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,§
*
Fearing Laboratory, Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Womens Hospital, Harvard Medical School, Boston, MA 02115;
AIDS Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02129;
Fenway Community Health Center, Boston, MA 02115; and
§
Memorial Hospital of Rhode Island, Pawtucket, RI 02860 and Brown University AIDS Program, Providence, RI 02903
| Abstract |
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| Introduction |
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Vigorous memory CTL responses against all the major HIV proteins have been demonstrated in the blood of infected individuals (8, 9, 10, 11). HIV-specific CTLs have also been isolated from various sites including the lymph node (12), spleen (12, 13), cerebrospinal fluid (14), and lung (15). Recently, SIV-specific CTLs were isolated from the vaginal mucosa of chronically infected macaques inoculated with SIV by the vaginal route (16), and HIV-specific CTLs were isolated from the cervical mucosa of infected women (17) indicating that, at least in the female, an antiviral response can be generated and maintained locally in the genital tract mucosa. We have recently demonstrated that the semen of HIV-infected men contains functional T lymphocytes, and that the majority of these cells are CD8+ and express a marker of cytolytic activity (18). In this study, we sought to determine whether T lymphocytes from the semen of seropositive men also had anti-HIV cytotoxic activity.
| Materials and Methods |
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Five seropositive men were recruited from Fenway Community
Health Center and Massachusetts General Hospital to provide semen and
blood samples. Informed consent was obtained from all individuals.
Eligibility criteria included a previous leukocytic semen specimen
(>5 x 104 viable leukocytes per ejaculate) and a CD4
count of >500/µl. The clinical data for each individual are
summarized in Table I
.
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Semen was obtained by masturbation into sterile specimen cups containing 10 ml of RPMI 1640. Blood was collected in EDTA-treated vacutainers. Viable semen round cells (SRCs)4 and PBMCs were isolated on density gradient separation medium (Ficoll-Hypaque, Pharmacia, Piscataway, NJ and washed three times in HBSS containing 100 µg/ml gentamicin and 1 µg/ml amphotericin B before resuspension in RPMI supplemented with 2 mM L-glutamine, 50 µg/ml gentamicin, 0.25 µg/ml amphotericin B, and 10% FCS (all obtained from Life Technologies, Grand Island, NY) (cRPMI). Since the isolated SRC fraction contains a large proportion of immature germ cells, SRCs (10% of sample) and PBMCs were applied to 8-spot slides, allowed to air dry, fixed in acetone, and later immunostained with Abs to CD3 and CD8 to enumerate exactly the number of T cells (18). Using published data obtained from leukocytic HIV+ individuals, we ascribed arbitrary values to the proportion of CD3 cells in each SRC population for immediate cloning purposes and adjusted the values after staining (18). Arbitrary values were 1% for SRCs and 70% for PBMCs. Cells were seeded in 96-well plates at numbers shown previously to approximate limiting dilution (10300 cells/well) in 100-µl volumes containing 1.5 x 106 irradiated (5000 rad) allogeneic PBMCs/ml, 1 µg/ml PHA, and 50 U/ml IL-2 (Boehringer Mannheim, Indianapolis, IN) in cRPMI. After 2 to 3 wk, wells exhibiting growth were restimulated with irradiated PBMCs, PHA, and IL-2.
Immunostaining
T cells were enumerated by a standard indirect immunohistology
technique that has been described previously in detail (18). Primary
Abs recognizing CD3 and CD8 Ags (Dako, Carpinteria, CA) were used, and
Ab-positive cells were visualized using an alkaline
phosphatase/anti-alkaline phosphatase kit (Dako). A total of 200
cells were counted per Ab, and the number of positive cells in the
semen sample was calculated from the SRC count. Clones were phenotyped
using similar methodology, with Abs recognizing the following Ags: CD3,
CD8, CD4, CD57 (Dako), TCR
ß (BF1, a kind gift of Dr. Michael
Brenner, Department of Rheumatology, Brigham and Womens Hospital),
and TIA-1 (a kind gift of Dr. P. Johnson, Dana-Farber Cancer Institute,
Boston, MA) (19).
B lymphoblastoid cell lines (BLCLs)
Before cloning, BLCLs were established by transformation of peripheral blood B cells by EBV obtained from the supernatant of the B95-8 cell line (8).
Recombinant vaccinia viruses and synthetic HIV-1 peptides
Recombinant vaccinia viruses constructed from the HIV IIIB isolate and expressing the following proteins were used in this study: env, gag, and pol (Vabt 408); gag (Vabt 401); p17 (Vabt 228); p24 (Vabt 286) (kind gifts of Therion Biologics, Cambridge, MA); env (PE16); and pol (CF21) (National Institutes of Health AIDS Repository, Rockville, MD). Wild-type vaccinia virus was used as a control (NYCBH, Therion Biologics). Synthetic p24 HIV peptides (1221 aa) were synthesized as described previously (20). Lyophilized peptides were resuspended at 2 mg/ml in 10% DMSO.
Cytotoxicity assay
Cloned T cells were tested for HIV-specific cytolytic activity in a standard chromium release assay (8). Target cells were autologous BLCLs pulsed with HIV peptides or infected with vaccinia constructs expressing HIV proteins (14). Partially MHC-mismatched allogeneic BLCLs were also used in MHC restriction experiments. In brief, BLCLs to be vaccinia infected were incubated with 3 to 4 multiplicities of infection per cell of recombinant virus for 16 to 18 h at 37°C. Cells were washed twice, labeled with 150 µCi Na251Cr for 2 to 3 h, and washed four times. The sensitization of BLCLs with peptides was achieved by incubating cells with 10 µg/ml of peptide with the chromium. Clones and labeled BLCLs were incubated together in various ratios in 150-µl volumes in 96-well plates at 37°C for 4 to 6 h. Supernatants (100 µl) were subsequently harvested and counted in a Cobra gamma counter (Packard Instrument, Meriden, CT). The percentage of specific lysis was calculated from the following formula: 100 x ([experimental release - spontaneous release]/[maximum release - spontaneous release]). Maximum release values were obtained by the lysis of targets with 5% Triton X-100. Assays were only evaluated if spontaneous release was <30% of maximum release. Clones were considered positive if lysis of the targets was at least three times greater than the lysis of the control vaccinia target and if the HIV-1-specific lysis was >10% (14, 21).
| Results |
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Our previous studies have shown that viable CD3+ cell
counts in HIV+ men range from undetectable to >2.2 x
105 per ejaculate, with a median value of 9.0 x
103 in men taking antiretroviral medication and 2.5 x
104 in men who are not on therapy (18). Since the number of
cells recovered from semen is relatively small and the estimated
frequency of HIV-specific T cells in asymptomatic individuals is
estimated to range from 1/102 to 104 in PBMCs
(11, 22, 23), we optimized the conditions of this study by recruiting
men who had previously had a leukocytic semen sample (defined as
>5 x 104 viable mononuclear leukocytes per
ejaculate). A previous study from our laboratory indicates that this is
not a major selection step, since 83% of HIV+ men with
peripheral blood CD4 counts of >200/µl that are not on
antiretroviral therapy are included in this category (18). As shown in
Table I
, the median CD4 count of the patients was 932, and the median
length of infection was 12 yr. None of the individuals were on
antiretroviral therapy, and all were asymptomatic, with the exception
of one man who had recently developed Kaposis lesions.
The numbers of viable round cells recovered from the semen samples used
in this study ranged from 2.5 to 34.0 x 105 cells per
ejaculate (Table II
). Immunostaining
revealed that between 1.1% and 14.3% of round cells (median 2.5%)
were CD3+, with CD8+ lymphocytes contributing
from 33 to 95% of the T cell population. Cells were successfully
cloned from semen at a limiting dilution with PHA and IL-2, but cloning
efficiencies were considerably lower than those derived from blood
(Fig. 1
). Fungal contamination was also
observed in some semen-derived cultures, but these wells were not taken
into account when calculating cloning efficiencies. Wells exhibiting
proliferation were restimulated, and those which were successfully
expanded were screened for anti-HIV cytolytic activity using
autologous BLCLs infected with a trivalent vaccinia vector expressing
env, gag, and pol proteins. HIV-specific cytolytic activity was found
in all five donors, with multiple lines isolated from each donor (Table II
).
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To precisely define the HIV cytolytic responses in semen, lines
from three individuals were expanded and subsequently tested for
activity against the individual gag, pol, and env proteins (Table III
). Activity against all three proteins
was noted in each donor, indicating that CTLs derived from the
urogenital tract have a broad-based activity to HIV. With the exception
of two lines, all lines had activity against a single protein. In donor
9320, the predominant protein recognized was pol (43% of all specific
activity), followed by gag (36%) and envelope (21%). In donors POGO
and 161J, the predominant protein recognized by CTLs was gag (67 and
57% of specific activities, respectively). In one individual (9320),
we also performed a parallel analysis on a small number of lines
derived from the peripheral blood. Although pol-specific activity
dominated in the semen of this individual, only one of four blood lines
was pol-specific.
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Two of the gag-specific lines from donor POGO were examined in
greater depth for fine epitope specificity, phenotype, and MHC
restriction. We first used vaccinia constructs expressing the p17 and
p24 regions of gag to demonstrate that both gag-specific lines
recognized epitopes within the p24 protein (Fig. 2
). When a series of nested 21-mer
peptides covering the p24 sequence in pools of four (data not shown)
were used followed by individual peptides, data indicated that both
lines recognized the gag peptide representing aa 303 to 324.
Analysis with shorter (12-mer) peptides indicated that both recognized
the aa sequence 307 to 318. Using BLCLs partially matched at MHC class
I loci, we were also able to determine that both of these lines were
restricted by HLA B44 (Fig. 3
).
Phenotyping studies indicated that 100% of the cells in both lines
stained positively for TCR
ß, CD8, and TIA-1.
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| Discussion |
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The presence of HIV-specific CTLs in a mucosal site was first
demonstrated with T cells isolated from bronchoalveolar lavages (15).
The first isolation of HIV- or SIV-specific CTLs from the genital tract
was by Lohman et al. (16). Macaques were vaginally infected with SIV,
acutely and chronically infected animals were sacrificed, and vaginal
IELs were extracted, expanded, and tested for CTL activity. IELs were
characteristically CD8+, TCR
ß+, and
CD2+; precursor frequencies were similar to that in macaque
blood; and chronically infected monkeys had greater numbers of
virus-specific cells than those that were acutely infected. More
recently, HIV-specific CTLs were cloned from cervical mononuclear cells
that had been extracted from HIV-infected women by cervical cytobrush
collection (17). Although cytobrush sampling can induce local bleeding,
the IEL-like phenotype of these cells was suggestive of their mucosal
derivation. The authors noted HIV-specific activity in the cervix of
63% of the subjects sampled; the highest anti-HIV cervical CTL
activity was associated with a peripheral blood CD4 count of >500
cells/µl. A comparison between small numbers of blood and
cervix-derived gag-specific lines in one donor indicated that CTLs
derived from the two sites recognized common epitopes. We did not
undertake a comparison of epitope specificities in the paired lines
that we derived from one of our donors, but we did note a predominance
of pol specificity in semen that was not seen in the blood of this
individual. Clearly, it still remains to be established whether blood
and mucosal CTLs exhibit different CTL repertoires, whether these will
reflect differences in TCR repertoires, where and how Ag is presented
to these cells, or whether distinct HIV variants are being recognized
(3).
The isolation of HIV-specific cytotoxic T cells from the female and male urogenital tracts indicates that virus-specific lymphocytes are recruited to the urogenital mucosa of HIV-infected individuals. The presence of these effector cells in the genital tract may be critical in controlling local HIV infection, thus reducing the viral load in mucosal secretions and the chance of transmission to partners during sexual intercourse. A study looking at the correlation of CTL activity with viral load in semen is currently underway. Indications that a local immune response may prevent dissemination of virus come from a study which found that some seronegative women with seropositive partners and a history of multiple unprotected sexual exposures had HIV-specific secretory IgA but not IgG in their vaginal secretions (31). We presently hypothesize that an appropriately immunized individual with a strong, local, antiviral mucosal immune response should be able to eradicate or to locally contain HIV following genital transmission. If partners are concordant for MHC class I molecules, an immunized individual may also be able to specifically kill donor HIV-infected cells derived from the genital secretions of their partner (32, 33). In contrast, MHC discordance may result in a host vs donor immune response, and this allogeneic recognition may result in an alternative mechanism of eradicating virally infected cells. Whether MHC discordance between sexual partners would decrease the chance of virus transmission or concordance would increase sexual transmission, as has been recently shown in a perinatal transmission study, has yet to be investigated (34).
Clearly it would be advantageous to develop an anti-HIV vaccine that would elicit HIV-specific mucosal CTLs. Although some studies indicate that immunization at a mucosal site is not a prerequisite for induction of a mucosal immune response (35, 36), there is a substantial amount of evidence to indicate that mucosal immunization strategies are more effective at generating a local response (37). In addition, long-lived antiviral CTLs can be detected in mucosal tissues after mucosal but not systemic immunization, suggesting that the maintenance of memory cells is also dependent upon the chosen route of immunization (38). Of further note is the observation that inoculation at proximal mucosal sites appears to be more effective at inducing measurable immune responses than inoculation at distant mucosal sites. For example, recent studies have indicated the effectiveness of a vaginal or rectal immunization protocol in inducing a genital tract immune response (39, 40, 41). Consequently, we plan to address in our future studies whether antiviral CTL responses can be induced in the male urogenital tract by vaccination and, if so, which routes of immunization are the most effective at inducing and maintaining a local immune response.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Alison Quayle, Fearing Laboratory. Thorn 217, 75 Francis Street, Brigham and Womens Hospital, Boston, MA 02115. E-mail address: ![]()
3 Mayer, K. H., S. L. Boswell, R. S. Goldstein, W. Lo, C. Xu, L. Tucker, M. P. Pasquale, R. DAquila, and D. J. Anderson. 1997. HIV persistence in semen after adding indinavir to combination antiretroviral therapy. Submitted for publication. ![]()
4 Abbreviations used in this paper: SRC, semen round cell; BLCL, B lymphoblastoid cell line; IEL, intraepithelial lymphocyte. ![]()
Received for publication January 22, 1998. Accepted for publication June 5, 1998.
| References |
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ß or 
) and CD3- lymphocytes isolated from normal human gut epithelium display phenotypical features different from their counterparts in peripheral blood. Eur. J. Immunol. 20:1097.[Medline]
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