|
|
||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Department of Experimental Oncology, Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy
| Abstract |
|---|
|
|
|---|
knockout (KO), but not from IL-4 KO, mice cured lung
metastases, thus indicating that IL-4 produced by Tc2 cells was
instrumental for tumor rejection. The antitumor effect of adoptively
transferred Tc2 lymphocytes needed host CD8 T cells and AsGM1 leukocyte
populations, and partially granulocytes. These data indicate that Tc2
CD8+ T cells exert immunoregulatory functions and induce
tumor rejection through the cooperation of bystander lymphoid effector
cells. Tumor eradication is thus not restricted to a type 1 response,
but can also be mediated by a type 2 biased T cell
response. | Introduction |
|---|
|
|
|---|
IL-4, initially known as B cell stimulatory factor (2), has a pivotal role in conditioning type 2 T cell differentiation (3) leading to IgG1 and IgE isotype switching. In several studies, IL-4 showed in vivo tumor growth inhibition through a strong inflammatory effect associated with local recruitment of granulocytes, macrophages, T lymphocytes, and dendritic cells (4, 5, 6, 7). Tumor rejection required polymorphonuclear cells, either eosinophils (8) or neutrophils (9), whereas the role of CD8 T cells remains controversial, since they have been found necessary in one study (6) but not in others (5, 10). IL-4-releasing tumor cell vaccines showed efficacy when used in preclinical therapeutic setting (5, 11), and pilot studies in cancer patients have been proposed (12, 13) and conducted (51).
The aim of this study was to test whether type 2 antitumor CD8 T cells
are activated by IL-4-producing tumor cell vaccines and thus studying
the mechanism by which they provoke tumor eradication. The colon
carcinoma C26/IL-4/FR
cells, engineered to produce IL-4 and to
express the human folate receptor
(FR
)3 as a model
Ag, were irradiated and used to treat mice bearing C26/FR
pulmonary
metastases. We have recently shown that vaccination with C26/IL-4/FR
elicits a strong anti-FR
IgG1 response that is not correlated
with the therapeutic outcome, thus suggesting that mechanisms other
than the Ab response should be implicated (14). We show
here that treatment with IL-4 vaccine induces noncytotoxic
CD8+ T cells producing type 2 cytokines able to
induce tumor rejection through interaction with host
CD8+, ASGm1+, and
GR-1+ cells.
| Materials and Methods |
|---|
|
|
|---|
Eight- to ten-week-old female BALB/c mice were purchased from
Charles River (Calco, Italy); BALB/c IL-4 knockout (KO) and BALB/c
IFN-
KO mice were from The Jackson Laboratory (Bar Harbor, ME). Mice
were maintained and treated in compliance with institutional
guidelines.
Immunotherapy by vaccinations with IL-4-producing C26/FR
cells
C26/FR
, C26/IL-4/FR
, and C26/IL-12/FR
cells producing
murine IL-4 or IL-12 and expressing human FR
were obtained by
retroviral transduction, as described (14). For
immunotherapy experiments, lung metastases were induced by the i.v.
injection of 104 C26/FR
cells, and mice were
vaccinated on days 3, 6, 9, and 13, by injecting s.c. 3 x
106 15,000 rad irradiated C26/IL-4/FR
cells,
producing 2030 ng/ml IL-4 (106 cells/ml/48 h).
CD4 and CD8 cell depletion was conducted by treating mice, on day 1 and
every 2 wk thereafter, with mAbs (0.5 mg, i.p.) obtained from the
hybridomas GK 1.5 and 2.43, respectively. For survival, follow-up mice
were euthanized when showing dyspnea; survivors were shown to be
tumor-free. Lymphocytes were collected from vaccinated mice 57 days
after last vaccination.
Adoptive transfer assay
Recipient mice (510 mice/group) were i.v. injected with
7.5 x 104 C26/FR
cells to induce lung
metastases and treated on the following day by i.v. injection of fresh
spleen cells (3.5 x 107) obtained from
donors vaccinated with C26/IL-4/FR
tumor cells, as detailed above,
and treated with anti-CD4 mAb 34 days previously.
CD8+ lymphocytes were enriched by elution on
nylon wool columns (Wako Chemicals, Dusseldorf, Germany), and 5 x
106 lymphocytes were transferred. The transferred
population was shown to be 8595% CD8+ by flow
cytometric analysis. Recipient mice were sacrificed 2 wk after
lymphocyte transfer, and the number of superficial lung metastases was
counted after lung insufflation, as previously described
(14). Recipient mice were depleted of lymphoid
subpopulations by treatment with specific mAbs. T cell depletion was
obtained by surgical thymectomy at 1 mo of age, followed by treatment
with anti-CD4 and/or anti-CD8 1 wk before the beginning of the
experiment. Treatment with anti-AsialoGM1 rabbit antiserum (Wako
Chemicals) and with anti-granulocyte mAb (RB6-8C5 hybridoma) was
given 3 days before and on the day of lymphocyte transfer, at the dose
of 10 µl and 0.5 mg, respectively. Ablating treatments were checked
by FACS analysis and functional assays to verify target leukocyte
depletion. Hybridomas were obtained from (American Type Culture
Collection, Manassas, VA); mAbs were purified by using a commercial kit
(E-Z-SEP; Amersham Pharmacia Biotech., Uppsala, Sweden).
Cytokine production
Lymphocytes obtained from mice vaccinated with C26/IL-4/FR
or
with C26/IL-12/FR
cells were restimulated in mixed lymphocyte tumor
cell cultures (MLTC) with C26/FR
irradiated cells for 6 days, as
described (15). CD4+ and
CD8+ cells were then positively selected by
paramagnetic beads conjugated with anti-CD8a mAb (Miltenyi Biotec,
Bergish Gladbach, Germany) and tested for cytokine production by
culturing lymphocytes (105/well) in 96-well
flat-bottom plates precoated or not with 0.5 µg/well of anti-CD3
mAb (145-2C11 hybridoma) at 37°C for 20 h. Supernatants were
assayed for cytokine content by specific ELISAs (PharMingen, San
Diego, CA).
Cell-mediated cytotoxicity and precursor (p) CTL determination in limiting dilution analysis (LDA) assay
CTL response was assessed in a standard 4-h
51Cr-release assay after 6 days MLTC, as
described (15). For LDA, lymphocytes were serially 1:2
diluted (from 8 x 104/well to 500/well) and
cultured with 15,000 rad irradiated C26/FR
cells (5 x
103/well), 2000 rad irradiated syngeneic
splenocytes as feeder cells (5 x 105/well),
and 50 U/ml rhIL-2 (Chiron-Italia, Milan, Italy), in 32 identical
replicates, in 96 U-well plates for 10 days.
51Cr-release assays were performed with
103 target cells/well. Specificity for C26/FR
was evaluated by testing replica plates with unrelated target cells.
Values of lysis exceeding three times the SD of the mean spontaneous
release were used as a threshold for scoring positive cytolysis.
Calculation of the frequencies from limiting dilution data was done as
previously described (16). The same method was used for
calculation of frequencies of IL-4 and IFN-
-producing precursors; in
this case, after 18 h of incubation with unlabeled target cells,
supernatants were tested for cytokine content by specific ELISA. The
experiments were conducted by directly comparing lymphocytes from mice
treated with IL-4 vaccine or with IL-12 vaccine.
Flow cytometry for cytokines
Lymphocytes from MLTC were cultured for 18 h with
immobilized anti-CD3 mAb and 10 µg/ml brefeldin A added for the
last 2 h (Sigma, Milan, Italy). Cells were suspended in PBS
containing 1% FCS, fixed with paraformaldehyde 4% for 20 min at room
temperature, and permeabilized with saponin buffer containing saponin
0.5% and 0.1% NaN3 (Sigma) for 10 min. For
triple staining, FITC-labeled anti-IFN-
, PE anti-IL-4, and
CyChrome anti-CD4 mAbs were used; for double staining, purified
CD8+ cells were labeled with FITC anti-CD8,
PE anti-IL-4, and PE anti-IFN-
. Isotype-matched conjugated
mAbs were used for background determination. All mAbs were purchased
from PharMingen. Cytofluorometric analysis was performed with a FACScan
(Becton Dickinson, Mountain View, CA). mAbs dilutions were established
by preliminary dose/response experiments, and 50,000 events were
acquired.
| Results |
|---|
|
|
|---|
Active immunotherapy with C26/FR
cells engineered to produce
IL-4 increased survival and cured 33% of mice bearing C26/FR
lung
metastases (Fig. 1
, and Ref.
14). The therapeutic effect was dependent on host T cells,
since it was abrogated in mice depleted of CD4 or CD8 T cells by in
vivo treatment with specific mAbs (Fig. 1
).
|
vaccination induces type 2 T cell polarization
We analyzed the type of T cell response activated by vaccinations
with C26/IL-4/FR
cells by assessing cytokine production by ELISA and
by flow cytometry. Splenic lymphocytes obtained 57 days after the
course of vaccinations were restimulated in MLTC with C26/FR
cells
for 6 days; CD4+ and CD8+ T
cells were then purified and cytokine production examined after
stimulation with anti-CD3 mAb for 18 h. The pattern of
cytokines produced by either CD4+ (Fig. 2
, upper panel) or
CD8+ lymphocyte subsets (Fig. 2
, lower
panel) indicated that treatment with an IL-4-releasing cell
vaccine induced polarization toward the type 2 phenotype in both
CD4+ and CD8+ T cells. In
fact, IL-4, IL-5, and IL-10 were measured at higher levels and IFN-
at lower quantity, compared with T cells from mice vaccinated with
C26/FR
cells engineered to produce IL-12, included in this analysis
as a control of type 1 T cell activation (15, 16, 17). The
analysis of cytokines produced by T cells from lymph nodes draining the
vaccination site showed similar results (data not shown).
|
in
IL-4-vaccinated mice (Fig. 3
were expressed by distinct cells in IL-4-vaccinated mice.
Similarly, in CD8+ T lymphocytes, the frequency
of IL-4-producing cells was higher than that of IFN-
-producing cells
(Fig. 3
|
Type 2 CD8+ T cells activated by
C26/IL-4/FR
vaccine were tested for CTL activity against the tumor.
Absence or low levels of C26/FR
tumor cell lysis were detected in
short-term cytotoxicity assays (Fig. 4
),
a result confirmed by testing the frequencies of anti-C26/FR
pCTL in LDA assays. In fact, the frequencies of pCTL against C26/FR
in IL-4-vaccinated mice were shown to be 5- to 10-fold lower than in
lymphocytes from IL-12-vaccinated mice in three different assays (Table I
).
|
|
was 1/1700,
whereas the frequency of those producing IFN-
was 1/20,345; in the
same experiment, lymphocytes from IL-12-vaccinated mice showed a
frequency of 1/207,597 and 1/6006 cells producing IL-4 and IFN-
,
respectively (Table INoncytotoxic type 2 CD8 are endowed with in vivo antitumor capacity
To test whether type 2 CD8+ T cells
(Tc2) may induce tumor rejection, splenic
lymphocytes from C26/IL-4/FR
-vaccinated mice were depleted of CD4
cells, and CD8+ lymphocytes were purified or not
before being adoptively transferred into syngeneic recipients bearing
C26/FR
lung metastases. Two weeks after lymphocyte transfer,
recipient mice were sacrificed to count superficial lung metastatic
nodules. Splenocytes depleted of the CD4 T cell population from
IL-4-vaccinated mice completely eliminated lung metastases (mean number
of metastases, 1.6 ± 0.7), whereas lymphocytes from C26/FR
tumor-bearing or from naive donors did not affect the number of
metastatic nodules compared with untreated controls (169 ± 38,
139 ± 39, and 147 ± 46). The transfer of
CD8+ cells, purified from the CD4-depleted
splenocytes, determined >85% reduction of metastases (24 ± 7),
while lymphocytes from vaccinated donors depleted of both CD4 and CD8
cells induced 60% reduction of lung metastases (52 ± 13) (Fig. 5
A). These data indicated that
adoptively transferred Tc2 cells can eliminate lung metastases, and
that their therapeutic activity is enhanced by coadministration of
uncharacterized splenocyte populations not belonging to
CD4+ cells.
|
vaccination of IL-4 KO mice induced
CD8+ T cells producing the same level of IFN-
than the wild-type vaccinated counterparts, but no IL-4 in response to
stimulation with C26/FR
tumor cells (data not shown). The transfer
of IL-4 KO-purified CD8+ T cells was ineffective
(Fig. 5
KO-vaccinated donors
significantly reduced the number of metastases, thus ruling out an
effect of IFN-
-producing CD8+ cells within the
Tc2 population in the rejection of metastases (Fig. 5Tc2 lymphocytes eliminate metastases by interacting with host CD8 T cells, NK cells, and granulocytes
To investigate the host lymphoid effectors enrolled in the
mechanism of tumor rejection, recipient mice were depleted of different
leukocyte populations by treatment with specific mAbs before lymphocyte
transfer. When recipients were depleted of CD8 T cells or of
AsGM1-positive cells, the eradication of metastases was abolished,
supporting a fundamental role of host CD8 and NK cells that are likely
activated by transferred Tc2 cells, to eliminate lung metastases. Also,
granulocyte depletion reduced the antimetastatic effect, whereas
depletion of CD4 cells did not change the therapeutic effect of
adoptively transferred Tc2 lymphocytes (Fig. 6
). Thus, Tc2 lymphocytes eradicated lung
metastases through the cooperation of bystander host CD8 T cells, NK
cells, and granulocytes, but not CD4 lymphocytes.
|
| Discussion |
|---|
|
|
|---|
or of IL-4 (18, 19). The IFN-
or IL-4 conditioned cytokine milieu in which
primary Ag stimulation takes place has a major role in directing the
differentiation of CD8 T cells from naive T lymphocytes into either
type 1 or type 2 effectors (20, 21, 22, 23). Tc2 have also been
isolated from PBL and mucosal tissues (24, 25) in healthy
individuals and during infectious diseases (26, 27). Tc2
are cytotoxic in some systems (20, 22) but not in others
(28, 29), can provide B cell help (29),
induce delayed-type hypersensitivity reactions (30), and
their type 2 phenotype is maintained in memory responses (22, 23). Although one of the first reports showing IL-4 production
by CD8 lymphocytes dealt with tumor immune mice (31), no
data are available about the presence and function of tumor-specific
Tc2 cells. For this reason, after Tc2 cells were detected in mice
treated with IL-4 vaccine, the present study was focused on the
assessment of their antitumor potential.
Tc2 cells activated in mice treated with IL-4-vaccine were poorly
cytolytic. When purified from MLTC and stimulated by anti-CD3 mAb,
CD8+ cells from mice treated with IL-4 vaccine
were shown to produce IL-4, IL-5, and IL-10, while IFN-
was measured
at lower quantities as compared with lymphocytes obtained from mice
treated with the IL-12-producing vaccine. In addition, TNF-
and
GM-CSF were released at levels similar between the two groups (data not
shown). Intracellular immunostaining directly demonstrated the presence
of IL-4-producing CD8+ cells. However, the
general poor staining of intracellular IL-4 (32), did not
allow to obtain a trustworthy quantitative data about the frequency of
IL-4-producing CD8+ cells in lymphocytes from
mice treated with IL-4 vaccine. To solve this difficulty, we set up LDA
experiments that showed frequencies of IL-4-producing, tumor-specific
CD8 lymphocytes 10-fold higher than that of IFN-
-producing cells and
20-fold higher than that of cytotoxic pCTL.
The adoptive transfer of enriched CD8+ cells from
mice vaccinated with C26/IL-4/FR
cells in mice bearing C26/FR
lung metastases resulted in an 80100% reduction in the number of
tumor nodules in four different experiments. Noncytolytic CD8
lymphocytes obtained from tumor infiltrate (TIL), as well as CD4 Th
cells, have been reported to eradicate tumors upon adoptive transfer
through their release of cytokines in different murine models
(33, 34, 35, 36) and in a recent pilot trial (37).
Although the production of type 2 cytokines has not been evaluated in
TILs (38, 39), the ability of a Th2-type CD4 T cell clone
to initiate tumor eradication has been reported (40).
Our data underline a direct relationship between IL-4 production and
the rejection of metastases. Tc2-secreted IL-4 may act through the
enhancement of cytotoxicity of host CD8 T cells (41) and
by activating eosinophils and basophils, in concert with IL-5
(42). In addition, the released TNF-
may synergize with
IL-4 in activating endothelial cells, thus increasing vascular
permeability and facilitating leukocyte infiltration, and by induction
of NK cell activation (43). Moreover, IL-10 has a
chemoattracting effect on CD8 T cells (44).
Depletion experiments clearly showed the participation of host CD8 T cells, asialoGM1-positive lymphocytes, and granulocytes in the process of metastases rejection. Although asialoGM1 is not expressed only on NK cells but also on a subset of CD8 T cells, these data indicate that all the mentioned leukocyte populations participate in the reduction of metastases.
The antitumor activity of Tc2 cells in adoptive immunotherapy can be
potentiated by other donor leukocyte populations. In fact, injection of
35 x 106 spleen cells depleted of CD4
lymphocytes reduced the number of metastases to a greater extent
compared with injection of 5 x 106 purified
CD8+ cells, the estimated
CD8+ content of such splenocytes (Fig. 6
A). Whether antitumor Ab-producing B cells, activated
macrophages, or granulocytes play the major role in this phenomenon
remains to be determined. Whether Tc2 are endowed with antitumor
activity similar to that of Tc1 cells was not evaluated in the present
study. When tested in parallel, CD8+ lymphocytes
obtained from mice treated with IL-4 vaccine or with IL-12 vaccine
reduced metastases to the same extent upon adoptive transfer (data not
shown). However, in the studied tumor model, IL-12-releasing vaccine
showed a superior therapeutic effect compared with IL-4 vaccine
treatment, probably because of the activation of a stronger Ab response
(14). Mice cured after either vaccine treatment were
immune to a subsequent tumor challenge injection, and either Tc2 or Tc1
CD8+ cells were shown when the memory response
was assayed in vitro (data not shown).
The data presented here have a number of important implications for
tumor immunotherapy. First, they indicate Tc2 cells as a new lymphocyte
population endowed with antitumor potential. Second, they highlight the
independence from a strict type 1 response for immune tumor rejection.
The T1/T2 paradigm implicated that cytokines produced by T1 cells being
primarily associated with cell-mediated immune response would augment T
cell response against tumors, whereas type 2 cytokines, like IL-4 and
IL-10, were considered immunosuppressive and therefore inhibiting
antitumor responses (45). Recent reports suggest that the
T1/T2 paradigm is not predictive of whether a particular pathway is
protective or not (46, 47). In addition, the requirement
for both IL-4 and IFN-
-dependent responses for obtaining B16
melanoma rejection in immune mice has been demonstrated
(48). The data shown here would argue for the
inconsistency of T1/T2 paradigm in immune response against tumors.
Finally, our data suggest that activation of cytokine-producing
tumor-specific T cells, not only IFN-
but also IL-4, might be a
useful indicator for the immunological follow-up of cancer patients
treated with active immunotherapy. To date, the major effort in
monitoring vaccination trials has focused on the detection of antitumor
CTL, though several preclinical and clinical studies had shown that CTL
activation is not correlated with the clinical response (16, 49, 50). The activation of noncytotoxic Tc2 cells should be
evaluated in patients treated with tumor vaccines producing
IL-4.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 Address correspondence and reprint requests to Dr. Monica Rodolfo, Experimental Oncology D, Istituto Nazionale Tumori, via Venezian, 1 I-20133 Milan, Italy. E-mail address: ![]()
3 Abbreviations used in this paper: FR
, folate receptor
; KO, knockout; MLTC, mixed lymphocytes tumor cell culture; LDA, limiting dilution analysis; Tc2, type 2 CD8+ T cells. ![]()
Received for publication March 15, 1999. Accepted for publication June 9, 1999.
| References |
|---|
|
|
|---|
. Proc. Natl. Acad. Sci. USA 90:2774.
, GM-CSF, and
-IFN gene or admixed with conventional adjuvants. Cancer Res. 54:6022.
and IL-5. J. Immunol. 145:68.[Abstract]
and IL-4 in acute graft-versus host disease after allogeneic bone marrow tranplantation in mice. J. Clin. Invest. 102:1742.[Medline]
This article has been cited by other articles:
![]() |
Z. Li, F. Pradera, T. Kammertoens, B. Li, S. Liu, and Z. Qin Cross-Talk between T Cells and Innate Immune Cells Is Crucial for IFN-{gamma}-Dependent Tumor Rejection J. Immunol., August 1, 2007; 179(3): 1568 - 1576. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Olver, P. Groves, K. Buttigieg, E. S. Morris, M. L. Janas, A. Kelso, and N. Kienzle Tumor-Derived Interleukin-4 Reduces Tumor Clearance and Deviates the Cytokine and Granzyme Profile of Tumor-Induced CD8+ T Cells Cancer Res., January 1, 2006; 66(1): 571 - 580. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. Kuwashima, F. Nishimura, J. Eguchi, H. Sato, M. Hatano, T. Tsugawa, T. Sakaida, J. E. Dusak, W. K. Fellows-Mayle, G. D. Papworth, et al. Delivery of Dendritic Cells Engineered to Secrete IFN-{alpha} into Central Nervous System Tumors Enhances the Efficacy of Peripheral Tumor Cell Vaccines: Dependence on Apoptotic Pathways J. Immunol., August 15, 2005; 175(4): 2730 - 2740. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Eguchi, N. Kuwashima, M. Hatano, F. Nishimura, J. E. Dusak, W. J. Storkus, and H. Okada IL-4-Transfected Tumor Cell Vaccines Activate Tumor-Infiltrating Dendritic Cells and Promote Type-1 Immunity J. Immunol., June 1, 2005; 174(11): 7194 - 7201. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Gillessen, Y. N. Naumov, E. E. S. Nieuwenhuis, M. A. Exley, F. S. Lee, N. Mach, A. D. Luster, R. S. Blumberg, M. Taniguchi, S. P. Balk, et al. CD1d-restricted T cells regulate dendritic cell function and antitumor immunity in a granulocyte-macrophage colony-stimulating factor-dependent fashion PNAS, July 22, 2003; 100(15): 8874 - 8879. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. M. M. Kelley, B. G. Rowan, and M. Ratnam Modulation of the Folate Receptor {alpha} Gene by the Estrogen Receptor: Mechanism and Implications in Tumor Targeting Cancer Res., June 1, 2003; 63(11): 2820 - 2828. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. Hao, H. Qi, and M. Ratnam Modulation of the folate receptor type {beta} gene by coordinate actions of retinoic acid receptors at activator Sp1/ets and repressor AP-1 sites Blood, June 1, 2003; 101(11): 4551 - 4560. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Koido, Y. Tanaka, D. Chen, D. Kufe, and J. Gong The Kinetics of In Vivo Priming of CD4 and CD8 T Cells by Dendritic/Tumor Fusion Cells in MUC1-Transgenic Mice J. Immunol., March 1, 2002; 168(5): 2111 - 2117. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. A. Kemp and F. Ronchese Tumor-Specific Tc1, But Not Tc2, Cells Deliver Protective Antitumor Immunity J. Immunol., December 1, 2001; 167(11): 6497 - 6502. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. J. Dobrzanski, J. B. Reome, and R. W. Dutton Role of Effector Cell-Derived IL-4, IL-5, and Perforin in Early and Late Stages of Type 2 CD8 Effector Cell-Mediated Tumor Rejection J. Immunol., July 1, 2001; 167(1): 424 - 434. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. Winter, H.-M. Hu, K. McClain, W. J. Urba, and B. A. Fox Immunotherapy of Melanoma: A Dichotomy in the Requirement for IFN-{{gamma}} in Vaccine-Induced Antitumor Immunity Versus Adoptive Immunotherapy J. Immunol., June 15, 2001; 166(12): 7370 - 7380. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |