
[Cancer Research 60, 1934-1941, April 1, 2000]
© 2000 American Association for Cancer Research
Granulocyte Macrophage Colony-stimulating Factor and Interleukin 4 Enhance the Number and Antigen-presenting Activity of Circulating CD14+ and CD83+ Cells in Cancer Patients1
Michael D. Roth2,
Barbara J. Gitlitz,
Sylvia M. Kiertscher,
Alice N. Park,
Marcy Mendenhall,
Nancy Moldawer and
Robert A. Figlin
Divisions of Pulmonary and Critical Care Medicine [M. D. R., S. M. K., A. N. P., M. M.] and Hematology/Oncology [B. J. G., N. M., R. A. F.] and the Jonsson Comprehensive Cancer Center [M. D. R., R. A. F.], University of California at Los Angeles School of Medicine, Los Angeles, California 90095
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ABSTRACT
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Antigen-presenting cells (APCs) are essential for stimulating
antigen-specific immunity, including immunity against tumor cells. We
hypothesized that systemic administration of granulocyte macrophage
colony-stimulating factor (GM-CSF) and interleukin (IL)-4, which
promote monocytes to differentiate into dendritic cells in
vitro, might enhance the number and antigen-presenting activity
of CD14+ cells in vivo. Patients with
metastatic solid malignancies were treated with daily s.c. injections
of either GM-CSF alone (2.5 µg/kg/day) or GM-CSF in combination with
IL-4 (0.56.0 µg/kg/day) in a multicohort study. When given alone,
GM-CSF increased the number of CD14+ cells but did not
enhance the cells expression of APC markers or antigen-presenting
activity. In contrast, combination therapy with GM-CSF and IL-4
stimulated CD14+ cells to acquire several APC
characteristics including increased expression of HLA-DR and CD11c,
decreased CD14, increased endocytotic activity, and the ability to
stimulate T cells in a mixed leukocyte reaction. Combination therapy
also induced a dose-dependent increase in the number of
CD14-/CD83+ cells with APC activity.
Clinically significant and sustained tumor regression was observed in
one patient. Systemic therapy with GM-CSF and IL-4 may provide a
mechanism for increasing the number and function of APCs in patients
with cancer.
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INTRODUCTION
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Professional
APCs,3
such as DCs, play a central role in stimulating antitumor immune
responses (1, 2, 3)
. Using chimeric mice, Huang et
al. (2)
observed that immunogenic tumors expressing
the B7-1 transgene were incapable of stimulating an immune response in
the absence of MHC-matched, bone marrow-derived APCs. In a more direct
approach, murine bone marrow-derived DCs have been loaded with tumor
antigen peptides (3
, 4)
, antigenic proteins
(5)
, tumor lysates (6)
, or tumor antigen
genes (7)
and have been shown in each case to stimulate
antitumor activity when used to vaccinate naive mice. APCs appear to
play a similar role in the response against human cancer.
Histopathology studies have long reported a correlation between the
number of tumor-associated APCs and patient survival
(8, 9, 10, 11)
. As in the murine models, in
vitro-generated DCs have also been loaded with tumor antigens and
used to vaccinate patients with a variety of cancers including B-cell
lymphoma (12)
, melanoma (13)
, or prostate
cancer (14
, 15)
. Antitumor immunity and objective clinical
responses were demonstrated in all three studies. This success with DC
therapy prompted us to examine other approaches for increasing the
number and/or function of APCs in cancer patients.
Whereas little is known about the in vivo origins and
trafficking of human DCs, in vitro studies have identified
two cell populations that can act as DC precursors: (a)
CD34+ stem cells originating from bone marrow
(16
, 17)
; and (b) circulating
CD14+ monocytes (18, 19, 20)
.
CD34+ stem cells mature into DCs in response to
GM-CSF and tumor necrosis factor
, an effect that can be enhanced by
a variety of other factors including IL-4, flt3 ligand, and CD40 ligand
(21
, 22)
. CD14+ monocytes mature
into DCs primarily in response to the combination of GM-CSF and IL-4
(19
, 23) , although similar effects have been reported when
GM-CSF is combined with IFN-
, CD40 ligand or IL-13
(24, 25, 26)
. Based on evidence that viable DC progenitors
exist in cancer patients (27)
and can respond to cytokine
stimulation, we set out to determine whether systemic therapy with the
combination of GM-CSF and IL-4 would work in vivo as it does
in vitro to increase the number and/or function of
circulating APCs. A total of 21 patients with metastatic solid tumors
were enrolled in a Phase I, dose-escalating, multicohort study to
evaluate the effects of daily therapy with GM-CSF alone
versus the combination of GM-CSF and IL-4 on the number,
phenotype, and function of circulating APCs.
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MATERIALS AND METHODS
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Subject Selection.
Patients with metastatic solid tumors who had failed or refused
standard treatment were enrolled. No other cancer therapy was allowed
for 4 weeks before or during this study. Primary exclusion criteria
included current central nervous system metastases, an Eastern
Cooperative Oncology Group performance status greater than 1, cardiac
insufficiency/infarction within the last 12 months, acute or chronic
infection, bleeding peptic ulcer disease within the last 6 months,
dependence on corticosteroids, organ transplantation, or laboratory
evidence of organ insufficiency. Written informed consent was obtained
in accordance with the University of California at Los Angeles
Institutional Review Board.
Clinical Protocol.
Patients were recruited into a total of six successive treatment
cohorts (cohorts AI, AII, B, C, D, and E) in a serial manner. Patients
were treated with daily s.c. injections of sterile human recombinant
GM-CSF (specific activity = 1.125 x 107 units/mg) and IL-4 (specific
activity = 2.414 x 107 units/mg) provided by Schering-Plough
Research Institute (Kenilworth, NJ). For cohorts AID, the 28-day
protocol included 14 continuous days of therapy followed by 14 days of
observation. For cohort E, the 28-day protocol alternated 7-day periods
of cytokine therapy with 7-day periods of observation. Injections were
self-administered s.c. to the skin of the thigh and/or abdomen as a
home-based therapy. Patients in cohort AI received a fixed dose of
GM-CSF (2.5 µg/kg/day), whereas patients in subsequent cohorts
received the same dose of GM-CSF in combination with IL-4 at 0.5
(cohort AII), 1.0 (cohort B), 2.0 (cohort C), 4.0 (cohort D), or 6.0
(cohort E) µg/kg/day. All patients successfully completing the AI
cohort were enrolled as subjects in the AII cohort, but new subjects
were enrolled into all subsequent groups (cohorts BE). Patients
achieving objective clinical responses or stable disease were eligible
to continue therapy without further determination of biological
activity. Patients were monitored twice weekly for evidence of toxicity
according to the National Cancer Institute Common Toxicity Criteria.
Blood was drawn on days 0, 7, 14, and 21 for in vitro
testing to assess the biological effects of therapy. To assess
antitumor efficacy, radiological imaging of measurable and evaluable
disease and tumor marker serologies (when applicable) were obtained
serially for as long as patients remained on therapy. Standard
Southwest Oncology Group response criteria were used to determine
objective responses.
Laboratory Reagents and Antibodies.
CM was composed of RPMI 1640 supplemented with glutamine (Irvine
Scientific, Irvine, CA), 0.01 M HEPES buffer,
antibiotic-antimycotic mixture (Life Technologies, Inc., Grand Island,
NY), and 10% heat-inactivated human AB serum (Gemini Bioproducts,
Inc., Calabasas, CA). Dulbeccos PBS (Life Technologies, Inc.) was
supplemented with 2% human AB serum. M450 magnetic beads coated with
goat antimouse IgG were obtained from Dynal Inc. (Lake Success, NY).
Fluorescein-labeled dextran (Mr
40,000) was purchased from Molecular Probes (Eugene, OR).
Fluorochrome-conjugated mAbs used for FACS analysis included anti-CD3,
anti-CD13, anti-CD14, anti-CD15, anti-CD20, anti-CD40, and anti-CD57
from Caltag Laboratories (South San Francisco, CA); anti-HLA-DR and
anti-CD80 (B7-1) from Becton Dickinson (San Jose, CA); anti-CD11c and
anti-CD86 (B7-2) from PharMingen (San Diego, CA); anti-CD1a from
Serotec (Raleigh, NC); and anti-CD83 (clone HB15a) from Beckman Coulter
(Fullerton, CA).
FACS Analysis.
Peripheral blood samples from study days 0, 7, 14, and 21 were
collected in heparinized tubes, and leukocytes were isolated by
differential centrifugation over Ficoll-Paque gradients
(Pharmacia Biotech, Inc., Alameda, CA). Leukocytes were analyzed for
their expression of cell surface markers by three-color FACS analysis
using a single FACScan II flow cytometer that was calibrated daily with
CaliBRITE beads and AutoCOMP software (all from Becton Dickinson).
Between 5,000 and 300,000 events (depending on the cell population and
marker) were acquired for each sample using CellQuest software (Becton
Dickinson) that simultaneously acquired data for forward scatter, side
scatter, FL1 (FITC label), FL2 (PE label), and FL3 (either
tricolor or PerCP label). The settings for all of these
parameters were optimized at the initiation of the study and maintained
constant during all subsequent analyses to allow direct comparison
between samples analyzed on different days. For cohort E, a new lot of
anti-CD14 mAb resulted in lower expression as compared to prior
cohorts. The relative expression of a given marker was expressed by the
LFI. The number of circulating CD14+ or
CD83+ cells per milliliter of blood was
determined by multiplying the percentage of leukocytes staining with a
given marker (as determined by FACS analysis) by the number of
leukocytes recovered per milliliter of blood.
Endocytosis Assay.
The temperature-dependent uptake of FITC-labeled dextran was used to
measure endocytotic function according to a modification of the
procedure described by Sallusto et al. (28)
.
Fresh leukocytes from study patients in the D cohort were resuspended
in 0.5 ml of CM (containing 25 mM HEPES) and
cultured with FITC-labeled dextran (1 mg/ml) for 60 min at either 0°C
or 37°C. Cells expressing CD14 were stained by adding anti-CD14-PE
during the last 5 min of the assay, and the reaction was terminated by
adding 3 ml of ice-cold PBS containing 0.1% azide. Cell pellets were
washed four times, and the CD14+ population was
analyzed immediately for the intracellular accumulation of the FITC
label by FACS analysis. The degree of endocytosis was determined by
comparing the intracellular uptake at 37°C with the nonspecific
binding that occurred at 0°C.
Allogeneic MLR.
APCs collected on different days of therapy were evaluated for their
ability to stimulate the proliferation of allogeneic T cells using a
one-way MLR. This approach, as compared to a soluble antigen
presentation assay, was specifically chosen to prevent any treatment-
or cancer-related effects on the patients own T cells from
interfering with the measurement of APC function (29
, 30)
.
APCs were prepared either by depleting contaminating neutrophils from
PBMCs with endotoxin-free anti-CD24 mAb (2
µg/106 cells; PharMingen) and immunomagnetic
beads (bead:cell ratio, 4:1) or by preparing purified
CD14+ or
CD14-/CD83+ cells by
fluorescence-activated cell sorting analysis using a
FACStarplus flow cytometer and Lysys II software
(Becton Dickinson) as described previously (19)
. APCs were
irradiated with 30 Gy (cesium source) and cocultured with 1 x 105 responder T cells for 6 days at APC:T
cell ratios of 1:5 to 1:100. Wells were pulsed with 1 µCi of
[3H]thymidine (DuPont New England Nuclear,
Boston, MA) and harvested 18 h later using an automated cell
harvester (PhD cell harvester; Cambridge Technology, Cambridge, MA).
cpm were determined by liquid scintillation counting, and each data
point represented the average ± SD of three to six
wells.
Data Analysis.
Data from replicate measurements of a single assay are expressed as the
mean value ± 1 SD, and data representing entire cohorts
are represented as the mean value for all of the subjects in a
cohort ± 1 SE. The hypothesis that treatment either
increased or decreased an outcome variable within a given cohort or
between different cohorts was evaluated using either a paired
Students t test or an unpaired Students t
test, respectively. A two-way ANOVA with correction for multiple
comparisons was used to compare MLR results for the same subject when
measured on different days of the treatment. A P of
0.05
was considered significant.
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RESULTS
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Cohort Characteristics.
Twenty-one patients with primary tumors including cancers of the lung,
kidney, colon, and prostate were enrolled into the six cohorts (Table 1)
. Reversible, cytokine-induced leukocytosis occurred in all patients
with maximal day 14 peripheral blood counts averaging 22,300 ± 10,070 in cohort A and 30,300 ± 7,238 in cohort
D (no significant differences). Maximal day 7 counts in the E cohort
averaged 15,100. Side effects consisted primarily of grade 1 and 2
constitutional symptoms: fever; bone pain; local injection site
erythema; nausea and vomiting; thrombocytopenia; or transaminitis.
Grade 3 hepatic toxicity (elevated alkaline phosphatase) occurred in
one subject each in cohorts C and D, and grade 3 headache occurred in
one subject in cohort E, all of which resolved spontaneously without
interruption in therapy. No dose-limiting toxicity was observed, but
one patient in cohort AI receiving GM-CSF alone voluntarily withdrew
from the study after developing a rash at the injection site.
Effects of Systemic GM-CSF and IL-4 on the Number, Phenotype, and
Endocytotic Function of Circulating CD14+ Cells.
GM-CSF increased the number of circulating CD14+
cells, an effect that peaked on day 7 (average, 6.29 x 105 cells/ml) and returned to baseline levels by
day 21 (average, 3.5 x 104
cells/ml). A similar result occurred when low doses of IL-4 (0.52.0
µg/kg/day) were administered in combination with GM-CSF. However,
when patients were treated with
4.0 µg/kg/day IL-4, there was a
further increase in the number of circulating
CD14+ cells beyond that observed with GM-CSF
alone (Fig. 1
). On day 7, peripheral blood CD14+ counts
averaged 5-fold higher in cohort D (P < 0.05) and 2.2-fold higher in cohort E as compared with the increase
that resulted from GM-CSF alone. The number of
CD14+ cells returned to baseline within 7 days of
completing cytokine therapy in all cohorts.

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Fig. 1. Circulating CD14+ cells and
CD83+/HLA-DR+ cells are increased in patients
receiving GM-CSF and IL-4. Patients were treated for 14 days with
either GM-CSF alone at 2.5 µg/kg/day (cohort A) or GM-CSF in
combination with IL-4 at 0.5, 1.0, 2.0, or 4.0 µg/kg/day (cohorts
AII-D, respectively). Peripheral blood leukocytes collected on days 0,
7, 14, and 21 were stained with fluorescence-labeled anti-CD14 or a
combination of anti-CD83 and anti-HLA-DR, and the percentage of cells
expressing these markers was determined by FACS analysis. This value
was multiplied by the number of cells isolated per milliliter of blood
to calculate the number of CD14+ (A) or
CD83+/HLA-DR+ (B) cells/ml.
Values represent the mean ± SE for each cohort. *,
P < 0.05 compared to the same cohort on
day 0, paired t test. , P < 0.05 compared to cohort AI or AII on the same day, unpaired
t test.
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As observed when GM-CSF and IL-4 were used to generate DCs in
vitro, the administration of these cytokines in vivo to
patients resulted in an IL-4-dependent decrease in the intensity of
CD14 staining (Table 2)
. This effect was detectable on day 7 in the C cohort and was
statistically significant at both days 7 and 14 in the D cohort.
Similar effects were observed by day 7 in the E cohort, where CD14
expression was decreased by 65% compared to the day 0 value.
Concurrent with the decrease in CD14, there was an IL-4-dependent
increase in the expression of HLA-DR in the same cells (Fig. 2
). By day 7 of treatment, HLA-DR expression increased to 229 ± 87% of day 0 levels in the D cohort (P < 0.05) and 308 ± 83% of day 0 levels in the E
cohort (P < 0.05). Significant increases in
the expression of HLA-DR were not observed in patients receiving GM-CSF
alone. A similar trend was observed for the up-regulation of CD11c
(Fig. 2
).

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Fig. 2. In vivo exposure to GM-CSF and IL-4
down-regulates the expression of CD14 and up-regulates the expression
of HLA-DR and CD11c in a dose-responsive manner. Peripheral blood was
collected from each subject on days 0 (white histograms)
and 7 (black histograms), and the CD14+
population was evaluated for expression of CD14, HLA-DR, and CD11c by
FACS analysis. Numbers indicate the average marker expression
(mean ± SE for the entire cohort) on day 7 as a
percentage of each individuals marker expression on day 0.
Representative histograms for a single individual from each cohort are
shown. *, P < 0.05 comparing day 7 to
day 0, paired t test. , P < 0.10 comparing day 7 to day 0, paired t test.
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However, in contrast to DCs generated from monocytes in
vitro (19)
, expression of CD80 was only modestly
increased (Fig. 3
) and expression of CD86 was not increased at all on circulating
CD14+ cells from treated patients. To evaluate
this further, peripheral blood leukocytes were isolated from cohort E
on day 7 of in vivo therapy and cultured for 24 h
in vitro in the absence of any exogenous cytokines. This
short-term culture resulted in a dramatic up-regulation of CD80, CD86,
CD11c, and HLA-DR on the CD14dim+ cells,
producing a pattern of expression similar to that observed when
monocytes are cultured in vitro with GM-CSF and IL-4 for a
full 7 days (19)
. Overnight culture also resulted in
expression of CD83, a marker usually expressed only on functionally
mature DCs.

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Fig. 3. Circulating CD14+ cells from patients treated
with GM-CSF and IL-4 rapidly mature into DCs in culture. Circulating
CD14+ cells collected from cohort E on day 7 expressed less
CD14 but increased levels of HLA-DR, CD80, and CD11c compared to
CD14+ cells collected from the same subjects on day 0. When
cultured in vitro in CM (no exogenous cytokines) for
24 h, day 7 cells rapidly up-regulated expression of HLA-DR, CD80,
CD86, CD11c, and CD83 in a pattern consistent with mature DCs. A
representative experiment is shown (subject E4).
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The maturation of monocytes into DCs is associated with an increase in
their ability to take-up and process antigens. As a measure of this
function, CD14+ cells from cohort D were serially
evaluated on days 0, 7, 14, and 21 for their capacity to take-up
FITC-labeled dextran. Cells collected from days 7 and 14 of therapy
showed a 56-fold greater uptake of FITC-labeled dextran as compared
with CD14+ cells collected from either day 0 or
day 21, suggesting functional activation of receptor-mediated
endocytosis (Fig. 4
).

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Fig. 4. In vivo exposure to GM-CSF and IL-4
increases receptor-mediated endocytosis. Peripheral blood leukocytes
from cohort D were collected on days 0, 7, 14, and 21 and cultured for
60 min at either 0°C (white histograms) or 37°C
(black histograms) in the presence of FITC-labeled
dextran (1 mg/ml). Cells were counterstained with anti-CD14-PE, and the
intracellular accumulation of FITC-labeled dextran on the
CD14+ population was determined by FACS analysis. Numbers
indicate LFI for the FITC label at 37°C minus that at 0°C.
Representative results are shown (subject D2).
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Effects of Systemic GM-CSF and IL-4 on the Number of Circulating
CD14-/CD83+ Cells.
In addition to its effect on CD14+ cells, the
combination of GM-CSF and IL-4 may play a role in the differentiation
of DCs from stem cells (16
, 21)
. This pathway of DC
maturation is associated with the early expression of several markers,
including CD83 and CD1a, which are only expressed on monocyte-derived
DCs at terminal stages in their development (17
, 31)
. This
pathway of DC maturation was monitored by staining peripheral blood
samples with fluorescence-labeled anti-CD83 and anti-HLA-DR mAb and
enumerating the percentage and number of
CD83+/HLA-DR+ cells by FACS
analysis (Figs. 1B
and 5
). The administration of GM-CSF, alone or in combination with 0.5 or 1.0
µg/kg/day IL-4, did not significantly increase the percentage of
CD83+/HLA-DR+ cells.
However, there was a dose-dependent increase in the percentage of
CD83+/HLA-DR+ cells at
higher IL-4 doses, with the maximal effect observed in the D cohort
(2.35 ± 1.8% of PBMCs in the D cohort
versus 0.09 ± 0.09% of PBMCs in the AI
cohort, P < 0.05). In terms of the total number
of circulating
CD83+/HLA-DR+ cells
recovered per milliliter of blood, there was an average 130-fold
increase by day 7 in patients treated with 4 µg/kg/day IL-4 (range,
26399-fold increase; Fig. 1B
). This
CD83+/HLA-DR+ population
was comprised of two distinct subsets, one containing smaller cells
with minimal autofluorescence, and the other containing larger cells
with a relatively high autofluorescence (Fig. 6
). Both subsets expressed HLA-DR and CD1a in the absence of CD14, a
pattern consistent with DCs of stem cell origin.

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Fig. 5. In vivo exposure to GM-CSF and IL-4
promoted a dose-responsive increase in the percentage of PBMCs
expressing CD83. Peripheral blood leukocytes collected from cohorts
AID on day 7 were stained with anti-CD83 and anti-HLA-DR to determine
the percentage of cells expressing the
CD83+/HLA-DR+ phenotype. Representative
two-dimensional dot-plots (CD83-stained cells versus
unstained cells) for each cohort are shown, and the average percentage
(± SE) of PBMCs expressing the CD83+/HLA-DR+
phenotype for that cohort is displayed numerically. *,
P < 0.05 compared to cohort AI, unpaired
t test.
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Fig. 6. Cells expressing CD83 did not express CD14 but expressed
high levels of HLA-DR and CD1a. Peripheral blood leukocytes were
stained with anti-CD83 in combination with either anti-HLA-DR,
anti-CD1a, or anti-CD14 and analyzed by FACS analysis.
CD83+ cells with high autofluorescence (region
R1) and low autofluorescence (region R2)
were identified by two-dimensional dot-plots as described in the Fig. 5
legend and analyzed individually for their size (FSC),
cellular complexity (SSC), and expression of the
indicated markers. Background autofluoresence is indicated by the
white histograms, and fluorescence after staining with
specific antibody is indicated by the black histograms.
Representative results for the D cohort, subject D2, are shown.
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Effects of Systemic GM-CSF and IL-4 on in Vitro
Measures of Antigen-presenting Activity and in Vivo
Measures of Antitumor Activity.
PBMCs collected from patients on days 0, 7, 14, and 21 of therapy were
evaluated for their ability to stimulate T-cell proliferation in an
allogeneic one-way MLR using T cells from a single normal donor as
responders. No consistent treatment effect was observed in patients
treated with GM-CSF alone or with GM-CSF in combination with low doses
of IL-4 (cohorts AII or B). However, PBMCs collected from one patient
in cohort C demonstrated increased MLR activity on treatment days (days
7 and 14) as compared with pre- and posttreatment days (Fig. 7
). In cohorts D and E, the CD14+ populations were
purified by cell sorting and compared for their allostimulatory
activity. A treatment-related increase in activity was observed in two
of the four patients in cohort D and in four of the four patients in
cohort E (Fig. 7
). In one patient (patient D4),
CD83+ cells were also prepared by cell sorting
and found to stimulate greater T-cell proliferation than either PBMCs
or sorted CD14+ cells collected from day 0.

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Fig. 7. In vivo exposure to GM-CSF and IL-4
increases APC activity in some subjects. PBMCs (cohorts AC) or the
purified CD14+ and/or CD83+ populations
prepared by cell sorting (cohorts D and E) were collected on days 0, 7,
14, and 21 and assayed for their ability to stimulate 1 x 105 allogeneic T cells from a normal healthy donor
in a MLR. T-cell proliferation was determined by
[3H]thymidine uptake. Cells from one of four patients in
cohort C, two of four patients in cohort D, and four of four patients
in cohort E demonstrated increased stimulatory activity during cytokine
therapy. No treatment-related increase in allostimulatory activity was
observed in cohorts AI, AII, or B. *, P < 0.05 compared to day 0. Representative assays are shown.
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All patients were assessed for therapy-associated changes in tumor
burden. Two of three patients (one in cohort D and one in cohort E)
with prostate cancer demonstrated objective responses. Patient D1, who
had hormone-refractory prostate cancer metastatic to two mediastinal
lymph nodes and multiple bones (confirmed by computed tomography scans,
positron emission tomography scans, and bone scans), experienced a
partial response with a marked improvement in bone pain and a lasting
decrease in serum PSA from 49 (pretreatment) to 0.8 ng/ml after four
cycles of therapy and to 2.3 ng/ml after 1 year. After four cycles of
therapy, he also experienced a >50% reduction in the size of involved
mediastinal lymph nodes (which continued to decrease over 1 year of
observation) and a persistent decrease in the size and intensity of all
bone lesions as determined by bone scan. Patient E4, who had a rising
postoperative PSA, responded with a decrease in PSA from 13 to 5.2
ng/ml after the first cycle of therapy. After three cycles of therapy,
PSA remained at 5.0 ng/ml but rose to 19.9 within 2 weeks of stopping
treatment, and the patient was switched to hormonal therapy. He
continues with stable disease after 10 months of follow-up. No other
patients demonstrated objective tumor responses.
 |
DISCUSSION
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DCs are bone marrow-derived APCs that express high levels of MHC,
adhesion molecules, and other important costimulatory molecules
required for antigen presentation (32
, 33)
. Their ability
to take-up antigens and induce antigen-specific immunity has stimulated
considerable interest in using them to treat cancer. However, naturally
occurring DCs are exceptionally rare, comprising only 0.010.5% of
circulating and tumor-infiltrating mononuclear leukocytes (19
, 34)
. Even when present, DCs harvested from cancer patients often
fail to express normal levels of antigen-presenting molecules and lack
the ability to stimulate effective immune responses (27
, 34
, 35)
. Enk et al. (35)
purified
CD83+ DCs from the tumors of patients with both
regressing and progressing melanoma metastases. Whereas the DCs from
regressing metastases expressed CD86 and functioned as APCs, the DCs
recovered from progressing metastases expressed little CD86 and induced
T-cell anergy instead of stimulation. Similarly, Gabrilovich et
al. (27)
found that DCs isolated from the circulation
of breast cancer patients were defective and that DC function inversely
correlated with tumor stage. A variety of tumor-derived factors,
including vascular endothelial growth factor, macrophage
colony-stimulating factor, IL-6, and IL-10, are believed to alter the
maturation and function of DCs (36, 37, 38)
. Despite the poor
function of mature DCs in cancer patients, DC precursors appear to be
relatively unaffected. By isolating PBMCs from cancer patients and
culturing them with cytokines in vitro, Gabriliovich
et al. (27)
and many others (13, 14
, 39)
have been able to generate large numbers of functionally
normal DCs. Using this strategy, DCs expanded from precursors in
vitro have been loaded with antigenic tumor peptides and used to
vaccinate patients. This approach has produced approximately 30%
response rates in initial trials for metastatic melanoma
(13)
and prostate cancer (14
, 15)
but has
produced no responses in a trial for colon cancer (40)
.
Whereas the ex vivo generation of cytokine-derived DCs
offers an important new approach to cancer therapy, it requires
considerable resources and expertise. A leukopharesis is required to
obtain precursors, recovered cells need to be purified and
differentiated in vitro under sterile conditions, and mature
DCs need to be loaded with antigen and returned to patients. As an
alternative to ex vivo therapy, we hypothesized that the
combination of GM-CSF and IL-4 might be administered directly to cancer
patients to generate cytokine-derived APCs in situ. This
approach has several potential advantages in terms of the large number
of CD14+ and CD34+
precursors that exist in vivo; the capacity to activate APCs
directly within lymphoid organs, tissues, and tumor sites; and the
potential for a simplified home-based therapy. Patients in this study
quickly learned how to administer their own injections at home. The
expansion of APCs in this manner could also be combined with standard
vaccine approaches to target responses against specific antigens.
However, even in the absence of antigen targeting, the placement of
cytokine-derived APCs directly within murine tumors has been shown to
induce tumor regression (41)
. Similarly, the in
vivo expansion of APCs with systemic flt3 ligand induces antitumor
immunity in a variety of tumor models (42, 43, 44)
. These
animal models, in combination with human studies that find a
correlation between the number of tumor-associated APCs and clinical
outcome (8, 9, 10, 11)
, support the hypothesis that increasing
the number of APCs in vivo might activate antitumor
immunity.
The feasibility of combining GM-CSF and IL-4 as an in vivo
therapy was based on past experience with these cytokines. As others
have reported (45
, 46)
, we found that a 2-week course of
GM-CSF was well tolerated and induced a 520-fold increase in the
number of circulating CD14+ cells. Although there
is less experience with IL-4, a prior study observed 56 µg/kg/day
to be the maximum tolerable dose when given alone as a daily injection
for 2 weeks (47)
. Pharmacokinetic analysis documented
blood levels in the range of 112 ng/ml after a 4 µg/kg/day
injection of IL-4 and suggested that peak levels might be sustained for
up to 8 h (48)
. Preliminary in vitro
studies (data not shown) confirmed that as little as 1.25 ng/ml IL-4
was sufficient, when combined with GM-CSF, to promote human monocytes
to mature into APCs, with higher levels producing more rapid and
complete DC maturation. The fact that neither GM-CSF nor IL-4 has
produced marked antitumor responses in the past when used as single
agents is not surprising (45
, 49
, 50)
. The capacity for
GM-CSF and IL-4 to differentiate precursors into DCs is highly
synergistic, requiring both cytokines to achieve an effect
(20)
. This type of synergism was readily apparent in our
study when the combination of GM-CSF and IL-4, but not GM-CSF alone,
dramatically increased the number of CD14+ and
CD83+ cells with APC characteristics. In terms of
tolerability, combined treatment with GM-CSF and IL-4 at doses of
4
µg/kg was similar to GM-CSF alone and was not associated with any
dose-limiting toxicity. At 6 µg/ml, patients experienced a higher
frequency and severity of constitutional symptoms, which prompted us to
shorten the treatment interval to 7 days.
Using the characteristics of in vitro monocyte-derived
DCs as a guide, we carefully evaluated circulating
CD14+ cells from patients for evidence of
maturation along a DC pathway. Down-regulation of CD14 expression was
used as a hallmark to identify monocyte-derived APCs and allowed us to
identify the concurrent up-regulation of HLA-DR and CD11c on these
cells. In contrast to the phenotypic changes that occurred under
optimal in vitro conditions, the cells from treated patients
retained modest CD14 expression and did not express high levels of
either CD80 or CD86. One conclusion would be that in vivo
cytokine therapy resulted in an intermediate stage of DC
differentiation. This would not be surprising because cytokine-induced
DC maturation occurs in a continuum that is both dose- and
time-dependent. Higher dosing with IL-4 or secondary stimulation by
CD40 ligand or other activating factors might be required to produce
more mature DCs. Alternatively, more mature DCs that developed in
response to therapy might have exited the circulation before our
sampling. We obtained blood only once a week and, in each case, 24 h after the last cytokine dose. Rapid margination and trafficking of
cytokine-activated cells to peripheral sites is a common phenomenon
after cytokine therapy, including therapy with GM-CSF (45
, 46)
. Unfortunately, biopsies from tumor sites and/or lymph nodes
were not obtained in this study and could not be evaluated for DC
infiltration. Finally, the failure to see full expression of CD80 and
CD86 on circulating APCs could have resulted from tumor-derived
immunosuppressive factors interfering with DC maturation.
To address these issues, we recovered circulating cells from treated
patients and placed them into short-term culture in the absence of any
exogenous cytokines. Within 24 h, we observed a dramatic
up-regulation of HLA-DR, CD80, CD86, CD11c, and CD83 on the
CD14dim+ population, a phenotype almost identical
to that generated by culturing monocytes for 78 days in high
concentrations of GM-CSF and IL-4. This rapid in vitro
maturation is similar to that reported when naturally occurring DCs are
isolated from the peripheral blood of control subjects (51
, 52)
. In addition to acquiring the phenotypic characteristics of
APCs, CD14+ cells from patients treated with
higher doses of IL-4 also increased their capacity to take-up
FITC-labeled dextran, a well-characterized marker of functionally
active DCs (28)
, as well as their capacity to stimulate T
cells in a MLR. Collectively, these findings suggest that combined
therapy with GM-CSF and higher doses of IL-4 induced myeloid precursors
to differentiate into functional APCs consistent with immature DCs.
Whether these circulating cells migrate into tissue and lymphoid organs
and terminally differentiate, as they did when cultured for 24 h
in vitro, remains to be determined.
In addition to their effects on peripheral blood monocytes, GM-CSF and
IL-4 are involved in the expansion of DCs directly from bone marrow
precursors. DCs generated in this manner mature either through a
CD14+ intermediate stage or more directly into
DCs as identified by the earlier acquisition of CD83 and CD1a in the
absence of CD14 (16
, 17)
. As with
CD14+ cells, we observed that GM-CSF in
combination with higher doses of IL-4 produced a significant increase
in the number of circulating CD83+ cells. These
cells lacked CD14, expressed CD1a and high levels of HLA-DR, and were
active APCs in preliminary sorting experiments. Two distinct
CD83+ populations emerged at higher IL-4 doses,
one composed of smaller cells, and one composed of larger cells. A
preliminary sorting experiment suggests that these
CD83+ cells are able to stimulate T-cell
proliferation, but further work is required to confirm their origins
and functional role. Although increased up to 300-fold in response to
GM-CSF and IL-4, the CD83+ population was still
outnumbered 10-fold by CD14dim APCs.
From a clinical perspective, it appears likely that the administration
of GM-CSF and IL-4 can be used to generate large numbers of APCs
in situ. Although this Phase I study enrolled only four
patients in each dose group, the development of objective antitumor
responses in two patients is striking. The changes in PSA, lymph node
involvement, and bone disease all correlated well with improvement in
the responding patients symptoms. PSA responses have been
described for patients vaccinated with GM-CSF/IL-4-generated DCs that
were loaded ex vivo with prostate-specific membrane antigen
(14
, 15) . It is interesting to speculate that the APCs
generated in vivo in our patients were able to gain access
to the patients own tumor antigens and initiate an antitumor
response. As stated previously (42, 43, 44)
, similar antitumor
responses have been reported in mice when flt3 ligand was used to
expand DCs in vivo. In a recent study (53)
,
patients with metastatic prostate cancer were treated with intermittent
2-week courses of GM-CSF alone (Leukine; 250
µg/m2/day). Ten of 22 patients treated
with this regimen developed intermittent decreases in serum PSA, but
their values uniformly rose to levels higher than the pretreatment
levels after each treatment cycle. High levels of GM-CSF were found to
directly down-regulate PSA expression when added to the LNCaP cell line
in culture, offering one potential mechanism for this phenomenon. In
contrast to that report with GM-CSF alone, our prostate cancer patients
treated with GM-CSF and IL-4 exhibited a progressive decline in PSA and
tumor burden over time. Other studies have either found minimal
antitumor effects of GM-CSF therapy alone (45
, 50)
or
documented significantly fewer patient responses when GM-CSF was
administered concurrently as an adjuvant with peptide vaccines or
peptide-pulsed DCs (54
, 55)
.
In conclusion, this Phase I study suggests that the combined
administration of GM-CSF and IL-4 to patients with advanced cancer
produces an IL-4-dependent increase in the number of circulating
CD14+ and CD83+ APCs with
many of the phenotypic and functional characteristics associated with
DCs. Systemic cytokine administration aimed at generating APCs in
situ, either alone or in combination with the administration of
targeting antigens, may provide an additional approach to cancer
immunotherapy.
ACKNOWLEDGMENTS
Support and recombinant human cytokines were kindly provided by
the Schering-Plough Research Institute (Kenilworth, NJ), under
the direction of Dr. Mary Ellen Rybak, past Director of Clinical
Oncology Research. We also thank Mitzi Ng for technical assistance.
 |
FOOTNOTES
|
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 Supported in part by the Jonsson Cancer Center
Foundation/University of California at Los Angeles (M. D. R.),
American Cancer Society Grant CRTG-97117-01-CCE (to B. J. G.), and
the Schering-Plough Research Institute. 
2 To whom requests for reprints should be
addressed, at the Division of Pulmonary and Critical Care Medicine,
Department of Medicine, University of California at Los Angeles School
of Medicine, Los Angeles, CA 90095-1690. Phone: (310) 206-7389; Fax:
(310) 267-2020; E-mail: mroth{at}mednet.ucla.edu 
3 The abbreviations used are: APC,
antigen-presenting cell; GM-CSF, granulocyte macrophage
colony-stimulating factor; IL, interleukin; DC, dendritic cell; MLR,
mixed leukocyte reaction; CM, complete medium; mAb, monoclonal
antibody; FACS, fluorescence-activated cell-sorting; PSA,
prostate-specific antigen; LFI, relative mean linear fluorescence
intensity; FL, fluorescence channel; PBMC, peripheral blood mononuclear
cell; PE, phycoerythrin; PerCP, peridin chlorophyll protein. 
Received 10/ 6/99.
Accepted 2/ 3/00.
 |
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S. Ponnazhagan, G. Mahendra, D. T. Curiel, and D. R. Shaw
Adeno-Associated Virus Type 2-Mediated Transduction of Human Monocyte-Derived Dendritic Cells: Implications for Ex Vivo Immunotherapy
J. Virol.,
October 1, 2001;
75(19):
9493 - 9501.
[Abstract]
[Full Text]
[PDF]
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Y. Gazitt
Immunologic Profiles of Effector Cells and Peripheral Blood Stem Cells Mobilized with Different Hematopoietic Growth Factors
Stem Cells,
November 1, 2000;
18(6):
390 - 398.
[Abstract]
[Full Text]
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