Altered ex vivo balance between CD28+ and CD28- cells within HIV-specific CD8+ T cells of HIV-seropositive patients

Increased Plasma Levels of the TH2 chemokine CCL18 associated with low CD4+ T cell counts in HIV-1-infected Patients with a Suppressed Viral Load

The chemokine (C-C motif) chemokine ligand 18 (CCL18) is a structural homolog of CCL3 primarily produced by monocyte-derived cells with an M2 phenotype. Elevated levels of CCL18 have been observed in several diseases associated with malignancies and chronic inflammation. The role of CCL18 in Human Immunodeficiency Virus (HIV-1) infection remains unknown. We analyzed expression levels of T helper cell-mediated (TH2) chemokines CCL18, CCL17, and CCL22 by ELISA in plasma collected from HIV-1-infected and healthy donors. In HIV-1-infected individuals, plasma viral loads were monitored by NucliSense HIV-1 QT assay and T cell counts and expression of the activation marker CD38 were determined by flow cytometry. Our data showed a significant increase in plasma levels of CCL18 in HIV-1-infected individuals compared to uninfected controls (p < 0.001) and a significant correlation between CCL18 levels and viral load in untreated patients. No significant difference of CCL18 levels was detected among the HIV-1-infected patients treated with combined antiretroviral therapy (cART) and HIV-1-untreated patients.CCL18 values are negatively correlated with CD4+CD38+ cell numbers and total CD4+ T cell counts in patients with a suppressed viral load. Notably, plasma levels of the TH2 chemokines CCL17 and CCL22 are also elevated during HIV-1 infection. However, no correlation of CCL17 and CCL22 production with CD4+ T cell counts was detected. Presented data shows that the chemokines, CCL17, CCL18, and CCL22 are increased during HIV-1 infection. However, only increased levels of CCL18, a marker of M2 macrophages, correlate with low CD4+ T cell counts in patients with suppressed viral load, raising the possibility that CCL18 and/or CCL18-producing cells may interfere with their reconstitution in HIV-1-infected patients on cART.

Human influenza viruses and CD8(+) T cell responses

Influenza A viruses (IAVs) cause significant morbidity and mortality worldwide, despite new strain-specific vaccines being available annually. As IAV-specific CD8(+) T cells promote viral control in the absence of neutralizing antibodies, and can mediate cross-reactive immunity toward distinct IAVs to drive rapid recovery from both mild and severe influenza disease, there is great interest in developing a universal T cell vaccine. However, despite detailed studies in mouse models of influenza virus infection, there is still a paucity of data on human epitope-specific CD8(+) T cell responses to IAVs. This review focuses on our current understanding of human CD8(+) T cell immunity against distinct IAVs and discusses the possibility of achieving a CD8(+) T cell mediated-vaccine that protects against multiple, distinct IAV strains across diverse human populations. We also review the importance of CD8(+) T cell immunity in individuals highly susceptible to severe influenza infection, including those hospitalised with influenza, the elderly and Indigenous populations.

Analysis of CD28 and bcl-2 Expression on Peripheral Blood and Liver-Infiltrating Mononuclear Cells in Patients with Autoimmune Hepatitis

Because the underlying mechanism of hepatocellular damages in autoimmune hepatitis (AIH) still remains unclear, analysis of CD28 and bcl-2 molecules, which are critical for T cell activation and survival, was performed in patients with AIH. The number of CD28(+)CD4(+) peripheral blood mononuclear cells (PBMC) in corticosteroid (CS)-treated patients was comparable to normal control individuals but decreased in untreated AIH patients. In contrast, the number of CD28(+)CD8(+) PBMC was decreased in both CS-treated and untreated AIH patients. Analysis of liver-infiltrating mononuclear cells (LIMC) showed that the number of CD28(+)CD4(+) and CD28(-)CD8(+) LIMC were positively correlated with the histology activity index score. Bcl-2(+)CD4(+) LIMC were observed in the portal area of the liver and the numbers fluctuated with disease activity during the time course after CS administration. By contrast, CD8(+) LIMC were shown not to express bcl-2. Taken collectively, these results suggest that bcl-2(+)CD28(+)CD4(+) and bcl-2(-)CD28(-)CD8(+) cells may play critical and distinct roles in hepatocellular damage in AIH.

Significance of senescence for virus-specific memory T cell responses: rapid ageing during chronic stimulation of the immune system

There is a generalized age-related decline in immune responses which leads to increased susceptibility of elderly to infection and, possibly, to autoimmune disease and cancer. This is associated with phenotypic changes of CD8+ T lymphocytes that include the loss of costimulatory molecules CD28 and CD27, which are important for proliferation and cell survival of CD8+ T cells. Loss of these molecules is associated with less ability to respond to recurrent infection. Functional changes within T cells during ageing include a reduction in the number of naive T cells and a progressively limited T cell repertoire. Furthermore, persistent life-long antigenic stress upon the memory pool leads to telomere erosion and concomittant loss of proliferative capacity, a phenomenon known as replicative senesence. In this review, we discuss that replicative senescence, or clonal exhaustion, may also occur in relatively young individuals, as evidenced from HIV-infected individuals and healthy Ethiopians. We discuss data suggesting that T cell defects may arise in individuals because of chronic antigen activation leading to rapid ageing of the memory CD8+ T cell pool.

Chronic immune activation associated with chronic helminthic and human immunodeficiency virus infections: role of hyporesponsiveness and anergy

Chronic immune activation is one of the hallmarks of human immunodeficiency virus (HIV) infection. It is present also, with very similar characteristics, in very large human populations infested with helminthic infections. We have tried to review the studies addressing the changes in the immune profiles and responses of hosts infected with either one of these two chronic infections. Not surprisingly, several of the immune derangements and impairments seen in HIV infection, and considered by many to be the "specific" effects of HIV, can be found in helminth-infected but HIV-noninfected individuals and can thus be accounted for by the chronic immune activation itself. A less appreciated element in chronic immune activation is the immune suppression and anergy which it may generate. Both HIV and helminth infections represent this aspect in a very wide and illustrative way. Different degrees of anergy and immune hyporesponsiveness are present in these infections and probably have far-reaching effects on the ability of the host to cope with these and other infections. Furthermore, they may have important practical implications, especially with regard to protective vaccinations against AIDS, for populations chronically infected with helminths and therefore widely anergic. The current knowledge of the mechanisms responsible for the generation of anergy by chronic immune activation is thoroughly reviewed.

Gamma interferon-mediated inflammation is associated with lack of protection from intravaginal simian immunodeficiency virus SIVmac239 challenge in simian-human immunodeficiency virus 89.6-immunized rhesus macaques

Although gamma interferon (IFN-gamma) is a key mediator of antiviral defenses, it is also a mediator of inflammation. As inflammation can drive lentiviral replication, we sought to determine the relationship between IFN-gamma-related host immune responses and challenge virus replication in lymphoid tissues of simian-human immunodeficiency virus 89.6 (SHIV89.6)-vaccinated and unvaccinated rhesus macaques 6 months after challenge with simian immunodeficiency virus SIVmac239. Vaccinated-protected monkeys had low tissue viral RNA (vRNA) levels, vaccinated-unprotected animals had moderate tissue vRNA levels, and unvaccinated animals had high tissue vRNA levels. The long-term challenge outcome in vaccinated monkeys was correlated with the relative balance between SIV-specific IFN-gamma T-cell responses and nonspecific IFN-gamma-driven inflammation. Vaccinated-protected monkeys had slightly increased tissue IFN-gamma mRNA levels and a high frequency of IFN-gamma-secreting T cells responding to in vitro SIVgag peptide stimulation; thus, it is likely that they could develop effective anti-SIV cytotoxic T lymphocytes in vivo. In contrast, both high tissue IFN-gamma mRNA levels and strong in vitro SIV-specific IFN-gamma T-cell responses were detected in lymphoid tissues of vaccinated-unprotected monkeys. Unvaccinated monkeys had increased tissue IFN-gamma mRNA levels but weak in vitro anti-SIV IFN-gamma T-cell responses. In addition, in lymphoid tissues of vaccinated-unprotected and unvaccinated monkeys, the increased IFN-gamma mRNA levels were associated with increased Mig/CXCL9, IP-10/CXCL10, and CXCR3 mRNA levels, suggesting that increased Mig/CXCL9 and IP-10/CXCL10 expression resulted in recruitment of CXCR3(+) activated T cells. Thus, IFN-gamma-driven inflammation promotes SIV replication in vaccinated-unprotected and unvaccinated monkeys. Unlike all unvaccinated monkeys, most monkeys vaccinated with SHIV89.6 did not develop IFN-gamma-driven inflammation, but they did develop effective antiviral CD8(+)-T-cell responses.

HIV infection and aging: enhanced Interferon- and Tumor Necrosis Factor-alpha production by the CD8+ CD28- T subset

BACKGROUND

T cells from HIV+ and aged individuals show parallels in terms of suppressed proliferative activity and interleukin-2 (I1-2) production and an increased number of CD8+ CD28- T cells. In order to compare cytokine production from T cells from these two states, CD4+ and CD8+ T cells from HIV+ aged, and normal young donors (controls) were monitored for cytokine production by flow cytometry, quantitative PCR and ELISA upon activation by PMA and anti-CD3. In addition, the CD8+ T cell subsets CD28+ and CD28- from the HIV+ and the aged groups were evaluated for cytokine production by flow cytometry, and compared with those from young controls.

RESULTS

Flow cytometric analysis indicated that CD8+ T cells from both HIV+ and aged donors showed an increase of approximately 2-3 fold over controls in percentage of cells producing inflammatory cytokines IFN-gamma and TNF-alpha. Similar analysis also revealed that the production of interleukins-4,6 and 10, production was very low (1-2% of cells) and unchanged in these cells. Quantitative PCR also showed a substantial increase (4-5 fold) in IFN-gamma and TNF-alpha mRNA from HIV+ and aged CD8+ T cells, as did ELISA for secreted IFN-gamma and TNF-alpha (2.3-4 fold). Flow cytometric analysis showed that the CD8+ CD28- T cell subset accounts for approximately 80-86% of the IFN-gamma and TNF-alpha production from the CD8+ subset in the aged and HIV+ states. The CD4+ T cell, while not significantly changed in the HIV+ or aged states in terms of IFN-gamma production, showed a small but significant increase in TNF-alpha production in both states.

CONCLUSIONS

Our data appear compatible with physiologic conditions existing in HIV+ and aged individuals, i.e. elevated serum levels and elevated CD8+ T cell production of IFN-gamma and TNF-alpha. Thus, the capacity for increased production of cytokines IFN-gamma and TNF-alpha in the aged individual by the dominant CD8+ CD28- subset may have a profound influence on the clinical state by aggravating inflammatory pathologies such as rheumatoid arthritis, and possibly Alzheimer's disease and Crohn's disease. In AIDS, these cytokines may contribute to wasting and cachexia. We theorize that the predominant phenotypic change to the cytotoxic CD8+ CD28- T cell subsets in both the HIV+ and the aged states may reflect a natural "endpoint" in CD8+ T cell differentiation induced after a lifetime of immune activity (toward viruses, etc) in the aged, and after a massive accelerated response to HIV in the HIV-positive individual.

Comprehensive analyses of a unique HIV-1-infected nonprogressor reveal a complex association of immunobiological mechanisms in the context of replication-incompetent infection

We recently demonstrated that a unique HIV-1-infected nonprogressor was infected with a nonevolving replication-incompetent HIV-1 strain, showing a total absence of viral evolution in vivo. Potent immune responses against HIV-1 were observed in his PBMC, despite an apparent lack of viral replication for at least 8 years. His PBMC resisted superinfection with CCR5, CXCR4, and dual-tropic HIV-1 strains, although highly purified CD4+ T cells supported infection, but without any visible cytopathic effect. Potent noncytolytic CD8+ T cell antiviral activity was shown to protect his PBMC from productive infection. This activity was not mediated by several known chemokines or IFN-gamma, which were produced at high levels after PHA activation of his CD8+ T cells, indicating the action of other CAF-like CD8 factors. This antiviral activity was a memory response, induced by HIV-specific stimulation to similar levels observed by PHA stimulation, but absent in ex vivo resting T cells. Immunological mechanisms associated with this antiviral suppressive activity included vigorous Gag-specific helper T cell proliferative responses and high-level IFN-gamma release by both CD4 and CD8 T cells. These responses were broadly directed against multiple Gag epitopes, both previously reported and some novel epitopes. Strong HIV-specific helper T cell function was also associated with strong neutralizing antibodies. Understanding how to induce these protective immune responses in other individuals could provide a major step forward in the design of effective immunotherapies or vaccines against HIV infection.

Role of 4-1BB (CD137) in the functional activation of cord blood CD28(-)CD8(+) T cells

The CD28(-) subset of CD8(+) T cells is associated with cytotoxic T lymphocyte (CTL) effector function. We investigated a potential role for 4-1BB, a costimulatory molecule structurally related to members of the tumor necrosis factor (TNF) receptor family, in the generation and functional activation of CD28(-) CTLs by using human cord blood (CB) cells composed exclusively of naive CD8(+) T cells with few or no CD28(-) CTLs. The 4-1BB was induced preferentially on the CB CD28(-)CD8(+) T cells when CD28 down-regulation was induced by interleukin 15 (IL-15) and IL-12 stimulation. Anti-4-1BB costimulation induced dramatic phenotypic changes in the CD28(-) CTLs, including restoration of CD28 expression as well as that of memory markers such as CD45RO and CC chemokine receptor 6 (CCR6). Anti-4-1BB costimulation also promoted long-term survival of CD28(-) CTLs, which were sensitive to activation-induced cell death upon anti-CD3 stimulation. The memory-type CD28(+) CTLs induced by anti-4-1BB costimulation acquired a greatly enhanced content of granzyme B, a cytolytic mediator, and enhanced cytotoxic activity as compared with CD28(-) CTLs. Strong cytotoxicity of memory-type CTLs to a 4-1BB ligand-expressing Epstein-Barr virus (EBV)-transformed B-cell line was almost completely abrogated by 4-1BB-Fc, a soluble form of 4-1BB, suggesting involvement of 4-1BB in cytolytic processes. Taken all together, our results suggest that 4-1BB plays a role in the differentiation of effector memory CTLs.

Immunological changes in simian immunodeficiency virus (SIV(agm))-infected African green monkeys (AGM): expanded cytotoxic T lymphocyte, natural killer and B cell subsets in the natural host of SIV(agm)

The African green monkey (AGM) model system for simian immunodeficiency virus (SIV(agm)) has been used to examine why prolonged infection with the relevant virus does not result in the development of immunodeficiency in its natural host. Blood lymphocyte subset values were determined in uninfected (n=88) and naturally SIV(agm)-infected AGMs (n=74). A number of blood cell subsets, such as CD8alpha(+)CD3(+)CD28(neg), CD8alpha(+)CD3(neg) and CD20(+) cells, were expanded significantly in clinically asymptomatic animals carrying a relatively high plasma load of viral RNA (10(4)-10(7) RNA copies/ml plasma). The expanded CD8alpha(+)CD3(+)CD28(neg) subpopulation (1094 +/- 986 cells/microl blood in infected animals versus 402 +/- 364 cells/microl blood, P=0.03) comprised cells that resembled terminally differentiated effector CD8 T cells (CD27(neg) and CD11a(+)). In SIV(agm)-infected animals, the expanded CD8alpha(+)CD3(neg) cell subset shared identity with the CD16(+) population (natural killer cells). These results demonstrate for the first time that apathogenic SIV(agm) infection causes significant changes in the immune system of its natural host. Although previous studies had indicated that noncytotoxic mechanisms might play an important role in the suppression of virus replication in the natural host of SIV(agm), this study sheds new light on the possible role of cytotoxic T lymphocytes, the innate immune system and double-positive T helper cells (CD4(+)CD8alpha(+)CD3(+)) in suppressing virus replication in this animal model of AIDS.

Human cytotoxic T lymphocyte responses to live attenuated 17D yellow fever vaccine: identification of HLA-B35-restricted CTL epitopes on nonstructural proteins NS1, NS2b, NS3, and the structural protein E

Yellow fever virus (YFV) is a re-emerging problem despite the existence of an effective live-attenuated vaccine. The induction of YFV-neutralizing antibodies undoubtedly contributes to vaccine efficacy, but T lymphocyte responses to YFV likely play a role in long-term efficacy. We studied the T lymphocyte responses to YFV in four vaccinees. Proliferation and cytolytic responses to YFV were demonstrated in all subjects. We isolated 13 YFV-specific CD8(+) CTL lines that recognized epitopes on the E, NS1, NS2b, and NS3 proteins; eight CTL lines were HLA-B35-restricted. YFV-specific T cell responses were detectable by IFN gamma ELISPOT assays 14 days postvaccination, with T cell frequencies sustained for up to 19 months. To our knowledge, this is the first report of human T lymphocyte responses following YFV vaccination. These results indicate that the live 17D YFV vaccine induced CD8(+) T cell responses directed against at least four different HLA-B35-restricted YFV epitopes.

Highly active antiretroviral therapy responders exhibit a phenotypic lymphocyte pattern comparable to that of long-term nonprogressors

BACKGROUND

The implementation of highly active antiretroviral therapy (HAART) in patients with progressive HIV-1 disease has resulted in a marked reduction of HIV-1-associated morbidity and mortality. In fact, the risk of HAART responders to develop opportunistic infections becomes similar to that of long-term nonprogressors (LTNPs).

METHODS

Reasoning that HAART may ultimately have consequences on both the quantity and quality of immune responses of a HIV-1-infected person, we assessed CD4+ and CD8+ T cell subsets in HAART recipients over a time period of 15 months and compared them to the lymphocyte phenotype of LTNPs and healthy controls. Evaluations included quantitative determinations of memory (CD45RO+CD62L-), naive (CD45RO-CD62L+), effector (CD27-, CD28-) and activated (HLA-DR+, CD38+, CD95+) CD4+ and CD8+ lymphocytes. The T cell function was assayed by skin tests.

RESULTS

Compared to healthy persons, treatment-naive patients with progressive disease exhibited a considerable reduction of CD4+ T cells with many of the remaining T cells showing signs of activation at baseline. CD8+ T cells were greatly increased in number, mainly because of an expansion of CD28- effector and memory CD8+ T cells. LTNPs, in contrast, had stable CD4+ and elevated CD8+ T cell counts, the latter being mainly due to a marked increase in CD27- effector cells. Essentially, the same immunophenotype was seen in HAART responders after 15 months of treatment when compared to LTNPs.

CONCLUSIONS

It is tempting to speculate that a HAART-induced reduction in viral load may influence the immune system's capacity to mount protective responses to pathogenic microorganisms.

Lipopeptide presentation pathway in dendritic cells

Lipopeptides are currently being evaluated as candidate vaccines in human volunteers. They elicit cytotoxic responses from CD8(+) T lymphocytes, whereas peptides without a lipidic moiety usually do not. The exact processing and presentation pathways leading to association with MHC class I molecules has not yet been defined. This is of particular interest in dendritic cells, which are required for primary T cell stimulation. We have tracked lipopeptides derived from an HLA-A2.1-restricted HIV-1 Reverse Transcriptase epitope, by N-terminal addition of an N-epsilon-palmitoyl-lysine. Entry of the lipopeptides into human monocyte-derived dendritic cells (MDC) was mediated by endocytosis, as assessed by colocalization using analogs labelled with rhodamine, and by confocal microscopy. This internalization in DC induced functional stimulation of CD8(+) T lymphocytes specific for the epitopes, quantified by Interferon-gamma ELISPOT assays. The peptide alone was not visualized inside the DC and was only presented through direct surface association to HLA-A*0201. Therefore, lipopeptides provide a model system to define precisely the cross-presentation pathways that lead exogenous proteins to associate with class I MHC molecules within dendritic cells. Using this approach, cross-presentation pathways can be better defined and vaccine lipopeptides can be further optimized for MHC class I association in human dendritic cells.

EBV-specific CD8+ T cell memory: relationships between epitope specificity, cell phenotype, and immediate effector function

EBV infection in humans induces CD8+ T cell memory to viral epitopes derived from both lytic and latent cycle Ags. We have analyzed the relationship between the phenotype and function of the memory pool of T cells specific for these Ags. Lytic epitope-specific populations were heterogeneous in terms of CD45RO/RA and CD28 expression, whereas latent epitope-specific populations were uniformly CD45RO+ and CD28+, consistent with the higher antigenic challenge from lytic epitopes driving some memory cells toward a CD45RA+, CD28- phenotype. However, both types of memory population showed immediate epitope-specific cytotoxicity and type 1 cytokine production in ex vivo assays. Cytotoxic function was not associated with preactivated T cells, as EBV-specific populations were negative for activation markers such as CD69 or CD38, nor could cytotoxic function be ascribed to CD27- or CD56+ subsets, as such cells were not detected in EBV-specific memory. Furthermore, cytotoxicity was not limited to CD45RA+ and/or CD28- fractions, but also was observed in CD45RO+, CD28+ populations in lytic and latent epitope-specific memory. Cytokine (IFN-gamma, TNF-alpha) responses, measured by intracytoplasmic staining after peptide stimulation, also were detectable in CD45RO+ and RA+ subsets as well as CD28+ and CD28- subsets. Of other markers that were heterogeneous in both lytic and latent epitope populations, CCR7 gave the best discrimination of functionality; thus, CCR7+ cells consistently failed to give an IFN-gamma or TNF-alpha response, whereas many CCR7- cells were responsive. Our data are consistent with effector functions having a broad distribution among phenotypically distinct subsets of "effector memory" cells that have lost the CCR7 marker.

Identification of the T cell clones expanding within both CD8+CD28+ and CD8+CD28− T cell subsets in recipients of allogeneic hematopoietic cell grafts and its implication in post-transplant skewing of T cell receptor repertoire

We have previously reported that skewed repertoires of T cell receptor-beta chain variable region (TCRBV) and TCR-alpha chain variable region (TCRAV) are observed at an early period after allogeneic hematopoietic cell transplantation. Furthermore, we found that T lymphocytes using TCRBV24S1 were increased in 28% of the recipients of allogeneic grafts and an increase of TCRBV24S1 usage was shown to result from clonal expansions. Interestingly, the arginine residue was frequently present at the 3' terminal of BV24S1 segment and was followed by an acidic amino acid residue within the CDR3 region. These results suggest that these clonally expanded T cells are not randomly selected, but are expanded by stimulation with specific antigens. This study was undertaken to elucidate the mechanisms of the post-transplant skewing of TCR repertoires. Since the CD8(+)CD28(-)CD57(+) T cell subset has been reported to expand in the peripheral blood of patients receiving allogeneic hematopoietic cell grafts, we examined the TCRAV and TCRBV repertoires of the CD8(+)CD28(-) T cell and CD8(+)CD28(+) T cell subsets, and also determined the clonality of both T cell populations. In all three recipients examined, the CD8(+)CD28(-) T cell subset appeared to define the post-transplant TCR repertoire of circulating blood T cells. Moreover, the CDR3 length of TCRBV imposed constraints in both CD8(+)CD28(-) T cell and CD8(+)CD28(+) T cell subsets. The DNA sequences of the CDR3 region were determined, and the same clones were identified within both CD8(+)CD28(-) and CD8(+)CD28(+) T cell subsets in the same individuals. These results suggest that the clonally expanded CD8(+)CD28(-) T cells after allogeneic hematopoietic cell transplantation derive from the CD8(+)CD28(+) T cell subset, possibly by an antigen-driven mechanism, resulting in the skewed TCR repertoire.

Oligoclonal expansion of CD4(+)CD28(-) T lymphocytes in recipients of allogeneic hematopoietic cell grafts and identification of the same T cell clones within both CD4(+)CD28(+) and CD4(+)CD28(-) T cell subsets

Recipients of allogeneic bone marrow grafts have clonally expanded CD8(+)CD28(-) T lymphocytes during the early period after transplantation, which leads to skewing of T cell receptor (TCR) repertoires. Here, we have addressed the question of whether clonal expansion of CD28(-) T cells is also observed in CD4(+) T lymphocytes after human allogeneic hematopoietic cell transplantation. We found that the fraction of T cells lacking CD28 expression in the CD4(+) subset was increased after transplantation, and expanded CD4(+)CD28(-) T lymphocytes carrying certain TCRBV subfamilies showed limited TCR diversity. In order to further study the ontogeny of CD4(+)CD28(-) T cells, we analyzed the complementarity-determining region 3 (CDR3) of the TCR-beta chain of CD4(+)CD28(+) and CD4(+)CD28(-) cells. We identified the same T cell clones within both CD4(+)CD28(-) and CD4(+)CD28(+) T cell subsets. These results suggest that both subsets are phenotypic variants of the same T cell lineage.

Enhanced interferon-gamma by CD8+ CD28- lymphocytes from HIV+ patients

Flow cytometric analysis of T cells from HIV+ and normal individuals activated for 15 hr showed that the percentage of cells producing interferon-gamma (INFgamma) was enhanced approximately threefold (39 compared to 14%) in the HIV+ CD8+ population. Activation modes, other than anti-CD3 with PMA, were ineffective, and in no case did the percentage of HIV+ CD4+ T cells show increased INFgamma production over controls. Enhanced INFgamma production was not induced by either anti-CD3 or PMA alone, or anti-CD3 or ConA with anti-CD28, or enhanced by N-acetylcysteine. In contrast to INFgamma production, the percentage of CD4+ T cells producing interleukin-2 (Il-2) greatly exceeded that of the CD8+ T cells. The results from flow cytometry analyses of HIV+ CD8+ T cells was supported by quantitative analysis of INFgamma mRNA (by PCR) and INFgamma secretion by ELISA. These methods showed a sixfold and three- to fivefold increase, respectively, on a per cell basis. As HIV infection progresses, as shown by loss of CD4+ T cells, the proportion of CD8+ CD28- T cells increases, and it is this T cell subset that is responsible for 80% or more of the enhanced INFgamma production. The enhanced INFgamma in HIV+ patients derives from two factors: the increase in CD8+ CD28- cells to 70% and the percentage producing INFgamma (60%, compared to 21% for CD8+ CD28+ cells). Our findings of a substantial increase in INFgamma production in HIV infection arising from the increased number of CD8+ CD28- T cells are compatible with clinical studies which show elevated INFgamma in HIV+ serum and INFgamma producing CD8+ T cells dominating HIV+ lymph nodes. We also found a significantly decreased proliferative response of the HIV+-derived CD8+ T cell fraction with coactivator anti-CD-28, in contrast to PMA (with anti-CD3), which is probably a reflection of the diminished population of CD8+ CD28+ T cells in HIV+ donors compared to normal donors (30.7 compared to 67.9%).

Longitudinal analysis of CD8+ T-cell phenotype and IL-7, IL-15 and IL-16 mRNA expressionin different tissues during primary simian immunodeficiency virus infection

Infection of macaques with pathogenic isolates of simian immunodeficiency virus (SIV) represents a useful model of HIV infection that offers the unique opportunity to investigate the very early modifications that affect CD8(+) T-lymphocyte subsets and related cytokines during lentiviral infection. Herein, three cynomolgus macaques were inoculated intravenously with a pathogenic isolate of SIVmac 251. In fresh isolated mononuclear cells from blood, lymph node and bronchoalveolar lavage, we analyzed changes in the phenotype of CD8(+) T cells and we used reverse transcription-PCR to monitor the expression of IL-7, IL-15 and IL-16 mRNA. We demonstrated that an expansion of CD8(+)CD28(-) T cells occurs from the third week of infection on in the peripheral blood and in the lung, whereas CD8(+)CD28(+) T cells expand in the lymph nodes. Concomitantly, we evidenced mRNA modulations in IL-16, IL-15 and IL-7 expression in the three compartments studied. The containment of systemic viral replication was associated with an overexpression of IL-16 mRNA in the lung and in the peripheral blood. Given the immunomodulatory properties of IL-15 and IL-7 and the potential antiviral ability of IL-16, these perturbations could have important implications in early viral dissemination and HIV immunopathogenesis.

Increased expression of NK cell markers on T lymphocytes in aging and chronic activation of the immune system reflects the accumulation of effector/senescent T cells

In humans, CD56, CD161, CD16, CD94 or CD57 represent prototypic markers of NK cells, although they are also found on a subset of CD8+ T cells. We propose here that the expression of NK receptors on CD8+ T cells can be considered a marker of cytotoxic effector T cells that are expanded in vivo after antigenic activation leading to extensive proliferation. The persistence of antigen will lead to loss of co-stimulatory molecules, telomere shortening and defective IL-2 production, changes that define the state replicative senescence in T lymphocytes. The majority of these "effector/senescent" T lymphocytes are CD8+, CD45RA+, CD11a(bright), CD28-, CD27-, CD62L- and CCR7-. They are cytotoxic T cells with strong expression of intracytoplasmic perforin and granzyme, but with low proliferative capacity and defective IL-2 production. Many of these characteristics are shared by the recently defined "effector/memory" T cells, being mainly distinguished by the absence of CD45RA expression on the memory cells. The expression of NK receptor in these effector cells will probably contribute to the regulation of their cytotoxic function. Expansion of cells with these characteristics can be found not only in the elderly but also in other clinical conditions involving chronic activation of the immune system such as viral infections, rheumatic and autoimmune diseases or tumors. Another subset of T cells that expresses the NK receptors is the alpha-galactosyl-ceramide specific T cell subset defined by the expression of canonical Valpha24JalphaQ TCR, recognition of CD1d and secretion of high amounts of IL-4 and IFN-gamma. However, the changes observed in the expression of NK-R on T cells associated to immunosenescence can not be attributed to expansion of this particular T cell subset, although alterations in the number and function of these cells have been demonstrated in some autoimmune diseases.

Loss of CD28 expression on CD8(+) T cells is induced by IL-2 receptor gamma chain signalling cytokines and type I IFN, and increases susceptibility to activation-induced apoptosis

CD8(+)CD28(-) T cells are selectively expanded during viral infections, indicating their importance in anti-viral immune responses. Since little is known about the differentiation of CD8(+)CD28(-) cells, we investigated the generation, function and survival characteristics of this subset. In healthy individuals CD8(+)CD28(-) T cells contained more elevated levels of perforin and IFN-gamma than the CD8(+)CD28(+) subset, indicating that they can have an effector function. CD8(+)CD28(-) cells were selectively expanded when activated CD8(+)CD28(+) T cells were cultured in IL-2, IL-7 or IL-15. Moreover, the generation of CD8(+)CD28(-) cells was accelerated by type I IFN suggesting that these cytokines which are released during viral infections influence CD8(+) T cell differentiation. We did not observe re-expression of CD28 by CD8(+)CD28(-) T cells in any of the experiments performed. Activated T cells are susceptible to activation-induced cell death (AICD) if re-stimulated in the absence of co-stimuli. AICD was induced in both CD28(+) and CD28(-) subsets of activated T cells when stimulated with anti-CD3 antibody in the absence of co-stimuli but the magnitude of death was greater in the CD28(-) subset. While co-stimulation through LFA-1 (CD11a and CD18) significantly reduced AICD in the CD8(+)CD28(+) subset, death was not prevented in CD8(+)CD28(-) cells. These results suggest that CD8(+)CD28(-) T cells are more functionally differentiated than the CD8(+)CD28(+) subset and indicate they may represent a terminally differentiated effector population which is destined for clearance by apoptosis at the end of the immune response.

Multiple HLA-class I-specific inhibitory NK receptor expression and IL-4/IL-5 production by CD8+ T-cell clones in HIV-1 infection

Several mechanisms may contribute to the decline in HIV-1 specific CD8+ cytotoxic T-lymphocyte (CTL) activity that is observed in infected patients, including loss of CD4+ cell help, antigenic shift, impaired clonogenicity and functional impairment due to expression of inhibitory NK receptors (iNKRs). In addition to a decrease in HIV-1-specific cytolytic activity, an increased proportion of CD8+ T-cells producing IL-4 and IL-5 has been recently observed in advanced HIV-1 infection. Remarkably, an impaired HIV-1-specific CTL activity was primarily detected among the TC0/Tc2 CD8+ CTLs. A series of CD3+CD8+ T-cell clones expressing inhibitory NK receptors (iNKRs) isolated from HIV-1 infected patients was analyzed in order to determine their cytokine production pattern and to assess the extent of iNKR expression at the single cell level. Our data indicate that iNKR+CD3+CD8+ clones isolated from infected patients frequently express multiple iNKR and may produce IL-4 and IL-5 to a relevant extent.

A novel sensitive approach for frequency analysis of measles virus-specific memory T-lymphocytes in healthy adults with a childhood history of natural measles

Measles virus (MV), a single-stranded negative-sense RNA virus, is an important pathogen causing almost 1 million deaths annually. Acute MV infection induces immunity against disease throughout life. The immunological factors which are responsible for protection against measles are still poorly understood. However, T-cell-mediated immune responses seem to play a central role. The emergence of new single-cell methods for quantification of antigen-specific T-cells directly ex vivo has prompted us to measure frequencies of MV-specific memory T-cells. As an indicator for T-cell activation IFN-gamma production was measured. PBMC were analysed by intracellular staining and ELISPOT assay after stimulation with MV-infected autologous B-lymphoblastoid cell lines or dendritic cells. T-cell responses were exclusively seen with PBMC from MV-seropositive healthy adults with a history of natural measles in childhood. The median frequency of MV-specific T-cells was 0.35% for CD3(+)CD4(+) and 0.24% for the CD3(+)CD8(+) T-cell subset. These frequencies are comparable with T-cell numbers reported by other investigators for persistent virus infections such as Epstein-Barr virus, cytomegalovirus or human immunodeficiency virus. Hence, this study illustrates that MV-specific CD4(+) and CD8(+) T-cells are readily detectable long after the acute infection, and thus are probably contributing to long-term immunity. Furthermore, this new approach allows efficient analysis of T-cell responses from small samples of blood and could therefore be a useful tool to further elucidate the role of cell-mediated immunity in measles as well as in other viral infections.

HLA-class I-specific inhibitory receptors in HIV-1 infection

One of the most characteristic and, at the same time, puzzling features of the cellular immune response towards HIV-1 is represented by an early vigorous HIV-specific CD8+ CTL response that does not prevent disease progression in the vast majority of patients. In this context, there is a striking mismatch over the course of disease progression between increasing numbers of activated CD8+ T cells and apparent decrease of virus-specific CD8+ CTLs. Inhibitory NK receptors (iNKRs) specific for HLA class I molecules can be expressed on CD8+ T-cells of healthy individuals and deliver inhibitory signals that determine decreased CTL function. Their expression on CD8+ CTL may be induced by IL-15 or TGFP in vitro, and may represent an important regulatory function for the fine-tuning of the antigen-specific T cell response against tumors and intracytoplasmic pathogens. In HIV-1 infected patients, relevant proportions of peripheral blood CD8+ T lymphocytes express iNKRs belonging to the Ig superfamily (p58/p70/p140) and CD94/NKG2A. Presence of iNKRs on CD8+ CTLs impairs HIV-1-specific cytolytic activity in vitro and may allow uncontrolled viral replication and spread following functional inhibition of CTL effectors in infected patients.

Weak anti-HIV CD8(+) T-cell effector activity in HIV primary infection

HIV-specific CD8(+) T cells play a major role in the control of virus during HIV primary infection (PI) but do not completely prevent viral replication. We used IFN-gamma enzyme-linked immunospot assay and intracellular staining to characterize the ex vivo CD8(+) T-cell responses to a large variety of HIV epitopic peptides in 24 subjects with early HIV PI. We observed HIV-specific responses in 71% of subjects. Gag and Nef peptides were more frequently recognized than Env and Pol peptides. The number of peptides recognized was low (median 2, range 0-6). In contrast, a much broader response was observed in 30 asymptomatic subjects with chronic infection: all were responders with a median of 5 peptides recognized (range 1-13). The frequency of HIV-specific CD8(+) T cells among PBMC for a given peptide was of the same order of magnitude in both groups. The proportion of HIV-specific CD8(+)CD28(-) terminally differentiated T cells was much lower in PI than at the chronic stage of infection. The weakness of the immune response during HIV PI could partially account for the failure to control HIV. These findings have potential importance for defining immunotherapeutic strategies and establishing the goals for effective vaccination.

Broad, intense anti-human immunodeficiency virus (HIV) ex vivo CD8(+) responses in HIV type 1-infected patients: comparison with anti-Epstein-Barr virus responses and changes during antiretroviral therapy

The ex vivo antiviral CD8(+) repertoires of 34 human immunodeficiency virus (HIV)-seropositive patients with various CD4(+) T-cell counts and virus loads were analyzed by gamma interferon enzyme-linked immunospot assay, using peptides derived from HIV type 1 and Epstein-Barr virus (EBV). Most patients recognized many HIV peptides, with markedly high frequencies, in association with all the HLA class I molecules tested. We found no correlation between the intensity of anti-HIV CD8(+) responses and the CD4(+) counts or virus load. In contrast, the polyclonality of anti-HIV CD8(+) responses was positively correlated with the CD4(+) counts. The anti-EBV responses were significantly less intense than the anti-HIV responses and were positively correlated with the CD4(+) counts. Longitudinal follow-up of several patients revealed the remarkable stability of the anti-HIV and anti-EBV CD8(+) responses in two patients with stable CD4(+) counts, while both antiviral responses decreased in two patients with obvious progression toward disease. Last, highly active antiretroviral therapy induced marked decreases in the number of anti-HIV CD8(+) T cells, while the anti-EBV responses increased. These findings emphasize the magnitude of the ex vivo HIV-specific CD8(+) responses at all stages of HIV infection and suggest that the CD8(+) hyperlymphocytosis commonly observed in HIV infection is driven mainly by virus replication, through intense, continuous activation of HIV-specific CD8(+) T cells until ultimate progression toward disease. Nevertheless, highly polyclonal anti-HIV CD8(+) responses may be associated with a better clinical status. Our data also suggest that a decrease of anti-EBV CD8(+) responses may occur with depletion of CD4(+) T cells, but this could be restored by highly active antiretroviral treatment.