Strong human immunodeficiency virus (HIV)-specific CD4+ T cell responses in a cohort of chronically infected patients are associated with interruptions in anti-HIV chemotherapy

Virus-specific CD4+ T-helper cell function is important in controlling human immunodeficiency virus (HIV) infection but is impaired in patients with progressive HIV disease. It has been reported that after highly active antiretroviral therapy (HAART), HIV-specific lymphoproliferative responses remain absent, whereas responses to non-HIV microbial antigens are restored. However, in analyzing immune responses in a cohort of chronically infected adults on HAART, we observed strong HIV-specific CD4+ T cell responses of Th-1 phenotype in 11 of 22 patients. The magnitude and frequency of HIV-specific lymphoproliferative responses was strongly associated with previous interruptions in HAART (P=.001). In contrast, the magnitude of CD8+ T cell responses to HIV Gag, Pol, Env, and Nef was similar in patients who had and those who had not interrupted HAART. We conclude that (1) a significant proportion of chronically HIV-infected patients on HAART can generate strong HIV-specific CD4+ and CD8+ T cell immunity and (2) transient interruptions in antiviral treatment may prime or boost HIV-specific CD4+ T-helper responses.     

Methods of using interleukin 2 to enhance HIV-specific immune responses

Interleukin 2 (IL-2) in combination with highly active antiretroviral therapy (HAART) can significantly increase CD4+ T cell counts but does not improve HIV-specific T cell-mediated immune responses that are associated with the control of viral replication. To characterize the immunomodulatory activity of IL-2 in HIV-infected individuals we studied the virus-specific immune response (VIR) by intracellular cytokine expression (interferon gamma, IFN-gamma) after mimicking HIV rebound in peripheral blood mononuclear cells (PBMCs). We found that the whole virus used as HIV antigen was able to activate HIV-specific T cells in the presence of a low concentration (50 IU/ml) of IL-2. Interestingly, increasing concentrations of IL-2 (400 or 1000 IU/ml) in combination with the same amount of HIV doubled the number of HIV-specific T cells. These cells were functionally intact because all of the IFN-gamma-producing CD8+ T cells contained perforin, a marker for cytotoxic T lymphocytes (CTLs). Induction of HIV-specific immune responses by IL-2 was not detected in the absence of HIV antigen both in vitro and in patients treated with HAART, indicating that IL-2 can amplify HIV-specific T cells in the presence of HIV antigen. Therefore, a combination of IL-2 with either structured treatment interruption, which results in a controlled viral load rebound, or with therapeutic vaccination is expected to improve HIV-specific T cell-mediated immune responses.     

Relationship between the frequency of HIV-specific CD8+ T cells and the level of CD38+CD8+ T cells in untreated HIV-infected individuals

CD8+ T cells are critical for effective host defenses against viral infections. Studies addressing HIV-induced immune responses in infected individuals have suggested that CD8+ T cells play an important role in controlling viral replication. However, despite an abundance of HIV-specific CD8+ T cells, HIV is not contained in many untreated patients. Active HIV replication is associated with numerous immunologic changes, the most notable and consistent of which is an increase in CD8+ T cells expressing CD38. Previous studies have demonstrated that the expression of CD38 on CD8+ T cells is associated with poor prognostic outcome in infected individuals with detectable plasma viremia; however, the relationship between the expression of CD38 and the frequency of HIV-specific CD8+ T cells is unclear. We demonstrate a correlation between levels of HIV-specific CD8+ T cells and levels of CD8+ T cells expressing CD38 in untreated patients. The distribution of HIV-specific CD8+ T cells was heavily skewed toward CD38+CD8+ T cells in patients with a high percentage of CD38+CD8+ T cells. Spontaneous/Fas-mediated apoptosis in CD38+CD8+ T cells was significantly higher in patients with high percentages of CD38+CD8+ T cells. Our data suggest that a substantial proportion of the HIV-specific CD8+ T cells present in CD38+CD8+ T cells in patients with active viral replication arise by HIV-driven aberrant immune activation and may not manifest effective cytolytic activity against infected targets due to a high degree of susceptibility to apoptosis, thus providing an explanation of why HIV is not successfully contained by CD8+ T cells in such individuals.     

Persistent low viral load on antiretroviral therapy is associated with T cell-mediated control of HIV replication

BACKGROUND: It is unclear how stable low-level viral replication and CD4 cell numbers can be maintained under highly active antiretroviral therapy (HAART). This study was designed to analyse whether HIV-specific responses in stable partially controlled patients during antiretroviral therapy (ART) differ from those observed in complete HAART failure and whether they contribute to the control of viral load (VL). METHODS: Three groups of patients were selected according to plasma HIV RNA levels during 18 months of ART: persistently low VL (LoVL; HIV RNA <10,000 copies/ml; n = 28), undetectable VL (UnVL; HIV RNA <200 copies/ml; n = 29) and high VL (HiVL; HIV RNA >10,000 copies/ml; n = 14). T-cell responses were studied using lymphoproliferative and interferon (IFN)-gamma-ELISpot assays against HIV-p24, -gp160, recall antigens, and 15 pools of HIV-(Gag + RT) peptides. RESULTS: Frequencies of IFN-gamma-producing CD4 T cells against HIV-p24 were higher in LoVL than in UnVL or HiVL groups [median, 131, 47 and 23 spot-forming cells (SFC)/1 x 10 peripheral blood mononuclear cells (PBMC), respectively; P = 0.012 and P = 0.047]. Lymphoproliferative responses to HIV-p24 and recall antigens were similar in LoVL and UnVL groups but lower in HiVL (P = 0.004). Frequencies of HIV-specific CD8 T cells were higher in LoVL than in UnVL (1340 versus 410 SFC/1 x 10 PBMC; P = 0.001). They correlated negatively with VL in the LoVL and HiVL (r, -0.393, P = 0.039 and r, -0.643, P = 0.024, respectively) and positively correlated with anti-HIV CD4 cell frequencies in the LoVL group only (r, 0.420; P = 0.026). CONCLUSION: Persistently low viral replication (<10,000 copies/ml) during ART stimulates high frequencies of HIV-specific CD4 and CD8 T cells compared to full virus suppression or complete ART failure. The association of high anti-HIV activity with large numbers of HIV-specific CD8 T cells contribute to the control of viral replication.     

Generation of HIV-1-specific CD8+ cell responses following allogeneic hematopoietic cell transplantation

This study tested whether donor-derived HIV-specific immune responses could be detected when viral replication was completely suppressed by the continuous administration of highly active antiretroviral therapy (HAART). A regimen of fludarabine and 200 cGy total body irradiation was followed by infusion of allogeneic donor peripheral blood cells and posttransplantation cyclosporine and mycophenolate mofetil. Viral load, lymphocyte counts, and HIV-1-specific CD8(+) cell immune responses were compared before and after hematopoietic cell transplantation (HCT). Uninterrupted administration of HAART was feasible during nonmyeloablative conditioning and after HCT. The HIV RNA remained undetectable and no HIV-associated infections were observed. CD8(+) T-cell responses targeting multiple epitopes were detected before HCT. After HCT a different pattern of donor-derived HIV-specific CTL responses emerged by day +80, presumably primed in vivo. We conclude that allogeneic HCT offers the unique ability to characterize de novo HIV-1-specific immune responses. This clinical trial was registered at ClinicalTrials.gov (identifier: NCT00112593).     

Rapid death of adoptively transferred T cells in acquired immunodeficiency syndrome

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) probably play the major role in controlling HIV replication. However, the value of adoptive transfer of HIV-specific CTL expanded in vitro to HIV+ patients has been limited: this contrasts with the success of CTL therapy in treating or preventing Epstein-Barr virus and cytomegalovirus disease after bone marrow transplantation (BMT). We investigated the fate of expanded HIV-specific CTL clones in vivo following adoptive transfer to a patient with acquired immunodeficiency syndrome (AIDS). Two autologous CTL clones specific for HIV Gag and Pol were expanded to large numbers (>10(9)) in vitro and infused into an HIV-infected patient whose viral load was rising despite antiretroviral therapy. The fate of one clone was monitored by staining peripheral blood mononuclear cells (PBMCs) with T-cell receptor-specific tetrameric major histocompatibility complex (MHC)-peptide complexes. Although the CTL transfer was well tolerated, there were no significant changes in CD4 and CD8 lymphocyte counts and virus load. By tracking an infused clone using soluble MHC-peptide complexes, we show that cells bearing the Gag-specific T-cell receptors were rapidly eliminated within hours of infusion through apoptosis. Thus, the failure of adoptively transferred HIV-specific CTL to reduce virus load in AIDS may be due to rapid apoptosis of the infused cells, triggered by a number of potential mechanisms. Further trials of adoptive transfer of CTL should take into account the susceptibility of infused cells to in vivo apoptosis.     

Expression of CD57 defines replicative senescence and antigen-induced apoptotic death of CD8+ T cells

Virus-specific CD8(+) T-cell responses play a pivotal role in limiting viral replication. Alterations in these responses, such as decreased cytolytic function, inappropriate maturation, and limited proliferative ability could reduce their ability to control viral replication. Here, we report on the capacity of HIV-specific CD8(+) T cells to secrete cytokines and proliferate in response to HIV antigen stimulation. We find that a large proportion of HIV-specific CD8(+) T cells that produce cytokines in response to cognate antigen are unable to divide and die during a 48-hour in vitro culture. This lack of proliferative ability of HIV-specific CD8(+) T cells is defined by surface expression of CD57 but not by absence of CD28 or CCR7. This inability to proliferate in response to antigen cannot be overcome by exogenous interleukin-2 (IL-2) or IL-15. Furthermore, CD57 expression on CD8(+) T cells, CD4(+) T cells, and NK cells is a general marker of proliferative inability, a history of more cell divisions, and short telomeres. We suggest, therefore, that the increase in CD57(+) HIV-specific CD8(+) T cells results from chronic antigen stimulation that is a hallmark of HIV infection. Thus, our studies define a phenotype associated with replicative senescence in HIV-specific CD8(+) T cells, which may have broad implications to other conditions associated with chronic antigenic stimulation.     

Pilot study of the effects of intermittent interleukin-2 on human immunodeficiency virus (HIV)-specific immune responses in patients treated during recently acquired HIV infection.

Highly active antiretroviral therapy (HAART) initiated during acute human immunodeficiency virus (HIV) infection may preserve HIV-specific CD4+ T cell responses that are thought to enhance HIV-specific CD8+ T cell function. The present pilot study was designed to determine whether preserved HIV-specific immune responses are augmented by the administration of the immunomodulatory agent interleukin (IL)-2. Nine persons recently (<6 months) infected with HIV were randomized to receive HAART alone or HAART plus 3 cycles of intermittent IL-2 during a 12-month period. Although HAART plus IL-2 significantly increased counts of total and naive CD4+ T cells, compared with HAART alone, there was no increase in CD4+ or CD8+ HIV-specific immune responses. In addition, adjuvant IL-2 therapy did not reduce the pool of HIV-infected resting CD4+ T cells. Thus, although intermittent IL-2 plus HAART quantitatively increased CD4+ T cells, this increase was not selective for HIV-specific CD4+ or CD8+ T cell responses in recently infected persons.     

Surface expression patterns of negative regulatory molecules identify determinants of virus-specific CD8+ T-cell exhaustion in HIV infection

A highly complex network of coinhibitory and costimulatory receptors regulates the outcome of virus-specific CD8(+) T-cell responses. Here, we report on the expression patterns of multiple inhibitory receptors on HIV-specific, cytomegalovirus-specific, and bulk CD8(+) T-cell memory populations. In contrast to cytomegalovirus-specific CD8(+) T cells, the majority of HIV-specific CD8(+) T cells exhibited an immature phenotype and expressed Programmed Death-1, CD160 and 2B4 but not lymphocyte activation gene-3. Notably, before antiretroviral therapy, simultaneous expression of these negative regulators correlated strongly with both HIV load and impaired cytokine production. Suppression of HIV replication by antiretroviral therapy was associated with reduced surface expression of inhibitory molecules on HIV-specific CD8(+) T cells. Furthermore, in vitro manipulation of Programmed Death-1 and 2B4 inhibitory pathways increased the proliferative capacity of HIV-specific CD8(+) T cells. Thus, multiple coinhibitory receptors can affect the development of HIV-specific CD8(+) T-cell responses and, by extension, represent potential targets for new immune-based interventions in HIV-infected persons.     

Persistent numbers of tetramer+ CD8(+) T cells, but loss of interferon-gamma+ HIV-specific T cells during progression to AIDS

Although CD8(+) T cells initially suppress human immunodeficiency virus (HIV) replication, cytotoxic T-cell precursor frequencies eventually decline and fail to prevent disease progression. In a longitudinal study including 16 individuals infected with HIV-1, we studied both the number and function of HIV-specific CD8(+) T cells by comparing HLA-peptide tetramer staining and peptide-induced interferon-gamma (IFN-gamma) production. Numbers of IFN-gamma-producing T cells declined during progression to acquired immunodeficiency syndrome (AIDS), whereas the number of tetramer+ T cells in many individuals persisted at high frequencies. Loss of IFN-gamma-producing T cells correlated with declining CD4(+) T-cell counts, consistent with the need of CD4(+) T-cell help in maintaining adequate CD8(+) T-cell function. These data indicate that the loss of HIV-specific CD8(+) T-cell activity is not due to physical depletion, but is mainly due to progressively impaired function of HIV-specific CD8(+) T cells.     

Suppression of HIV replication in the resting CD4+ T cell reservoir by autologous CD8+ T cells: implications for the development of therapeutic strategies

CD8+ T cell-mediated antiviral activity against HIV has been described consistently in infected individuals; however, the role of this activity in controlling replication of HIV in the latently infected, resting CD4+ T cell reservoir is unclear. By using an ex vivo system, we show that replication of HIV in this viral reservoir is effectively suppressed in coculture by autologous CD8+ T cells in long-term nonprogressors (LTNPs) and in patients whose viremia was controlled by highly active antiretroviral therapy (HAART), but not in therapy-naive patients who had substantial levels of plasma viremia. This antiviral activity was largely independent of cytotoxic CD8+ T lymphocytes (CTL). When the role of soluble CD8+ T cell-derived factors was examined, we found that CC-chemokines played a major role in inhibition of viral replication in the latent viral reservoir in some LTNPs and patients receiving HAART, but not in chronically infected patients who were not receiving antiretroviral therapy. Potent antiviral activity, independent of CC-chemokines, was found mainly in patients in whom HAART was initiated shortly after the acute phase of HIV infection. These results indicate that CD8(+) T cells provide potent suppressive activity against HIV replication in the latent viral reservoir via direct cellular contact in patients who are naturally LTNPs or in those who are treated with HAART. Furthermore, the profound antiviral activity exerted by non-CC-chemokine soluble factors in infected patients who began HAART early in HIV infection suggests that preservation of this HIV-suppressive mechanism by early initiation of therapy may play an important role in the containment of viral replication in infected patients following interruption of therapy.     

Enhanced HIV-specific immune responses in chronically HIV-infected patients receiving didanosine plus hydroxyurea

BACKGROUND: The role of hydroxyurea (HU) in the treatment of HIV infection remains controversial. HU potentiates didanosine (ddI) antiviral activity and might exert immunomodulatory effects. PATIENTS AND METHODS: Immunologic parameters were examined in HIV-infected patients enrolled in a simplification trial in which ddI-HU was provided to subjects who had been on complete virus suppression under highly active antiretroviral therapy (HAART) for longer than 6 months. A total of 84 of these patients showed plasma viraemia repeatedly below 5000 HIV-RNA copies/ml, and were the main study population. A group of 22 patients who continued on HAART and another of 22 drug-naive HIV-positive individuals were taken as controls. RESULTS: At 12 months, the levels of naive and memory T-cell subsets were similar in patients on ddI-HU and under HAART, whereas immune activation tended to be lower in the former group. The frequency of HIV-specific CD8+ T cells (CTL) directed against 125 peptides derived from Gag, Pol, Env, Nef and HIV regulatory proteins was similar among patients on ddI-HU and untreated controls, and significantly higher than in patients under HAART. This higher CTL response in patients on ddI-HU was seen even when considering only subjects with undetectable viral load. HIV-specific CD4+ T-cell responses were absent in almost all patients on HAART, whereas they were present in up to 19% of patients on ddI-HU. CONCLUSION: Treatment with ddI-HU provides higher levels of HIV-specific CD8+ and CD4+ T-cell responses than standard triple drug regimens. Thus, hydroxyurea might exert a beneficial immunomodulatory effect in HIV infection.     

Divergent in vitro and in vivo correlates of HIV-specific T-cell responses during onset of HIV viraemia

BACKGROUND: Cellular immune responses to HIV-1 have been examined mainly in peripheral blood mononuclear cells (PBMC). During onset of HIV replication and antigenaemia after discontinuation of highly active antiretroviral therapy (HAART), PBMC may theoretically contain HIV-specific T cells that are qualitatively and quantitatively different from specific T cells dominating in the tissues. PBMC responses throughout HIV immunotherapy trials may therefore be skewed during recurrent viraemia. OBJECTIVE: To compare cellular HIV-specific in vitro responses in PBMC during onset of HIV viraemia with corresponding in vivo responses, represented by classical delayed-type hypersensitivity tests (DTH). METHODS: HIV patients (n = 38), pre-immunized with four HIV-1 p24-like consensus peptides (Vacc-4x) during HAART, were subjected to a 14-week treatment interruption with recurrent HIV viraemia. Proliferative T-cell responses to Vacc-4x p24 peptides, HIV p24 protein, and cytomegalovirus (CMV) proteins were measured in PBMC. Corresponding Vacc-4x peptide DTH were expressed as skin infiltrate areas after 48 h. RESULTS: After 14 weeks without HAART, HIV-1 RNA increased to 72,500 copies/ml (median). The Vacc-4x p24 peptide- and HIV-1 p24 protein-induced T-cell proliferation concurrently decreased by 81 and 93% in PBMC during viraemia (medians, P < or = 0.03), whereas proliferative responses to CMV antigens were stable. In contrast, the Vacc-4x DTH areas, rather tended to increase by 36% (P = 0.08) and contained infiltrates dominated by proliferating T cells and macrophages. CONCLUSIONS: Divergent in vitro and in vivo HIV-specific cellular immune responses were found during recurrent HIV viraemia. The clinical relevance of both surrogate markers for HIV-related immune responses should be compared in future studies.     

Human immunodeficiency virus interactions with CD8+ T lymphocytes

Human immunodeficiency virus (HIV)-specific CD8+ T cells can mediate anti-HIV activity by both cytolytic (cytotoxic T lymphocyte or CTL) and non-cytolytic mechanisms (antiviral) and play a crucial role in HIV pathogenesis. Both mechanisms actively contribute to the control of HIV in vivo. The non-cytolytic CD8+T cells from individuals infected with HIV suppress virus replication in CD4+ T cells in vitro by a non-cytolytic mechanism that involves interplay of several chemokines and an unidentified secreted soluble CD8 (+)-cell antiviral factor (CAF). There is immense value of these two distinct CD8 activities in anti-HIV responses and their necessity to be maintained during highly active antiretroviral therapy (HAART). The aim of this review is to provide an overview of some of the novel aspects of CD8+ T cell interactions with HIV, their role in HIV pathogenesis, HAART therapy, HIV disease progression, gene expression and interactions with other cell types during HIV infection.     

Suppression of HIV-specific T cell activity by lymph node CD25+ regulatory T cells from HIV-infected individuals

CD25(+) CD4(+) FoxP3(+) regulatory T (Treg) cells isolated from the peripheral blood of asymptomatic HIV-infected individuals have been demonstrated to significantly suppress HIV-specific immune responses in vitro. CD25(+) Treg cell suppressor activity in the peripheral blood seems to diminish with progression of HIV disease, and it has been suggested that loss of Treg cells contributes to aberrant immune activation and disease progression. However, phenotypic studies suggest that Treg cells may migrate to, and be maintained or even expanded in, tissue sites of HIV replication. Currently, it is not known whether tissue-associated Treg cells maintain suppressive activity in the context of HIV infection, particularly in individuals with advanced disease. The present study demonstrates that CD25(+) Treg cells isolated from lymph nodes and peripheral blood of HIV(+) subjects, even those with high viral loads and/or low CD4(+) T cell counts, maintain potent suppressive activity against HIV-specific cytolytic T cell function. This activity was better in lymph node as compared with peripheral blood, particularly in patients with high levels of plasma viremia. In addition, the expression of certain CD25(+) Treg-associated markers on CD4(+) T cells isolated from lymph nodes differed significantly from those on CD4(+) T cell subsets isolated from the peripheral blood. These data suggest that CD25(+) Treg cell-mediated suppression of HIV-specific responses continues throughout the course of HIV disease and, because of their particularly potent suppression of HIV-specific CTL activity in lymphoid tissue, may considerably impact the ability to control HIV replication in vivo.     

Prognostic value of HIV-1 Gag-specific CD4+ T-cell responses for progression to AIDS analyzed in a prospective cohort study

The causal relationship between HIV-specific CD4+ T-cell responses and viral control and the effect of these responses on the natural history of HIV infection is unclear. In a detailed longitudinal study, functional HIV-1 Gag-specific CD4+ T cells were analyzed in long-term asymptomatic individuals (LTA; n = 6) and progressors to AIDS (n = 7) with a median follow-up of, respectively, 118 and 57 months. Next, HIV-specific CD4+ T-helper cell responses were measured in a prospective cohort study among 96 HIV seroconverters and were related to clinical endpoints using Cox proportional hazard analyses. In the detailed study, no difference for HIV-specific helper-cell responses between LTAs and progressors was observed early in infection, but Gag-specific CD4+ T cells producing IL-2 or IFNgamma were lost in progressors late in infection. Multivariate proportional hazard analyses in the prospective cohort study showed that HIV-specific IL-2+, IFNgamma+, or IL-2+IFNgamma+ CD4+ T cells early after seroconversion had no prognostic value for the rate of progression to AIDS. Our results are compatible with viral load determining the nature and magnitude of HIV-specific CD4+ T-cell responses, rather than HIV-specific CD4+ T-cell responses controlling HIV plasma viral load.     

Nadir CD4+ T-cell count and numbers of CD28+ CD4+ T-cells predict functional responses to immunizations in chronic HIV-1 infection

OBJECTIVE: To ascertain whether delaying the initiation of highly active antiretroviral therapy (HAART) compromises functional immune reconstitution in HIV-1 infection in persons who regain 'normal' CD4 T-cell counts after suppressive antiretroviral therapies. DESIGN: Prospective open-label study carried out at two University-affiliated HIV-outpatient clinics in the USA. SUBJECTS AND METHODS: Response to immunization was used as a model for in vivo functional immune competence in 29 HIV-1 infected patients with CD4 T-cell counts > 450 x 106 cells/l and HIV-RNA < 400 copies/ml for > 12 months after HAART and nine HIV-1 seronegative controls. After immunization with tetanus toxoid, diphtheria-toxoid, and keyhole limpet hemocyanin, immune response scores (IRS) were calculated using postimmunization antibody concentrations, lymphocyte proliferation, and delayed-type hypersensitivity responses to vaccine antigens. RESULTS: Despite normal numbers of circulating CD4 T-cells, the CD4 T-cell nadir before HAART initiation predicted the immune response to immunization (rho = 0.5; P < 0.005) while current CD4 T-cell count did not. Likewise, CD4 T-lymphocyte expression of the co-stimulatory molecule CD28 was also an independent predictor of response to immunization (rho = 0.5; P < 0.005). CONCLUSIONS: Even among persons who controlled HIV replication and normalized CD4 T-cell counts with HAART, pretreatment CD4 T-cell count and numbers of circulating CD4+CD28+ T-cells at immunization, but not current CD4 T-cell count, predict the ability to respond to vaccination. Delaying the initiation of HAART in chronic HIV-1 infection results in impaired functional immune restoration despite normalization of circulating CD4 T-cell numbers.     

HIV patients on antiretroviral therapy have high frequencies of CD8 T cells specific for Immediate Early protein-1 of cytomegalovirus

OBJECTIVE: To assess the frequency and phenotype of cytomegalovirus (CMV)-specific CD8 T cells in previously immunocompromised HIV patients with stable undetectable HIV viremia due to highly active antiretroviral therapy (HAART). METHODS: Twenty-one CMV-seropositive HIV patients with nadir CD4 T-cell counts < 50 x 10(6) cells/l, at least 4 years on HAART and 6 months of complete viral suppression (< 50 HIV RNA copies/ml) and 12 CMV-seropositive, HIV-seronegative age/sex-matched controls were studied. CD4 and CD8 T-cell responses to whole CMV and two HLA-A*02 restricted CMV peptides [NLV from pp65 and VLE from Immediate Early 1 (IE1)] were measured by interferon (IFN)gamma ELISpot. Phenotypes of peptide-specific CD8 T cells were determined by tetramer staining. RESULTS: In the ELISpot assay, HIV patients had significantly more CD8 T cells producing IFN gamma in response to VLE than controls, whereas numbers of NLV-specific and CMV-specific IFN gamma spots were similar. Four HIV patients and one control had large VLE and/or NLV-specific CD8 T-cell populations despite the absence of CMV-specific CD4 T cells. The majority of peptide-specific CD8 T cells from HIV patients and controls were CD28-, CD45RO+ and CD45RA-. However, a significantly higher proportion of VLE-specific CD8 T cells expressed perforin compared to NLV-specific CD8 T cells in HIV patients. CONCLUSIONS: HIV patients had elevated numbers of IE1-specific, IFNgamma-producing perforin-positive CD8 T cells compared to controls. As IE1 is expressed early during CMV reactivation, these cells may be important for preventing CMV replication to pathogenic levels. In addition, CMV-specific CD4 T cells are not essential for maintenance of large populations of CMV-specific CD8 T cells in aviremic HIV patients on HAART.     

CD25+ regulatory T cells isolated from HIV-infected individuals suppress the cytolytic and nonlytic antiviral activity of HIV-specific CD8+ T cells in vitro

HIV infection is characterized by CD4(+) T cell depletion and progressive immune dysfunction; particularly impacted are HIV-specific T cell responses. An important component of immune-mediated control of HIV replication, killing of infected cells, appears to be impaired, in part due to poor cytolytic activity of HIV-specific cytotoxic T cells (CTL). In vitro, several functions of HIV-specific T cells, such as cytokine production, can be enhanced by the depletion of the immunosuppressive CD25(+) FoxP3(+) CD4(+) regulatory (Treg) cell subset. However, the effect of CD25(+) Treg cells on virus-specific cytolytic activity in the context of HIV or any human viral infection has not been investigated. The present study demonstrates that CD25(+) Treg cells isolated from the peripheral blood of HIV-infected subjects significantly suppress HIV Gag-specific cytolytic activity in vitro. In addition, CD25(+) Treg cells suppress effector function (coexpression of TNF-alpha and IFN-gamma) of HIV-specific CD8(+) T cells that proliferate in response to HIV antigen. Finally, the secretion of HIV-inhibitory CC-chemokines by HIV-specific and nonspecific CD8(+) T cells is significantly reduced in the presence of CD25(+) Treg cells. These data suggest that CD25(+) Treg-mediated suppression of the antiviral activity of HIV-specific CD8(+) T cells could impact the ability of HIV-infected individuals to control HIV replication in vivo.