Memory CD8+ T cells vary in differentiation phenotype in different persistent virus infections

Immunodominance among herpes simplex virus-specific CD8 T cells expressing a tissue-specific homing receptor

The study of immunodominance within microbe-specific CD8 T cell responses has been challenging. We used a previously undescribed approach to create unbiased panels of CD8 cytotoxic T lymphocyte clones specific for herpes simplex virus type 2, a pathogen with a complex genome encoding at least 85 polypeptides. Circulating herpes simplex virus type 2-specific cells were enriched and cloned after sorting for expression of the skin homing-associated receptor, cutaneous lymphocyte-associated antigen, bypassing restimulation with antigen. The specificity of the resultant cytotoxic clones was determined. Clonal frequencies were compared with each other and with the total number of cytotoxic clones. For each subject within the homing receptor-positive compartment, the CD8 cytotoxic response was dominated by T cells specific for only a few peptides. Previously undescribed antigens and epitopes in viral tegument, capsid, or scaffold proteins were immunodominant in some subjects. Clone enumeration analyses were confirmed in some subjects with dominance studies by using herpes simplex mutants, vaccinia recombinants, and/or enzyme-linked immune spots. We conclude that among circulating cells expressing a homing-associated receptor, during chronic herpes type 2 infection, the CD8 T cell response becomes quite focused despite the presence of many potential antigenic peptides.

Functional leukemia-associated antigen-specific memory CD8+ T cells exist in healthy individuals and in patients with chronic myelogenous leukemia before and after stem cell transplantation

Antigens implicated in the graft-versus-leukemia (GVL) effect in chronic myeloid leukemia (CML) include WT1, PR1, and BCR-ABL. To detect very low frequencies of these antigen-specific CD8+ T cells, we used quantitative polymerase chain reaction (qPCR) to measure interferon-gamma (IFN-gamma) mRNA production by peptide-pulsed CD8+ T cells from HLA-A*0201+ healthy volunteers and from patients with CML before and after allogeneic stem cell transplantation (SCT). Parallel assays using cytomegalovirus (CMV) pp65 tetramers demonstrated the IFN-gamma copy number to be linearly related to the frequency of tetramer-binding T cells, sensitive to frequencies of 1 responding CD8+ T cell/100 000 CD8+ T cells. Responses to WT1 and PR1 but not BCR-ABL were detected in 10 of 18 healthy donors. Responses to WT1, PR1, or BCR-ABL were observed in 9 of 14 patients with CML before SCT and 5 of 6 after SCT, often to multiple epitopes. Responses were higher in patients with CML compared with healthy donors and highest after SCT. These antigen-specific CD8+ T cells comprised central memory (CD45RO+CD27+CD57-) and effector memory (CD45RO-CD27-CD57+) T cells. In conclusion, leukemia-reactive CD8+ T cells derive from memory T cells and occur at low frequencies in healthy individuals and at higher frequencies in patients with CML. The increased response in patients after SCT suggests a quantitative explanation for the greater effect of allogeneic SCT.

Population analysis of antiviral T cell responses using MHC class I-peptide tetramers

MHC class I-peptide tetrameric complexes ('tetramers') have revolutionized the study of antiviral CD8+ T cell responses. They allow accurate quantification of immune responses ex vivo independent of function, with high levels of sensitivity. They have revealed unexpectedly large frequencies of 'memory' T cell responses against viruses such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV), and provided information about their phenotypic and functional variation. However, such studies have generally concentrated on limited numbers of individuals analysed in detail. To allow larger population-based studies, we devised a method for tetramer analysis using 50-100 microlitre blood volumes in a 96-well plate format. We adapted this method to study the effect of age on responses in a cohort of nearly 600 individuals to an immunodominant HLA-A2 restricted response to CMV pp65 (NLVPMVATV). We observed the phenomenon of steady 'memory inflation' with age, similar to recently observed longitudinal data from murine studies. These data show that tetramers can be used as population screening tools and could be used to study age-related, geographical or seasonal effects in a number of other viral infections.

Restoration of CD28 expression in CD28- CD8+ memory effector T cells reconstitutes antigen-induced IL-2 production

The control of many persistent viral infections by Ag-specific cytolytic CD8+ T cells requires a concurrent virus-specific CD4+ Th cell response. This reflects in part a requirement of activated effector CD8+ T cells for paracrine IL-2 production as a growth and survival factor. In human CMV and HIV infection, the majority of differentiated virus-specific CD8+ T cells notably lose the ability to produce IL-2 but also lose expression of CD28, a costimulatory molecule. Analysis of the fraction of memory CD8+ T cells that continue to express CD28 revealed these cells retain the ability to produce IL-2. Therefore, we examined if IL-2 production by CD28- CD8+ T cells could be restored by introduction of a constitutively expressed CD28 gene. Expression of CD28 in CD28- CD8+ CMV- and HIV-specific CD8+ T cells reconstituted the ability to produce IL-2, which could sustain an autocrine proliferative response after Ag recognition. These results suggest that the loss of CD28 expression during differentiation of memory/effector CD8+ T cells represents a decisive step in establishing regulation of responding CD8+ T cells, increasing the dependence on CD4+ Th for proliferation after target recognition, and has implications for the treatment of viral disease with adoptively transferred CD8+ T cells.

Characterization of the CD4+ T cell response to Epstein-Barr virus during primary and persistent infection

The CD8+ T cell response to Epstein-Barr virus (EBV) is well characterized. Much less is known about the evolution of the CD4+ T cell response. Here we show that EBV stimulates a primary burst of effector CD4+ T cells and this is followed by a period of down-regulation. A small population of EBV-specific effector CD4+ T cells survives during the lifelong persistent phase of infection. The EBV-specific effector CD4+ T cells accumulate within a CD27+ CD28+ differentiation compartment during primary infection and remain enriched within this compartment throughout the persistent phase of infection. Analysis of CD4+ T cell responses to individual epitopes from EBV latent and lytic cycle proteins confirms the observation that the majority of the effector cells express both CD27 and CD28, although CD4+ T cells specific for lytic cycle antigens have a greater tendency to express CD45RA than those specific for the latent antigens. In clear contrast, effector CD4+ T cells specific for cytomegalovirus (CMV) accumulate within the CD27- CD28+ and CD27- CD28- compartments. There are striking parallels in terms of the differentiation of CD8+ T cells specific for EBV and CMV. The results challenge current ideas on the definition of memory subsets.

CD28 costimulation independence of target organ versus circulating memory antigen-specific CD4+ T cells

T cell receptor engagement with CD28 costimulation is generally required for naive T cell activation, whereas reactivation of memory cells is less dependent on CD28 costimulation. We studied this process in chronic beryllium disease, in which the frequency of antigen-specific CD4+ T cells in the lung is large and circulating antigen-specific cells are also detectable. In the lung, a large fraction of CD4+ T cells stopped expressing CD28 mRNA and protein, and this change in phenotype correlated with lung inflammation. In the presence of concentrations of CTLA-4Ig that inhibited the CD28-B7 interaction, beryllium-specific CD4+ T cells in lung were still able to proliferate and secrete IFN-gamma in response to beryllium in culture. This functional independence of CD28 costimulation included lung CD28+ effector cells. Although lung CD4+CD28- cells retained the ability to secrete Th1-type cytokines in response to beryllium, they showed less proliferative capacity and were more susceptible to cell death compared with CD28+ T cells. In contrast to lung cells, inhibition of the CD28-B7 interaction markedly reduced responses of beryllium-specific T cells in blood. Taken together, these findings suggest transition within memory CD4+ T cells from CD28 dependence in central memory cells to functional independence and then loss of CD28 expression in effector cells.

Coevolution of markers of innate and adaptive immunity in skin and peripheral blood of patients with erythema migrans

We used multiparameter flow cytometry to characterize leukocyte immunophenotypes and cytokines in skin and peripheral blood of patients with erythema migrans (EM). Dermal leukocytes and cytokines were assessed in fluids aspirated from epidermal suction blisters raised over EM lesions and skin of uninfected controls. Compared with corresponding peripheral blood, EM infiltrates were enriched for T cells, monocytes/macrophages, and dendritic cells (DCs), contained lower proportions of neutrophils, and were virtually devoid of B cells. Enhanced expression of CD14 and HLA-DR by lesional neutrophils and macrophages indicated that these innate effector cells were highly activated. Staining for CD45RO and CD27 revealed that lesional T lymphocytes were predominantly Ag-experienced cells; furthermore, a subset of circulating T cells also appeared to be neosensitized. Lesional DC subsets, CD11c(+) (monocytoid) and CD11c(-) (plasmacytoid), expressed activation/maturation surface markers. Patients with multiple EM lesions had greater symptom scores and higher serum levels of IFN-alpha, TNF-alpha, and IL-2 than patients with solitary EM. IL-6 and IFN-gamma were the predominant cytokines in EM lesions; however, greater levels of both mediators were detected in blister fluids from patients with isolated EM. Circulating monocytes displayed significant increases in surface expression of Toll-like receptor (TLR)1 and TLR2, while CD11c(+) DCs showed increased expression of TLR2 and TLR4; lesional macrophages and CD11c(+) and CD11c(-) DCs exhibited increases in expression of all three TLRs. These results demonstrate that Borrelia burgdorferi triggers innate and adaptive responses during early Lyme disease and emphasize the interdependence of these two arms of the immune response in the efforts of the host to contain spirochetal infection.

The impact of highly active antiretroviral therapy by the oral route on the CD8 subset in monkeys infected chronically with SHIV 89.6P

The objective of this study was to assess the impact of highly active antiretroviral therapy (HAART) by an oral route on the peripheral blood CD8 subset in the monkeys infected persistently with a pathogenic strain, SHIV(89.6P). Two rhesus macaques were inoculated intravenously with SHIV(89.6P), then treated with the combination of AZT, 3TC and Lopinavir/Ritonavir (LPV/RTV) as recommended in humans by the oral route with confectionery continued for 28 days. In one of two chronically infected macaques, MM260, the viral load was maintained in the range of 10(4)-10(5) copies/ml before HAART. The plasma viral load and proviral DNA decreased dramatically during the treatment, and cessation of this therapy the viral load rebounded to the pre-treatment level but the proviral DNA rebound was delayed. The other monkey, MM242, had low viral loads (1.2x10(3)-<5x10(2) copies/ml) both before and after HAART. CD4(+) and CD8(+) T cell counts and proviral DNA level were not significantly changed after the treatment. The percentages of CD8(+)CD45RA(-)Ki67(+)cells increased during (MM260) or after (MM242) HAART and the subset was maintained at a high percentage until 18 weeks post HAART in MM242. These findings suggest that this primate model might serve an important role in testing the virological and immunological efficacy of novel therapeutic strategies combined with HAART.

A transgenic mouse model genetically tags all activated CD8 T cells

Identifying and characterizing Ag-specific CD8+ T cells are central to the study of immunological memory. Although powerful strategies such as MHC tetramers and peptide-induced cytokine production assays exist for identifying Ag-specific CD8+ T cells, alternate strategies that are not dependent upon a priori knowledge of the immunodominant and subdominant antigenic epitopes, as well as the MHC background of the animal are of obvious utility. In this study, we present a transgenic mouse model that uses Cre-loxP recombination to permanently mark all activated CD8+ T cells with beta-galactosidase. We used the lymphocytic choriomeningitis virus infection model to track the dynamics of the antiviral CD8+ T cell responses. We show that in this transgenic mouse model system, all of the antiviral effector and memory CD8+ T cells are contained within the beta-gal-marked CD8+ T cell population.

Ex vivo characterization of human CD8+ T subsets with distinct replicative history and partial effector functions

After antigenic challenge, naive T lymphocytes enter a program of proliferation and differentiation during the course of which they acquire effector functions and may ultimately become memory cells. In humans, the pathways of effector and memory T-cell differentiation remain poorly defined. Here we describe the properties of 2 CD8+ T-lymphocyte subsets, RA+CCR7-27+28+ and RA+CCR7-27+28-, in human peripheral blood. These cells display phenotypic and functional features that are intermediate between naive and effector T cells. Like naive T lymphocytes, both subsets show relatively long telomeres. However, unlike the naive population, these T cells exhibit reduced levels of T-cell receptor excision circles (TRECs), indicating they have undergone additional rounds of in vivo cell division. Furthermore, we show that they also share effector-type properties. At equivalent in vivo replicative history, the 2 subsets express high levels of Fas/CD95 and CD11a, as well as increasing levels of effector mediators such as granzyme B, perforin, interferon gamma, and tumor necrosis factor alpha. Both display partial ex vivo cytolytic activity and can be found among cytomegalovirus-specific cytolytic T cells. Taken together, our data point to the presence of T cells with intermediate effector-like functions and suggest that these subsets consist of T lymphocytes that are evolving toward a more differentiated effector or effector-memory stage.

T cell dynamics in HIV-1 infection

In the absence of antiretroviral treatment, HIV-1 establishes a chronic, progressive infection of the human immune system that invariably, over the course of years, leads to its destruction and fatal immunodeficiency. Paradoxically, while viral replication is extensive throughout the course of infection, deterioration of conventional measures of immunity is slow, including the characteristic loss of CD4(+) T cells that is thought to play a key role in the development of immunodeficiency. This conundrum suggests that CD4(+) T cell-directed viral cytopathicity alone cannot explain the course of disease. Indeed, recent advances now indicate that HIV-1 pathogenesis is likely to result from a complex interplay between the virus and the immune system, particularly the mechanisms responsible for T cell homeostasis and regeneration. We review these data and present a model of HIV-1 pathogenesis in which the protracted loss of CD4(+) T cells results from early viral destruction of selected memory T cell populations, followed by a combination of profound increases in overall memory T cell turnover, damage to the thymus and other lymphoid tissues, and physiological limitations in peripheral CD4(+) T cell renewal.

Differentiation of CD8+ T cells from tumor-invaded and tumor-free lymph nodes of melanoma patients: role of common gamma-chain cytokines

Differentiation of CD8(+) T cells at the tumor site toward effector and memory stages may represent a key step for the efficacy of antitumor response developing naturally or induced through immunotherapy. To address this issue, CD8(+) T lymphocytes from tumor-invaded (n = 142) and tumor-free (n = 42) lymph nodes removed from the same nodal basin of melanoma patients were analyzed for the expression of CCR7, CD45RA, perforin, and granzyme B. By hierarchical cluster analysis, CD8(+) T cells from all tumor-free lymph nodes and from 56% of the tumor-invaded lymph node samples fell in the same cluster, characterized mainly by CCR7(+) CD45RA(+/-) cytotoxic factor(-) cells. The remaining three clusters contained only samples from tumor-invaded lymph nodes and showed a progressive shift of the CD8(+) T cell population toward CCR7(-) CD45RA(-/+) perforin(+) granzyme B(+) differentiation stages. Distinct CD8(+) T cell maturation stages, as defined by CCR7 vs CD45RA and by functional assays, were identified even in melanoma- or viral Ag-specific T cells from invaded lymph nodes by HLA tetramer analysis. Culture for 7 days of CCR7(+) perforin(-) CD8(+) T cells from tumor-invaded lymph nodes with IL-2 or IL-15, but not IL-7, promoted, mainly in CCR7(+)CD45RA(-) cells, proliferation coupled to differentiation to the CCR7(-) perforin(+) stage and acquisition of melanoma Ag-specific effector functions. Taken together, these results indicate that CD8(+) T cells differentiated toward CCR7(-) cytotoxic factor(+) stages are present in tumor-invaded, but not in tumor-free, lymph nodes of a relevant fraction of melanoma patients and suggest that cytokines such as IL-2 and IL-15 may be exploited to promote Ag-independent maturation of anti-tumor CD8(+) T cells.

Quantitative studies of CD8+ T-cell responses during microbial infection

MHC class I tetramer staining, intracellular cytokine staining and ELISPOT assays have made it possible to quantify CD8(+) T-cell responses precisely during and following viral and bacterial infection. Although these quantitative methods are by now familiar and trusted components of the immunologist's toolbox, their application to models of microbial infection continues to provide surprising insights into mammalian adaptive immunity. In the past year there have been many exciting new findings on CD8(+) T-cell priming, expansion and memory formation in response to microbial infection.

Age-associated accumulation of CMV-specific CD8+ T cells expressing the inhibitory killer cell lectin-like receptor G1 (KLRG1)

Large clonal expansions of peripheral CD8+ T cells carrying receptors for single epitopes of CMV and EBV are common in the elderly and may be associated with an immune risk phenotype predicting mortality. Here we show that the frequency of CD8+ T cells expressing the inhibitory killer cell lectin-like receptor G1 (KLRG1), a marker of cells unable to undergo further clonal expansion, was markedly elevated in CD8+ T cells from old donors. Moreover, tetramer staining revealed that the elevated frequency of CMV-specific CD8+ T cells in the elderly was due to an accumulation of cells bearing this dominant negative receptor. The fraction of CMV-specific T cells able to secrete interferon-gamma after specific antigenic stimulation was significantly lower in the elderly than in the young, although the total number of functional cells was comparable. Therefore, the majority of the clonally expanded virus-specific CD8+ cells in the elderly was dysfunctional. Thus, T cell responses are altered in the aged by an accumulation of replicatively senescent dysfunctional T cells carrying receptors for persistent herpes viruses. The presence of clonal expansions of such virus-specific cells may shrink the available repertoire for other antigens and contribute to the increased incidence of infectious disease in the elderly.

Expansion of CMV-specific CD8+CD45RA+CD27- T cells in B-cell chronic lymphocytic leukemia

In patients with B-cell chronic lymphocytic leukemia (B-CLL), the absolute number of T cells is increased. Although it has been suggested that these T cells might be tumor specific, concrete evidence for this hypothesis is lacking. We performed a detailed immunophenotypic analysis of the T-cell compartment in the peripheral blood of 28 patients with B-CLL (Rai 0, n = 12; Rai I-II, n = 10; Rai III-IV, n = 6) and 12 healthy age-matched controls and measured the ability of these patients to mount specific immune responses. In all Rai stages a significant increase in the absolute numbers of CD3+ cells was observed. Whereas the number of CD4+ cells was not different from controls, patients with B-CLL showed significantly increased relative and absolute numbers of CD8+ cells, which exhibited a CD45RA+CD27- cytotoxic phenotype. Analysis of specific immune responses with tetrameric cytomegalovirus (CMV)-peptide complexes showed that patients with B-CLL had significantly increased numbers of tetramer-binding CMV-specific CD8+ T cells. The rise in the total number of CD8+ cytotoxic T cells was evident only in CMV-seropositive B-CLL patients. Thus, our data suggest that in patients with B-CLL the composition of T cells is shifted toward a CD8+ cytotoxic cell type in an effort to control infections with persistent viruses such as CMV. Moreover, they offer an explanation for the high incidence of CMV reactivation in CLL patients treated with T cell-depleting agents, such as the monoclonal antibody (mAb) alemtuzumab (Campath; alpha-CD52 mAb). Furthermore, because in CMV-seronegative patients no increase in cytotoxic CD8+ T cells is found, our studies do not support the hypothesis that tumor-specific T cells account for T-cell expansion in B-CLL.

Hepatitis C virus infection: when silence is deception

Hepatitis C virus (HCV) uses complex and unique mechanisms to prevent, evade or subvert innate and adaptive immune responses and to establish persistent infection and chronic hepatitis. Recently developed experimental systems have significantly facilitated the analysis of HCV replication, virus-host interaction and pathogenesis of chronic hepatitis and have provided new insights into the mechanisms of HCV clearance and persistence.

Mature CD8(+) T lymphocyte response to viral infection during fetal life

Immunization of newborns against viral infections may be hampered by ineffective CD8(+) T cell responses. To characterize the function of CD8(+) T lymphocytes in early life, we studied newborns with congenital human cytomegalovirus (HCMV) infection. We demonstrate that HCMV infection in utero leads to the expansion and the differentiation of mature HCMV-specific CD8(+) T cells, which have similar characteristics to those detected in adults. High frequencies of HCMV-specific CD8(+) T cells were detected by ex vivo tetramer staining as early as after 28 weeks of gestation. During the acute phase of infection, these cells had an early differentiation phenotype (CD28(-)CD27(+)CD45RO(+), perforin(low)), and they acquired a late differentiation phenotype (CD28(-)CD27(-)CD45RA(+), perforin(high)) during the course of the infection. The differentiated cells showed potent perforin-dependent cytolytic activity and produced antiviral cytokines. The finding of a mature and functional CD8(+) T cell response to HCMV suggests that the machinery required to prime such responses is in place during fetal life and could be used to immunize newborns against viral pathogens.

Original antigenic sin and apoptosis in the pathogenesis of dengue hemorrhagic fever

Dengue virus presents a growing threat to public health in the developing world. Four major serotypes of dengue virus have been characterized, and epidemiological evidence shows that dengue hemorrhagic fever (DHF), the more serious manifestation of the disease, occurs more frequently upon reinfection with a second serotype. We have studied dengue virus-specific T-cell responses in Thai children. During acute infection, few dengue-responsive CD8+ T cells were recovered; most of those present showed an activated phenotype and were undergoing programmed cell death. Many dengue-specific T cells were of low affinity for the infecting virus and showed higher affinity for other, probably previously encountered strains. Profound T-cell activation and death may contribute to the systemic disturbances leading to DHF, and original antigenic sin in the T-cell responses may suppress or delay viral elimination, leading to higher viral loads and increased immunopathology.

Characterizing the immune system after long-term undetectable viral load in HIV-1-infected children

Thirty two HIV-infected children, on highly active antiretroviral therapy (HAART) and > 500 CD4+ T cells/mm3, were rated according to the time-course of viral load (VL) during the whole follow-up period (> 18 months) in a longitudinal retrospective study. (a) uVL group: 15 children with VL below 400 copies/mL; (b) dVL group: 17 children with higher VL. The uVL group showed higher memory (CD4+CD45RO+) T cells than did dVL group, and higher number of memory activated CD4+CD45RO+HLA-DR+ than did control group (healthy age-matched uninfected children), whereas CD4+CD45RA(hi)+CD62L+ was similar. However, TCR rearrangement excision circles (TRECs) were higher in uVL group than in dVL group. uVL Group showed CD8+CD45RO+ and CD8+CD45RO+CD38- higher number than the control group, but lower than the dVL group. The percentage of CD8+CD45RA(hi)+CD62L+, CD8+CD45RA+, CD8+CD62L-, and CD8+CD28+ was higher in uVL group than in dVL group, and lower than in control group. The uVL group showed higher number of activated (HLA-DR+CD38+, HLA-DR+, HLA-DR+CD38-) CD4+ T cells and lower percentages of CD4+HLA-DR-CD38+ than dVL group. In activated CD8- T cell, the uVL group had lower CD8+HLA-DR+CD38+, CD8+HLA-DR+, and CD8+CD38+ than the dVL group. Preeffector (CD8+CD57-CD28- and CD8+CD45RA-CD62L-) T cells were lower in the uVL group than in dVL group. In the effector (CD8+CD57+, CD8+CD57+CD28-, and CD8+CD45RA+CD62L-) T cells, HIV-infected-children had higher values than control group. HIV-infected-children who respond to HAART had TRECs reconstitution, decreased immune activation, and lower effector CD8+ T cells. Moreover, successful HAART allow the increment of activated CD4+ T cells.

Immunopathogenesis and immunotherapy in AIDS virus infections

The heterogeneity of HIV and the different human leukocyte antigen (HLA) backgrounds of infected individuals have posed challenges to understanding the pathogenesis of HIV infection. But continuing advances in our knowledge of the role of immune responses in controlling HIV viremia should help to define goals for immune-based therapies and vaccine strategies against AIDS.

Differences in CCR5 expression on peripheral blood CD4+CD28- T-cells and in granulomatous lesions between localized and generalized Wegener's granulomatosis

Wegener's granulomatosis (WG) is an autoimmune disease characterized by granulomatous lesions and a necrotizing vasculitis. Th1-type-cells lacking CD28 are expanded independent of age and immunosuppressive therapy in WG. To address their migratory properties of CD4(+)CD28(-) T-cells we studied the expression of the inducible inflammatory Th1-type chemokine receptor CCR5 in localized WG and generalized WG. Expansion of CD4(+)CD28(-) T-cells was more prominent in generalized WG compared to localized WG. In localized WG a larger fraction of CD4(+)CD28(-) T-cells displayed CCR5 expression compared to generalized WG. CCR5 expression was also higher in granulomatous lesions in localized WG. Higher levels of CCR5 expression on CD4(+)CD28(-) T-cells in localized WG may favor stronger CCR5-mediated recruitment of this T-cell subset into granulomatous lesions in localized WG. Expansion of Th-1-type CD4(+)CD28(-)CCR5(+) effector memory T-cells might contribute to disease progression and autoreactivity, either directly, by maintaining the inflammatory response, or as a result of bystander activation.

Alterations in the phenotype of CMV-specific and total CD8+ T-cell populations in Wegener’s granulomatosis

Wegener's granulomatosis (WG) is an autoimmune disease of as yet unknown etiology. To date it has remained obscure what causes WG or determines disease progression. Case reports suggest that viral infections such as cytomegalovirus (CMV) reactivation may contribute to disease flares. In this study we found a skewing of the phenotype of CMV-specific CD8+tet(ramer)+ T-cells in WG. A marked proportion of these cells displayed a late differentiated "effector memory" T-cell phenotype with decreased expression of CD28 and CD62L, and heterogeneous CD27 expression, features which were also seen in CD8+tet- T-cells in WG, but not in controls. Our results might reflect profound generalized changes in the CD8+ T-cell compartment also affecting virus-specific T-cell responses in WG.

Cytokine profiles in adult mink infected with Aleutian mink disease parvovirus

The aim of this study was to examine the levels of gamma interferon (IFN-gamma)-, interleukin 4 (IL-4)-, and IL-8-producing cells in peripheral blood mononuclear cells from mink infected with the Aleutian mink disease parvovirus (ADV). As expected, ADV-infected mink developed high plasma gamma globulin values (hypergammaglobulinemia) and enhanced quantities of CD8-positive (CD8(+)) cells in the blood during the infection. We quantified the percentages of IFN-gamma- and IL-4-positive lymphocytes and IL-8-positive monocytes up to week 38 after virus challenge. The results clearly indicated marked increases in the percentages of IFN-gamma- and IL-4-producing lymphocytes during ADV infection. The total number of IL-8-producing monocytes in the blood of ADV-infected mink stayed fairly constant during the infection. In order to characterize the phenotype of the cytokine-producing cells, we performed double-labeling fluorescence-activated cell sorter (FACS) experiments with CD8 surface labeling in one channel and cytokine intracellular staining in the other. We found that most IFN-gamma and IL-4 in ADV-infected mink was produced by CD8(+) cells, while in the uninfected mink, these cytokines were primarily produced by a cell type that was not CD8 (possibly CD4-positive cells). We also observed that IL-8 was almost exclusively produced by monocytes. All of the above findings led us to conclude that both Th1- and Th2-driven immune functions are found in mink plasmacytosis.

The chemokine receptor CX3CR1 controls homing and anti-viral potencies of CD8 effector-memory T lymphocytes in HIV-infected patients

OBJECTIVES

We have recently reported that the polymorphism of the fractalkine receptor, CX3CR1, provides a new marker for prognosis in HIV disease. In order to understand the mechanism by which CX3CR1 participates in the regulation of HIV-immune responses, we investigated its expression and role on T lymphocytes in HIV-infected patients.

DESIGN

For that purpose, we analysed the expression of CX3CR1 on CD4 and CD8 effector-memory subsets in HIV-positive individuals by flow cytometric analyses, and studied its potential role in the migration and function of CD8 effector cells.

RESULTS

We observed an increased frequency of CD8 cells expressing CX3CR1 that was correlated with disease progression in HIV-infected patients compared with normal individuals. CX3CR1+ was expressed mainly on activated and differentiated CCR7-CD45RA-negative memory lymphocytes. Interestingly, CX3CR1 appeared as the main homing receptor of these cells that have downmodulated most other chemokine receptors. The CD8+CX3CR1+ lymphocytes were engaged in the cytotoxic lineage (perforin+, CD27-negative and CD57+). Ex-vivo analysis showed that CX3C ligand-1 inhibits IFNgamma production in response to T cell receptor engagement.

CONCLUSION

CX3CR1 and its ligand could contribute to the specific migratory pattern of late-stage differentiated CD8 cells and participate in the regulation of effector function of CD8 lymphocytes during HIV infection.

Mature CD8(+) T lymphocyte response to viral infection during fetal life

Immunization of newborns against viral infections may be hampered by ineffective CD8(+) T cell responses. To characterize the function of CD8(+) T lymphocytes in early life, we studied newborns with congenital human cytomegalovirus (HCMV) infection. We demonstrate that HCMV infection in utero leads to the expansion and the differentiation of mature HCMV-specific CD8(+) T cells, which have similar characteristics to those detected in adults. High frequencies of HCMV-specific CD8(+) T cells were detected by ex vivo tetramer staining as early as after 28 weeks of gestation. During the acute phase of infection, these cells had an early differentiation phenotype (CD28(-)CD27(+)CD45RO(+), perforin(low)), and they acquired a late differentiation phenotype (CD28(-)CD27(-)CD45RA(+), perforin(high)) during the course of the infection. The differentiated cells showed potent perforin-dependent cytolytic activity and produced antiviral cytokines. The finding of a mature and functional CD8(+) T cell response to HCMV suggests that the machinery required to prime such responses is in place during fetal life and could be used to immunize newborns against viral pathogens.

Proliferation and differentiation potential of human CD8+ memory T-cell subsets in response to antigen or homeostatic cytokines

Four human CD8+ T-cell subsets, naive (CCR7+CD45RA+), central memory (TCM, CCR7+CD45RA-), effector memory (TEM, CCR7-CD45RA-), and CD45RA+ effector memory cells (TEMRA, CCR7-CD45RA+) were compared for their capacity to proliferate and differentiate in response to antigen or homeostatic cytokines. Cytokine responsiveness and interleukin-15 receptor expression were low in naive T cells and progressively increased from TCM to TEM and TEMRA. In contrast, the capacity to accumulate in response to T-cell receptor (TCR) or cytokine stimulation showed a reciprocal pattern and was associated with resistance to cell death and Bcl-2 expression. Whereas all TCR-stimulated cells acquired a CD45RA-CCR7- phenotype, cytokine-stimulated cells maintained their phenotype with the exception of TCM cells, which expressed CCR7, CD45RA, and perforin in various combinations. Single CD8+ TCM cells, but not TEM cells, could be expanded with cytokines, and the obtained clones displayed several distinct phenotypes, suggesting that TCM cells are heterogeneous. Consistently, CCR4 expression in the CD8+ TCM pool discriminated CCR4+ type 2 polarized cells (Tc2) and CCR4-CTL precursors. Finally, ex vivo bromodeoxyuridine (BrdU) incorporation experiments revealed that memory subsets have different in vivo proliferation rates, with CCR4-TCM having the highest turnover and TEMRA the lowest. These results show that human CD8+ memory T-cell subsets have different proliferation and differentiation potentials in vitro and in vivo. Furthermore, they suggest that TEMRA cells are generated from a TCM subset upon homeostatic proliferation in the absence of antigen.

CD8+ T-cell interaction with HCV replicon cells: evidence for both cytokine- and cell-mediated antiviral activity

The interaction between the host immune response and infected hepatocytes plays a central role in the pathogenesis of hepatitis C virus (HCV). The lack of a suitable animal or in vitro model has hindered our understanding of the host T-cell/HCV interaction. Our aim was to develop an in vitro model to study the mechanisms of HCV-specific T-cell-mediated antiviral and cytolytic function. The HCV replicon was HLA typed and lymphocytes were obtained from an HLA class I-matched subject. CD8(+) T cells were expanded with 2 HCV-specific/HLA-restricted peptides for NS3. Lymphocyte preparations were cocultured with HCV replicon (FCA1) and control (Huh7) cells labeled with (51)Cr. After a 48-hour incubation, the cells were harvested for RNA extraction. Standard blocking assays were performed in the presence of anti-interferon gamma (IFN-gamma), anti-tumor necrosis factor alpha (TNF-alpha), and anti-FasL. Cytolytic activity was measured by (51)Cr release. HCV replicon cells express homozygous HLA-A11 alleles and present HCV nonstructural proteins. HCV-specific expansion of CD8(+) cells led to a 10-fold decrease in HCV replication by Northern blot analysis and 21% specific lysis of FCA1 cells (compared with 2% of control Huh7 cells). Twenty percent of this antiviral activity was independent of T-cell binding, suggesting cytokine-mediated antiviral activity. The CD8(+) antiviral effect was markedly reduced by blocking either IFN-gamma or FasL but was unaffected by blocking TNF-alpha. In conclusion, HCV-specific CD8(+) cells inhibit viral RNA replication by cytokine-mediated and direct cytolytic effects. This T-cell/HCV subgenomic replicon system represents a model for the investigation of CD8 cell interaction with HCV-infected hepatocytes.

Soluble HIV-specific T cell receptor: expression, purification and analysis of the specificity

We have produced soluble T cell receptor (TCR) derived from a human CD8(+) cytotoxic T lymphocyte (CTL) clone D3 that recognizes the immunodominant HIV Gag peptide SLYNTVATL (SL9) in association with major histocompatibility complex (MHC) class I protein HLA-A2. Drosophila Schneider cells (S2) were used to express genes coding the TCR alpha and beta chains under an inducible promoter. Both chains were labeled with two different tags: a (His)(6) was introduced at the C-terminal end of alpha chain, while beta chain was terminated by c-myc. Since an isolated alpha chain is unstable unless it is associated with a beta chain, this design permits rapid separation of alpha,beta-heterodimer from unpaired beta chain in a single step of Ni-NTA Agarose chromatography yielding 90% pure alpha,beta-TCR. Introduction of the c-myc epitope to the beta chain allows capture of soluble D3 from the culture supernatant by immobilized anti-c-myc antibody, without the need for receptor purification. The TCR specificity was then examined by analyzing the binding of peptide-HLA-A2/tetramer in an ELISA assay. Using this assay, we have also evaluated the binding of monomeric SL9-HLA-A2 complex to the immobilized D3 TCR and determined that the affinity measurement of the D3-SL9-HLA-A2 reaction is similar to that obtained by a biosensor instrument. We propose that the approach described here is generally useful for purification of other soluble TCRs and will allow rapid analysis of their specificity.

The dynamics of T-cell fratricide: application of a robust approach to mathematical modelling in immunology

Fratricide between CD8(+) T lymphocytes is known to occur in HTLV-I and possibly HSV-1 and HIV-1 infection. However it is not known what effect, if any, T-cell fratricide has on the course of infection. Here we present simple mathematical techniques to investigate T-cell fratricide with particular reference to HTLV-I infection. Using a general model we predict the qualitative and quantitative effect of fratricide on HTLV-I equilibrium proviral load. We also investigate the effect of fratricide on the probability of viral clearance. We show that, surprisingly, fratricide can lead either to an increase or a decrease in equilibrium proviral load. We derive the conditions necessary for fratricide to cause a decrease in load and deduce that, for the five HTLV-I-positive patients considered here, fratricide has probably caused an increase in equilibrium load. We also estimate the percentage increase in load that is attributable to fratricide and determine the parameters that should be measured in order to improve this estimate. Finally, we show that fratricide reduces the probability of viral clearance. Mathematical modelling of HTLV-I infection, as is often the case in biology, is severely hampered by a lack of experimental data. Consequently it is difficult to know what functional form a model should take. The behaviour of complex nonlinear systems is highly model-dependent. Predictions based on theoretical models are therefore sensitive to the choice of model; this is a very severe problem that undermines and limits the success of the application of mathematics to immunology. In this paper we reduce the model dependency of the results in two ways-by considering (analytically) a general model with a minimal number of assumptions and, where this is not possible, by checking (numerically) that a wide range of models yield the same results. We therefore begin to develop two practical methods for dealing with the problem of robustness in mathematical models of the immune system.

Cellular and humoral immune reconstitution after autologous peripheral blood stem cell transplantation (PBSCT)

Immune reconstitution after autologous peripheral blood stem cell transplantation (PBSCT) is of particular interest because of its importance for clinical outcome. Despite prolonged immunosuppression, especially of CD4(+) cells, few infections after neutrophil recovery occur. Only reactivation of varicella zoster virus (VZV) is more frequent in the first year after transplantation. From August 1997 to May 2001, we prospectively evaluated 38 patients prior to conditioning and during follow-up of 12 months post-transplant for virus antibodies [measles, mumps, rubella, polio, herpes simplex, varicella zoster, mononucleosis, cytomegalovirus (CMV)] and lymphocyte subpopulations by flow cytometry. CD3(+) T lymphocytes, CD8(+) T cells, and B-lymphocyte reconstitution in our study confirms previous reports. Complete CD4(+) lymphocyte reconstitution was not achieved in the 12 months post-transplant leading to a suppressed CD4/CD8 ratio. IgG antibody titers against measles, mumps, rubella, and polio were present in almost all patients pretransplant and during 12 months post-transplant, indicating persistent humoral immunity. CD3(+) and CD8(+) counts of patients with clinical VZV reactivation ( n=5) post-transplant were significantly higher (median: 1201/microl and 938/microl, respectively) than in patients without VZV reactivation (median: 594/microl and 482/microl, respectively) 6-12 months post-transplant. Positive CMV titers pretransplant ( n=19) were also correlated with higher CD3(+) and CD8(+) counts 3-6 months post-transplant (median: 1050/microl and 1056/microl, respectively) compared to CMV-negative patients (738/microl and 584/microl, respectively), although none of the patients suffered from CMV disease. Therefore, we conclude that persistent viral infections can contribute to the CD8(+) T-cell reconstitution after PBSCT by oligoclonal expansion of antigen-specific memory CD8(+) T cells.

Apoptosis as an HIV strategy to escape immune attack

Viruses have evolved numerous mechanisms to evade the host immune system and one of the strategies developed by HIV is to activate apoptotic programmes that destroy immune effectors. Not only does the HIV genome encode pro-apoptotic proteins, which kill both infected and uninfected lymphocytes through either members of the tumour-necrosis factor family or the mitochondrial pathway, but it also creates a state of chronic immune activation that is responsible for the exacerbation of physiological mechanisms of clonal deletion. This review discusses the molecular mechanisms by which HIV manipulates the apoptotic machinery to its advantage, assesses the functional consequences of this process and evaluates how new therapeutics might counteract this strategy.

Interleukin-10 induces the upregulation of the inhibitory receptor ILT4 in monocytes from HIV positive individuals

A characteristic of human immunodeficiency virus infected individuals is an impairment of immune responses, which can result in opportunistic infections. Elevated levels of interleukin-10 (IL-10), produced by virally infected monocytes, are found in the sera of HIV infected individuals. Such elevated levels have been associated with the impaired function of CD4(+) and CD8(+) T cells, and antigen presenting cells (APC), such as monocytes. IL-10 has been reported to upregulate the cell surface expression of the inhibitory receptors ILT3 and ILT4 on monocytes and dendritic cells. This study demonstrates that the decreased antigen presenting ability of monocytes in HIV(+) individuals is in part due to the upregulation of ILT4 on the monocytes caused by the elevated serum IL-10 levels seen in these individuals.

Adoptive immunotherapy: engineering T cell responses as biologic weapons for tumor mass destruction

Adoptive T cell immunotherapy is an evolving technology with the potential of providing a means to safely and effectively target tumor cells for destruction.

Frequencies of circulating cytolytic, CD45RA+CD27-, CD8+ T lymphocytes depend on infection with CMV

Viral infections may cause serious disease unless the adaptive immune system is able to clear the viral agents through its effector arms. Recent identification and functional characterization of subpopulations of human CD8(+) T cells has set the stage to study the correlation between the appearance of particular subsets and common viral infections during childhood, i.e., EBV, CMV, varicella-zoster virus (VZV), and the attenuated measles-mumps-rubella (MMR) vaccine strains. In a cohort of 220 healthy children we analyzed lymphocytes and subpopulations of CD4(+) and CD8(+) T cells. The presence of the cytolytic CD45RA(+)CD27(-) subset of CD8(+) T cells correlated with prior CMV infection as defined by seroconversion (p < 0.0001). The number of this CD8(+) T cell subset remained stable during follow-up over 3 years in 40 children. The CD45RA(+)CD27(-) subset of CD8(+) T cells first appeared during acute CMV infection and subsequently stabilized at an individual set-point defined by age and immunocompetence. The functional importance of these cells in CMV surveillance was reflected by their increased numbers in immunosuppressed pediatric kidney transplant patients. Preferential expansion of CD8(+)CD45RA(+)CD27(-) cytolytic T cells seems unique for CMV.

Detection of virus-specific T cells and CD8+ T-cell epitopes by acquisition of peptide-HLA-GFP complexes: analysis of T-cell phenotype and function in chronic viral infections

Antigen-specific CD8+ T cells acquire peptide-major histocompatibility complex (MHC) clusters through T-cell receptor (TCR)-mediated endocytosis after specific antigen stimulation. We generated an antigen-presenting cell (APC) expressing human leukocyte antigen (HLA)-A*201 coupled to the enhanced green fluorescent protein (GFP), which delivered GFP to an antigen-specific T cell when pulsed with antigenic peptide. We quantitatively identified human T-cell lymphotropic virus type I (HTLV-I) Tax(11-19) peptide-specific T-cell populations in peripheral blood mononuclear cells (PBMCs) from patients with HTLV-I-associated neurologic disease and defined a new CD8+ T-cell epitope in the HTLV-I envelope region. Acquisition of peptide-HLA-GFP complexes by antigen-specific T cells could distinguish, with respect to phenotype and perforin production, T cells from the chronic viral infections cytomegalovirus and HTLV-I. This approach will be a powerful tool in understanding the role of antigen-specific T-cell responses in health and disease.

Primary immune responses to human CMV: a critical role for IFN-gamma-producing CD4+ T cells in protection against CMV disease

The correlates of protective immunity to disease-inducing viruses in humans remain to be elucidated. We determined the kinetics and characteristics of cytomegalovirus (CMV)-specific CD4(+) and CD8(+) T cells in the course of primary CMV infection in asymptomatic and symptomatic recipients of renal transplants. Specific CD8(+) cytotoxic T lymphocyte (CTL) and antibody responses developed regardless of clinical signs. CD45RA(-)CD27(+)CCR7(-) CTLs, although classified as immature effector cells in HIV infection, were the predominant CD8 effector population in the acute phase of protective immune reactions to CMV and were functionally competent. Whereas in asymptomatic individuals the CMV-specific CD4(+) T-cell response preceded CMV-specific CD8(+) T-cell responses, in symptomatic individuals the CMV-specific effector-memory CD4(+) T-cell response was delayed and only detectable after antiviral therapy. The appearance of disease symptoms in these patients suggests that functional CD8(+) T-cell and antibody responses are insufficient to control viral replication and that formation of effector-memory CD4(+) T cells is necessary for recovery of infection.

Viral persistence alters CD8 T-cell immunodominance and tissue distribution and results in distinct stages of functional impairment

Chronic viral infections often result in ineffective CD8 T-cell responses due to functional exhaustion or physical deletion of virus-specific T cells. However, how persisting virus impacts various CD8 T-cell effector functions and influences other aspects of CD8 T-cell dynamics, such as immunodominance and tissue distribution, remains largely unknown. Using different strains of lymphocytic choriomeningitis virus (LCMV), we compared responses to the same CD8 T-cell epitopes during acute or chronic infection. Persistent infection led to a disruption of the normal immunodominance hierarchy of CD8 T-cell responses seen following acute infection and dramatically altered the tissue distribution of LCMV-specific CD8 T cells in lymphoid and nonlymphoid tissues. Most importantly, CD8 T-cell functional impairment occurred in a hierarchical fashion in chronically infected mice. Production of interleukin 2 and the ability to lyse target cells in vitro were the first functions compromised, followed by the ability to make tumor necrosis factor alpha, while gamma interferon production was most resistant to functional exhaustion. Antigen appeared to be the driving force for this loss of function, since a strong correlation existed between the viral load and the level of exhaustion. Further, epitopes presented at higher levels in vivo resulted in physical deletion, while those presented at lower levels induced functional exhaustion. A model is proposed in which antigen levels drive the hierarchical loss of different CD8 T-cell effector functions during chronic infection, leading to distinct stages of functional impairment and eventually to physical deletion of virus-specific T cells. These results have implications for the study of human chronic infections, where similar T-cell deletion and functional dysregulation has been observed.

CD7 is a differentiation marker that identifies multiple CD8 T cell effector subsets

The adaptive immune response of human CD8 T cells to invading pathogens involves the differentiation of naive cells into memory and effector cells. However, the lineage relationship between memory and effector cells and the differentiation of CD8 T cells into distinct subsets of effector cell subpopulations are subjects of considerable debate. CD7 identifies three populations of CD8 T cells: CD7 high (CD7(high)), low (CD7(low)), and negative (CD7(neg)) that translate into subsets with distinct functional properties. The CD7(high) subset contains naive and memory cells and the CD7(low) and CD7(neg) subsets contain effector cells. The effector cells can functionally be divided into cytokine-secreting effector CD8 T cells and lytic effector CD8 T cells. These data provide a model of human CD8 T cell differentiation in which specialized distinct subpopulations can be identified by expression of CD7.

Lineage relationship and protective immunity of memory CD8 T cell subsets

Memory CD8 T cells can be divided into two subsets, central (T(CM)) and effector (T(EM)), but their lineage relationships and their ability to persist and confer protective immunity are not well understood. Our results show that T(CM) have a greater capacity than T(EM) to persist in vivo and are more efficient in mediating protective immunity because of their increased proliferative potential. We also demonstrate that, following antigen clearance, T(EM) convert to T(CM) and that the duration of this differentiation is programmed within the first week after immunization. We propose that T(CM) and T(EM) do not necessarily represent distinct subsets, but are part of a continuum in a linear naive --> effector --> T(EM) --> T(CM) differentiation pathway.

Memory T-cell competition for bone marrow seeding

The presence in the bone marrow of memory CD8 T cells is well recognized. However, it is still largely unclear how T-cell migration from the lymphoid periphery to the bone marrow is regulated. In the present report, we show that antigen-specific CD4 T cells, as well as antigen-specific CD8 T cells, localize to the bone marrow of immunized mice, and are sustained there over long periods of time. To investigate the rules governing T-cell migration to the bone marrow, we generated chimeric mice in which the lymphoid periphery contained two genetically or phenotypically distinct groups of T cells, one of which was identical to the host. We then examined whether a distinct type of T cell had an advantage over the others in the colonization of bone marrow. Our results show that whereas ICAM1 and CD18 molecules are both involved in homing to lymph nodes, neither is crucial for T-cell bone marrow colonization. We also observed that memory-phenotype CD44high T cells, but not virgin-type CD44-/low T cells, preferentially home to the bone marrow upon adoptive transfer to normal young mice, but not to thymectomized old recipients where an existing memory T-cell pool precludes their free access. Thus, T-cell colonization of the bone marrow uses distinct molecules from those implicated in lymph node homing, and is regulated both by the properties of the T cell and by the competitive efficacy of other T cells inhabiting the same, saturable niche. This implies that the homing potential of an individual lymphocyte is not merely an intrinsic property of the cell, but rather a property of the lymphoid system taken as a whole.

Memory inflation: continuous accumulation of antiviral CD8+ T cells over time

CD8+ T lymphocytes play an important role in the control of intracellular pathogens during both acute and persistent infections. This is particularly true in the case of persistent herpesviruses such as human CMV, which are typified by large virus-specific CD8+ T cell populations during viral latency. To understand the origin of these populations and the factors shaping them over time, we investigated the CD8+ T cell response after murine CMV (MCMV) infection. The kinetics of the acute response were characterized by rapid expansion of activated T cells, followed by a contraction phase. Thereafter, we observed a striking pattern, where MCMV-specific memory CD8+ T cells steadily accumulated over time, with 20% of all CD8+ T cells at 1 year specific for one MCMV epitope. Accumulation of MCMV-specific CD8+ T lymphocytes was seen in all organs tested and was associated with continuous activation of specific CD8+ T lymphocytes, primarily within lymph nodes. The pattern of accumulation was observed in only two of five epitopes tested, and was accompanied by a gradual restriction in usage of the variable region of the TCR beta-chain over time. This novel pattern of a virus-specific CD8+ T cell response suggests that continuous or repetitive exposure to Ag can slowly mold memory T cell populations over time. This may be relevant for understanding the evolution of the large human CMV-specific CD8+ T cell populations seen in humans.

Comprehensive epitope analysis of human immunodeficiency virus type 1 (HIV-1)-specific T-cell responses directed against the entire expressed HIV-1 genome demonstrate broadly directed responses, but no correlation to viral load

Cellular immune responses play a critical role in the control of human immunodeficiency virus type 1 (HIV-1); however, the breadth of these responses at the single-epitope level has not been comprehensively assessed. We therefore screened peripheral blood mononuclear cells (PBMC) from 57 individuals at different stages of HIV-1 infection for virus-specific T-cell responses using a matrix of 504 overlapping peptides spanning all expressed HIV-1 proteins in a gamma interferon-enzyme-linked immunospot (Elispot) assay. HIV-1-specific T-cell responses were detectable in all study subjects, with a median of 14 individual epitopic regions targeted per person (range, 2 to 42), and all 14 HIV-1 protein subunits were recognized. HIV-1 p24-Gag and Nef contained the highest epitope density and were also the most frequently recognized HIV-1 proteins. The total magnitude of the HIV-1-specific response ranged from 280 to 25,860 spot-forming cells (SFC)/10(6) PBMC (median, 4,245) among all study participants. However, the number of epitopic regions targeted, the protein subunits recognized, and the total magnitude of HIV-1-specific responses varied significantly among the tested individuals, with the strongest and broadest responses detectable in individuals with untreated chronic HIV-1 infection. Neither the breadth nor the magnitude of the total HIV-1-specific CD8+-T-cell responses correlated with plasma viral load. We conclude that a peptide matrix-based Elispot assay allows for rapid, sensitive, specific, and efficient assessment of cellular immune responses directed against the entire expressed HIV-1 genome. These data also suggest that the impact of T-cell responses on control of viral replication cannot be explained by the mere quantification of the magnitude and breadth of the CD8+-T-cell response, even if a comprehensive pan-genome screening approach is applied.

Pathways to a robust immune response in the elderly

Circumstantial evidence suggests that infectious disease is the major cause of morbidity and mortality in the elderly, and immune-system dysfunction may contribute to this finding. Because innate and humoral immunity seem to be relatively unaffected by aging and because the T-cell compartment shows marked age-associated alterations, this article focuses on the association between T cells and aging. Longitudinal studies suggest that immune parameters, which predominantly are related to T cells, can be clustered to yield an IRP that is predictive of mortality in the elderly. Determining the IRP also may be helpful in younger individuals, particularly those under chronic antigenic stress (eg, patients with cancer or chronic infections) who experience premature aging of the immune system. Some changes in T cells can be modeled in clonal cultures in vitro to discover new biomarkers of immune aging. These biomarkers, which need to be validated in vivo, could be used to refine IRP. Interventions to selectively target changes that are identified as part of IRP may improve the health and quality of life of the elderly, reduce healthcare costs, and avoid potential unwanted side effects of global intervention approaches, such as triggering or exacerbating autoimmunity and inflammation.

Viral escape and T cell exhaustion in hepatitis C virus infection analysed using Class I peptide tetramers

Hepatitis C virus (HCV) has infected over 170 million people world wide, and in the majority sets up a chronic infection associated with hepatic inflammation. How it evades host immunity, particularly CD8+ T cells (CTL) is unclear, but two major factors are likely to operate, viral escape mutation and T cell exhaustion. We have investigated the role of CTL in control of infection during acute disease using Class I peptide tetramers. Although the immune response is quite diverse and numerous epitopes can be targeted, we observe that, especially during acute disease, one epitope (NS3 1073-81) is commonly recognised in HLA-A2 positive individuals. However, the levels of response to this epitope (and others) are very much lower if persistence is established. We examined in detail whether the cause of this low level of reactivity is due to mutation within the epitope. We find that, in fact this epitope is highly conserved during chronic infection, at a clonal level, between individuals, and over time. Thus, although variation within the epitope does occur, lack of reactivity in peripheral blood against this epitope in chronic disease, and loss of control of virus cannot be explained entirely by viral escape. Escape through mutation probably does play an important role in persistence of HCV, but we also discuss other mechanisms which lead to attenuation of T cell responses which may be important in determining the outcome.

Definition of the HLA-A2 restricted peptides recognized by human CD8+ effector T cells by flow-assisted sorting of the CD8+ CD45RA+ CD28- T cell subpopulation

In response to antigenic stimulation, naive MHC-class I restricted and antigen-specific CD8+ CD45RA+ CD28+ T cells undergo clonal expansion, differentiate into CD8+ CD45RO+ memory T cells and convert to CD8+ CD45RA+ CD28- T cells displaying potent immune effector functions upon re-encounter with the nominal antigen. We show that the effector CD8+ CD45RA+ CD28- T cell subset is expanded in peripheral blood lymphocytes (PBL) from patients with human papilloma virus (HPV)+ cervical lesions as well as in PBL from patients with pulmonary tuberculosis. Flow-cytometric cell sorted CD8+ CD45RA+ CD28- and CD8+ CD45RA+ CD28- T cells were tested for recognition of HLA-A2 restricted peptides derived either from the human papillomavirus (HPV)16-E7 gene product, or from M. tuberculosis antigens. Mostly CD8+ CD45+ CD28- T cells define antigen/peptide-specific and MHC-restricted responses. These data were confirmed in PBL from patients with tuberculosis using HLA-A2 tetramer-complexes loaded with a peptide from the M. tuberculosis Ag85b antigen by flow cytometry. The sorting of this T cell subset enables to determine the fine specificity of CD8+ effector T cells without the need for in vitro manipulation.

IL-4-producing CD8+ T cells with a CD62L++(bright) phenotype accumulate in a subgroup of older adults and are associated with the maintenance of intact humoral immunity in old age

An increased production of proinflammatory cytokines occurs in a high percentage of elderly persons and is associated with an impaired humoral immune response. However, high IL-4 production has also been observed in old age. We now demonstrate an IL-4-producing subpopulation of CD8+ T cells in a subgroup of healthy older adults. This T cell subset is substantial in size and has a characteristic phenotype expressing CD45RO, CD28, CD62L, and CD25. IL-4-producing CD8+ T cells produce large amounts of IL-2 but not IFN-gamma or perforin, and these cells do not have a regulatory suppressive effect on other T cells. In vivo IL-4-producing CD8+ T cells can be stably detected over a year. When put into culture they also have a stable cytokine production pattern but fail to produce perforin even in the presence of IL-12. This special T cell type does not occur in persons under the age of 40, but is present in 36% of the persons >60 years of age. In this age group, IL-4-producing CD8+ T cells are more frequent in persons who are still capable of raising a humoral immune response following immunization than in others who fail to produce protective Abs after vaccination. Our results suggest that CD8+ T cells with a CD62L++(bright) phenotype accumulate in a subgroup of older adults. Due to their phenotype that enables them to migrate into lymphoid tissues and to their capacity to produce IL-4, these cells may counterbalance the overproduction of proinflammatory cytokines in old age.