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Blood, Vol. 94 No. 9 (November 1), 1999:
pp. 3048-3054
Shwachman-Diamond Syndrome: An Inherited Preleukemic Bone Marrow
Failure Disorder With Aberrant Hematopoietic Progenitors and Faulty
Marrow Microenvironment
By
Yigal Dror and
Melvin H. Freedman
From the Division of Hematology and Oncology and the Research
Institute, The Hospital for Sick Children, and the University of
Toronto, Toronto, Ontario, Canada.
 |
ABSTRACT |
Shwachman-Diamond syndrome (SD), an inherited disorder with varying
cytopenias and a marked tendency for malignant myeloid transformation,
is an important model for understanding genetic determinants in
hematopoiesis. To define the basis for the faulty hematopoietic
function, 13 patients with SD (2 of whom had myelodysplasia with a
clonal cytogenetic abnormality) and 11 healthy marrow donors were
studied. Patients with SD had significantly lower numbers of
CD34+ cells on bone marrow aspirates. SD
CD34+ cells plated directly in standard clonogenic assays
showed markedly impaired colony production potential, underscoring an
intrinsically aberrant progenitor population. To assess marrow stromal
function, long-term marrow stromal cell cultures (LTCs) were
established. Normal marrow CD34+ cells were plated over
either SD stroma (N/SD) or normal stroma (N/N); SD CD34+
cells were plated over either SD stroma (SD/SD) or normal stroma (SD/N). Nonadherent cells harvested weekly from N/SD LTCs were strikingly reduced compared with N/N LTCs; numbers of
granulocyte-monocyte colony-forming units (CFU-GM) derived from N/SD
nonadherent cells were also lower. SD/N showed improved production of
nonadherent cells and CFU-GM colonies compared with SD/SD, but much
less than N/N. Stem-cell and stromal properties from the 2 patients
with SD and myelodysplasia did not differ discernibly from SD patients without myelodysplasia. We conclude that in addition to a stem-cell defect, patients with SD have also a serious, generalized marrow dysfunction with an abnormal bone marrow stroma in terms of its ability
to support and maintain hematopoiesis. This dual defect exists in SD
with and without myelodysplasia.
© 1999 by The American Society of Hematology.
| |
INTRODUCTION |
SHWACHMAN-DIAMOND SYNDROME (SD) is a
multisystem autosomal-recessive disorder characterized by exocrine
pancreatic dysfunction, bony metaphyseal dysostosis, and varying
degrees of marrow dysfunction with cytopenias.1-3 In
addition, myelodysplastic syndrome (MDS) and acute myeloid leukemia
(AML) have been recognized as major complications in this disease and
occur in up to one third of patients.2,3 The genetic defect
and molecular basis for SD that predispose patients to bone marrow
failure and malignant myeloid transformation are not known.
Reduced numbers of bone marrow progenitors, eg, granulocyte-monocyte
colony-forming units (CFU-GM) and erythrocyte burst-forming units
(BFU-E) have been demonstrated in most patients, compatible with a
defective stem-cell origin for the marrow failure in SD.4-6 In these published studies from about 25 years ago, the proliferative capacity and frequency of committed myeloid progenitors varied widely,
as did peripheral blood cell counts. Production of
"colony-stimulating activity" from patients' peripheral
leukocytes appeared normal when tested on normal marrow
progenitors.4 Since these original observations were
published, understanding of the hematopoietic defects in this disorder
has not progressed further.
The bone marrow microenvironment has a central role in supporting,
maintaining, and regulating hematopoiesis by providing compartmentalization and production of soluble regulatory messages in
"stem-cell niches" to which CD34+ cells are
anchored.7,8 A defective microenvironment as assessed by
long-term bone marrow cultures (LTCs) has been suggested as a cause for
certain cases of acquired aplastic anemia9,10 and for adult
patients with MDS.11
Marrow stomal function has never been studied in SD. Since this
disorder is an inherited bone marrow failure syndrome with a wide range
of hematologic abnormalities, it is clearly an important model for
understanding genetic determinants in hematopoiesis and in
developmental biology. Further, the link between SD and MDS/AML
underscores an important association between heredity and
leukemogenesis. For these reasons, we characterized progenitor cell/marrow stromal cell function in SD to define the basis for the
flawed hematopoiesis.
| |
MATERIALS AND METHODS |
Patient population and clinical diagnosis.
Patients were included if they fulfilled the diagnostic criteria from
our institution.12 Accordingly, 13 patients were included in this study, conducted from February 1997 to February 1998 inclusively. Clinical characteristics of the patients are summarized in
Table 1. No patient was
transfusion-dependent. One patient (no. 13) received treatment with
granulocyte-colony stimulating factor (G-CSF) because of severe
neutropenia and infection. No patient had been previously diagnosed
with MDS or AML; however, during the study, MDS was unmasked in 2 patients (no. 1 and no. 2, Table 1). Both had marrow cytogenetic
abnormalities of clonal i(7q); one of them also had clonal del(20q) and
dysplastic changes of the myeloid series. Clinical aspects of
these 2 patients have been previously reported.13,14
Consent was obtained from the patients or their parents for the study.
Bone marrow samples were also obtained from hematologically healthy
donors during the harvest for bone marrow transplant. Informed, written
consent was obtained in all cases.
Bone marrow samples.
Patients underwent bone marrow aspiration and biopsy under conscious
sedation with intravenous propafol and local infiltration with
lidocaine. Bone marrow aspirates were collected from the posterior
superior iliac crest into  -medium containing 10 U of preservative-free heparin per milliliter, layered over percoll, and
centrifuged at 2,000 rpm for 10 minutes. Light-density mononuclear cells were collected and washed twice in Iscove's medium. Mononuclear cells were either plated directly for LTC or underwent
CD34+ fractionation and were cryopreserved.
CD34+ cell fractionation.
CD34+ cells were separated by the Mini-MACS immunomagnetic
separation system (Miltenyi Biotec, Auburn, CA) as previously
described15 with few modifications. Post-percoll
mononuclear cells were washed in cold buffer containing
phosphate-buffered saline (PBS) with 0.5% bovine serum albumin,
treated with biotinylated anti-CD34 antibodies, and incubated on ice
for 15 minutes. Cells were then washed, treated with Streptavidin
Microbeads (Miltenyi Biotec), incubated for 15 minutes, washed again,
and applied to a magnetic column. Columns were then removed from the
magnetic fields and the CD34+ cells eluted with a plunger.
To reach a purification of approximately 98%, cells were passed
through a second magnetic column. The collected cells were then
cryopreserved in liquid nitrogen until used.
Percentage of CD34+ cells in marrow cell samples.
Freshly obtained 3-mL aliquots of bone marrow aspirates were layered
over Ficoll and centrifuged at 1,600 rpm for 25 minutes. Light-density
cell layer was collected and washed in PBS/bovine serum albumin 0.5%.
Cells (1 × 105) were incubated with either
fluorescein-isothiocyanate (FITC)-conjugated anti-CD34+
antibody or IgG1-FITC isotype control (both from Immunex, Seattle, WA),
and then resuspended in PBS with paraformaldehyde 0.5%; cells were
immediately analyzed by a Coulter Epics XL-MCL flow cytometer (Coulter, Hialeah, FL). A minimum of 12,000 events was
collected. Events that fell outside the negative staining regions
identified by the isotype control sample were considered
CD34+ cells.
Standard short-term colony assays from CD34+
cells.
Standard short-term colony assays of CD34+ cells were
performed as previously described15 with few modifications.
CD34+ cells were plated in duplicate at a cell density of
1.8 × 103 cells per 0.6 mL well (of a 24-well plate)
in 0.8% methylcellulose (Fluka, Buchs, Switzerland), 20% normal human
plasma, 10-5 mol/L 2-mercaptoethanol (Sigma, St Louis,
MO), 40 U/mL interleukin-3 (Immunex), 10 ng/mL G-CSF (Amgen, Thousand
Oaks, CA), 50 ng/mL mast cell growth factor (Immunex), and 2 U/mL
erythropoietin (Ortho Biologics, Manati, PR). Cultures were incubated
at 37°C in a humidified atmosphere (5% CO2 and air).
Colonies of 50 cells or more were scored after 14 days under an
inverted microscope as CFU-GM, BFU-E, or mixed colony-forming units
(CFU-mix).
For megakaryocyte CFU (CFU-Meg) colony assays, 0.2 × 105 CD34+ cells were placed in 0.2-mL duplicate
cultures (in a 24-well plate) containing 0.8% methylcellulose, 20%
normal human plasma, 50 ng/mL mast cell growth factor (Immunex), and 50 ng/mL megakaryocyte growth and development factor (Amgen). Colonies of
at least 3 mature megakaryocytes were scored after 14 days.
Long-term cell cultures.
Stromal layers from 10 patients and 11 normal subjects were established
as previously described16 by plating 2 × 106 post-percoll bone marrow mononuclear cells in 2 mL LTC
medium (Myelocult; Stem Cell Technologies, Vancouver, Canada),
containing -medium with 12.5% fetal calf serum, 12.5% horse serum,
0.1 mmol/L 2-mercaptoethanol, 0.016 mmol/L folic acid, 2.0 mmol/L
glutamine, 0.16 mmol/L inositol, and 10-5 mol/L
hydrocortisone. LTCs were placed in a humidified 37°C incubator with a maintained atmosphere of 5% CO2 in air for 3 to 5 days, then transferred to a 33°C incubator with the same
atmosphere. Stromal layers were grown for 4 to 5 weeks, with weekly
feeding using one-half medium replacement.
Support of hematopoiesis was then assessed by crossover experiments
performed by plating 2 × 105 patient or control
CD34+ cells over patient or control LTCs after irradiation
(15 Gy) of the stroma. Four combinations of experiments were performed: normal CD34+ cells on normal stroma (N/N, n = 11); normal
CD34+ cells on SD stroma (N/SD, n = 10); SD
CD34+ cells on normal stroma (SD/N, n = 4); and SD
CD34+ cells on SD stroma (SD/SD, n = 4). Five of the 11 sets of control experiments (N/N) were allogeneic combinations, whereby
normal CD34+ cells from 1 donor source were plated over a
control stromal layer from a different donor. Similarly, 2 of the 4 SD/SD experiments were allogeneic combinations in which patient
CD34+ cells were plated on a different patient's stromal
layer. All other control and patient combinations were autologous.
For morphologic evaluation of LTC, 10-week-old LTCs were trypsinized
and prepared in paraffin blocks for histochemical stains for
endothelial cells (von Willebrand's factor), monocytic elements (CD68), and fibroblast markers (vimentin). Fat cell clusters were counted directly under an inverted microscope and expressed as numbers
of clusters per 2 × 106 marrow mononuclear cells
plated initially in the LTC.
LTC nonadherent cell numbers and secondary short-term colony assays.
After CD34+ cells were layered over stromal layers,
hematopoiesis was assessed weekly. Nonadherent cells (6 × 103) harvested by weekly half-medium replacement of LTCs
were plated in 0.6-mL secondary short-term cultures, and assayed for
CFU-GM, BFU-E, and CFU-mix colony formation as described for short-term cultures from CD34+ cells. LTC-initiating cell studies by
limiting dilution analysis are very difficult from SD hypocellular bone
marrows because of the paucity of hematopoietic stem cells, so we
elected to measure the production of CFU-GM from the nonadherent
layer.9,17 With this method we did not assess the
clonogenic potential of stem cells embedded in the stromal layers;
however, we did assess the ability of stroma to support hematopoiesis
over 10 weeks of the experiments without the need to sacrifice the LTC
after 5 weeks.9
Effect of supernatants from LTCs of normal controls and patients on
clonogenic assays of normal CD34+ cells.
Stromal layers from 2 controls and 2 SD patients were established as
described. However, after stromal irradiation, CD34+ cells
were not plated over the stromal layers. Instead, on days 1, 7, and 14 after irradiation, supernatant was replaced with fresh medium. The
supernatant collected on day 14 after irradiation was stored at
 80°C until tested.
Control CD34+ samples (n = 2) were plated (3 × 103 cells/mL) in duplicate cultures containing
0.8% methylcellulose (Fluka), 30% fetal calf serum,
10 5 mol/L 2-mercaptoethanol (Sigma), 40 U/mL
interleukin-3 (Immunex), 10 ng/mL G-CSF (Amgen), 50 ng/mL mast cell
growth factor (Immunex), and 2 U/mL erythropoietin (Ortho Biologics),
and varied concentrations (0%, 7.5%, and 15%) of filtered-thawed
LTC-supernatant from controls or patients. Cultures were incubated at
37°C in a humidified atmosphere (5% CO2 and air).
CFU-GM colonies containing 50 cells or more were scored after 14 days
under an inverted microscope.
Statistics.
Using mean numbers of nonadherent cells harvested weekly from the LTCs,
colony numbers in short-term cultures, and marrow CD34+
cells, Student's t test was used to determine significance of differences between patients and controls. P values less than .05 were considered significant.
| |
RESULTS |
Percentage of CD34+ cells in marrow cell samples.
The percentage of CD34+ cells in marrow from 8 SD patients
(mean ± SEM, 1.8% ± 0.5%) was significantly lower
(P < .01) than the percentage from 10 normal controls (4.4% ± 0.5%). Ages of patients (mean ± SEM, 13 ± 2 years) and
controls (13 ± 4 years) were comparable (P =
.97).
Short-term colony assays from CD34+ cells.
Results of clonogenic assays are shown in Fig
1. Mean values of CFU-GM, CFU-mix, and
CFU-Meg colonies were reduced compared with normal controls (P < .05). Mean BFU-E colony numbers were also reduced (26 v
52), but the difference was not statistically significant (P = .14).
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| Fig 1.
Numbers of colonies in duplicate short-term
cultures from CD34+ cells of patients with SD or healthy
controls (mean ± SEM).
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Stroma formation and morphologic evaluation.
There was no difference between patients and controls in the length of
time needed or ability to produce a confluent stromal layer. All
patient and control samples achieved at least 75% confluent stromal
layers within 4 weeks. There was also no difference between LTCs from
four SD patients and from 2 controls with regard to immunostaining with
von Willebrand's factor for presence of endothelial cells, CD68 for
monocytic cells, or vimentin for fibroblasts. However, fat cell cluster
numbers in LTCs from 11 SD patients (mean ± SEM, 693 ± 542 per
2 × 106 marrow mononuclear cells) were significantly
lower (P < .01) than for 9 controls (3,185 ± 773 per 2 × 106 marrow mononuclear cells; Fig
2A and B). The only patient with relatively
high numbers of fat cell clusters (6,094 per 2 × 106
marrow mononuclear cells) was patient no. 13, who received G-CSF treatment for neutropenia.
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| Fig 2.
Stromal layers from long-term cultures of (A) a normal
control showing an abundance of clusters, and (B) a patient with SD,
showing the characteristic paucity of fat cell clusters.
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Nonadherent cell numbers generated from LTCs and secondary short-term
colony assays from the nonadherent cells.
When the 4 sets of experimental combinations of CD34+ cells
on stromal cells were compared, numbers of total nonadherent cells harvested from N/SD LTCs from week 2 onwards were lower than those from
N/N LTCs (Fig 3). The difference was
statistically significant between weeks 4 to 6 (P < .05),
when LTC-initiating cells are best assessed.16 Means of
CFU-GM colony numbers (Fig 4) in short-term cultures derived from nonadherent cells harvested from N/SD LTCs were
lower than those from N/N LTCs, although the difference was not
statistically significant (P = .07 to .08 between weeks 4 to
6).
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| Fig 3.
Nonadherent cell numbers harvested weekly from long-term
cultures (means ± SEM). Normal CD34+ cells from
healthy controls were plated over stroma of either SD patients (N/SD)
or normal donors (N/N); SD CD34+ cells were plated over
either SD (SD/SD) or normal (SD/N) stroma.
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| Fig 4.
CFU-GM numbers derived from long-term culture nonadherent
cells, plated weekly in short-term clonogenic assays (means ± SEM).
Normal CD34+ cells from healthy controls were plated over
stroma of either SD patients (N/SD) or normal donors (N/N); SD
CD34+ cells were plated over either SD (SD/SD) or normal
(SD/N) stroma.
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Plating CD34+ cells from SD patients over stromal layers
from controls augmented nonadherent numbers and colony formation, but
not to the same values obtained when normal CD34+ cells
were plated on normal stromas, thereby confirming a colony-producing progenitor defect in SD marrow (Figs 3 and 4). The combination of SD
CD34+ cells on SD stroma showed a profoundly impaired
hematopoietic interaction in which marrow function was almost totally
absent (Figs 3 and 4).
No statistical differences in the nonadherent cell numbers and in the
secondary CFU-GM colony numbers were observed when allogeneic and
autologous control experiments (N/N) were compared, in keeping with
previous reports.18 Also, plating patient
CD34+cells on stromal layer from a different patient in the
allogeneic SD/SD experimental combination did not correct the
profoundly impaired hematopoiesis seen with the 2 autologous SD/SD combinations.
Effect of supernatants from LTCs of controls and patients on
clonogenic assays of normal CD34+ cells.
Three experimental conditions were performed for controls (n = 2) and
for patients (n = 2), whereby varied concentrations of supernatant from
their LTCs were plated with control allogeneic CD34+ cells
(n = 2) in short-term clonogenic assays. With control LTC-supernatants, there was a stepwise increment in CFU-GM colonies by adding increasing concentrations from 0% to 15% (from mean colony numbers in duplicate cultures of 83 to 124, and 138 to 182, respectively, per 3 × 103 normal CD34+ cells plated). With patient
LTC-supernatants, no substantial change in the number of CFU-GM
colonies was observed (from mean colony numbers of 83 to 93, and 138 to
139, respectively, per 3 × 103 normal
CD34+ cells plated).
Patients with and without MDS.
By comparing colony formation in clonogenic assays of CD34+
cells, no difference was noted between the 2 patients with MDS and
those without; CFU-GM colony numbers were 0 and 26 per 1.8 × 103 CD34+ cells, respectively, compared with a
range of 0 to 72 (mean, 24) in patients without MDS. Also, both
patients with MDS had abnormal stroma, but which were
indistinguishable from SD patients without MDS. For example,
nonadherent cell numbers recovered at week 6 after plating 2 × 105 normal CD34+ cells on stromal layers from
both SD patients with MDS were 0 and 0.16 × 105,
respectively, compared with a range of 0 to 0.85 × 105 (mean, 0.16) in SD patients without MDS. Similarly,
numbers of CFU-GM colonies in secondary short-term cultures derived
from 6 × 103 nonadherent cells generated from the MDS
patient stroma were 0 and 8, respectively, as compared with a range of
0 to 8 (mean, 1.6) from stromal studies of SD patients without MDS.
Patient no. 13 differed from the other SD patients somewhat; the marrow
stromal LTC showed normal numbers of fat clusters. Also, nonadherent
cell numbers recovered at week 6 after plating 2 × 105 normal CD34+ cells on this patient's
stromal layers were at the lower range of controls (0.09 × 105; controls' mean, 1.40 × 105; range,
0.03 to 3.89 × 105). However, no CFU-GM colony growth
was observed from these nonadherent cells in secondary short-term
cultures (controls' mean, 12; range, 1 to 27). Further, the CFU-GM,
BFU-E, CFU-mix, and CFU-Meg colony numbers in direct short-term
cultures were also low: 5, 16, 1, and 24, respectively, per 1.8 × 103 fresh CD34+ cells.
| |
DISCUSSION |
Our goal for the studies described here was to characterize the marrow
dysfunction in SD. As a classic example of an inherited bone marrow
failure disorder with a predisposition to MDS/AML, SD is pivotal for
understanding the role of genetic factors in hematopoiesis. Once the SD
gene is identified and cloned, definition of the marrow cellular
abnormalities in this condition will be a prerequisite for
demonstrating that transfected SD cDNA, when it becomes available, has
a corrective effect on faulty hematopoiesis.
Until now, almost all information about bone marrow function in SD came
from studies performed between 1979 and 1982 using light-density marrow
mononuclear cells.4-6 These investigators demonstrated, in
clonogenic assays, that granulocytic and erythroid progenitors were
either numerically deficient in marrow or had impaired proliferative
properties in most, but not all, patients. Additionally, in one
study,4 there were no serum inhibitors against
"CFU-C" progenitors nor against "colony-stimulating
activity" when tested on control or on autologous marrow; coculture
of SD patients' peripheral blood lymphocytes with control marrow did not inhibit CFU-C colony growth either.
We used these published data as the entry point for our current study.
Using contemporary technology, we have discovered new and important
information about SD bone marrow dysfunction. First, we worked with a
fairly homogeneous population of marrow cells, which were
subfractionated into CD34+ elements. The CD34 antigen
identifies cell populations that are enriched for pluripotent and
lineage-restricted hematopoietic progenitors in vitro, some of which
are capable of marrow reconstitution in vivo.19-21
Second, we used long-term bone marrow cultures in our study because LTC
is the most physiologic in vitro system to study interactions of
hematopoietic progenitors and the hematopoietic microenvironment. The
microenvironment has a central role in regulating hematopoiesis because
it orchestrates the interaction between adhesion-mediated cellular
events and the production and compartmentalization of soluble
regulatory messages.7,8,22-24 Because of this, one hypothesis at the start of the study was that the microenvironment was
involved in the pathogenesis of the SD marrow disorder.
The first SD abnormality was evident on quantitation of
CD34+ cells in marrows from patients with SD and in
clonogenic assays of CD34+ cells. In SD marrows we found
lower numbers of CD34+ cells compared with normal controls.
In addition, a qualitative defect was identified: on plating freshly
obtained primary samples that were subfractionated into
CD34+ cells, we demonstrated reduced potential for SD
samples to generate colonies of all lineages compared with controls.
This finding substantiates the results obtained from 1979 to
19824-6 and underscores the intrinsically aberrant behavior
of SD hematopoietic progenitors.
The second abnormal finding was a faulty marrow microenvironment. This
observation, which has not been previously reported, points to a more
generalized marrow disorder than was formerly suspected. In our study,
we assessed stromal support of hematopoiesis by first counting the
nonadherent cells that were generated weekly, and also by looking at
the clonogenic potential of these nonadherent cells in short-term
clonogenic assays. Differences between patients and controls were
obvious. The numbers of nonadherent cells harvested from N/SD LTCs from
these cells in short-term cultures were clearly lower than the numbers
obtained from the N/N LTCs. The production of CFU-GM colonies from the
nonadherent cells in secondary clonogenic assays proved the existence
of hematopoietic progenitors in the nonadherent cell population.
Although CFU-GM colony numbers from N/SD nonadherent cells were lower
than those from N/N nonadherent cells, the difference was not
statistically significant. This is probably because in both N/SD and
N/N experimental combinations the nonadherent cells were derived from
normal CD34+ cells (only the stromal layers were
different), and since they were plated in equal numbers in the
secondary short term cultures. As expected, SD
CD34+ cells plated over normal stroma (SD/N) showed
impaired generation of nonadherent cells and deficient colony formation
from these cells, consistent with intrinsically flawed progenitors.
SD/SD illustrated a profoundly impaired hematopoietic interaction,
whereby marrow function in vitro was almost totally absent. Of note, we discerned no differences in results between SD patients without MDS and
the 2 SD patients with MDS.
To determine the basis for the stromal defect, LTCs from SD patients
were evaluated morphologically. The production of fat cell clusters was
markedly reduced in all patients except 1 compared with that of
controls. Lack of this nutrient source might be a contributing factor
for the reduced ability of stroma to support hematopoiesis in vitro.
However, it is difficult to reconcile this with the relatively high fat
component in hypocellular bone marrow specimens from patients with SD.
Alternatively, it can be merely a morphologic marker in vitro for the
abnormal stroma. The latter explanation is more likely since the
quantitatively normal fat cell clusters in patient no. 13 were not
sufficient to improve stromal function to the level of controls.
Interestingly, patient no. 13 had a relatively high number of fat cell
clusters while being administered G-CSF treatment. This might be
explained because G-CSF, which stimulates various cell types and early
progenitors,25,26 also has a stimulatory effect on stem
cells that are committed to develop into adipocytes. Compared with
controls, no difference in the timeline or in ability to form a
confluent stromal layer could be demonstrated. Neither were any
differences noticed in the potential of bone marrow precursors to form
fibroblastoid, endothelial, or monocytic components, as assessed by 3 different cellular markers.
Cytokine production by peripheral leukocytes from SD patients was shown
to be adequate as measured by "colony-stimulating activity" on
normal marrow progenitors,4 and no serum inhibitors of
myelopoiesis could be demonstrated.4 However, this does not
exclude impaired cytokine production by the bone marrow
microenvironment, since paracrine production of cytokines from marrow
stromal cells might be more important in hematopoietic stem-cell
production. In the current study, adding supernatants from LTCs of SD
patients to clonogenic assays of normal CD34+ cells did not
suppress colony production, but did not augment colony growth, either.
This suggests that the impaired stromal function observed is not
related to inhibitory factors, but more likely, to a deficiency of one
or more stroma-derived stimulatory factors. In contrast, adding
supernatants from LTCs of normal subjects to clonogenic assays of
normal CD34+ cells resulted in increased production of
CFU-GM colonies, which is consistent with the normal, physiologic role
of the marrow microenvironment in supporting hematopoiesis.
Bone marrow stroma is not only a source of hematopoietic growth
factors, it also produces the adhesive matrices required for docking of
hematopoietic progenitors and compartmentalization of soluble growth
factors.7,8,22-24 The basis for stromal impairment in SD
can be related to either reduced production of essential cytokines (eg,
stem-cell factor and stromal-derived factor-1), abnormal provision of
extracellular matrix (eg, collagen and glycosaminoglycans), or abnormal
expression of antigens required for adhesive interactions between
hematopoietic progenitors and stromal cells (eg,
 1-integrins).
Although each of these components can be studied separately, we
assessed SD bone marrow stroma by examining its functional capacity as
an integral unit of various cell types. This represents a more
physiologic in vitro assay overall. However, further studies are now
necessary to identify if a specific or an individual abnormal cellular
component can account for the abnormalities that we observed. The
problem may involve either cells such as fibroblasts, endothelial cells, adipocytes, or mesenchymal progenitor cells, or can originate with an unknown element. As suggested by Aiuti et al,27
stromal cell clones differ in their capacity to preserve
CD34+/CD38, or to allow their
differentiation into CD34+/CD38+, suggesting
that distinct elements of the bone marrow stroma control growth and
differentiation of hematopoietic stem cells and progenitors.
A stromal cell defect has been previously reported in some cases of
acquired aplastic anemia.9,10 However, this is the first
report of a consistent stromal defect in an inherited syndrome of bone
marrow failure. Furthermore, Tennant et al11 have recently reported for the first time a stromal cell defect in adult patients with MDS. The presence of such a defect in SD may provide an important link with the preleukemic nature of this syndrome, particularly since
the same abnormality was noticed in the SD patients with or without
MDS. In addition, the poor outcome of patients with SD after bone
marrow transplantation for severe aplastic anemia, MDS, or acute
myeloblastic leukemia28-34 can be explained by the presence
of such a stromal defect, which is not corrected by the bone marrow
transplantation, and might be further aggravated by the conditioning regimen.
| |
ACKNOWLEDGMENT |
We thank our friends and colleagues in the Severe Chronic Neutropenia
International Registry for their valuable input; Rebecca Herman and
Wilma Vanek for technical assistance; and Lynda Ellis, RN, Peter Durie,
MD, and Richard Axtell, MD, for collaboration in patient-related
matters. This report was prepared with the assistance of Editorial
Services, The Hospital for Sick Children, Toronto, Canada.
| |
FOOTNOTES |
Submitted February 11, 1999; accepted June 25, 1999.
Supported in part by grants from the Audey Stanley Memorial Leukemia
Research Fund, Shwachman Syndrome Support Canada, Aplastic Anemia
Association of Canada, and The Severe Chronic Neutropenia International Registry.
The publication costs of this
article were defrayed in part by
page charge payment. This article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. section
1734 solely to indicate this fact.
Address reprint requests to Yigal Dror, MD, Department of
Pediatric Hematogy/Oncology, Chaim Sheba Medical Center, Tel-Hashomer
52621, Israel.
| |
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