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CUTTING EDGE |
,

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Laboratoire dImmunologie Cellulaire, Unité Mixte de Recherche 7627, Centre National de la Recherche Scientifique Bâtiment CERVI, Hôpital Pitié-Salpétrière, Paris, France;
Unité Mixte de Recherche 146, Centre National de la Recherche Scientifique, Institut Curie, Orsay, France;
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138;
Biomedical Research Centre, University of British Columbia, Vancouver, BC, Canada; and
¶
Theodor Kocher Institute, University of Bern, Bern, Switzerland
| Abstract |
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| Introduction |
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Activated CD8+ HIV-specific CTLs were also shown to produce
chemokines that may contribute to the overall HIV-suppressing activity.
First, they were shown to compete for HIV coreceptor usage. More
recently, we and others (6, 7) have demonstrated that chemokines also
influence CD8 HIV-specific immune responses. In addition, it was shown
that SDF-1 (stromal cell-derived factor-1) chemokine could increase
TNF-
/TNFRII expression through CXCR-4 (8), questioning to what
extend programmed cell death may depend upon a chemokine receptor
ligation, particularly in HIV disease.
Because we have previously shown that RANTES enhances the HIV-specific cytotoxicity of CD8+ T cells (6), we have investigated the effect of this CC chemokine on both cytotoxicity pathways using HIV-specific MHC class I-restricted CTL lines established from infected individuals. Our data show that RANTES regulates FasL expression on HIV-specific CD8+ T cells that kill through the Fas/FasL pathway.
| Materials and Methods |
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Eight individuals with a CD4 count ranging between 200 and 500/µl and no history of antiretroviral therapy were chosen as donors of PBMCs used to establish HIV-specific CTL lines (6).
Generation of HIV-1-specific and allogeneic CTL lines
PBMCs were isolated from venous blood of HIV-infected individuals by centrifugation over Ficoll-Hypaque density gradients (Eurobio, Les Ulis, France) and were activated overnight with irradiated PHA-stimulated (Murex, Dartford, U.K.) autologous PBMCs. Polyspecific CTL lines were generated by coculture with irradiated autologous PHA blasts in the presence of IL-2 (Boehringer Mannheim, Mannheim, Germany) and were used for the cytotoxicity assays after 20 days (6). CD8+ T cells accounted for >90% of the total. Allogeneic CTL lines were generated by culturing PBMCs from HIV seropositive individuals with irradiated allogeneic PHA blasts of healthy seronegative donors in the presence of IL-2. At day 21, CD8+ allogeneic CTLs were positively selected with anti-CD8-conjugated magnetic beads (5 beads/CD8+ cell; Dynal, Oslo, Norway). CD8+ T cells accounted for >95% of the preparation, and no NK cells were detected. Allogeneic specificity was assessed at days 11 and 21 using the appropriate PHA blasts and PHA blasts from control donors as target cells.
Cytotoxicity assays
HIV-specific CTL activity was tested against autologous EBV-transformed lymphoblastoid B cell lines (B-LCL) that were established from each CTL donor (6). The B-LCL were infected with wild-type vaccinia virus or with vaccinia virus expressing the HIVLAI proteins Gag, Pol, or Env (Transgene, Strasbourg, France) at a multiplicity of infection of 5 PFU/cell for 18 h at 37°C. They were then labeled for 2 h at 37°C with Na251CrO2 (100 µCi/106 cells; Amersham, Les Ulis, France) and washed twice with culture medium. The 51Cr-labeled target cells (4 x 103/well) were distributed in round-bottom 96-well microtiter plates (Dutcher, Brumath, France), and effector cells were added at E:T ratios ranging between 120:1 and 3:1. The plates were centrifuged and incubated for 4 h at 37°C. The supernatants were then harvested, and 51Cr release was measured in a gamma counter. Spontaneous 51Cr release values ranged between 10 and 20% of the total incorporated radioactivity. Relative, specific 51Cr release was calculated as described (9). All experiments were performed in triplicate. If not stated otherwise, the results are presented after subtraction of the lysis obtained with control targets. Standard error of triplicates was always <5% of the mean value and was omitted for clarity. NK activity was tested with freshly isolated PBMCs from healthy donors using K562 cells as target. The conditions for chromium release assays were the same as for the CTL assays.
RT-PCR analysis
Total RNA was isolated (9), and cDNA products were obtained from
1 µg of total RNA treated with DNase I (Promega, Charbonnière,
France) using the First Strand Synthesis kit (Pharmacia Biotech, Orsay,
France). To estimate transcript expression, cDNA products were
amplified by PCR for 35 cycles using the FasL primer set,
5'-CGACTCTTCCACCTGCAGAAGG-3' and 5'-AGATTCCTCAAAATTGATCAGAGAGAG-3';
the perforin primer set, 5'-CCTAAGCCCACCAGCAATGTG-3' and
5'-GGTGGAGGCGTTGGGAAGTG-3'; and the CCR3 primer set,
5'-ATGACAACCTCACTAGATACAG-3' and 5'-AACACAATAGAGAGTTCC-3'.
One-sixteenth of the cDNA products was amplified by PCR for 30 cycles
in the presence of 1 µM [
-33P]dCTP (10 mCi/mM, NEN
Life Science Products, Le Blanc Mesnil, France) to detect G3PDH
transcripts. The reaction products were detected by autoradiography
after electrophoresis on 4% nondenaturing polyacrylamide gels and were
quantified in a PhosphorImager (Pharmacia Biotech).
Flow cytometry
Cell surface expression of FasL was assessed on CTLs using the anti-FasL FITC-conjugate clone H11 (Alexis, Paris, France) or anti-FasL (IgG2a, NOK-1) (PharMingen, San Diego, CA). For direct fluorescence analysis, 5 x 105 cells were incubated with 5 µg anti-FasL at 4°C for 30 min, washed with PBS, fixed with 1% paraformaldehyde in PBS, and analyzed in a FACScan flow cytometer (Becton Dickinson, San Jose, CA). For each sample, 105 events were collected and analyzed using the Cellquest software (Becton Dickinson). In staining by PharMingen mAb, CTLs were first incubated with 5 µg/ml anti-FasL at 4°C for 30 min, washed, and then incubated with 5 µg/ml FITC-goat anti-IgG2a (Tebu, Santa Cruz, CA).
Reagents
RANTES and eotaxin were prepared by chemical synthesis (10). They were added to the assays at the time of mixing effector and target cells. The following neutralizing mAbs were used: anti-RANTES (R&D Systems, Minneapolis, MN), anti-CCR3 (7B11; kindly provided by LeukoSite, Cambridge, MA), anti-Fas (clone ZB4; Immunotech, Marseille, France), anti-FasL FITC-conjugate clone H11 (Alexis), or anti-FasL (IgG2a, NOK-1; PharMingen). Pretreatment of effector or target cells was done with 1 µg/ml Ab in RPMI 1640 containing 10% FCS for 1 h at 37°C without washing to assure neutralizing activity during the cytotoxicity assay. Concanamycin A (CMA; Fluka, Saint-Quentin Fallavier, France) was used as inhibitor of perforin-dependent cytotoxicity (11, 12). Effector cells were preincubated with CMA 90 min before mixing with the target cells.
| Results and Discussion |
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The effect of RANTES and of its neutralizing Ab was studied on
different effectors CD8 T cells using Fas/FasL or perforin-dependent
cytolytic pathway. We first examined HIV-specific MHC class
I-restricted CTL lines that were generated from PBMCs of HIV-infected
donors. They were shown to kill through Fas/FasL cytolytic pathway,
because their specific lysis was inhibited by anti-FasL
neutralizing Ab, but not by CMA (13), a selective inhibitor blocking
only the perforin-based cytotoxicity (Fig. 1
, top panel). The
cytotoxic activity of HIV-specific CTLs was also abrogated when the
autologous B-LCL, which were used as targets, were pretreated with an
anti-Fas neutralizing Ab, confirming that the killing occurred
through the Fas/FasL pathway (data not shown). Interestingly the
HIV-specific lysis mediated by these PBMC-derived Fas/FasL-dependent
effector T cells was markedly enhanced by RANTES and suppressed by
anti-RANTES or anti-CCR3 mAbs (Fig. 1
, top panel).
We then studied the effect of RANTES on perforin-dependent allogeneic
CTLs and NK cells (Fig. 1
, middle and bottom
panels). The cytotoxicity of these effector cells was abrogated in
presence of CMA but was not influenced by anti-FasL. In this
context, addition of RANTES, anti-RANTES, or anti-CCR3 does not
affect the specific killing.
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The data presented in Figs. 1
and 2
demonstrate that the killing
by RANTES-dependent HIV-specific CTLs is mediated by the Fas/FasL
pathway. We therefore studied the effect of RANTES on the expression of
FasL mRNA in effector T cells. As shown in Fig. 3
, RANTES enhanced the expression of FasL
transcripts in a concentration-dependent manner without enhancing the
expression of perforin or CCR3. In HIV-specific CTL lines from six
different individuals, the enhancement was statistically significant
(p < 0.02) in the presence of 25 or 100 nM
RANTES. RANTES, by contrast, did not influence FasL mRNA expression in
NK cells (data not shown). Fig. 4
shows
the time-dependent expression of FasL mRNA in HIV-specific CTLs. In the
presence of RANTES, expression doubled within 4 h and was
increased nearly 4-fold after 17 h. RANTES neutralization with an
Ab, by contrast, led to a marked, progressive decrease FasL expression.
Using flow cytometry, we finally examined the expression of FasL on the
surface of HIV-specific CTL lines. Incubation with 25 or 100 nM RANTES
for 4 h significantly enhanced the density of FasL as detected
with fluorescence-labeled Abs and as shown in Fig. 5
A for 100 nM RANTES. Because
RANTES binds to several chemokine receptors that are found in T
lymphocytes, namely CCR1 (14), CCR3 (15, 16), CCR4 (17), and CCR5 (18),
these experiments were also performed with eotaxin, a selective ligand
for CCR3, which was equally effective as RANTES (Fig. 5
B),
further indicating that the observed enhancement of FasL expression is
CCR3 dependent.
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/TNFRII death
pathway (8). In combining chemotactic recruitment via CCR1 and CCR5,
and lytic activity via CCR3, RANTES may play a key role in HIV-specific
immune responses. The observed stimulation of FasL expression by RANTES
can be seen as a defence mechanism leading to the elimination of
HIV-infected cells, which is likely to function in concert with the
HIV-suppressive activity of the same chemokine as blocker of CCR5. On
the other hand, enhanced expression of FasL in CTLs may also contribute
to pathogenesis by accelerating the decline of CD4+ or
CD8+ cells that express Fas (5). The identification of
RANTES and CCR3 as structurally defined effector molecules opens
possibilities to devise therapeutic measures to regulate apoptosis of
virus infected targets (23).
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr.
Patrice Debré, Laboratoire dImmunologie Cellulaire, UMR 7627,
Centre National de la Recherche Scientifique, Bâtimont CERVI,
Hôpital Pitié-Salpétriére, 75651 Paris, France.
E-mail address: ![]()
3 Abbreviations used in this paper: FasL, Fas ligand; CMA,
concanamycin A; B-LCL, lymphoblastoid B cell line. ![]()
Received for publication April 26, 1999. Accepted for publication May 18, 1999.
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