Foxp3+CD4+CD25+ T cells control virus-specific memory T cells in chimpanzees that recovered from hepatitis C

Hepatitis C virus (HCV) poses a global health problem because it readily establishes persistent infection and a vaccine is not available. CD4(+)CD25(+) T cells have been implicated in HCV persistence because their frequency is increased in the blood of HCV-infected patients and their in vitro depletion results in increased IFN-gamma production by HCV-specific T cells. Studying a well-characterized cohort of 16 chimpanzees, the sole animal model for HCV infection, we here demonstrate that the frequency of Foxp3(+)CD4(+)CD25(+) regulatory T cells (T(Regs)) and the extent of suppression was as high in spontaneously HCV-recovered chimpanzees as in persistently HCV-infected chimpanzees. Foxp3(+)CD4(+)CD25(+) T(Regs) suppressed IFN-gamma production, expansion, and activation-induced cell death of HCV-specific T cells after recovery from HCV infection and in persistent HCV infection. Thus, T(Reg) cells control HCV-specific T cells not only in persistent infection but also after recovery, where they may regulate memory T-cell responses by controlling their activation and preventing apoptosis. However, Foxp3(+)CD4(+)CD25(+) T(Reg) cells of both HCV-recovered and HCV-infected chimpanzees differed from Foxp3(+)CD4(+)CD25(+)T(Reg) cells of HCV-naive chimpanzees in increased IL-2 responsiveness and lower T-cell receptor excision circle content, implying a history of in vivo proliferation. This result suggests that HCV infection alters the population of Foxp3(+)CD4(+)CD25(+) T(Reg) cells.     

Differential antigenic hierarchy associated with spontaneous recovery from hepatitis C virus infection: implications for vaccine design

BACKGROUND: Cellular immune responses play a central role in the control of hepatitis C virus (HCV) infection, and in some individuals the adaptive immune response can spontaneously eradicate HCV infection. The development of vaccine candidates to prevent the spread of this infection remains a top priority; however, understanding the correlates of effective immunological containment is an important prerequisite. METHODS: Using 750 overlapping peptides, we directly characterized ex vivo total and subgenomic HCV-specific CD4(+) and CD8(+) T cell responses in a large cohort of participants with either chronic infection or spontaneously resolved infection. RESULTS: In chronic infection, the frequency of total CD4(+) T cells specific for HCV averaged 0.06%, compared with 0.38% in resolved infection. Total HCV-specific CD4(+) and CD8(+) T cell responses were strongly correlated in the setting of spontaneous resolution but not in the setting of viral persistence. NS3 protein-specific responses comprised a significantly greater proportion of the total response in resolved infection than in chronic infection, whereas responses to different regions comprised a larger proportion of responses in chronic infection. CONCLUSION: Because these data comprehensively define the breadth, specificity, and threshold of the T cell response associated with spontaneous recovery from HCV infection, they have important implications in the development of multigenic vaccine candidates for this common infection.     

The magnitude and breadth of hepatitis C virus-specific CD8+ T cells depend on absolute CD4+ T-cell count in individuals coinfected with HIV-1

CD8(+) T-cell responses are an essential antiviral host defense in persistent viral infections, and their sustained effectiveness is thought to be critically dependent on CD4(+) T-helper cells. To determine the relationship between HIV-1-induced CD4(+) T-cell depletion and hepatitis C virus (HCV)-specific CD8(+) T-cell responses during viral persistence, we studied 103 persons positive for HCV, 74 coinfected with HIV-1. CD8(+) T-cell responses to the entire HCV polyprotein were determined by using an interferon-gamma enzyme-linked immunospot (ELISpot) assay. Although HIV-1 infection by itself was not associated with a diminished HCV-specific response, HIV-1-associated CD4(+) depletion was associated with significantly lower HCV-specific CD8(+) T cells (R = 0.48, P < .0001). In contrast, declining CD4(+) counts over the same range were not associated with diminished Epstein-Barr virus (EBV)- (R = 0.19, P = .31) or HIV-1-specific (R = -0.13, P = .60) CD8(+) T-cell responses in persons infected with all viruses. These data indicate that frequencies of circulating HCV-specific CD8(+) T-cell responses are sensitive to absolute CD4(+) T-cell counts and provide a possible explanation for the accelerated HCV disease course in persons coinfected with HIV-1 and HCV.     

Differential CD4(+) and CD8(+) T-cell responsiveness in hepatitis C virus infection

This study was performed to compare the vigor and phenotype of virus-specific CD4(+) and CD8(+) T-cell responses in patients with different virologic and clinical outcomes after hepatitis C virus (HCV) infection. The results show that a vigorous and multispecific CD4(+) proliferative T-cell response is maintained indefinitely after recovery from HCV infection whereas it is weak and focused in persistently infected patients. In contrast, the HCV-specific CD8(+) T-cell response was quantitatively low in both groups despite the use of sensitive direct ex vivo intracellular interferon gamma (IFN-gamma) staining. Furthermore, although HCV-specific cytolytic CD8(+) memory T cells were undetectable ex vivo, they were readily expanded from the peripheral blood of chronically HCV-infected patients but not from recovered subjects after in vitro stimulation, suggesting that ongoing viremia is required to maintain the HCV-specific memory CD8(+) T-cell response. HCV-specific CD8(+) T cells displayed a type 1 cytokine profile characterized by production of IFN-gamma despite persistent HCV viremia. The paradoxical observation that HCV-specific CD4(+) T cells survive and CD8(+) T cells are lost after viral clearance while the opposite occurs when HCV persists suggests the existence of differential requirements for the maintenance of CD4(+) and CD8(+) T-cell memory during HCV infection. Furthermore, the relative rarity of circulating CD8(+) effector T cells in chronically infected patients may explain the chronic insidious nature of the liver inflammation and also why they fail to eliminate the virus.     

CD8+ cell responses to hepatitis C virus (HCV) in the liver of persons with HCV-HIV coinfection versus HCV monoinfection

OBJECTIVE: Cellular immune responses are difficult to detect in the peripheral blood of persons with chronic hepatitis C virus (HCV) infection. We sought to determine whether T cell responses were present in the liver of patients with human immunodeficiency virus (HIV) and HCV coinfection. METHODS: T cells were expanded from liver-biopsy samples from 10 patients coinfected with HIV and HCV (median CD4(+) cell count, 456 cells/mm(3)) and 8 patients infected with HCV alone. CD8(+) cell responses were detected by use of a modified enzyme-linked immunospot (ELISpot) assay with recombinant vaccinia virus, and CD4(+) cell responses were detected by use of ELISpot with recombinant HCV proteins core, nonstructural (NS) 3, and NS5. RESULTS: Intrahepatic CD8(+) cell responses to HCV were detected in 7 of 10 patients coinfected with HCV and HIV (median frequency, 638 spot-forming cells [sfc]/1 x 10(6) cells) and were similar to those observed in patients singly infected with HCV (7/8; median, 647 sfc/1 x 10(6) cells). Intrahepatic HCV-specific CD4(+) cell responses were also comparable in both groups and correlated with the intrahepatic CD8(+) cell responses (r=0.59; P=.03). CONCLUSION: HCV-specific CD8(+) cell responses are present in the liver of persons with chronic HCV infection even when they are coinfected with HIV; these correlate with intrahepatic HCV-specific CD4(+) cell responses.     

High prevalence of autoreactive, neuroantigen-specific CD8+ T cells in multiple sclerosis revealed by novel flow cytometric assay

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system (CNS) with features suggestive of T-cell-mediated pathology. Most prior reports have focused on CD4(+) T cells with the underlying assumption that MS is predominantly a CD4(+) T helper 1 (Th1)-mediated disease. In this report, we used a novel flow cytometric approach to evaluate autoreactive T-cell responses against a large variety of neuroantigenic targets. We found that both CD4(+) and CD8(+) T cells targeted against several CNS autoantigens were widely prevalent in patients with MS and healthy individuals. Whereas the distribution of CD4(+) responses was similar in different groups, patients with relapsing-remitting MS showed a higher proportion of CNS-specific CD8(+) responses. Autoreactive CD4(+) T cells from patients with MS exhibited a more differentiated Th1 phenotype compared with healthy subjects. Similarly, CNS-specific CD8(+) T-cell responses from patients with MS were functionally distinct from those in healthy individuals. Collectively, these studies reveal the high prevalence of class I-restricted autoreactive CD8(+) T-cell responses in MS that has been underappreciated thus far. The results emphasize the need to evaluate both CD4(+) and CD8(+) T-cell responses in MS and to make both subsets a consideration in the development of novel therapeutic strategies.     

Reversal of nonstructural protein 3-specific CD4(+) T cell dysfunction in patients with persistent hepatitis C virus infection

Hepatitis C virus (HCV)-specific T cell responses are essential for HCV control, and chronic infection is characterized by functionally altered antigen-specific T cells. It has been proposed that the early inactivation of specific CD4(+) T cell responses may be involved in establishment of HCV persistence. We have investigated whether HCV-specific CD4(+) T cells dysfunction can be reversed in vitro. Nonstructural protein 3 (NS3) and core-specific CD4(+) T cells from eight chronically infected and eight spontaneously resolved HCV individuals were selected through transient CD154 (CD40 ligand) expression, and their functional profile (IFN-γ, IL-2, TNF-α, IL-10 and IL-4 production by enzyme-linked immunospot assay, cytometric bead array and intracellular cytokine staining, and proliferation by carboxy-fluorescein diacetate succinimidyl ester dilution assay) was determined both ex vivo and after in vitro expansion of sorted CD154-expressing cells in the absence of specific antigen in IL-7/IL-15-supplemented medium. Ex vivo bulk CD4(+) T cells from chronic patients expressed CD154 in most cases, albeit at lower frequencies than those of resolved patients (0.11%vs 0.41%; P = 0.01), when stimulated with NS3, but not core, although they had a markedly impaired capacity to produce IL-2 and IFN-γ. Antigen-free in vitro expansion of NS3-specific CD154(+) cells from chronic patients restored IFN-γ and IL-2 production and proliferation to levels similar to those of patients with spontaneously resolved infection. Hence, NS3-specific CD4(+) T cell response can be rescued in most chronic HCV patients by in vitro expansion in the absence of HCV-specific antigen. These results might provide a rationale for adoptive immunotherapy.     

Peripheral CD4(+)CD8(+) T cells are differentiated effector memory cells with antiviral functions

Although an increased frequency of CD4(+)CD8(+) T cells has been observed in the peripheral blood during viral infections, their role, function, and biologic significance are still poorly understood. Here we demonstrate that the circulating CD4(+)CD8(+) T-cell population contains mature effector memory lymphocytes specific for antigens of multiple past, latent, and high-level persistent viral infections. Upon in vitro antigenic challenge, a higher frequency of CD4(+)CD8(+) than single-positive cells displayed a T helper 1/T cytotoxic 1 (Th1/Tc1) cytokine profile and proliferated. Ex vivo, more double-positive than single-positive cells exhibited a differentiated phenotype. Accordingly, their lower T-cell receptor excision circles (TREC) content and shorter telomeres proved they had divided more frequently than single-positive cells. Consistent with expression of the tissue-homing marker CXCR3, CD4(+)CD8(+) T cells were demonstrated in situ at the site of persistent viral infection (ie, in the liver during chronic hepatitis C). Finally, a prospective analysis of hepatitis C virus (HCV) infection in a chimpanzee, the only animal model for HCV infection, showed a close correlation between the frequency of activated CD4(+)CD8(+) T cells and viral kinetics. Collectively, these findings demonstrate that peripheral CD4(+)CD8(+) T cells take part in the adaptive immune response against infectious pathogens and broaden the perception of the T-cell populations involved in antiviral immune responses.     

Vigorous hepatitis C virus-specific CD4+ and CD8+ T cell responses induced by protein immunization in the presence of Montanide ISA720 plus synthetic oligodeoxynucleotides containing immunostimulatory cytosine-guanine dinucleotide motifs

BACKGROUND: A prophylactic vaccine for hepatitis C virus (HCV) requires generation of strong humoral as well as CD4(+) and CD8(+) T cell responses. METHODS: The immunomodulatory effects of the combination of 2 adjuvants, synthetic oligodeoxynucleotides containing immunostimulatory cytosine-guanine dinucleotide motifs emulsified with Montanide ISA720 (M-ISA720/CpG), were investigated using the murine model. RESULTS: Administration of recombinant HCV (rHCV) nonstructural (NS) 3 and NS5B proteins plus M-ISA720/CpG (hereafter, "M-ISA720/CpG/rHCV protein") induced high anti-NS3 and anti-NS5B immunoglobulin (Ig) G titers, with the IgG2a isotype being predominant. NS3- and NS5B-specific interferon (IFN)- gamma - and interleukin-2-producing CD4(+) T cell responses, as assessed by enzyme-linked immunospot assay, were significantly more vigorous in mice immunized with M-ISA720/CpG/rHCV protein than in control mice immunized without adjuvant. NS3- and NS5B-specific IFN- gamma -producing CD8(+) T cell percentages, as measured by direct ex vivo intracellular cytokine staining assay, were, respectively, a mean+/-SD of 0.14% +/- 0.04% and 0.15% +/- 0.05% in mice immunized with M-ISA720/CpG/rHCV protein. Furthermore, boosting with recombinant NS3 expression plasmid DNA after priming with M-ISA720/CpG-adjuvanted rNS3 strikingly enhanced both CD4(+) and CD8(+) T cell responses. CONCLUSION: Immunization with M-ISA720/CpG/rHCV protein is capable of inducing potent humoral as well as HCV-specific T helper type 1-biased CD4(+) and CD8(+) T cell responses. A DNA boost after a protein prime--a reversal of the conventional approach--may provide an alternative path to the development of an effective HCV vaccine.     

Kinetics of intrahepatic hepatitis C virus (HCV)-specific CD4+ T cell responses in HCV and Schistosoma mansoni coinfection: relation to progression of liver fibrosis

The kinetics of intrahepatic hepatitis C virus (HCV)-specific CD4(+) T cell responses and their role in progression of fibrosis have not previously been characterized. Subjects with HCV/Schistosoma mansoni coinfection have a more rapid progression of HCV liver fibrosis than do those with HCV infection alone. The present prospective longitudinal study compared the liver histology, HCV-specific intrahepatic and peripheral CD4(+) T cell proliferative responses, and cytokines (enzyme-linked immunospot) in 48 subjects with unresolved acute HCV infection with or without S. mansoni coinfection, at 6-10 months after acute infection and at the end of follow-up (96+/-8.7 months), and the findings were correlated to the rate of progression of fibrosis per year. Coinfected subjects had significant worsening of fibrosis, compared with subjects with HCV infection alone. At baseline, subjects with HCV infection alone had stronger multispecific intrahepatic HCV-specific CD4(+) T helper 1 responses than did coinfected subjects, who had either no responses or weak, narrowly focused responses, and, over time, these T cell responses were maintained only in the liver. The rate of progression of fibrosis and virus load inversely correlated with intrahepatic HCV-specific CD4(+) T cell response. The present prospective analysis indicates that enhancement of progression of liver fibrosis is associated with failure to develop early, multispecific, HCV-specific CD4(+) Th1 responses, suggesting that novel therapeutic approaches inducing strong cellular immune responses might limit subsequent liver damage in individuals with chronic hepatitis C.     

Clinical responders to antiviral therapy of chronic HCV infection show elevated antiviral CD4+ and CD8+ T-cell responses

Summary. Chronic hepatitis C virus (HCV) infection is characterized by attenuated antiviral T‐cell responses, making their detection and characterization a technological challenge. The role and the dynamics of antiviral T‐cell responses during antiviral therapy are incompletely understood. To assess HCV‐specific T‐cell responses during antiviral therapy of genotype‐1‐infected patients, we adopted a flow cytometric approach to comprehensively evaluate virus‐specific CD4+ and CD8+ T‐cell proliferative responses against pools of genotype‐ and subtype‐specific serial, overlapping peptides spanning the entire virus. Studies in cross‐sectional cohorts of treatment‐naïve (TN) patients , early and sustained clinical virological responders (EVRs and SVRs) or clinical nonresponders (NRs) showed that this proliferative assay had significantly greater sensitivity in detecting HCV‐specific responses, compared with ex vivo cytokine flow cytometry. At the same time, it could be used to detect and quantify both CD4+ and CD8+ responses simultaneously. EVRs and SVRs showed significantly more HCV‐specific CD4+ and CD8+ responses, compared with either TN patients or NRs. This corresponded to a higher magnitude of responses as well as a greater breadth of reactivity with higher responses against the core/E1, NS3, NS4 and NS5b regions of the virus. Interestingly, both clinical responders and NRs showed higher cytomegalovirus‐specific CD4+ responses, compared with TN patients. These results demonstrate an association between clinically successful antiviral therapy and enhanced magnitude and breadth of antiviral responses. Moreover, the study demonstrates the clinical relevance of this flow cytometric proliferation assay system, in combination with an unbiased library of viral peptides, in evaluating the biology of antiviral T‐cell responses during infection and therapy.     

Suppression of HCV-specific T cells without differential hierarchy demonstrated ex vivo in persistent HCV infection

Hepatitis C virus (HCV) has a high propensity for persistence. To better define the immunologic determinants of HCV clearance and persistence, we examined the circulating HCV-specific T-cell frequency, repertoire, and cytokine phenotype ex vivo in 24 HCV seropositive subjects (12 chronic, 12 recovered), using 361 overlapping peptides in 36 antigenic pools that span the entire HCV core, NS3-NS5. Consistent with T-cell-mediated control of HCV, the overall HCV-specific type-1 T-cell response was significantly greater in average frequency (0.24% vs. 0.04% circulating lymphocytes, P =.001) and scope (14/36 vs. 4/36 pools, P =.002) among the recovered than the chronic subjects, and the T-cell response correlated inversely with HCV titer among the chronic subjects (R = -0.51, P =.049). Although highly antigenic regions were identified throughout the HCV genome, there was no apparent difference in the overall HCV-specific T-cell repertoire or type-1/type-2 cytokine profile relative to outcome. Notably, HCV persistence was associated with a reversible CD4-mediated suppression of HCV-specific CD8 T cells and with higher frequency of CD4(+)CD25(+) regulatory T cells (7.3% chronic vs. 2.5% recovered, P =.002) that could directly suppress HCV-specific type-1 CD8 T cells ex vivo. In conclusion, we found that HCV persistence is associated with a global quantitative and functional suppression of HCV-specific T cells but not differential antigenic hierarchy or cytokine phenotype relative to HCV clearance. The high frequency of CD4(+)CD25(+) regulatory T cells and their suppression of HCV-specific CD8 T cells ex vivo suggests a novel role for regulatory T cells in HCV persistence.     

Comprehensive analyses of CD8+ T cell responses during longitudinal study of acute human hepatitis C

We comprehensively studied the cellular immune response during acute human hepatitis C virus (HCV) infection by monthly prospective sampling of persons at high risk of infection. In 19 of 23 subjects, interferon-gamma-secreting T cells specific for 1 or more peptides spanning the entire HCV polyprotein were detected 1 to 3 months after infection. The median time to development of interferon gamma responses to HCV peptides was 33 days (range, 29-50 days), and these responses peaked between 180 and 360 days. Nineteen subjects had sufficient follow-up to determine outcome, with 15 (79%) developing persistent viremia and 4 (21%) clearing viremia spontaneously. Of those with progression to chronic infection and detectable T cell responses, all lost recognition of one or more antigens recognized during acute infection, and the median reduction in the magnitude of responses was 85%. Most significantly, despite ongoing viremia, those who had persistent infection did not develop new epitope specificities after the first 6 months of infection. In conclusion, in most individuals, the CD8+ T cell responses generated early in HCV infection decline in peripheral blood and are not replaced with new responses. Supplementary material for this article can be found on the HEPATOLOGY website (http://www.interscience.wiley.com/jpages/0270-9139/suppmat/index.html).     

HIV-1 envelope T cell epitope "hotspots " among mice and humans and among CD4+ and CD8+ T cell subpopulations

HIV-1-specific T cell responses correlate with control of infection and disease, thus encouraging a full understanding of the peptides and antigen-processing mechanisms that govern T cell activation. We have previously demonstrated that CD4(+) T cell epitopes cluster nonrandomly within envelope protein "hotspot" regions. The current study was initiated to determine whether envelope-specific CD8(+) T cells might share epitope "hotspots" with the CD4(+) T cell population. Identification of CD8(+) T cell determinants by ELISPOT assays with peripheral blood mononuclear cells from four HIV-1-infected individuals, in conjunction with a survey of determinants in the Los Alamos database, revealed similarities among "hotspot" positions for CD4(+) and CD8T(+) cells within mice and humans. These results emphasized the important influence that envelope peptide position may have on antigen processing, and the consequent impact such processing may have on HIV-1-specific CD4(+) and CD8(+) T-cell activities.     

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.     

Hepatitis C virus‐specific CD8+ T cell frequencies are associated with the responses of pegylated interferon‐α and ribavirin combination therapy in patients with chronic hepatitis C virus infection

Aim: Hepatitis C virus (HCV)‐specific cytotoxic T lymphocytes (CTLs) play critical roles in elimination of the HCV‐infected hepatocytes. However, the mechanism of HCV elimination by pegylated interferon‐α (peg‐IFNα) plus ribavirin is not fully understood. We examined HCV‐specific CTL responses during this combination therapy. Methods: CD8+ T cells were isolated from 16 HCV infected patients treated by this combination therapy and were subjected to IFN‐γ enzyme‐linked immunospot (ELISPOT) assay. Results: The numbers of IFN‐γ spots against HCV Core or NS3 protein‐derived peptides in HCV patients before treatment were similar to those in healthy donors, and those in HCV patients significantly increased 4 weeks after the initiation of combination therapy. All HCV Core or NS3 proteins‐derived peptides specific CD8+ T cells responses in pre‐treated patients were not associated with ALT levels and HCV viral loads of HCV patients before treatment. And those in pre‐treated patients were similar between sustained virologic responder (SVR) patients and non‐SVR patients. Significant increase of HCV Core or NS3 proteins‐derived peptides specific CD8+ T cells responses between before and 4 weeks after this combination therapy were observed in SVR patients, but not in non‐SVR patients. Conclusions: These results demonstrated that significant increase of HCV‐specific CD8+ T cells at 4 weeks after the initiation of IFN treatment might be associated with the elimination of HCV. Our findings suggest that the reactivity against HCV Core and NS3 proteins‐derived peptides might be useful in predicting the clinical outcome of the combination therapy of peg‐IFNα and ribavirin.     

Analysis of the relationship between cytokine secretion and proliferative capacity in hepatitis C virus infection

CD4(+) T-cell responses are important for the outcome of hepatitis C virus (HCV) infection. However, the functional status of HCV-specific CD4(+) T cells in persistent infection is poorly understood. It is generally recognized that proliferative capacity of HCV-specific CD4(+) T cells is weak or absent in persistent infection, but whether this results from deletion of antigen-specific cells or represents maintenance of antigen-specific but poorly proliferative populations is not defined. We used a set of ex vivo assays to evaluate the functionality of HCV specific CD4(+) T cells in persistent and resolved infection. Peripheral blood mononuclear cells (PBMC) from 24 prospectively recruited HCV polymerase chain reaction (PCR) positive individuals, 12 spontaneously resolved individuals (i.e. anti-HCV+, PCR-) and 11 healthy controls were analysed for interferon-gamma (IFN-gamma) and interleukin 2 (IL-2) secretion by enzyme linked immunospot assays (ELISpot). HCV-specific CD4(+) proliferative responses of carboxy fluorescein succinimidyl ester-labelled PBMC were assessed using a sensitive single cell flow cytometric assay. Sustained IFN-gamma ELISpot responses were observed in the PCR+ group. However, proliferation of HCV-specific CD4(+) T cells in the PCR+ group was substantially reduced on a per cell basis, in parallel to IL-2 secretion, compared with responses in the PCR- group. In PCR- individuals, a strong relationship between cytokine secretion and proliferative capacity was seen. However, in PCR+ individuals, IFN-gamma secretion far exceeded proliferative capacity. During persistent HCV infection, some CD4(+) T-cell specificities appear to be lost, as measured using a range of techniques, but others, potentially important, are maintained as IFN-gamma secretors but with low proliferative capacity even using a highly sensitive assay. Such subsets may yet play a significant role in vivo and also provide a template for modulation in immunotherapeutic interventions.     

Expansion of CD8+ T cells lacking Sema4D/CD100 during HIV-1 infection identifies a subset of T cells with decreased functional capacity

Sema4D, also known as CD100, is a constitutively expressed immune semaphorin on T cells and NK cells. CD100 has important immune regulatory functions that improve antigen-specific priming by antigen-presenting cells, and can also act as a costimulatory molecule on T cells. We investigated the consequence of HIV-1 infection on CD100 expression by T cells, and whether CD100 expression signifies functionally competent effector cells. CD100 expression on T cells from healthy individuals was compared with HIV-1-infected subjects including elite controllers, noncontrollers, and patients receiving antiretroviral therapy. The frequency and fluorescence intensity of CD100 on CD8(+) and CD4(+) T cells were decreased during HIV-1 infection. Furthermore, the absolute number of CD100-expressing CD8(+) T cells was positively associated with the magnitude of HIV-1-specific T-cell responses. CD8(+) T cells lacking CD100 expression were functionally impaired and present in increased numbers in HIV-1-infected individuals. The number of CD100(-)CD8(+) T cells positively correlated with T-cell immunosenescence, immune activation, and viral load. Loss of CD100 expression appears to result from direct antigen stimulation, as in vitro cytokine exposure and viral replication did not significantly impact CD100 expression. These data suggest that loss of CD100 expression probably plays an important role in dysfunctional immunity in HIV-1 infection.     

Recurrence of hepatitis C virus after loss of virus-specific CD4(+) T-cell response in acute hepatitis C.

BACKGROUND & AIMS: The prospective comparison of patients with acute hepatitis C virus (HCV) who spontaneously clear the virus with those who cannot achieve viral elimination and progress to chronic hepatitis offers the unique opportunity to analyze natural mechanisms of viral elimination. METHODS: We studied the HCV-specific CD4(+) T-cell response in 38 patients with acute HCV and correlated the clinical course with the antiviral immune response. The individual HCV-specific T-cell response was assessed in a proliferation assay ((3)H-thymidine uptake) and an enzyme-linked immunospot assay. RESULTS: Patients were classified according to their clinical course and pattern of CD4(+) T-cell responses in 3 categories: first, patients mounting a strong and sustained antiviral CD4(+)/Th1(+) T-cell response who cleared the virus (HCV RNA-negative; n = 20); second, patients who were unable to mount an HCV-specific CD4(+) T-cell response and developed chronic disease (n = 12); and third, patients who initially displayed a strong CD4(+) T-cell response and eliminated the virus (HCV PCR-negative) but subsequently lost this specific T-cell response (n = 6). The loss of the HCV-specific CD4(+) T-cell response was promptly followed by HCV recurrence. CONCLUSIONS: The results indicate that a virus-specific CD4(+)/Th1(+) T-cell response that eliminates the virus during the acute phase of disease has to be maintained permanently to achieve long-term control of the virus. The induction and/or maintenance of virus-specific CD4(+) T cells could represent a promising therapeutic approach in HCV infection.