Increased cytolytic T lymphocyte activity and decreased B7 responsiveness are associated with CD28 down-regulation on CD8+ T cells from HIV-infected subjects

Chemerin triggers migration of a CD8 T cell subset with natural killer cell functions

The recruitment of cells with effector functions into the tumor microenvironment holds potential for delaying cancer progression. We show that subsets of human CD28-effector CD8 T cells, CCR7- CD45RO+ effector memory, and CCR7- CD45RO- effector memory RA phenotypes, express the chemerin receptor CMKLR1 and bind chemerin via the receptor. CMKLR1-expressing human CD8 effector memory T cells present gene, protein, and cytotoxic features of NK cells. Active chemerin promotes chemotaxis of CMKLR1-expressing CD8 effector memory cells and triggers activation of the α4β1 integrin. In an experimental prostate tumor mouse model, chemerin expression is downregulated in the tumor microenvironment, which is associated with few tumor-infiltrating CD8+ T cells, while forced overexpression of chemerin by mouse prostate cancer cells leads to an accumulation of intra-tumor CD8+ T cells. Furthermore, α4 integrin blockade abrogated the chemerin-dependent recruitment of CD8+ T effector memory cells into implanted prostate tumors in vivo. The results identify a role for chemerin:CMKLR1 in defining a specialized NK-like CD8 T cell, and suggest the use of chemerin-dependent modalities to target effector CMKLR1-expressing T cells to the tumor microenvironment for immunotherapeutic purposes.

Raltegravir Inclusion Decreases CD4 T-Cells Intra-Cellular Viral Load and Increases CD4 and CD28 Positive T-Cells in Selected HIV Patients

Raltegravir (RLT) prevents the integration of HIV DNA in the nucleus, but published studies remain controversial, suggesting that it does not decrease proviral DNA. However, there are only a few studies focused on virus-targeted cells. We aimed our study on the impact of RLT inclusion on total intra-cellular viral DNA (TID) in cellular subsets and immune effects in patients with newly acquired undetectable plasmatic viral load (UVL). Six patients having UVL using an antiretroviral combination for 6 months and CD4 T-cells > 350/mL and <500/mL were selected to receive RLT for 3 months from M0 to M3. Patients had 7 sequential viro-immunological determinations from M-1 to M5. Immune phenotypes were determined by flow cytometry and TID quantification was performed using PCR assay on purified cells. TID (median values) at the initiation of RLT in CD4 T-cells was 117 copies/millions of cells, decreased to 27.5 on M3, and remained thereafter permanently under the cut-off (<10 copies/millions of cells) in 4 out of 6 patients. This was associated with an increase of CD4 and CD4 + CD28+ T-cells and a decrease of HLA-DR expression and apoptosis of CD4 T-cells. RLT inclusion led to decreases in the viral load along with positive immune reconstitution, mainly for CD4 T-cells in HIV patients.

NK and CD8+ T cell phenotypes predict onset and control of CMV viremia after kidney transplant

CMV causes mostly asymptomatic but lifelong infection. Primary infection or reactivation in immunocompromised individuals can be life-threatening. CMV viremia often occurs in solid organ transplant recipients and associates with decreased graft survival and higher mortality. Furthering understanding of impaired immunity that allows CMV reactivation is critical to guiding antiviral therapy and examining the effect of CMV on solid organ transplant outcomes. This study characterized longitudinal immune responses to CMV in 31 kidney transplant recipients with CMV viremia and matched, nonviremic recipients. Recipients were sampled 3 and 12 months after transplant, with additional samples 1 week and 1 month after viremia. PBMCs were stained for NK and T cell markers. PBMC transcriptomes were characterized by RNA-Seq. Plasma proteins were quantified by Luminex. CD8⁺ T cell transcriptomes were characterized by single-cell RNA-Seq. Before viremia, patients had high levels of IL-15 with concurrent expansion of immature CD56^bright NK cells. After viremia, mature CD56^dim NK cells and CD28^–CD8⁺ T cells upregulating inhibitory and NK-associated receptors were expanded. Memory NK cells and NK-like CD28^–CD8⁺ T cells were associated with control of viremia. These findings suggest that signatures of innate activation may be prognostic for CMV reactivation after transplant, while CD8⁺ T cell functionality is critical for effective control of CMV.

Autoreactive T effector memory differentiation mirrors β cell function in type 1 diabetes

In type 1 diabetes, cytotoxic CD8+ T cells with specificity for β cell autoantigens are found in the pancreatic islets, where they are implicated in the destruction of insulin-secreting β cells. In contrast, the disease relevance of β cell-reactive CD8+ T cells that are detectable in the circulation, and their relationship to β cell function, are not known. Here, we tracked multiple, circulating β cell-reactive CD8+ T cell subsets and measured β cell function longitudinally for 2 years, starting immediately after diagnosis of type 1 diabetes. We found that change in β cell-specific effector memory CD8+ T cells expressing CD57 was positively correlated with C-peptide change in subjects below 12 years of age. Autoreactive CD57+ effector memory CD8+ T cells bore the signature of enhanced effector function (higher expression of granzyme B, killer-specific protein of 37 kDa, and CD16, and reduced expression of CD28) compared with their CD57- counterparts, and network association modeling indicated that the dynamics of β cell-reactive CD57+ effector memory CD8+ T cell subsets were strongly linked. Thus, coordinated changes in circulating β cell-specific CD8+ T cells within the CD57+ effector memory subset calibrate to functional insulin reserve in type 1 diabetes, providing a tool for immune monitoring and a mechanism-based target for immunotherapy.

Production of anti-CD3/28 expanded CD4⁺ T lymphocytes from HIV-infected patients with different degrees of disease progression

AIMS

CD4+ T lymphocytes from HIV-infected patients with different degrees of disease progression based on CD4 count were expanded in vitro using anti-CD3/28-coated beads.

MATERIALS & METHODS

Purified CD4+ T lymphocytes from healthy subjects and patients were expanded for 3 weeks. Moreover, the improvement of cell expansion by IL-2 supplementation was also determined.

RESULTS

Expanded CD4+ T lymphocytes from patients had lower fold expansion when compared with healthy subjects. Furthermore, patients with high CD4 counts had higher fold expansion than patients with low CD4 count, and IL-2 supplementation further increased cell expansion.

CONCLUSIONS

Anti-CD3/28 activation failed to potently induce expansion of CD4+ T lymphocytes from patients. However, the cell expansion could be improved by IL-2 supplementation.

Reference ranges of lymphocyte subsets in healthy adults and adolescents with special mention of T cell maturation subsets in adults of South Florida

BACKGROUND

Analysis of peripheral blood lymphocyte subsets has become an essential tool in the evaluation of outcome of diagnostic and research related questions in immunological and pathological conditions. Periodic evaluation and establishment of normal lymphocyte reference ranges are required in clinical and research settings of various immunodeficiency disorders for evaluation of the significance of observations. It is also important that age and gender specific lymphocyte subset reference ranges should be locally established for meaningful comparison and accurate result interpretation as age plays a significant role in the development of immune system.

METHODS

We performed dual platform flow cytometry to determine reference ranges for lymphocyte subsets (CD3, CD4, CD8, CD19 [B cells] and CD16+CD56+ [Natural Killer - NK cells]) in 50 adolescents (age range: 12-18) and 100 adults (age range: 21-67) along with T cell maturation, activation and co-stimulatory molecules in healthy multiracial adult population of South Florida.

RESULTS

The lymphocyte reference ranges percentages [absolute counts - Abs, cells/μl] unadjusted for gender differences for adolescents are: CD3: 49-83 [939-2959]; CD4: 27-53 [467-1563]; CD8: 16-40 [259-1262]; CD19+ B cells: 8-31 [169-1297] and CD16+CD56+ NK cells: 3-30 [59-1178] and for adults are: CD3: 65-88 [983-3572]; CD4: 26-62 [491-2000]; CD8: 14-44 [314-2,087]; CD19+ B cells: 2-27 [64-800] and CD16+CD56+ NK cells: 2-27 [27-693]. The ranges for CD4:CD8 ratio for adolescents and adults are 0.7-2.6 and 0.6-4.4, respectively. Gender based analysis of relative percentages of lymphocyte subsets showed no significant differences between adult and adolescent males and females. The mean CD4:CD8 ratio was significantly higher in adult females than males (P=0.04) and in adolescents this difference was not significant between genders. The mean CD3 and CD4 T cell percentages were higher and CD19 cell percentages were lower in adults compared to adolescents (P<0.0001). Absolute lymphocyte counts showed a positive correlation with the absolute counts of CD3+, CD4+, CD8+, CD19+, CD16+CD56+, CD45RO+ and CD45RA+ cells (all correlations with P<0.0001 except CD45RO [P=0.01] and CD45RA [P=0.03]).

CONCLUSION

The reference values of peripheral blood lymphocyte subsets were analyzed in healthy adolescent and adult population of South Florida. This study indicates the need for periodic evaluation and establishment of lymphocyte reference ranges for patient population served based on gender and age since these could influence immune status and treatment outcome.

Improvements in Immune Function and Activation with 48-Week Darunavir/Ritonavir-Based Therapy: GRACE Substudy

Objective. During the course of HIV infection, progressive immune deficiency occurs. The aim of this prospective substudy was to evaluate the recovery of functional immunity in a subset of patients from the GRACE (Gender, Race, And Clinical Experience) study treated with a DRV/r-based regimen. Methods. The recovery of functional immunity with a darunavir/ritonavir-based regimen was assessed in a subset of treatment-experienced, HIV-1 infected patients from the GRACE study. Results. 19/32 patients (59%) enrolled in the substudy were virologically suppressed (<50 copies/mL). In these patients, median (range) CD4+ cell count increased from 222 (2, 398) cells/mm³ at baseline to 398 (119, 812) cells/mm³ at Week 48. CD8+% decreased significantly from baseline to Week 48 (P = .03). Proliferation of CD4+ lymphocytes in response to CD3+/CD28+, phytohemagglutinin, and pokeweed was significantly increased (P < .01) by Week 12. Proliferation in response to Candida and tetanus was significantly increased by Week 48 (P < .01 and P = .014, resp.). Staphylococcal enterotoxin B-stimulated tumor necrosis factor-alpha and interleukin-2 in CD4+ cells was significantly increased by Week 12 (P = .046) and Week 48 (P < .01), respectively. Conclusions. Darunavir/ritonavir-based therapy demonstrated improvements in CD4+ cell recovery and association with progressive functional immune recovery over 48 weeks. This trial is registered with NCT00381303.

Baseline numbers of circulating CD28-negative T cells may predict clinical response to abatacept in patients with rheumatoid arthritis

OBJECTIVE

To evaluate the number of circulating CD28-negative (CD28-) T cells as a predictor of clinical response to abatacept in patients with rheumatoid arthritis (RA).

METHODS

Peripheral blood CD28- T cell subsets were evaluated by flow cytometry at baseline in 32 patients with RA treated with abatacept. Receiver-operator curves were applied to examine the predictive value of T cell populations and to choose the cutoff for the best performance of the test. Remission was defined using the Disease Activity Score 28 based on C-reactive protein.

RESULTS

The overall predictive values of the CD8+CD28- and CD4+CD28- cells for remission after 6 months of abatacept therapy were 0.802 (SE 0.078) and 0.743 (SE 0.089), respectively. Cutoff values of < 87 CD8+CD28- cells/μl and < 28 CD4+CD28- cells/μl had 80.0% sensitivity and 81.8% specificity (Fisher test: p = 0.001), and 60.0% sensitivity and 77.3% specificity (p = 0.043), respectively, for prediction of remission at 6 months. Patients having low baseline numbers of CD8+CD28- T cells had a more than 4-fold higher probability of achieving remission within 6 months than patients with higher levels of these cells.

CONCLUSION

A simple laboratory measure, the baseline number of circulating CD28- T cells, predicted remission after 6 months of abatacept treatment in patients with RA.

Decreased expression of T-cell costimulatory molecule CD28 on CD4 and CD8 T cells of mexican patients with pulmonary tuberculosis

Patients with tuberculosis frequently develop anergy, a state of T-cell hyporesponsiveness in which defective T-cell costimulation could be a factor. To know if the expression of T-cell costimulatory molecules was altered in tuberculosis, we analyzed the peripheral blood T-cell phenotype of 23 Mexican patients with pulmonary tuberculosis. There was severe CD4 (P < .001) and CD8 (P < .01) lymphopenia and upregulation of costimulatory molecule CD30 on CD4 and CD8 T cells (P < .05); this increase was higher in relapsing tuberculosis. The main finding was severe downregulation of the major costimulatory molecule CD28 on both CD8 and CD4 T cells (P < .001). Depletion of the CD4/CD28 subset, a hitherto undescribed finding, is relevant because CD4 T cells constitute the main arm of the cell-mediated antimycobacterial immune response.

Decreased circulating CD28-negative T cells in patients with rheumatoid arthritis treated with abatacept are correlated with clinical response

OBJECTIVE

To verify the hypothesis that blockade of CD28 costimulation by treatment with abatacept in patients with rheumatoid arthritis (RA) might induce a reduction in the number of CD28- T cells, as well as other effector T cell populations. We evaluated whether these variations correlate with clinical response.

METHODS

Peripheral blood T cell subsets were longitudinally evaluated by flow cytometry through the analysis of CD28, CD45RA, and CCR7 expression in 16 patients with RA who were treated with abatacept.

RESULTS

After 48 weeks of treatment, the proportion and the absolute number of circulating CD8+CD28- T cells decreased (p = 0.008, p = 0.055, respectively, compared with baseline), as well as the proportion of the CD8+CD45RA+CCR7- cells, thought to represent terminally differentiated effector T cells (p = 0.03). Reductions of percentages of circulating CD4+CD28- and CD8+CD28- T cells, and (CCR7-) CD8+ total effector T cells were directly correlated with the reduction of Disease Activity Score 28 C-reactive protein (r = 0.58, p = 0.014; r = 0.47, p = 0.059; r = 0.59, p = 0.012, respectively).

CONCLUSION

After therapy with abatacept, circulating CD28- T cells and other effector populations decrease in patients with RA. This decrease is correlated with clinical response.

Adenosine deaminase modulation of telomerase activity and replicative senescence in human CD8 T lymphocytes

Increased proportions of CD8 T lymphocytes lacking expression of the CD28 costimulatory receptor have been documented during both aging and chronic infection with HIV-1, and their abundance correlates with numerous deleterious clinical outcomes. CD28-negative cells also arise in cell cultures of CD8(+)CD28(+) following multiple rounds of Ag-driven proliferation, reaching the end stage of replicative senescence. The present study investigates the role of a second T cell costimulatory receptor component, adenosine deaminase (ADA), on the process of replicative senescence. We had previously reported that CD28 signaling is required for optimal telomerase upregulation. In this study, we show that the CD8(+)CD28(+) T lymphocytes that are ADA(+) have significantly greater telomerase activity than those that do not express ADA and that ADA is progressively lost as cultures progress to senescence. Because ADA converts adenosine to inosine, cells lacking this enzyme might be subject to prolonged exposure to adenosine, which has immunosuppressive effects. Indeed, we show that chronic exposure of CD8 T lymphocytes to exogenous adenosine accelerates the process of replicative senescence, causing a reduction in overall proliferative potential, reduced telomerase activity, and blunted IL-2 gene transcription. The loss of CD28 expression was accelerated, in part due to adenosine-induced increases in constitutive caspase-3, known to act on the CD28 promoter. These findings provide the first evidence for a role of ADA in modulating the process of replicative senescence and suggest that strategies to enhance this enzyme may lead to novel therapeutic approaches for pathologies associated with increases in senescent CD8 T lymphocytes.

Clonal Cytotoxic T Cells in Myeloma

Multiple myeloma (MM) is a malignant disease characterized by accumulation of morphologically recognizable plasma cells producing immunoglobulin (Ig) in the bone marrow. The occurrence of clonal T cells in MM, as defined by the presence of rearrangements in the T-cell receptor (TCR)-beta chains detected on Southern blotting, is associated with an improved prognosis. This review aims to describe the various ways in which we have demonstrated the presence of such T cell clones, and to describe the phenotype of these cells. Finally, the specificities of these clinically important CD8+ T cell populations will be discussed in the context of immunotherapy.

Modulation of T lymphocyte replicative senescence via TNF-{alpha} inhibition: role of caspase-3

Expanded populations of CD8(+) T lymphocytes lacking CD28 expression are associated with a variety of deleterious clinical outcomes, including early mortality in the elderly, more rapid progression to AIDS, cardiovascular disease, and enhanced tumor cell growth. In cell culture, irreversible loss of CD28 expression correlates with increased production of TNF-alpha as CD8(+) T cells are driven to the nonproliferative end stage of replicative senescence by multiple rounds of Ag-driven cell division. Interestingly, in patients with rheumatoid arthritis, inhibition or neutralization of TNF-alpha reduces the proportion of T cells lacking CD28 in the disease joints, consistent with studies showing a direct involvement of this cytokine in CD28 gene transcription. Here, we show that modulation of TNF-alpha levels in long-term cultures of human CD8(+) T lymphocytes, by chronic exposure either to a neutralizing Ab or to an inhibitor of the TNF-alpha receptor-1, increases proliferative potential, delays loss of CD28 expression, retards cytokine profile changes, and enhances telomerase activity. We also show that constitutive caspase-3, one of the downstream effectors of TNF-alphaR1 binding, increases in parallel with the loss of CD28 in long-term cultures, but this effect is blunted in the presence of the TNF-alpha inhibitors. Consistent with the in vitro culture data, CD8(+)CD28(-) T lymphocytes tested immediately ex vivo also show significantly higher levels of caspase-3 compared with their CD28(+) counterparts. These findings help elucidate the complex nature of CD28 gene regulation, and may ultimately lead to novel therapeutic approaches for diseases associated with increased proportions of CD28(-) T lymphocytes.

Significantly skewed memory CD8+ T cell subsets in HIV-1 infected infants during the first year of life

HIV-1 infection causes a severe T cell compromise; however, little is known about changes in naive, memory, effector and senescent T cell subsets during the first year of life. T cell subsets were studied over the first year of life in blood from 3 infant cohorts: untreated HIV-infected, HIV-exposed but uninfected, and HIV-unexposed. In HIV-infected infants, the frequency of CCR7(+)CD45RA(+) naive CD8(+) T cells was significantly decreased, while the frequency of CCR7(-)CD45RA(-) effector memory CD8(+) T cells was increased, compared with the control cohorts. A larger population of CD8(+) T cells in HIV-infected infants displayed a phenotype consistent with senescence. Differences in CD4(+) T cell subset frequencies were less pronounced, and no significant differences were observed between exposed and unexposed HIV-uninfected infants. We concluded that the proportion of naive, memory, effector and senescent CD8(+) T cells during the first year of life is significantly altered by HIV-1 infection.

Impaired function of human T-lymphotropic virus type 1 (HTLV-1)–specific CD8+ T cells in HTLV-1–associated neurologic disease

Despite abundant activated virus-specific cytotoxic T lymphocytes (CTLs), patients with human T-lymphotropic virus type 1 (HTLV-1)–associated myelopathy/tropical spastic paraparesis (HAM/TSP) showed a significantly higher frequency of infected T cells than did healthy virus carriers (HVCs). Here, we demonstrate that at a given proviral load, the frequency of CD8+ T cells that are negative for specific costimulatory molecules was significantly higher in HAM/TSP than in age-matched HVCs and uninfected healthy controls (HCs), whereas the frequency of intracellular perforin-positive CD8+ T cells was significantly lower in both HAM/TSP and HVCs than in HCs. An inverse correlation between HTLV-1 proviral load (PVL) and percent perforin-positive CD8+ T cells were observed only in disease-protective allele HLA-A*02–positive HVCs, but not in HAM/TSP patients, whether HLA-A*02 positive or negative, nor in HLA-A*02–negative HVCs. Significantly lower perforin expression was observed in HTLV-1–specific than in cytomegalovirus-specific CD8+ T cells. Majority of HTLV-1–specific CD8+ T cells in HVCs showed a CD28−CD27+ phenotype, whereas HAM/TSP showed a CD28−CD27− phenotype. HTLV-1–specific CD8+ T cells from HAM/TSP patients showed significantly lower degranulation than HVCs by CD107a mobilization assay. These findings suggest that an impaired function of HTLV-1–specific CTLs is associated with failing antiviral control and disease HAM/TSP.

Dynamics of T cell memory in human cytomegalovirus infection

Primary human cytomegalovirus (HCMV) infection of an immunocompetent individual leads to the generation of a robust CD4+ and CD8+ T cell response which subsequently controls viral replication. HCMV is never cleared from the host and enters into latency with periodic reactivation and viral replication, which is controlled by reactivation of the memory T cells. In this article, we discuss the magnitude, phenotype and clonality of the T cell response following primary HCMV infection, the selection of responding T cells into the long-term memory pool and maintenance of this memory T cell population in the face of a latent/persistent infection. The article also considers the effect that this long-term surveillance of HCMV has on the T cell memory phenotype, their differentiation, function and the associated concepts of T cell memory inflation and immunosenescence.

Soluble PD-1 rescues the proliferative response of simian immunodeficiency virus-specific CD4 and CD8 T cells during chronic infection

Phenotypic and functional studies of the programmed death-1 (PD-1) molecule on CD4(+) and CD8(+) T cells were performed on peripheral blood mononuclear cells from uninfected and simian immunodeficiency virus (SIV)-infected rhesus macaques. These data demonstrated a rapid upregulation of PD-1 expression on tetramer-positive CD8(+) T cells from MamuA.01(+) SIV-infected macaques upon infection. Upregulation of PD-1 on total CD8(+) T cells was not detectable. In contrast, CD4(+) T-cell PD-1 expression was markedly higher in total CD4(+) T cells during chronic, but not acute, infection and there was a correlation between the level of PD-1 expression on naive and central memory CD4(+) T cells and the levels of viral loads. Such association was emphasized further by a marked decrease of PD-1 expression on tetramer-positive CD8 T cells as well as on CD4(+) T cells on longitudinal samples collected before and after the initiation of antiretroviral therapy and downregulation of viral replication in vivo. Cloning of PD-1 and its two ligands from several non-human primate species demonstrated > 95% conservation for PD-1 and PD-L2 and only about 91% homology for PD-L1. Functional studies using soluble recombinant PD-1 protein or PD-1-immunoglobulin G fusion proteins induced marked increases in the SIV-specific proliferative responses of both CD4(+) and CD8(+) T cells from rhesus macaques. The results of these studies serve as a foundation for future in vivo trials of the use of rMamu-PD-1 to potentially enhance and/or restore antiviral immune responses in vivo.

Impact of opportunistic Mycobacterium tuberculosis infection on the phenotype of peripheral blood T cells of AIDS patients

While the detrimental consequences of opportunistic tuberculosis (TB) in the course and outcome of HIV-1 infection are well studied, little information about the impact of the mycobacterial infection on the phenotype of T lymphocytes is available. In this study we analyzed by cytofluorimetry the peripheral blood T cell phenotype of 13 patients with AIDS, 23 HIV-1 negative patients with active pulmonary TB, nine HIV-1/Mycobacterium tuberculosis coinfected individuals, and 21 age- and sex-matched healthy controls. CD4+ T cells were equally depleted in AIDS and coinfection (P<0.001). The findings suggest a rescuing effect of the added mycobacterial infection. CD3 T cell loss was not observed in coinfection, whereas it was severe in AIDS (P<0.001). Similar (albeit less striking) effects were observed with other markers (CD45RA, CD45RO, and CD27) that were diminished in CD4+ T cells of AIDS patients. Apparent detrimental effects of the added mycobacterial infection were the increased expression of the proapoptotic molecule CD95 on CD4+ T cells, and decreased expression of the major costimulatory molecule CD28 on CD8+ T cells. In this work we show that M. tuberculosis infection modifies the T cell phenotype of the HIV-1 infected individual.

The role of CD8+ T-cell replicative senescence in human aging

The strict limit in proliferative potential of normal human somatic cells - a process known as replicative senescence - is highly relevant to the immune system, because clonal expansion is fundamental to adaptive immunity. CD8(+) T cells that undergo extensive rounds of antigen-driven proliferation in cell culture invariably reach the end stage of replicative senescence, characterized by irreversible cell-cycle arrest and a critically short telomere length. Cultures of senescent CD8(+) T cells also show resistance to apoptosis, permanent loss of CD28 expression, altered cytokine profiles, reduced ability to respond to stress, and various functional changes. Cells with similar characteristics accumulate during normal aging as well as in younger persons infected with human immunodeficiency virus, suggesting that the process of replicative senescence is not an artifact of cell culture but is also occurring in vivo. Interestingly, in elderly persons, the presence of high proportions of CD8(+) T cells with characteristics of replicative senescence is correlated with reduced antibody responses to vaccines as well as with osteoporotic fractures. CD8(+)CD28(-) T cells also accumulate in patients with certain types of cancer. The emerging picture is that senescent CD8(+) T cells may modulate both immune and non-immune functions, contributing not only to reduced anti-viral immunity but also to diverse age-related pathologies.

Therapeutic role of CD8+ T cells in HIV-1 infection: targets and suppressors of viral replication

CD8+ T cells are pivotal in controlling viral replication in HIV-1-infected subjects. However, in chronic infection, HIV-1-specific CD8+ T cells fail to adequately control infection, presenting incomplete maturation and more severe functional impairment with advanced disease. Accumulating evidence has shown that CD8+ T cells can also be productively infected by HIV-1. Whether HIV-1 infection of CD8+ T lymphocytes impacts on their antiviral activity remains to be determined. This review explores the potential mechanisms of HIV-1 infection of CD8+ T cells, its likely contribution to the immunopathogenesis of HIV-1 infection and potential therapeutic interventions.

T-cell receptor excision circles (TREC) in SHIV 89.6p and SIVmac251 models of HIV-1 infection

T-cell receptor excision circles (TREC) may be a useful surrogate marker in HIV-1 infection for evaluating the likelihood of continued clinical stability and/or the response to therapeutics, including vaccines. Analysis of TREC in SHIV and SIV models of HIV-1 infection may provide additional information concerning the utility of TREC as a marker. We measured TREC in peripheral blood mononuclear cells (PBMC) from rhesus macaques in SHIV89.6p (n = 20) and SIVmac251 (n = 11) models of HIV-1 infection. TREC were also evaluated in tissues in the SIVmac251 model at end-point. In the SHIV89.6p model, TREC in PBMC were significantly lower at 12 weeks postinfection compared to preinfection levels. The decrease in TREC correlated with the decline in CD4+ T cells (r(s) = 0.496; P = 0.026), which in turn correlated inversely with serum viral loads at end-point (r(s) = -0.517; P = 0.019). Macaques that controlled SHIV89.6p infection to some degree (n = 6) had higher TREC at study end-point (P = 0.017). In the SIVmac251 model, TREC in PBMC were significantly reduced after 17 months of infection (P = 0.012) despite receiving highly active antiretroviral therapy (HAART) consisting of didanosine (ddI) and (R)-9-(2-phosphonylmethoxypropyl)-adenine (PMPA) when not cycling off therapy during scheduled treatment interruptions (STI). However, macaques that received continuous hydroxyurea (HU) in addition to the HAART regimen had higher end-point TREC compared to the non-HU group (P = 0.041), and the reduction in TREC observed at end-point within the HU group was not significant. In the SIVmac251 model, TREC correlated with the percentage of CD4+ T cells (r(s) = 0.426; P = 0.048) and CD4+CD28+ T cells (r(s) = 0.624; P = 0.002), and inversely with CD8+ T cells (r(s) = -0.622; P = 0.002), CD8+CD28- T cells (r(s) = -0.516; P = 0.014), and serum viral loads (r(s) = -0.627; P = 0.039). High levels of TREC were observed in the thymus, levels comparable to PBMC were seen in the lymph node, and low but detectable levels of TREC were present in bone marrow. The use of correlates of TREC as covariates in ANCOVA revealed that the decline in TREC in the SHIV 89.6p model reflected the decline in the percentage of CD4+ T-cells due to viral cytopathogenicity. In the SIVmac251 model, the decline in TREC was related to increased immune activation and proliferation due to viral replication, as reflected by decreases in percentages of CD4+CD28+ T cells and increases in CD8+ and CD8+CD28- T cells.

Cellular immune response of fetuses to cytomegalovirus

Primary infection with cytomegalovirus (CMV) in immunocompetent hosts is accompanied with activation and differentiation of naive CD8(+) T cells to effector/memory cells secreting interferon-gamma (IFN-gamma). Alteration of these responses during the perinatal period is suggested by a higher rate of CMV diseases in congenital infection. For addressing this issue, immunologic investigations were performed in 15 fetuses (22-36 wk of gestation) with documented congenital CMV infection. Results show that cellular immune responses can be detected as soon as the 22nd week of gestation (the youngest fetus analyzed). Compared with age-matched control subjects, infected fetuses evidence a dramatic increase in the percentages of activated and terminally differentiated CD8 T cells. Indeed, median percentages (interquartile range) of HLA-DR(+) and of CD28(-)CD8(+) T cells were 24% (19-34) and 38% (24-52), respectively in infected fetuses versus 3% (0-4) for each subset in control subjects. In addition, the percentages of T cells secreting IFN-gamma after in vitro stimulation with phorbol myristate acetate and ionomycin was significantly higher in infected fetuses [10% (5-25)] than in healthy fetuses [0.8% (0.6-1.2)] with IFN-gamma being mostly secreted by CD8(+) T cells and to a lesser extend by CD4(+) T cells. These cellular immune responses have clear similarities with responses previously reported in adults. Cellular immunity to CMV, however, might not be fully functional in fetuses. Indeed, the number of T cells capable of secreting IFN-gamma is strikingly lower after in vitro stimulation with the CMV-specific antigen than after in vitro stimulation with phorbol myristate acetate/ionomycin that bypasses signaling through the T-cell receptor.

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.

Phenotypic and functional T-cell aging in rhesus macaques (Macaca mulatta): differential behavior of CD4 and CD8 subsets

A prominent theory of immune senescence holds that repeated antigenic stimulation and decreased production of naive cells combine to progressively exhaust the reserve of lymphocytes available to fight new pathogens, culminating in an accumulation of lymphocytes that achieved replicative senescence. A well-defined primate model of immune senescence in vivo would greatly facilitate testing of this theory. Here, we investigated phenotypic and functional T-cell aging in the rhesus macaques (RMs), currently the dominant primate model of AIDS. Our results show that sharp differences exist between the CD8 and CD4 T-cell subsets in (1) cell-cycle programs (as assessed by both in vitro proliferation and in vivo turnover measurement); (2) CD28 regulation on cell-cycle entry; and (3) accumulation of immediate effector cells among the CD28- cells, believed to be close to or at replicative senescence. These results further suggest poor reliability of CD28 as a marker for senescence. We suggest that some of the T-cell aging phenomenology in RMs can be ascribed to accentuation over time of the inherent differences in activation programs in CD8 and CD4 T cells.

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.

Expression patterns of phenotypic markers on lymphocytes from human immunodeficiency virus type 2-infected baboons

The development of AIDS in HIV-1-infected humans is associated with profound changes in the expression patterns of lymphocyte phenotypic markers associated with increased immune activation and with decreased recall immune responses. In assessing these immunologic changes in an animal model, we characterized the expression patterns of immune activation markers on lymphocyte subsets during the acute, chronic, and end stages of HIV-2 infection in baboons. Using flow cytometry, we identified 21 human-specific monoclonal antibodies that were cross-reactive with baboon lymphocytes; however, expression of only 2 of these markers was altered significantly after HIV-2 infection. We found an increase in baboon class II antigen (as measured by anti-HLA-DR) in the CD4(+) T cell subset within 8 weeks of infection (p = 0.045). Moreover, after 1 year of infection, CD11b was downregulated on CD8(+) T lymphocytes (p = 0.027). This downregulation of CD11b was consistently observed in all of the groups of baboons that were chronically infected with three different HIV-2 isolates. In addition, we found substantial downregulation of the interleukin 2 receptor (CD25) and upregulation of class II antigen on CD8(+) lymphocytes in a baboon with an AIDS-like disease. These and other phenotypic markers of immune activation may facilitate characterization of the immunopathogenesis of AIDS in nonhuman primate animal models.

Increased frequency of IFN-gamma-producing peripheral CD8+ T cells with memory-phenotype in patients with chronic hepatitis C

To identify the capacity for cytokine production and the phenotypic characteristics of peripheral CD8(+) T cells in patients with chronic hepatitis C, 31 patients with chronic hepatitis C and 22 healthy controls were studied at the single cell level by three-color flow cytometry. Whole blood was stained with surface CD8, intracellular interferon-gamma (IFN-gamma), and interleukin-4 (IL-4), surface CD8, CD28, and intracellular IFN-gamma after stimulation with PMA plus ionomycin, and then surface CD8, CD45RA, and CD28. IFN-gamma-producing peripheral CD8(+) T cells were found frequently in patients than in controls (P < 0.05), whereas IL-4-producing peripheral CD8(+) T cells were not. Although the frequency of peripheral CD28(+)CD8(+) and CD28(-)CD8(+) T cells in patients was not different from that of controls, CD28(+)CD8(+) T cells exceeded CD28(-)CD8(+) T cells in the capacity for IFN-gamma-production after mitogenic stimulation (P < 0.01). In a more detailed analysis of the CD28(+)CD8(+) T cells, CD45RA(-)CD28(+)CD8(+) T cells, defined phenotypically as memory cells, were found frequently in patients than in controls (P < 0.05). There were no significant correlations between the frequency of IFN-gamma-producing peripheral CD8(+) T cells and hepatitis C virus RNA level or serum alanine aminotransferase level in patients. These data suggest that functionally T cytotoxic type 1 and memory CD8(+) T cells are predominant in the peripheral blood of chronic hepatitis C patients and that such activated CD8(+) T cells are associated with liver damage.

A reduction in the number of peripheral CD28+CD8+T cells in the acute phase of influenza

Influenza patients show a high incidence of T lymphocytopenia in the acute phase of the illness. Since CD8+ T cells play an important role in influenza virus infection, we investigated which subset of CD8+ T cells was involved in this lymphocytopenia. CD8+ T cells from eight patients with influenza A were studied for lymphocyte count, surface marker, and intracellular IFN-gamma production in the acute (days 1-3) and recovery phases (days 9-12). Total and T lymphocyte counts in the acute phase were approximately three times less than in the recovery phase; however, the CD4/8 ratio was the same in both phases. The cell count reduction in the acute phase was attributed predominantly to the CD28+ CD8+ subset, compared with the CD28- CD8+ subset. The memory/activation marker CD45RO on the CD8+ T cells was assessed. The CD28+ CD45RO- subset, a naive phenotype, was reduced significantly in number in the acute phase compared with the recovery phase. The CD28+ CD45RO+ subset, a memory phenotype, was also reduced in the acute phase, but the reduction was not statistically significant. Intracellular IFN-gamma in the CD8+ subset after mitogenic stimulation was measured by flow cytometry; the percentage of CD28+ IFN-gamma-/CD8+ subset in the acute phase was significantly less than in the recovery phase. These results indicated that the predominant reduction of peripheral CD8+ T cells in the acute phase of influenza was from naive-type lymphocytes, suggesting that these quantitative and qualitative changes of CD8+ T cells in influenza are important for understanding the immunological pathogenesis.

The CD28/HLA-DR expressions on CD4+T but not CD8+T cells are significant predictors for progression to AIDS

To investigate the changes of CD28 and HLA-DR molecules on CD4+ and CD8+ T cells during HIV infection, we classified 130 HIV-infected Koreans into four groups by the CD4 level as follows: group I (> or = 500 cells/mm3), group II (201-499 cells/mm3), group III (51-200 cells/mm3), and group IV (< or = 50 cells/mm3). In CD4+ T cells, the proportion of CD28 expression decreased significantly with the CD4 level while the proportion of HLA-DR expression increased gradually. In particular, the changes of HLA-DR expressions on CD4+ T cells were parallel to the loss of CD28 molecules from stage III to IV. However, the CD28 expression on CD8+ T cells decreased dramatically in the early stage of HIV infection, and the sum and pattern of CD28 and HLA-DR expressions on CD8+ T cells was stable after the first stage. Even though CD28 down-regulation on CD8+ T cells was very severe from the early stage of HIV infection, it might not influence the survival time of HIV-infected Koreans. The sum of the CD28+ subsets and HLA-DR subsets in each T cell was stable in all stages of disease progression. The sums of the CD28+ subsets and HLA-DR+ subsets in CD4+ T and CD8+ T cells were constant as approximately 100% and 55-60% of each T cell. These results suggested that the changes of CD28/HLA-DR expressions on CD4+ T cells were more predictable than those on CD8+ T cells in the evaluation of the disease progression during HIV-infected periods. However, we need further studies to understand why the sum of two molecules in each T cell are constant.

Clonal cytotoxic T cells are expanded in myeloma and reside in the CD8(+)CD57(+)CD28(-) compartment

The occurrence of clonal T cells in multiple myeloma (MM), as defined by the presence of rearrangements in the T-cell receptor (TCR)-beta chains detected on Southern blotting, is associated with an improved prognosis. Recently, with the use of specific anti-TCR-variable-beta (anti-TCRV(beta)) antibodies, the presence in MM patients of expanded populations of T cells expressing particular V(beta) regions was reported. The majority of these T-cell expansions have the phenotype of cytotoxic T cells (CD8(+)CD57(+) and perforin positive). Since V(beta) expansions can result from either a true clonal population or a polyclonal response, the clonality of CD8(+)TCRV(beta)(+) T cells was tested by TCRV(beta) complementarity-determining region 3 length analysis and DNA sequencing of the variable region of the TCR. In this report, the CD57(+) and CD57(-) subpopulations within expanded TCRV(beta)(+)CD8(+) cell populations are compared, and it is demonstrated that the CD57(+) subpopulations are generally monoclonal or biclonal, whereas the corresponding CD57(-) cells are frequently polyclonal. The oligoclonality of CD57(+) expanded CD8(+) T cells but not their CD57(-) counterparts was also observed in age-matched controls, in which the T-cell expansions were mainly CD8(-). The CD8(+)CD57(+) clonal T cells had a low rate of turnover and expressed relatively lower levels of the apoptotic marker CD95 than their CD57(-) counterparts. Taken together, these findings demonstrate that MM is associated with CD57(+)CD8(+) T-cell clones, raising the possibility that the expansion and accumulation of activated clonal CD8(+) T cells in MM may be the result of persistent stimulation by tumor-associated antigens, combined with a reduced cellular death rate secondary to reduced expression of the apoptosis-related molecule CD95.

Increased expression of CTLA-4 (CD152) by T and B lymphocytes in Wegener's granulomatosis

CTLA-4 (CD152) is a surface molecule of activated T cells with sequence homology to CD28. Both molecules bind to the same ligands, B7.1 (CD80) and B7.2 (CD86) but have antagonistic functions. While CD28 is an important costimulator, CTLA-4 has an essential inhibitory function in maintaining the homeostasis of the immune system. Furthermore, CTLA-4 has a role in inducing a Th1 response and suppressing Th2 cytokines, an effect which is antagonized by CD28. Many autoimmune diseases are characterized by an overwhelming production of Th1 cytokines. Recently, the predominance of the Th1 cytokine pattern has been directly observed in the granulomatous inflammation of patients with Wegener's granulomatosis. The balance between CD28 and CTLA-4 expression by T lymphocytes could be a factor in the pathogenesis of autoimmune diseases. Down regulation of CD28 predominantly on CD8+ T cells has been described in Wegner's granulomatosis; however, analysis of CTLA-4 is complicated by its low expression levels. Here we have used potent signal enhancement to study CTLA-4 on PBMC in patients with Wegener's granulomatosis (n = 25) in comparison with healthy controls (n = 19). Expression levels of CTLA-4 were significantly increased selectively on CD4+ and possibly also on CD4-/CD8- T cells in Wegener's granulomatosis. High CTLA-4 expression by T lymphocytes was associated with more severe disease. In contrast, after stimulation with the mitogen PHA, CTLA-4 levels were strongly increased on T cells from controls but in T cells from Wegener's granulomatosis patients this response was severely impaired. Interestingly, while CTLA-4 was seen exclusively on T cells in control individuals, about half of the Wegener's patients showed CTLA-4 expression by a fraction of peripheral B lymphocytes. CTLA-4 positive B cells in the periphery were associated with less acute disease.

Markers of cell death-activation in lymphocytes of vertically HIV-infected children naive to highly active antiretroviral therapy: the role of age

BACKGROUND

Apoptosis plays a major role in depleting CD4(+) lymphocytes during infection with HIV-1. Few data exist on its role during HIV infection of children. Sensitivity of peripheral blood lymphocytes (PBLs) to apoptotic stimuli and the importance of the patient's age remain unclear.

OBJECTIVES

We sought to analyze the following: (1) markers of cell death-activation (CD95, CD45 isoforms, and CD28) in PBLs from vertically HIV-infected children of different ages before highly active antiretroviral therapy; (2) changes in other PBL populations; (3) PBL sensitivity to cell death and mitochondrial damages; and (4) role of age during progression of infection.

METHODS

Cell culture techniques and flow cytometry were used to analyze surface antigens, PBL susceptibility to apoptosis, or PBL susceptibility to change of mitochondrial membrane potential.

RESULTS

Donor age had a strong negative correlation with numbers of CD4(+) and CD8(+) T cells. Virgin T lymphocyte (CD45RA(+), CD95(-)) levels and those of CD95(+) cells showed no correlation with the children's clinical status but did show a correlation with patient age. CD28(-) T lymphocytes were markedly augmented in HIV-infected children but were unrelated to stage of infection or age. A relevant decrease in B lymphocytes and an increase in natural killer cells were also found. Finally, PBLs from HIV-positive children had a marked tendency to undergo apoptosis and mitochondrial damage.

CONCLUSION

Changes in PBL phenotype, increased expression of CD95, and high sensitivity to apoptosis suggest that a precocious aging of the immune system occurs in HIV-infected children.

TH1 cytokine response of CD57+ T-cell subsets in healthy controls and patients with alcoholic liver disease

Patients with chronic inflammatory diseases, including Crohn's disease and rheumatoid arthritis, as well as those with certain viral infections, and patients who are transplant recipients or who have certain hematologic malignancies have been observed to have CD57+ T cell expansion in both CD4+ and CD8+ subsets. We have reported previously that alcoholic patients also have CD57+ T cell expansion. Because many alcoholics become seriously deficient in cell-mediated immunity, it is of interest to determine whether the expanded CD57+ subsets can respond to stimulation with normal T helper cell subtype 1 (TH1) cytokine production. We report evaluation of the CD57 T-cell subsets of patients with alcoholic liver disease (ALD) with the use of cytoplasmic staining after stimulation through the T-cell receptor (TCR). The CD57+ subsets of the T cells of both healthy individuals and patients with ALD express significantly higher amounts of cytoplasmic tumor necrosis factor-alpha (TNF-) and interferon-gamma (IFN-) after 6 h of stimulation than do the CD57- subsets. This increased production can persist up to 46 h of continuous stimulation. Under these assay conditions, very little cytoplasmic interleukin (IL)-4 is observed in the T cells of either healthy control subjects or patients with ALD. Measurement of cytokine secretion by sort-purified CD57 T-cell subsets with the use of enzyme-linked immunosorbent assay (ELISA) shows that the CD57+ T-cell subset produces 18- to 30-fold more TNF- and IFN-, respectively, than does the CD57- subset in the first 12 h of stimulation. This response requires only stimulation through the TCR for the CD57+ subset, whereas significant secretion by the CD57- subset requires added IL-2 or anti-CD28 antibody. These results are consistent with the concept of the CD57+ T-cell subset as a differentiated effector cell and demonstrate that patients with ALD who are not drinking at the time of evaluation have normal or increased immediate TH1 T-cell responses.

Telomere shortening and decreased replicative potential, contrasted by continued proliferation of telomerase-positive CD8+CD28(lo) T cells in patients with systemic lupus erythematosus

To evaluate whether the immune system of systemic lupus erythematosus (SLE) patients shows features of premature aging, we compared telomere length and proliferative potential of SLE peripheral blood mononuclear cells (PBMC) (N = 90) to those of controls (N = 64). SLE samples showed accelerated loss of telomeric DNA (P = 0.00008) and higher levels of senescent (< or =5 kb) telomeric DNA (P = 0.00003). Viability cell counts and CFSE tracking in 6-week-old cell cultures indicated that SLE PBMC (CD8+ and CD4+ T cells) underwent fewer mitotic cycles and had shorter telomeres than controls (P = 0.04). However, a CD8(+)CD28(lo) T cell subset expanded preferentially in SLE-derived bulk cultures (P = 0.0009), preserved telomeric DNA (P = 0.01 vs entire CD8+), and displayed telomerase activity [2.1 telomerase arbitrary units (TAU) vs 0.5 TAU in CD8+CD28(hi) cells and 0.3 TAU in bulk PBMC; P = 0.05]. These T cell anomalies could be due to chronic in vivo stimulation of the immune system and may contribute to the immune dysregulation found in SLE.

Protective immune responses induced by a non-pathogenic simian/human immunodeficiency virus (SHIV) against a challenge of a pathogenic SHIV in monkeys

A simian/human immunodeficiency virus (SHIV)-NM3n containing the human nef, but not the monkey nef, and vpr genes of SIV was inoculated into two cynomolgus monkeys, resulting in systemic infection with a minimum level of transient virus load. In order to study the nature of immune responses associated with the prevention of a pathogenic SHIV, the SHIV-NM3n-inoculated monkeys and three naive monkeys were intravenously challenged with a pathogenic SHIV containing the envelope gene of HIV-1 89.6. After the heterologous virus challenge, all of the SHIV-NM3n-inoculated animals completely avoided the loss of CD4+ T lymphocytes in PBMC as well as lymphoid tissues compared to pathogenic SHIV-injected control animals. The inhibition of CD4+ cell depletion was associated with maintaining the proliferative response of helper T-cells against SIV p27 in the previously nonpathogenic virus-inoculated animals following the pathogenic virus challenge. Furthermore, the decline of CD28+ cells, the increase in CD95+ cells, and the enhancement of in vitro apoptosis in PBMC were inhibited in the non-pathogenic virus-inoculated animals. These results suggest that nonpathogenic SHIV-NM3n infection induces the protection of monkeys from heterologous pathogenic viruses that may be associated with blocking the change in immune responses and the cell loss induced by a pathogenic virus.

Functional heterogeneity and high frequencies of cytomegalovirus-specific CD8(+) T lymphocytes in healthy seropositive donors

Human cytomegalovirus (HCMV) infection is largely asymptomatic in the immunocompetent host, but remains a major cause of morbidity in immunosuppressed individuals. Using the recently described technique of staining antigen-specific CD8(+) T cells with peptide-HLA tetrameric complexes, we have demonstrated high levels of antigen-specific cells specific for HCMV peptides and show that this may exceed 4% of CD8(+) T cells in immunocompetent donors. Moreover, by staining with tetramers in combination with antibodies to cell surface markers and intracellular cytokines, we demonstrate functional heterogeneity of HCMV-specific populations. A substantial proportion of these are effector cytotoxic T lymphocytes, as demonstrated by their ability to lyse peptide-pulsed targets in "fresh" killing assays. These data suggest that the immune response to HCMV is periodically boosted by a low level of HCMV replication and that sustained immunological surveillance contributes to the maintenance of host-pathogen homeostasis. These observations should improve our understanding of the immunobiology of persistent viral infection.

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.

T-cell expansions in patients with multiple myeloma have a phenotype of cytotoxic T cells

The presence of T-cell clones in peripheral blood has been previously shown to be associated with a survival advantage in patients with multiple myeloma and suggests that the expanded T-cell populations may be involved in an anti-tumour response. We studied the T-cell receptor (TCR) repertoire of 38 patients with myeloma to identify and characterize the expanded T-cell populations by flow cytometry. T-cell expansions were found in 79% of the patients. The expansions occurred randomly among the 21 variable regions of the TCR beta chain (Vbeta) studied, representing 62% of the V-beta repertoire, and were stable during an 18-month follow-up. The phenotype of the expanded V-beta populations was predominantly CD8+, CD57+, CD28- and perforin+, which differed significantly from the other non-expanded Vbeta populations. The expression of the apoptosis markers Fas (CD95) and bcl-2 were similar between the expanded and non-expanded Vbeta populations. In conclusion, expanded T-cell populations were frequent in patients with myeloma, they remained unchanged during follow-up and had phenotypic characteristics of cytotoxic T cells. These data add further support to the concept that the T-cell expansions may have an immunoregulatory role in myeloma.

CD28 costimulation and CD28 expression in T lymphocyte subsets in HIV-1 infection with and without progression to AIDS

In a prospective study of 152 HIV-1 patients (with and without progression to AIDS) we examined CD28 MoAb costimulation and CD3 MoAb response using whole blood culture at baseline and up to either the time of AIDS diagnosis or the end of the observation period. CD28 antigen expression on both CD4+ and CD8+ T lymphocytes was also studied in both groups of patients. In patients who progressed to AIDS, CD28 MoAb costimulation was found to be decreased. Univariate time-dependent analysis showed that decreases in (i) absolute numbers of either CD4+, CD4+CD28+, CD8+CD28+ T cells, (ii) CD28 MoAb costimulation, and (iii) CD3 MoAb response, and an increase in CD8+CD28- %, are significant predictors for progression to AIDS. In addition, multivariate time-dependent analysis demonstrated that a decrease in CD28 MoAb costimulation (but not a decrease in CD3 MoAb response) was predictive for progression to AIDS, as were decreases in the percentage of CD4+ T cells and the absolute number of CD4+CD28+ T cells. Thus, CD28 MoAb costimulation can be considered a useful assay for monitoring HIV-1 infection. Furthermore, apart from the early increase in the percentage of CD8+CD28- T cells and an increase in the percentage of CD28- on CD8+ T cells in both groups of patients at baseline compared with normal controls, a negative correlation was found to exist between the percentages of CD4+ or CD4+CD28+ T cells and the percentage of CD8+CD28- T cells; this suggests that these cells are probably mutually regulated.

Impaired expression of CD28 on T cells in hairy cell leukemia

T cells from patients with active hairy cell leukemia (HCL), a chronic B cell malignancy, show poor proliferation in response to allogeneic peripheral blood mononuclear cells (PBMC). In order to study the T cell dysfunction, the expression of several adhesion and costimulatory molecules was analyzed by flow cytometry. Circulating T cells from HCL patients showed increased percentages of CD28(-) in all T cell subsets. In some patients the percentage of CD28(-) T cells within the CD4(+) subset was increased up to 80%. These CD4(+)CD28(-) T cells did not proliferate in a mixed lymphocyte culture (MLC) against allogeneic PBMC. After enrichment for CD4(+)CD28(+) T cells, the proliferative response in the MLC was recovered, but this response was still lower than the proliferative response from control T cells. In conclusion, lack of CD28 on T cells and a restricted T cell repertoire may contribute to immune deficiency in patients with HCL.

Large clonal expansions of human virus-specific memory cytotoxic T lymphocytes within the CD57+ CD28- CD8+ T-cell population

The proportion of human peripheral blood CD8+ T cells that are CD57+ CD28- is low at birth but increases with age and in individuals infected with human cytomegalovirus (HCMV) or human immunodeficiency virus (HIV). These CD57+ CD28- CD8+ T cells contain large oligoclonal T-cell expansions whose antigen specificity is unknown. We identified clonal expansions of virus-specific memory cytotoxic T-lymphocyte precursors (CTLp) in both healthy carriers of HCMV and in asymptomatic HIV-infected subjects. In each subject, from the T-cell receptor (TCR) beta-chain hypervariable sequence of each immunodominant CTL clone, we designed complementary oligonucleotide probes to quantify the size and phenotypic segregation of individual virus-specific CTL clones in highly purified populations of peripheral blood CD8+ T cells. We found large clonal expansions of virus-specific CTL clonotypes in CD57+ CD28- CD8+ T cells. Using limiting dilution analysis, we found functional peptide-specific CTLp at high frequency in CD57+ CD28- cells. Thus, memory CTL specific for persistent viruses account for many oligoclonal expansions within CD57+ CD28- CD8+ T cells.

Decreased CD40 ligand induction in CD4 T cells and dysregulated IL-12 production during HIV infection

During HIV infection various cytokines are overproduced in early stages, whereas in advanced disease cytokines of the T helper 1 type (e.g. interferon-gamma (IFN-gamma)) are selectively deficient. During antigenic stimulation, the production of type-1 cytokines is enhanced by IL-12, secreted by antigen-presenting cells (APC) after their interaction with activated CD4 T cells. Two factors are essential in this process: priming APC with IFN-gamma and triggering the CD40 receptor on APC by CD40 ligand (CD40L). In view of the importance of this pathway, we compared its regulation in HIV-infected and control subjects. After cross-linking of the T cell receptor (TCR)/CD3 complex, the proportional expression of CD40L was similar on CD4+ T cells from controls and from patients with high circulating CD4 T counts (> 500/microl), but CD40L up-regulation was significantly reduced in patients with more advanced disease. Simultaneous triggering of the costimulatory receptor CD28 on T cells through its natural ligand CD80 partly corrected the CD40L defect in patients with intermediate CD4 T counts (200-500), but not in AIDS patients. Early production of IFN-gamma was preserved in lymphocytes from HIV+ patients. The expression of CD40 on peripheral monocytes from HIV+ subjects was increased in a disease stage-related fashion. Stimulation of mononuclear cells through cell-bound CD40L and soluble IFN-gamma induced significantly higher IL-12 in cultures from patients with > 200 circulating CD4 T cells, whereas IL-12 production was marginally decreased in cultures from patients with < 200 CD4 T cells, compared with healthy control cultures. In conclusion, our data suggest that impaired CD40L induction on CD4 T cells contributes to deficient type-1 responses through decreased IL-12 production in AIDS infection, whereas enhanced CD40-mediated IL-12 production in less advanced stages might contribute to increased levels of various cytokines in early disease

Costimulation of CD28- T cells through CD3 and beta1-integrins induces a limited Th1 cytokine response

The costimulatory molecule CD28 regulates antigen-specific T-cell proliferation and the synthesis of multiple cytokines. The absence of CD28 on a subset of CD8bright+ T cells suggests that these cells may utilize alternative costimulatory pathways or have a limited cytokine response to presented antigen. We used fibronectin, a ligand for the beta1-integrins alpha4beta1 and alpha5beta1, as an alternate costimulatory ligand to assess the functional phenotype of CD8bright+CD28- T cells. CD25 expression was significantly up-regulated in CD8bright+CD28- T cells by immobilized anti-CD3i with fibronectin. Costimulation with fibronectin also significantly augmented anti-CD3i-induced IFN-gamma production only among CD8bright+CD28- T cells. The CD8bright+CD28- T cells did not produce significant IL-2 and IL-10 even in response to maximal stimulation with phorbol myristate acetate and ionomycin. These data support a costimulatory role for ss1-integrins in CD8bright+CD28- T cells and indicate that CD8bright+ CD28- T cells have a restricted Th1 cytokine repertoire.

C1.7 Antigen Expression on CD8+ T Cells Is Activation Dependent: Increased Proportion of C1.7+CD8+ T Cells in HIV-1-Infected Patients with Progressing Disease

The C1.7 Ag is a surface marker previously shown to be expressed on all NK cells and on a subset of CD8+ T cells. We report in this study that C1.7 Ag expression on peripheral blood-derived CD8+ T cells overlaps with activation markers S6F1high and CD29high and is reciprocally expressed with CD62L. C1.7 Ag expression can be induced in vitro on CD8+ T cells by anti-CD3 cross-linking, suggesting that C1.7 Ag is activation dependent. In contrast to NK cells, C1.7 Ag does not signal on CD8+ T cells, nor does it induce redirected lysis upon ligation. The proportion of C1.7 Ag+CD8+ T cells is increased in HIV-infected patients compared with healthy donors. In 69 HIV-infected patients, we observed a significant inverse correlation between the percentage of C1.7 Ag-expressing CD8+ T cells and the absolute CD4+ T cell count. Two-year clinical follow-up of patients with initial CD4+ T cell count of &gt;400 cells/mm3 and a normal proportion of C1.7 Ag+CD8+ T cells revealed that these patients were clinically stable with minimal HIV-associated symptoms. In contrast, 10 of 12 patients with CD4+ T cell counts of &gt;400 cells/mm3 and an elevated proportion of C1.7 Ag+CD8+ T cells were symptomatic. ANOVA analysis of patients indicates that C1.7 Ag is a better predictor of disease progression than CD4 count. Overall, our findings indicate that C1.7 Ag is the first described marker for activated/memory CD8+ T cells and a useful parameter for evaluating the level of CD8+ T cell activation in vivo.

IL-13 and IFN-γ Secretion by Activated T Cells in HIV-1 Infection Associated with Viral Suppression and a Lack of Disease Progression

The immunopathology of HIV-1 infection includes immune defects in T cell cytokine secretion, resulting in decreased Ag-specific responses. In this report, IL-13 and IFN-γ were analyzed in progressive HIV-1 disease. Both cytokines exert positive effects on Ag presentation and inhibit HIV-1 infection of macrophages. Anti-CD3/anti-CD28-activated PBMC from HIV-1-infected individuals (n = 74) compared with uninfected subjects (n = 30) secreted significantly less IL-13 (median, 0.64 ng/ml vs 2.07 ng/ml; p &lt; 0.001) and IFN-γ (median, 40.96 ng/ml vs 129.5 ng/ml; p &lt; 0.005). Decreased IL-13 and IFN-γ secretion in HIV infection was present in sorted CD4+ and CD8+ T cell subsets, and additional analysis determined concurrent deficiency at the protein and transcriptional level. Longitudinal analysis showed that cytokine secretion levels correlated positively with CD4 count and negatively with plasma HIV-1 viral load. Patients changing to suppressive antiretroviral therapy during the study showed increases in IL-13 and IFN-γ secretion. Overall, results show a decline in IL-13 and IFN-γ secretion in progressive HIV-1 infection and suggest a role for both cytokines as part of T cell adaptive responses associated with a lack of disease progression.

Human CD28−CD8+ T Cells Contain Greatly Expanded Functional Virus-Specific Memory CTL Clones

At birth, almost all human peripheral blood CD8+ T cells express the costimulatory molecule CD28. With increasing age, the proportion of CD8+ T cells that lack CD28 increases. Because the Ag specificity of CD28−CD8+ T cells has not previously been defined, we studied the contribution of CD28−CD8+ T cells to the memory CD8+ CTL response against two human persistent viruses, human CMV (HCMV) and HIV. From PBMC of healthy virus carriers we generated multiple independent CTL clones specific for defined viral peptides and sequenced their TCR β-chains. We designed clonotypic oligonucleotides complementary to each β-chain hypervariable sequence and quantified the size of individual immunodominant CTL clones in PBMC. Some individual CTL clones were very large, comprising up to 3.1% of all CD8+ T cells in PBMC, and were generally maintained at a stable level for months. Individual virus-specific CTL clones were consistently more abundant in purified CD28− cells than in the CD8+ population as a whole. Because CD28−CD8+ cells as a population have been reported to proliferate poorly in response to mitogen, we studied the function of these virus-specific CD28− CTL clones by quantifying the frequency of peptide-specific CTL precursors using limiting dilution analysis. CD28−CD8+ T cells contained high frequencies of functional memory CTL precursors specific for peptides of HCMV or HIV, generally higher than in the CD8+ T cell population as a whole. We conclude that in asymptomatic HCMV and HIV infection, human CD28−CD8+ T cells contain high frequencies of functional virus-specific memory CTL clones.

Modulation of CD28 Expression: Distinct Regulatory Pathways During Activation and Replicative Senescence

The costimulatory molecule CD28 has a restricted tissue distribution and is expressed on T cells and some plasmacytoma cells. Although CD28 is constitutively expressed, its expression is transiently down-regulated following T cell activation and declines progressively with in vitro senescence. In vivo, CD8+ T cells and, less frequently, CD4+ T cells may completely lose CD28 surface expression during chronic infections and with aging. This correlates with changes of nuclear protein-binding activities to two motifs, site α and β, within the CD28 minimal promoter. Both α- and β-bound complexes are found only in lymphoid tissues, in CD28+ T cells, and in some transformed B cells. These complexes are coordinately expressed except during replicative senescence, which is characterized by the down-modulation of site β- but not site α-binding activities. In contrast, T cell activation induces a parallel decline in both site α- and β-binding activities. CD4+ and CD8+ T cells differ in their β-binding profiles, which may explain the more pronounced down-regulation of CD28 in senescent CD8+ T cells. In vivo expanded CD4+CD28null and CD8+CD28null T cells uniformly lack α- and β-bound complexes, resembling the pattern seen in chronically activated cells and not of senescent cells.