Unusually high frequencies of HIV-specific cytotoxic T lymphocytes in humans

CTL specific for the HIV belong to the CD8 subset of T lymphocytes, and their activity is restricted by class I HLA transplantation Ag. In this report, HIV-specific CTL and their precursor cells were quantified by limiting dilution analysis. CTL were recovered from the lungs, lymph nodes, and blood of asymptomatic seropositive carriers and of patients with AIDS. HIV was found to be very immunogenic. High frequencies of both HIV-specific CTL and CTL precursor cells were detected in infected individuals. These CTL killed autologous HIV-infected macrophages and T4 lymphoblasts. They also killed doubly transfected P815-A2-env-LAV mouse tumor cells, which express the human HLA-A2 gene and the HIV-1 env gene. In the longitudinal studies of two HIV-infected patients, CTL and CTL precursor cell frequencies decreased as the clinical and immunologic status of the patients deteriorated. Most surprisingly, PBL from seronegative donors also responded to HIV stimulation in vitro and generated large numbers of HLA-restricted, HIV-specific CTL.     

The anti-idiotypic antibody 1F7 selectively inhibits cytotoxic T cells activated in HIV-1 infection

Circulating CD8+ T lymphocyte numbers rise substantially following infection with HIV-1. This expanded CD8+ T cell population includes HIV-specific CTL and CTL that kill activated uninfected CD4+ lymphocytes. Experimental, epidemiological and clinical evidence supports the possibility that expansion of CD8+ CTL contributes to CD4+ T cell depletion and disease progression in human HIV infection. Therefore, modulation of CD8+ T cell numbers or of certain CD8+ CTL activated in HIV-infected individuals may be beneficial. It was found that 1F7, a mAb against an idiotype common to anti-HIV and anti-simian immunodeficiency virus (SIV) antibodies, selectively inhibited both anti-HIV CTL and CTL against uninfected CD4+ T cells. Alloantigen-specific CTL and NK cells from either HIV-infected individuals or controls were unaffected by 1F7. Prolonged incubation of CD8+ T cells from HIV-infected individuals with 1F7 induces apoptosis, which was shown to be reflected functionally in reduced total CTL activity and in especially reduced CTL activity against uninfected CD4+ lymphocytes. The selective reactivity of 1F7 with certain CD8+ CTL could be applied towards the modulation of CD8+ T cell responses involved in AIDS pathogenesis.     

Frequencies of ex vivo-activated human immunodeficiency virus type 1-specific gamma-interferon-producing CD8+ T cells in infected children correlate positively with plasma viral load

HIV-specific CD8+ T cells are critical in controlling human immunodeficiency virus (HIV) replication. We present the evaluation of a gamma-interferon (IFN-gamma)-based enzyme linked immunospot (ELISPOT) assay for the quantification of HIV-specific CD8+ T cells from HIV-infected children. We studied 20 HLA-A*0201-positive HIV-infected children. The IFN-gamma production in response to stimulation with two HLA-A*0201-restricted immunodominant CD8 epitopes (SLYNTVATL [SL9] in Gag and ILKEPVHGV [IV9] in Pol) was tested using the ELISPOT assay. The results were compared to labeling with the corresponding tetramers. Among the 20 children, 18 had detectable responses against the SL9 and/or the IV9 epitope using the ELISPOT assay (medians, 351 and 134 spot-forming cells/10(6) peripheral blood mononuclear cells, respectively). Comparison of results from the tetramer and ELISPOT assays suggests that only a fraction of HIV-specific CD8+ T cells were able to produce IFN-gamma. Most importantly, we found that the frequencies of IFN-gamma-producing CD8+ T cells were positively correlated with the viral load whereas the frequencies of tetramer-binding CD8+ T cells were not. The high sensitivity of the ELISPOT assay and the fact that this functional assay provided information different from that of tetramer labeling support its use for measurement of HIV-specific CD8+ T cells. In conclusion, our results show that the ex vivo-activated IFN-gamma-producing HIV-specific CD8+ T-cell subset is dependent upon continuous antigenic stimulation.     

Characterization of porcine T lymphocytes and their immune response against viral antigens.

T lymphocytes play a central role in the antigen-specific immune response against various pathogens. To detect and to characterize porcine T lymphocytes, monoclonal antibodies (mAb) against leukocyte differentiation antigens had been raised and classified for their specificity. Analyses of porcine T lymphocytes with specific mAb against CD4 and CD8 differentiation antigens revealed differences in the composition of the porcine T-lymphocyte population compared to other species. In addition to the known subpopulations, CD4+CD8- T helper cells and CD4-CD8+ cytolytic T lymphocytes, extra-thymic CD4+CD8+ T lymphocytes and a substantial proportion of CD2-CD4-CD8- T cell receptor (TcR)-gamma delta+ T cells could be detected in swine. Functional analyses of porcine T-lymphocyte subpopulations revealed the existence of two T-helper cell fractions with the phenotype CD4+CD8- and CD4+CD8+. Both were reactive in primary immune responses in vitro, whereas only cells derived from the CD4+CD8+ T-helper-cell subpopulation were able to respond to recall antigen in a secondary immune response. With regard to T lymphocytes with cytolytic activities, two subsets within the CD4-CD8+ T-cell subpopulation could be defined by the expression of CD6 differentiation antigens: CD6- cells which showed spontaneous cytolytic activity and CD6+ MHC I-restricted cytolytic T lymphocytes including virus-specific cytolytic T lymphocytes. These results enable now a detailed view into the porcine T-cell population and the reactivity of specific T cells involved in the porcine immune response against pathogens. Furthermore this knowledge offers the possibility to investigate specific interactions of porcine T lymphocytes with virus-specific epitopes during vaccination and viral infections.     

HIV-specific cytotoxic T lymphocytes against alveolar macrophages: specificities and downregulation

To analyse the evolution of alveolar-lymphocyte-mediated cytotoxic activity directed against autologous alveolar macrophages (AM), cytotoxic assays against various HIV⁺ target cells were performed in a cohort of 75 patients with HIV-associated lymphoid interstitial pneumonitis (LIP) studied at distinct stages of HIV infection. Our data confirm that alveolar HIV-specific cytotoxic T lymphocytes (CTL) against AM were detectable before AIDS in patients with CD8⁺ LIP. Mild CD8⁺ lymphocytic alveolitis occurs silently in 62% of stage II and III patients with no respiratory symptoms. In these cases, the lack of spontaneous alveolar-lymphocyte-mediated cytotoxic activity against autologous AM may contrast with the detection of primary alveolar CTL specific for HIV proteins such as nef. In AIDS patients, the alveolar CTL lytic efficiency against both AM- and HIV-antigen-expressing cells can be inhibited by a suppressore factor produced by alveolar CD8⁺ CD57⁺ cells. Therefore, spontaneous CTL lysis of AM may be (1) limited to a subgroup of patients with active LIP and (2) controlled by distinct mechanisms, including suppressor phenomenons, and HIV replication levels in AM.     

Novel Mucosal DNA-MVA HIV Vaccination in Which DNA-IL-12 Plus Cholera Toxin B Subunit (CTB) Cooperates to Enhance Cellular Systemic and Mucosal Genital Tract Immunity

Induction of local antiviral immune responses at the mucosal portal surfaces where HIV-1 and other viral pathogens are usually first encountered remains a primary goal for most vaccines against mucosally acquired viral infections. Exploring mucosal immunization regimes in order to find optimal vector combinations and also appropriate mucosal adjuvants in the HIV vaccine development is decisive. In this study we analyzed the interaction of DNA-IL-12 and cholera toxin B subunit (CTB) after their mucosal administration in DNA prime/MVA boost intranasal regimes, defining the cooperation of both adjuvants to enhance immune responses against the HIV-1 Env antigen. Our results demonstrated that nasal mucosal DNA/MVA immunization schemes can be effectively improved by the co-delivery of DNA-IL-12 plus CTB inducing elevated HIV-specific CD8 responses in spleen and more importantly in genital tract and genito-rectal draining lymph nodes. Remarkably, these CTL responses were of superior quality showing higher avidity, polyfunctionality and a broader cytokine profile. After IL-12+CTB co-delivery, the cellular responses induced showed an enhanced breadth recognizing with higher efficiency Env peptides from different subtypes. Even more, an in vivo CTL cytolytic assay demonstrated the higher specific CD8 T-cell performance after the IL-12+CTB immunization showing in an indirect manner its potential protective capacity. Improvements observed were maintained during the memory phase where we found higher proportions of specific central memory and T memory stem-like cells T-cell subpopulations. Together, our data show that DNA-IL-12 plus CTB can be effectively employed acting as mucosal adjuvants during DNA prime/MVA boost intranasal vaccinations, enhancing magnitude and quality of HIV-specific systemic and mucosal immune responses.     

Cutting edge: RANTES regulates Fas ligand expression and killing by HIV-specific CD8 cytotoxic T cells.

Based on the previous observation that RANTES mediates the cytotoxic activity of human HIV-specific CD8+ T cells via the chemokine receptor CCR3, we studied the effect of this chemokine on different effector CD8+ cytolytic cells requiring Fas/Fas ligand (FasL) or perforin-dependent pathway. In CTLs derived from PBMCs of HIV-infected patients, both the spontaneous and the RANTES-induced cytotoxicity were inhibited by anti-FasL neutralizing Abs. In contrast, allogeneic CTLs or NK cells killing through perforin were not affected by RANTES and anti-FasL Ab. Accordingly, RANTES enhanced the expression of FasL in a concentration- and time-dependent manner in HIV-specific CTLs, whereas anti-RANTES Ab decreased markedly FasL expression. Finally, cell surface expression of FasL protein in HIV-specific CTLs was also up-regulated by eotaxin, a selective ligand for CCR3. Our observations show that the action of RANTES via CCR3 is necessary to regulate FasL expression on HIV-specific CD8+ T cells that kill through the Fas/FasL pathway.     

Human immunodeficiency virus gag and pol-specific CD8 T cells in perinatal HIV infection.

BACKGROUND: Binding of fluorochrome-conjugated MHC class I tetramers is a powerful means to detect antigen-specific CD8 T lymphocytes. In human immunodeficiency virus (HIV) infection, cellular immune response is essential in curtailing HIV disease progression but gaps persist in our understanding of HIV-specific cells during the disease course. In this study, we evaluated tetramer binding HIV-specific CD8 T cells in HIV-infected children. METHODS: Fluorescently labeled tetramers for HIV gag and pol were utilized to quantify antigen-specific cells by flow cytometry using a whole blood labeling method in a cohort of 19 HLA-A2+ HIV-infected children (age range 1 month to 17 years). RESULTS: Fourteen children had detectable gag (median 0.4%) and pol (median 0.1%) binding CD8 T cells, three children had gag binding cells only, and two had neither. Numbers of gag and pol binding cells correlated with each other and each correlated independently with total CD8 T cells and total CD4 T cells. CONCLUSIONS: HIV gag and pol-specific CD8 T cells are maintained during the chronic phase of HIV infection in children and CD4 lymphocytes appear to be important for sustaining their levels.     

Cell-mediated suppression of HIV-specific cytotoxic T lymphocytes

CTL specific for HIV have been described in lungs of infected patients at early stages of HIV disease. In order to characterize the evolution over time of HIV-specific CTL, we have analyzed the cytotoxic function and the cell surface phenotype of the alveolar lymphocytes from 41 patients at various stages of HIV disease. We demonstrated a progressive decline of alveolar anti-HIV CTL activity and detected Ts cells from the lungs of patients with advanced HIV disease. These alveolar T cells strongly suppressed the effector phase of anti-HIV CTL lysis. They lacked a marked specificity of function because they also block anti-HLA CTL response and were not restricted by the HLA-class-I transplantation Ag. They displayed the CD3, CD8, and HNK1 markers, were CD4 and CD16 negative, and lacked NK activity. The presence of Ts cells at late stages of HIV disease could thus partly explain the inefficiency of host defenses against HIV.     

HIV-specific cytotoxic cell frequencies measured directly ex vivo by the Lysispot assay can be higher or lower than the frequencies of IFN-gamma-secreting cells: anti-HIV cytotoxicity is not generally impaired relative to other chronic virus responses

CD8(+) T cells in HIV-infected patients are believed to contribute to the containment of the virus and the delay of disease progression. However, the frequencies of HIV-specific CD8(+) T cells, as measured by IFN-gamma secretion and tetramer binding, often do not correlate with a delay in disease progression during chronic infection. Using the Lysispot and ELISPOT assays, we measured the frequencies of cytotoxic and IFN-gamma-secreting T cells responding to overlapping peptides from Gag, Nef, Env, and Pol consensus HIV-1 clade B sequences. PBMC from the majority of HIV-infected subjects have significant frequencies of HIV-specific cells that killed targets within 5 h directly ex vivo. The relative frequencies of IFN-gamma-secreting and cytotoxic cells varied markedly between different HIV peptide pools within the same patient, and some T cells lysed targets without secreting IFN-gamma. These results indicate that measurement of IFN-gamma production alone may be insufficient to evaluate the breadth of the HIV-specific T cell response. Also, neither the CTL to IFN-gamma ratios nor the ex vivo CTL frequencies specific for different HIV proteins were consistently lower than responses specific for two other chronic viral infections, human CMV and EBV, within the same subjects. Thus ex vivo cytotoxic T cell frequencies do not provide evidence for a model of "preterminal differentiation" of HIV-specific CD8(+) T cells during chronic HIV infection. Analysis of the frequency of directly cytotoxic HIV-specific T cells may be of considerable value in the assessment of disease progression and the potential efficacy of HIV vaccines.     

Dynamics of HIV-specific CD8+ T lymphocytes with changes in viral load.The RESTIM and COMET Study Groups

The influence of HIV burden variations on the frequencies of Ag-specific CD8+ T cell responses was evaluated before and during highly active antiretroviral therapy by analyzing the number, diversity, and function of these cells. The frequencies of HLA-A2-restricted CD8+ PBL binding HLA-A2/HIV-epitope tetramers or producing IFN-gamma were below 1%. A panel of 16 CTL epitopes covering 15 HLA class I molecules in 14 patients allowed us to test 3.8 epitopes/patient and to detect 2.2 +/- 1.8 HIV epitope-specific CD8+ subsets per patient with a median frequency of 0.24% (0.11-4. 79%). During the first month of treatment, viral load rapidly decreased and frequencies of HIV-specific CD8 PBL tripled, eight new HIV specificities appeared of 11 undetectable at entry, while CMV-specific CD8+ PBL also appeared. With efficient HIV load control, all HIV specificities decayed involving a reduction of the CD8+CD27+CD11ahigh HIV-specific effector subset. Virus rebounds triggered by scheduled drug interruptions or transient therapeutic failures induced four patterns of epitope-specific CD8+ lymphocyte dynamics, i.e., peaks or disappearance of preexisting specificities, emergence of new specificities, or lack of changes. The HIV load rebounds mobilized both effector/memory HIV- and CMV-specific CD8+ lymphocytes. Therefore, frequencies of virus-specific CD8 T cells appear to be positively correlated to HIV production in most cases during highly active antiretroviral therapy, but an inverse correlation can also be observed with rapid virus changes that might involve redistribution, sequestration, or expansion of these Ag-specific CD8 T cells. Future strategies of therapeutic interruptions should take into account these various HIV-specific cell dynamics during HIV rebounds.     

Peripheral blood cytotoxic gammadelta T lymphocytes from patients with human immunodeficiency virus type 1 infection and AIDS lyse uninfected CD4+ T cells,and their cytocidal potential correlates with viral load

Progression of human immunodeficiency virus type 1 (HIV-1) infection in humans is marked by declining CD4+-T-cell counts and increasing virus load (VL). Cytotoxic T lymphocytes (CTL) play an important role in the lysis of HIV-infected cells, especially during the early phase of asymptomatic infection. CTL responses in the later phase of disease progression may not be as effective since progressors with lower CD4+-T-cell counts have consistently higher VL despite having elevated CTL counts. We hypothesized that, apart from antiviral effects, some CTL might also contribute to AIDS pathogenesis by depleting CD4+ T cells and that this CTL activity may correlate with the VL in AIDS patients. Therefore, a cross-sectional study of 31 HIV-1-infected patients at various clinical stages was carried out. Purified CTL from these donors as well as HIV-seronegative controls were used as effectors against different human cell targets by using standard 51Cr release cytolytic assays. A direct correlation between VL and CTL-mediated, major histocompatibility complex (MHC)-unrestricted lysis of primary CD4+-T-cell, CEM.NKR, and K562 targets was observed. CD4+-T-cell counts and duration of infection also correlated with MHC-unrestricted cytolytic activity. Our data clearly show that gammadelta CTL are abnormally expanded in the peripheral blood of HIV-infected patients and that the Vdelta1 subset of gammadelta T cells is the main effector population responsible for this type of cytolysis. The present data suggest that gammadelta CTL can contribute to the depletion of bystander CD4+ T cells in HIV-infected patients as a parallel mechanism to HIV-associated immunopathogenesis and hence expedite AIDS progression.     

Human immunodeficiency virus-specific circulating CD8 T lymphocytes have down-modulated CD3zeta and CD28, key signaling molecules for T-cell activation

Although human immunodeficiency virus (HIV)-infected subjects without AIDS have a high frequency of HIV-specific CD8 T lymphocytes, cellular immunity is unable to control infection. Freshly isolated lymphocytes often do not lyse HIV-infected targets in 4-h cytotoxicity assays. A large fraction of circulating CD8 T cells from HIV-infected donors down-modulate CD3zeta, the signaling component of the T-cell receptor complex, which is reexpressed in vitro coincident with the return of cytotoxic function. To investigate further the link between CD3zeta down-modulation and possible CD8 T-cell functional defects, we used flow cytometry to characterize further the properties of the CD3zeta-down-modulated subset. HIV-specific CD8 T cells, identified by tetramer staining, are CD3zeta(-). CD8 T cells with down-modulated CD3zeta also do not express the key costimulatory receptor CD28 and have the cell surface phenotype of activated or memory T cells (HLA-DR(+) CD62L(-)). After T-cell activation, CD3zeta-down-modulated cells express the activation marker CD69 but not the high-affinity interleukin 2 (IL-2) receptor alpha-chain CD25 and produce gamma interferon but not IL-2. Therefore HIV-specific CD8 T cells have down-modulated key signaling molecules for T-cell activation and costimulation and require exogenous cytokine stimulation. The typical impairment of HIV-specific CD4 T helper cells, which would normally provide specific CD8 T-cell stimulation, means that in vivo CTL function in vivo is compromised in most HIV-infected individuals. In AIDS patients, the functional defect is more severe, since CD3zeta is not reexpressed even after IL-2 exposure.     

Administration of a Toll-Like Receptor 9 Agonist Decreases the Proviral Reservoir in Virologically Suppressed HIV-Infected Patients

Toll-like receptor (TLR) agonists can reactivate HIV from latently infected cells in vitro. We aimed to investigate the TLR-9 agonist, CPG 7909''s in vivo effect on the proviral HIV reservoir and HIV-specific immunity. This was a post-hoc analysis of a double-blind randomized controlled vaccine trial. HIV-infected adults were randomized 1∶1 to receive pneumococcal vaccines with or without 1 mg CPG 7909 as adjuvant at 0, 3 and 9 months. In patients on suppressive antiretroviral therapy we quantified proviral DNA at 0, 3, 4, 9, and 10 months (31 subjects in the CPG group and 37 in the placebo-adjuvant group). Furthermore, we measured HIV-specific antibodies, characterized T cell phenotypes and HIV-specific T cell immunity. We observed a mean reduction in proviral DNA in the CPG group of 12.6% (95% CI: −23.6–0.0) following each immunization whereas proviral DNA in the placebo-adjuvant group remained largely unchanged (6.7% increase; 95% CI: −4.2–19.0 after each immunization, p = 0.02). Among participants with additional cryo-preserved PBMCs, HIV-specific CD8+ T cell immunity as indicated by increased expression of degranulation marker CD107a and macrophage inflammatory protein 1β (MIP1β) tended to be up-regulated following immunization with CPG 7909 compared with placebo as adjuvant. Further, increasing proportion of HIV-specific CD107a and MIP1β-expressing CD8+ T cells were strongly correlated with decreasing proviral load. No changes were observed in T cell phenotype distribution, HIV-specific CD4+ T cell immunity, or HIV-specific antibodies. TLR9-adjuvanted pneumococcal vaccination decreased proviral load. Reductions in proviral load correlated with increasing levels of HIV specific CD8+ T cells. Further investigation into the potential effect of TLR9 agonists on HIV latency is warranted.     

Reduced frequency, diversity, and function of human T cell leukemia virus type 1-specific CD8+ T cell in adult T cell leukemia patients

Human T cell lymphotropic virus type 1 (HTLV-1)-specific CTL are thought to be immune effectors that reduce the risk of adult T cell leukemia (ATL). However, in vivo conditions of anti-HTLV-1 CTL before and after ATL development have yet to be determined. To characterize anti-HTLV-1 CTL in asymptomatic HTLV-1 carriers (AC) and ATL patients, we analyzed the frequency and diversity of HTLV-1-specific CD8+ T cells in PBMC of 35 AC and 32 ATL patients using 16 distinct epitopes of HTLV-1 Tax or Env/HLA tetramers along with intracellular cytolytic effector molecules (IFN-gamma, perforin, and granzyme B). Overall frequency of subjects possessing Tax-specific CD8+ T cells was significantly lower in ATL than AC (53 vs 90%; p = 0.001), whereas the difference in Env-specific CD8+ T cells was not statistically significant. AC possessed Tax11-19/HLA-A*0201-specific tetramer+ cells by 90% and Tax301-309/HLA-A*2402-specific tetramer+ cells by 92%. Some AC recognized more than one epitope. In contrast, ATL recognized only Tax11-19 with HLA-A*0201 and Tax301-309 with HLA-A*2402 at frequencies of 30 and 55%. There were also significant differences in percentage of cells binding Tax11-19/HLA-A*0201 and Tax301-309/HLA-A*2402 tetramers between AC and ATL. Anti-HTLV-1 Tax CD8+ T cells in AC and ATL produced IFN-gamma in response to Tax. In contrast, perforin and granzyme B expression in anti-HTLV-1 CD8+ T cells of ATL was significant lower than that of AC. Frequency of Tax-specific CD8+ T cells in AC was related to proviral load in HLA-A*0201. These results suggest that decreased frequency, diversity, and function of anti-HTLV-1 Tax CD8+ T cell clones may be one of the risks of ATL development.     

Mycobacterial lipopeptides elicit CD4+ CTLs in Mycobacterium tuberculosis-infected humans

In searching for immunogenic molecules with the potential to induce protective immune responses against tuberculosis, we developed an ex vivo model to study frequency, phenotype, and effector functions of human T lymphocytes recognizing hydrophobic Ags of Mycobacterium tuberculosis (M.Tb). To obtain unbiased results, we characterized T lymphocytes responding to a crude cell wall extract (chloroform methanol extract of M.Tb (M.Tb-CME)) containing a broad spectrum of mycobacterial glycolipids and lipopeptides. A significant proportion of T lymphocytes recognized M.Tb-CME (290 IFN-gamma+ T cells/10(5) PBMCs) and developed to effector memory cells as determined by the expression of CD45RO and the chemokine receptors CXCR3 and CCR5. Expanded lymphocytes fulfilled all criteria required for an efficient immune response against tuberculosis: 1) release of macrophage-activating Th1 cytokines and chemokines required for the spatial organization of local immune responses, 2) cytolytic activity against Ag-pulsed macrophages, and 3) recognition of infected macrophages and killing of the intracellular bacteria. Phenotypically, M.Tb-CME-expanded cells were CD4+ and MHC class II restricted, challenging current concepts that cytotoxic and antimicrobial effector cells are restricted to the CD8+ T cell subset. Pretreatment of M.Tb-CME with protease or chemical delipidation abrogated the biological activity, suggesting that responses were directed toward mycobacterial lipopeptides. These findings suggest that lipidated peptides are presented by M.Tb-infected macrophages and elicit CD4+ cytolytic and antimicrobial T lymphocytes. Our data support an emerging concept to include hydrophobic microbial Ags in vaccines against tuberculosis.     

Maintenance of large numbers of virus-specific CD8+ T cells in HIV-infected progressors and long-term nonprogressors

The virus-specific CD8+ T cell responses of 21 HIV-infected patients were studied including a unique cohort of long-term nonprogressors with low levels of plasma viral RNA and strong proliferative responses to HIV Ags. HIV-specific CD8+ T cell responses were studied by a combination of standard cytotoxic T cell (CTL) assays, MHC tetramers, and TCR repertoire analysis. The frequencies of CD8+ T cells specific to the majority of HIV gene products were measured by flow cytometric detection of intracellular IFN-gamma in response to HIV-vaccinia recombinant-infected autologous B cells. Very high frequencies (0.8-18.0%) of circulating CD8+ T cells were found to be HIV specific. High frequencies of HIV-specific CD8+ T cells were not limited to long-term nonprogressors with restriction of plasma virus. No correlation was found between the frequency of HIV-specific CD8+ T cells and levels of plasma viremia. In each case, the vast majority of cells (up to 17.2%) responded to gag-pol. Repertoire analysis showed these large numbers of Ag-specific cells were scattered throughout the repertoire and in the majority of cases not contained within large monoclonal expansions. These data demonstrate that high numbers of HIV-specific CD8+ T cells exist even in patients with high-level viremia and progressive disease. Further, they suggest that other qualitative parameters of the CD8+ T cell response may differentiate some patients with very low levels of plasma virus and nonprogressive disease.     

Predominant involvement of CD8+CD28- lymphocytes in human immunodeficiency virus-specific cytotoxic activity.

Distinct functional CD8+ T-cell populations have been observed during human immunodeficiency virus (HIV) infection. One of these functions is the inhibition of viral replication by a noncytotoxic mechanism, which was shown to be mediated by the CD8+CD28+ subpopulation. On the other hand, CD8+ T cells exert an HIV-specific cytotoxic activity. The present study shows that CD8+CD28- lymphocytes display this HIV-specific cytotoxic activity, which is detectable immediately after the cells are purified from peripheral blood. The CD28- population is also able to proliferate and to retain its cytotoxic activity after in vitro restimulation with autologous blast cells. Finally, HIV-specific cytotoxic T cells can be obtained in vitro from the CD8+CD28+ population.     

CD8 T-Cells from Most HIV-Infected Patients Lack Ex Vivo HIV-Suppressive Capacity during Acute and Early Infection

The strong CD8+ T-cell-mediated HIV-1-suppressive capacity found in a minority of HIV-infected patients in chronic infection is associated with spontaneous control of viremia. However, it is still unclear whether such capacities were also present earlier in the CD8+ T cells from non controller patients and then lost as a consequence of uncontrolled viral replication. We studied 50 patients with primary HIV-1-infection to determine whether strong CD8+ T-cell-mediated HIV suppression is more often observed at that time. Despite high frequencies of polyfunctional HIV-specific CD8+ T-cells and a strong CD4+ T-helper response, CD8+ T-cells from 48 patients lacked strong HIV-suppressive capacities ex vivo. This indicates that the superior HIV-suppressive capacity of CD8+ T-cells from HIV controllers is not a general characteristic of the HIV-specific CD8+ T cell response in primary HIV infection.     

HIV-1-specific mucosal CD8+ lymphocyte responses in the cervix of HIV-1-resistant prostitutes in Nairobi

Understanding how individuals with a high degree of HIV exposure avoid persistent infection is paramount to HIV vaccine design. Evidence suggests that mucosal immunity, particularly virus-specific CTL, could be critically important in protection against sexually acquired HIV infection. Therefore, we have looked for the presence of HIV-specific CD8+ T cells in cervical mononuclear cells from a subgroup of highly HIV-exposed but persistently seronegative female sex workers in Nairobi. An enzyme-linked immunospot assay was used to measure IFN-gamma release in response to known class I HLA-restricted CTL epitope peptides using effector cells from the blood and cervix of HIV-1-resistant and -infected sex workers and from lower-risk uninfected controls. Eleven of 16 resistant sex workers had HIV-specific CD8+ T cells in the cervix, and a similar number had detectable responses in blood. Where both blood and cervical responses were detected in the same individual, the specificity of the responses was similar. Neither cervical nor blood responses were detected in lower-risk control donors. HIV-specific CD8+ T cell frequencies in the cervix of HIV-resistant sex workers were slightly higher than in blood, while in HIV-infected donor cervical response frequencies were markedly lower than blood, so that there was relative enrichment of cervical responses in HIV-resistant compared with HIV-infected donors. HIV-specific CD8+ T cell responses in the absence of detectable HIV infection in the genital mucosa of HIV-1-resistant sex workers may be playing an important part in protective immunity against heterosexual HIV-1 transmission.