Content uploaded by Huldrych F Günthard
Author content
All content in this area was uploaded by Huldrych F Günthard
Content may be subject to copyright.
A preview of the PDF is not available
Cellular immune responses to HCV core increase and HCV RNA levels decrease during successful antiretroviral therapy
Abstract and Figures
Hepatitis C virus (HCV) infection is a major cause of morbidity in HIV infected individuals. Coinfection with HIV is associated with diminished HCV-specific immune responses and higher HCV RNA levels.
To investigate whether long-term combination antiretroviral therapy (cART) restores HCV-specific T cell responses and improves the control of HCV replication.
T cell responses were evaluated longitudinally in 80 HIV/HCV coinfected individuals by ex vivo interferon-gamma-ELISpot responses to HCV core peptides, that predominantly stimulate CD4(+) T cells. HCV RNA levels were assessed by real-time PCR in 114 individuals.
The proportion of individuals with detectable T cell responses to HCV core peptides was 19% before starting cART, 24% in the first year on cART and increased significantly to 45% and 49% after 33 and 70 months on cART (p=0.001). HCV-specific immune responses increased in individuals with chronic (+31%) and spontaneously cleared HCV infection (+30%). Median HCV RNA levels before starting cART were 6.5 log(10) IU/ml. During long-term cART, median HCV-RNA levels slightly decreased compared to pre-cART levels (-0.3 log10 IU/ml, p=0.02).
Successful cART is associated with increasing cellular immune responses to HCV core peptides and with a slight long-term decrease in HCV RNA levels. These findings are in line with the favourable clinical effects of cART on the natural history of hepatitis C and with the current recommendation to start cART earlier in HCV/HIV coinfected individuals.
Figures - uploaded by Huldrych F Günthard
Author content
All figure content in this area was uploaded by Huldrych F Günthard
Content may be subject to copyright.
... Studies using hepatocyte cell lines have demonstrated that non-nucleoside reverse transcriptase inhibitors (NNRTIs) can interfere with mitochondrial function leading to increase intracellular lipid accumulation which can further enhance liver damage (172,173). In contrast, other reports suggested that ART enhances HCV-specific T cell responses with a significant decline in HCV-RNA levels (188) and reduction in the rate of hepatic decompensation events and (157) leading to accumulation of ROS which triggers an NF-kb mediated oxidative stress (158,159). HIV also activates TNF-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis via upregulation of TRAIL receptor 1 (DR4), and 2 (DR5) (160), aggravating HCV fibrotic complications (161). ...
Nearly 2.3 million individuals worldwide are coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV). Odds of HCV infection are six times higher in people living with HIV (PLWH) compared to their HIV-negative counterparts, with the highest prevalence among people who inject drugs (PWID) and men who have sex with men (MSM). HIV coinfection has a detrimental impact on the natural history of HCV, including higher rates of HCV persistence following acute infection, higher viral loads, and accelerated progression of liver fibrosis and development of end-stage liver disease compared to HCV monoinfection. Similarly, it has been reported that HCV coinfection impacts HIV disease progression in PLWH receiving anti-retroviral therapies (ART) where HCV coinfection negatively affects the homeostasis of CD4+ T cell counts and facilitates HIV replication and viral reservoir persistence. While ART does not cure HIV, direct acting antivirals (DAA) can now achieve HCV cure in nearly 95% of coinfected individuals. However, little is known about how HCV cure and the subsequent resolution of liver inflammation influence systemic immune activation, immune reconstitution and the latent HIV reservoir. In this review, we will summarize the current knowledge regarding the pathogenesis of HIV/HCV coinfection, the effects of HCV coinfection on HIV disease progression in the context of ART, the impact of HIV on HCV-associated liver morbidity, and the consequences of DAA-mediated HCV cure on immune reconstitution and HIV reservoir persistence in coinfected patients.
... Detri- mental effect of HCV on HIV infection includes a significant reduction of CD4 cells and total CD4 percent [16]. Independent of HIV or HCV infection, depletion of CD4 cell enhances pro- gression to cirrhosis [17]. ...
Hepatitis C virus (HCV) infection has been associated with liver disease including liver cirrhosis and hepatocellular carcinoma (HCC) in chronically-infected persons. However, in HIV/HCV co-infected patients, increased rate of progression to cirrhosis and HCC has been reported. Limited information exists regarding genetic variants of HCV circulating among co-infected patients, which could be important in the design of broadly protective vaccine and management of the disease. Here, we determined the genotypes of HCV isolates circulating among HIV/HCV co-infected patients in Ibadan, southwestern Nigeria. One hundred and twenty-five HIV/HCV IgM positive samples obtained from HIV laboratory, University of Ibadan were used for this study. HCV NS5B gene was amplified using polymerase chain reaction (PCR). The amplified NS5B gene was sequenced using gene specific primers. Twenty isolates were amplified, out of which 13 were successfully sequenced. Phylogenetic analysis of the 13 sequenced isolates showed three HCV subtypes 1a, 3a and 5a belonging to genotypes 1, 3 and 5 respectively. Ten isolates (77%) belong to subtype 5a, followed by 2 isolates (15%) subtype 1a and 1 isolate (8%) was subtype 3a. The predominant HCV genotype was 5, followed by genotype 1 (subtype 1a). The findings, as well as the observed mutations in NS5B gene, indicate the need for screening and monitoring of HIV/HCV co-infected patients. Further study to determine the phylogeny of isolates circulating in other parts of Nigeria will be carried out.
... In many studies, HIV/HCV-coinfected patients demonstrated an inverse correlation between the CD4+ T-cell count and the HCV viral load [33][34][35][36][37]. Moreover, in those patients, low CD4+ T-lymphocyte quantity was used as a liver fibrosis predictor [34, 38,39]. ...
... November 2017 | Volume 8 | Article 1461 considered to be beneficial, especially in HBV or HCV coinfected individuals, and are considered to outweigh the potential risks of long-term toxicity (172,173). ...
Even after attainment of sustained viral suppression following implementation of highly active antiretroviral therapy, HIV-infected persons continue to experience persistent, low-grade, systemic inflammation. Among other mechanisms, this appears to result from ongoing microbial translocation from a damaged gastrointestinal tract. This HIV-related chronic inflammatory response is paralleled by counteracting, but only partially effective, biological anti-inflammatory processes. Paradoxically, however, this anti-inflammatory response not only exacerbates immunosuppression but also predisposes for development of non-AIDS-related, non-communicable disorders. With respect to the pathogenesis of both sustained immunosuppression and the increased frequency of non-AIDS-related disorders, the anti-inflammatory/profibrotic cytokine, transforming growth factor-β1 (TGF-β1), which remains persistently elevated in both untreated and virally suppressed HIV-infected persons, may provide a common link. In this context, the current review is focused on two different, albeit related, harmful activities of TGF-β1 in HIV infection. First, on the spectrum of anti-inflammatory/immunosuppressive activities of TGF-β1 and the involvement of this cytokine, derived predominantly from T regulatory cells, in driving disease progression in HIV-infected persons via both non-fibrotic and profibrotic mechanisms. Second, the possible involvement of sustained elevations in circulating and tissue TGF-β1 in the pathogenesis of non-AIDS-defining cardiovascular, hepatic, pulmonary and renal disorders, together with a brief comment on potential TGF-β1-targeted therapeutic strategies.
In patients infected with human immunodeficiency virus (HIV) in 20 - 30% of cases co-in- fection with hepatitis C virus (HCV) is observed, that is associated with common routes of transmis- sion for these causative agents. The main cause of lethal outcome for co-infected patients is liver damage. Thus, analysis of mechanisms of mutual influence of HIV and HCV under the conditions of co-infection gains special attention, that can be examined from both standpoints of direct inter- molecular interaction of 2 viral causative agents, as well as from the position of their immune- mediated effect. Negative effect of HIV on the course of fibrosis process in liver during HCV infection is associated with the feature of this virus to cause deep alteration in the immune system by direct damage of CD4+ cells, disruption of mechanisms of immunological memory, suppression of functions of liver fraction of NK and NKT, as well as its ability of co-receptor interaction with hepatocytes and stellate cells, enhancing progress of fibrosis alterations and HCV replication in liver. HCV.is also established to effect replication of HIV, stimulate infection of macrophages with this virus. All these events facilitate the rise in lethality during HIV and HCV co-infection.
Hepatotropic viruses induced hepatitis progresses much faster and causes more liver- related health problems in people co-infected with human immunodeficiency virus (HIV). Although treatment with antiretroviral therapy has extended the life expectancy of people with HIV, liver disease induced by hepatitis B virus (HBV) and hepatitis C virus (HCV) causes significant numbers of non-acquired immune deficiency syndrome (AIDS)-related deaths in co-infected patients. In recent years, new insights into the mechanisms of accelerated fibrosis and liver disease progression in HIV/HCV and HIV/HBV co-infections have been reported. In this paper, we review recent studies examining the natural history and pathogenesis of liver disease in HIV-HCV/HBV co-infection in the era of direct acting antivirals (DAA) and antiretroviral therapy (ART). We also review the novel therapeutics for management of HIV/HCV and HIV/HBV co-infected individuals.
Antibody responses have not been fully characterised in chronically HIV/HCV patients receiving antiretroviral therapy (ART). Seventeen HIV/HCV patients receiving ART were followed for a median (range) interval of 597 (186–766) weeks. Prior to ART, HIV/HCV patients had lower levels of antibodies reactive with HCV core and JFH-1, and lower genotype cross-reactive neutralising antibodies (nAb) titres, than HCV patients. Levels of JFH-1 reactive antibody increased on ART, irrespective of CD4⁺ T-cell counts or changes in serum ALT levels. The appearance of nAb coincided with control of HCV viral replication in five HIV/HCV patients. In other patients, HCV viral loads remained elevated despite nAb responses. Sustained virological responses following HCV therapy were associated with reduced antibody responses to JFH-1 and core but elevated responses to non-structural proteins. We conclude that nAb responses alone may fail to clear HCV, but contribute to control of viral replication in some HIV/HCV patients responding to ART.
Objectives:
Studies have shown that hepatitis C virus (HCV) RNA levels remain stable over time in HIV/HCV-coinfected individuals taking combination antiretroviral therapy (cART), while spontaneous clearance of HCV RNA during the persistent infection phase has been documented only rarely among those with the CC interleukin (IL)-28B genotype. This study describes HCV RNA profiles and factors associated with changes over time in HCV RNA levels in the ESPRIT study.
Methods:
HIV/HCV-coinfected individuals positive for HCV RNA were included in the study. Follow-up was counted from the first HCV RNA positive test and censored at the initiation of interferon-based treatment. HCV RNA and IL-28B measurements were performed in the same reference laboratory. Random effects mixed models were used to analyse changes over time in HCV RNA.
Results:
A total of 312 ESPRIT patients were included in the study (151 in the arm receiving subcutaneous recombinant IL-2 and 161 in the control arm). Most of the patients were white (89%) and male (76%), and they had a median of 5 HCV RNA measurements per person [interquartile range (IQR) 3-6; range 1-9]. Median follow-up was 5 years (IQR: 2-6 years). At baseline, 96% of patients were taking cART and 93% had undetectable HIV RNA. Mean HCV RNA levels decreased by 13% per year over the study period [95% confidence interval (CI) 8-18%; P < 0.0001]. Baseline HCV RNA levels and the change over time in HCV RNA did not differ by randomization arm (P = 0.16 and P = 0.56, respectively). Nine individuals spontaneously cleared HCV RNA during follow-up [IL-28B genotypes: CC, five patients (56%); CT, four patients (44%)].
Conclusions:
HCV RNA levels decreased over time in this population with well-controlled HIV infection. Spontaneous clearance of HCV RNA was documented in five individuals with IL-28B genotype CC and four with the CT genotype.
With shared routes of transmission, viral hepatitis is very common in patients with HIV infection. The increase in liver-related mortality is causing concern. It is important, therefore, to screen individuals infected with HIV for viral hepatitis and to consider antiviral therapy. For patients with HIV and chronic hepatitis B virus (HBV) infection, an antiretroviral regimen with activity against HBV is recommended. Pegylated interferon (PEG-IFN) and ribavirin (RBV) therapy has reduced efficacy in HIV-positive patients with chronic hepatitis C virus (HCV) infection, and it is hoped that the newer directly antiviral agents, despite potentially challenging drug interactions, will improve the success rate in this group. There are many important epidemiological and clinical interactions between HIV and the hepatotropic viruses. The pattern of co-infection varies according to the risk group. In men who have sex with men (MSM), for example, hepatitis A virus (HAV) and HBV are common, whereas the injecting drug user (IDU) or recipient of contaminated blood products is more likely to be exposed to hepatitis C virus (HCV) infection. Recent reports, however, describe outbreaks of HCV infection in HIV-positive MSM. There are also reports of chronic hepatitis E virus (HEV) infection in this setting. It is recognized that HIV infection can modify the clinical course of viral hepatitides whether these occur before the onset of HIV infection, simultaneously, or subsequently. The clinical importance of this has increased with the improved survival of the HIV-infected individual.
Human and animal model evidence suggests that CD4+ T cells play a critical role in the control of chronic hepatitis C virus (HCV) infection. However, despite their importance, the mechanism behind the failure of such populations in chronic disease is not understood and the contribution of viral mutation is not known. To address this, this study defined the specificity and virological footprint of CD4+ T cells in chronic infection. CD8+ T-cell-depleted peripheral blood mononuclear cells from 61 HCV genotype 1-infected patients were analysed against a panel of peptides covering the HCV genotype 1 core--a region where CD4+ T-cell responses may be reproducibly obtained. In parallel, the core region and E2 protein were sequenced. Gamma interferon-secreting CD4+ T-cell responses directed against multiple epitopes were detected in 53% of individuals, targeting between one and four peptides in the HCV core. Viral sequence evaluation revealed that these CD4+ T-cell responses were associated with mutants in 2/21 individuals. In these two cases, the circulating sequence variant was poorly recognized by host CD4+ T cells. Bioinformatics analyses revealed no overall evidence of selection in the target epitopes and no differences between the groups with and without detectable CD4+ T-cell responses. It was concluded that sustained core peptide-specific CD4+ T-cell responses may be reproducibly measured during chronic HCV infection and that immune escape may occur in specific instances. However, overall the virological impact of such responses is limited and other causes for CD4+ T-cell failure in HCV must be sought.
Unlabelled:
Human leukocyte antigen B27 (HLA-B27) is associated with protection in human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infection. This protective role is linked to single immunodominant HLA-B27-restricted CD8+ T-cell epitopes in both infections. In order to define the relative contribution of a specific HLA-B27-restricted epitope to the natural course of HCV infection, we compared the biological impact of the highly conserved HCV genotype 1 epitope, for which the protective role has been described, with the corresponding region in genotype 3 that differs in its sequence by three amino acid residues. The genotype 3a peptide was not recognized by CD8+ T cells specific for the genotype 1 peptide. Furthermore, patients with acute or chronic infection with HCV genotype 3a did not mount T-cell responses to this epitope region, and their autologous viral sequences showed no evidence of T-cell pressure. Finally, we found a significantly higher frequency of HLA-B27 positivity in patients with chronic HCV genotype 3a infection compared to genotype 1 infection, indicating that there is no protection by HLA-B27 in HCV genotype 3 infection.
Conclusion:
Our data indicate that the protective effect of HLA-B27 is limited to HCV genotype 1 infection and does not expand to other genotypes such as genotype 3a. This can most likely be explained by intergenotype sequence diversity leading to the loss of the immunodominant HLA-B27 epitope in viral strains other than genotype 1. Our results underline the central role of a single HLA-B27-restricted epitope-specific CD8+ T-cell response in mediating protection in HCV genotype 1 infection.
To estimate stage-specific transition probabilities in individuals coinfected with HIV and hepatitis C virus (HCV), to examine the effect of covariates on these rates, and to investigate the effect of HIV on HCV-related cirrhosis in the era of highly active antiretroviral therapy (HAART).
Systematic review of natural history studies among HCV-infected individuals.
Markov maximum likelihood estimation method was used to estimate stage-specific transition probabilities. A meta-analysis was performed to obtain pooled transition probabilities, and a meta-regression to investigate the impact of covariates on these rates. Risk of cirrhosis between individuals monoinfected with HCV and coinfected with HIV/HCV were compared by HAART status.
The estimated mean (95% confidence intervals) annual transition probabilities of 3567 individuals coinfected with HIV/HCV (n = 17 studies) were as follows: fibrosis stage (F) F0 --> F1 0.122 (0.098-0.153); F1 --> F2 0.115 (0.095-0.140); F2 --> F3 0.124 (0.097-0.159); and F3 --> F4 0.115 (0.098-0.135) units/year. The prevalence of cirrhosis after 20 and 30 years of HCV infection was 21% (16-28%) and 49% (40-59%), respectively. Longer duration of HCV infection was significantly associated with slower rate of fibrosis progression. The overall rate ratio of cirrhosis between individuals coinfected with HIV/HCV and monoinfected with HCV (n = 27 studies) was 2.1 (1.5-3.0), 2.5 (1.8-3.4) in the non-HAART group, and 1.7 (1.1-2.8) in the HAART group.
The rate of fibrosis progression among individuals coinfected with HIV/HCV appears constant. Our results confirm that chronic hepatitis C outcomes are worse among coinfected individuals. Over the period studied, HAART did not appear to fully correct the adverse effect of HIV infection on HCV prognosis.
Treatment predictors are important tools for the management of therapy in patients with chronic hepatitis B and C virus (HBV, HCV) infection. In chronic hepatitis B, several pretreatment parameters have been identified for prediction of virologic response to interferon alfa-based antiviral therapies or treatment with polymerase inhibitors. In interferon alfa and pegylated interferon alfa-treated patients, low baseline HBV DNA concentrations, HBV genotype A (B), and high baseline ALT levels are significantly associated with treatment response. In patients treated with nucleos(t)ide analogues, low baseline HBV DNA but not viral genotype is positively associated with virologic response. During treatment the best predictor of response is HBV DNA kinetics. Early viral suppression is associated with favourable virologic response and reduced risk for subsequent resistance mutations. For the current standard treatment with pegylated interferon alfa and ribavirin in patients with chronic hepatitis C, infection with HCV genotypes 2 and 3, baseline viral load below 400,000-800,000 IU/ml, Asian and Caucasian ethnicity, younger age, low GGT levels, absence of advanced fibrosis/cirrhosis, and absence of steatosis in the liver have been identified as independent pretreatment predictors of a sustained virologic response. After initiation of treatment, initial viral decline with undetectable HCV-RNA at week 4 of therapy (RVR) is the best predictor of sustained virologic response independent of HCV genotype.
The availability of new antiretroviral drugs and formulations, including drugs in new classes, and recent data on treatment choices for antiretroviral-naive and -experienced patients warrant an update of the International AIDS Society-USA guidelines for the use of antiretroviral therapy in adult human immunodeficiency virus (HIV) infection.
To summarize new data in the field and to provide current recommendations for the antiretroviral management and laboratory monitoring of HIV infection. This report provides guidelines in key areas of antiretroviral management: when to initiate therapy, choice of initial regimens, patient monitoring, when to change therapy, and how best to approach treatment options, including optimal use of recently approved drugs (maraviroc, raltegravir, and etravirine) in treatment-experienced patients.
A 14-member panel with expertise in HIV research and clinical care was appointed. Data published or presented at selected scientific conferences since the last panel report (August 2006) through June 2008 were identified.
Data that changed the previous guidelines were reviewed by the panel (according to section). Guidelines were drafted by section writing committees and were then reviewed and edited by the entire panel. Recommendations were made by panel consensus.
New data and considerations support initiating therapy before CD4 cell count declines to less than 350/microL. In patients with 350 CD4 cells/microL or more, the decision to begin therapy should be individualized based on the presence of comorbidities, risk factors for progression to AIDS and non-AIDS diseases, and patient readiness for treatment. In addition to the prior recommendation that a high plasma viral load (eg, >100,000 copies/mL) and rapidly declining CD4 cell count (>100/microL per year) should prompt treatment initiation, active hepatitis B or C virus coinfection, cardiovascular disease risk, and HIV-associated nephropathy increasingly prompt earlier therapy. The initial regimen must be individualized, particularly in the presence of comorbid conditions, but usually will include efavirenz or a ritonavir-boosted protease inhibitor plus 2 nucleoside reverse transcriptase inhibitors (tenofovir/emtricitabine or abacavir/lamivudine). Treatment failure should be identified and managed promptly, with the goal of therapy, even in heavily pretreated patients, being an HIV-1 RNA level below assay detection limits.
A working group of the European AIDS Clinical Society (EACS) have developed these guidelines for European clinicians to help them in the treatment of adults with HIV infection. This third version of the guidelines includes, as new topics, the assessment of patients at initial and subsequent clinic visits as well as post-exposure prophylaxis. A revision of the 2005 guidelines based on current data includes changes in the sections on primary HIV infection, when to initiate therapy, which drug combinations are preferred as initial combination regimens for antiretroviral-naïve patients, how to manage virological failure and the treatment of HIV during pregnancy.
In Europe, there is a wide range of clinical practices in antiretroviral therapy depending on various factors such as drug registration, national policies, local availability, reimbursement and access to treatment. These can vary greatly from one country to another, especially in Central and Eastern parts of Europe.
These guidelines are intended to help clinicians achieve the best care for their patients. In some countries, particularly where the quality of and access to care are not optimal, these guidelines should help AIDS societies and physicians or patient group organizations to negotiate with their national health authorities with a view to implementing what should be the standard of care for HIV-infected patients all over Europe.
To explore the parameters of specific immunity to hepatitis C virus (HCV) associated with virus clearance during acute HCV infection in HIV coinfection.
HIV-infected patients without prior HCV infection were prospectively enrolled for acute hepatitis C and followed up over 15 months. HCV-specific T cells were assessed by proliferation, ELISpot, intracellular cytokine staining and pentamer assays. Pegylated-interferon-alpha and ribavirin were proposed if HCV persisted at M3.
Thirty eight acutely HCV-infected HIV-positive patients were enrolled. HCV genotypes were predominantly 4 and 1. Five patients (13%) showed spontaneous clearance and 20 initiated treatment, of whom 13 (65%) showed sustained virologic responses. Before M3, HCV-specific proliferative responses observed in 35% cases, were associated with lower HCV viral load (P = 0.04) and predictive of spontaneous clearance (P = 0.02), particularly anti-NS4 responses (P = 0.03). These HCV-specific proliferative responses were associated with HIV-p24-specific responses (P = 0.002) independently from the HIV stage. Interferon-gamma-producing T cells specific for HCV were detectable ex vivo in 81% cases but at low intensity (<150 spot forming cells/10 peripheral blood mononuclear cells) and were independent of the HCV outcome. Low frequencies of pentamer-positive HCV-specific CD8 cells (0.01-0.05%) detected in nine of 12 patients were mainly effector-memory PD-1-negative T cells. Twelve days of HCV-specific in-vitro culture induced amplification of CD4 T cells coproducing interleukin-2 and interferon-gamma but rarely of CD8 T cells.
Acute HCV infection in HIV-coinfected patients is characterized by a low rate of spontaneous clearance and weak HCV-specific memory T cells, not strictly related to HIV-induced immune defects, and which correlate with virus clearance.
Hepatitis C virus (HCV) causes chronic infection in approximately two-thirds of cases, leading to chronic hepatitis, liver cirrhosis, liver disease, liver failure, and hepatocellular carcinoma in a substantial proportion of the 170 million HCV-infected individuals worldwide. It is generally accepted that the cellular immune response plays the most important role in determining the outcome of HCV infection. First, vigorous, multispecific and sustained CD4+ and CD8+ T-cell responses are associated with viral clearance. Second, depletion studies in chimpanzees, the only other host of HCV besides humans, have shown that both CD4+ and CD8+ T-cells are required for virus elimination. Third, the host's human leukocyte antigen alleles, which restrict the repertoire of CD4+ and CD8+ T-cell responses, influence the outcome of infection. Of note, protective immunity has been demonstrated in population-based studies, as well as in experimentally infected chimpanzees. Thus, a detailed understanding of the mechanisms contributing to the failure of the antiviral immune response should allow successful development of prophylactic and therapeutic vaccination strategies.
Hepatitis C virus (HCV) infects an estimated 170 million people globally and persistent infection within the liver is the usual outcome of infection. The resulting liver disease leads to substantial morbidity and to date no vaccine exists. Furthermore the treatments available are frequently ineffective. A minority of those exposed will however successfully control the virus and the factors that dictate this remain elusive. The events that occur in the immediate and early phase post exposure are thought to play a crucial role in determining the outcome and virus specific T cells have a confirmed role in directing the immune response towards a successful outcome. An understanding of the T cell responses and the strategies, which allow the virus to evade these responses in the majority, is an essential prerequisite both for vaccine design and the development of therapeutic agents. We review here the characteristics of the cellular immune responses in acute infection and how the virus manages to undermine these responses and establish chronicity.