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IMMUNOBIOLOGY
From the Centro de Biología Molecular "Severo
Ochoa," CSIC, Facultad de Biología, Universidad
Autónoma de Madrid, Spain.
In this study, the finding that a significant proportion of all
dendritic cells (DCs) resident in vivo in the human postnatal thymus
displayed a myeloid-related phenotype prompted us to re-examine the
developmental origin of thymic DCs, a cell type hitherto considered to
represent a homogeneous lymphoid-derived population. We show here that
these novel intrathymic DCs are truly myeloid, as they arise from
CD34+ early thymic progenitors through CD34lo
intermediates which have lost the capacity to generate T cells, but
display myelomonocytic differentiation potential. We also demonstrate
that phenotypically and functionally equivalent myeloid precursors
devoid of T-cell potential do exist in vivo in the postnatal thymus.
Moreover, although interleukin 7 (IL-7) supports the generation of such
myeloid intermediates, we show that their developmental branching from
the main intrathymic T-cell pathway is linked to the up-regulation of
the myelomonocytic granulocyte macrophage-colony-stimulating factor
(GM-CSF) receptor, to the down-regulation of the IL-7 receptor and to
the lack of pre-T-cell receptor Dendritic cells (DCs) are hematopoietic-derived
highly specialized antigen-presenting cells (APCs) that display potent
ability to induce both specific immune responses and deletion of
potentially autoreactive T cells.1-3 These nonoverlapping
functions have been proposed to result from the actions of 2 major DC
populations which have been characterized as myeloid and lymphoid DCs,
respectively, on the basis of their anatomical localization and
cell-surface phenotypes and, ultimately, of their distinct
developmental origin.1-5 In mice, DCs bearing the myeloid
marker CD11b (Mac-1), but lacking CD8 There are 2 subsets of DCs with distinct phenotype, localization, and
function which have been described also in humans.12,13 One subset of CD11c+ DCs, also termed DC1, which expresses
myeloid markers and high levels of CD1a, can be generated from
peripheral blood monocytes in response to granulocyte
macrophage-colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4)14,15 and therefore is considered of myeloid origin.
DCs with a DC1-like phenotype can also develop in response to GM-CSF
and tumor necrosis factor alpha (TNF- A second subset of CD11c Despite the proposed lymphoid origin of intrathymic DCs, our knowledge
about their immediate precursors in humans is limited. We have
previously reported that IL-7, a conventional "lymphoid" cytokine,
is able to support the generation in vitro of mature functional DCs
from the earliest CD34+ intrathymic precursors, which
display both T cell and natural killer (NK) cell precursor potential as
well.22-25 Such thymocyte-derived DCs were shown to
develop through a predominant CD1a+
pathway22-24 equivalent to that reported for DCs derived
from a common T/NK/DC lymphoid precursor (CLP) resident in bone
marrow,26 a fact that further supports their lymphoid
origin. However, regardless of their thymic origin, in vitro-derived
DCs displayed a myeloid-related phenotype similar to that of peripheral
DC1, but fully distinct from that of the recently identified
intrathymic DC2 subset. Whereas the myeloidlike phenotype displayed by
in vitro-derived thymic DCs could be attributed to the particular
differentiation/cytokine assay used, evidence has recently been
provided that, besides DC2, DCs bearing a myeloid phenotype similar to
that of peripheral DC1 can be found in the human
thymus.27,28 However, the ontogeny of such DCs remains to
be clarified. Therefore, the aim of the present study has been to
re-examine the developmental origin of human intrathymic DCs. Based on
precursor-product relationships, we have characterized the intrathymic
differentiation pathway of these novel myeloid-related DCs and provided
evidence that they are authentic myeloid DCs in developmental terms.
The possible meaning of the existence of early intrathymic progenitors
able to develop through a myeloid DC pathway is discussed in the
context of the current view that the thymus is seeded by a
lymphoid-restricted progenitor derived from the bone marrow.
Flow cytometry
Isolation of thymocyte subsets and cell sorting
For the isolation of thymic DCs, Lin CD14+ and CD14 Cell cultures DCs were generated either from CD34+CD33lo early thymic progenitors or from CD34loCD44hi and CD34loCD44lo intermediates cultured (5 × 105/mL) for the indicated time periods in 24-well (5 × 105 cells/well) or 96-well (105 cells/well) plates (Costar, Cambridge, MA) in RPMI 1640 medium (Gibco, Paisley, United Kingdom) supplemented with 10% fetal calf serum (FCS) (Gibco) and the following cytokines: 100 IU/mL recombinant human interleukin-7 (rhIL-7), 60 IU/mL rhIL-1 , 50 IU/mL rhIL-6, 100 IU/mL
recombinant human stem cell factor (rhSCF), and 100 IU/mL recombinant
human GM-CSF (rhGM-CSF) from the National Institute of Biological
Standards and Controls (NIBSC, Potters Bar, Hertfordshire, United
Kingdom). These cultures are referred to as multicytokine-supported cultures throughout the text. For the simultaneous generation of NK
cells and DCs, these cultures were supplemented with 50 IU/mL rhIL-2
(Hoffman La Roche, Basel, Switzerland).
To assess the generation CD14+CD1a Real-time quantitative polymerase chain reaction Total RNA from thymocyte subsets was isolated using standard procedures. We used 10 ng to 50 ng of RNA per polymerase chain reaction (PCR) after reverse transcription into cDNA with an oligo-dT primer (Gibco). Real-time quantitative reverse transcriptase-PCR (RT-PCR) was carried out with a Taqman assay. The primers and Taqman probe for RT-PCR were designed using Primer Express software (Applied Biosystems, Foster City, CA). The sense 5'-GTGTCCAGCCCTACCCAC-3' and antisense 5'-ATCCACCAGCAGCATGATTG-3' primers were used in combination with the 5'-TGTGGGCGGCACACCCTTTC-3' Taqman (6-FAM-labeled) probe (Applied Biosystems). Primers and probes were used at a final concentration of 300 nM and 200 nM, respectively. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) amplifications were carried out with the Pre-Developed Taqman Assay Reagent specific for human GAPDH gene expression quantification (Applied Biosystems), according to the manufacturer's instructions. All PCR reactions were set in triplicates using the TaqMan Universal PCR Master Mix (Applied Biosystems). Amplifications, detections, and analyses were performed in an ABI PRISM 7700 system (Applied Biosystems). pT quantitative values were
obtained after interpolation in a standard curve constructed by
amplification of serial dilutions of total human thymocyte cDNA,
followed by normalization to GAPDH.
DCs with a myeloidlike phenotype are resident in vivo in the human postnatal thymus We have previously shown that the earliest CD34hiCD33lo intrathymic progenitors in man can generate mature functional DCs in multicytokine-supported cultures including IL-7, IL-1, SCF, IL-6, and GM-CSF.23 As summarized in Table 1 and Figure
1A, an extensive phenotypic analysis of such in vitro-derived DCs revealed a prominent expression of the myeloid-related antigens CD11b, CD11c, CD13, and CD33, as well
as high expression of several markers characteristic of peripheral DC1
but absent on DC2, such as CD1a, CD1c, and CD45RO; but a sparse
expression of the IL-3 receptor (IL-3R, CD123) expressed on DC2. In
addition, we found high expression of CD44, CD54, major histocompatibility complex (MHC) class II (HLA-DR), and CD4, and variable surface levels of CD40, CD80, and CD86 costimulatory markers
and the mature DC marker CD83. Therefore, these in vitro-derived DCs
displayed a surface phenotype that seemed closer to that of myeloid-derived DC1 than to lymphoid-derived DC2.
To investigate whether equivalent DC1-like cells are resident in vivo
in the human thymus, HLA-DR+ cells were magnetically sorted
from total thymocytes. As shown in Figure 1B, electronic gates set
independently on Lin Thymic DC1 cells develop from CD34hiCD33lo pro-T cells through a CD34loCD44hi intermediate precursor that has lost the capacity to generate T cells The surface phenotype of the intrathymic DC1-like population would suggest an immediate myeloid origin of these DCs. This prompted us to investigate their pathway of differentiation from the earliest thymic progenitors, with the final aim of defining precursor-product relationships that could help to conclusively establish their lineage derivation. To this end, CD34hiCD33lo thymic precursors were set up in the multicytokine culture system previously reported by Márquez et al23 to support the development of NK cells, DCs, and T-lineage cells. T/NK/DC progenitors were shown to differentiate in this system along 2 independent pathways that progressed through separate CD34lo intermediate progenitors of distinct cell size and opposite expression of CD5, CD33, and CD44,22,23 whose developmental potential has not been directly addressed. Therefore, we next evaluated the developmental outcome of both pathways, focusing on the lymphoid and myeloid potential of the 2 CD34lo intermediate progenitors, as compared with that of their immediate CD34hiCD33lo precursors. As shown in Figure 2A, CD34lo intermediates derived from CD34hiCD33lo precursors by day 3.5 of culture (> 98% of total viable cells) were sorted on the basis of CD44 and CD5 expression levels. As expected, sorted CD44hiCD5 /lo cells were homogeneously
large-sized CD33+CD34lo thymocytes, whereas
CD5+CD44lo precursors were small-sized
CD33CD34lo cells. Both intermediate
CD34lo cell subsets (hereafter referred to as
CD34loCD44hi and
CD34loCD44lo, respectively) were then assayed
for their potential to generate lymphoid and/or myeloid cells in the
appropriate in vitro assays. Freshly isolated
CD34hiCD33lo intrathymic precursors were
analyzed as well for comparison.
As shown in Table 2,
CD34loCD44hi intermediates simultaneously
generated DCs and NK cells (defined respectively as
CD7loCD56
When the same subsets were analyzed for their T-cell potential in
a hu/moFTOC, early CD34hiCD33lo
progenitors and CD34loCD44lo
intermediates were found to behave as efficient pro-T cells, although pro-T-cell activity was consistently higher in the former population. Surprisingly, however, CD34loCD44hi
cells were devoid of pro-T-cell activity (Table 2). As shown in Figure
3, CD34loCD44lo
intermediates were capable of generating up to 35% of
CD3+TCR
CD34hiCD33lo early thymic precursors can develop along a myelomonocytic pathway of differentiation that proceeds through CD34loCD44hi intermediates Although early progenitors seeding the human postnatal thymus are currently envisaged as lymphoid-restricted precursors devoid of myeloid potential,5,10,30 generation of CD14+ monocytes has been reported to occur in vitro from human CD34+ thymocytes when the myelomonocytic cytokine macrophage-colony-stimulating factor (M-CSF) is provided to the cultures.24 Therefore, we next analyzed the myeloid potential of early CD34hiCD33lo intrathymic progenitors and their CD34lo progenies under culture conditions favoring monocytic generation (ie, IL-7, SCF, and M-CSF). We found that, after 7 days, cultures derived from ex vivo-isolated CD34hiCD33lo immature thymocytes contained an unexpectedly large number (up to 40%; 15% on average) of cells that coexpressed the myelomonocytic antigen CD14, together with CD11b, CD13, and CD33 (Table 2, and data not shown). These cells lacked expression of CD1a and maintained their CD14+CD1a
phenotype during the whole culture period (18 days), suggesting that
they represented differentiated monocytes. Supporting this possibility,
we identified monocytic colony formation from
CD34hiCD33lo precursors in methylcellulose
cultures supplemented with IL-7, SCF, GM-CSF, and IL-3 (data not shown).
Strikingly, CD34loCD44hi intermediates
generated in multicytokine-supported cultures also displayed the
capacity to generate CD14+CD1a CD14+CD1a CD1a+ cells represented a major progeny,
CD14+CD1a monocytes were also generated from
CD34hiCD33lo early precursors as well as from
CD34loCD44hi intermediates (up to 35% by day
6) in multicytokine-supported cultures (Figure
4A, and data not shown). Interestingly,
CD14+CD1a monocytes decreased steadily in
those cultures devoid of M-CSF, whereas
CD14CD1a+ cells with a mature
CD83+CD80+CD86+ DC1 phenotype
increased concurrently (data not shown). These results would suggest
that growth and/or terminal differentiation of CD14+
monocytes could not be supported in the absence of M-CSF, thus allowing
the outgrowth of DC1. Alternatively, DC1 would stem from CD14+ myelomonocytes that lose CD14 and acquire
CD1a.
To discriminate between both possibilities, CD14+ and
CD14 Constitutive expression of the myelomonocytic receptor for GM-CSF on myeloid DC1 precursors resident in the human thymus Our findings above are compatible with the possibility that early thymic precursors retain a myeloid-lineage differentiation activity that, as proposed for bone marrow hematopoietic stem cells, can be triggered by signaling through cytokine pathways that drive myeloid cell development, such as the GM-CSF pathway.31 This would imply that GM-CSFR is expressed on thymic precursors able to generate DC1. Confirming this possibility, expression of GM-CSFR was
prominent on CD34loCD44hi DC1 precursors, but
was essentially undetectable on CD34loCD44lo
precursors arising from CD34hiCD33lo precursors
in multicytokine-supported cultures (Figure 2A). This supports the
lymphoid-restricted potential of the latter subset.
To assess the physiologic relevance of this finding, we investigated
whether expression of GM-CSFR
To next investigate whether reciprocal expression of GM-CSFR and
IL-7R on intermediate intrathymic precursors paralleled functional differences in terms of their developmental outcome, sorted
CD34loCD44hi and
CD34loCD44lo thymocytes were analyzed for their
lymphoid and myeloid precursor potential as described above. As shown
in Figure 5B, both subsets, representing 0.02% and 0.8% of total
thymocytes, respectively, behaved as their in vitro-derived
counterparts in developmental terms, as both displayed NK cell
precursor potential, but only CD34loCD44hi
precursors were able to generate DC1 (Figure 5B). However, the proliferation and DC/NK differentiation capacities of the latter were
consistently lower than those of the equivalent in vitro-derived population, probably reflecting a decreased cell viability during their
isolation procedure. Also, generation of TCR Selective lack of pT + thymic lymphoid DC2 express high levels of
pT transcripts,20 it would be informative to know
whether pT transcription is selective of DC2 or if it is shared by
the intrathymic IL3R myeloid DC1 pathway. This was
assessed by real-time quantitative RT-PCR, which provides a unique
means to quantify transcription accurately. Sample-to-sample variations
were corrected by normalization to GAPDH expression, used as endogenous
control. Therefore, cDNA samples were derived from
CD13IL3R+ and
CD13+IL3R thymic DCs, as well as from both
CD34loCD44hi and
CD34loCD44lo intermediate precursors isolated
ex vivo. In addition, CD34hiCD33lo
early precursors and downstream CD34hiCD33
thymocytes were included in the study for comparison. cDNA samples were
amplified in parallel for GAPDH and pT, and quantitative values were
obtained by interpolation in standard curves of total thymocyte cDNA.
Final quantitative data were the result of calculating pT/GAPDH
ratios for each sample.
As shown in Figure 6, pT
The finding that DCs with a myeloid-related phenotype represent a significant proportion of all DCs resident in vivo in the postnatal human thymus (0.1% of total thymic cells) prompted us to re-examine in this study the developmental origin of thymic DCs,5,9 a cell type currently considered to be lymphoid derived. Based on precursor-product relationships, we have traced the developmental pathway of such DCs from their intrathymic CD34hi precursors, and provide evidence that, besides their surface phenotype, they are authentic myeloid DCs in terms of their lineage origin. Our previous studies showed that T-lineage cells and functional DCs could arise simultaneously from the earliest CD34+ postnatal thymocytes in response to IL-7.22 DCs with a similar phenotype were reported by others26 to arise from a bone marrow subset of CD34+ CLP, distinct from stem cells, which displayed the potential to generate T, B, and NK cells as well, but not myeloid cells. This finding led to the general view that the thymus was seeded by a CLP subset coming from the bone marrow and, hence, thymic DCs have hitherto been considered as a unique population of lymphoid-derived DCs. More recently, the characterization of "plasmacytoid" T cells as
DCs (DC2) and their identification in the human thymus have offered new
clues on the phenotypic and functional features of putative lymphoid
DCs. Accumulating evidence supports that DC2 represent the population
of lymphoid-derived DCs in man.12 This concept relies not
only on their phenotypic differences with myeloid-derived DCs (DC1),
but also on functional differences including their GM-CSF-independent
generation, in contrast to the GM-CSF dependence of DC1
precursors.16,17,32 More importantly, recent findings support the notion of shared molecular cues for the development of DC2
and lymphoid cells.21 In addition, DC2 and T cells share high pT Recently, DCs bearing myeloid-associated antigens have been found by others in the human thymus although at lower frequencies than those observed by us, perhaps due to different isolation techniques.27,28 However, whether such myeloid-related DCs represent DCs that have entered the thymus directly from the bloodstream or are produced in situ from early intrathymic progenitors is a question that was not resolved. Also, definitive conclusions on the lineage derivation of such DCs could not be drawn based on their phenotypic features.33,34 Therefore, we sought to characterize their ontogeny in this study with the final aim of defining their lineage affiliation. Precursor-product relationship studies based on multicytokine-supported cultures23 have allowed us to trace the developmental pathway of intrathymic DC1-like cells, and to identify intermediate DC1 progenitors with myeloid potential, but devoid of T-cell potential, within the human postnatal thymus. Collectively, our results allowed us to propose a model (summarized in
Figure 7), supporting that the most
primitive CD34hiCD33lo progenitors in the human
thymus differentiate along 2 independent pathways that progress through
separate CD34lo intermediate precursors, which are placed
at a critical branch point of lineage decision along intrathymic
development. Both intermediates, which display reciprocal phenotypes in
terms of myeloid and lymphoid markers, represent progenitors which have definitively lost the potential to generate either T cells
(CD34loCD44hi) or DC1-like cells
(CD34loCD4lo), respectively. Strikingly, we
show here that this developmental T/DC1 decision correlates in vivo
with the acquisition of reciprocal cytokine receptor profiles; so that
upregulation of the receptor for GM-CSF occurs on DC1 precursors
which show down-regulated levels of IL-7R
While this possibility has to be confirmed at the clonal level when
multilineage clonal assays are available, our results provide
unequivocal evidence that myeloid development takes place within the
human postnatal thymus. The existence of human CD34+
precursor thymocytes endowed with a latent myelomonocytic capacity has
been suggested before by independent in vitro studies from our group
and others.22,24 However, the physiologic relevance of
such intrathymic myeloid precursors has not been directly addressed, nor have the precursors been tested for their full developmental potential. Here, the identification of downstream
CD34loCD44hi progenitors with increased ability
to generate myeloid cells, but devoid of T-cell precursor activity,
provides direct evidence that a myeloid differentiation pathway
dissociated from that of lymphoid cells does physiologically exist in
the human thymus. Furthermore, the potential of such myeloid
intermediates to generate DC1-like cells, either directly from their
CD1a+ progeny, or indirectly from CD14+
monocytes, demonstrates that intrathymic DC1 cells have an
immediate myeloid origin. It is thus likely that the myeloid pathway of intrathymic DC development identified in this study is equivalent to
that previously reported for CD34+ cord blood stem cells,
which can give rise to epidermal LCs and dermal DCs through separate
CD14 Besides CD34loCD44hi myeloid intermediates, we
identify CD34loCD44lo lymphoid-committed
progenitors which lack myeloid potential and are unable to generate
DC1, but behave as efficient lymphoid precursors with T and NK cell
differentiation potential. Although the latter subset may include
bipotential T/NK progenitors equivalent to those identified
previously,35 a more attractive possibility is that they
are multipotent lymphoid precursors able to generate thymic DC2 as
well. This possibility is fully consistent with our finding that
up-regulation of pT Our model, however, is difficult to reconcile with our finding that NK
cells can be derived also from sorted GM-CSFR According to the proposed model, it has to be concluded that the
postnatal thymus, at least in humans, is colonized by progenitors which
still have myeloid potential, regardless of whether these progenitors
are truly multipotent stem cells (HSC) or intermediate lymphoid/myelomonocytic precursors equivalent to those identified in
mouse fetal liver.36 As such precursor thymocytes, like
HSC,31 display low GM-CSFR Finally, a relevant question is the functional meaning of the intrathymic myeloid DC1 subset. Since the only known function of thymic DCs is to mediate negative selection of self-reactive T cells,1-3 it is an upcoming challenge to identify the physiologic roles of the 2 ontogenically distinct DC subsets identified in the human thymus.
We thank Drs J. L. San Millán and C. Hernández for advice on real-time PCR, Drs A. Alvarez and J. C. Segovia for invaluable help with cell sorting, and the pediatric cardiosurgery units from Centro Especial Ramón y Cajal and Ciudad Sanitaria La Paz (Madrid) for the thymus samples.
Submitted July 31, 2001; accepted December 13, 2001.
Supported by grants from the Comisión Interministerial de Ciencia y Tecnología (SAF 97-0161), Dirección General de Enseñanza Superior (PB97-1194), Comunidad Autónoma de Madrid (08.3/0015.1/99 and 08.3/0021/2000), and Fondo de Investigación Sanitaria (FIS 00/1044), and by an institutional grant from the Fundación Ramón Areces.
The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked "advertisement" in accordance with 18 U.S.C. section 1734.
Reprints: María L. Toribio, Centro de Biología Molecular "Severo Ochoa," Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain; e-mail: mtoribio{at}cbm.uam.es.
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© 2002 by The American Society of Hematology.
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  A. Dominguez-Soto, L. Aragoneses-Fenoll, E. Martin-Gayo, L. Martinez-Prats, M. Colmenares, M. Naranjo-Gomez, F. E. Borras, P. Munoz, M. Zubiaur, M. L. Toribio, et al. The DC-SIGN-related lectin LSECtin mediates antigen capture and pathogen binding by human myeloid cells Blood, June 15, 2007; 109(12): 5337 - 5345. [Abstract] [Full Text] [PDF]
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 M. Garcia-Peydro, V. G. de Yebenes, and M. L. Toribio Notch1 and IL-7 Receptor Interplay Maintains Proliferation of Human Thymic Progenitors while Suppressing Non-T Cell Fates J. Immunol., September 15, 2006; 177(6): 3711 - 3720. [Abstract] [Full Text] [PDF]
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F. Weerkamp, M. R. M. Baert, M. H. Brugman, W. A. Dik, E. F. E. de Haas, T. P. Visser, C. J. M. de Groot, G. Wagemaker, J. J. M. van Dongen, and F. J. T. Staal Human thymus contains multipotent progenitors with T/B lymphoid, myeloid, and erythroid lineage potential Blood, April 15, 2006; 107(8): 3131 - 3137. [Abstract] [Full Text] [PDF]
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J. Soulier, E. Clappier, J.-M. Cayuela, A. Regnault, M. Garcia-Peydro, H. Dombret, A. Baruchel, M.-L. Toribio, and F. Sigaux HOXA genes are included in genetic and biologic networks defining human acute T-cell leukemia (T-ALL) Blood, July 1, 2005; 106(1): 274 - 286. [Abstract] [Full Text] [PDF]
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 T. Kikuchi, S. Ichimiya, T. Kojima, L. Crisa, S. Koshiba, A. Tonooka, N. Kondo, P. T. van der Saag, S. Yokoyama, and N. Sato Expression profiles and functional implications of p53-like transcription factors in thymic epithelial cell subtypes Int. Immunol., June 1, 2004; 16(6): 831 - 841. [Abstract] [Full Text] [PDF]
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M. Garcia-Peydro, V. G. de Yebenes, and M. L. Toribio Sustained Notch1 signaling instructs the earliest human intrathymic precursors to adopt a {gamma}{delta} T-cell fate in fetal thymus organ culture Blood, October 1, 2003; 102(7): 2444 - 2451. [Abstract] [Full Text] [PDF]
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V. Asnafi, K. Beldjord, E. Boulanger, B. Comba, P. Le Tutour, M.-H. Estienne, F. Davi, J. Landman-Parker, P. Quartier, A. Buzyn, et al. Analysis of TCR, pTalpha , and RAG-1 in T-acute lymphoblastic leukemias improves understanding of early human T-lymphoid lineage commitment Blood, April 1, 2003; 101(7): 2693 - 2703. [Abstract] [Full Text] [PDF]
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| Copyright © 2002 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
Top
Abstract
Introduction
and TCR
from Endogen (Woburn, MA); and CD1c
from Miltenyi Biotec GmbH (Bergisch Gladbach, Germany). Phycoerythrin (PE)-labeled MoAbs against CD3, CD5, CD13, CD33, CD34, CD56, and IL-3R
) or CD44lo (
)
intermediate CD34lo progenitors derived in vitro and sorted
as shown in (A), upon reculture in IL-2-supplemented
multicytokine-supported conditions. Absolute numbers are referred to
105 input progenitors. Results are presented as the mean of
5 independent experiments.
progenitor-derived dendritic cells: predominance of CD1a+ differentiation pathway.
J Immunol.
1999;162:5821-5828