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*
SyStemix, Palo Alto, CA 94304; and
Departments of Pathology and Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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B2 pathway (8) and
CBF1-independent pathways (9) have been reported. Thus,
the activation of Notch could trigger multiple pathways that induce
various cellular responses in Notch-activated cells. Notch signaling
can also be modified or regulated by other proteins, such as Fringe, so
that only a subset of cells responds to Notch signals. Ectopic
expression of Fringe during Drosophila eye or wing
development linked boundaries of Fringe expression and Notch activation
(10, 11, 12). In addition to cell-autonomous modifications,
non-cell-autonomous modifications mediated by secreted factors from
Notch-activated cells have been documented in Drosophila
morphogenesis (13).
Notch receptors and ligands are expressed in the mammalian hemopoietic
system, and several reports have demonstrated the involvement of Notch
activation in hemopoietic cell fate choices (reviewed in Ref.
14). Transgenic overexpression of Notch1IC (a
constitutively active form of Notch1) was associated with an increased
ratio of CD8 over CD4 single-positive (SP) thymocytes
(15). Another study using the same proximal Lck promoter
to drive the Notch1IC transgene similarly showed that Notch1 activation
led to the generation of an excess of mature CD8 SP thymocytes, but the
development of SP CD4 thymocytes was also shown to be stimulated
(16). At an earlier time in T cell development, Notch1IC
was shown to promote the adoption of a 
TCR phenotype in the
TCR vs TCR
cell fate decision process (17).
More conclusively, complementary studies using gain- and
loss-of-function of Notch1 activity showed that Notch1 signaling
favored the commitment of common lymphoid progenitors to T cell fate in
the T vs B lymphoid cell fate choices. Pear et al. (18, 19) demonstrated the development of T cell leukemia/lymphomas
concomitantly with a block in B cell lymphopoiesis in mice
transplanted with bone marrow (BM) overexpressing Notch1IC. Conversely,
Radtke et al. (20, 21) demonstrated that T cell
development was blocked at an early stage and that B cells accumulated
in the thymus of conditional Notch1 knockout mice, suggesting an
instructive role of Notch1 in T cell lineage induction. This was
confirmed in transgenic mice overexpressing a modifier of Notch1
signaling, lunatic fringe, under control of the Lck promoter.
Transgenic thymocytes acted non-cell-autonomously to inhibit Notch1
activation, which inhibited T cell commitment and promoted B cell
development in the thymus (22).
In contrast to the numerous reports describing the role for Notch in lymphopoiesis (reviewed in Refs. 1, 14 , and 23), there has not been any study demonstrating the effect of Notch on myeloid development in vivo. In vitro studies based on the myeloid cell line 32D have been described, and these have generated contradictory results on the effects of Notch1 activation on myeloid differentiation (24, 25).
In this report we describe the non-cell-autonomous effects of Notch1 on hemopoiesis by transplanting irradiated mice with a mixture of cells overexpressing Notch1IC and normal bystander cells and explore the function of Notch in mammalian hemopoiesis.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The murine Notch1IC cDNA encoding the totality of the intracellular domain (from codons 1474–2531; a gift from Dr. M. Cleary, Stanford University School of Medicine, Stanford, CA) was cloned into the retroviral vector MIE (MSCV-IRES-eGFP) (26, 27).
The enhanced green fluorescence protein (eGFP)+ or eGFP- cells were separated from BM of Notch1IC-transplanted mice by sorting the cells for high or no expression of eGFP, respectively, using a FACSVantage (BD Biosciences, San Jose, CA). The reanalysis of the sorted eGFP- population from Notch1IC BM showed that 95% of the cells were negative for eGFP expression. Total RNA was isolated from respective sorted fraction with Stat-60 RNA extraction reagent (Tel-Test B, Friendswood, TX). A total of 15 µg of total RNA was fractionated by electrophoresis through 1.2% agarose/formaldehyde denaturing gel and transferred to a nylon membrane (Roche, Mannheim, Germany). The membrane was hybridized with 32P-labeled Notch1IC probe covering DNA sequence 5441–5961 and with a G3PDH probe (Clontech Laboratories, Palo Alto, CA).
cDNA was generated from total RNA with random hexamers and Superscript (Life Technologies, Gaithersburg, MD). PCR was performed using primers coding for murine Notch1 DNA sequences 5441–5460 and 5942–5961, and TaqPlus polymerase (Stratagene, La Jolla, CA).
Retroviral transduction of BM cells and reconstitution of mice
C57BL/Ka-Ly5.2, Thy1.1 mice (known as BA.1), C57BL/Ka-Ly5.1, Thy1.1 mice (known as BS/BA), and BALB/c were bred and maintained in the animal facility at SyStemix (Palo Alto, CA). Four-week-old BA.1 (Ly5.2) mice were injected i.v. with 150 mg/kg 5-fluorouracil (5-FU) in PBS 5 days before sacrifice. BM cells from 4-wk-old BA.1 mice were collected, followed by RBC lysis. Primitive hemopoietic precursors were enriched by depleting lineage-positive cells using a panel of Abs directed against CD3, CD5, CD8a, CD11b (Mac-1), Gr-1, and B220 (BD PharMingen, San Diego, CA), followed by a step of negative selection using Dynabeads M-450 (Dynal Biotech, Oslo, Norway). The retroviral transduction of the resulting Linneg/low cells was performed as described previously (28). The transduction efficiency was determined by flow cytometry measurement of eGFP expression among the Linneg/low population on the day following the second round of spinoculation. Lethally irradiated (1050 rad, one total gamma irradiation) BS/BA. (Ly5.1) recipient mice were transplanted with 15,000–20,000 Linneg/low-transduced BA.1 cells together with 100,000 syngenic whole BM (Ly5.1) cells for short-term irradiation protection.
Flow cytometric analysis and methylcellulose assay
The cells harvested from BM, PB, spleen, and thymus or following culture in vitro were stained with Abs directed against Ly5.1, CD4, CD8a, CD3, CD11b (Mac-1), CD19, CD24, CD43, BP-1, IgM, or Gr-1 (BD PharMingen). Stained cells were resuspended with propidium iodide (5 µg/ml) to exclude nonviable cells and analyzed on a FACSCaliber (BD Biosciences) or a FACSVantage (BD Biosciences). Light scatter gating was set to include all nucleated cells.
Twenty thousand BM cells from MIE control or Notch1IC-transplanted mice were seeded in 1.1 ml of Methocult M3320 methylcellulose medium (StemCell Technologies, Vancouver, Canada) supplemented with murine IL-3, IL-6, GM-CSF (all at 10 ng/ml; R&D Systems, Minneapolis, MN), and stem cell factor (SCF; 100 ng/ml; supplied by Novartis Pharmaceuticals, East Hanover, NJ). After 2 wk of culture, colonies were scored, and cells pooled from the culture dish were harvested, counted, and analyzed by flow cytometry for eGFP expression and myeloid maturation markers.
Coculture and conditioned medium experiments
Lethally irradiated BA.1 (Ly5.2) mice were transplanted with Notch1IC-transduced Linneg/low BA.1 BM cells. BA.1 mice transplanted with Linneg/low BA.1 BM cells transduced with empty vector (MIE) were used as a control. BM cells from BA.1 Notch1 IC mice (1 million cells/ml) were cocultured with normal Linneg/low BS/BA (Ly5.1) BM cells (0.2 million cells/ml) in RPMI 1640 (JRH Biosciences, Lenexa, KS), 10% FCS (Gemini Bioproducts, Calabasas, CA), and 50 µM 2-ME (Sigma-Aldrich, St. Louis, MO) in the presence of IL-7 (10 ng/ml), SCF (100 ng/ml), and Flk-L (50 ng/ml). The total cell number was determined every 2 days, and cells were split at a density of 1–1.5 million cells/ml. The phenotype of the cells in coculture was examined by flow cytometry. Supernatant from cultured BM cells of BA.1 Notch1IC mice or BA.1 MIE mice (1 million cells/ml at the initiation of culture) was harvested and filtered every 3 days and added to the test Linneg/low BS/BA BM cells cultured at a density of 0.2–1 million cells/ml in the presence of IL-7, SCF, and Flk-L. The supernatant of BM cells from transplanted mice was diluted in fresh medium as indicated to evaluate a dose-dependent effect.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Early BM hemopoietic precursors from 5-FU-treated BA.1 (Ly5.2)
donor mice were enriched by depletion of the lineage-positive cells.
The resulting Linneg/low donor population
consisted of 
2% of the 5-FU-treated whole BM. These cells were
transduced with a constitutively active form of Notch1, Notch1
intracellular domain (Notch1IC), using the MIE retroviral
vector (26) that encodes an internal ribosomal entry site
(IRES) and the eGFP. The transduced Linneg/low
cells were inoculated to lethally irradiated BS/BA (Ly5.1) recipient
mice together with syngenic (Ly5.1) BM to ensure short-term
radioprotection (Fig. 1
A). The
initial transduction efficiencies of Linneg/low
cells with MIE or Notch1IC at the time of transplantation were 65 or
25%, respectively. The BM, spleen, thymus, and peripheral blood from
the transplanted mice were harvested for flow cytometric analyses at
3–4 wk post-transplantation. The phenotypes of the BM among the
transduced and the nontransduced populations are shown in Fig. 1B; similar results were found in the spleen and peripheral
blood cells (data not shown). As described in an earlier report using a
similar transplantation model performed with BALB/c mice
(19), B cell development in the transduced fraction of
Notch1IC mice was completely blocked. Strikingly, we also found that
virtually no B cells were present in the eGFP-
population of Notch1IC mice (Fig. 1B). This absence of B
cells among the nontransduced congenic (Ly5.2) and the cotransplanted
syngenic (Ly5.1) donor cells (see Fig. 1A) suggested that
Notch1IC could modify the lineage determination of cells through a
non-cell-autonomous mechanism(s). To further explore this hypothesis we
examined the expression of Notch1IC in the eGFP-
population. BM cells from a Notch1IC mouse were sorted by FACS in
eGFP+ and eGFP-
populations from which total RNA was extracted to assess the expression
of Notch1IC message by Northern blotting. As shown in Fig. 1C, no Notch1IC message could be detected in the
eGFP- population. Semiquantitative PCR assay
performed on the same eGFP+/--sorted populations
revealed that the estimated expression of Notch1IC message in the
eGFP--sorted fraction was 
6.25% of the
amount present in the eGFP+ population (data not
shown). This percentage is in the same range as the fraction of
eGFP+ cells that contaminates the
eGFP- population obtained by FACS. These results
indicate that the alterations seen in the eGFP-
cells cannot be accounted for by the intracellular expression of
Notch1IC but are truly non-cell-autonomous.
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To explore the mechanism underlying the absence of B cells in the
eGFP- compartment of Notch1IC mice, we repeated
the transduction/transplantation experiment in different genetic
backgrounds and/or with retroviral supernatant of varying titers. When
the initial transduction efficiency of Linneg/low
cells was 20%, we were able to reproduce our finding in BALB/c mice
(Fig. 2). We found that the initial
transduction efficiency had a drastic influence on the outcome of the
experiment. While the block in B cell differentiation among the
transduced (eGFP+) cells was always virtually
complete, the degree of inhibition of B cell development among the
nontransduced compartment of the transplanted mice analyzed 3 wk
post-transplantation clearly correlated with the percentage of donor
cells expressing Notch1IC at the time of inoculation (Fig. 2). The
proportion of eGFP+ cells 3 wk
post-transplantation displayed a high variability from mouse to mouse.
However, the high percentage of eGFP+ cells in
the BM of some of the Notch1IC mice inoculated with BM progenitors
infected at a lower efficiency probably reflects the growth advantage
of the Notch1IC-transduced cells and the proliferation of
eGFP+ T cells in these mice (Fig. 2). We also
observed that the efficiency of transduction impacted the time of
survival of the mice post-transplantation. If the initial transduction
rate was 20% or more, no B cells were present in the BM, and the mice
died of T cell leukemia/lymphomas in 4 wk. If the initial transduction
rate was 13%, a partial suppression of the B cells among the BM
eGFP- compartment could be seen at 3 wk
post-transplantation. These mice were healthy at this time point and
survived for 40–50 days. If 2% or less of the
Linneg/low cells were transduced, the
eGFP- fraction displayed a normal B cell
compartment at 3 wk post-transplantation, and the mice survived as long
as 8–10 wk.
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The myeloid compartment in the eGFP+
fraction of Notch1IC-transplanted mice was suppressed by the
proliferating double-positive (DP) T cells, resulting in a reduction of
the size of the former in the course of the transplantation experiment.
Interestingly, flow cytometric analyses suggested that the
nontransduced BM fraction was predominantly made up of mature myeloid
cells (Fig. 3).
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and Fig. 3
, Notch1IC BM cells had a
very low seeding efficiency, and this activity was confined to the
fraction of cells expressing low levels of eGFP+.
The lower eGFP intensity in these Notch1IC cells probably reflects the
fact that the fraction of BM expressing higher levels of eGFP before
culture was essentially made up of DP T cells and mature myeloid cells
that do not survive the myeloid culture conditions used for the assay
(data not shown). The lack of eGFP- cells
recovered from the myeloid clonogenic assay (Fig. 3) is consistent with
the more mature phenotype of myeloid cells observed among the BM
eGFP- compartment, as these would be expected to
have lost their colony-forming potential. In agreement with a previous
study of Notch1-expressing myeloid cell line 32D (11), the
myeloid maturation of the eGFP+ cells recovered
from the myeloid clonogenic assay was blocked (data not shown).
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The altered phenotype and growth potential of the
eGFP- compartment of the Notch1IC mice suggested
that the cells with constitutively activated Notch1 could influence the
cell fate of the nontransduced population. To investigate whether the
inhibition of B cell maturation in the nontransduced population was
mediated by direct cell-to-cell interaction or by secreted molecules,
we set up ex vivo culture experiments that are schematically depicted
in Fig. 4A. We cocultured
normal Linneg/low cells from BS/BA (Ly5.1) mice
with BM cells from BA.1 (Ly5.2) mice that had been transplanted 4 wk
before with BA.1 (Ly5.2) progenitors transduced by Notch1IC with an
efficiency of 8–13%. At the time of sacrifice these Notch1IC mice
were healthy, and the percentage of DP T cells in their BM ranged from
18 to 42%, while the nontransduced fraction displayed a moderate to
marked deficiency of B cells. As controls, we cocultured the test
Linneg/low Ly5.1 cells with BM from
MIE-transplanted BA.1 mice or with BM of normal BA.1 mice. We analyzed
the expression of CD19 and CD24 in the Ly5.1 population at 5 days of
culture, because the proliferative potential of immature
Linneg/low cells is much higher than that
of whole BM cells, and at later time points the progeny of
the Linneg/low Ly5.1 cells greatly outgrew the
Ly5.2 population. As shown in Fig. 4B, the presence of
Notch1IC BM considerably inhibited the maturation of the test
population along the B cell lineage. Additionally, a higher proportion
of these cells differentiated toward the myeloid lineage, as evidenced
by the increase in the percentage of cells expressing the Gr-1 and
Mac-1 Ags (Fig. 4B). The percentages of B cells and myeloid
cells among the test cells (Ly5.1) on day 5 of coculture are shown in
Fig. 4B. We looked for the proliferation of neoplastic T
cells in these cultures on day 4 by flow cytometric analyses using
anti-CD3, anti-CD4, and anti-CD8 Abs. No T cells were found
in either Ly5.1 or Ly5.2 fractions (data not shown), suggesting that
even the Notch1IC-transduced T cells could not be maintained in the
culture conditions used here.
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, C and D, we observed that the Notch1IC BM
supernatant inhibited B cell maturation in a dose-dependent manner,
with a nearly total block when a 2-fold dilution of the medium was
used. Again, we found that suppression of the B cell compartment was
coupled with an expansion of the myeloid compartment. Effect of Notch1IC on T cell development
In the BM of Notch1IC mice, DP T cells dominated among the
eGFP+ fraction. As shown in Fig. 5, we also observed an interesting BM
profile of CD4 and CD8 expression among the
eGFP- fraction. These nontransduced cells
expressed unusually high levels of CD4 and CD8 compared with the
double-negative population that normally resides in the BM (Fig. 5, see
region R2 on FACS dot plot). The same CD4/CD8 profile was observed
among the Ly5.1 host cells that were not exposed to the
Notch1IC-encoding retrovirus, thus confirming that non-cell-autonomous
phenomena underlie this unusual T cell maturation (Fig. 5 and Table II). It is noteworthy that the T cells
present in the BM of the Notch1IC mice did not have the phenotype of
normal mature lymphocytes, making it unlikely that their presence is
due to the redistribution of circulating lymphocytes to the BM as can
be seen in stressed animals.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Because the non-cell-autonomous effects are seen in transplanted mice
that eventually succumb to fatal neoplasia, we cannot formally rule out
that the malignant clones do not secrete or induce the secretion of
substances in the terminally ill mice that underlie the effects we see
in the nontransduced cells independently of Notch activation. However,
several facts render this hypothesis unlikely. Firstly, the activity
capable of suppressing B cell maturation in vitro was measured in the
conditioned medium of BM harvested from Notch1IC mice before they
displayed signs of disease. Similarly, the mice transplanted with an
inoculum in which 13% of the cells were transduced by Notch1IC
displayed a considerable suppression of B cells among the nontransduced
population as early as 3 wk post-transplantation when they were healthy
(see Fig. 2). Second, the Ly5.2 Notch1IC mice used for the coculture
and the conditioned medium experiments were still healthy when
terminated at 4 wk post-transplantation, yet we found a clear
suppression of B cells among the Ly5.1 test cells (see Fig. 4). Third,
when the mice that had been transplanted with a population of
progenitors of which 1.5% were transduced did eventually develop
tumors, nontransduced B cells were still present in their BM, although
this fraction was greatly suppressed by the malignant DP T cell
population (data not shown). We cannot attribute the suppression of the
B cell compartment to a mass effect of the proliferating T cells in the
BM either, because the total number of BM cells at 3 wk
post-transplantation was actually lower than that in the MIE control
mice (Fig. 1B). Furthermore, the BM T cells could not
survive in the culture with IL-7, Flk ligand, and SCF, yet we found a
clear suppression of B cells in the coculture and conditioned medium
experiments (see Fig. 4). Our results demonstrate, rather, that the
level of non-cell-autonomous B cell suppression at 3 wk
post-transplantation correlates with the initial Notch1IC transduction
efficiency at the time of transplantation and not with the clinical
stage of the disease or the degree of proliferation of DP T cells in
the BM. This suggests that the Notch1IC-expressing cells could
influence the cell fate of the repopulating progenitors in a
dose-dependent manner by acting shortly after transplantation.
The non-cell-autonomous effects of Notch signaling described in this report are reminiscent of developmental phenomena described in the fly. Secreted morphogens such as Wingless have been shown to result from Notch activation and activate signaling of neighboring cells in a paracrine fashion (13). Similarly, a recent report by Koch and colleagues (22) showed that the overexpression of Lunatic Fringe, a modulator of Notch1, in thymocytes could inhibit Notch1 activation in a non-cell-autonomous fashion, and thus increase B cells and decrease T cells in the thymus. During the development of fly wings and eye, Fringe also restricts Notch activation in a non-cell-autonomous fashion to cells at the dorsal-ventral boundary to ensure proper morphogenesis. Although the mechanisms by which Notch1 or Fringe exerts non-cell-autonomous effects in hemopoiesis need to be elucidated, these findings point to the conserved mechanisms of Notch1 activation between Drosophila morphogenesis and mammalian hemopoiesis.
Our findings raise the question of the identity of the factor(s)
secreted by NotchIC-transduced cells that mediates the multiple
hemopoietic alterations described in this report. In attempt to
identify such a factor(s) we performed ELISA to look for the presence
of certain cytokines in the conditioned medium of the BM of NotchIC
mice. The positive effect seen on the expansion of myeloid progenitors
(Fig. 4C) prompted us to measure the concentration of GM-CSF
in this supernatant. This cytokine was detected in the BM supernatant
of three of the 11 Notch1IC mice tested by ELISA and in none of the 11
MIE controls studied (data not shown). Although additional testing
would perhaps help clarify the issue, this result suggests that GM-CSF
is unlikely to be a key mediator of the non-cell-autonomous effect of
Notch. The similar B cell impairment seen in the Notch1IC-transduced
and nontransduced fractions suggests that Notch activation might
interfere with Notch modulators such as Lunatic Fringe that act
non-cell-autonomously to alter the T/B lineage decision
(22).
Notch1IC overexpression has been shown to induce thymic-independent accumulation of DP T cells in the BM at the expense of B cell precursors, suggesting that Notch1 signaling could instruct T cell development in a common lymphoid precursor (19). We show here that among the nontransduced BM compartment of the Notch1IC-chimeric mice, both a defect in B cell maturation and abnormal DN T cells are observed. This indicates that non-cell-autonomous mechanisms might also play a role in the ability of Notch1 to direct T lineage commitment from multipotent progenitor cells. Secreted factors from Notch1IC-transduced cells could contribute to the ectopic development of T cells by modifying the BM microenvironment and/or the developmental potentials of precursors. These non-cell-autonomous modifications could cooperate with the cell-autonomous consequences of Notch1 overexpression, such as the antiapoptotic effect of Notch1 on the transduced-T cell population (29, 30), to generate T cell leukemia/lymphomas in Notch1IC-transplanted mice.
The alteration of hemopoiesis in the nontransduced cells obtained in our experimental model as a result of Notch1 activation is certainly supraphysiological. It is more likely that local concentrations of Notch1-activated cells in the BM microenvironment could affect the fate of surrounding cells in a paracrine fashion. It is also possible that secreted factors act in an autocrine manner and further modify the hemopoietic potentials of Notch1-activated cells. Altogether, our in vivo and in vitro data suggest that tight regulation of notch signaling is indispensable to ensure proper distribution and development of hemopoietic cells and that this probably involves both intracellular and non-cell-autonomous mechanisms.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Catherine Lavau at the current address: Centre National de la Récherche Scientifique, UPR 9051, Hopital Saint-Louis 1, Avenue Claude Vellefaux, 75475 Paris Cedex 10, France. E-mail address: catlav{at}chu-stlouis.fr
3 Abbreviations used in this paper: NotchIC, intracellular domain of Notch; BM, bone marrow; DP, double-positive; eGFP, enhanced green fluorescence protein; 5-FU, 5-fluorouracil; IRES, internal ribosomal entry site; SCF, stem cell factor; SP, single positive.
Received for publication August 2, 2001. Accepted for publication December 12, 2001.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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-1 activation of notch-1 signaling results in HES-1 transactivation. Mol. Cell. Biol. 18:7423.B2 is a putative target gene of activated Notch-1 via RBP-J. Mol. Cell. Biol. 18:2077. versus T cell lineage decision. Cell 88:833.[Medline]
cell fate in the thymus. J. Exp. Med. 194:1003. (RAR) recapitulates retinoic acid-sensitive transformation of primary myeloid progenitors by acute promyelocytic leukemia RAR-fusion genes. Blood 94:793.This article has been cited by other articles:
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  Y. Tanaka, T. Era, S.-i. Nishikawa, and S. Kawamata Forced expression of Nanog in hematopoietic stem cells results in a {gamma}{delta}T-cell disorder Blood, July 1, 2007; 110(1): 107 - 115. [Abstract] [Full Text] [PDF]
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S. M. Vercauteren and H. J. Sutherland Constitutively active Notch4 promotes early human hematopoietic progenitor cell maintenance while inhibiting differentiation and causes lymphoid abnormalities in vivo Blood, October 15, 2004; 104(8): 2315 - 2322. [Abstract] [Full Text] [PDF]
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 T. Schroeder, H. Kohlhof, N. Rieber, and U. Just Notch Signaling Induces Multilineage Myeloid Differentiation and Up-Regulates PU.1 Expression J. Immunol., June 1, 2003; 170(11): 5538 - 5548. [Abstract] [Full Text] [PDF]
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T. Yamada, H. Yamazaki, T. Yamane, M. Yoshino, H. Okuyama, M. Tsuneto, T. Kurino, S.-I. Hayashi, and S. Sakano Regulation of osteoclast development by Notch signaling directed to osteoclast precursors and through stromal cells Blood, March 15, 2003; 101(6): 2227 - 2234. [Abstract] [Full Text] [PDF]
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M. De Smedt, K. Reynvoet, T. Kerre, T. Taghon, B. Verhasselt, B. Vandekerckhove, G. Leclercq, and J. Plum Active Form of Notch Imposes T Cell Fate in Human Progenitor Cells J. Immunol., September 15, 2002; 169(6): 3021 - 3029. [Abstract] [Full Text] [PDF]
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