Supplemental Methods.
Acquisition of samples from normal human donors
The CD34+ cells from bone marrows (BMCD34+, N = 10), CD34+ cells from
peripheral blood stem cell products (PBCD34+, N = 11), and naïve T-cells form
peripheral blood (T-cells, N = 44) were either obtained from volunteer donors at
the Fred Hutchinson Cancer Research Center (FHCRC), Adult Changes In
Thought Cohort from Group Health Cooperative (Seattle, WA),1 or purchased
from commercially available vendors (Cambrex, Rutherford, NJ or AllCells,
Emeryville, CA). Donors with a history of previous radiation, chemotherapy, or
hematologic malignancies were excluded. In the case of the BMCD34+ and
PBCD34+ samples, donors of all ages were included in order to obtain adequate
sample numbers for analyses. For the T-cells samples, there was a larger pool
of potential donors, and thus, two populations were selected: younger (age ≤ 30)
and older (age  70) adults. All samples were obtained under Institutional
Review Board (IRB) approved protocols according to the Declaration of Helsinki.
The demographics and age of each donor is provided in Supplement 2.
Anti-CD34 immunomagnetic beads CD34+ cells (Miltenyi Biotec, Auburn, CA)
were used to select highly purified populations of CD34+ cells as previously
described.2,3 Percentage of viable CD34+ cells was determined to be  88%
(range 88% – 98%). The percent of viable CD34 cells for the BMCD34+ and
PBCD34+ did not significantly correlate with age (R = 0.35, p = 0.35 and R =
0.22, p = 0.55, respectively). Some of PBCD34+ samples with adequate material
were further purified into a highly enriched population of PBCD34+/38- cells by
flow-cytometric sorting.4 Naïve T-cells were selected from fresh peripheral blood
samples following mononuclear cell separation with Hypague-Ficoll via dual
negative selection with a CD4+ T-cell Isolation Kit II (No. 130-091-155, Miltenyi
Biotec Inc., Auburn CA) and CD45 RO+ Microbeads (No. 130-046-001, Miltenyi
Biotec Inc.) as per manufacturer’s recommendations (www.miltenyibiotec.com).
The naïve T-cells underwent expansion using Dynabeads CD3/CD28 T-cell
expander beads (No. 111.31, Invitrogen, Carlsbad, CA) as per manufacturer’s
recommendations (www.invitrogen.com) and as previously described.5 The
purity of naïve T-cells prior to expansion was  90%. The mean number of days
of T-cell expansion (MDE) prior to harvest and RNA extraction was 8.9 days.
There were no significant difference in the MDE between the samples from the
younger and older subjects (T-cells in microarray studies, young 9.3 MDE older
10.00 MDE, p = 0.30 and T-cells in Q-RT/PCR studies, young 8.0 MDEs. older
8.4 MDE, p = 1.00).
RNA extraction and hybridization to microarrays
RNA was extracted from CD34+ cells and T-cells using TRIzol reagent
(Invitrogen), and RNA quality was analyzed on a HP 2100 Bioanalyzer (Agilent
Technologies, Palo Alto, CA).6,7 RNA was not pooled, treating each sample as
an independent variable. Five micrograms of total RNA from BMCD34+ and Tcells was prepared for microarrays using a Enzo BioArrayTM High YieldTM RNA
Transcript Labeling Kit (Enzo Life Technologies, Farmingdale, NY) according to
the Eukaryotic Target Labeling protocol as described in GeneChipTM Expression
Analyses Technical Manual (Affymetrix, Santa Clara, CA).
7,8
For the
PBCD34+/38- arrays, the single-stranded linear amplification protocol was used
to amplify 100 nanograms of total RNA, which then biotin-labeled using Enzo
BioArrayTM High YieldTM RNA Transcript Labeling Kit (Enzo Life Technologies).7
A total of 15 µg of biotin-labeled, fragmented target was hybridized to HG-U133A
arrays (Affymetrix).7,8
Microarrays and analyses of human hematopoietic blood cells
DAT files were generated with GCOS 1.2.1 software (Affymetrix). Target
signals were scaled to 500, and CEL files were generated using MAS 5.0
software (Affymetrix).6 All arrays met previously published quality control
standards.6,8-10 Robust multi-array average (gcRMA) was used to normalize data
and to generate log2 expression values from CEL files.6,11,12 Normalization was
performed separately for each data set (e.g. BMCD34+, PBCD34+/38-, and Tcells). Log2 expression values were analyzed in GenePlus software (Enodar
Biologic, Seattle, WA).6 Demographic data and CEL files are available at the
Gene Expression Omnibus (www.ncbi.nlm.nih.gov/geo).
Analyses for age-associated expression changes were performed
independently in BMCD34+ (N = 8 donors), PBCD34+38- (N = 4) and expanded
T-cell (N = 18 donors, 8 younger and 10 older).13 In the case of the BMCD34+
and PBCD34+38- analyses, age was treated as a continuous variable. In the
case of the T-cell analyses, a two group comparison analysis (young, age ≤ 30
vs. older, age > 70) was performed. For the BMCD34+ and T-cell studies,
analyses controlled for gender. In the case of the PBCD34+38-, there were no
females in the data set. Age-associated expression changes with Z-values 
4.75 or ≤ -4.75 were deemed to be statistically significant, which has been
established as statistical cut-off for similar array studies.14,15
Microarray analyses of murine hematopoietic stem cells
Studies of age-associated expression changes were also performed using
microarray data of murine hematopoietic stem cells (HSCs). The murine Rossi et
al. data set (GEO, GEO accession: GSE 4332) included expression profiles of
HSCs from aging C57GL/6 mice (3 arrays for younger: 2 – 3 months and 5
arrays from older: 22 – 24 months).16 The C57GL/6 HSCs represented a highly
enriched long-term repopulating (LTR) population as defined by multilineage
reconstitution in murine transplant models and the KLSflk-CD34- phenotype.16
The Chambers et al. data set (GEO, GEO accession: GSE 6503) included
expression profiles of hematopoietic stem/progenitor cells from C57B1/6 mice at
varying ages (2, 6, 12, and 21 months). 17 Two arrays at each age were
available.17 The C57GL/6 hematopoietic stem/progenitor cells were selected
based upon side population (SPlow), c-Kitpos, lineageneg, and Sca-1pos (e.g.
SParKLS).17
gcRMA was used to normalize the murine CEL file data and to compute
log2 expression values.6,11,12 Because different Affymetrix murine array platforms
were used with the murine studies (Rossi, 430-2.0 and Chambers, MOE430A),
normalization and analyses were performed independently for each study. Log2
expression values were analyzed in GenePlus software (Enodar Biologic). For
the Rossi data, a two group comparison (young vs. old) was performed. In the
case of the Chamber data, data at 4 different ages were available; thus, age was
examined as a continuous variable. As with the human analyses, Z-values 
4.75 or ≤ -4.75 were consider to be statistically significant.14,15
Of the 161 significant age-associated genes from the human BMCD34+
data set, homologous murine probe sets were available for 144 and 130 genes
on the murine arrays used by Rossi and Chambers, respectively. Of the 918
significant genes from the human PBCD34+38- data set, homologous murine
probe sets were available for 651 and 570 genes on the murine arrays used by
Rossi and Chambers, respectively.
Network generation and pathway analyses
Data sets of statistically significant genes, including Affymetrix probe ID
and corresponding Z-score, were loaded into Ingenuity Pathways Analysis
(IPA) software (Ingenuity Systems, www.ingenuity.com) and analyzed.6,18,19
The significance of functional pathways was measured by IPA based on righttailed Fisher Exact Test as previously described.18,19 Functional pathways with a
P-value ≤ 0.05 were considered to be statistically significant.
Quantitative RT/PCR IRF8 assays in PBSC CD34 and T-cells
Quantiative RT/PCR (Q-RT/PCR) assays were primarily performed using
samples that had not been previously examined by arrays (Supplement 2).
However, the limited number of BMCD34+ and PBCD34+ samples required that
some of the samples previously examined by arrays also be used in the QRT/PCR studies. Four of the six BMCD34+ samples in the Q-RT/PCR studies
had previously been examined using microarrays, while one of the five PBCD34+
samples in the Q-RT/PCR studies had previously been sorted into PBCD34+38subpopulations and used for arrays. None of the T-cells (N = 26) or
PBCD34+38- samples in Q-RT/PCR studies had previously been examined in
array analyses.
Q-RT/PCR assays were performed using universal TaqMan conditions
and the ABI PRIZM 7900HT Sequence Detection System (Applied Biosystems,
Foster City, CA).6,20 RT was performed using 0.5 µg of total RNA, AMVRT
(Invitrogen, Carlsbad, CA), and Oligo dT primer (Invitrogen) as per
manufacturer’s protocol. The cDNA equivalent of 0.05 µg of starting total RNA
was used as template for Q-PCR. Each reaction included 2x TaqMan®
Universal PCR Master Mix without uraci-N-glycosylase (Applied Biosystems),
800 µM of Reverse and Forward primers, 200 µM of probe, and enough water to
bring the total volume up to 25 µL. Sequence specific primers and probe for both
IRF8 are as follows:
IRF8F (forward): 5’-GAGAGCTGCAGCAGTTCTATAACA-3’;
IRF8R (reverse): 5’GCCAGTTGCCGGACATACAG-3’; and
Probe: 5’-FAM-CCAAACTCATTCTCGTGCAGATTGAGCAG-TAMRA-3.
Primers were shown to amplify the gene of interest by sequencing without
aberrant amplification of DNA or other transcripts. Plasmids containing the
amplicons for IRF8 and beta-2 microglobulin (B2M) were cloned into pCR2.1TOPO vectors (Invitrogen), and isolated using Plasmid Midi-prep Kit (Qiagen,
Valencia, CA). These plasmids were quantified and used to develop standard
dilution curves. The copy numbers for IRF8 and B2M were determined based on
cycle thresholds (Cts), which were extrapolated to the Cts of standard curves as
previously described.20-23 IRF8 copy numbers were adjusted by B2M copies to
correct for possible variations in RNA integrity, eliminating samples with poor
RNA quality (B2M ≤ 105 copies/50ng).20,22,23 All experiments had a negative
control (reaction without a template) to assess for contamination. Linear
regression analyses were used to determine the association between age and
IRF8 expression when age was treated as a continuous variable. Student’s t-test
with two-tail distribution and two-sample unequal variance was used to determine
statistical significance between two groups.
Western blots
Protein lysates were obtained from PBCD34+ cells and quantified as previously
described.21 Twenty micrograms of protein combined with 4x buffer (Invitrogen),
boiled 5 minutes, loaded into precast 4 – 12% BisTris Gels (Invitrogen),
electrophoresed and then transferred to a Hybond-P PVDF membrane (GE
Healthcare, Piscataway, NJ) with a mini trans-blot cell (BioRad, Hercules, CA)
using a transfer buffer of 25 mM Tris, 192 mM glycine, and 20% methanol.21 The
membranes were blocked overnight with 5% nonfat dry milk in ddH2O, washed
with TBST x times, and incubated for 1 hour at room temperature (RT) in ddH2O
with 5% milk containing polyclonal goat anti-IRF8 at 1:100 dilution (SC-6058,
Santa Cruz Inc., Santa Cruz, CA). The blot membrane was then washed with
TBST 0.1% 5 times, and reprobed with donkey anti-goat secondary antibody at
1:2500 dilution (SC-2020, Santa Cruz). The membrane was washed 6 times and
immunological complexes were visualized using enhanced chemiluminescence
(RPN2106, GE Healthcare). Blot membranes were washed overnight in TBST
0.1%, blocked 1 hour at RT in ddH2O with 5% milk, and then incubated with
polyclonal rabbit anti-GAPDH (ab-9485-100, Abcam, Cambridge, MA) for 1 hour
in ddH2O with 5% milk. The blot membrane was then washed with TBST 0.1% 5
times, and reprobed with donkey ant-rabbit antibody (NA934V, GE, Healthcare)
at 1:2500 for 1 hour in ddH2O with 5% milk. The membrane was washed 6 times
and immunological complexes were visualized using enhanced
chemiluminescence (RPN2106, GE Healthcare). The image was scanned into
ImageJ, inverted, and background subtracted using a roller ball radius 20.24 The
integrated density for IRF8 and GAPDH were calculated 3 times for each sample,
and the average of the 3 calculations used for comparison analyses.24 IRF8
signal was adjusted to GAPDH signal by multiplying the IRF8 signal of the
sample by the GAPDH signal for sample divided by median GAPDH signal
[IRF8s x (GAPDHm/GAPDHs)].
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