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Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892;
Partners AIDS Research Center and Infectious Disease Division, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129; and
Immunex Corporation, Seattle, WA 98101
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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HIV-1 infection is characterized by chronic, persistent viral replication in the face of ongoing detectable CD8+ CTL responses (19, 20). In addition, early qualitative and later quantitative abnormalities in CD4+ T cells are seen typically in HIV-1-infected individuals (21, 22, 23, 24). It is unclear whether the deficient CD4+ T helper function in HIV-1 infection is responsible for the inability of CD8+ T cells to completely contain HIV-1 replication. Progressive loss of CTL responses is observed with CD4+ T cell decline and the onset of AIDS (7, 25). Studies by Rosenberg et al. (26) have shown that individuals with strong HIV-1-specific CD4+ T cell-proliferative responses to HIV p24 Ag are able to better control their viremia than individuals with diminished or absent responses. Some of these former individuals have also been shown to have higher levels of circulating Gag-specific CTL precursors (27). Thus, these findings suggest that for HIV-1 infection, a strong CD4+ T cell immune response may be necessary to maintain an effective CD8+ CTL response to HIV-1.
Recent studies in murine systems have demonstrated that CD4+ T cells help CD8+ T cells through interactions with dendritic cells (28, 29, 30, 31). After contact with their cognate Ag, CD4+ T cells are activated to express CD40 ligand, which then induces a signal through the CD40 receptor on dendritic cells. This interaction activates dendritic cells to become more efficient inducers of CD8+ CTL responses, probably due to the up-regulation of costimulatory molecules such as B7-1 and B7-2, as well as to the induction of cytokines including IL-12 (32, 33, 34, 35, 36). Two recent studies have used in vivo CD40 receptor ligation in conjunction with vaccination to break tolerance against tumor and viral Ags in mice (37, 38, 39). These findings suggest that CD40 ligation may represent a novel strategy to induce effective antiviral CTL responses in CD4+ T cell-deficient states such as HIV-1 infection.
Using a peptide-pulsed, dendritic cell-based coculture system in which endogenous cytokines produced by dendritic cells allow expansion of memory CTL responses, this study defines the role of CD4+ T cells in the ex vivo expansion of memory CD8+ CTL responses in two human viral infections, namely, influenza-specific responses in recently vaccinated HIV-1-uninfected individuals and HIV-1-specific responses from HIV-1-infected individuals at various stages of disease. We also address whether CD40 ligand trimer (CD40LT; Ref. 40) can enhance CTL responses or replace CD4+ T cell help in CD4+ T cell-depleted culture conditions.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Two HIV-1-uninfected individuals, who were HLA-A*0201 positive
and had been vaccinated to influenza virus (A/H3N2) within the previous
year, were recruited for apheresis to obtain large amounts of PBMCs.
Ten HIV-1-seropositive individuals at varying stages of disease and
treatment were also studied (Table I
).
Before the study, all ten HIV-1-infected individuals manifested CTL
responses to HLA-restricted HIV-1 peptides using standard CTL assays
after peptide stimulation in the presence of IL-7 and IL-2 or
anti-CD3 and IL-2 (41, 42) (data not shown). All
investigational protocols were approved by the National Institute of
Allergy and Infectious Diseases and the Massachusetts General Hospital
Institutional Review Boards.
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Peptides were synthesized by F-moc chemistry using a Zinnser Analytical Synthesizer (Research Genetics, Huntsville, AL) and purity was established by HPLC. Peptides were dissolved in RPMI 1640 medium, and concentrations were determined using the Bio-Rad Protein Assay kit (Bio-Rad, Richmond, CA). The following peptides were used for CD8+ T cell expansion: 1) the HLA-A*0201-restricted matrix peptide of influenza, FLU (GILGFVFTL); and 2) the HIV-1-specific peptides HLA-A*0201-restricted P17 (SLYNTVATL), HLA-A*0201-restricted POL (ILKEPVHGV),HLA-A3-restricted P17 (KIRLRPGGK), HLA-B*3501-restricted NEF (VPLRPMTY), and HLA-B8-restricted NEF (FLKEKGGL). The peptide used as a T-helper epitope for CD4+ T cell stimulation was the universal tetanus helper epitope TET830–843 (QYIKANSKFIGITE) (43).
Preparation of monocyte-derived dendritic cells (MDDCs)2
MDDCs were prepared as previously described (44)
with minor modifications. Briefly, PBMCs obtained by the Ficoll-Paque
method (Organon Teknika, Durham, NC) were separated on multistep
Percoll gradients (Sigma, Steinheim, Germany). The recovered monocytes
were depleted of contaminating B and T cells using anti-CD19- and
anti-CD2-conjugated magnetic beads (Dynal, Oslo, Norway). Monocytes
were cultured at 1 x 106/ml in RPMI 1640,
10% FCS, 2 mM glutamine, 25 mM HEPES, and antibiotics supplemented
with 50 ng/ml GM-CSF and 100 ng/ml IL-4 (PeproTech, Rocky Hill, NJ) for
7–9 days. MDDCs were then matured with 10 ng/ml TNF-
for 24 h
(R&D Systems, Minneapolis, MN) before use.
Proliferation assays
Cells (5 x 105/well) were cultured in six replicate wells of 96-well U-bottom plates in the presence of test proteins including 1.0 µg/ml of p24 Ag (Protein Science, Meriden, CT) and 10 µg/ml tetanus toxoid Ag (Wyeth-Ayerst Laboratories, Marietta, PA). Six days later, cells were pulsed with [3H]thymidine at 1.0 µCi/well, and uptake was measured 12 h later with a scintillation counter.
Induction of peptide-specific CTL
The protocol for expanding circulating memory CTL ex vivo is
illustrated (See Fig. 1). MDDCs (see above) were pulsed with the
specific HLA class I-restricted peptide at 40 µg/ml for 1 h at
37°C. In addition, to provide a stimulus to
CD4+ T cells, these MDDCs were also pulsed with
the universal tetanus-specific helper epitope,
TET830–843 (4 µg/ml). MDDCs were plated in
24-well plates (5 x 105 pulsed or nonpulsed
MDDCs/well) in RPMI 1640 plus 10% FCS, 25 mM HEPES, 2 mM glutamine,
and antibiotics. Freshly isolated or thawed autologous PBMCs were
prepared both in unfractionated and CD4+ T
cell-depleted conditions and added to MDDCs at a 10:1 ratio (5 x
106 cells/well in 2 ml medium).
CD4+ T cells were depleted from PBMCs using two
rounds of magnetic bead depletion (Dynal); the purity of depletion as
tested by FACS analysis was always <0.1% CD4+ T
cell contamination. The percentage of CD8+ T
cells within total PBMCs and CD4+ T cell-depleted
PBMCs was determined by FACS analysis so that equal input of
CD8+ T cells could be plated in both
unfractionated (total PBMCs) and CD4+ T
cell-depleted conditions. Soluble CD40LT was added to certain cultures
at a final concentration of 2 µg/ml. CD40LT was obtained as a gift
from Immunex (Seattle, WA) at a stock concentration of 13.6 mg/ml
dissolved in 25 mM Tris, 4% mannitol, and 1% sucrose buffer. Thus,
the following three conditions were included in all experiments using
both unfractionated (total) PBMCs and CD4+ T
cell-depleted PBMCs: 1) MDDCs not pulsed with peptides; 2)
peptide-pulsed MDDCs; and 3) CD40LT plus peptide-pulsed MDDCs. In
certain experiments, CD40LT was also added to MDDCs that were not
pulsed with peptides. In selected experiments, the effect of exogenous
cytokines was also tested in CD4+ T
cell-depleted, peptide-pulsed MDDC conditions, which included 20 U/ml
IL-2, (Boehringer-Mannheim, Mannheim, Germany), 5 ng/ml IL-12, or 1
ng/ml IL-15 (R&D Systems). On days 3 and 5, medium was changed and
supernatants were saved for cytokine analysis. On day 7, wells were
pooled and cells were harvested and tested for CTL activity by standard
51chromium lysis assay and for intracellular
IFN-
staining. Percentages of CD8+ T cells in
both unfractionated or CD4+ T cell-depleted
conditions were again determined by FACS analysis before CTL assays to
assure for equal inputs of CD8+ T cells.
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Autologous B-lymphoblastoid cell lines (B-LCL) were labeled with sodium [51Cr] chromate and pulsed with the specific peptide at 10 µM. Control B-LCL were either pulsed with an irrelevant peptide or cultured in RPMI 1640 10% medium alone. Effector cells were added in triplicate at various E:T ratios. Supernatants were collected 4–6 h later and counted on a flatbed scintillation counter (Wallac, Gaithersburg, MD). Background chromium release was always <20%. Percentage of lysis was calculated from the formula 100 x (E - M/T - M), where E is experimental release, M is the release in the presence of RPMI 1640 10% medium, and T is release in the presence of 5% Triton X-100 detergent. Specific lysis was determined by subtracting lysis of control targets from peptide-pulsed targets.
Intracellular staining
Intracellular staining was performed to enumerate the number of
IFN-- or IL-12-producing cells, as previously described
(45). Briefly, for peptide-specific IFN- staining,
0.25 x 106 cells were cultured in U-bottom
96-well plates in the presence of peptide-pulsed (1–10 µM)
autologous B-LCL or autologous CD8+ T
cell-depleted PBMC as stimulator cells; nonpeptide-pulsed stimulator
cells were used as background controls. Positive control cells were
stimulated with PMA (10 ng/ml) and ionomycin (500 ng/ml). Cells were
incubated with peptide-pulsed and nonpeptide-pulsed stimulator cells
for 6 h at 37°C in 6% CO2. Monensin was
added for the duration of the culture period to facilitate
intracellular cytokine accumulation. After this period of culture, cell
surface staining was followed by intracellular cytokine staining using
the Cytofix/Cytoperm kit (PharMingen, San Diego, CA) in accordance with
the manufacturer’s recommendations. For IL-12 staining, MDDCs were
cultured in 96-well plates either in the presence of medium alone, or
CD40LT (2 µg/ml) for 6 h in the presence of Monensin, and then
harvested for staining. For intracellular staining, the following Abs
were used: anti-IFN- (clone 4S.B3) and anti-IL-12 (p40/p70)
Ab (clone C11.5). All Abs were obtained through PharMingen.
Flow cytometry
PBMCs or MDDCs were stained in PBS/1%
FCS/0.02%NaN3 using flourochrome-conjugated Abs.
The Abs used were anti-CD80, anti-CD86, anti-CD1a,
anti-HLA-ABC, anti-CD4, anti-CD8, and anti-CD3. All Abs
were obtained through PharMingen. After staining, cells were fixed in
PBS/2% paraformaldehyde, and events were acquired using a FACScalibur
flow cytometer (Becton Dickinson, San Diego, CA). Dead cells were
excluded on the basis of forward and side light scatter. For
intracellular IFN- assays, a total of 50,000–100,000 events were
collected for each sample, and CD8+ T cells were
enumerated after gating on CD3-positive cells. Data were analyzed using
CELLQuest (Becton Dickinson).
Measurement of cytokine production
ELISAs specific for IL-2, IL-15, and IL-10 were performed on cell culture supernatants in duplicate according to the manufacturer’s guidelines (R&D Systems).
Statistical analysis
Data were compared using the Wilcoxon signed rank test for paired samples.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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To study the role of CD4+ T cell help on the
expansion of virus-specific memory CTL, we used a coculture method in
which peptide-pulsed dendritic cells stimulate
CD8+ T cells in the absence of exogenous
cytokines (Fig. 1
). After 1 wk of
culture, CTL effector activity was assessed by two assays: direct
cytolysis of peptide-pulsed targets and intracellular IFN-
production after exposure to peptide-pulsed PBMCs or B-LCL. We have
found excellent correlation between these two assays. Of note,
intracellular IFN- production yielded a greater degree of
sensitivity because significant cytolysis was generally seen only when
a frequency of 100 IFN--producing cells/10,000 CD8 cells was
detected by flow cytometry (our unpublished observations). We believe
that our protocol predominantly measures memory rather than naive
CD8+ T cell responses, as we have not been able
to induce detectable HIV-1-specific responses in two uninfected
individuals using our culture conditions (data not shown). Because
HIV-1 infection is associated with multiple immune function defects
(21, 22, 24), we initially studied influenza-specific
CD8+ T cell responses in uninfected individuals
to establish a baseline for comparison. Two HIV-1-uninfected
individuals who recently received the standard influenza vaccine were
studied. They had previously demonstratable CTL activity against an
HLA-A*0201-restricted epitope to the influenza matrix protein using
conventional in vitro methods (41, 42) (data not shown).
Coculture of PBMCs with peptide-pulsed dendritic cells promoted
expansion of CTL because the frequency of influenza-specific
CD8+ T cells in ex vivo PBMCs from Subject 1 was
8:10,000 CD8+ T cells by IFN- staining before
coculture, but 101:10,000 CD8+ T cells after 7
days of coculture (data not shown, and Fig. 2A). We found greater
influenza-specific CTL responses as measured by cytolysis or IFN-
staining of influenza-specific CD8+ T cells when
CD4+ T cells were included in the cocultures
(Fig. 2). CD4+ T cell help has been proposed to
operate though CD40 ligation on dendritic cells (28, 29, 30, 31).
Addition of CD40LT to the cultures not only substituted for
CD4+ T cells but increased CTL activity in both
total PBMCs and CD4+ T cell-depleted conditions
(Fig. 2).
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Ten HIV-1-infected individuals at various stages of disease, with
previously demonstrable CTL activity against a dominant HLA class
1-restricted HIV-1-specific epitope (41, 42), were
examined in this study (see Tables I and II). Again, coculture of PBMCs with
peptide-pulsed dendritic cells promoted expansion of HIV-specific CTL.
For example, the baseline frequency of HIV-1-specific
CD8+ T cells in ex vivo PBMC from patient 4 was
21:10,000 CD8+ T cells by IFN- staining and
185:10,000 CD8+ T cells after 7 days of coculture
(data not shown, and Table II). After coculturing total
(unfractionated) PBMCs with peptide-pulsed MDDCs for 1 wk,
HIV-1-specific memory CD8+ T cell responses
ranging from 19 to 1300 IFN--producing CD8+ T
cells/10,000 were detected (Table II). In comparison to total PBMC
conditions, CD4+ T cell depletion reduced the
ability of peptide-pulsed dendritic cells to expand memory
HIV-1-specific CTL responses in 9 of 10 patients (Fig. 3 and Table III). The frequency of HIV-1-specific
IFN--producing cells was, on average, reduced by 91% (±15%,
geometric mean) in CD4+ T cell-depleted
conditions (p < 0.05). Of note, in one
long-term nonprogressor (patient 7), memory CD8+
T cells were able to expand slightly without CD4+
T cell help (Fig. 3). This expansion was markedly enhanced in the
presence of CD40LT (Fig. 3). We found variable effects of CD40LT on
CD8+ memory T cell expansion when
CD4+ T cells were present in the cultures (i.e.,
total PBMCs), from suppression to no change to enhancement (Fig. 3).
Taken as a group, there was no significant effect of CD40LT on
CD8+ T cell responses in total PBMC conditions
(p = 0.6). The addition of CD40LT to
CD4+ T cell-depleted cultures significantly
enhanced memory CD8+ T cell expansion in 9 of 10
patients (p < 0.05); however, the degree of
enhancement was variable among patients (Fig. 3 and Table III). In 6 of
10 HIV-1-infected patients, addition of CD40LT in
CD4+ T cell-depleted conditions was able to
expand IFN--producing HIV-1-specific cells to within at least 50%
of the levels produced in total PBMC conditions (Fig. 3; patients 1, 2,
5, 6, 7, and 9). An example of the ability of CD40LT to fully restore
CTL responses in CD4+ T cell-depleted conditions
to those of total PBMC conditions is illustrated in patient 5, a
long-term nonprogressor (Fig. 4A). In this patient, when
unfractionated PBMCs were cocultured with peptide-pulsed MDDCs, 11% of
CD8+ T cells produced IFN- in response to the
A2/p17 epitope, whereas only 1.0% of CD8+ T
cells in CD4+ T cell-depleted PBMC cultures
produced IFN- (Fig. 4B). The addition of CD40LT to
CD4+ T cell-depleted cultures increased the
frequency of A2/p17-specific CD8+ T cells to that
found in unfractionated cultures (Fig. 4B). In patients 3,
4, 8, and 10 (Fig. 3 and Table III), CD40LT was unable to fully
compensate for CD4+ T cell help (HIV-1-specific
IFN--producing CD8+ T cells <50% of that in
total PBMC conditions). These four patients also had poor p24
Ag-proliferative responses (Table III). Of note, CD40LT did not
appreciably enhance HIV-1-specific CD8+ T cell
responses in those cultures in which MDDCs were not pulsed with
HIV-1-specific peptide (data not shown).
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). The effects of CD40LT on MDDC
activation in patient 3, who did not show enhancement of CTL to CD40LT
is illustrated in Fig. 5. CD40LT activated the MDDCs from this patient
as manifested by morphological changes, up-regulation of costimulatory
molecules, and IL-12 expression (Fig. 5). Thus, the level of activation
of MDDCs did not appear to explain the variable responses to CD40LT.
The addition of individual exogenous cytokines such as IL-2, IL-12, or
IL-15 was usually able to enhance CTL responses in
CD4+ T cell-depleted conditions to the level of
that seen in unfractionated conditions. This included those patients
who gave poor in vitro responses to CD40LT. IL-2 tended to have a
greater effect on in vitro CD8+ T cell expansion
than IL-15 or IL-12. Representative experiments from two patients
(patients 3 and 8) who showed poor in vitro responses to CD40LT are
illustrated in Fig. 6. In patient 3 (Fig. 6A), the addition of CD40LT to CD4+ T
cell-depleted cultures had, in fact, suppressed
CD8+ CTL activity, whereas the addition of IL-2,
IL-12, or IL-15 had expanded CD8+ CTL responses
to the level of total PBMC conditions. In patient 8 (Fig. 6B), CD40LT could only minimally enhance
CD8+ T cell responses in
CD4+ T cell-depleted conditions, whereas the
addition of IL-2 expanded CD8+ T cell responses
exceeding those produced by total PBMC without cytokines. This
indicates that although CD8+ T cells in some
patients were not able to optimally expand in the presence of a
CD40LT-conditioned dendritic cell, they could fully respond given the
appropriate cytokine milieu. To further characterize which cytokines
might be driving influenza-specific (i.e., in HIV-1-uninfected
subjects) or HIV-1-specific CD8+ T cell (i.e., in
HIV-1-infected patients) proliferation in vitro, supernatants from
total PBMC, CD4+ T cell-depleted, and
CD40LT-stimulated CD4+ T cell-depleted conditions
were examined for IL-2, IL-10, and IL-15 by ELISA. IL-2 could only be
detected in those cocultures which contained CD4+
T cells (total PBMC). Alternatively, IL-15 was only detectable in
CD40LT-stimulated cocultures. IL-10 was always detectable; however,
CD40LT tended to enhance IL-10 production to a greater degree in
cultures from HIV-1-infected individuals compared with those from
HIV-1-uninfected subjects (data not shown). However, we could not
clearly correlate the level of IL-10 production with an impaired
induction of CD8+ T cell responses by CD40LT in
the HIV-1-infected cohort (data not shown). Thus, in 4 of 10
HIV-1-infected patients, CD40LT could not completely substitute for
CD4+ T cell help, although MDDCs were activated
by CD40LT, and the CD8+ T cells could be expanded
with the addition of exogenous cytokines.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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HIV-1-infected individuals have numerous immunologic perturbations
including chronic immune activation and CD4+ T
cell depletion (21, 22, 23, 24). We observed variable but
reproducible levels of enhancement of CD8+ memory
T cell responses with in vitro CD40LT stimulation in our HIV-1-infected
cohort. In total PBMC conditions, i.e., in the presence of
CD4+ T cells, we saw considerable variability in
the effects of CD40LT in HIV-1-infected individuals compared with
HIV-1-uninfected controls. The reasons for this observation are not
readily apparent and likely reflect complex interactions between CD40LT
and CD4+ T cells in these cultures. It is
possible that the combination of CD4+ T cells and
excess CD40LT may provide excessive stimulation in some instances and
result in the induction of counterregulatory signals to
CD8+ T cells. In CD4+ T
cell-depleted cocultures, CD40LT could enhance
CD8+ T cell responses to some degree in most
HIV-1-infected patients. CD40LT could not sufficiently substitute for
CD4+ T cell help in 4 of 10 patients, despite the
fact that CD40LT could activate the dendritic cells from these
patients. However, the addition of exogenous cytokines such as IL-2 was
able to enhance CD8+ T cell responses to the
levels found in CD4+ T cell-containing
conditions, even when CD40LT could not. These findings suggest that in
some HIV-1-infected patients, memory CD8+ T cells
are heavily dependent on cytokines such as IL-2 to proliferate despite
receiving optimal signals from dendritic cells. A similar defect in
CD8+ T cell effector function from later stage
HIV-1-infected individuals has also been demonstrated by Trimble et al.
(46). In these patients, CD3
down-regulation on T cells
was observed, which could be reversed with exogenous IL-2.
It is also possible that a lack of CD4+ T cell help in vivo may be responsible for a lack of response to CD40LT in vitro. Of note was the fact that those patients with a suboptimal response to CD40LT also had absent proliferation to p24 Ag. Hay et al. (47) recently reported an HIV-1-infected rapid progressor who had absent HIV-1-specific CD4+ T cell-proliferative responses in association with detectable circulating but dysfunctional HIV-1-specific CD8+ T cells in the face of a high level plasma viremia. Their findings suggested that a lack of CD4+ T cell help in vivo in this patient prevented circulating memory CD8+ T cells from expanding to sufficient numbers that would contain viral replication. It is of interest that these four individuals were also receiving HAART. Recent studies have shown an inhibitory effect of therapeutic levels of ritonavir on in vitro CTL responses (48). Thus, we cannot rule out an alternative possibility that concurrent protease inhibitor use may have interfered with Ag processing and the in vitro response to CD40LT stimulation.
Examination of cytokine production in our cultures provided some insight into potential mechanisms of CD40LT action. Although IL-2 could be detected when CD4+ T cells were present, we did not detect IL-2 in CD40LT-stimulated, CD4-depleted cocultures, reflecting the inability of memory CD8+ T cells to produce appreciable IL-2 upon restimulation (49). However, IL-15 was detected in CD40LT, CD4-depleted conditions. IL-15 has been shown to share a number of biological activities with IL-2. Of note, IL-15 has been used to expand memory CTLs in vitro in an IL-2-independent fashion (50), and IL-15 has recently been shown to be induced in dendritic cells after CD40 ligation (R. Seder and J. McDyer, unpublished observations; Ref. 51). Thus, CD40LT may bypass the role of CD4+ T cell help in part through IL-15 induction. IL-10 production was also increased during CD40LT stimulation, especially in cocultures from HIV-1-infected patients. This indicates that CD40 ligation can also induce counterregulatory cytokines. Thus, the net result of CD40 ligation on expanding CD8+ T cell responses will reflect a balance of both positive and negative regulatory effects. This may also explain in part the variable effects of CD40 ligation in both CD4+ T cell-containing and CD4+ T cell-depleted conditions in our HIV-1-infected patients.
Although CD40LT was able to expand in vitro virus-specific responses in uninfected and most HIV-1-infected individuals, a similar effect could also be demonstrated with exogenous cytokines, such as IL-2, IL-12, and IL-15 in our culture system. This suggests that, in the absence of CD4+ T cell help, there may be more than one way to supplement CD8+ T cell function.
This study has potentially important implications for the use of CD40LT in vaccine strategies or as an effective immunotherapy. The incorporation of CD40LT in the design of current anti-viral vaccines that give poor CTL immune responses in vivo would be an important strategy to pursue. Furthermore, the use of CD40LT in association with HIV-1-specific vaccines as an immunotherapy in HAART-treated HIV-1-infected patients would also be an attractive approach for clinical application, with the caveat that HIV-1-specific CTL may not be expandable in all infected individuals.
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Acknowledgments |
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Footnotes |
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2 Abbreviations used in this paper: MDDCs, monocyte-derived dendritic cells; CD40LT, CD40 ligand trimer; B-LCL, B-lymphoblastoid cell lines.
Received for publication May 3, 2000. Accepted for publication August 29, 2000.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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) interferon in the acquired immunodeficiency syndrome. N. Engl. J. Med. 310:883.[Abstract]
. J. Exp. Med. 179:1109., the signaling chain of the T-cell receptor complex. Blood 91:585.This article has been cited by other articles:
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Q. Yu, F. Y. Yue, X. X. Gu, H. Schwartz, C. M. Kovacs, and M. A. Ostrowski OX40 Ligation of CD4+ T Cells Enhances Virus-Specific CD8+ T Cell Memory Responses Independently of IL-2 and CD4+ T Regulatory Cell Inhibition J. Immunol., February 15, 2006; 176(4): 2486 - 2495. [Abstract] [Full Text] [PDF]
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C. C. Clay, D. S. Rodrigues, D. J. Harvey, C. M. Leutenegger, and U. Esser Distinct Chemokine Triggers and In Vivo Migratory Paths of Fluorescein Dye-Labeled T Lymphocytes in Acutely Simian Immunodeficiency Virus SIVmac251-Infected and Uninfected Macaques J. Virol., November 1, 2005; 79(21): 13759 - 13768. [Abstract] [Full Text] [PDF]
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U. Kumaraguru, K. Banerjee, and B. T. Rouse In vivo rescue of defective memory CD8+ T cells by cognate helper T cells J. Leukoc. Biol., October 1, 2005; 78(4): 879 - 887. [Abstract] [Full Text] [PDF]
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F. Y. Yue, C. M. Kovacs, R. C. Dimayuga, X. X. J. Gu, P. Parks, R. Kaul, and M. A. Ostrowski Preferential Apoptosis of HIV-1-Specific CD4+ T Cells J. Immunol., February 15, 2005; 174(4): 2196 - 2204. [Abstract] [Full Text] [PDF]
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Q. Yu, C. Kovacs, F. Y. Yue, and M. A. Ostrowski The Role of the p38 Mitogen-Activated Protein Kinase, Extracellular Signal-Regulated Kinase, and Phosphoinositide-3-OH Kinase Signal Transduction Pathways in CD40 Ligand-Induced Dendritic Cell Activation and Expansion of Virus-Specific CD8+ T Cell Memory Responses J. Immunol., May 15, 2004; 172(10): 6047 - 6056. [Abstract] [Full Text] [PDF]
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R. Zhang, C. J. Fichtenbaum, D. A. Hildeman, J. D. Lifson, and C. Chougnet CD40 Ligand Dysregulation in HIV Infection: HIV Glycoprotein 120 Inhibits Signaling Cascades Upstream of CD40 Ligand Transcription J. Immunol., February 15, 2004; 172(4): 2678 - 2686. [Abstract] [Full Text] [PDF]
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C. Chougnet Role of CD40 Ligand dysregulation in HIV-associated dysfunction of antigen-presenting cells J. Leukoc. Biol., November 1, 2003; 74(5): 702 - 709. [Abstract] [Full Text] [PDF]
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L. Santodonato, G. D'Agostino, R. Nisini, S. Mariotti, D. M. Monque, M. Spada, L. Lattanzi, M. Paola Perrone, M. Andreotti, F. Belardelli, et al. Monocyte-Derived Dendritic Cells Generated After a Short-Term Culture with IFN-{alpha} and Granulocyte-Macrophage Colony-Stimulating Factor Stimulate a Potent Epstein-Barr Virus-Specific CD8+ T Cell Response J. Immunol., May 15, 2003; 170(10): 5195 - 5202. [Abstract] [Full Text] [PDF]
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J. M. Brenchley, N. J. Karandikar, M. R. Betts, D. R. Ambrozak, B. J. Hill, L. E. Crotty, J. P. Casazza, J. Kuruppu, S. A. Migueles, M. Connors, et al. Expression of CD57 defines replicative senescence and antigen-induced apoptotic death of CD8+ T cells Blood, April 1, 2003; 101(7): 2711 - 2720. [Abstract] [Full Text] [PDF]
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B. Samten, B. Wizel, H. Shams, S. E. Weis, P. Klucar, S. Wu, R. Vankayalapati, E. K. Thomas, S. Okada, A. M. Krensky, et al. CD40 Ligand Trimer Enhances the Response of CD8+ T Cells to Mycobacterium tuberculosis J. Immunol., March 15, 2003; 170(6): 3180 - 3186. [Abstract] [Full Text] [PDF]
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Q. Yu, J. X. Gu, C. Kovacs, J. Freedman, E. K. Thomas, and M. A. Ostrowski Cooperation of TNF Family Members CD40 Ligand, Receptor Activator of NF-{kappa}B Ligand, and TNF-{alpha} in the Activation of Dendritic Cells and the Expansion of Viral Specific CD8+ T Cell Memory Responses in HIV-1-Infected and HIV-1-Uninfected Individuals J. Immunol., February 15, 2003; 170(4): 1797 - 1805. [Abstract] [Full Text] [PDF]
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D. Zhang, P. Shankar, Z. Xu, B. Harnisch, G. Chen, C. Lange, S. J. Lee, H. Valdez, M. M. Lederman, and J. Lieberman Most antiviral CD8 T cells during chronic viral infection do not express high levels of perforin and are not directly cytotoxic Blood, January 1, 2003; 101(1): 226 - 235. [Abstract] [Full Text] [PDF]
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G. T. Brice, N. L. Graber, D. J. Carucci, and D. L. Doolan Optimal induction of antigen-specific CD8+ T cell responses requires bystander cell participation J. Leukoc. Biol., December 1, 2002; 72(6): 1164 - 1171. [Abstract] [Full Text] [PDF]
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M. J. Boaz, A. Waters, S. Murad, P. J. Easterbrook, and A. Vyakarnam Presence of HIV-1 Gag-Specific IFN-{gamma}+IL-2+ and CD28+IL-2+ CD4 T Cell Responses Is Associated with Nonprogression in HIV-1 Infection J. Immunol., December 1, 2002; 169(11): 6376 - 6385. [Abstract] [Full Text] [PDF]
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J. D. Ahlers, I. M. Belyakov, M. Terabe, R. Koka, D. D. Donaldson, E. K. Thomas, and J. A. Berzofsky A push-pull approach to maximize vaccine efficacy: Abrogating suppression with an IL-13 inhibitor while augmenting help with granulocyte/macrophage colony-stimulating factor and CD40L PNAS, October 1, 2002; 99(20): 13020 - 13025. [Abstract] [Full Text] [PDF]
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X.-Q. Zhao, X.-L. Huang, P. Gupta, L. Borowski, Z. Fan, S. C. Watkins, E. K. Thomas, and C. R. Rinaldo Jr. Induction of Anti-Human Immunodeficiency Virus Type 1 (HIV-1) CD8+ and CD4+ T-Cell Reactivity by Dendritic Cells Loaded with HIV-1 X4-Infected Apoptotic Cells J. Virol., February 22, 2002; 76(6): 3007 - 3014. [Abstract] [Full Text] [PDF]
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G. M. Ortiz, J. Hu, J. A. Goldwitz, R. Chandwani, M. Larsson, N. Bhardwaj, S. Bonhoeffer, B. Ramratnam, L. Zhang, M. M. Markowitz, et al. Residual Viral Replication during Antiretroviral Therapy Boosts Human Immunodeficiency Virus Type 1-Specific CD8+ T-Cell Responses in Subjects Treated Early after Infection J. Virol., January 1, 2002; 76(1): 411 - 415. [Abstract] [Full Text] [PDF]
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P. F. McKay, J. E. Schmitz, D. H. Barouch, M. J. Kuroda, M. A. Lifton, C. E. Nickerson, D. A. Gorgone, and N. L. Letvin Vaccine Protection Against Functional CTL Abnormalities in Simian Human Immunodeficiency Virus-Infected Rhesus Monkeys J. Immunol., January 1, 2002; 168(1): 332 - 337. [Abstract] [Full Text] [PDF]
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J. Pacanowski, S. Kahi, M. Baillet, P. Lebon, C. Deveau, C. Goujard, L. Meyer, E. Oksenhendler, M. Sinet, and A. Hosmalin Reduced blood CD123+ (lymphoid) and CD11c+ (myeloid) dendritic cell numbers in primary HIV-1 infection Blood, November 15, 2001; 98(10): 3016 - 3021. [Abstract] [Full Text] [PDF]
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P. J. Norris, M. Sumaroka, C. Brander, H. F. Moffett, S. L. Boswell, T. Nguyen, Y. Sykulev, B. D. Walker, and E. S. Rosenberg Multiple Effector Functions Mediated by Human Immunodeficiency Virus-Specific CD4+ T-Cell Clones J. Virol., October 15, 2001; 75(20): 9771 - 9779. [Abstract] [Full Text] [PDF]
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J. Lieberman, P. Shankar, N. Manjunath, and J. Andersson Dressed to kill? A review of why antiviral CD8 T lymphocytes fail to prevent progressive immunodeficiency in HIV-1 infection Blood, September 15, 2001; 98(6): 1667 - 1677. [Abstract] [Full Text] [PDF]
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