Blood, Vol. 96 No. 1 (July 1), 2000:
pp. 9-23
REVIEW ARTICLE
Fates of human B-cell precursors
Tucker W. LeBien
From the Department of Laboratory Medicine and Pathology, University
of Minnesota Cancer Center, and Center for Immunology, University of
Minnesota, Minneapolis.
 |
Abstract |
Development of mammalian B-lineage cells is characterized by
progression through a series of checkpoints defined primarily by
rearrangement and expression of immunoglobulin genes. Progression through these checkpoints is also influenced by stromal cells in the
microenvironment of the primary tissues wherein B-cell development
occurs, ie, fetal liver and bone marrow and adult bone marrow. This
review focuses on the developmental biology of human bone marrow
B-lineage cells, including perturbations that contribute to
the origin and evolution of B-lineage acute lymphoblastic leukemia and
primary immunodeficiency diseases characterized by agammaglobulinemia.
Recently described in vitro and in vivo models that support development
and expansion of human B-lineage cells through multiple checkpoints
provide new tools for identifying the bone marrow stromal cell-derived
molecules necessary for survival and proliferation. Mutations in genes
encoding subunits of the pre-B cell receptor and molecules involved in
pre-B cell receptor signaling culminate in X-linked and non-X-linked
agammaglobulinemia. A cardinal feature of these immunodeficiencies is
an apparent apoptotic sensitivity of B-lineage cells at the pro-B to
pre-B transition. On the other end of the spectrum is the apoptotic resistance that accompanies the development of B-lineage acute lymphoblastic leukemia, potentially a reflection of genetic
abnormalities that subvert normal apoptotic programs. The triad of
laboratory models that mimic the bone marrow microenvironment,
immunodeficiency diseases with specific defects in B-cell development,
and B-lineage acute lymphoblastic leukemia can now be integrated to
deepen our understanding of human B-cell development.
(Blood. 2000;96:9-23)
© 2000 by The American Society of Hematology.
| |
Introduction |
Development of mature blood cells from
lymphohematopoietic progenitors is a complex process governed by
sequential changes in gene expression and external cues emanating from
lymphohematopoietic microenvironments, such as fetal liver and bone
marrow (BM). The last decade has witnessed dramatic progress in
elucidating the molecular mechanisms that govern blood cell
development. Mice with alterations in gene content (transgenics,
knockouts, knockins) have been extraordinarily useful in elucidating
the role of transcription factors, cytokines, and cytokine receptors in
blood cell development. This review focuses on the developmental
biology of human BM B-lineage cells and on perturbations in development
that can contribute to the progression of B-lineage acute lymphoblastic
leukemia (ALL) and immunodeficiency diseases characterized by
agammaglobulinemia. My objective is to provide an update on key issues
in human B-cell development and, where appropriate, compare and
contrast B-cell development in mouse and human. The discussion of
B-lineage ALL and immunodeficiency diseases will consider the
developmental biology of these diseases as they constitute a deviation
from normal programs.
The terminology used in this review is largely consistent with the
terminology used by other laboratories studying human B-cell development. Pro-B cells are those B-lineage cells that express cell-surface CD19 but do not express cytoplasmic or cell-surface µ heavy chains (HCs). Pre-B cells express cell-surface CD19 and cytoplasmic µHCs, and variably express cell-surface µHCs associated with surrogate light chains (
LCs)
ie, the pre-B cell receptor (pre-BCR). Immature B cells express cell-surface CD19 and
cell-surface µHCs associated with 
or 
LCsie, the B-cell
receptor (BCR). B-cell precursors include all B-lineage cells prior to
immature B cells expressing the BCR.
| |
Sites of B-cell development |
Human B-lineage cells are present in multiple tissue sites in early
fetal development. However, from midgestation through the eighth decade
of life, the BM is the exclusive site of B lymphopoiesis. Pre-B cells
are present in 7- to 8-week gestational age fetal liver1
and 10-week gestational age fetal omentum.2 A thorough analysis of 18- to 20-week fetal tissues revealed that B-cell development is multifocal; CD19+/surface
µHC
B-cell precursors and
CD19+/surface µHC+ immature B cells are
present in BM, liver, lung, kidneys, and spleen.3 The
frequency of B-cell precursors as a percentage of the total lymphoid
cell pool is much higher in fetal BM compared with adult
BM.3,4 Adult BM also differs from fetal BM by the presence
of recirculating CD19+/surface µ, 
HC+
mature B cells in the former.3 Similar levels of
recombinase-activating gene (RAG)-1, RAG-2, and terminal
deoxynucleotidyl transferase (TdT) are detectable by reverse
transcriptase-polymerase chain reaction (RT-PCR) in pro-B cells from
18-week fetal BM and 62-year adult BM, underscoring the functional
integrity of BM B-cell development throughout life.3 It is
noteworthy that recent studies of T-cell development indicate that
T-cell receptor (TCR) gene rearrangements actively occur in thymocytes
from individuals in their sixth decade of life.5 Thus,
ongoing development of B and T lymphocytes throughout life complements
the existence of memory B and T lymphocytes in maintaining a functional
immune system.
| |
Developmental stages of B-lineage cells |
Analysis of gene expression in developing lymphoid cells can be
accomplished by multiparameter flow cytometry,
immunohistochemistry/fluorescence microscopy, and RT-PCR. Immunologic
phenotyping of B-lineage ALL using monoclonal antibodies (mAbs) and
flow cytometry has been conducted in many laboratories, and it is not
my intent to summarize the many published reports. The reader is
referred elsewhere for an in-depth review.6
Although lymphoid progenitors are the descendants of hematopoietic stem
cells (HSCs) with the capacity to develop into all lymphohematopoietic
lineages, the earliest populations of lineage-restricted lymphoid
progenitors are poorly characterized. Figure
1 shows potential relationships between
so-called common lymphoid progenitors (CLPs) and progenitors with
increased fitness to form specific lymphoid lineages. The CLP is
defined as a progenitor with the capacity to develop into T, B, or
natural killer (NK) cells, but little or no capacity to develop into
nonlymphoid lineages, such as myeloid/erythroid cells. A cell with the
developmental potential of a CLP has been included in the blood cell
developmental schemes of hematology textbooks for many years. However,
data supporting its existence have only recently been
published.7-10 Galy and colleagues used
fluorescence-activated cell sorting (FACS) to purify
CD34+/CD10+/CD45RA+ BM progenitors
that do not express T, B, or NK lineage surface markers (ie, CD2, CD4,
CD8, CD16, CD19, CD20, and CD56). A battery of in vitro assays and the
severe combined immunodeficiency (SCID)-hu (human) mouse were employed
to demonstrate that
CD34+/CD10+/CD45RA+ progenitors are
capable of developing into B, T, NK, and lymphoid dendritic cell (DC)
lineages, but not myeloid/erythroid lineages.7 However,
this study did not clarify whether T- and B-lineage cells are derived
from a single progenitor. A subsequent study by Ryan and colleagues
showed that CD34+/CD19 lymphoid
progenitors expressing the interleukin 7 receptor (IL-7R) (CD127) gave
rise to CD19+ cells in a colony-forming assay.8
The CD34+/IL-7R+ lymphoid progenitors were
uniformly TdT+, and the majority expressed CD10. RT-PCR
analysis indicated the expression of RAG-1, immunoglobulin (Ig)
(CD79b), and the paired domain transcription factor
PAX-5.8 Ryan and colleagues did not assay for T, NK, or DC potential, but the
CD34+/IL-7R+/CD19 population
contained granulo-monocytic colony-forming units at a
frequency 10-fold to 100-fold lower than
IL-7R/CD19 cells.8 A
recent report indicated that CD34+ BM cells expressing the
CXCR4 chemokine receptor for stromal cell-derived factor-1 (discussed
in more detail below) could develop into B- and T-lineage cells, but
not myeloid/erythroid cells.9 It seems likely that the 3 reports7-9 described a human lymphoid progenitor with
similar developmental potential. A population of IL-7R+
adult murine BM cells are also developmentally restricted to become T,
B, and NK cells10 and may be the murine counterpart of the
lymphoid progenitors isolated from human BM.7-9
View larger version (66K):
[in this window]
[in a new window]
| Fig 1.
Developmental relationship between hematopoietic stem
cells (HSCs), common lymphoid progenitors (CLPs), and putative early-B
or T/NK/dendritic cell (DC) progenitors.
HSCs include all primitive CD34+/lineage
hematopoietic developmental stages prior to the CLP, shown
schematically as 3 cells. Arrows with solid lines indicate
developmental flow culminating in increased lineage restriction. Dashed
arrows indicate possible cellular targets of IL-7 signaling or an
unknown (?) ligand. Numbers on the cell surface indicate CD antigens
useful in distinguishing the developmental compartments. Although not
shown in this figure, the 3 reports that described the cell surface
phenotype of CD19 lymphoid progenitors revealed
considerable heterogeneity.7,8,13 For example, CD7 and CD33
were detected on a minority of the lymphoid progenitors in each
study.7,8,13 There is no known surface marker that
distinguishes the CLP from the early-B cell. It is also likely that
IL-7R expression and signaling vary both within and between the
lymphoid progenitor compartments.
|
|
The model in Figure 1 proposes that CLP can differentiate into 1 of 2 lymphoid progenitor intermediates: early-B cells or T/NK/DC tri-lineage
cells. Early-B cells are characterized by the initiation of
DJH rearrangements and the expression of B-lineage specific
proteins such as VpreB and Ig
(CD79a). Support for the existence of
an early-B cell comes from reports showing that DJH rearrangements,11,12 cytoplasmic Ig
protein,13 and VpreB protein14 are present in
CD19 lymphoid progenitors. The CLP could also
differentiate into a T/NK/DC tri-lineage progenitor possibly defined by
the acquisition of CD7. Either the CLP or the T/NK/DC progenitor could
migrate to the thymus and undergo subsequent development.15
It is unknown whether specific signals transduced by BM stromal
cell-derived molecules can promote CLP differentiation into an early-B
cell or a T/NK/DC progenitor.
Murine CLPs and possibly human CLPs are particularly sensitive to IL-7
stimulation. Signaling through the IL-7R is essential for the
development of murine CLPs, although not by virtue of inducing
self-renewal.16 A role for IL-7 signaling in the
development of human CD19+ B-lineage cells from
CD10+/TdT+/CD19 lymphoid
progenitors has been demonstrated in vitro,8 but whether
IL-7 exerts an effect on CLPs and/or early-B cells is unknown. The
relationship between signaling pathways activated following IL-7
stimulation of CLPs and the developmental fate of CLPs are unknown.
IL-7 activation of phosphatidylinositol (PI)-3 kinase/protein kinase B
activation is essential for survival/proliferation of human T-cell
precursors, whereas IL-7 activation of STAT5 favors T-cell differentiation.17 It will be interesting to
determine whether PI-3 kinase, STAT5, or other IL-7
signaling pathways activated in human CLPs can lead to different
developmental fates. The CLP
early-B cell step cannot
require IL-7 (see below), and other cytokines or BM stromal
cell-derived compensatory signals must be important.
Figure 2 shows the stages of human B-cell
development and counterpart stages in murine B-cell development.
Several classification schemes have been developed for the
mouse,18 but Figure 2 shows the A through E fractions
originally described by Hardy and colleagues.19 Figure 2
proposes the existence of an early-B cell (as discussed above) that
does not express the cell surface protein CD19. Early-B cells have
initiated DJH rearrangements and express cytoplasmic Ig
(and to some degree Ig) as well as VpreB proteins. I would emphasize
that this is a tentative definition of an early-B cell, since no cell
surface markers that could distinguish early-B cells from CLP have been
reported. This early-B cell may be similar to the
CD19 B-lineage fractions A1 and/or
A2 recently described by Hardy and
colleagues,20 or the
lin/c-kitlo
and lin/c-kit progenitors
described by Payne and colleagues.21 Human
pro-B cells are a well-characterized population expressing CD10, CD34, and CD19.22 The vast majority of pro-B cells express
TdT,22-24 and V-to-DJH rearrangements are
easily detected.11,12 However, single-cell PCR analysis
indicated that a minority of CD19+/CD34+ pro-B
cells have both HC alleles in germ-line configuration.24 Thus, assigning the early-B cell population a DJH
rearrangement status and the pro-B cell population a VDJH
rearrangement status is probably an oversimplification. A difference of
opinion exists as to whether CD19+/CD34+ pro-B
cells express cytoplasmic µHC. Two groups have concluded that pro-B
cells express neither cytoplasmic nor low cell-surface µHC.24,25 In contrast, using FACS-purified
CD19+/CD34+ pro-B cells, we can reproducibly
detect cytoplasmic µHC in 5% to 10% of pro-B cells.26
This result is consistent with the existence of readily detectable
VDJH rearrangements in pro-B cells.11,12 The
human pro-B cell may correspond to Hardy fraction B ± fraction C,
based on analysis of VDJH rearrangements.24,27
View larger version (60K):
[in this window]
[in a new window]
| Fig 2.
Stages in human B-cell development.
Six stages beginning with the CLPs and culminating with immature B
cells are shown as one model of B-cell development in human BM. The
letters in parentheses represent an approximation of the counterpart
stages in murine B-cell development, using the nomenclature of Hardy
and colleagues.19,20 Numbers on the cell surface indicate
CD antigens frequently used to define the individual stages in human
B-cell development. Patterns of gene expression inside the cells have
been determined by RT-PCR and/or flow cytometry. Dashed arrows indicate
possible cellular targets for positive (+) and negative ( )
growth regulators/chemotactic factors produced by BM stromal cells.
Cells in a particular developmental stage are not necessarily uniform
in the expression of a specific receptor. For example, only 10% to
20% of the pre-BI plus the pre-BII cells express the µ-LC
pre-BCR.
|
|
A functional VDJH rearrangement is essential for normal
pro-B cell differentiation into the pre-BI compartment (Figure 2). Pro-B cells that fail to make a functional VDJH
rearrangement undergo apoptosis and are probably phagocytized by BM
macrophages. Pro-B cell differentiation into pre-BI cells is
characterized by loss of CD34 and TdT, and acquisition of cytoplasmic
µHC in more than 95% of the cells.22-24 Similarly to the
mouse,18 human pre-B cells can be generally subdivided into
large proliferating cells (designated pre-BI in Figure 2) and small
postmitotic cells (designated pre-BII in Figure 2) on the basis of
cell-cycle analysis.24 The human pre-BI cells would
partially overlap with Hardy fraction C.19,20 Pre-BII cells
are actively undergoing LC rearrangements.24 In general,
rearrangement precedes rearrangement, and pre-BII cells that
fail to make a functional rearrangement can proceed to rearrange
the LC locus. Interestingly, a very small percentage (approximately
1%) of immature B cells in human BM and peripheral blood express and LC on individual cells.28-30 This dual LC expression
may reflect immature B cells undergoing receptor editing.
| |
The pre-BCR and related structures |
Mammalian B-lineage cells must traverse several critical checkpoints
on the road to becoming functional antigen-specific B cells. The cell
surface molecular complex appearing at a critical initial checkpoint is
the pre-BCR. The pre-BCR is a complex of proteins consisting of
µHC, LC, and the Ig/Ig signal transducing heterodimer.31 The mammalian LC consists of 2 proteins
generally referred to as VpreB and 5. The genes encoding these 2 proteins were originally discovered in the mouse (Melchers et
al32 and references therein) and their organization differs
between mouse and human (Minegishi et al33 and references
therein) VpreB and 5 proteins are noncovalently associated on the
surface of B-cell precursors and together form a LC-like structure.
In turn, 5 is covalently coupled to the CH1 domain of
µHC via a carboxy-terminal cysteine. Readers are referred to an
earlier review for details on the original identification and
characterization of the VpreB and 5 genes and their encoded
proteins.32
Analysis of the structure, expression, and function of the human
pre-BCR has been facilitated by the development of mAbs against recombinant LC proteins.34-39 The initial panel of mAbs
made against the human LC was used to characterize cytosolic and
cell-surface µHC/LC complexes and surface expression of
LC.34,40 A major conclusion in the original
study34 was that surface µHC/LC expression was
restricted to the pre-B cell compartment (ie,
CD19+/CD34 cells in Figure 2); this
suggests a critical role for the pre-BCR at a relatively late stage of
B-cell development. Subsequent studies using other mAbs yielded
conflicting results.24,35,36 A major difference was the
identification of normal and leukemic pro-B cells (ie,
CD19+/CD34+/µHC) that
stained with anti-VpreB mAb.24,35,36 The low levels of
cell-surface LC, differences in the subtype of the mAb (ie, IgM
versus IgG1), and differences in epitope recognition by various anti-VpreB mAbs were among the explanations offered for the conflicting results.
A series of papers describing new antihuman VpreB mAbs37-39
has provided some resolution to past discrepancies. The recent vintage
of anti-VpreB mAbs includes mostly IgG1 subclass mAbs, thereby
eliminating potential problems that can confound the use of IgM
reagents. The anti-VpreB mAb produced by Wang and colleagues binds to
the surface of pre-B cell lines, but only binds to pro-B cell lines
following permeabilization.37 As expected, normal CD19+ human B-lineage cells coexpressed low levels of cell
surface µHC and VpreB, and approximately 20% of the
CD19+/VpreB+ cells were weakly
CD34+.37 Interestingly, cytoplasmic
VpreB+ is expressed in
CD34+/CD19 lymphoid progenitors at a
stage prior to V-to-DJH rearrangement,37 possibly the early-B cells proposed in Figure 2. Tsuganezawa and colleagues generated mAbs that recognized human VpreB, human 5, or
an epitope expressed only on the assembled pre-BCR.38 Their anti-VpreB mAb binds to the surface of pre-B ALL cell lines but not
pro-B ALL cell lines.38 However, cytoplasmic VpreB or 5 were detected in the majority of pro-B ALL cell lines and freshly isolated pro-B ALL.38 In contrast, the anti-VpreB mAb
produced by Gauthier and colleagues39 binds to the surface
of some µ pro-B ALL cell lines.25 One
of these pro-B ALL cell lines (designated JEA2) was shown to
express cell surface VpreB in association with poorly characterized
molecules of approximately 105 to 130 kd. Interestingly, cross-linking
VpreB on the µ JEA2 pro-B ALL cell line led to an
increase in Ca++ flux, suggesting that VpreB was one
component of a putative signaling receptor on the surface of at least
some pro-B ALL cells.25 These authors also detected
cell-surface VpreB on CD19+/CD34+ normal pro-B
cells and used this data to argue for the existence of 2 distinct
populations:
CD19+/CD34+/µHC/VpreB+
and
CD19+/CD34/µHC+/VpreB+.
However, there is no biochemical evidence that VpreB is associated with
a protein (or proteins) other than µHC on the surface of normal human
B-cell precursors. We have used one of the anti-VpreB mAbs (VpreB8)
made by Wang and colleagues37 to analyze VpreB expression
in fetal BM B-lineage cells. Our results indicate that VpreB is
expressed on the surface of 5% to 10% of the B-cell precursors (ie,
pro-B plus pre-BI plus pre-BII in Figure 2). Furthermore, within the VpreB+ population, approximately 90% of the
cells are CD19+/CD34, and approximately
10% are CD19+/CD34+. Results from our
laboratory show that CD34+/VpreB+ cells also
express cell surface µHC (J. A. R. Pribyl, N. Shah, F. E. Bertrand,
T. W. LeBien, 1999, unpublished data). Thus, we believe that most, if not all,
CD19+/CD34+/VpreB+ normal B-lineage
cells express the conventional pre-BCR. Since the vast majority of
surface VpreB+ cells are CD34, I show
the expression of the pre-BCR on pre-BI and pre-BII cells only (Figure
2). The VpreB+ cells that weakly express CD34 could be
developmentally more similar to pre-BI cells than pro-B cells, but this
has not been tested. The vast majority of B-lineage ALLs express
cytoplasmic or surface VpreB,25,38 probably reflecting the
general phenotypic similarity between normal and leukemic B-cell precursors.
The importance of the LC to normal B-cell development was first
elucidated in a classic study demonstrating that mice with a targeted
disruption in the 5 locus exhibit a block at the pro-B to pre-B
transition.41 The block in B-cell development probably occurs because cells at this transition fail to receive a positive selection signal through the pre-BCR. However, the block is not absolute since the number of B cells in secondary lymphoid tissues gradually increases over time, probably owing to the emergence of B
cells that rearranged LC genes prior to µHC
genes.42,43 The importance of the LC in human B-cell
development has been underscored by the discovery of an
agammaglobulinemia patient with mutations in both 5
alleles33 (see below). Immunologic analysis of this single
patient indicated a disruption in B-cell development more severe than
what occurs in 5-deficient mice. Since only a single patient with a
mutation in the 5 locus has been described to date, it is unclear
whether the gradual recovery of B cells observed in 5-deficient mice
would occur in humans.
How does the pre-BCR perform its critical role at the
pro-Bpre-B transition? Despite heuristic appeal, the notion
that the pre-BCR functions as a receptor for a specific ligand in the
BM or fetal liver microenvironment has not been supported by
experimental evidence. What has become clear is that only about one
half the µHC proteins encoded by functional VDJH
rearrangements are capable of pairing with LC in the
mouse.44-46 Circumstantial evidence suggests that a similar
type of preferential pairing of µHC and LC also occurs in human
pre-B cells.47,48 This pairing is essential for pre-BCR
assembly and expression on the cell surface. Formation of the pre-BCR
heralds a sequence of events, including (1) suppression of RAG-1/RAG-2
expression to ensure allelic exclusion at the µHC locus, (2) a rapid
burst of proliferation in cells expressing the pre-BCR, and (3)
reexpression of RAG-1/RAG-2 and initiation of LC gene rearrangement.
Are there separable roles for LC and µHC in pre-BCR function? This
is controversial. Shaffer and Schlissel reported that transgenic mice
expressing a truncated murine µHC (incapable of pairing with LC)
could still transduce signals leading to changes in surface markers,
transcription, and retargeting of the recombinase ensemble in B-lineage
cells.49 The authors concluded that the LC
functions as a chaperone to facilitate pre-BCR assembly and
expression, but plays no direct role in signal transduction. They also
argued that the capacity of truncated µHC to mediate B-cell
differentiation in the absence of LC ruled against the
pre-BCR/ligand model. However, truncated µHC may undergo enhanced
aggregation compared with full-length µHC, thereby leading to
increased constitutive signaling.50
Pre-BCR cross-linking in vitro initiates signaling events, including
Ca++ flux and protein tyrosine kinase
activation.51,52 How could this occur in vivo in the
absence of an external cross-linking ligand? Elegant recent studies
have provided new insight into the complexity of pre-BCR subunit
protein-protein interactions involving µHC, VpreB, and
5.39,53 These studies suggest mechanisms to explain
pre-BCR assembly, VH repertoire selection, and cell signaling. We might assume that signaling through the pre-BCR minimally
requires the dimerization/aggregation of at least 2 distinct pre-BCR
molecular complexes on the cell surface. With the realization that the
LC is a non-transmembrane-spanning polypeptide complex
disulfide-linked to the µHC and exhibiting VpreB-VH
interactions, it seems possible (as proposed by Melchers54)
that the LC itself could assume a ligand function for the µHC.
Other protein complexes with potentially similar functions to the
pre-BCR have been described. Murine pro-B cell lines express the LC
associated with several proteins ranging from 65 to 200 kd, including a
predominant protein of 130 kd.55 These pro-B cell lines do
not express µHC.55 The protein or proteins associated with LC in these cells have been occasionally referred to as the
surrogate HC. A recent study using a human µ pro-B
leukemic cell line (JEA2) showed that VpreB is noncovalently associated
with a p105 and possibly several other proteins on the cell
surface.25 However, there is no evidence that VpreB associates with p105 (or any other protein other than µHC) on normal
human B-cell precursors. The identity of the murine and human
LC-associated surface proteins is unknown. A novel complex that has
been referred to as the "calnexin pre-BCR"56 was
recently described by Nagata and colleagues.57 The calnexin
pre-BCR consists of Ig/Ig noncovalently associated with the
molecular chaperone calnexin, and was detected on the surface of
pro-B cell lines and early B-lineage cells from RAG-2-deficient
mice.57 Cross-linking Ig on these cells induced the
tryosine phosphorylation of syk, ERK, and PI-3 kinase in vitro, and
pro-B to pre-B cell differentiation in vivo. A potential
µ-independent role for Ig was discovered when mice with a targeted
disruption of the Ig gene were shown to exhibit a block in B-cell
development prior to V-to-DJH rearrangement.58 These
results57,58 suggest a role for
Ig+/µHC molecular complexes in the
earliest stages of murine B-cell development.
| |
The IL-7 story |
An unresolved issue in studies of human B-cell development is the
identity of the molecule(s) essential for the growth of normal B-cell
precursors. Much has been written of IL-7, and some historical
perspective is warranted. Following the initial cloning and
characterization of IL-7 from murine BM stromal cells more than 10 years ago,59 IL-7 was shown to be crucial for the
proliferation and development of murine B-cell precursors. IL-7 has
been cast as a survival, proliferation, or differentiation factor
depending upon the experimental system being employed.60,61
Mechanistic insight has been gleaned from studying the effect of single
amino acid substitutions on IL-7R chain function. Corcoran and
colleagues showed that a Y-to-F mutation at amino acid residue 449 abrogated the capacity of B-cell precursors to undergo IL-7-induced
proliferation through a PI-3 kinase-dependent pathway.62
Interestingly, functional studies of the IL-7R chain harboring this
mutation uncovered a novel signaling pathway (PI-3 kinase
independent?) that triggered IgH rearrangements and
subsequent B-cell differentiation.62 Recent studies from
the same group indicated that IL-7R signaling can alter recombinase
accessibility of 5' VH genes.63 The
criticality of IL-7 for normal murine B-cell development has been
elucidated in gene-targeted mice. Targeted disruptions in the genes
encoding IL-7,64 the IL-7R chain,65 the
c subunit of the receptors for IL-2, 4, 7, 9, and
15,66,67 and the Jak3 tyrosine kinase68,69 all
lead to severe impairment in B-cell development. Thymocyte and T-cell
development are also impaired, reflecting the multiple actions these 5 cytokines exert on lymphopoiesis. IL-7 is, however, not the only
cytokine implicated in the regulation of murine B-cell development.
Kincade and colleagues have suggested that at least 16 distinct stromal
cell products can exert positive effects on murine B-cell
development.61 One recent addition to the list is thymic
stromal lymphopoietin (TSLP). TSLP was originally isolated from a
murine thymic stromal cell line.70 TSLP reportedly has the
capability to replace IL-7 in supporting murine B-cell development in
vitro71 and promote the development of surface
IgM+ immature B cells from surface IgM
precursors.72 Interestingly, the TSLP receptor complex
consists of the IL-7R chain and a second subunit distinct from the
c. Furthermore, TSLP induced the activation of
STAT5 but not any of the known Jak kinases.72
Whether IL-7 and TSLP work in a hierarchical or cooperative manner in
regulating murine B-cell development is unknown. Human TSLP has been
cloned (S. Lyman, PhD, Immunex, written communication,
May 1999), but there are no published reports on its bioactivity on
human B-cell precursors.
The role of IL-7 in human B-cell development is strikingly different
from its role in murine B-cell development. In fact, there is a
widespread misconception that IL-7 stimulates the proliferation of
human B-cell precursors. Part of the difficulty in determining IL-7
effects can be attributed to differences in the assay systems employed
and the biological endpoints measured. Initial studies by
us73 and others74,75 demonstrated that
recombinant human IL-7 could exert weak proliferative effects on normal
human B-cell precursors in vitro. However, it was difficult to exclude
the possibility that IL-7 was simply enhancing survival. A stronger effect of IL-7 was observed when normal B-cell precursors were cultured
on human BM stromal cells.26,73,75,76 Under these conditions, CD19+ B-lineage cell numbers increased by
10-fold to 20-fold over 2 to 3 weeks in vitro, but underwent rapid cell
death thereafter.
Biological insight into IL-7 function in human B-cell development has
been gleaned from congenital immunodeficiency patients. Patients with
X-linked severe combined immunodeficiency (XSCID) have
mutations in the c subunit of the receptors for IL-2,
IL-4, IL-7, IL-9, and IL-15. XSCID patients have severe defects in
development of T and NK cells, but have normal or even elevated numbers
of peripheral blood B cells.77 Furthermore,
immunodeficiency patients with autosomal recessive mutations in the
Jak3 tyrosine kinase exhibit a developmental phenotype
indistinguishable from XSCID, including normal numbers of peripheral
blood B cells.78,79 Likewise, 2 patients with mutations in
the IL-7R chain that led to defective expression also had normal
numbers of peripheral blood B cells.80 These collective
experiments of nature clearly indicate that IL-7 signaling is not
essential for at least the numerically normal development of human B
lymphocytes. My laboratory used a human BM stromal cell culture system
to show that HSCs could develop into B-lineage cells independently of
IL-7 stimulation.81 Our results are in accord with B-cell
development occurring in patients with XSCID. However, extensive
proliferation of the pro-B cell compartment does not
occur,81 and it is presumptuous to assume that this in
vitro model completely mimics B-cell development occurring in patients
with mutations in the IL-7 pathway.
Although not essential for human B-cell development, IL-7 does
transduce signals that lead to specific changes in gene expression. Proliferation of CD19+/CD34+ pro-B cells on
human BM stromal cells is enhanced by inclusion of exogenous
IL-7.26 IL-7 stimulation induces a specific increase in
cell-surface CD19 on human pro-B cells82,83 and a decrease in RAG-1, RAG-2, and TdT messenger RNA (mRNA) levels.83
There may be physiologic relevance to these results. For example, IL-7 expression in situ has been detected by RT-PCR analysis of human BM
biopsies.84 The identity of the human BM cell producing
IL-7 in vivo is unknown, although small amounts (less than 2 pg/mL) of
IL-7 can be detected in supernatants from vascular cell adhesion molecule-1 (VCAM-1) (CD106)+ BM stromal cells
in vitro.76,81,85 Similarly, purified VCAM-1+
murine BM reticular cells express cytoplasmic IL-7
protein.86
The complete identity of the human BM stromal cell-derived molecule
(or molecules) that transduce signals essential for human B-cell
development (including the counterpart of the murine IL-7 "signal") is unknown. Part of the difficulty in identifying an IL-7 alternative is that IL-7 could act on at least 3 distinct stages
of lymphoid cell development: CLPs, early-B cells, and pro-B cells
(Figure 2). The cell-cycle disposition and self-renewal capacity of
these compartments have not been determined. However, we do know that
human CD19 progenitors8 and pro-B
cells26 are IL-7 responsive. Figure 3 shows several cytokines that could
regulate human B-cell development. The cytokine-responsive target cells
would include CLPs, early-B cells, and pro-B cells. The BM stromal cell
molecules that regulate development could be secreted or cleaved from
the stromal cell surface. The secreted or cleaved products could in
turn be bound to stromal cell proteoglycans such as heparan sulfate
proteoglycans (HSPGs). Several candidates come to mind. Namikawa and
colleagues reported that a combination of IL-7, IL-3, and Flt3 ligand
is superior to IL-7 alone in supporting human pro-B cell growth on murine BM stromal cells.87 My laboratory has confirmed
their observation using human BM stromal cells (J.A.R. Pribyl and T.W. LeBien, unpublished observations, February 1999). Flt3
ligand is produced by BM stromal cells88,89 (also in our
unpublished observations, February 1999) and could
potentially stimulate similar cellular compartments and transduce
similar signals to IL-7. Oritani and Kincade developed a cloning
strategy to identify murine BM stromal cell gene products that bind to
murine pre-B cells.90 One of the molecules identified was a
secreted extracellular matrix glycoprotein designated
SC1/ECM2.90 Soluble and immobilized SC1/ECM2 enhance the
growth of IL-7-dependent murine pre-B cells,90,91 but the
mechanism of enhancement is unknown. Interestingly, the carboxy
terminus of SC1/ECM2 has high amino acid sequence homology to
osteonectin/SPARC,92 which reportedly can bind cytokines, such as platelet-derived growth factor.93 A human homologue of SC1/ECM2 (designated hevin) has been cloned from high endothelial venules,94 but it is not known whether hevin has any effect on the growth of human B-cell precursors. HSPGs play a critical role in
"presenting" cytokines to survival/growth factor receptors on
lymphohematopoietic cells. HSPGs expressed on murine B-lineage and BM
stromal cells can bind IL-7 and enhance the growth of IL-7-dependent murine pre-B cell lines.95 Furthermore, heparan sulfate is
important for cytokine-mediated expansion of human
long-term-culture-initiating cells.96 Therefore, a
currently unknown molecule produced by BM stromal cells could bind to
HSPGs and mediate survival/growth of human B-cell precursors (Figure
3).
View larger version (51K):
[in this window]
[in a new window]
| Fig 3.
BM stromal cell-derived molecules that could transduce
survival/growth, differentiation, or chemotactic signals to CLP,
early-B, or pro-B cells.
HSPG indicates heparan sulfate proteoglycan. The dashed arrow indicates
that the membrane-bound form of Flt3 ligand is cleaved at the stromal
cell surface. The question mark indicates the unknown growth factor
that could bind to HSPG. IL-7 and the unknown growth factor are shown
binding directly to their cognate receptors, or binding HSPG followed
by binding to their cognate receptors.
|
|
A BM stromal cell product shown in Figure 3 that potentially provides a
unique function in B-cell development is the chemokine stromal
cell-derived factor-1 (SDF-1). Mice with targeted disruptions in the
genes encoding SDF-1 and its receptor CXCR4 exhibit perinatal mortality
owing to perturbations in organ vascularization and lymphohematopoiesis.97-99 B lymphopoiesis and myelopoiesis
are severely impaired,97-99 and a recent study concluded
that a functional CXCR4 receptor is essential for retention of B-cell
precursors in the BM microenvironment.100 CXCR4 has a
complex pattern of expression on CD34+ lymphohematopoietic
cells and CD19+ B-lineage cells.9,100-102 CXCR4
is expressed at all stages of B-cell development, but
CD19+/CD34/LC pre-B
cells and mature B cells express higher levels than
CD19+/CD34+ pro-B cells.102,103
Interestingly, SDF-1-mediated signaling pathways leading to calcium
mobilization and chemotaxis are more rigorously activated in less
mature B-lineage cells expressing lower levels of cell surface
CXCR4.102,103 Thus, BM SDF-1 may trigger signaling pathways
that regulate chemotaxis of B-cell precursors to "preferred
sites" of proliferation within the stromal cell milieu. It is
noteworthy that SDF-1 is expressed in human fetal liver biliary ductal
plate epithelial cells, in apposition to lymphoid cells expressing
VpreB.104
| |
Models of human B-cell development |
Establishment and characterization of in vitro culture systems that
at least partially mimic the in vivo BM microenvironment have been
extremely important for advancing our understanding of human B-cell
development. Progress in this area has been facilitated by the use of
BM stromal cells as a supportive microenvironment. Adherence of B-cell
precursors to BM stromal cells is essential for normal murine and human
B-cell development (reviewed in Kincade et al,61 Jarvis et
al,105 and Ryan et al106). Binding of very late
antigen-4 (VLA-4) (CD49d/CD29) expressed on human B-cell precursors to
VCAM-1 on human BM stromal cells is the primary molecular interaction
that facilitates adhesion of these 2 cell types.107-109
Cytokines can regulate levels of BM stromal cell surface VCAM-1,
thereby influencing the capacity of these cells to support B-cell
precursor adhesion.108 There is substantial evidence that cross-linking VLA-4 with VCAM-1 or the CS-1 domain of fibronectin can
trigger a protein tyrosine kinase cascade in B-lineage cells. However,
there is no evidence that VLA-4 triggers a reciprocal activation of
VCAM-1 culminating in a signal transduced in BM stromal cells. Lymphoid
cell contact with human BM stromal cells can transduce signals leading
to protein tyrosine kinase activation110 and tyrosine
phosphorylation of focal adhesion kinase, paxillin, and
ERK2.111 This signaling pathway is independent of
VCAM-1.110 To what degree these bi-directional (B-cell
precursor 
BM stromal cell) signaling events might
influence B-cell developmental fates in vivo is unknown.
Prompted by our success in establishing in vitro human BM stromal cell
culture conditions that support the adhesion108 and short-term growth26,73 of B-cell precursors, we asked
whether a more expanded model of B-cell development could be
established. In an effort to foster physiologic relevance, we
FACS-purified fetal BM CD34++/CD19 HSC
and plated them onto third-passage, nontransformed human fetal BM
stromal cells.81 CD34++/CD19
HSCs underwent commitment and differentiation into the B-lineage over a 3-week period.81 A hierarchy of developmental
changes consonant with B-cell development in vivo occurs in this in
vitro model, including (1) loss of CD34 expression, (2) a continuum of
increase in cell surface CD19, (3) emergence of cytoplasmic µHC+ pre-B cells, including some expressing the
cell-surface pre-BCR, and (4) emergence of immature B cells expressing
µ/ or µ/ BCR. As discussed above, several lines of evidence
rule out a mandatory role for IL-7 in this culture
system.81 The fact that
CD34++/CD19 HSC can differentiate all
the way to immature B cells demonstrates that human fetal BM stromal
cells can provide the developmental cues necessary to traverse the
major checkpoints defined by rearrangement of HC and LC genes. This
human BM stromal cell culture does not support a dramatic numerical
expansion of any specific compartment of B-lineage cells, probably
attributable to the exclusion of fetal bovine serum and exogenous
cytokines. It is also conceivable that the BM stromal cells in this
culture (which are exclusively adventitial
reticular/fibroblastlike cells by third passage) do not represent the
totality of BM stromal cell components essential for optimal
proliferation in vivo.
At the time we were developing our human BM stromal cell culture,
Rawlings and his colleagues were developing an in vitro culture using
the murine S17 stromal cell line.112 They originally showed
that enriched CD34+ cord blood cells would develop into
CD19+ B-lineage cells after 3 to 4 weeks.112
The CD19+ B-lineage cells were at a very early stage of
B-cell development since bulk culture analysis by Southern blotting
indicated no rearrangements at the IgH locus.112 These
CD19+ B-lineage cells could be expanded following transfer
to fresh S17 stromal cells, but did not proliferate following
stimulation with IL-7 or stem cell factor (SCF). A
follow-up report showed that inclusion of Flt3 ligand enhanced the
development of CD19+ B-lineage cells by twofold to
threefold.113 We have recently shown that inclusion of Flt3
ligand at the initiation of our human BM stromal cell culture also
enhances the development of CD19+ B-lineage cells
(J.A.R. Pribyl and T.W. LeBien, unpublished
observations, February 1999), providing additional
support for a role of Flt3 ligand in human B-cell development (Figure
3).
Given the differences in the tempo and degree of B-cell development in
the 2 models, we conducted a side-by-side comparison of murine S17
stromal cells and human fetal BM stromal cells.114 When
human fetal BM CD34+ HSCs were cultured on human fetal BM
stromal cells or human skin fibroblasts, robust differentiation to the
immature B-cell stage occurred within 3 weeks.114 In
contrast, CD19+ B-lineage cells emerging on S17 stromal
cells within the same time frame had twofold to fourfold higher levels
of cell-surface CD19, but no cells expressing the BCR.114
Human and murine S17 stromal cells therefore differ in their capacity
to support human B-cell differentiation under the conditions in which
we compared them. The identity of the soluble or membrane-bound stromal
cell molecules important in both cultures is unknown. When
CD34+ cord blood HSCs are cultured on S17 stromal cells for
6 to 8 weeks, small numbers of cytoplasmic and surface
µHC+ cells can be detected.115 Furthermore,
transferring these 6- to 8-week cultures onto CD40 ligand
(CD154+) fibroblasts supplemented with IL-4
and IL-10 results in terminal human B-cell differentiation to
Ig-secreting cells.115 Murine stromal cell lines other than
S17 also support the development of CD19+ human B-lineage
cells from CD34+ cord blood HSCs.116-119 Two of
these studies showed that a combination of SCF and granulocyte
colony-stimulating factor would enhance the outgrowth of
B-cell precursors.117,118
The nonobese diabetic-severe combined immunodeficient (NOD-SCID)
mouse120 has become a popular tool for studying engraftment and development of human HSCs in vivo (for review, see Greiner et
al121). The CD34++/CD38 HSC
that engrafts in NOD-SCID mice has been designated the
SCID-repopulating cell.122 Development of CD19+
B-lineage cells from human CD34+ BM or cord blood HSCs
transplanted into NOD-SCID mice has been reported by several
groups.122-126 The degree of human B-cell differentiation was variable in these studies, although spleen and peripheral blood B
cells expressing surface µHC and or LC were detected in 2 studies.124,125 These results indicate that xenogeneic
factors produced in NOD-SCID mice can promote and support multiple
stages of human B-cell development. The murine BM appears to be the
primary site of engraftment by human CD34+ HSCs. It follows
that commitment into the human B-lineage and traversal through the
pre-BCR and BCR checkpoints is likely to occur in murine BM,
although this has not been directly demonstrated.
How can these in vitro and in vivo models of human B-cell development
be further refined? None of the in vitro BM stromal cell cultures
described thus far fully recapitulate the complex microenvironment in
which B cells develop. For example, the adventitial reticular (fibroblastlike) adherent cell in the human BM stromal cell
culture is only 1 component of the BM microenvironment. No one has
examined the capacity of other BM microenvironmental cells (eg,
osteoblasts, BM microvascular endothelial cells, macrophages) to
support or modulate B-cell development. One technical problem is the
difficulty in purifying and establishing long-term cultures of human BM
stromal cell components. SV40 large t antigen127 or human
papilloma virus E6/E7 genes128 are capable of immortalizing human BM stromal cells. These stromal cell "lines" have been used to study hematopoiesis (eg, Li et al129), but
no reports have described their capacity to support human B-cell
development. Another possible strategy for long-term maintenance of BM
stromal cells would be overexpression of the catalytic subunit of
telomerase, which has been shown to exceed the life span of human
fibroblasts by up to 20 doublings.130
Development of stable long-term BM stromal cell cultures would
facilitate the isolation of potentially novel genes that encode
survival/growth factors regulating human B-cell development using, for
example, the cloning/screening strategy of Oritani and
Kincade.90 A more detailed analysis of the NOD-SCID mouse
might focus on whether fetal liver or BM stromal cells are comparable
to human BM stromal cells in supporting human B-cell development. It is
conceivable that a highly conserved murine cytokine is as effective as
its human homologue, in which case murine stromal cell complementary
DNA (cDNA) libraries could be screened for binding to human B-lineage
cells.90
| |
B-lineage immunodeficiencies |
Dramatic progress has recently been made in identifying the genetic
defects in many congenital human immunodeficiency
diseases.131 These diseases are largely classified on the
basis of which cellular component or function of the immune response is
defective.132 By the grace of good hindsight, it is not
surprising that immunodeficiency diseases that primarily affect B-cell
development or B-cell function involve genes encoding protein
components of the pre-BCR, BCR, or signaling pathways activated
following cross-linking these receptors.133 The degree to
which B-cell development or function is altered in these patients shows
many similarities and some differences compared with the phenotype
observed in gene-targeted mice.
| |
X-linked agammaglobulinemia (XLA) |
XLA is the prototype immunodeficiency disease that specifically
affects the B-lineage.131-133 The Bruton's tyrosine kinase
(BTK) gene encodes a cytosolic 659-amino acid protein that is
mutated in the vast majority of boys diagnosed with
XLA.134,135 BTK mutations are found in 80% to 90%
of patients following a presumptive diagnosis of XLA based on
early-onset hypogammaglobulinemia and few or no detectable peripheral
blood B cells.136 More than 300 mutations have been
identified in the BTK gene,137 and mutations have
been mapped to all 6 of the functional domains.138 The
majority of XLA patients have profound hypogammaglobulinemia afflicting
all immunoglobulin classes and fewer than 1% of normal numbers of peripheral blood B cells. A single study of 8 patients indicated that
maturation arrest occurred at the pro-B/pre-B interface, ie, between
CD19+/TdT+/cytoplasmic µHC
and CD19+/TdT/cytoplasmic
µHC+ populations.139
The xid mouse, a murine model of X-linked immunodeficiency disease,
harbors a mutation in the Btk gene.140 Mice with
targeted disruptions of Btk have a defect in B-cell development
that is identical to the xid mouse.141-143 As discussed in
detail elsewhere,131,133,140-143 xid and Btk
gene-targeted mice have a much milder form of B-cell immunodeficiency
than XLA patients, characterized by reduced levels of only 2 immunoglobulin subclasses (IgM and IgG3) and B cell numbers reduced by
only 30% to 50%. Comparison of B-cell developmental defects in mice
and humans led many investigators to conclude that loss of BTK function
has more severe consequences in humans. This could be explained by
compensatory/redundant kinases operating in murine B-cell development
or by a difference in the role of BTK in murine and human pre-BCR
and/or BCR signaling pathways. A more intriguing possibility is the
potential contribution of modifying genetic factors/modifier alleles
(ie, their gene products) in facilitating the traversal of pro-B to
pre-B cells in XLA patients.133,138 This may explain the
variability in immunologic symptoms present in family members with
identical genetic backgrounds. Despite considerable effort, no
correlation has been determined between XLA genotype and the severity
of clinical symptoms in XLA patients. Whether human XLA has a more
severe defect in B-cell development than the murine models is still a
matter of some controversy, but the unique function of BTK in B-cell
development in both species is undeniable.
The role of BTK in signal transduction pathways has been extensively
studied, and Rawlings has recently reviewed this
subject.138 BTK is expressed throughout the B-lineage, but
expression decreases in terminally differentiated plasma
cells.144,145 BTK activation following BCR cross-linking
has been studied in detail.138 Briefly, BCR cross-linking
activates PI-3 kinase, which generates limiting amounts of
membrane-associated PI-3,4,5-trisphosphate. The latter recruits
cytosolic BTK to the membrane by interacting with the BTK SH3
domain.146 BTK activation then proceeds through 2 steps: transphosphorylation of Y551 within the BTK kinase domain (most likely
by the src family kinase Lyn), followed by
autophosphorylation of Y223 in the BTK SH3 domain.147
Membrane-associated BTK then binds to an unidentified
tyrosine-phosphorylated ligand,138 which facilitates
co-localization of BTK with phospholipase C
(PLC-), activation of PLC-, and
culmination in a sustained calcium signal involving extracellular
calcium influx.148 Very recent studies suggest that the
"unidentified tyrosine-phosphorylated ligand" could be the B-cell
linker protein (BLNK).149 The outcome of this complex
pathway leading to sustained calcium signaling is enhanced
proliferation and changes in transcription. I would emphasize that this model of BTK function has been developed with the use of BCR
cross-linking as an activation stimulus. Evidence that BTK functions
through the same pathway following pre-BCR activation is lacking. It is
possible that once the pre-BCR becomes activated (eg, through
ligand-independent tonic signals as discussed above), BTK
occupies a critical point in the pre-BCR signaling pathway whose
function is nonredundant. Given the complexity of BTK protein domain
organization, it is remarkable that so many distinct BTK mutations culminate in a relatively similar block in B-cell development.
| |
Non-X-linked agammaglobulinemia |
As discussed above, 10% to 20% of B-lineage immunodeficiency
patients do not harbor BTK mutations. Mary Ellen Conley and her colleagues have systematically screened BM DNA samples from patients lacking BTK mutations in an effort to identify other mutated
genes that could underlie these immunodeficiency diseases. By this
approach, they have identified patients with mutations in the
µHC,150 the 5/14.1 component of the
LC,33 and Ig.151 Seven patients from 3 families harbored mutations that disrupted the µHC.150 These included 75-kb to 100-kb homozygous deletions of the D and J
regions plus the µ constant region, and a homozygous base-pair substitution that removed an alternate splice site used to generate the
membrane form of the µHC. Analysis of peripheral blood from 4 of 7 patients revealed no detectable B cells, and analysis of the BM from 1 of the 4 evaluable patients indicated maturation arrest at the pro-B to
pre-B interface.150 In a second report, a 5-year-old boy
with severe hypogammaglobulinemia was found to have fewer than 1% of
the normal number of peripheral blood B cells.33 A detailed
analysis of the mutated 5 alleles and their encoded proteins suggested that the mutated 5 protein underwent improper folding and was subsequently degraded.33 Analysis
of this patient's BM suggested a block at the pro-B to pre-B
transition. In the most recent report, a 2-year-old girl with
agammaglobulinemia was found to have a deletion of exon 3 in the gene
encoding Ig.151 This exon encodes the transmembrane
domain of Ig leading to the prediction that the Ig transcript
made in this patient would encode a truncated protein incapable of
assembling with the pre-BCR. Analysis of this patient further
revealed the complete absence of peripheral blood B cells and a
block at the pro-B to pre-B transition. A non-XLA patient with a block
at the pro-B cell stage and a decrease in Ig, Ig, and
VH-Cu transcripts may represent yet another distinct
mutation in genes essential for B-cell development.152 It
is remarkable that mutations in BTK and genes encoding
components of the pre-BCR can lead to a relatively similar block
in B-cell development at the pro-B to pre-B transition. Figure
4 suggests why this may occur. Expression
of the pre-BCR requires assembly of the µHC, LC, and Ig/Ig
subunits. Any mutation that leads to an absence of one subunit will
block full assembly of the pre-BCR. The physical absence of an intact
pre-BCR will result in a failure of the pre-BI compartment (Figure 2)
to expand. Independently of how the pre-BCR signals, the presence of
the Ig/Ig heterodimer predicts that pre-BCR and BCR signaling
pathways will be highly conserved.31,138 Thus, in XLA
patients, pre-BCR cross-linking would be normal at least to the point
where BTK is translocated to the membrane, but BTK-dependent events
leading to a sustained increase in Ca++ flux would be
greatly decreased or absent (Figure 4).
View larger version (26K):
[in this window]
[in a new window]
| Fig 4.
Components of the pre-BCR and pre-BCR signaling
pathways disrupted in B-lineage immunodeficiencies.
The left side shows the assembly of the structural
components of the pre-BCR: µHC, LC, and the Ig/Ig
heterodimer. For simplicity, only the formation of a Fab is shown. As
discussed in the text, the mechanism of pre-BCR cross-linking is
unknown. By whatever mechanism, pre-BCR cross-linking activates protein
tyrosine kinases (PTKs) such as Lyn, followed by a
complex series of events (see Benschop et al31 and
Rawlings138 for detailed reviews) culminating in initial
activation of PLC-. Concomitant activation of PI-3
kinase leads to production of PI (3,4,5) P3, which recruits BTK to the
membrane where it is phosphorylated by Lyn. BTK then
phosphorylates PLC-, leading to sustained
Ca++ flux and enhancement of growth. The assembly (solid
arrows) or signaling pathways (dashed arrows) disrupted in
antibody-deficiency diseases are shown by an X and a number (1 indicates mutation in Ig that would impair pre-BCR assembly; 2 indicates mutation in LC that would impair pre-BCR assembly; 3 indicates mutation in µHC that would impair pre-BCR assembly; 4 indicates BTK mutation in pleckstrin homology domain that would
compromise binding to PI (3,4,5) P3; and 5 indicates BTK
mutation in catalytic site that would compromise tyrosine
phosphorylation of PCL-).
|
|
| |
B-lineage ALL |
In approximately 75% of pediatric patients with newly diagnosed
ALL, the disease is classified as B-lineage in origin on the basis of
immunoglobulin gene rearrangements and expression of cell surface
markers.153-155 The karyotypic and molecular genetic abnormalities in B-lineage ALL have been extensively
characterized,153-155 and chromosomal translocations giving
rise to distinct fusion genes including TEL-AML1, MLL-AF4 (or
MLL rearrangements with other genes), and E2A-PBX
are present in more than 30% of newly diagnosed pediatric B-lineage
ALL.153 However, the totality of molecular genetic
abnormalities in B-lineage ALL is much greater than these landmark
translocations. Despite this impressive progress, there is still a
deficiency in our understanding of how these many genetic abnormalities
ultimately subvert normal B-cell precursor developmental programs.
Related questions are how these genetic abnormalities tip the survival
scale to apoptotic resistance and whether external cues (ie, cytokines)
play any role in regulating the survival/growth of B-lineage ALL in vivo.
The universal common denominator of pediatric B-lineage ALL is a BM
origin of the disease. However, as discussed by Greaves,156 infant and pediatric ALLs are biologically and clinically distinct diseases. For purposes of this discussion, we will consider both of
them as "B-lineage," even though infant ALL with MLL-AF4
translocations have characteristics of bi-phenotypic B-lineage/myeloid
cells.156 Manifestation of molecular genetic abnormalities
shifts the B-cell precursor developmental program from (1) a process
governed by functional immunoglobulin gene rearrangements and
appropriate homeostatic response to positive and negative growth
regulators to (2) a transformed clone more resistant to apoptosis and
(generally) incapable of undergoing differentiation. The apoptotic
death of normal B-cell precursors probably resembles death by
neglect,157 ie, an apoptotic fate that follows decreased
availability or absence of a continuous survival signal. Neglect might
reflect primarily the fate of a cell that cannot express the pre-BCR
(eg, a cell with 2 nonfunctional µHC rearrangements) and hence does
not receive a tonic (survival) signal that follows pre-BCR expression.
Normal murine and human B-cell precursors express antiapoptotic bcl-2 family members such as bcl-2 and bcl-x,27,158-160 but are
nonetheless very sensitive to apoptotic stimuli.158,159
Many laboratories have studied B-lineage ALL for expression of bcl-2
family members in an attempt to determine whether expression can be
correlated with the clinical or biological characteristics of the
disease.161-166 The results of these studies are quite
variable, and no simple conclusion can be drawn regarding bcl-2 family
member expression and clinical outcome. Subcellular distribution
(particularly in mitochondrial membranes) and
homodimerization/heterodimerization characteristics of bcl-2 family
members are crucial in determining apoptotic sensitivity in many
eukaryotic cells.167-169 It is therefore interesting that a
recent study suggested that mitochondrial levels of bcl-2 may portend
the sensitivity of leukemic cells to apoptosis.164
A fascinating relationship between a molecular genetic abnormality and
apoptotic resistance in B-lineage ALL is the E2A-HLF translocation. The
E2A-HLF fusion gene occurs as a consequence of the
t(17;19)(q23;p13) in some cases of pro-B ALL.170,171 The E2A-HLF fusion protein contains the transactivation domains of the
transcription factor E2A tethered to the basic leucine zipper DNA-binding domain of the transcription factor HLF. Inaba and colleagues demonstrated that a dominant-negative form of E2A-HLF induced apoptosis in a human pro-B ALL cell line harboring the E2A-HLF
translocation, and transfection of a murine IL-3-dependent pro-B cell
line with E2A-HLF reversed apoptosis that normally occurred
following IL-3 withdrawal.172 These data strongly suggest that E2A-HLF functions by blocking an early step in an apoptotic pathway.172 Reasoning that IL-3 mediates cell survival by
activation of 1 or more transcription factors whose activity can be
substituted by E2A-HLF, the same group went on to show that nuclear
factor regulated by IL-3 (NFIL3) is a target gene of
E2A-HLF.173 Enforced expression of NFIL3 promoted the
IL-3-independent survival of pro-B cells.173 Two recent
studies used representational difference analysis to identify
additional genes regulated by E2A-HLF.174,175 One study
identified Annexin VIII and a novel cDNA designated SRPUL, but neither
protein prevented apoptosis in murine pro-B cells deprived of
IL-3.174 In the second study, E2A-HLF was shown to
up-regulate a zinc-finger transcription factor designated
SLUG.175 Importantly, SLUG was nearly as effective as bcl-2
or bcl-x in preventing apoptosis in IL-3-deprived pro-B
cells.175 Murine models of E2A-HLF mediated oncogenesis
have been developed.176,177 In both studies, E2A-HLF
transgenic mice exhibited thymic hypoplasia and subsequent development
of thymic lymphomas. Although a block in splenic B-cell maturation was
noted in one of the studies,177 leukemias involving
B-lineage progenitors were rare.
A second fusion gene containing E2A that is grudgingly giving up its
function is E2A-PBX1. The E2A-PBX1 fusion gene was originally identified in pre-B ALL blasts harboring the t(1;19)(q23;p13) cytogenetic abnormality by two groups.178,179 The E2A-PBX1
fusion protein contains the N-terminal domain of E2A fused to the
homeodomain of PBX1. This genetic abnormality is specific for pre-B ALL
expressing cytoplasmic µHC and is present in approximately 25% of
newly diagnosed pre-B ALL (reviewed in
Hunger180).Transgenic mice expressing the E2A-PBX1
fusion gene develop thymic lymphomas and myeloid leukemias, but not
B-lineage malignancies.181,182 Surprisingly, BM B-lineage
cells are reduced to 20% of normal values in E2A-PBX1 transgenic mice,
suggesting that the fusion protein increases the sensitivity of these
cells to apoptosis.181 Representational difference analysis
was used to isolate a novel WNT gene, designated WNT-16, as an
activating target of E2A-PBX1.184 WNT-16 is a member of the
vertebrate WNT family, which includes more than 20 genes encoding
cysteine-rich secreted proteins that mediate cell-cell interactions.183 WNT-16 mRNA is expressed in
E2A-PBX1+ pre-B ALL but not a variety of
E2A-PBX1 B-lineage malignancies.184
Furthermore, Frizzled genes that encode receptors
for WNT family members are expressed in B-lineage ALL, including those
expressing E2A-PBX1. These data implicate WNT-16 as one component in a
survival/growth pathway that is operative in pre-B ALL harboring the
E2A-PBX1 fusion gene.184
The earliest stages of clonal expansion in B-lineage ALL (ie, the
subclinical phase of the disease wherein the progeny of a single clone
begin to expand) may be characterized by a dependency on BM stromal
cells for survival and growth. This would be a stage in the natural
history of the disease in which the BM microenvironment is completely
intact and lymphohematopoiesis is unperturbed. How long this BM stromal
cell dependency might be retained is unknown. Acquisition of sequential
genetic changes may portend the emergence of a dominant subclone with a
decreased, or complete absence of, a requirement for BM stromal
cell-derived survival/growth factors. By the time a patient is
diagnosed with B-lineage ALL and the marrow is filled with leukemic
blasts, a physical displacement of normal lymphohematopoiesis and BM
architecture will have occurred. Indeed, physical
disruption/displacement of the BM stromal cell microenvironment is more
frequently seen in ALL than in AML or CML.185 It is likely
that a dominant B-lineage ALL subclone would be BM stromal
cell-independent at this stage.
In addition to the subversion of apoptotic programs by genetic changes
in B-lineage ALL, are there external cues that could regulate
survival/growth? Several laboratories have examined the effect of
recombinant cytokines on the growth of B-lineage ALL using short-term
in vitro assays. Sporadic responsiveness to IL-3, IL-7, and flt3-ligand
was observed.186-195 However, no single cytokine has been
demonstrated to exert a consistent proliferative effect on a
significant percentage of cases. Furthermore, the response to these
cytokines (ie, the degree of proliferation) is generally weak. A
potentially more rational approach to identifying growth factors is to
assume that BM stromal cells produce the collective array of
survival/growth factors essential for clonal expansion of B-lineage
ALL. This assumes that adhesive interactions exist to bring the
leukemic clone into apposition with BM stromal cell surfaces and the
surrounding extracellular matrix. Similarly to their normal
counterparts,107-109 B-lineage ALL cells generally adhere to BM stromal cells through VLA-4/VCAM-1
interactions.109,196-198 Using a fluorescent bead adhesion
assay that facilitated flow cytometric analysis of integrin
expression/function, Geijtenbeek and colleagues reported that leukemic
cells from 17 of 20 B-lineage ALL BM specimens exhibited defects in
expression or activation of LFA-1 and VLA-4.199 The
biological significance of their results is uncertain. On the one hand,
weaker or reduced adhesion of leukemic cells to BM stromal cells could
lead to more rapid egress into the peripheral blood. On the other hand,
interaction of leukemic cells with BM stromal cells generally inhibits
apoptosis (see below), indicating that adherence could play an
important role in the survival/growth of B-lineage ALL.
Adherence of B-lineage ALL cells to BM stromal cells could be followed
by a more complex, energy-dependent interaction, characterized by
migration of the leukemic cells underneath BM stromal cells. Interestingly, migration (at least in vitro) is
VCAM-1-independent.196,198 The biological significance of
in vitro migration is unclear, but may reflect a chemotactic
response by the leukemic cells to BM stromal cells. The CXCR4 chemokine
receptor and its SDF-1 ligand may be involved in leukemic cell
migration since at least some B-lineage ALLs undergo chemotaxis in
response to SDF-1.102,103 SDF-1 may also promote the
survival of B-lineage ALL.200
Campana's laboratory has extensively examined the capacity of
nontransformed human BM stromal cells to inhibit the apoptotic fate of
freshly isolated B-lineage ALL. They initially showed that allogeneic
BM stromal cells support survival or inhibit apoptosis of the majority
of B-lineage ALLs tested, although survival of a minority of B-lineage
ALL was unaffected.201 They went on to demonstrate that
direct contact with BM stromal cells was necessary for optimal survival
of normal B-cell precursors and some (but not all) B-lineage
ALLs.202 Heterogeneity in BM stromal cell contact
requirements for B-lineage ALL survival/growth was also reported by
other investigators.203,204 The survival of B-lineage ALL
on allogeneic BM stromal cells also correlates with prognosis. The
probability of 4-year event-free survival was greater among patients
whose leukemic cells exhibited reduced survival on BM stromal cells,
compared with patients whose leukemic cells exhibited elevated survival
on BM stromal cells.205 A very recent report from
Campana's group provided strong evidence that hyperdiploidy (51 to 65 chromosomes) in B-lineage ALL showed a significant correlation with
reduced capacity of the leukemic cells to survive on BM stromal cells.206 This is a strong endorsement for the utility of
this biological assay in predicting clinical outcome and likely
reflecting the in vivo apoptotic sensitivity of this subcategory of
B-lineage ALL.
Many B-lineage ALL cell lines have been established, but the vast
majority (if not all) require only supplementation of tissue culture
medium with fetal bovine serum for optimal growth.207 My
own laboratory has established a panel of human B-lineage ALL cell
lines that retain a dependency on human BM stromal cells for long-term
survival and growth. Using the same human BM stromal cell culture
employed for studies of normal B-cell precursors,26,81 we
established a cell line designated BLIN-2 (B-lineage 2).208 BLIN-2 cells express the pre-BCR, have a dic(9;20) chromosomal abnormality and a bi-allelic deletion of the
p16INK4a and p14ARF genes.
BLIN-2 has an absolute dependence on human BM stromal cells for
survival and growth, and direct contact is necessary for optimal
growth. Removal of BLIN-2 from BM stromal cells results in membrane
blebbing and apoptotic body formation in 72 hours. Using a variety of
assays to characterize apoptotic fate, we have recently shown that
BLIN-2 cell death has caspase-dependent and caspase-independent
features.209 Although the identity of the BM stromal cell
molecules that are essential for growth of BLIN-2 are unknown, heparan
sulfate proteoglycans may play at least a partial role.210
We have also produced 2 additional cell lines, designated BLIN-3 and
BLIN-4, that have overlapping but unique growth factor requirements
compared with BLIN-2.210 BLIN-3 requires human BM stromal
cells supplemented with exogenous IL-7 for optimal growth, survives but
does not proliferate in the presence of BM stromal cells alone, and
undergoes apoptosis in the absence of BM stromal cells.210
BLIN-4 grows on BM stromal cells and undergoes apoptosis in their
absence. However, growth of BLIN-4 can be supported by a cooperative
stimulus of exogenous IL-7 plus flt3-ligand in the absence of BM
stromal cells.210 The BLIN cell lines represent a composite
of growth-factor requirements that may mirror the physiologic
dependency of normal and leukemic B-cell precursors on the BM microenvironment.
| |
Conclusion |
The general blueprint for mammalian B-cell development has been
determined, and the investigative fine-tuning has begun. A number of
questions regarding human B-cell development remain unanswered. For
example, how does a B-lineage cell develop from a multilineage
progenitor (eg, a CLP in Figure 1), and how is B-lineage commitment
defined in molecular terms? Transcription factors are obviously the
key. One of the great accomplishments in hematology during the nineties
was the isolation and characterization of transcription factors that
regulate the development of murine lymphohematopoietic lineages (for
recent reviews, see Glimcher et al211 and Engel et
al212). A stunning recent discovery directly implicated the
paired box transcription factor PAX5 in murine B-lineage
commitment.213,214 The major message from these 2 studies is that PAX5-deficient murine pro-B cells (ie, B-lineage cells that
have undergone DJH but not VDJH rearrangements)
harbor the capacity to differentiate into a constellation of other
lineagesincluding macrophages, osteoclasts, dendritic cells,
granulocytes, NK cells, and thymocytes.213,214 This
surprising result was used to propose that PAX5 plays an essential role
in fostering B-lineage commitment by suppressing the expression of
genes that (directly or indirectly) promote development of non-B
lineage cells. It is reasonable to assume that human B-lineage
commitment and development are governed by similar transcription
factors, but is there experimental evidence? Answers may be
forthcoming. Jaleco and colleagues have very recently described a strategy that represents the first success in elucidating the role of transcription factors in human B-cell
development. They constructed a retroviral vector encoding green
fluorescent protein (GFP) and the dominant negative helix loop helix
protein Id3.215 Human fetal liver HSCs were then infected
with this vector and plated on murine or human stromal cells, and GFP
expression was used to trace the effect of overexpression of Id3 on
B-cell development. The results indicated that Id3 overexpression
blocked B-cell development at a stage prior to expression of the IL-7 receptor.
Another issue that requires resolution is the identity of the molecule
(or molecules) produced in the BM microenvironment that are essential
for the survival/proliferation of human B-cell precursors. I propose
that stromal cell-derived molecules potentially bound to HSPGs (Figure
3) are reasonable candidates. Time will tell if these molecules turn
out to be previously cloned cytokines/chemokines. These putative
cytokines/chemokines could also play an important role in the
survival/proliferation of at least some B-lineage ALL. The
intracellular signaling pathways that affect survival/proliferation in
normal and leukemic B-lineage cells are not completely understood. Very
recent reports reveal a critical role for the linker protein BLNK in
human216 and murine217,218 B-cell development,
although the absence of BLNK function may result in a more severe
phenotype in humans than mice. Thus, additional efforts will lead to
the discovery of new components, or novel functions for known
components, in signaling pathways essential for the proliferation and
differentiation of B-cell precursors. The identity of the essential
survival/proliferation factor is linked to a related question: what is
the mechanism of cell death that ensues in a B-cell precursor that does
not receive a survival/proliferation signal (eg, in a pre-BI cell that
fails to express the pre-BCR)? Which caspase pathways are involved? Are
these pathways subverted in B-lineage ALL and accentuated in XLA?
Finally, "genome prospecting,"219 using DNA
microarray technology with all its analytical power and bio-informatic
challenges, has burst onto the scene. Golub and colleagues used
DNA microarrays to evaluate gene expression in human
acute leukemias, included B-lineage ALL.220 Their results
indicate that microarray-based quantitation of gene expression (1)
confirms well-known leukemia classifications, (2) provides a new tool
for diagnosis, and (3) generates a staggering amount of new information
of unknown significance (ie, quantitative expression of approximately
6800 human genes). Once this technology is applied to normal B-cell
precursors, we will witness the beginning of a complete fingerprint of
comparative gene expression. This database will provide an
investigative substrate for the next millenium, taking us deeper into
regulation of cell fate/function in normal and abnormal human B-cell development.
| |
Acknowledgments |
Mary Ellen Conley (St. Jude Children's Research Hospital) and Les
Silberstein (Harvard Medical School) kindly provided preprints of their
work. I thank Ted Bertrand for helpful comments on the manuscript and
Sandi Sherman for word-processing support.
| |
Footnotes |
Submitted November 30, 1999; accepted February 2, 2000.
Supported by grants R01 CA31685 and R01 CA76055 from the
National Cancer Institute, National Institutes of Health, Bethesda, MD.
Reprints: Tucker W. LeBien, University of Minnesota
Cancer Center, 420 Delaware St SE, Box 806 Mayo, University of Minnesota, Minneapolis, MN 55455; e-mail: lebie001{at}tc.umn.edu.
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.
| |
References |
1.
Gathings WE, Lawton AR, Cooper MD.
Immunofluorescent studies of the development of pre-B cells, B lymphocytes and immunoglobulin isotype diversity in humans.
Eur J Immunol.
1977;7:804-810[Medline]
[Order article via Infotrieve].
2.
Solvason N, Kearney JF.
The human fetal omentum: a site of B cell generation.
J Exp Med.
1992;175:397-404[Abstract/Free Full Text].
3.
Nuñez C, Nishimoto N, Gartland GL, et al.
B cells are generated throughout life in humans.
J Immunol.
1996;156:866-872[Abstract].
4.
Brashem CJ, Kersey JH, Bollum FJ, LeBien TW.
Ontogenic studies of lymphoid progenitor cells in human bone marrow.
Exp Hematol.
1982;10:886-892[Medline]
[Order article via Infotrieve].
5.
Jamieson BD, Douek DC, Killian S, et al.
Generation of functional thymocytes in the human adult.
Immunity.
1999;10:569-575[Medline]
[Order article via Infotrieve].
6.
Jennings CD, Foon KA.
Recent advances in flow cytometry: application to the diagnosis of hematologic malignancy.
Blood.
1997;90:2863-2892[Free Full Text].
7.
Galy A, Travis M, Cen D, Chen B.
Human T, B, natural killer, and dendritic cells arise from a common bone marrow progenitor cell subset.
Immunity.
1995;3:459-473[Medline]
[Order article via Infotrieve].
8.
Ryan DH, Nuccie BL, Ritterman I, Liesveld JL, Abboud CN, Insel RA.
Expression of interleukin-7 receptor by lineage-negative human bone marrow progenitors with enhanced lymphoid proliferative potential and B-lineage differentiation capacity.
Blood.
1997;89:929-940[Abstract/Free Full Text].
9.
Ishii T, Nishihara M, Ma F, et al.
Expression of stromal cell-derived factor-1/pre-B cell growth-stimulating factor receptor, CXC chemokine receptor 4, on CD34+ human bone marrow cells is a phenotypic alteration for committed lymphoid progenitors.
J Immunol.
1999;163:3612-3620[Abstract/Free Full Text].
10.
Kondo M, Weissman IL, Akashi K.
Identification of clonogenic common lymphoid progenitors in mouse bone marrow.
Cell.
1997;91:661-672[Medline]
[Order article via Infotrieve].
11.
Bertrand FE III, Billips LG, Burrows PD, Gartland GL, Kubagawa H, Schroeder HW Jr.
Ig DH gene segment transcription and rearrangement before surface expression of the pan-B-cell marker CD19 in normal human bone marrow.
Blood.
1997;90:736-744[Abstract/Free Full Text].
12.
Davi F, Faili A, Gritti C, et al.
Early onset of immunoglobulin heavy chain gene rearrangements in normal human bone marrow CD34+ cells.
Blood.
1997;90:4014-4021[Abstract/Free Full Text].
13.
Dworzak MN, Fritsch G, Fröschl G, Printz D, Gadner H.
Four-color flow cytometric investigation of terminal deoxynucleotidyl transferase-positive lymphoid precursors in pediatric bone marrow: CD79a expression precedes CD19 in early B-cell ontogeny.
Blood.
1998;92:3203-3209[Abstract/Free Full Text].
14.
Wang Y-H, Nomura J, Faye-Petersen OM, Cooper MD.
Surrogate light chain production during B cell differentiation: differential intracellular versus cell surface expression.
J Immunol.
1998;161:1132-1139[Abstract/Free Full Text].
15.
Spits H, Blom B, Jaleco AC, et al.
Early stages in the development of human T, natural killer and thymic dendritic cells.
Immunol Rev.
1998;165:75-86[Medline]
[Order article via Infotrieve].
16.
Akashi K, Traver D, Kondo M, Weissman IL.
Lymphoid development from hematopoietic stem cells.
Int J Hematol.
1999;69:217-226[Medline]
[Order article via Infotrieve].
17.
Pallard C, Stegmann APA, van Kleffens T, Smart F, Venkitaraman A, Spits H.
Distinct roles of the phosphatidylinositol 3-kinase and STAT5 pathways in IL-7-mediated development of human thymocyte precursors.
Immunity.
1999;10:525-535[Medline]
[Order article via Infotrieve].
18.
Osmond DG, Rolink A, Melchers F.
Murine B lymphopoiesis: towards a unified model.
Immunol Today.
1998;19:65-80[Medline]
[Order article via Infotrieve].
19.
Hardy RR, Carmack CE, Shinton SA, Kemp JD, Hayakawa K.
Resolution and characterization of pro-B and pre-pro-B cell stages in normal mouse bone marrow.
J Exp Med.
1991;173:1213-1225[Abstract/Free Full Text].
20.
Li YS, Wasserman R, Hayakawa K, Hardy RR.
Identification of the earliest B-lineage stage in mouse bone marrow.
Immunity.
1996;5:527-535[Medline]
[Order article via Infotrieve].
21.
Payne KJ, Medina KL, Kincade PW.
Loss of c-kit accompanies B-lineage commitment and acquisition of CD45R by most murine B-lymphocyte precursors.
Blood.
1999;94:713-725[Abstract/Free Full Text].
22.
Loken MR, Shah VO, Dattilio KL, Civin CI.
Flow cytometric analysis of human bone marrow, II: normal B lymphocyte development.
Blood.
1987;70:1316-1324[Abstract/Free Full Text].
23.
LeBien TW, Wormann B, Villablanca JG, et al.
Multiparameter flow cytometric analysis of human fetal bone marrow B cells.
Leukemia.
1990;4:354-358[Medline]
[Order article via Infotrieve].
24.
Ghia P, ten Boekel E, Sanz E, de la Hera A, Rolink A, Melchers F.
Ordering of human bone marrow B lymphocyte precursors by single-cell polymerase chain reaction analyses of the rearrangement status of the immunoglobulin H and L chain gene loci.
J Exp Med.
1997;184:2217-2229[Abstract/Free Full Text].
25.
Lemmers B, Gauthier L, Guelpa-Fonlupt V, Fougereau M, Schiff C.
The human (L+µ) proB complex: cell surface expression and biochemical structure of a putative transducing receptor.
Blood.
1999;93:4336-4346[Abstract/Free Full Text].
26.
Dittel BN, LeBien TW.
The growth response to IL-7 during normal human B cell ontogeny is restricted to B-lineage cells expressing CD34.
J Immunol.
1995;154:58-67[Abstract].
27.
Li YS, Hayakawa K, Hardy RR.
The regulated expression of B lineage associated genes during B cell differentiation in bone marrow and fetal liver.
J Exp Med.
1993;178:951-960[Abstract/Free Full Text].
28.
Pauza ME, Rehmann JA, LeBien TW.
Unusual patterns of immunoglobulin gene rearrangement and expression during human B cell ontogeny: human B cells can simultaneously express cell surface kappa and lambda light chains.
J Exp Med.
1993;178:139-149[Abstract/Free Full Text].
29.
Ghia P, Gratwohl A, Signer E, Winkler TH, Melchers F, Rolink AG.
Immature B cells from human and mouse bone marrow can change their surface light chain expression.
Eur J Immunol.
1995;25:3108-3114[Medline]
[Order article via Infotrieve].
30.
Giachino C, Padovan E, Lanzavecchia A.
Kappa+lambda+ dual receptor B cells arepresent in the human peripheral repertoire.
J Exp Med.
1995;181:1245-1250[Abstract/Free Full Text].
31.
Benschop RJ, Cambier JC.
B cell development: signal transduction by antigen receptors and their surrogates.
Curr Opin Immunol.
1999;11:143-151[Medline]
[Order article via Infotrieve].
32.
Melchers F, Karasuyama H, Haasner D, et al.
The surrogate light chain in B-cell development.
Immunol Today.
1993;14:60-68[Medline]
[Order article via Infotrieve].
33.
Minegishi Y, Coustan-Smith E, Wang Y-H, Cooper MD, Campana D, Conley ME.
Mutations in the human 5/14.1 gene result in B cell deficiency and agammaglobulinemia.
J Exp Med.
1998;187:71-77[Abstract/Free Full Text].
34.
Lassoued K, Nunez CA, Billips L, et al.
Expression of surrogate light chain receptors is restricted to a late stage in pre-B cell differentiation.
Cell.
1993;73:73-86[Medline]
[Order article via Infotrieve].
35.
Sanz E, de la Hera A.
A novel anti-Vpre-B antibody identifies immunoglobulin-surrogate receptors on the surface of human pro-B cells.
J Exp Med.
1996;183:2693-2698[Abstract/Free Full Text].
36.
Meffre E, Fougereau M, Argenson JN, Aubaniac JM, Schiff C.
Cell surface expression of surrogate light chain (LC) in the absence of µ on human pro-B cell lines and normal pro-B cells.
Eur J Immunol.
1996;26:2172-2180[Medline]
[Order article via Infotrieve].
37.
Wang Y-H, Nomura J, Faye-Petersen OM, Cooper MD.
Surrogate light chain production during B cell differentiation: differential intracellular versus cell surface expression.
J Immunol.
1998;161:1132-1139.
38.
Tsuganezawa K, Kiyokawa N, Matsuo Y, et al.
Flow cytometric diagnosis of the cell lineage and developmental stage of acute lymphoblastic leukemia by novel monoclonal antibodies specific to human pre-B cell receptor.
Blood.
1998;92:4317-4324[Abstract/Free Full Text].
39.
Gauthier L, Lemmers B, Guelpa-Fonlupt V, Fougereau M, Schiff C.
µ-Surrogate light chain physicochemical interactions of the human preB cell receptor: implications for VH repertoire selection and cell signaling at the preB cell stage.
J Immunol.
1999;162:41-50[Abstract/Free Full Text].
40.
Lassoued K, Illges H, Benlagha K, Cooper MD.
Fate of surrogate light chains in B lineage cells.
J Exp Med.
1996;183:421-429[Abstract/Free Full Text].
41.
Kitamura D, Kudo A, Schaal S, Müller W, Melchers F, Rajewsky K.
A critical role of lambda 5 protein in B cell development.
Cell.
1992;69:823-831[Medline]
[Order article via Infotrieve].
42.
Kubagawa H, Cooper MD, Carroll AJ, Burrows PD.
Light-chain gene expression before heavy-chain rearrangement in pre-B cells transformed by Epstein-Barr virus.
Proc Natl Acad Sci USA.
1989;86:2356-2360[Abstract/Free Full Text].
43.
Novobrantseva TI, Martin VM, Pelanda R, Müller W, Rajewsky K, Ehlich A.
Rearrangement and expression of immunoglobulin light chain genes can precede heavy chain expression during normal B cell development in mice.
J Exp Med.
1999;189:75-88[Abstract/Free Full Text].
44.
ten Boekel E, Melchers F, Rolink AG.
Changes in the VH gene repertoire of developing precursor B lymphocytes in mouse bone marrow mediated by the pre-B cell receptor.
Immunity.
1997;7:357-368[Medline]
[Order article via Infotrieve].
45.
Kline GH, Hartwell L, Beck-Engeser GB, et al.
Pre-B cell receptor-mediated selection of pre-B cells synthesizing functional µ heavy chains.
J Immunol.
1998;161:1608-1618[Abstract/Free Full Text].
46.
Wasserman R, Li YS, Shinton SA, et al.
A novel mechanism for B cell repertoire maturation based on response by B cell precursors to pre-B receptor assembly.
J Exp Med.
1998;187:259-264[Abstract/Free Full Text].
47.
Shiokawa S, Mortari F, Lima JO, et al.
IgM heavy chain complementarity-determining region 3 diversity is constrained by genetic and somatic mechanisms until two months after birth.
J Immunol.
1999;162:6060-6070[Abstract/Free Full Text].
48.
Rao SP, Riggs JM, Friedman DF, Scully MS, LeBien TW, Silberstein LE.
Biased VH gene usage in early lineage human B cells: evidence for preferential Ig gene rearrangement in the absence of selection.
J Immunol.
1999;163:2732-2740[Abstract/Free Full Text].
49.
Shaffer AL, Schlissel MS.
A truncated heavy chain protein relieves the requirement for surrogate light chains in early B cell development.
J Immunol.
1997;159:1265-1275[Abstract].
50.
Pillai S.
The chosen few? Positive selection and the generation of naive B lymphocytes.
Immunity.
1999;10:493-502[Medline]
[Order article via Infotrieve].
51.
Bossy D, Salamero J, Olive D, Fougereau M, Schiff C.
Structure, biosynthesis, and transduction properties of the human µ- L complex: similar behavior of preB and intermediate preB-B cells in transducing ability.
Int Immunol.
1993;5:467-478[Abstract/Free Full Text].
52.
Kuwahara K, Kawai T, Mitsuyoshi S, et al.
Cross-linking of B cell antigen receptor-related structure of pre-B cell lines induces tyrosine phosphorylation of p85 and p110 subunits and activation of phosphatidylinositol 3-kinase.
Int Immunol.
1996;8:1273-1285[Abstract/Free Full Text].
53.
Minegishi Y, Hendershot LM, Conley ME.
Novel mechanisms control the folding and assembly of 5/14.1 and VpreB to produce an intact surrogate light chain.
Proc Natl Acad Sci U S A.
1999;96:3041-3046[Abstract/Free Full Text].
54.
Melchers F.
Fit for life in the immune system? Surrogate L chain tests H chains that test L chains.
Proc Natl Acad Sci U S A.
1999;96:2571-2573[Free Full Text].
55.
Karasuyama H, Rolink A, Melchers F.
A complex of glycoproteins is associated with VpreB/lambda 5 surrogate light chain on the surface of mu heavy chain-negative early precursor B cell lines.
J Exp Med.
1993;178:469-478[Abstract/Free Full Text].
56.
LeBien TW.
B-cell lymphopoiesis in mouse and man.
Curr Opin Immunol.
1998;10:188-195[Medline]
[Order article via Infotrieve].
57.
Nagata K, Nakamura T, Kitamura F, et al.
The Ig/Ig heterodimer on mu-negative proB cells is competent for transducing signals to induce early B cell differentiation.
Immunity.
1997;7:559-570[Medline]
[Order article via Infotrieve].
58.
Gong S, Nussenzweig MC.
Regulation of an early developmental checkpoint in the B cell pathway by Ig.
Science.
1996;272:411-414[Abstract].
59.
Namen AE, Lupton S, Hjerrild K, et al.
Stimulation of B-cell progenitors by cloned murine interleukin-7.
Nature.
1988;333:571-573[Medline]
[Order article via Infotrieve].
60.
Candéias S, Muegge K, Durum SK.
IL-7 receptor and VDJ recombination: trophic versus mechanistic actions.
Immunity.
1997;6:501-508[Medline]
[Order article via Infotrieve].
61.
Kincade PW, Medina K, Smithson G, et al.
Life/death decisions in B lymphocyte precursors. In:
Monroe JG,Rothenberg EV, eds.
Molecular Biology of B-Cell and T-Cell Development. Totowa, NJ: Humana Press; 1998:177-196.
62.
Corcoran AE, Smart FM, Cowling RJ, Crompton T, Owen MJ, Venkitaraman AR.
The interleukin-7 receptor chain transmits distinct signals for proliferation and differentiation during B lymphopoiesis.
EMBO J.
1996;15:1924-1932[Medline]
[Order article via Infotrieve].
63.
Corcoran AE, Riddell A, Krooshoop D, Venkitaraman AR.
Impaired immunoglobulin gene rearrangement in mice lacking the IL-7 receptor.
Nature.
1998;391:904-907[Medline]
[Order article via Infotrieve].
64.
von Freeden-Jeffry U, Vieira P, Lucian LA, McNeil T, Burdach SE, Murray R.
Lymphopenia in interleukin (IL)-7 gene-deleted mice identifies IL-7 as a nonredundant cytokine.
J Exp Med.
1995;181:1519-1526[Abstract/Free Full Text].
65.
Peschon JJ, Morrissey PJ, Grabstein KH, et al.
Early lymphocyte expansion is severely impaired in interleukin-7 receptor-deficient mice.
J Exp Med.
1994;180:1955-1960[Abstract/Free Full Text].
66.
Cao X, Shores EW, Hu-Li J, et al.
Defective lymphoid development in mice lacking expression of the common cytokine receptor chain.
Immunity.
1995;2:223-238[Medline]
[Order article via Infotrieve].
67.
DiSanto JP, Muller W, Guy-Grand D, Fischer A, Rajewsky K.
Lymphoid development in mice with a targeted deletion of the interleukin-2 receptor chain.
Proc Natl Acad Sci U S A.
1995;92:377-381[Abstract/Free Full Text].
68.
Nosaka T, van Deursen JMA, Tripp RA, et al.
Defective lymphoid development in mice lacking Jak3.
Science.
1995;270:800-802[Abstract/Free Full Text].
69.
Thomis DC, Gurniak CB, Tivol E, Sharpe AH, Berg LJ.
Defects in B lymphocyte maturation and T lymphocyte activation in mice lacking Jak3.
Science.
1995;270:794-797[Abstract/Free Full Text].
70.
Friend SL, Hosier S, Nelson A, Foxworthe D, Williams DE, Farr A.
A thymic stromal cell line supports in vitro development of surface IgM+ B cells and produces a novel growth factor affecting B and T lineage cells.
Exp Hematol.
1994;22:321-328[Medline]
[Order article via Infotrieve].
71.
Ray RJ, Furlonger C, Williams DE, Paige CJ.
Characterization of thymic stromal-derived lymphopoietin (TSLP) in murine B cell development in vitro.
Eur J Immunol.
1996;26:10-16[Medline]
[Order article via Infotrieve].
72.
Levin SD, Koelling RM, Friend SL, et al.
Thymic stromal lymphopoietin: a cytokine that promotes the development of IgM+ B cells in vitro and signals via a novel mechanism.
J Immunol.
1999;162:677-683[Abstract/Free Full Text].
73.
Wolf ML, Buckley JA, Goldfarb A, Law C-L, LeBien TW.
Development of a bone marrow culture for maintenance and growth of normal human B cell precursors.
J Immunol.
1991;147:3324-3330[Abstract].
74.
Saeland S, Duvert V, Pandrau D, et al.
Interleukin-7 induces the proliferation of normal human B-cell precursors.
Blood.
1991;78:2229-2238[Abstract/Free Full Text].
75.
Moreau I, Duvert V, Banchereau J, Saeland S.
Culture of human fetal B-cell precursors on bone marrow stroma maintains highly proliferative CD20dim cells.
Blood.
1993;81:1170-1178[Abstract/Free Full Text].
76.
Moreau I, Duvert V, Caux C, et al.
Myofibroblastic stromal cells isolated from human bone marrow induce the proliferation of both early myeloid and B-lymphoid cells.
Blood.
1993;82:2396-2405[Abstract/Free Full Text].
77.
Noguchi M, Yi H, Rosenblatt HM, et al.
Interleukin-2 receptor chain mutation results in X-linked severe combined immunodeficiency in humans.
Cell.
1993;73:147-157[Medline]
[Order article via Infotrieve].
78.
Maachi P, Villa A, Giliani S, et al.
Mutations of Jak-3 gene in patients with autosomal severe combined immune deficiency (SCID).
Nature.
1995;377:65-68[Medline]
[Order article via Infotrieve].
79.
Russell SM, Tayebi N, Nakajima H, et al.
Mutation of Jak3 in a patient with SCID: essential role of Jak3 in lymphoid development.
Science.
1995;270:797-800[Abstract/Free Full Text].
80.
Puel A, Ziegler SF, Buckley RH, Leonard WJ.
Defective IL7R expression in T()B(+)NK(+) severe combined immunodeficiency.
Nature Genet.
1998;20:394-397[Medline]
[Order article via Infotrieve].
81.
Pribyl JAR, LeBien TW.
Interleukin 7 independent development of human B cells.
Proc Natl Acad Sci U S A.
1996;93:10348-10353[Abstract/Free Full Text].
82.
Wolf ML, Weng W-K, Stieglbauer K, Shah N, LeBien TW.
Functional effect of IL-7-enhanced CD19 expression on human B-cell precursors.
J Immunol.
1993;151:138-148[Abstract].
83.
Billips LG, Nunez CA, Bertrand FE III, et al.
Immunoglobulin recombinase gene activity is modulated reciprocally by interleukin 7 and CD19 in B cell progenitors.
J Exp Med.
1995;182:973-982[Abstract/Free Full Text].
84.
Cluitmans FHM, Esendam BHJ, Landegent JE, Willemze R, Falkenburg JH.
Constitutive in vivo cytokine and hematopoietic growth factor gene expression in the bone marrow and peripheral blood of healthy individuals.
Blood.
1995;85:2038-2044[Abstract/Free Full Text].
85.
Ryan DH, Nuccie BL, Ritterman I, Liesveld JL, Abboud CN.
Cytokine regulation of early human lymphopoiesis.
J Immunol.
1994;152:5250-5258[Abstract].
86.
Funk PE, Stephan RP, Witte PL.
Vascular cell adhesion molecule 1-positive reticular cells express interleukin-7 and stem cell factor in the bone marrow.
Blood.
1995;86:2661-2671[Abstract/Free Full Text].
87.
Namikawa R, Muench MO, De Vries JE, Roncarolo MG.
The FLK2/FLT3 ligand synergizes with interleukin-7 in promoting stromal-cell-independent expansion and differentiation of human fetal pro-B cells in vitro.
Blood.
1996;87:1881-1890[Abstract/Free Full Text].
88.
McClanahan T, Culpepper J, Campbell D, et al.
Biochemical and genetic characterization of multiple splice variants of the Flt3 ligand.
Blood.
1996;88:3371-3382[Abstract/Free Full Text].
89.
Lisovsky M, Braun SE, Ge Y, et al.
Flt3-ligand production by human bone marrow stromal cells.
Leukemia.
1996;10:1012-1018[Medline]
[Order article via Infotrieve].
90.
Oritani K, Kincade PW.
Identification of stromal cell products that interact with pre-B cells.
J Cell Biol.
1996;134:771-782[Abstract/Free Full Text].
91.
Oritani K, Kanakura Y, Aoyama K, et al.
Matrix glycoprotein SC1/ECM2 augments B lymphopoiesis.
Blood.
1997;90:3404-3413[Abstract/Free Full Text].
92.
Sage H, Vernon RB, Funk SE, Everitt EA, Angello J.
SPARC, a secreted protein associated with cellular proliferation, inhibits cell spreading in vitro and exhibits Ca2+-dependent binding in the extracellular matrix.
J Cell Biol.
1989;109:341-356[Abstract/Free Full Text].
93.
Raines EW, Lane TF, Iluera-Arispe ML, Ross R, Sage EH.
The extracellular glycoprotein SPARC interacts with platelet-derived growth factor (PDGF)-AB and -BB and inhibits binding of PDGF to its receptors.
Proc Natl Acad Sci U S A.
1992;89:1281-1285[Abstract/Free Full Text].
94.
Girard J-P, Springer TA.
Cloning from purified high endothelial venule cells of hevin, a close relative of the antiadhesive extracellular matrix protein SPARC.
Immunity.
1995;2:113-123[Medline]
[Order article via Infotrieve].
95.
Borghesi LA, Yamashita Y, Kincade PW.
Heparan sulfate proteoglycans mediate interleukin-7-dependent B lymphopoiesis.
Blood.
1999;93:140-148[Abstract/Free Full Text].
96.
Gupta P, McCarthy JB, Verfaillie CM.
Stromal fibroblast heparan sulfate is required for cytokine-mediated ex vivo maintenance of human long-term culture-initiating cells.
Blood.
1996;87:3229-3236[Abstract/Free Full Text].
97.
Nagasawa T, Hirota S, Tachibana K, et al.
Defects in B-cell lymphopoiesis and bone marrow myelopoiesis in mice lacking the CXC chemokine PBSF/SDF-1.
Nature.
1996;383:635-638.
98.
Tachibana K, Hirota S, Lizasa H, et al.
The chemokine receptor CXCR4 is essential for vascularization of the gastrointestinal tract.
Nature.
1998;393:591-594[Medline]
[Order article via Infotrieve].
99.
Ma Q, Jones D, Borghesan PR, et al.
Impaired B-lymphopoiesis, myelopoiesis, and derailed cerebellar neuron migration in CXCR4- and SDF-1-deficient mice.
Proc Natl Acad Sci U S A.
1998;95:9448-9453[Abstract/Free Full Text].
100.
Ma Q, Jones D, Springer TA.
The chemokine receptor CXCR4 is required for the retention of B lineage and granulocytic precursors within the bone marrow microenvironment.
Immunity.
1999;10:463-471[Medline]
[Order article via Infotrieve].
101.
Aiuti A, Tavian M, Cipponi A, et al.
Expression of CXCR4, the receptor for stromal cell-derived factor-1 on fetal and adult human lympho-hematopoietic progenitors.
Eur J Immunol.
1999;29:1823-1831[Medline]
[Order article via Infotrieve].
102.
Fedyk ER, Ryan DH, Ritterman I, Springer TA.
Maturation decreases responsiveness of human bone marrow B lineage cells to stromal-derived factor 1 (SDF-1).
J Leukoc Biol.
1999;66:667-673[Abstract].
103.
Honczarenko M, Douglas RS, Mathias C, Lee B, Ratajczak MZ, Silberstein LE.
SDF-1 responsiveness does not correlate with CXCR4 expression levels of developing human bone marrow B cells.
Blood.
1999;94:2990-2998[Abstract/Free Full Text].
104.
Coulomb-L'Hermin A, Amara A, Schiff C, et al.
Stromal cell-derived factor 1 (SDF-1) and antenatal human B cell lymphopoiesis: expression of SDF-1 by mesothelial cells and biliary ductal plate epithelial cells.
Proc Natl Acad Sci U S A.
1999;96:8585-8590[Abstract/Free Full Text].
105.
Jarvis LJ, LeBien TW.
Cytokine and stromal influences on early B-cell development. In:
Monroe JG,Rothenberg EV, eds.
Molecular Biology of B-Cell and T-Cell Development. Totowa, NJ: Humana Press; 1998:231-251.
106.
Ryan DH, Tang J.
Regulation of human B cell lymphopoiesis by adhesion molecules and cytokines.
Leuk Lymphoma
1995;17:375-389[Medline]
[Order article via Infotrieve].
107.
Ryan DH, Nuccie BL, Abboud CN, Winslow JM.
Vascular cell adhesion molecule-1 and the integrin VLA-4 mediate adhesion of human B-cell precursors to cultured bone marrow adherent cells.
J Clin Invest.
1991;88:995-1004.
108.
Dittel BN, McCarthy JB, Wayner EA, LeBien TW.
Regulation of human B-cell precursor adhesion to bone marrow stromal cells by cytokines that exert opposing effects on the expression of vascular cell adhesion molecule-1 (VCAM-1).
Blood.
1993;81:2272-2282[Abstract/Free Full Text].
109.
Murti KG, Brown PS, Kumagai MA, Campana D.
Molecular interactions between human B-cell progenitors and the bone marrow microenvironment.
Exp Cell Res.
1996;10:47-58.
110.
Jarvis LJ, LeBien TW.
Stimulation of human bone marrow stromal cell tyrosine kinases and IL-6 production by contact with B lymphocytes.
J Immunol.
1995;155:2359-2368[Abstract].
111.
Jarvis LJ, Maguire JE, LeBien TW.
Contact between human bone marrow stromal cells and B lymphocytes enhances very late antigen-4/vascular cell adhesion molecule-1-independent tyrosine phosphorylation of focal adhesion kinase, paxillin, and ERK2 in stromal cells.
Blood.
1997;90:1626-1636[Abstract/Free Full Text].
112.
Rawlings DJ, Quan SG, Kato RM, Witte ON.
Long-term culture system for selective growth of human B cell progenitors.
Proc Natl Acad Sci U S A.
1995;92:1570-1574[Abstract/Free Full Text].
113.
Rawlings DJ, Quan S, Hao Q-L, et al.
Differentiation of human CD34+/CD38 cord blood stem cells into B cell progenitors in vitro.
Exp Hematol.
1997;25:66-72[Medline]
[Order article via Infotrieve].
114.
Kurosaka D, LeBien TW, Pribyl JAR.
Comparative studies of different stromal cell microenvironments in support of human B cell development.
Exp Hematol.
1999;27:1271-1281[Medline]
[Order article via Infotrieve].
115.
Fluckiger A-C, Sanz E, Garcia-Lloret M, et al.
In vitro reconstitution of human B-cell ontogeny: from CD34+ multipotent progenitors to Ig-secreting cells.
Blood.
1998;92:4509-4520[Abstract/Free Full Text].
116.
Berardi AC, Meffre E, Pflumio F, et al.
Individual CD34+CD38lowCD19CD10 progenitor cells from human cord blood generate B lymphocytes and granulocytes.
Blood.
1997;89:3554-3564[Abstract/Free Full Text].
117.
Nishihara M, Wada Y, Ogami K, et al.
A combination of stem cell factor and granulocyte colony-stimulating factor enhances the growth of human progenitor B cells supported by murine stromal cell line MS-5.
Eur J Immunol.
1998;28:855-864[Medline]
[Order article via Infotrieve].
118.
Ohkawara J-I, Ikebuchi K, Fujihara M, et al.
Culture system for extensive production of CD19+IgM+ cells by human cord blood CD34+ progenitors.
Leukemia.
1998;12:764-771[Medline]
[Order article via Infotrieve].
119.
Miller JS, McCullar V, Punzel M, Lemischka IR, Moore KA.
Single adult human CD34(+)/Lin-/CD38() progenitors give rise to natural killer cells, B-lineage cells, dendritic cells, and myeloid cells.
Blood.
1999;93:96-106[Abstract/Free Full Text].
120.
Shultz LD, Schweitzer PA, Christianson SW, et al.
Multiple defects in innate and adaptive immunologic function in NOD/LtSz-scid mice.
J Immunol.
1995;154:180-191[Abstract].
121.
Greiner DL, Hesselton RA, Shultz LD.
SCID mouse models of human stem cell engraftment.
Stem Cells.
1998;16:166-177[Medline]
[Order article via Infotrieve].
122.
Bhatia M, Wang JCY, Kapp U, Bonnet D, Dick JE.
Purification of primitive human hematopoietic cells capable of repopulating immune-deficient mice.
Proc Natl Acad Sci U S A.
1997;94:5320-5325[Abstract/Free Full Text].
123.
Conneally E, Cashman J, Petzer A, Eaves C.
Expansion in vitro of transplantable human cord blood stem cells demonstrated using a quantitative assay of their lympho-myeloid repopulating activity in nonobese diabetic-scid/scid mice.
Proc Natl Acad Sci U S A.
1997;94:9836-9841[Abstract/Free Full Text].
124.
Hogan CJ, Shpall EJ, McNulty O, et al.
Engraftment and development of human CD34(+)-enriched cells from umbilical cord blood in NOD/LtSz-scid/scid mice.
Blood.
1997;90:85-96[Abstract/Free Full Text].
125.
van der Loo JC, Hannenberg H, Cooper RJ, Luo FY, Lazaridis EN, Williams DA.
Nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mouse as a model system to study the engraftment and mobilization of human peripheral blood stem cells.
Blood.
1998;92:2556-2570[Abstract/Free Full Text].
126.
Robin C, Pflumio F, Vainchenker W, Coulombel L.
Identification of lymphomyeloid primitive progenitor cells in fresh human cord blood and in the marrow of nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice transplanted with human CD34(+) cord blood cells.
J Exp Med.
1999;189:1601-1610[Abstract/Free Full Text].
127.
Harigaya K, Handa H.
Generation of functional clonal cell lines from human bone marrow stroma.
Proc Natl Acad Sci U S A.
1985;82:3477-3480[Abstract/Free Full Text].
128.
Roecklein BA, Torok-Storb B.
Functionally distinct human marrow stromal cell lines immortalized by transduction with the human papilloma virus E6/E7 genes.
Blood.
1995;85:997-1005[Abstract/Free Full Text].
129.
Li L, Milner LA, Deng Y, et al.
The human homolog of rat Jagged1 expressed by marrow stroma inhibits differentiation of 32D cells through interaction with Notch1.
Immunity.
1998;8:43-55[Medline]
[Order article via Infotrieve].
130.
Bodnar AG, Ouellette M, Frolkis M, et al.
Extension of life-span by introduction of telomerase into normal cells.
Science.
1998;279:349-352[Abstract/Free Full Text].
131.
Fischer A, Malissen B.
Natural and engineered disorders of lymphocyte development.
Science.
1998;280:237-243[Abstract/Free Full Text].
132.
Rosen FS, Wedgwood RJ, Eibl MM, et al.
Primary immunodeficiency diseases: report of a WHO scientific group.
Clin Exp Immunol.
1997;109(suppl):S1.
133.
Conley ME, Cooper MD.
Genetic basis of abnormal B cell development.
Curr Opin Immunol.
1998;10:399-406[Medline]
[Order article via Infotrieve].
134.
Tsukada S, Saffran DC, Rawlings DJ, et al.
Deficient expression of a B cell cytoplasmic tyrosine kinase in human X-linked agammaglobulinemia.
Cell.
1993;72:279-290[Medline]
[Order article via Infotrieve].
135.
Vetrie D, Vorechovsky I, Sideras P, et al.
The gene involved in X-linked agammaglobulinemia is a member of the src family of protein-tryosine kinases.
Nature.
1993;361:226-233[Medline]
[Order article via Infotrieve].
136.
Conley ME, Mathias D, Treadaway J, Minegishi Y, Rohrer J.
Mutations in btk in patients with presumed X-linked agammaglobulinemia.
Am J Hum Genet.
1998;62:1034-1043[Medline]
[Order article via Infotrieve].
137.
Vihinen M, Brandau O, Branden LJ, et al.
BTKbase, mutation database for X-linked agammaglobulinemia (XLA).
Nucleic Acids Res.
1998;26:242-247[Abstract/Free Full Text].
138.
Rawlings DJ.
Bruton's tyrosine kinase controls a sustained calcium signal essential for B lineage development and function.
Clin Immunol.
1999;91:243-253[Medline]
[Order article via Infotrieve].
139.
Campana D, Farrant J, Inamdar N, Webster AD, Janossy G.
Phenotypic features and proliferative activity of B cell progenitors in X-linked agammaglobulinemia.
J Immunol.
1990;145:1675-1680[Abstract].
140.
Thomas JD, Sideras P, Smith CIE, Vorechovsky I, Chapman V, Paul WE.
Colocalization of X-linked agammaglobulinemia and X-linked immunodeficiency genes.
Science.
1993;261:355-358[Abstract/Free Full Text].
141.
Khan WN, Alt FW, Gerstein RM, et al.
Defective B cell development and function in BTK-deficient mice.
Immunity.
1995;3:283-299[Medline]
[Order article via Infotrieve].
142.
Kerner JD, Appleby MW, Mohr RN, et al.
Impaired expansion of mouse B cell progenitors lacking BTK.
Immunity.
1995;3:301-312[Medline]
[Order article via Infotrieve].
143.
Hendriks RW, de Bruijn MFTR, Maas A, Dingjan GM, Karis A, Grosveld F.
Inactivation of BTK by insertion of lacZ reveals defects in B cell development only past the pre-B cell stage.
EMBO J.
1996;15:4862-4872[Medline]
[Order article via Infotrieve].
144.
de Weers M, Verschuren MCM, Kraakman MEM, et al.
The Bruton's tryosine kinase gene is expressed throughout B cell differentiation, from early precursor B cell stages preceding immunoglobulin gene rearrangement up to mature B cell stages.
Eur J Immunol.
1993;23:3109-3114[Medline]
[Order article via Infotrieve].
145.
Smith CIE, Baskin B, Humire-Greiff P, et al.
Expression of Bruton's agammaglobulinemia tryosine kinase gene, BTK, is selectively downregulated in T lymphocytes and plasma cells.
J Immunol.
1994;152:557-565[Abstract].
146.
Scharenberg AM, El-Hillal O, Fruman DA, et al.
Phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P3)/Tec kinase-dependent calcium signaling pathway: a target for SHIP-mediated inhibitory signals.
EMBO J.
1998;17:1961-1972[Medline]
[Order article via Infotrieve].
147.
Rawlings DJ, Scharenberg AM, Park H, et al.
Activation of BTK by a phosphorylation mechanism initiated by Src family kinases.
Science.
1996;271:822-825[Abstract].
148.
Fluckiger AC, Li Z, Kato RM, et al.
BTK/Tec kinases regulate sustained increases in intracellular Ca2+ following B-cell receptor activation.
EMBO J.
1998;17:1973-1985[Medline]
[Order article via Infotrieve].
149.
Hashimoto S, Iwamatsu A, Ishiai M, et al.
Identification of the SH2 domain binding protein of Bruton's tyrosine kinase as BLNK: functional significance of BTK-SH2 domain in B-cell antigen receptor-coupled calcium signaling.
Blood.
1999;94:2357-2364[Abstract/Free Full Text].
150.
Yel L, Minegishi Y, Coustan-Smith E, et al.
Mutations in the mu heavy-chain gene in patients with agammaglobulinemia.
N Engl J Med.
1996;335:1486-1493[Abstract/Free Full Text].
151.
Minegishi Y, Coustan-Smith E, Rapalus L, Ersoy F, Campana D, Conley ME.
Mutations in Ig (CD79a) result in a complete block in B-cell development.
J Clin Invest.
1999;104:1115-1121[Medline]
[Order article via Infotrieve].
152.
Meffre E, LeDeist F, de Saint-Basile G, et al.
A human non-XLA immunodeficiency disease characterized by blockage of B cell development at an early proB cell stage.
J Clin Invest.
1996;98:1519-1526[Medline]
[Order article via Infotrieve].
153.
Look AT.
Oncogenic transcription factors in the human acute leukemias.
Science.
1997;278:1059-1064[Abstract/Free Full Text].
154.
Pui CH.
Recent advances in the biology and treatment of childhood acute lymphoblastic leukemia.
Curr Opin Hematol.
1998;5:292-301[Medline]
[Order article via Infotrieve].
155.
Kersey JH.
Fifty years of studies of the biology and therapy of childhood leukemia.
Blood.
1997;90:4243-4251[Free Full Text].
156.
Greaves M.
Molecular genetics, natural history and the demise of childhood leukaemia.
Eur J Cancer.
1999;35:173-185.
157.
Raff MC.
Social controls on cell survival and cell death.
Nature.
1992;356:397-400[Medline]
[Order article via Infotrieve].
158.
Campana D, Coustan-Smith E, Manabe A, et al.
Prolonged survival of B-lineage acute lymphoblastic leukemia cells is accompanied by overexpression of bcl-2 protein.
Blood.
1993;81:1025-1031[Abstract/Free Full Text].
159.
Griffiths SD, Goodhead DT, Marsden SJ, et al.
Interleukin 7-dependent B lymphocyte precursor cells are ultrasensitive to apoptosis.
J Exp Med.
1994;179:1789-1797[Abstract/Free Full Text].
160.
Fang W, Mueller DL, Pennell CA, et al.
Frequent aberrant immunoglobulin gene rearrangements in pro-B cells revealed by a bcl-xL transgene.
Immunity.
1996;4:291-299[Medline]
[Order article via Infotrieve].
161.
Coustan-Smith E, Kitanaka A, Pui CH, et al.
Clinical relevance of BCL-2 overexpression in childhood acute lymphoblastic leukemia.
Blood.
1996;87:1140-1146[Abstract/Free Full Text].
162.
Salomons GS, Brady HJ, Verwijs-Janssen M, et al.
The Bax alpha:Bcl-2 ratio modulates the response to dexamethasone in leukaemic cells and is highly variable in childhood acute leukaemia.
Int J Cancer.
1997;71:959-965[Medline]
[Order article via Infotrieve].
163.
Uckun FM, Yang Z, Sather H, et al.
Cellular expression of antiapoptotic BCL-2 oncoprotein in newly diagnosed childhood acute lymphoblastic leukemia: a Children's Cancer Group Study.
Blood.
1997;89:3769-3777[Abstract/Free Full Text].
164.
Jia L, Macey MG, Yin Y, Newland AC, Kelsey SM.
Subcellular distribution and redistribution of Bcl-2 family proteins in human leukemia cells undergoing apoptosis.
Blood.
1999;93:2353-2359[Abstract/Free Full Text].
165.
Campos L, Sabido O, Viallet A, Vasselon C, Guyotat D.
Expression of apoptosis-controlling proteins in acute leukemia cells.
Leuk Lymphoma.
1999;33:499-509[Medline]
[Order article via Infotrieve].
166.
Hogarth LA, Hall AG.
Increased BAX expression is associated with an increased risk of relapse in childhood acute lymphocytic leukemia.
Blood.
1999;93:2671-2678[Abstract/Free Full Text].
167.
Green DR, Reed JC.
Mitochondria and apoptosis.
Science.
1998;281:1309-1312[Abstract/Free Full Text].
168.
Adams JM, Cory S.
The Bcl-2 protein family: arbiters of cell survival.
Science.
1998;281:1322-1326[Abstract/Free Full Text].
169.
Gross A, McDonnell JM, Korsmeyer SJ.
BCL-2 family members and the mitochondria in apoptosis.
Genes Dev.
1999;13:1899-1911[Free Full Text].
170.
Inaba T, Roberts WM, Shapiro LH, et al.
Fusion of the leucine zipper gene HLF to the E2A gene in human acute B-lineage leukemia.
Science.
1992;257:531-534[Abstract/Free Full Text].
171.
Hunger SP, Ohyashiki K, Toyama K, Cleary ML.
Hlf, a novel hepatic bZIP protein, shows altered DNA-binding properties following fusion to E2A in t(17;19) acute lymphoblastic leukemia.
Genes Dev.
1992;6:1608-1620[Abstract/Free Full Text].
172.
Inaba T, Inukai T, Yoshihara T, et al.
Reversal of apoptosis by the leukaemia-associated E2A-HLF chimaeric transcription factor.
Nature.
1996;382:541-544[Medline]
[Order article via Infotrieve].
173.
Ikushima S, Inukai T, Inaba T, Nimer SD, Cleveland JL, Look AT.
Pivotal role for the NFIL3/E4BP4 transcription factor in interleukin 3-mediated survival of pro-B lymphocytes.
Proc Natl Acad Sci U S A.
1997;94:2609-2614[Abstract/Free Full Text].
174.
Kurosawa H, Goi K, Inukai T, et al.
Two candidate downstream target genes for E2A-HLF.
Blood.
1999;93:321-332[Abstract/Free Full Text].
175.
Inukai T, Inoue A, Kurosawa H, et al.
SLUG, a ces-1-related zinc finger transcription factor gene with antiapoptotic activity, is a downstream target of the E2A-HLF oncoprotein.
Mol Cell.
1999;4:343-352[Medline]
[Order article via Infotrieve].
176.
Honda H, Inaba T, Suzuki T, et al.
Expression of E2A-HLF chimeric protein induced T-cell apoptosis, B-cell maturation arrest, and development of acute lymphoblastic leukemia.
Blood.
1999;93:2780-2790[Abstract/Free Full Text].
177.
Smith KS, Whan Rhee J, Naumovski L, Cleary ML.
Disrupted differentiation and oncogenic transformation of lymphoid progenitors in E2A-HLF transgenic mice.
Mol Cell Biol.
1999;19:4443-4451[Abstract/Free Full Text].
178.
Nourse J, Mellentin JD, Galili N, et al.
Chromosomal translocation t(1;19) results in synthesis of a homeobox fusion mRNA that codes for a potential chimeric transcription factor.
Cell.
1990;60:535-545[Medline]
[Order article via Infotrieve].
179.
Kamps MP, Murre C, Sun XH, Baltimore D.
A new homeobox gene contributes the DNA binding domain of the t(1;19) translocation protein in pre-B ALL.
Cell.
1990;60:547-555[Medline]
[Order article via Infotrieve].
180.
Hunger SP.
Chromosomal translocations involving the E2A gene in acute lymphoblastic leukemia: clinical features and molecular pathogenesis.
Blood.
1996;87:1211-1224[Free Full Text].
181.
Dedera DA, Waller EK, LeBrun DP, et al.
Chimeric homeobox gene E2A-PBX1 induces proliferation, apoptosis, and malignant lymphomas in transgenic mice.
Cell.
1993;74:833-843[Medline]
[Order article via Infotrieve].
182.
Kamps MP, Baltimore D.
E2A-Pbx1, the t(1;19) translocation protein of human pre-B cell acute lymphocytic leukemia, causes acute myeloid leukemia in mice.
Mol Cell Biol.
1993;13:351-357[Abstract/Free Full Text].
183.
Cadigan KM, Nusse R.
Wnt signaling: a common theme in animal development.
Genes Dev.
1997;11:3286-3305[Free Full Text].
184.
McWhirter JR, Neuteboom ST, Wancewicz EV, Monia BP, Downing JR, Murre C.
Oncogenic homeodomain transcription factor E2A-Pbx1 activates a novel WNT gene in pre-B acute lymphoblastoid leukemia.
Proc Natl Acad Sci U S A.
1999;96:11464-11469[Abstract/Free Full Text].
185.
Dilly SA, Jagger CJ.
Bone marrow stromal cell changes in hematological malignancies.
J Clin Pathol.
1990;43:942-946[Abstract/Free Full Text].
186.
Wormann B, Gesner TG, Mufson RA, LeBien TW.
Proliferative effect of interleukin-3 on normal and leukemic human B cell precursors.
Leukemia.
1989;3:399-404[Medline]
[Order article via Infotrieve].
187.
Uckun FM, Gesner TG, Song CW, Myers DE, Mufson A.
Leukemic B-cell precursors express functional receptors for human interleukin-3.
Blood.
1989;73:533-542[Abstract/Free Full Text].
188.
Touw I, Groot-Loonen J, Broeders L, et al.
Recombinant hematopoietic growth factors fail to induce a proliferative response in precursor B acute lymphoblastic leukemia.
Leukemia.
1989;3:356-362[Medline]
[Order article via Infotrieve].
189.
Touw I, Pouwels K, van Agthoven T, et al.
Interleukin-7 is a growth factor of precursor B and T acute lymphoblastic leukemia.
Blood.
1990;75:2097-2101[Abstract/Free Full Text].
190.
Eder M, Ottmann OG, Hansen-Hagge TE, et al.
Effects of recombinant human IL-7 on blast cell proliferation in acute lymphoblastic leukemia.
Leukemia.
1990;4:533-540[Medline]
[Order article via Infotrieve].
191.
Skjonsberg C, Erikstein BK, Smeland EB, et al.
Interleukin-7 differentiates a subgroup of acute lymphoblastic leukemias.
Blood.
1991;77:2445-2450[Abstract/Free Full Text].
192.
Makrynikola V, Kabral A, Bradstock KF.
Effects of recombinant human cytokines on precursor-B acute lymphoblastic leukemia cells.
Exp Hematol.
1991;19:674-679[Medline]
[Order article via Infotrieve].
193.
Mirro Jr J, Hurwitz CA, Behm FG, et al.
Effects of recombinant human hematopoietic growth factors on leukemic blasts from children with acute myeloblastic or lymphoblastic leukemia.
Leukemia.
1993;7:1026-1033[Medline]
[Order article via Infotrieve].
194.
Eder M, Hemmati P, Kalina U, et al.
Effects of Flt3 ligand and interleukin-7 on in vitro growth of acute lymphoblastic leukemia cells.
Exp Hematol.
1996;24:371-377[Medline]
[Order article via Infotrieve].
195.
Pontvert-Delucq S, Hibner U, Vilmer E, et al.
Heterogeneity of B lineage acute lymphoblastic leukemias (B-ALL) with regard to their in vitro spontaneous proliferation, growth factor response and BCL-2 expression.
Leuk Lymphoma.
1996;21:267-280[Medline]
[Order article via Infotrieve].
196.
Tang J, Scott G, Ryan DH.
Subpopulations of bone marrow fibroblasts support VLA-4-mediated migration of B-cell precursors.
Blood.
1993;82:3415-3423[Abstract/Free Full Text].
197.
Bradstock K, Makrynikola V, Bianchi A, Byth K.
Analysis of the mechanism of adhesion of precursor-B acute lymphoblastic leukemia cells to bone marrow fibroblasts.
Blood.
1993;82:3437-3444[Abstract/Free Full Text].
198.
Makrynikola V, Bianchi A, Bradstock K, Gottlieb D, Hewson J.
Migration of acute lymphoblastic leukemia cells into human bone marrow stroma.
Leukemia.
1994;8:1734-1743[Medline]
[Order article via Infotrieve].
199.
Geijtenbeek TB, van Kooyk Y, van Vliet SJ, Renes MH, Raymakers RA, Figdor CG.
High frequency of adhesion defects in B-lineage acute lymphoblastic leukemia.
Blood.
1999;94:754-764[Abstract/Free Full Text].
200.
Nishii K, Katayama N, Miwa H, et al.
Survival of human B-cell precursors is supported by stromal cells and cytokines: association with the expression of bcl-2 protein.
Br J Haematol.
1999;105:701-710[Medline]
[Order article via Infotrieve].
201.
Manabe A, Coustan-Smith E, Behm FG, Raimondi SC, Campana D.
Bone marrow-derived stromal cells prevent apoptotic cell death in B-lineage acute lymphoblastic leukemia.
Blood.
1992;79:2370-2377[Abstract/Free Full Text].
202.
Manabe A, Murti KG, Coustan-Smith E, et al.
Adhesion-dependent survival of normal and leukemic human B lymphoblasts on bone marrow stromal cells.
Blood.
1994;83:758-766[Abstract/Free Full Text].
203.
Ashley DM, Bol SJ, Kannourakis G.
Human bone marrow stromal cell contact and soluble factors have different effects on the survival and proliferation of paediatric B-lineage acute lymphoblastic leukaemic blasts.
Leuk Res.
1994;18:337-346[Medline]
[Order article via Infotrieve].
204.
Bradstock K, Bianchi A, Makrynikola V, Filshie R, Gottlieb D.
Long-term survival and proliferation of precursor-B acute lymphoblastic leukemia cells on human bone marrow stroma.
Leukemia.
1996;10:813-820[Medline]
[Order article via Infotrieve].
205.
Kumagai M, Manabe A, Pui C-H, et al.
Stroma-supported culture of childhood B-lineage acute lymphoblastic leukemia cells predicts treatment outcome.
J Clin Invest.
1996;97:755-760[Medline]
[Order article via Infotrieve].
206.
Ito C, Kumagai M, Manabe A, et al.
Hyperdiploid acute lymphoblastic leukemia with 51-65 chromosomes: a distinct biological entity with a marked propensity to undergo apoptosis.
Blood.
1999;93:315-320[Abstract/Free Full Text].
207.
Matsuo Y, Drexler HG.
Establishment and characterization of human B cell precursor-leukemia cell lines.
Leuk Res.
1998;22:567-579[Medline]
[Order article via Infotrieve].
208.
Shah N, Oseth LL, LeBien TW.
Development of a model for evaluating the interaction between human pre-B acute lymphoblastic leukemic cells and the bone marrow stromal cell microenvironment.
Blood.
1998;92:3817-3828[Abstract/Free Full Text].
209. Lysholm AS, Shah N, LeBien TW. Characterization of apoptotic pathways
induced following bone marrow stromal cell-deprivation of the human
pre-B ALL cell line BLIN-2. In preparation.
210. Shah N, Oseth LL, Hirsch BA, LeBien TW. Analysis of the bone
marrow stromal cell dependency of novel human B-lineage ALL cell lines.
In preparation.
211.
Glimcher LH, Singh H.
Transcription factors in lymphocyte development: T and B cells get together.
Cell.
1999;96:13-23[Medline]
[Order article via Infotrieve].
212.
Engel I, Murre C.
Transcription factors in hematopoiesis.
Curr Opin Genet Dev.
1999;9:575-579[Medline]
[Order article via Infotrieve].
213.
Rolink AG, Nutt SL, Melchers F, Busslinger M.
Long-term in vivo reconstitution of T-cell development by Pax5-deficient B-cell progenitors.
Nature.
1999;401:603-606[Medline]
[Order article via Infotrieve].
214.
Nutt SL, Heavey B, Rolink AG, Busslinger M.
Commitment to the B-lymphoid lineage depends on the transcription factor Pax5.
Nature.
1999;401:556-562[Medline]
[Order article via Infotrieve].
215.
Jaleco AC, Stegmann AP, Heemskerk MH, et al.
Genetic modification of human B-cell development: B-cell development is inhibited by the dominant negative helix loop helix factor Id3.
Blood.
1999;94:2637-2646[Abstract/Free Full Text].
216.
Minegishi Y, Rohrer J, Coustan-Smith E, et al.
An essential role for BLNK in human B cell development.
Science.
1999;286:1954-1957[Abstract/Free Full Text].
217.
Pappu R, Cheng AM, Li B, et al.
Requirement for B cell linker protein (BLNK) in B cell development.
Science.
1999;286:1949-1954[Abstract/Free Full Text].
218.
Jumaa H, Wollscheid B, Mitterer M, Wienands J, Reth M, Nielsen PJ.
Abnormal development and function of B lymphocytes in mice deficient for the signaling adaptor protein SLP-65.
Immunity.
1999;11:547-554[Medline]
[Order article via Infotrieve].
219.
Marshall E.
Do-it-yourself gene watching.
Science.
1999;286:444-447[Free Full Text].
220.
Golub TR, Slonim DK, Tamayo P, et al.
Molecular classification of cancer: class discovery and class prediction by gene expression monitoring.
Science.
1999;286:531-537[Abstract/Free Full Text].
Top
Abstract
Introduction
