JOURNAL OF VIROLOGY, Nov. 2002, p. 11659–11676
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Vol. 76, No. 22
Both Mucosal and Systemic Routes of Immunization with the Live,
Attenuated NYVAC/Simian Immunodeficiency Virus SIVgpe
Recombinant Vaccine Result in Gag-Specific
CD8?T-Cell Responses in Mucosal
Tissues of Macaques
Liljana Stevceva,1Xavier Alvarez,2† Andrew A. Lackner,2† Elzbieta Tryniszewska,1
Brian Kelsall,3Janos Nacsa,1Jim Tartaglia,4Warren Strober,2
and Genoveffa Franchini1*
Basic Research Laboratory, National Cancer Institute, Bethesda, Maryland 208921; Division of Comparative Pathology, New
England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772-91022;
Laboratory of Clinical Investigation, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland
20892-18903; and Aventis-Pasteur, Toronto, Ontario, Canada M2R 3T44
Received 11 April 2002/Accepted 19 August 2002
As most human immunodeficiency virus (HIV) infection occurs via mucosal surfaces, an important goal of
vaccination may be the induction of virus-specific immune responses at mucosal sites to contain viral infection
early on. Here we designed a study in macaques carrying the major histocompatibility complex class I
Mamu-A?01 molecule to assess the capacity of the highly attenuated poxvirus NYVAC/simian immunodefi-
ciency virus (SIV) SIVgpevaccine candidate administered by the intranasal, intramuscular, or intrarectal route
to induce mucosal immunity. All macaques, including one naive macaque, were exposed to SIVmac251by the
intrarectal route and sacrificed 48 h after infection. The kinetics of immune response at various time points
following immunization with NYVAC/SIVgpeand the anamnestic response to SIVmac251at 48 h after challenge
were assessed in blood, in serial rectal and vaginal biopsy samples, and in tissues at euthanasia with an SIVmac
Gag-specific tetramer. In addition, at euthanasia, antigen-specific cells producing gamma interferon or tumor
necrosis factor alpha from the jejunum lamina propria were quantified in all macaques. Surprisingly, antigen-
specific CD8?T cells were found in the mucosal tissues of all immunized macaques regardless of whether the
vaccine was administered by a mucosal route (intranasal or intrarectal) or systemically. In addition, following
mucosal SIVmac251challenge, antigen-specific responses were mainly confined to mucosal tissues, again
regardless of the route of immunization. We conclude that immunization with a live vector vaccine results in
the appearance of CD8?T-cell responses at mucosal sites even when the vaccine is delivered by nonmucosal
Transmission of human immunodeficiency virus (HIV) oc-
curs predominantly via mucosal surfaces. Effective neutraliza-
tion of the virus at this anatomic site depends on several
components. Preexisting virus-specific immunoglobulin A
(IgA) antibodies in rectal secretions are associated with de-
creased viral burden but are not sufficient to prevent infection
(52). HIV-1/simian immunodeficiency virus (SIV)-specific
CD8?cytotoxic T lymphocytes are another such component
and have been shown to be present during the early weeks
following infection, before a neutralizing antibody response is
demonstrable (8, 26, 27). Such cell-mediated immunity (40)
and direct killing by cytotoxic lymphocytes from the vagina and
colon lamina propria may be an important factor in containing
viral infection at the site of primary infection (35), and it may
explain the fact that, despite the rapid heterosexual dissemi-
nation of HIV-1 in the world, mucosal transmission of HIV-1
appears to be relatively inefficient and is estimated to occur
only once in 300 or more high-risk exposures (47).
While many studies have investigated the effect of the route
of immunization on antibody production at the local or sys-
temic level, few have directly investigated the induction of
cell-mediated responses at mucosal sites. Studies in mice im-
munized with synthetic, multideterminant HIV peptides plus
cholera toxin adjuvant have shown that intrarectal immuniza-
tion induces cytotoxic T lymphocyte responses in Peyer’s
patches, the spleen, and lamina propria of the intestine (4) and
that these responses were able to reduce the viral titer in the
ovaries and the colorectal tissue upon intrarectal recombinant
vaccinia virus challenge. In contrast, subcutaneous immuniza-
tion induced cytotoxic T lymphocytes only in the spleen and
not in the Peyer’s patches or lamina propria of the intestinal
tract and was not able to reduce the viral titers (4).
Similar results were obtained with an modified vaccinia virus
Ankara-based recombinant expressing the simian-human im-
munodeficiency virus (SHIV) strain SHIV89.6 gp160 (6), and
more recently, it has been demonstrated that mucosal immu-
* Corresponding author. Mailing address: National Cancer Institute,
Basic Research Laboratory, 41/D804, Bethesda, MD 20892. Phone:
(301) 496-2386. Fax: (301) 496-2386. E-mail: email@example.com.
† Present address: Tulane Regional Primate Research Center, Cov-
ington, LA 70433.
nization of macaques afforded better protection than subcuta-
neous immunization following intrarectal exposure to SHIVku2
(5). These studies suggest that cutaneous or intramuscular
immunization generates antigen-specific cells that may not
travel to mucosal sites (3, 11, 22, 32, 49).
A somewhat different conclusion was suggested by studies in
which macaques were immunized intramuscularly with the
highly attenuated poxvirus vector NYVAC encoding the
SIVmak6wGag, Pol, and Env products (7, 19). In this case
immunization resulted in long-term viremia containment fol-
lowing intravenous or intrarectal challenge with SIVmac251(7,
18a). Since, in these studies, all macaques were immunized by
the intramuscular route, the results suggested that even in the
absence of priming at mucosal sites, systemic immunization
can lead to virological control following SIVmacmucosal chal-
lenge exposure (7, 18a, 19).
To further explore these results, we designed a study to
directly assess the extent of mucosal immune responses to a
Gag immunodominant SIVmac251epitope following immuniza-
tion of macaques by either the intramuscular, intranasal, or
intrarectal route. Accordingly, two female macaques express-
ing the Mamu-A?01 major histocompatibility complex class I
molecule were used for each route of immunization, and the
extent and kinetics of the immune response following both
immunization and SIV challenge were measured in the blood
and in serial mucosal biopsy samples with Gag-specific tet-
ramer-staining reagents (1). Importantly, the size and specific-
ity of the anamnestic virus-specific CD8?T-cell responses to
the virus were investigated within 48 h of a SIVmac251intra-
rectal challenge exposure to determine whether it differed in
various anatomical compartments according to the route of
MATERIALS AND METHODS
Animals and procedures. Seven Mamu-A?01-positive macaques were involved
in this study. Animals 536 and 815 were immunized with three inoculations of 108
PFU of NYVAC/SIVgpeby the intramuscular route. Animals 582 and 816 were
immunized intranasally and animals 814 and 818 were immunized intrarectally
with three inoculations of 5 ? 108PFU of NYVAC/SIVgpeeach. The first boost
was given 1 month after the first immunization, and the second boost was given
3 months after the second immunization. All six immunized macaques and a
control naive macaque (no. 654) were challenged intrarectally with 30 mucosal
infectious doses of the SIVmac251(561)isolate (37) and sacrificed 48 h after
Blood samples were collected at several time points during the immunization
schedule as well as on the day of SIV exposure and sacrifice. Similarly, multiple
vaginal and rectal pinch biopsy samples were taken prior to and during the
At the time of sacrifice, blood, spleen, mesenteric, iliac, and pararectal lymph
nodes, vagina, cervix, jejunum, colon, and rectum samples were collected. The
tissues were placed in RPMI supplemented with 10% bovine serum and peni-
cillin/streptomycin. Rectal tissue was also placed in phosphate-buffered saline
(PBS)-bovine serum albumin solution and used for in situ tetramer staining.
FIG. 1. Control staining for tetramers. Staining of isolated lamina propria lymphocytes from vaginal and rectal biopsy samples obtained from
infected Mamu-A?01-negative and naive Mamu-A?01-positive macaques and macaque 654 before viral challenge, and staining with unrelated
tetramer on isolated vaginal and rectal lamina propria lymphocytes from immunized, infected Mamu-A?01-positive macaques (a) was used to
control for the specificity of the staining. Nonspecific binding accounted for up to 0.13% of the CD3?CD8?lymphocytes. Therefore, values above
this percentage could be considered positive. Tetramer staining of peripheral blood mononuclear cells (PBMCs) isolated prior to immunization
was negative in the five macaques examined (b).
11660STEVCEVA ET AL.J. VIROL.
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Isolation of tissue lymphocytes. Mononuclear cells were isolated from periph-
eral blood mononuclear cells, lymph nodes, spleen, intestines, vagina, and cervix.
Mononuclear cells from spleen and lymph nodes were isolated by mechanical
dissociation of the tissue and consecutive Ficoll gradient centrifugation. Tissues
from jejunum, colon, rectum, vagina, and cervix were isolated by a modification
of a previously published method (9, 21). Tissues were treated with 1 mM
dithiothreitol (ICN Biomedicals Inc., Aurora, Ohio) for 30 min, followed by
incubation in calcium- and magnesium-free Hanks’ balanced salt solution (Life
Technologies, Baltimore, Md.) three (intestines) to four (vagina and cervix)
times for 1 h with stirring at room temperature to remove the epithelial layer. At
this stage, pieces of tissue were fixed in 10% neutral formalin and embedded in
paraffin, and sections were cut and stained with hematoxylin and eosin. Micro-
scopic examination was performed to ensure that all of the epithelium was
removed and the lamina propria was intact.
Intraepithelial lymphocytes were then purified by Percoll gradient density
Tissue sections were cut into smaller pieces and incubated at 37°C in Iscove’s
medium supplemented with 10% fetal calf serum and penicillin/streptomycin
containing 400 U of collagenase D (Boehringer GmbH, Mannheim, Germany)
and 25 U of DNase (Worthington Biochemical Corporation, Lakewood, N.J.)
per ml for 2 to 3 h. Vaginal and cervical tissues were digested with 0.5 mg of
collagenase type IV (Sigma Chemical, St. Louis, Mo.) (50). The mononuclear
cells were isolated from the supernatant containing dissociated cells by Percoll
Flow cytometry. Fresh cells were directly stained with phycoerythrin-conju-
gated tetrameric complexes folded with the immunodominant Gag181-189 CM9
(p11c) peptide. Fluorescein isothiocyanate-conjugated anti-CD3? (Pharmingen,
San Diego, Calif.) and peridinin chlorophyll protein (PerCP)-conjugated anti-
CD8 (Becton Dickinson, San Jose, Calif.) were used in conjunction with the
As confirmation of results obtained from freshly isolated lymphocytes, lym-
phocytes were also cultured at a concentration of 3 ? 106/ml in RPMI enriched
with 10% human serum, with addition of 1 ?g of the appropriate peptide and 20
U of interleukin-2 per ml for 7 days (data not shown). Staining with tetrameric
complexes was done afterward as described above. Staining with unrelated tet-
ramer and of cells isolated from Mamu-A?01-negative or naive animals was used
as a negative control. Staining with phycoerythrin-CD4 (Becton Dickinson) was
used as a positive control.
In addition, cells were stained with fluorescein isothiocyanate-conjugated ac-
tivation markers CD25, CD69, and HLA-DR. Briefly, 5 ? 105lymphocytes
isolated by Ficoll diatrizoate or Percoll gradient centrifugation were incubated
with 2 ?g of tetrameric complexes and/or selected antibodies for 30 min at room
temperature. After washing the cells twice in Dulbecco’s phosphate-buffered
saline supplemented with 2% fetal calf serum and fixation in 1% paraformalde-
hyde (pH 7.4), samples were analyzed by flow cytometry with CellQuest and the
FACScalibur (Becton Dickinson) instrument.
Tetramer staining in situ. In situ tetramer staining was performed on fresh
tissues as previously described with some modifications (17, 48). Briefly, tissues
were collected by pinch biopsy, washed in cold PBS, and cut into small strips. The
resulting sections (n ? 4 to 6) were then incubated with 10 ?l of antigen-specific
tetramer labeled with indocarbocyanine (Amersham, Piscataway, N.J.) per sec-
tion and gently agitated at 37°C for 15 min. The tissue was then rinsed repeatedly
at 37°C with PBS and then twice with ice-cold PBS prior to fixation with cold 2%
paraformaldehyde for 20 min.
After additional washes, antibodies to CD3 (rabbit polyclonal; Dako) and CD8
(directly conjugated to fluorescein isothiocyanate; Becton Dickinson) were ap-
plied singly or together for 1 h. The tissues were then washed and incubated with
anti-rabbit immunoglobulin-Alexa 488 (Molecular Probes) when using only CD3
or anti-rabbit immunoglobulin-Alexa 568 when using both CD3 and CD8. Tis-
sues were then washed, mounted on a glass slide with antifading medium
(Vectashield; Vector Laboratories, Inc., Burlingame, Calif.), and examined by
Confocal microscopy was performed with a Leica TCS SP laser scanning
microscope equipped with three lasers (Leica Microsystems, Exton, Pa.). Indi-
vidual optical slices represent 0.2 ?m, and 20 to 60 optical slices were collected
at a 512- by 512-pixel resolution. The fluorescence of individual fluorochromes
was captured separately in sequential mode after optimization to reduce
bleedthrough between channels (photomultiplier tubes) with Leica software.
NIH Image version 1.62 and Adobe Photoshop version 6 software were used to
assign colors to each fluorochrome and the differential interference contrast
image (gray scale). Colocalization of antigens was indicated by the addition of
colors as indicated in the figure legends.
Intracellular cytokine staining. Intracellular cytokine staining was done on
jejunal lamina propria lymphocytes isolated at necropsy by a modified previously
published method (16, 24, 53). Isolated and previously frozen lamina propria
lymphocytes were thawed and washed. Viability was assessed by trypan blue dye
exclusion, and viable cells were counted. Cells were incubated for 1 h at 37°C in
5% CO2at a concentration of 106/ml in the presence of 1 ?l of anti-CD28
(Becton Dickinson), 1 ?l of anti-CD49d (Becton Dickinson), and 2 ?g of the SIV
Gag181-189 CM9 peptide per ml. Stimulation with 25 ng of phorbol myristate
acetate (Sigma-Aldrich Corp., St. Louis, Mo.) and 1 ?g of ionomycin (Sigma-
Aldrich Corp.) per ml for gamma interferon (IFN-?) or staphylococcal entero-
toxin B (Toxin Technology, Inc.) for tumor necrosis factor alpha (TNF-?) was
used as a positive control.
After 1 h of incubation, 10 ?g of brefeldin A (Sigma-Aldrich Corp.) was added
and cells were incubated for an additional 5 h. Cells were then washed twice with
PBS–2% fetal calf serum and stained for surface antigens with fluorescein iso-
thiocyanate-labeled anti-CD3 and PerCP-labeled anti-CD8. After incubating
them at room temperature for 30 min and washing them twice with PBS–2% fetal
calf serum, cells were fixed in Cytofix/Cytoperm (Pharmingen) for 20 min at 4°C.
Following two washes with Wash/Perm buffer (Pharmingen), cells were incu-
bated with phycoerythrin-conjugated anti-IFN-? or allophycocyanin-conjugated
anti-TNF-? antibodies for 30 min at 4°C. This was followed with two washes in
Wash/Perm buffer and direct reading of the samples on the FACScalibur flow
Cytotoxic T-lymphocyte assay. Cytotoxic T-lymphocyte assays were performed
as previously described (7). Fresh cells were cultured overnight in the presence
of 300 IU of interleukin-2 per ml and then incubated at different effector-to-
target cell ratios for 6 h with Mamu-A?01-positive,51Cr-labeled autologous
transformed B cells pulsed overnight with 1 ?g of a specific peptide per ml,
without peptide, or with an unrelated peptide.
Induction of CD8?T-cell response to Gag181-189 CM9 im-
munodominant peptide in blood and at mucosal sites by vac-
cination. Two Mamu-A?01-positive female macaques each re-
ceived three immunizations with NYVAC/SIVgpeby either the
intramuscular, intrarectal, or intranasal route. Virus-specific
CD8?T-cell response to the immunodominant Gag181-189
CM9 peptide in the blood and tissues of the immunized ma-
caques was quantitated by staining CD3?CD8?T cells with
the specific Mamu-A?01/Gag181-189 CM9 tetramer after each
immunization. The specificity of tetramer staining was assessed
following each immunization in isolated lymphocytes from bi-
opsy samples of both Mamu-A?01-positive uninfected ma-
caques and Mamu-A?01-negative infected macaques. Staining
with unrelated tetramer was also performed (Fig. 1a).
Staining of cells from tissue biopsy samples of a Mamu-
A?01-positive, SIVmac251-infected macaque revealed the pres-
ence of a population of tetramer-positive CD3?CD8?cells.
Many, if not most, of those tetramer-positive cells were found
to be larger (that is, to have a higher forward and side profile)
than those which would normally be included in more conven-
tional lymphocyte gating (Fig. 2) (2, 13, 30, 45). To explore the
possibility that this population represents activated CD8 T
cells, the same sample was stained with the activation markers
CD69 and CD25. By gating on cells of larger size, we demon-
strated that, in the tissues of this macaque, these large cells
expressed both the CD8 and CD69 markers, suggesting that
they might have been recently activated (data not shown).
Therefore, a slightly enlarged gate as shown in Fig. 2, upper
left panel, that included these cells was used for all further flow
cytometric analyses of tetramer-positive cells in the tissues and
blood of the immunized and control macaques.
With these gates, the percentage of CD3?CD8?T cells
staining with the Gag181-189 CM9 tetramer in the blood of the
11662STEVCEVA ET AL.J. VIROL.
FIG. 2. Gating of tissue lymphocytes for flow cytometry analysis. Extending the lymphocyte gate to include larger cells revealed a population of CD3?CD8?tetramer-positive cells
that was concealed when the conventional lymphocyte gate was used.
VOL. 76, 2002Gag-SPECIFIC CD8?T-CELL RESPONSES IN MACAQUES11663
FIG. 3. Tetramer staining during immunization. Immune responses during the immunization procedure were assessed by measuring the
percentage of CD3?CD8?Gag181-189 CM9-positive cells in blood (upper graphs in panels a, b, c, and d; arrows indicate time of immunization)
and in isolated lymphocytes from rectal and vaginal biopsy samples (flow charts in panels a, b, c, and d). Cells were gated through the CD3?CD8?
gate, and the percentage of Gag181-189 CM9-positive cells was determined by histogram analysis. The flow charts are shown here as dot blots
rather than histograms in order to better demonstrate the population of cells. An equal number of CD3?CD8?cells (104) was acquired for each
sample analyzed. Samples in which fewer than 5 ? 103CD3?CD8?cells were acquired are indicated (?). Times of immunization are indicated
on the graphs with arrows. (a) Findings in intrarectally (I.R.) immunized macaques 814 and 818 shown as a graph for blood and as flow charts for
biopsy samples underneath the graph. (b) Findings in intranasally (I.N.) immunized animals 816 and 582. (c) Findings in intramuscularly (I.M.)
immunized macaque 815. (d) Findings in intramuscularly immunized macaque 536. LP, lamina propria.
11664STEVCEVA ET AL.J. VIROL.
macaques immunized by the intranasal, intramuscular, and
intrarectal routes was determined (top panels of Fig. 3a to d).
These studies demonstrated the presence of tetramer-positive
cells in the blood of all immunized animals and showed no
significant difference among immunization routes. At the end
of the immunization period, the percentage of CD3?CD8?T
cells that were specifically recognized by the Gag-specific tet-
ramer in blood was in the range expected with this vaccine
modality (19). The cytotoxic T lymphocyte assay performed 2
weeks after the second immunization revealed specific lysis of
Gag181-189 CM9-pulsed, Mamu-A?01-positive,
autologously transformed B cells in some of the macaques (816
and 815) (data not shown).
The presence of Gag181-189 CM9-specific CD3?CD8?T
cells at mucosal sites was assessed on isolated lamina propria
lymphocytes from rectal and vaginal biopsy samples (bottom
panels of Fig. 3a, b, c, and d). We did not attempt to quantify
these cells because often the number of cells obtained from the
biopsy samples was insufficient to reliably compare frequen-
cies. In both macaques 814 and 818 immunized by the intra-
rectal route, a discrete population of cells staining the Gag181-
189 CM9 tetramer was detected in serial biopsy samples (Fig.
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11666 STEVCEVA ET AL.J. VIROL.
VOL. 76, 2002Gag-SPECIFIC CD8?T-CELL RESPONSES IN MACAQUES11667
3a, bottom panels). Similarly, in animals 816 and 582 immu-
nized by the intranasal route, a convincing staining for Gag181-
189 CM9 tetramer-positive cells in vaginal lamina propria was
detected at week 19 and/or week 20 in both macaques (bottom
panels of Fig. 3b). At week 20, a discrete population was also
found in the rectal lamina propria of macaque 816 (Fig. 3b).
Unexpectedly, in both macaques immunized by the intra-
muscular routes (815, bottom panels of Fig. 3c, and 536, bot-
tom panels of Fig. 3d), Gag181-189 CM9-positive CD3?CD8?
T cells were detected as early as week 6 from immunization in
both the rectal and vaginal lamina propria. Thus, Gag181-189
CM9-specific CD3?CD8?cell populations in the gastrointes-
tinal lamina propria and the cervicovaginal compartment were
induced by NYVAC/SIVgpein all of the immunized animals
regardless of the route of immunization.
To confirm these results with an independent approach,
tetramer-positive cells were visualized by in situ tetramer stain-
ing of rectal biopsy samples from a few macaques. Tissues from
a lymph node of a chronically infected macaque known to have
an extremely high percentage of CD3?CD8?Gag181-189
CM9-positive cells as well as cultured spleen cells from the
same animal were used as a positive control, and biopsy sam-
ples from uninfected, nonimmunized macaques were used as a
negative control. Spleen culture cells or lymph node tissue
(Fig. 4a) of chronically infected macaques had clusters of dou-
ble positive cells for Gag181-189 CM9 and CD8. Single cells
FIG. 4. In situ tetramer staining. Double immunofluorescent staining and image analysis were initially done on positive samples from cultured
spleen cells and from lymph nodes taken from a known Gag181-189 CM9-positive animal (a). In immunized macaques, positive staining is shown
in the colonic tissue from animal 816 2 weeks after the boost (b). Images for individual channels (CD3, green; SIV-Gag tetramer, red; differential
interference contrast, gray scale) are shown on the left side, and a larger merged image containing all three channels is shown on the right (b).
Several CD3?cells are present, and one is also labeled with the SIV-Gag tetramer. Bar, 10 ?m (b). FITC, fluorescein isothiocyanate; CY3,
11668STEVCEVA ET AL. J. VIROL.
with similar staining patterns were detected in vaginal and
rectal biopsy samples of the immunized macaques. Figure 4b
shows tetramer-positive cells in the colonic lamina propria of
animal 816 2 weeks after the second immunization.
Influence of route of immunization on anamnestic immune
response in systemic and mucosal compartments following
SIVmac251challenge exposure. All seven macaques were ex-
posed intrarectally to SIV251and euthanized 48 h postexpo-
sure. The time frame of 48 h postexposure was chosen because,
at the time of euthanasia, we wanted to capture and quantitate
the local secondary response to Gag181-189 CM9 before the
systemic spread of infection. The choice of a time frame of 48 h
postexposure was based on the information that mucosal ex-
posure to SIVmac251results in colonization of local lymph
nodes by day 2 to 3 postinfection (20; Chris Miller, personal
communication). Since the commitment to proliferation of
primed T cells upon encounter with the antigen occurs quickly
(0.5 to 2 h) (28) and a cycle of viral replication requires ap-
proximately 12 to 18 h, it is therefore reasonable to assume
that Gag-specific local memory T cells might be able to un-
dergo mitoses within 48 h and/or be recruited to this locale.
At necropsy, an SIV-specific response, higher than that
found after the last immunization in blood to the Gag181-189
CM9 epitope, was found in macaques 815 and 536, immunized
intramuscularly, both in some systemic and most mucosal com-
partments, and appeared to be higher in the latter (Fig. 5a). In
macaques immunized intranasally (macaques 816 and 582), the
response to the Gag181-189 CM9 epitope following challenge
exposure was present in most compartments and was generally
higher in mucosal compartments (Fig. 5b). However, in the
two macaques immunized intrarectally (macaques 814 and
818), this response appeared to be mainly confined to mucosal
sites (Fig. 5c). In animal 654, naive at the time of challenge
exposure, CD3?CD8?T cells staining the Gag181-189 CM9
tetramer were not found in any tissues (Fig. 5d).
These findings suggested that early viral replication follow-
ing rectal challenge may have preferentially expanded virus-
specific immune responses at the mucosal sites, since at 48 h
the virus may not be amplified sufficiently to induce a sizable
immune response at systemic sites. In fact, in the macaques
immunized by the intrarectal route, an expansion of virus-
specific responses was evident only at mucosal sites (Fig. 5c).
To correlate the observed immune responses after viral chal-
lenge to the level of virus in tissues, we isolated RNA either
from lymphocytes collected from tissues or from the entire
tissue of all seven macaques and quantitated viral RNA by
nucleic acid sequence-based amplification (NASBA) assay as
previously described. With this assay we can detect as few as
500 copies of RNA per ?g of total RNA (43). From our
estimate, derived from the yield of RNA from a known number
of cells cultured in vitro, 1 ?g of RNA corresponds to a total
of 104to 105cells. Analysis of RNAs from the spleen, blood,
vagina, and rectum of each macaque by NASBA resulted in
fewer than 500 copies of viral RNA in all samples (data not
VOL. 76, 2002Gag-SPECIFIC CD8?T-CELL RESPONSES IN MACAQUES11669
shown), suggesting that viral expression was still at too low a
level to be detected by the technique. We do not believe that
this lack of detection of viral RNA was related to an abortive
infection, since we infected a total of 34 naive macaques with
the same viral stock by the rectal route (37; our unpublished
Gag181-189 CM9-specific functional responses in the jejunal
lamina propria of all seven macaques were assessed by intra-
cellular cytokine staining of isolated lymphocytes following in
vitro stimulation with the specific peptide, using as a read-out
both TNF-? and IFN-? production. In all six immunized ma-
caques, considerable numbers of CD8?/??cells producing
both cytokines were found, and as expected, these cells were
absent in macaque 654 (Fig. 6, top panel). Surprisingly, a
number of CD8?/??cells also appeared to be producing either
IFN-? or TNF-? (Fig. 6, flow charts). This finding could be
related to a downregulation of the CD3 or the CD8?/? recep-
tor on the cell surface during the procedure, as noted by others
(29). The graphs on the top of Fig. 6 include only CD8?/??
cells that produced IFN-? (left top panel) or TNF-? (right top
FIG. 5. Tetramer staining after challenge. Macaques were challenged with SIVmac251and sacrificed 48 h later. SIV-specific cells were
determined as a percentage of Gag181-189 CM9-positive cells of the CD3?CD8?population in lymphocytes isolated from each tissue. An equal
number of CD3?CD8?cells (104) was acquired for each sample analyzed. SIV-specific responses in intramuscularly (I.M.) immunized macaques
536 and 815 (a) are shown as a graph (?, not done). Samples of blood lymphocytes at the time of necropsy and highly positive mucosal tissue
samples are shown as flowcharts beneath the graph for each macaque. Tetramer-positive cells in intranasally (I.N.) immunized animals 816 and
582 (only 1.152 ? 103CD3?CD8?cervical lamina propria cells were analyzed for animal 582) (b) and in intrarectally (I.R.) immunized macaques
818 and 814 (c) are shown. Animal 654, which was not immunized but was challenged, is shown (d). LP, lamina propria; LN, lymph node.
11670STEVCEVA ET AL.J. VIROL.
The percentage of Gag-specific CD8?cells expressing
IFN-? or TNF-? was derived by subtracting the spontaneous
secretion of cytokines in the absence of peptide stimulation
(see raw data on the flow charts in Fig. 6).
The extent of this response, although variable among the
animals, did not appear to be related to the route of immuni-
zation. Overall, the ability of lymphocytes at mucosal sites to
express cytokines did not differ among macaques immunized
by different routes.
The main finding in this study is that immunization of
macaques with a live attenuated vaccine, NYVAC/SIVgpe,
by either a mucosal (intrarectal and intranasal) or systemic
(intramuscular) route results in the appearance of Gag181-
189 CM9 tetramer-positive CD8?cells in mucosal tissues.
Furthermore, intrarectal challenge of such immunized ma-
caques with SIVmac251followed by sacrifice of the animals at
48 h after challenge led to the expansion of tetramer-posi-
tive CD8?cells in mucosal tissues in all macaques regardless
of the route of immunization. This confirmed that a systemic
(intramuscular) immunization led to mucosal CD8?T-cell
responses, as did mucosal immunization.
These results are somewhat at odds with studies reviewed
above (4–6) that show that the route of induction deter-
mines whether or not there is a mucosal immune response
and that, in fact, mucosal immunization is necessary for a
mucosal response. Thus, intramuscular and intradermal im-
VOL. 76, 2002 Gag-SPECIFIC CD8?T-CELL RESPONSES IN MACAQUES 11671
munization with naked DNA generates systemic immune
responses but is unable to confer protection at mucosal sites
(36). Similarly, subcutaneous immunization in mice with
HIV-1 gp160 expressing recombinant vaccinia virus induced
cytotoxic T lymphocytes only in the spleen but not in Peyer’s
patches or intestinal lamina propria (3).
However, it should be noted that systemic immunization
with recombinant vaccinia virus vac-gp160 protected three of
four macaques against intrarectal challenge with SIVmnevirus
47 (39) or, in another model, cats against feline immunodefi-
ciency virus (38). Similarly, such protection has been achieved
with live attenuated virus (41, 42) and whole killed virus (10).
Finally, in the case of the NYVAC/SIVgpevaccine, intramus-
cular immunization was previously shown to be able to protect
50% of the macaques that were challenged intrarectally with
SIVmac251from high viremia ((7) and an even higher number
of macaques when a DNA prime/NYVAC/SIVgpeboost was
It should be noted that in the studies where systemic
immunization led to at least some degree of mucosal immu-
nity, live virus vaccines were used. Such vaccines, as opposed
to peptide vaccines, may be more capable of leading to the
appearance of immune cells at mucosal sites, either because
of antigen circulation or because of the traffic of cells that
take up antigen.
Several additional conclusions concerning the responses
11672STEVCEVA ET AL. J. VIROL.
elicited by immunization by different routes could be drawn
from this study. First, tetramer-positive CD8?T cells were
found in the blood in all macaques regardless of the route of
immunization. This is in agreement with data obtained in
animals infected by different routes (18, 34, 51). Second,
intrarectal immunization induced CD8?T cells mainly in
mucosal tissue. Thus, while intramuscular and intranasal
immunization led to some level of tetramer-positive CD8?
cells in systemic tissues (spleen, iliac lymph node), intrarec-
tal immunization led to little or no tetramer-positive CD8?
cells at these locations. This finding is in agreement with
previous studies showing that intrarectal immunization is
less effective in inducing systemic responses (31). Since in-
trarectal immunization with a multicomponent-peptide HIV
vaccine led to cytotoxic T lymphocyte responses in the
spleen only when cholera toxin was used as an adjuvant (23),
it may be that systemic responses following mucosal immu-
nization require the use of adjuvants.
Intranasal immunization has been proven by numerous
reports to be particularly effective in inducing immune re-
sponses in the female genital tract (14, 15, 25, 44, 46).
Studies done in macaques with attenuated vaccinia virus
that express Env and Gag proteins of SIV or recombinant
live attenuated poliovirus expressing the SIV proteins p17gag
and gp41envconfirmed these findings regarding antibody
responses (12, 33). Studies in macaques that looked for
cellular responses in the cervicovaginal tract following in-
tranasal immunization, to our knowledge, have not been
performed. In this study, intranasal immunization induced
T-cell responses in both mucosal and systemic compart-
ments. In addition, cytokine production (IFN-? or TNF-?)
in response to stimulation with the specific peptide Gag181-
189 CM9 was high in both animals immunized intranasally.
One caveat of the results of this study is that, while responses
to immunization and challenge were measured, protection
against infection was not. Thus, it may be that mucosal immu-
nization is still necessary, even with live virus vaccines, to
achieve optimum protection. In a previous study with ALVAC/
SIV, another poxvirus-based vaccine, mucosal/systemic immu-
nization was not shown to provide better protection than sys-
temic immunization alone, but in this study, the mucosal and
systemic routes of immunization alone were not directly com-
pared (37). Clearly, studies in larger numbers of macaques
investigating protection achieved with different routes of im-
munization are now warranted.
VOL. 76, 2002Gag-SPECIFIC CD8?T-CELL RESPONSES IN MACAQUES11673
11674STEVCEVA ET AL.J. VIROL.
The base grants for the New England Regional Primate Research
Center and the Tulane Regional Primate Research Center are
RR00164 and RR00168.
We thank Tatiana Karpova from the Confocal Imaging Facility at
the National Cancer Institute for help, Nancy Miller for helpful dis-
cussion, John D. Altman for the Gag181-189 CM9 tetramer, Ruth
Woodward for animal care, and Steven Snodgrass for editorial assis-
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