hind limb BM of the recipient
and a reduced number 0.27% ± 0.2% in the spleen. If we
label R/O BM cells with PKH26, we can identify 0.01% ± 0.03%
PKH+ cells in the hind limb BM and 0.65% ± 0.19 % in
the spleen. Because tibia and femur marrow pooled represent
approximately 8% of the whole marrow skeleton,9 we
extrapolate that FR25Lin recovery is actually a mean
of 12.75% ± 1.0% from the recipient's whole BM and the R/O
recovered cells from recipient's whole marrow is 10 times less (1.25% ± 0.55%, Table 1; P < .001).
Taken together, these results indicate that more donor long-term
repopulating cells are found in the marrow than the spleen at 48 hours
posttransplant.
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| Fig 1.
Comparison of the number of PKH26+ marrow
cells detected in (A) FR25Lin and (B) R/O fractions at
different times posttransplant. These series of dot plots represent the
flow diagrams of FR25Lin (A) and R/O (B) frequencies of
PKH-labeled cells present before (0 hours) and various times
posttransplant of 2.5 × 106 cells. The number at the top
right of each panel represents the percentage frequency of PKH bright
cells detected. All plots represent equal numbers of cells counted
(100,000).
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Examination of WBM for cell cycle at time 0 demonstrates 17.0% of
cells are in S phase (data not shown). Cell cycle analysis shows that
at time 0 FR25Lin cells are mostly in
G1/G0 with very few percent of cells in S phase
(Fig 2A), but the fraction of R/O cells in
S phase appears to be greater (Fig 2D). At 48 hours posttransplant,
there is no increase in the percentage of cells in S phase of
FR25Lin cells recovered in either marrow (Fig 2B) or
spleen (Fig 2C) of primary recipients. Recovered
PKH+-labeled R/O cells at 48 hours display 12% to 14%
cells (Fig 2E and F) in S phase of the cell cycle.
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| Fig 2.
Examination of cell cycle activity from BM and spleen
from FR25 Lin and R/O cells pre- and
posttransplant (48 hours). A, B, and C represent FR25Lin
propidium iodide (PI)-labeled cell cycle analyses of preinjection (A),
48 hours in the BM (B), and 48 hours in the spleen (C). D, E, and F are
R/O PI cell cycle analyses of preinjection (D), 48 hours in the BM (E),
and 48 hours in the spleen (F). Values represent the mean ± standard
error of mean (SEM) for five experiments. Comparison of A to B and A to
C show no statistically significant differences for S phase.
Statistical analysis showed significant difference when comparing D to
E (P < .03) and D to F (P < .01) for the S phase of
the cell cycle. The histograms and the curve fitting software allowed
the determination of the percentage of cells in the phases of the cell
cycle (Multi-cycle from Phoenix Flow Systems Inc, San Diego, CA).
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In a second set of experiments, the PKH26+ cells from the
primary recipients' spleen and BM were obtained by cell sorting. These
male PKH26 bright cells were injected into secondary female recipients
along with 2 × 104 female R/O cells to provide a
source of radioprotection (in preliminary experiments, PKH26 bright
cells recovered from the FR25Lin cell inoculum given
alone failed to radioprotect secondary recipients after 48 hours in the
primary recipient, data not shown). We observed that survival of
secondary recipients at doses from 101 to 103
FR25Lin recovered PKH26 bright cells was possible
(Table 2). Interestingly, if the
FR25Lin PKH26 bright cells are harvested from the
spleen of primary recipients, the cells fail to support survival and
long-term repopulation of the secondary recipients at concentrations as
high as 104 cells per recipient (Table 2).
The percentage of male cells present at periods from 6 weeks to 6 months in secondary recipients after injection of only 102
FR25Lin or R/O PKH26 bright cells from the BM is
shown in Fig 3. As early as 6 weeks
posttransplant, 102 FR25Lin or R/O cells
provide small numbers of donor mature cells in the periphery, but only
recipients of FR25Lin cells continue to demonstrate
increases to over 90% donor cells at 6 months posttransplant. Animals
that received either 102 (Fig 3) or 103 (data
not shown) male R/O PKH26+ cells that had been in the
primary recipients for 48 hours failed to long-term repopulate
secondary recipients (all died by 12.1 ± 5.2 weeks) when given
along with 2 × 104 female R/O cells.
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| Fig 3.
Engraftment of FR25Lin or R/O cells into
secondary recipients of PKH+ cells. One hundred PKH
bright BM cells recovered 48 hours posttransplant from male
FR25Lin donors ( ) or male R/O donors (*) were
injected into secondary female hosts. Peripheral blood was obtained
from these recipients at 6, 12, and 24 weeks posttransplant and
analyzed for the presence of male cells. Values represent the mean
percent male cells for 4 to 6 recipients. The mean survival for
secondary recipients receiving R/O PKH+ cells was 12.1 ± 5.4 weeks.
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| |
DISCUSSION |
Our studies demonstrate that early after transplantation cell
populations enriched for both short-term radioprotection (R/O) and
long-term engraftment (FR25Lin) home to the
hematopoietic organs of lethally irradiated recipient mice. We can
recover only a few PKH26-labeled cells in the peripheral blood at 48 hours after transplant, but can find these cells from 3 hours to 96 hours in the BM (Fig 1) and at 48 hours in the spleen of the primary
recipients (Table 1). Thus, this assay can be used to determine the
site of stem or progenitor cell homing after transplant. Hendrikx et
al7 showed that CFU-S cells rapidly undergo proliferation
in vivo. CFU-S and long-term repopulating cells have been suggested to
be separate populations.1 We show that
long-term repopulating cells (FR25Lin) at 48 hours
remain relatively quiescent. Nilsson et al10 recently showed that stem cells can be killed by 5-fluorouracil
(5-FU) very shortly posttransplant, suggesting a rapid
entering of these cells into cell cycle. However, their study did not
directly measure the cell cycle activity shortly after transplant, but
relied on engraftment postdrug treatment 6 weeks later (at a time
indicative of radioprotection). We believe our assay more directly
studies the function of the donor cells by direct harvest 48 hours
posttransplant in lethally irradiated recipients. At 48 hours, the stem
cell population can still short-term and long-term engraft secondary recipients at low numbers (102 cells, Table 2, Fig 3),
whereas up to 104 later progenitors (R/O cells) fail to do
so. In the R/O fraction, 29.0% ± 4.4% of the cells are in S phase
of the cell cycle before injection into the mice. Of the R/O cells that
we collect after 48 hours in the primary recipient, the percent in
cycle decreases (14 ± 4.2 in the BM). Many of the cells in this
population are no longer PKH bright as evidenced by our significant
reduction of the frequency and total number of PKH bright cells that we recovered from R/O-treated mice after 48 hours (Fig 1 and Table 1).
These cells home equally well to the marrow and spleen when we account
for tissue volumes. The R/O cells that remain PKH bright contain cells
that might be expected to offer a short wave of engraftment.11 We have observed (Fig 3) from R/O PKH bright cells limited male reconstitution at 6 weeks. These cells are more
mature functionally as evidenced by the fact that engraftment is not
sustained and secondary recipients of R/O PKH bright cells were all
dead by 12 weeks.
PKH26 has been used to label potential human stem cells, which do not
divide (quiescent) in vitro.12 Recent elegant
studies13,14 have shown that human CD34 positive cells
residing in G0 are more primitive than those in
G1 by in vitro assay and their responsiveness to cytokines
may be different than cells in cycle. Our observation that our
primitive population remains relatively quiescent at 2 days in vivo is
consistent with the ability of these cells to continue to long-term
repopulate a lethally irradiated host at small numbers. The observation
that the cells, which home to the spleen shortly after transplant
(FR25Lin PKH26 bright cells), also fail to
repopulate secondary recipients is intriguing. The spleen
microenvironment, which also maintains the donor cells in a relatively
quiescent state (only 3% in S phase of the cell cycle, Fig 2),
contains less recoverable FR25Lin PKH bright cells
at least at 48 hours. The failure of up to 104 of these
FR25Lin recovered PKH+ donor cells from
the spleen to long-term engraft secondary recipients may be a
reflection of fewer stem cells homing at 48 hours to the spleen. We
further find it interesting that Fr25Lin, but not
R/O cells, are recovered in significantly greater number in the BM than
the spleen at 48 hours, suggesting that only early and not late
precursors favor the marrow environment at this time point. Some
evidence exists that more CFU are found in BM compared with spleen
after transplant.15 Others, comparing spleen to the femur,
showed equal homing of later progenitors,6 but whole marrow
was not compared with the spleen. Alternatively, but less likely, our
stem cell population (FR25Lin cells) could be
contaminated with donor lymphoid cells, which are preferentially homing
to the marrow. The spleen, however, may also contain stem cell
inhibitory accessory cells. We have evidence that lymphoid subsets can
inhibit both erythroid growth,16 as well as stem cell
engraftment.17 It is clear that cells from the same
experiment, which home to the BM of primary recipients did have
long-term engraftment potential. We favor the hypothesis that long-term
repopulating cells early after transplant are located in a
microenvironment, which may be favorable for their proliferation and differentiation.
Future potential applications for this assay include its use in further
defining the biology of stem cell homing. Papayannopoulou et
al5 has demonstrated that cell surface antigens (ie, VLA-4) act as homing receptors for progenitors like CFU-S. Using an antibody to VLA-4, they have shown that lodgement of CFU-S within the BM can be
blocked and that long-term reconstituting cells can be mobilized to the
peripheral blood using a similar antibody.18 Given that our
assay allows identification of quiescent cells shortly after injection
it could be used along with antibodies to cell surface adhesion
molecules to investigate more closely the interaction of long-term
engrafting cells with the microenvironment.
We have described an assay of stem cell homing, which allows us to
further study the biology of stem cell growth in vivo and which allows
us to identify and isolate cells that provide long-term engraftment.
| |
ACKNOWLEDGMENT |
We thank Marie C. Moineau and Chriscinthia Blount for their assistance
with manuscript preparation.
| |
FOOTNOTES |
Submitted June 8, 1998; accepted November 2, 1998.
Supported in part by Grants No. RO1-HL54330 and T32HL007525 from the
National Institutes of Health.
The publication costs of this
article were defrayed in part by
page charge payment. This article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. section
1734 solely to indicate this fact.
Address reprint requests to Saul J. Sharkis, PhD, Johns Hopkins
Oncology Center, Room 2-127, 600 North Wolfe St, Baltimore, MD
21287-8967.
| |
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P. A. Plett, S. M. Frankovitz, and C. M. Orschell
Distribution of marrow repopulating cells between bone marrow and spleen early after transplantation
Blood,
September 15, 2003;
102(6):
2285 - 2291.
[Abstract]
[Full Text]
[PDF]
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C. Lacout, E. Haddad, S. Sabri, F. Svinarchouk, L. Garcon, C. Capron, A. Foudi, R. Mzali, S. B. Snapper, F. Louache, et al.
A defect in hematopoietic stem cell migration explains the nonrandom X-chromosome inactivation in carriers of Wiskott-Aldrich syndrome
Blood,
August 15, 2003;
102(4):
1282 - 1289.
[Abstract]
[Full Text]
[PDF]
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K. A. Hinds, J. M. Hill, E. M. Shapiro, M. O. Laukkanen, A. C. Silva, C. A. Combs, T. R. Varney, R. S. Balaban, A. P. Koretsky, and C. E. Dunbar
Highly efficient endosomal labeling of progenitor and stem cells with large magnetic particles allows magnetic resonance imaging of single cells
Blood,
August 1, 2003;
102(3):
867 - 872.
[Abstract]
[Full Text]
[PDF]
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M. Schmidt, G. Sun, M. A. Stacey, L. Mori, and S. Mattoli
Identification of Circulating Fibrocytes as Precursors of Bronchial Myofibroblasts in Asthma
J. Immunol.,
July 1, 2003;
171(1):
380 - 389.
[Abstract]
[Full Text]
[PDF]
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N. D. Theise, D. S. Krause, and S. Sharkis
Comment on "Little Evidence for Developmental Plasticity of Adult Hematopoietic Stem Cells"
Science,
February 28, 2003;
299(5611):
1317a - 1317a.
[Full Text]
[PDF]
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P. A. Plett, S. M. Frankovitz, and C. M. Orschell-Traycoff
In vivo trafficking, cell cycle activity, and engraftment potential of phenotypically defined primitive hematopoietic cells after transplantation into irradiated or nonirradiated recipients
Blood,
November 15, 2002;
100(10):
3545 - 3552.
[Abstract]
[Full Text]
[PDF]
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J. F. Zhong, Y. Zhan, W. F. Anderson, and Y. Zhao
Murine hematopoietic stem cell distribution and proliferation in ablated and nonablated bone marrow transplantation
Blood,
November 15, 2002;
100(10):
3521 - 3526.
[Abstract]
[Full Text]
[PDF]
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O. Kollet, I. Petit, J. Kahn, S. Samira, A. Dar, A. Peled, V. Deutsch, M. Gunetti, W. Piacibello, A. Nagler, et al.
Human CD34+CXCR4- sorted cells harbor intracellular CXCR4, which can be functionally expressed and provide NOD/SCID repopulation
Blood,
September 26, 2002;
100(8):
2778 - 2786.
[Abstract]
[Full Text]
[PDF]
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T. Graf
Differentiation plasticity of hematopoietic cells
Blood,
May 1, 2002;
99(9):
3089 - 3101.
[Full Text]
[PDF]
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A. Jetmore, P. A. Plett, X. Tong, F. M. Wolber, R. Breese, R. Abonour, C. M. Orschell-Traycoff, and E. F. Srour
Homing efficiency, cell cycle kinetics, and survival of quiescent and cycling human CD34+ cells transplanted into conditioned NOD/SCID recipients
Blood,
March 1, 2002;
99(5):
1585 - 1593.
[Abstract]
[Full Text]
[PDF]
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T. Papayannopoulou, G. V. Priestley, B. Nakamoto, V. Zafiropoulos, and L. M. Scott
Molecular pathways in bone marrow homing: dominant role of {alpha}4{beta}1 over {beta}2-integrins and selectins
Blood,
October 15, 2001;
98(8):
2403 - 2411.
[Abstract]
[Full Text]
[PDF]
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T. C. C. Kerre, G. De Smet, M. De Smedt, F. Offner, J. De Bosscher, J. Plum, and B. Vandekerckhove
Both CD34+38+ and CD34+38- Cells Home Specifically to the Bone Marrow of NOD/LtSZ scid/scid Mice but Show Different Kinetics in Expansion
J. Immunol.,
October 1, 2001;
167(7):
3692 - 3698.
[Abstract]
[Full Text]
[PDF]
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S. J. Szilvassy, T. E. Meyerrose, P. L. Ragland, and B. Grimes
Differential homing and engraftment properties of hematopoietic progenitor cells from murine bone marrow, mobilized peripheral blood, and fetal liver
Blood,
October 1, 2001;
98(7):
2108 - 2115.
[Abstract]
[Full Text]
[PDF]
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O. Kollet, A. Spiegel, A. Peled, I. Petit, T. Byk, R. Hershkoviz, E. Guetta, G. Barkai, A. Nagler, and T. Lapidot
Rapid and efficient homing of human CD34+CD38{-}/lowCXCR4+ stem and progenitor cells to the bone marrow and spleen of NOD/SCID and NOD/SCID/B2mnull mice
Blood,
May 15, 2001;
97(10):
3283 - 3291.
[Abstract]
[Full Text]
[PDF]
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L. E. Perez, H. M. Rinder, C. Wang, J. B. Tracey, N. Maun, and D. S. Krause
Xenotransplantation of immunodeficient mice with mobilized human blood CD34+ cells provides an in vivo model for human megakaryocytopoiesis and platelet production
Blood,
March 15, 2001;
97(6):
1635 - 1643.
[Abstract]
[Full Text]
[PDF]
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R. A. J. Oostendorp, J. Audet, and C. J. Eaves
High-resolution tracking of cell division suggests similar cell cycle kinetics of hematopoietic stem cells stimulated in vitro and in vivo
Blood,
February 1, 2000;
95(3):
855 - 862.
[Abstract]
[Full Text]
[PDF]
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TOP
ABSTRACT
INTRODUCTION