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Clinical Trials |
Departments of Laboratory Medicine [J. M. R., B-N. L., H. J., H. F.], Leukemia [H. M. K.], and Bioimmunotherapy [M. T.], The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| ABSTRACT |
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has proven to be an
effective therapy, inducing cytogenetic remission in CML patients.
However, it is unknown whether IFN-
can restore normal immune
function for patients who achieve a complete cytogenetic remission. To
address this question, we used a method of intracellular staining and
flow cytometric analysis to ascribe the syntheses of Th1 or Th2
cytokines to T-cell subsets of patients in chronic, in accelerated, and
in blast crisis phases as well as patients who had achieved a complete
cytogenetic remission with IFN-
. We assessed the cytoplasmic
synthesis of cytokine in phorbol ester (phorbol 12-myristate
13-acetate)-activated CD4+ and CD8+ T-cell subsets of 81 patients with
various stages of CML and 21 normal controls. The percentages of CD4+
and CD8+ T cells from patients in chronic, in accelerated, and in blast
crisis phases that synthesized Th1 cytokines interleukin (IL)-2,
IFN-
, and tumor necrosis factor-
were significantly lower than
those of remission patients and normal controls. Conversely, the
percentages of CD4+ and CD8+ T cells of patients in chronic, in
accelerated, and in blast crisis phases of CML preferentially
synthesized the Th2 cytokine IL-10. Patients who achieved a durable
complete cytogenetic remission for >2 years without maintenance
IFN-
therapy restored their preference for a Th1 cytokine profile
that is necessary for efficient cytotoxic T-cell function. | INTRODUCTION |
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20%
basophils in the blood or bone marrow. The natural course of CML is a
transformation that closely resembles an acute leukemia, known as the
BC phase, during which blasts of both lymphoid and myeloid origin make
up at least 30% of the WBCs in bone marrow or blood (6)
.
Transformation is often associated with karyotypic evolution
(7)
. Patients become refractory to chemotherapy
(8)
, and survival for patients in ACC/BC is on the order
of only 312 months (6)
.
Conventional treatment of CML with chemotherapeutic agents normalizes
the WBC count of patients but indiscriminately kills both the leukemia
clone and normal cells (9)
; the chemotherapeutic agents
are often considered palliative because they do not delay the onset of
BC (10)
. Treatment with IFN-
, on the other hand,
not only reduces the WBC count but also reduces the neoplastic, Ph+
cells (11
, 12) . Possible mechanisms of action by IFN-
include the reduction of tumor burden (11
, 12)
, through
the down-regulation of BCR/ABL mRNA and P210 (BCR/ABL) protein
(13)
, regulation of tumor necrosis factor-related
apoptosis-inducing ligand-mediated T-cell cytotoxicity
(14)
, suppression of the chemotactic protein IL-8
(15)
, induction of the inflammatory factors IL-1 receptor
antagonist (16)
and soluble receptor p55 of tumor necrosis
factor (17)
, and the regulation of the cytokine network by
suppressing Th2-like cytokine responses (18)
that are
capable of suppressing normal T-cell proliferation (19)
.
Although IFN-
is known to inhibit the growth of bone marrow
progenitors and to restore adherence properties to stroma in CML
(20
, 21)
, little is known of the effect of IFN-
therapy
on the synthesis of Th1 and Th2 cytokines by T cells. Because Th1 and
Th2 cytokines are important mediators of the host cellular immunity
(22)
, the contribution of individual T-cell subsets with
respect to cytokine synthesis warrants investigation. A shift from a
Th1 to a Th2 cytokine profile is widely accepted as a prognosticator of
disease progression in individuals with neoplasm (23
, 24)
or infection (25, 26, 27, 28)
.
We expected to find a Th2 cytokine profile in CML patients in Chronic
and ACC/BC phases of disease and a Th1 cytokine profile of patients in
complete cytogenetic remission after treatment with IFN-
.
Furthermore, we hypothesized that CCR patients would have a Th1
cytokine profile comparable with normal controls. To test this
hypothesis, we used a method of flow cytometry that permitted the
evaluation of Th1 and Th2 cytokine syntheses in the cytoplasm of CD4+
and CD8+ T cells of CML patients at different stages of disease and
compared their responses to patients who had achieved a CCR with
IFN-
therapy.
| MATERIALS AND METHODS |
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as their primary treatment or
chemotherapy at the M. D. Anderson Cancer Center were included in this
analysis. Treatment response criteria were defined previously
(29
, 30)
. BC was defined as >30% blasts in blood or bone
marrow; ACC phase consisted of patients with blasts
15% and
30%
or >30% blasts and promyelocytes and
20% basophils in the blood or
bone marrow; the Chronic or benign phase of CML comprised of all other
patients who did not fit the above clinical disease stages. Patients in
whom a CCR was induced with IFN-
were subdivided into Late-CCR and
Early-CCR. Late-CCR patients were those who had a continuous CCR for
>2 years and in whom IFN-
therapy was discontinued, whereas
Early-CCR patients had a remission duration of <2 years and required
maintenance IFN-
therapy.
|
Intracellular Cytokine Synthesis by T-Cell Subsets after Activation
with PMA
Each subject provided 5 ml of blood in EDTA (Vacutainer; Becton
Dickinson, San Jose, CA) for a complete blood count, leukocyte
differential analysis, and determination of lymphocyte phenotypes by
flow cytometry. Another 10 ml of blood in heparin was obtained for
cytokine studies. Informed consent was obtained from each subject with
approval for the study from the Human Experimentation Committee of the
University of Texas M. D. Anderson Cancer Center.
Activation of T Cells by PMA.
Blood samples from patients with a WBC count >15 x
103/µl were diluted to 15 x
103/µl to bring the WBC to within normal range.
Intracellular cytokine synthesis was conducted in three stages as
described previously (24)
. Briefly, 25 ng of PMA were
added to 1 ml of whole blood, and the mixture was incubated for 4 h at 37°C in the presence of 1 µg of ionomycin and 10 µg of
brefeldin-A [a nontoxic but potent inhibitor of intracellular
transport (31)
]. All reagents were purchased from Sigma
Chemical Co.(St. Louis, MO).
Staining of the Activated T cells.
The PMA-activated cells were stained for the presence of cytoplasmic
cytokines as described previously (24)
using a panel of
cytokine-specific monoclonal antibodies conjugated with PE to detect
one of the following cytokines: IL-2, IL-10, IFN-
, and TNF-
.
Additionally, samples were reacted with anti-CD8 monoclonal antibody
conjugated with FITC and anti-CD3 monoclonal antibody to delineate CD8+
and CD8- (or CD4+) T cells. The percentage of cells that expressed the
early activation antigen, CD69 (32)
, was indicative of
lymphocyte activation by PMA. All monoclonal antibody reagents except
for IL-10 were purchased from Becton Dickinson Immunocytometry Systems,
Inc. (Mountain View, CA); anti-IL-10 conjugated with PE was purchased
from Caltag (Burlingame, CA). Stained cell preparations were fixed in a
solution of 1% paraformaldehyde and analyzed immediately or stored at
4°C for analysis within 24 h.
Determination of Cytokines in the Cytoplasm of Activated T Cells by
Flow Cytometry
Cell preparations of PMA-activated cells were analyzed with the
FACSCalibur flow cytometer (Becton Dickinson) using the CellQuest
software. Briefly, 10,000 events were collected based on side scatter
and anti-CD3 reactivity. Immunoglobulin isotype controls were used to
verify the staining specificity of the anti-cytokine reagents and to
set markers delineating positive and negative populations. Cytokine
synthesis by the two T-cell subsets (CD3+/CD8+/CD4- and
CD3+/CD8-/CD4+) were measured based on the reactivity of the
lymphocytes with anti-CD8. Anti-CD69-PE was used to identify activated
T cells after exposure to PMA.
Statistical Analysis
The mean ± SE percentages of T-cell subsets synthesizing the
cytokines of interest were obtained for each sample. Data are presented
as histograms of the mean ± SE percentages of CD8+ and CD4+ T
cells/µl synthesizing a cytokine. Statistical differences between
study groups with respect to the percentages of T cells synthesizing
cytokines were determined by the Mann-Whitney test.
| RESULTS |
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Intracellular Synthesis of IL-2 by PMA-activated T Cells.
Mean ± SE percentage of CD8+ T cells synthesizing IL-2 in
response to stimulation with PMA is shown in Fig. 1A
. The mean percentages (±
SE) of CD8+ T cells producing IL-2 from normal controls (13.7% ±
1.5%) and CML patients in Early-CCR (11.7% ± 1.5%) or Late-CCR
(14.0% ± 2.5%) were similar. However, there was a significant
difference in the mean percentages of CD8+ T cells synthesizing IL-2
from normal controls and those of patients in Chronic (3.6% ± 1.3%)
and in ACC/BC (4.7% ± 2.3%) phases (P < 0.001).
Moreover, the mean percentages of IL-2-producing CD8+ T cells of
patients in Chronic and in ACC/BC phases were significantly lower than
those of Early-CCR and Late-CCR patients (P < 0.01).
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Intracellular Synthesis of IFN-
by PMA-activated T Cells.
The mean percentage ± SE of CD8+ T cells that synthesized IFN-
was greatest in normal controls (44.7% ± 3.5%) and followed in
descending order by patients in Late-CCR (30.5% ± 5.6%), in
Early-CCR (25.0% ± 3.3%), in ACC/BC (9.6% ± 2.9%), and in Chronic
phases (9.3% ± 2.9%), respectively (Fig. 2A)
. The percentages of CD8+ T
cells that synthesized IFN-
were significantly higher in normal
controls than in remission patients (P < 0.01).
However, patients in ACC/BC and in Chronic phase had significantly
lower percentages of CD8+ T cells that synthesized IFN-
compared
with normal controls and both remission groups (P <
0.01).
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production was seen in CD4+ T cells as with
CD8+ T cells. Normal controls had the greatest mean percentage of CD4+
T cells (25.8% ± 2.2%) that synthesized IFN-
, followed in
decreasing order by the patients in Late-CCR (24.7% ± 5.2%),
Early-CCR (16.2% ± 2.0%), Chronic phase (8.6%± 3.3%), and ACC/BC
(9.2% ± 2.6%), respectively (Fig. 2B)
were similar. On the other hand, patients in Early-CCR, in
ACC/BC, and in Chronic phases had significantly lower percentages of
CD4+ T cells that produced IFN-
than normal controls
(P < 0.001). There was a direct correlation between
IFN-
synthesis and disease progression because patients in Chronic
and in ACC/BC phases who had significantly lower percentages of CD4+ T
cells that synthesized IFN-
than patients in Early-CCR and Late-CCR
(P < 0.05).
Intracellular Synthesis of TNF-
by PMA-activated T Cells.
Similar mean ± SE percentages of CD8+ T cells synthesizing
TNF-
were found in normal controls (33.6% ± 9.3%) and patients in
Late-CCR (31.9% ± 6.9%) and Early-CCR (25.3% ± 3.2%; Fig. 3A
). Significantly lower
percentages of CD8+ T cells from patients in Chronic phase (6.8%±
2.6%) synthesized TNF-
compared with normal controls
(P < 0.004) and patients in Late-CCR
(P < 0.002) and Early-CCR (P <
0.001). Similarly, a significantly lower percentage of CD8+ T cells of
patients in ACC/BC phase (11.0% ± 3.6%) synthesized TNF-
compared
with normal controls (P < 0.02), Early-CCR
(P < 0.01), and Late-CCR patients (P < 0.05). There was no difference in TNF-
synthesis by CD8+ T cells
from patients with Chronic and ACC/BC phases.
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was seen
in normal controls (Fig. 3B)
than normal controls
(P < 0.02), Early-CCR (P < 0.001),
and Late-CCR (P < 0.02), respectively.
Synthesis of IL-10 by PMA-activated T Cells.
The means ± SE percentages of IL-10-producing CD8+ T cells in
Early-CCR (9.6% ± 1.5%), in Chronic (9.2% ± 4.0%), in ACC/BC
(8.0% ± 2.4%), in Late-CCR (7.9% ± 2.5%) patients, and in normal
controls (4.4% ± 1.5%) were similar (Fig. 4A)
. By contrast, a
statistically greater percentage of CD4+ T cells from patients in
Early-CCR (26.9% ± 3.4%; P < 0.003), Chronic
(23.1% ± 5.1%; P < 0.02), and ACC/BC (25.3% ±
5.0%; P < 0.03) phases synthesized IL-10 than CD4+ T
cells of normal controls (10.8% ± 5.1%; Fig. 4B
).
Late-CCR (12.9% ± 3.6%) patients and normal controls had similar
percentages of CD4+ T cells that synthesized IL-10. Late-CCR patients
also had a significantly smaller percentage of CD4+ T cells that
synthesized IL-10 than Early-CCR (P < 0.002) and
ACC/BC (P < 0.02) phase patients.
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| DISCUSSION |
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.
These observations are consistent with an earlier report from this
institution (33)
. The low percentage of peripheral T cells
in Chronic and in ACC/BC patients deterred earlier evaluation of Th1
and Th2 cytokine production by these cells. Recent technological
advancements make it possible to measure cytokine synthesis on a
single-cell basis in whole-blood cultures without the requisite of
isolating mononuclear cells (34)
. This experimental
approach permitted the measurement of Th1 and Th2 cytokine production
by T-cell subsets of CML patients in Chronic, ACC/BC, and CCR phases
with IFN-
therapy.
In preliminary studies, we were unable to detect constitutive
production of Th1 and Th2 cytokines in the cytoplasm of resting T cells
cultured for 16 h (data not shown). Upon short-term activation
with PMA, the percentages of CD4+ and CD8+ T cells from Chronic and
ACC/BC patients synthesizing the Th1 cytokines, IL-2 and IFN-
, were
significantly lower than the percentages of CD4+ and CD8+ T cells from
patients in Early-CCR and in Late-CCR and normal controls. The lower
percentage of Th1 cytokine-producing T cells of Chronic and ACC/BC
patients was not unexpected because these CML patients had circulating
leukemia cells that are known to preferentially secrete the Th2
cytokine IL-10 (19)
. IL-10 can suppress the production of
IL-2 and IFN-
(35
, 36)
and can affect the quality and
magnitude of the host immune response. Possible mechanisms by which
IL-10 mediates suppression of the immune response include the
inhibition of MHC class II-dependent antigen presentation
(37)
, T-cell proliferation, and IL-2 production (36
, 38)
. Among the lymphocytes evaluated, IL-10 was primarily
produced by the CD4+ T cells of Chronic, ACC/BC, and Early-CCR
patients, whereas the production of IL-10 in Late-CCR patients and
normal controls by CD4+ T cells was negligible. These results
strengthen our hypothesis that the increase in Th2-type cytokines and
in particular IL-10 is a direct correlate of disease progression, and a
shift from a Th2 to a Th1 cytokine profile is highly suggestive of
improvement in clinical status.
Because patients achieved a CCR with IFN-
therapy and sustained the
CCR without maintenance therapy for >2 years, the percentages of T
cells producing Th1 cytokines increased to levels characteristic of
normal controls. The synthesis of Th1 by T cells in remission was
accompanied by normalization in the percentage and number of T cells.
Preferential syntheses of IL-2 by CD4+ T cells and IFN-
by CD8+ T
cells are desirable for leukemia-specific CTL responses in CML patients
(39)
because IL-2 is needed for the proliferation of the
CTLs (40)
, and both IFN-
and TNF-
are essential for
cytotoxic activity (41
, 42)
. The T cells of Late-CCR
patients and normal donors were equally capable of Th1 cytokine
synthesis, and these data suggested restoration of normal T-cell
function in Late-CCR patients. Furthermore, IFN-
can increase the
frequency of IFN-
-producing human CD4+ T cells and ablate the
suppressive effect of IL-4 on IFN-
production (43)
.
In the current study, significantly higher percentages of CD4+
and CD8+ T cells from patients in Early-CCR and Late-CCR and normal
controls synthesized TNF-
compared with the percentages of CD4+ and
CD8+ T cells from CML patients in the Chronic and in ACC/BC phases of
CML. TNF-
exerts both stimulatory and inhibitory control on
hematopoiesis in vitro, depending on the conditions of the
cell culture, making the role of TNF-
in CML ambivalent
(44, 45, 46, 47, 48, 49)
. Because high levels of TNF-
receptors were
found in leukemic cells (50)
, it is tempting to suggest
that the higher percentage of TNF-
-producing T cells in remission
CML patients may contribute to the elimination of leukemic cells.
Furthermore, others have identified CD8+ T cells with Th1 cytokines,
IFN-
and TNF-
, to be the classical CTLs (51)
capable
of producing perforin and granzyme, molecules needed for an effective
cytotoxic response. Although we have shown that the synthesis of
cytokines necessary for an effective cytotoxic response are restored in
T cells of CML patients in CCR, further investigation is warranted to
determine whether these T cells actually elicit effective cytotoxic
activities.
To appreciate the inverse relationship between the syntheses of
Th1 and Th2 cytokines by T cells from CML patients, the data can be
examined as a ratio of T cells producing Th1 cytokine to that of T
cells producing IL-10. In active CML disease, the number of lymphocytes
were significantly outnumbered by leukemic myeloid cells that are known
to produce Th2 cytokines (19)
, thereby suppressing Th1
responses and diminishing the ability of T cells to mount an effective
host defense. When patients achieved a durable CCR of >2 years without
maintenance IFN-
therapy, the ratio of Th1- to Th2-producing cells
was comparable with that of normal controls. The switch from a Th2 to a
Th1 cytokine profile is less apparent in Early-CCR patients; however,
because these patients are more a heterogeneous group of individuals
with clinical responses to IFN-
of varying lengths of time, there is
a higher level of residual leukemic cells (52)
and a
higher incidence of
relapse3
compared
with Late-CCR. However, when patients achieved a Late-CCR with
IFN-
, the imbalance in myeloid and lymphoid cells was reversed and
resulted in a reduction in myeloid cells capable of producing Th2
cytokines. Upon antigenic stimulation of Th0 cells from CCR patients,
the expansion of Th1 effector cells would be favored. Thus, IFN-
can
be an effective therapeutic agent against CML by suppressing Th2
cytokine responses of leukemia cells and by restoring Th1 cytokine
synthesis by T cells of patients in CCR. Whether the restoration of Th1
cytokine responses in CML patients achieving CCR is unique to IFN-
therapy or can be obtained with other forms of therapy that induce CCR
in CML patients awaits further investigation.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 To whom requests for reprints should be
addressed, at Division of Pathology and Laboratory Medicine, Box 7, The
University of Texas M. D. Anderson Cancer Center, 1515 Holcombe
Boulevard, Houston, TX 77030. Phone: (713) 792-3559; Fax:
(713) 792-4296; E-mail: jreuben{at}mdanderson.org ![]()
2 The abbreviations used are: CML, chronic
myelogenous leukemia; ACC, accelerated (phase of CML); BC, blast
crisis; IL, interleukin; CCR, complete cytogenetic remission; Late-CCR,
long-term remissions; Early-CCR, early remissions; PMA, phorbol
12-myristate 13-acetate; PE, phycoerythrin; TNF, tumor necrosis
factor. ![]()
3 M. Talpaz, unpublished data. ![]()
Received 12/19/99; revised 2/11/00; accepted 2/11/00.
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