Exposure to low infective doses of HCV induces cellular immune responses without consistently detectable viremia or seroconversion in chimpanzees

Cellular immunity to SARS-CoV-2 following intrafamilial exposure in seronegative family members

Introduction

Family studies of antiviral immunity provide an opportunity to assess virus-specific immunity in infected and highly exposed individuals, as well as to examine the dynamics of viral infection within families. Transmission of SARS-CoV-2 between family members represented a major route for viral spread during the early stages of the pandemic, due to the nature of SARS-CoV-2 transmission through close contacts.

Methods

Here, humoral and cellular immunity is explored in 264 SARS-CoV-2 infected, exposed or unexposed individuals from 81 families in the United Kingdom sampled in the winter of 2020 before widespread vaccination and infection.

Results

We describe robust cellular and humoral immunity into COVID-19 convalescence, albeit with marked heterogeneity between families and between individuals. T-cell response magnitude is associated with male sex and older age by multiple linear regression. SARS-CoV-2-specific T-cell responses in seronegative individuals are widespread, particularly in adults and in individuals exposed to SARS-CoV-2 through an infected family member. The magnitude of this response is associated with the number of seropositive family members, with a greater number of seropositive individuals within a family leading to stronger T-cell immunity in seronegative individuals.

Discussion

These results support a model whereby exposure to SARS-CoV-2 promotes T-cell immunity in the absence of an antibody response. The source of these seronegative T-cell responses to SARS-CoV-2 has been suggested as cross-reactive immunity to endemic coronaviruses that is expanded upon SARS-CoV-2 exposure. However, in this study, no association between HCoV-specific immunity and seronegative T-cell immunity to SARS-CoV-2 is identified, suggesting that de novo T-cell immunity may be generated in seronegative SARS-CoV-2 exposed individuals.

Molecular Determinants of Mouse Adaptation of Rat Hepacivirus

The lack of robust immunocompetent animal models for hepatitis C virus (HCV) impedes vaccine development and studies of immune responses. Norway rat hepacivirus (NrHV) infection in rats shares HCV-defining characteristics, including hepatotropism, chronicity, immune responses, and aspects of liver pathology. To exploit genetic variants and research tools, we previously adapted NrHV to prolonged infection in laboratory mice. Through intrahepatic RNA inoculation of molecular clones of the identified variants, we here characterized four mutations in the envelope proteins responsible for mouse adaptation, including one disrupting a glycosylation site. These mutations led to high-titer viremia, similar to that observed in rats. In 4-week-old mice, infection was cleared after around 5 weeks compared to 2 to 3 weeks for nonadapted virus. In contrast, the mutations led to persistent but attenuated infection in rats, and they partially reverted, accompanied by an increase in viremia. Attenuated infection in rat but not mouse hepatoma cells demonstrated that the characterized mutations were indeed mouse adaptive rather than generally adaptive across species and that species determinants and not immune interactions were responsible for attenuation in rats. Unlike persistent NrHV infection in rats, acute resolving infection in mice was not associated with the development of neutralizing antibodies. Finally, infection of scavenger receptor B-I (SR-BI) knockout mice suggested that adaptation to mouse SR-BI was not a primary function of the identified mutations. Rather, the virus may have adapted to lower dependency on SR-BI, thereby potentially surpassing species-specific differences. In conclusion, we identified specific determinants of NrHV mouse adaptation, suggesting species-specific interactions during entry. IMPORTANCE A prophylactic vaccine is required to achieve the World Health Organization's objective for hepatitis C virus elimination as a serious public health threat. However, the lack of robust immunocompetent animal models supporting hepatitis C virus infection impedes vaccine development as well as studies of immune responses and viral evasion. Hepatitis C virus-related hepaciviruses were discovered in a number of animal species and provide useful surrogate infection models. Norway rat hepacivirus is of particular interest, as it enables studies in rats, an immunocompetent and widely used small laboratory animal model. Its adaptation to robust infection also in laboratory mice provides access to a broader set of mouse genetic lines and comprehensive research tools. The presented mouse-adapted infectious clones will be of utility for reverse genetic studies, and the Norway rat hepacivirus mouse model will facilitate studies of hepacivirus infection for in-depth characterization of virus-host interactions, immune responses, and liver pathology.

Second hepatitis C virus transmission by blood components since introduction of mandatory NAT screening in Germany

BACKGROUND

Viral safety of blood products in Germany has improved significantly over the last two decades. We describe the second documented transfusion-transmitted (TT) episode for the hepatitis C virus (HCV) in Germany since mandatory nucleic acid amplification techniques (NAT) screening was introduced in 1999.

STUDY DESIGN AND METHODS

When a repeat donor who had tested negative for anti-HCV tested positive for HCV RNA by NAT in a minipool (MP) of eight, a look-back procedure was initiated. Qualitative, quantitative and genotyping assays were used to investigate the titers of the quarantined fresh frozen plasma (FFP) from the donor and a serum sample from the recipient of the pooled platelet concentrate (PPC). Amplified products of 5'UTR and HVR1 were used for sequence comparison to characterize the HCV genomic identity of donor and recipient samples.

RESULTS

All NAT tests utilized in this procedure were able to detect a low HCV RNA titer (~15 IU/ml) in the FFP from the donation. Dilution of FFP by factor 8 was performed to mimic an MP, and the detection rate correlated well with the claimed sensitivity of the tests. Analysis of donor and recipient samples revealed genotype 3a viral transmission confirmed by sequence analysis.

CONCLUSION

This TT HCV case could have been prevented by individual donation (ID) NAT. However, a low titer blood donation in the window period (WP) is very rare. Residual risk calculation for TT HCV in the WP revealed that, compared to MP-NAT testing, ID-NAT would improve blood safety only marginally.

Exposed seronegative: Cellular immune responses to SARS-CoV-2 in the absence of seroconversion

The factors determining whether infection will occur following exposure to SARS-CoV-2 remain elusive. Certain SARS-CoV-2-exposed individuals mount a specific T-cell response but fail to seroconvert, representing a population that may provide further clarity on the nature of infection susceptibility and correlates of protection against SARS-CoV-2. Exposed seronegative individuals have been reported in patients exposed to the blood-borne pathogens Human Immunodeficiency virus and Hepatitis C virus and the sexually transmitted viruses Hepatitis B virus and Herpes Simplex virus. By comparing the quality of seronegative T-cell responses to SARS-CoV-2 with seronegative cellular immunity to these highly divergent viruses, common patterns emerge that offer insights on the role of cellular immunity against infection. For both SARS-CoV-2 and Hepatitis C, T-cell responses in exposed seronegatives are consistently higher than in unexposed individuals, but lower than in infected, seropositive patients. Durability of T-cell responses to Hepatitis C is dependent upon repeated exposure to antigen - single exposures do not generate long-lived memory T-cells. Finally, exposure to SARS-CoV-2 induces varying degrees of immune activation, suggesting that exposed seronegative individuals represent points on a spectrum rather than a discrete group. Together, these findings paint a complex landscape of the nature of infection but provide clues as to what may be protective early on in SARS-CoV-2 disease course. Further research on this phenomenon, particularly through cohort studies, is warranted.

Dose-Dependent Hepacivirus Infection Reveals Linkage between Infectious Dose and Immune Response

More than 70 million people worldwide are still infected with the hepatitis C virus 30 years after its discovery, underscoring the need for a vaccine. To develop an effective prophylactic vaccine, detailed knowledge of the correlates of protection and an immunocompetent surrogate model are needed. In this study, we describe the minimum dose required for robust equine hepacivirus (EqHV) infection in equids and examined how this relates to duration of infection, seroconversion, and transcriptomic responses. To investigate mechanisms of hepaciviral persistence, immune response, and immune-mediated pathology, we inoculated eight EqHV naive horses with doses ranging from 1-2 copies to 1.3 × 106 RNA copies per inoculation. We characterized infection kinetics, pathology, and transcriptomic responses via next generation sequencing. The minimal infectious dose of EqHV in horses was estimated at 13 RNA copies, whereas 6 to 7 copies were insufficient to cause infection. Peak viremia did not correlate with infectious dose, while seroconversion and duration of infection appeared to be affected. Notably, seroconversion was undetectable in the low-dose infections within the surveillance period (40 to 50 days). In addition, transcriptomic analysis revealed a nearly dose-dependent effect, with greater immune activation and inflammatory response observed in high-dose infections than in low-dose infections. Interestingly, inoculation with 6-7 copies of RNA that did not result in productive infection, but was associated with a strong immune response, similar to that observed in the high-dose infections. IMPORTANCE We demonstrate that the EqHV dose of infection plays an important role for inducing immune responses, possibly linked to early clearance in high-dose and prolonged viremia in low-dose infections. In particular, pathways associated with innate and adaptive immune responses, as well as inflammatory responses, were more strongly upregulated in high-dose infections than in lower doses. Hence, inoculation with low doses may enable EqHV to evade strong immune responses in the early phase and therefore promote robust, long-lasting infection.

In the era of rapid mRNA-based vaccines: Why is there no effective hepatitis C virus vaccine yet?

Hepatitis C virus (HCV) is responsible for no less than 71 million people chronically infected and is one of the most frequent indications for liver transplantation worldwide. Despite direct-acting antiviral therapies fuel optimism in controlling HCV infections, there are several obstacles regarding treatment accessibility and reinfection continues to remain a possibility. Indeed, the majority of new HCV infections in developed countries occur in people who inject drugs and are more plausible to get reinfected. To achieve global epidemic control of this virus the development of an effective prophylactic or therapeutic vaccine becomes a must. The coronavirus disease 19 (COVID-19) pandemic led to auspicious vaccine development against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus, which has renewed interest on fighting HCV epidemic with vaccination. The aim of this review is to highlight the current situation of HCV vaccine candidates designed to prevent and/or to reduce HCV infectious cases and their complications. We will emphasize on some of the crossroads encountered during vaccine development against this insidious virus, together with some key aspects of HCV immunology which have, so far, hampered the progress in this area. The main focus will be on nucleic acid-based as well as recombinant viral vector-based vaccine candidates as the most novel vaccine approaches, some of which have been recently and successfully employed for SARS-CoV-2 vaccines. Finally, some ideas will be presented on which methods to explore for the design of live-attenuated vaccines against HCV.

Hepatitis C Contamination of Medication Vials Accessed with Sterile Needles and Syringes

BACKGROUND

Health care-associated hepatitis C virus outbreaks from contaminated medication vials continue to be reported even though most practitioners deny reusing needles or syringes. The hypothesis was that when caring for hepatitis C virus-infected patients, healthcare providers may inadvertently contaminate the medication vial diaphragm and that subsequent access with sterile needles and syringes can transfer hepatitis C virus into the medication, where it remains stable in sufficient quantities to infect subsequent patients.

METHODS

A parallel-arm lab study (n = 9) was performed in which contamination of medication vials in healthcare settings was simulated using cell culture-derived hepatitis C virus. First, surface-contaminated vials were accessed with sterile needles and syringes, and then hepatitis C virus contamination was assessed in cell culture. Second, after contaminating several medications with hepatitis C virus, viral infectivity over time was assessed. Last, surface-contaminated vial diaphragms were disinfected with 70% isopropyl alcohol to determine whether disinfection of the vial surface was sufficient to eliminate hepatitis C virus infectivity.

RESULTS

Contamination of medication vials with hepatitis C virus and subsequent access with sterile needles and syringes resulted in contamination of the vial contents in sufficient quantities to initiate an infection in cell culture. Hepatitis C virus remained viable for several days in several commonly used medications. Finally, a single or 2- to 3-s wipe of the vial diaphragm with 70% isopropyl alcohol was not sufficient to eliminate hepatitis C virus infectivity.

CONCLUSIONS

Hepatitis C virus can be transferred into commonly used medications when using sterile single-use needles and syringes where it remains viable for several days. Furthermore, cleaning the vial diaphragm with 70% isopropyl alcohol is not sufficient to eliminate the risk of hepatitis C virus infectivity. This highlights the potential risks associated with sharing medications between patients.

Modeling of patient virus titers suggests that availability of a vaccine could reduce hepatitis C virus transmission among injecting drug users

The major route of hepatitis C virus (HCV) transmission in the United States is injection drug use. We hypothesized that if an HCV vaccine were available, vaccination could affect HCV transmission among people who inject drugs by reducing HCV titers after viral exposure without necessarily achieving sterilizing immunity. To investigate this possibility, we developed a mathematical model to determine transmission probabilities relative to the HCV RNA titers of needle/syringe-sharing donors. We simulated sharing of two types of syringes fitted with needles that retain either large or small amounts of fluid after expulsion. Using previously published viral kinetics data from both naïve subjects infected with HCV and reinfected individuals who had previously cleared an HCV infection, we estimated transmission risk between pairs of serodiscordant injecting drug users, accounting for syringe type, rinsing, and sharing frequency. We calculated that the risk of HCV transmission through syringe sharing increased ~10-fold as viral titers (log₁₀ IU/ml) increased ~25-fold. Cumulative analyses showed that, assuming sharing episodes every 7 days, the mean transmission risk over the first 6 months was >90% between two people sharing syringes when one had an HCV RNA titer >5 log₁₀ IU/ml. For those with preexisting immunity that rapidly controlled HCV, the cumulative risk decreased to 1 to 25% depending on HCV titer and syringe type. Our modeling approach demonstrates that, even with transient viral replication after exposure during injection drug use, HCV transmission among people sharing syringes could be reduced through vaccination if an HCV vaccine were available.

Evaluating the Role of Cellular Immune Responses in the Emergence of HCV NS3 Resistance Mutations During Protease Inhibitor Therapy

The efficacy of protease inhibitor drugs in hepatitis C virus (HCV) treatment is limited by the selection and expansion of drug-resistant mutations. HCV replication is error-prone and genetic variability within the dominant epitopes ensures its persistence. The aims of this study are to evaluate the role of cellular immune response in the emergence of HCV protease resistance mutations and its effects on treatment outcome. Ten chronically HCV-infected subjects were treated with boceprevir (BOC)-based triple therapy. HCV-RNA was tested for BOC resistance-associated viral variants. HCV protease resistance mutations were investigated pretreatment and 24 weeks post-treatment. Synthetic peptides representing the wild-type and the potential nonstructural (NS)3 variants were used to evaluate T cell responses and human leukocyte antigen binding. Sustained viral response was achieved in 70% of patients, two patients were treatment nonresponders (NRs) and one was classified as a relapse. Pretreatment, the proportion of drug-resistant variants within individuals was higher in sustained viral responders (SVRs) than in NR patients. However, resistance-associated variants increased in NRs after BOC combined triple therapy. In contrast to NR patients, significant stronger cell-mediated immune responses were observed at the baseline among those who achieved sustained viral response for all T cell epitopes tested. Despite the increase in cell-mediated immune responses at week 24 in NRs, they failed to control the virus replication, leading to development of overt drug-resistant variants. Our data suggest that strong NS3-specific T cell immune responses at the baseline may predict a positive outcome of directly acting antiviral-based therapy, and the presence of pre-existent resistance mutations does not play a significant role in the outcome of anti-HCV combined therapy.

Cellular immune response to hepatitis-C-virus in subjects without viremia or seroconversion: is it important?

Hepatitis C Virus (HCV) causes chronic infection and represents a global health burden. To date, there is no licensed vaccine for HCV. The high viral replication rate and the existence of several HCV genotypes and quasispecies hamper the development of an effective universal vaccine. In this regard, the current HCV vaccine candidates show genotype-specific protection or narrow cross reactivity against other genotypes. Importantly, HCV spontaneous clearance occurs in 15-50 % of infected subjects, indicating that natural resistance to chronic infection exists. This phenomenon was demonstrated among humans and chimpanzees and continues to motivate researchers attempting to develop an effective HCV vaccine. However, what constitutes a protective immune response or correlate of protection against HCV infection is still vague. Additionally, the mechanisms behind successful HCV clearance suggest the coordination of several arms of the immune system, with cell-mediated immunity (CMI) playing a crucial role in this process. By contrast, although neutralizing antibodies have been identified, they are isolate-specific and poorly correlate with viral clearance. Antigen-specific CD4 T cells, instead, correlate with transient decline in HCV viremia and long-lasting control of the infection. Unfortunately, HCV has been very successful in evading host immune mechanisms, leading to complications such as liver fibrosis, cirrhosis and hepatocellular carcinoma. Interestingly, CMI to HCV antigens were shown among exposed individuals without viremia or seroconversion, suggesting the clearance of prior HCV infection(s). These individuals include family members living with HCV-infected subjects, healthcare workers, IV drug users, and sexual contacts. The correlates of protection could be closely monitored among these individuals. This review provides a summary of HCV-specific immune responses in general and of CMI in particular in these cohorts. The importance of these CMI responses are discussed.

Persistence of Hepatitis C Virus Traces after Spontaneous Resolution of Hepatitis C

Hepatitis C virus (HCV) frequently causes chronic hepatitis, while spontaneous recovery from infection is infrequent. Persistence of HCV after self-limited (spontaneous) resolution of hepatitis C was rarely investigated. The current study aimed to assess incidence and robustness of HCV persistence after self-resolved hepatitis C in individuals with normal liver enzymes and undetectable virus by conventional tests. Applying high sensitivity HCV RNA detection approaches, we analyzed plasma and peripheral blood mononuclear cells (PBMC) from individuals with previous hepatitis C infection. Parallel plasma and PBMC from 24 such non-viraemic individuals followed for 0.3–14.4 (mean 6.4) years were examined. Additional samples from 9 of them were obtained 4.5–7.2 (mean 5.9) years later. RNA was extracted from 250 μl plasma and, if HCV negative, from ~5 ml after ultracentrifugation, and from ex vivo stimulated PBMC. PBMC with evidence of HCV replication from 4 individuals were treated with HCV protease inhibitor, telaprevir. HCV RNA was detected in 14/24 (58.3%) plasma and 11/23 (47.8%) PBMC obtained during the first collection. HCV RNA replicative strand was evident in 7/11 (63.6%) PBMC. Overall, 17/24 (70.8%) individuals carried HCV RNA at mean follow-up of 5.9 years. Samples collected 4.5–7.2 years later revealed HCV in 4/9 (44.4%) plasma and 5/9 (55.5%) PBMC, while 4 (80%) of these 5 PBMC demonstrated virus replicative strand. Overall, 6/9 (66.7%) individuals remained viraemic for up to 20.7 (mean 12.7) years. Telaprevir entirely eliminated HCV replication in the PBMC examined. In conclusion, our results indicate that HCV can persist long after spontaneous resolution of hepatitis C at levels undetectable by current testing. An apparently effective host immune response curtailing hepatitis appears insufficient to completely eliminate the virus. The long-term morbidity of asymptomatic HCV carriage should be examined even in individuals who achieve undetectable HCV by standard testing and their need for treatment should be assessed.

Resistance to hepatitis C virus: potential genetic and immunological determinants

Studies of individuals who were highly exposed but seronegative (HESN) for HIV infection led to the discovery that homozygosity for the Δ32 deletion mutation in the CCR5 gene prevents viral entry into target cells, and is associated with resistance to infection. Additionally, evidence for protective immunity has been noted in some HESN groups, such as sex workers in The Gambia. Population studies of individuals at high risk for hepatitis C virus infection suggest that an HESN phenotype exists. The body of evidence, which suggests that protective immunity allows clearance of hepatitis C virus without seroconversion is growing. Furthermore, proof-of-principle evidence from in-vitro studies shows that genetic polymorphisms can confer resistance to establishment of infection. This Review discusses the possibility that genetic mutations confer resistance against hepatitis C virus, and also explores evidence for protective immunity, including via genetically programmed variations in host responses. The data generally strengthens the notion that investigations of naturally arising polymorphisms within the hepatitis C virus interactome, and genetic association studies of well characterised HESN individuals, could identify potential targets for vaccine design and inform novel therapies.

A comparison of seminal hepatitis C virus (HCV) RNA levels during recent and chronic HCV infection in HIV-infected and HIV-uninfected individuals

BACKGROUND

We aimed to characterize seminal hepatitis C virus (HCV) RNA dynamics in human immunodeficiency virus (HIV)-positive men with acute HCV infection given its potential role in sexual transmission of HCV.

METHODS

Men with acute HCV infection (duration, ≤12 months) or chronic HCV infection (duration, >12 months) were prospectively recruited. Paired semen and blood samples were assayed for HCV RNA levels. Results were analyzed using χ(2), Fisher exact, Mann-Whitney U, and Kruskal-Wallis tests.

RESULTS

Eighteen men (27.3%) had acute HCV and HIV coinfection, 22 (33.3%) had chronic HCV infection and HIV coinfection, and 26 (39.4%) had chronic HCV monoinfection. HCV RNA was detected in semen specimens from 29 of 66 men (43.9%). The median HCV RNA level in blood was 4.0 log IU/mL higher than that in semen. HCV RNA levels were correlated in semen and blood (r(2) = 0.142). Neither HIV positivity nor acute HCV infection was associated with an increased frequency of seminal HCV RNA detection. Among men with acute HCV and HIV coinfection, the median HCV RNA level in blood specimens from those with seminal HCV RNA was higher than that in blood specimens from those without seminal HCV RNA (P = .001). Seminal HCV RNA was detected in ≥1 sample for 26 of 35 men (74.3%) attending follow up.

CONCLUSIONS

HCV RNA was detected in semen during both acute and chronic HCV infection. This was unaffected by HIV positivity or the phase of HCV infection. Elevated seminal HCV RNA levels could contribute to sexual transmission of HCV, but other factors, including high-risk behaviors, may be the main drivers for HCV transmission in HIV-infected individuals.

Protection against hepatitis C infection via NK cells in highly-exposed uninfected injecting drug users

BACKGROUND & AIMS

HCV seroprevalence surveys in longstanding injecting drug users (IDUs) reveal a small minority who remain seronegative, with some exhibiting HCV-specific cellular immunity. This study aimed to characterise this immunity, assess associations with risk behaviours and protection against infection.

METHODS

A nested case-control series from a prospective cohort of seronegative IDUs was selected with incident cases (IN; n = 28) matched by demographics and risk behaviour to exposed uninfected (EU) subjects (n = 28). Samples were assayed for natural killer (NK) cell phenotypes and function, HCV-specific IFNγ in ELISpot, and HCV-specific CD4 T effector responses. IL28B and HLA-C/KIR2DL3 genotypes were tested.

RESULTS

Numbers of activated (CD69(+)) NK cells in the mature CD56(dim)CD16(+) subset, and cytotoxic (NKp30(+)) cells in the CD56(bright)CD16(+) subset were higher in the EU subjects (p = 0.040, p = 0.038 respectively). EU subjects had higher frequencies of interferon gamma (IFNγ) producing NK cells, and lower frequencies of CD107a expression (p = 0.003, p = 0.015 respectively). By contrast, the frequency, magnitude, and breadth of HCV-specific CD4 and CD8 T cell responses did not differ, nor did IL28B, HLA-C, or KIR2DL3 allele frequencies.

CONCLUSIONS

Sustained NK cell activation contributes to protection against HCV infection. HCV-specific cellular immunity is prevalent in EU subjects but does not appear to be protective.

Seronegative hepatitis C virus infection in patients with lymphoproliferative disorders

It has been reported that hepatitis C virus (HCV) RNA may be present in serum and/or lymphoid cells in the absence of specific circulating antibodies. The current study analysed seronegative HCV infection in patients with lymphoproliferative disorders. We studied 77 anti-HCV-negative patients (45 male and 32 female, mean age 54.8 ± 14.2 years) with various lymphoproliferative disorders. HCV-RNA was detected by RT-PCR in plasma, peripheral blood mononuclear cells (PBMC) and bone marrow. Furthermore, the presence of viral nonstructural protein 3 (NS3) was determined in PBMC and bone marrow by immunostaining. HCV-RNA was detectable in at least one compartment in 27 (35.1%) patients. Viral RNA was found in bone marrow in 22 patients (28.6%), in PBMC in 13 (16.9%) and in plasma in 10 (13%) patients. In nine patients, evidence of infection was confined to the bone marrow compartment. Viral load in HCV-RNA-positive plasma ranged from 15 to 1.17 × 10(3) IU/mL. NS3 was detected in all but two HCV-RNA-positive bone marrow samples and in all but one HCV-RNA-positive PBMC samples. All 27 HCV-RNA-positive patients remained anti-HCV-negative when tested again after 6-12 months, but only four remained HCV-RNA positive. In conclusion, among patients with lymphoproliferative disorders, HCV can be present in plasma, PBMC and bone marrow despite the lack of circulating specific antibodies. Further studies are required to analyse the phenomenon of seronegative infection and to determine whether such patients are infectious.

Detection of HCV-Specific IFN-γ Responses in HCV Antibody and HCV RNA Negative Injecting Drug Users

BACKGROUND

Detectable HCV-specific cellular immune responses in HCV antibody and RNA negative people who inject drugs (PWID) raise the question of whether some are resistant to HCV infection. Immune responses from people who have been exposed to hepatitis C virus (HCV) and remain anti-HCV negative are of interest for HCV vaccine development; however, limited research addresses this area.

OBJECTIVES

In a cohort of HCV antibody and RNA negative PWID, we assessed whether the presence of HCV-specific IFN-γ responses or genetic associations provide any evidence of protection from HCV infection.

PATIENTS AND METHODS

One hundred and ninety-eight participants were examined longitudinally for clinical, behavioral, social, environmental and genetic characteristics (IFNL3 genotype [formally IL-28B] and HLA type). Sixty-one of the 198 participants were HCV antibody and RNA negative, with 53 able to be examined longitudinally for HCV-specific IFN-γ ELISpot T cell responses.

RESULTS

Ten of the 53 HCV antibody and RNA negative participants had detectable HCV-specific IFN-γ responses at baseline (18%). The magnitude of IFN-γ responses averaged 131 +/- 96 SFC/106 PBMC and the breadth was mean 1 +/- 1 pool positive. The specificity of responses were mainly directed to E2, NS4b and NS5b. Participants with (10) and without (43) HCV-specific IFN-γ responses did not differ in behavioral, clinical or genetic characteristics (P > 0.05). There was a larger proportion sharing needles (with 70%, without 49%, P = 0.320) and a higher incidence of HCV (with 35.1 per 100 py, 95% CI 14.6, 84.4, without 16.0 per 100 py, 95% CI 7.2, 35.6, P = 0.212) in those with IFN-γ responses, although not statistically significant. Half the participants with baseline IFN-γ responses became HCV RNA positive (5/10), with one of these participants spontaneously clearing HCV. The spontaneous clearer had high magnitude and broad Th1 responses, favorable IFNL3 genotype and favorable HLA types.

CONCLUSIONS

This study demonstrated the detection of HCV-specific IFN-γ responses in HCV antibody and RNA negative individuals, with a tendency for HCV-specific IFN-γ responses to be associated with HCV exposure. The potential role of HCV-specific IFN-γ responses in those who remained HCV RNA negative is of value for the development of novel HCV therapeutics.

Innate immune responses in hepatitis C virus-exposed healthcare workers who do not develop acute infection

Hepatitis C virus (HCV) infection typically results in chronic disease with HCV outpacing antiviral immune responses. Here we asked whether innate immune responses are induced in healthcare workers who are exposed to small amounts of HCV, but do not develop systemic infection and acute liver disease. Twelve healthcare workers with accidental percutaneous exposure to HCV-infected blood were prospectively studied for up to 6 months for phenotype and function of natural killer T (NKT) and NK cells, kinetics of serum chemokines, and vigor and specificity of HCV-specific T-cell responses. Eleven healthcare workers tested negative for HCV RNA and HCV antibodies. All but one of these aviremic cases displayed NKT cell activation, increased serum chemokines levels, and NK cell responses with increased CD122, NKp44, NKp46, and NKG2A expression, cytotoxicity (as determined by TRAIL and CD107a expression), and interferon-gamma (IFN-γ) production. This multifunctional NK cell response appeared a month earlier than in the one healthcare worker who developed high-level viremia, and it differed from the impaired IFN-γ production, which is typical for NK cells in chronic HCV infection. The magnitude of NKT cell activation and NK cell cytotoxicity correlated with the magnitude of the subsequent HCV-specific T-cell response. T-cell responses targeted nonstructural HCV sequences that require translation of viral RNA, which suggests that transient or locally contained HCV replication occurred without detectable systemic viremia.

CONCLUSION

Exposure to small amounts of HCV induces innate immune responses, which correlate with the subsequent HCV-specific T-cell response and may contribute to antiviral immunity.

Occupational exposure to hepatitis C virus: early T-cell responses in the absence of seroconversion in a longitudinal cohort study

BACKGROUND

T-cell responses have been described in seronegative patients who test negative for hepatitis C virus (HCV) RNA despite frequent HCV exposure. However, the cross-sectional design of those studies did not clarify whether T cells were indeed induced by low-level HCV exposure without seroconversion or whether they resulted from regular acute infection with subsequent antibody loss.

METHODS

Over a 10-year period, our longitudinal study recruited 72 healthcare workers with documented HCV exposure. We studied viremia and antibody and T-cell responses longitudinally for 6 months.

RESULTS

All healthcare workers remained negative for HCV RNA and antibodies. However, 48% developed proliferative T-cell response and 42% developed responses in interferon-gamma enzyme-linked immunosorbent spot assays, with 29 healthy HCV-unexposed controls used to define assay cutoffs. The response prevalence was associated with the transmission risk score. T-cell responses peaked at week 4 and returned to baseline by week 12 after exposure. They predominantly targeted nonstructural HCV proteins, which are not part of the HCV particle and thus must have been synthesized in infected cells.

CONCLUSIONS

Subclinical transmission of HCV occurs frequently, resulting in infection and synthesis of nonstructural proteins despite undetectable systemic viremia. T-cell responses are more sensitive indicators of this low-level HCV exposure than antibodies.

Two distinct functional patterns of hepatitis C Virus (HCV)-specific T cell responses in seronegative, aviremic patients

In hepatitis C Virus (HCV) high-risk groups, HCV-specific T cell responses have been detected in seronegative, aviremic persons who have no evidence of HCV infection. Herein, we investigated functional profiles of HCV-specific T-cell responses in seronegative, aviremic patients of a HCV high-risk group. Seventy seven hemodialysis patients with chronic renal disease were analyzed by IFN-γ ELISpot assays, and eight of 71 (11.3%) seronegative, aviremic patients displayed HCV-specific T-cell responses. Their HCV-specific memory T cells were characterized by assessing cytokine polyfunctionality, known to provide antiviral protection. By intracellular staining of IFN-γ, TNF-α, IL-2 and MIP-1β, we identified two distinct populations in the seronegative, aviremic patients: polyfunctional responders and TNF-α-predominant responders. In further analysis, occult HCV infection was excluded as a cause of the HCV-specific T cell response via secondary nested RT-PCR of HCV RNA in peripheral blood mononuclear cell samples. HCV-specific T cells targeted multiple epitopes including non-structural proteins in a single patient, implying that their T cells might have been primed by HCV proteins synthesized within the host. We conclude that HCV-specific memory T cells of seronegative, aviremic patients arise from authentic HCV replication in the host, but not from current occult HCV infection. By functional pattern of HCV-specific T cells, there are two distinct populations in these patients: polyfunctional responders and TNF-α-predominant responders.

Correlates and characteristics of hepatitis C virus-specific T-cell immunity in exposed uninfected high-risk prison inmates

Some hepatitis C (HCV)-uninfected, high-risk individuals have HCV-specific cellular immunity without viraemia or seroconversion. The characteristics of these responses and the risk behavioural associations were studied in 94 subjects in a prospective cohort of recently seronegative prisoners reporting injecting drug use (IDU). Detailed behavioural data were collected. HCV antibody and PCR testing were performed. ELISpot assays for HCV-induced interferon (IFN)-γ and interleukin (IL)-2 production by T lymphocytes, as well as multiplex in vitro cytokine production assays, were performed. Seventy-eight subjects remained antibody and PCR negative and 16 seroconverted. Of the seronegative group, 22 (28%) had IFN-γ ELISpot responses in comparison with 13 of the 16 seroconverters (82%). This seronegative immune status was associated positively with injecting anabolic steroids and negatively with a recent break from IDU. The IFN-γ ELISpot responses involved both CD4 and CD8 T lymphocytes and were comparable in magnitude, but narrower in specificity, in uninfected subjects than in seroconverters. A subset of seronegative subjects had HCV-induced cytokine production patterns comparable with the seroconverters with increased production of IFN-γ, IL-2 and tumour necrosis factor (TNF)-α and reduced IL-10 in response to nonstructural peptides. In conclusion, comparable patterns of HCV-specific cellular immunity are found in recently infected subjects and in a minority of high-risk, uninfected subjects. Further characterization of these responses and their protective efficacy will inform HCV vaccine development.

Hepatitis C virus-specific cell-mediated immune responses in children born to mothers infected with hepatitis C virus

OBJECTIVE

To investigate the association between hepatitis C virus (HCV)-specific cell-mediated immunity (CMI) responses and viral clearance in children born to mothers infected with HCV.

STUDY DESIGN

A cross-sectional study of children from a mother-infant cohort in Egypt were enrolled to detect CMI responses to recombinant core and nonstructural HCV antigens (nonstructural segments NS3, NS4a/b, and NS5 of the HCV genome) using an interferon-gamma enzyme-linked immunospot assay. Children born to mothers with chronic HCV were enrolled into 3 groups: transiently viremic (n = 5), aviremic (n = 36), and positive control (n = 6), which consisted of 1 child with chronic HCV from this cohort and another 5 children with chronic HCV from a companion study. Children without HCV born to mothers without HCV (n = 27) served as a negative control group. Wilcoxon rank sum test was used to compare the magnitude of CMI responses between groups.

RESULTS

None of the 6 control children who were positive for HCV responded to any HCV antigen, and 4 (80%) of 5 children with transient viremia responded to at least one HCV antigen, compared with 5 (14%) of 36 and 3 (11%) of 27 children in the aviremic and negative control groups, respectively. Children with transient viremia elicited stronger responses than did negative controls (P = .005), positive controls (P = .011), or children without HCV viremia (P = .012), particularly to nonstructural antigens.

CONCLUSIONS

HCV-specific CMI responses were significantly higher in magnitude and frequency among transiently infected children compared with those persistently infected. This suggests CMI responses may be associated with past viral clearance and can identify children at high risk of infection, who can be targeted for health education, screening, and follow-up.

Transfusion transmission of HCV, a long but successful road map to safety

Improved blood banking practices and the development and implementation of increasingly sensitive serological and nucleic acid amplification technology assays for screening donors for HCV over the past few decades have helped minimize the residual risk from transfusion transmitted HCV in the developed world. Furthermore, studies of transfusion transmitted infections and of donors identified as infected by routine screening have provided significant insights into HCV transmission, epidemiology and pathogenesis. However, transfusion transmission of HCV is still a significant route of infection in the developing world. Key preventive mechanisms to ensure safe blood include elimination of paid donors and development of national donor pools comprising volunteer repeat blood donors, combined with implementation of standardized and maximally sensitive screening assays for HCV. There is also a need to develop up-to-date data on HCV disease burden on a global scale, in part, derived from systematic screening of donors for HCV infection. We suggest the creation of blood donor databases and specimen repositories, both at national and international levels, to facilitate epidemiological surveillance and pathogenesis and treatment studies in the future.

Transmission of hepatitis C virus among people who inject drugs: viral stability and association with drug preparation equipment

BACKGROUND

Hepatitis C virus (HCV) transmission among people who inject drugs remains a challenging public health problem. We investigated the risk of HCV transmission by analyzing the direct association of HCV with filters, water to dilute drugs, and water containers.

METHODS

Experiments were designed to replicate practices by people who inject drugs and include routinely used injection equipment. HCV stability in water was assessed by inoculation of bottled water with HCV. Viral association with containers was investigated by filling the containers with water, inoculating the water with HCV, emptying the water, and refilling the container with fresh water. Transmission risk associated with drug preparation filters was determined after drawing virus through a filter and incubating the filter to release infectious particles.

RESULTS

HCV can survive for up to 3 weeks in bottled water. Water containers present a risk for HCV transmission, as infectious virions remained associated with water containers after washing. Physical properties of the water containers determined the degree of HCV contamination after containers were refilled with water. HCV was also associated with filter material, in which around 10% of the viral inoculum was detectable.

CONCLUSIONS

This study demonstrates the potential risk of HCV transmission among injection drug users who share water, filters, and water containers and will help to define public health interventions to reduce HCV transmission.

Two pathogen reduction technologies--methylene blue plus light and shortwave ultraviolet light--effectively inactivate hepatitis C virus in blood products

BACKGROUND

Contamination of blood products with hepatitis C virus (HCV) can cause infections resulting in acute and chronic liver diseases. Pathogen reduction methods such as photodynamic treatment with methylene blue (MB) plus visible light as well as irradiation with shortwave ultraviolet (UVC) light were developed to inactivate viruses and other pathogens in plasma and platelet concentrates (PCs), respectively. So far, their inactivation capacities for HCV have only been tested in inactivation studies using model viruses for HCV. Recently, a HCV infection system for the propagation of infectious HCV in cell culture was developed.

STUDY DESIGN AND METHODS

Inactivation studies were performed with cell culture-derived HCV and bovine viral diarrhea virus (BVDV), a model for HCV. Plasma units or PCs were spiked with high titers of cell culture-grown viruses. After treatment of the blood units with MB plus light (Theraflex MB-Plasma system, MacoPharma) or UVC (Theraflex UV-Platelets system, MacoPharma), residual viral infectivity was assessed using sensitive cell culture systems.

RESULTS

HCV was sensitive to inactivation by both pathogen reduction procedures. HCV in plasma was efficiently inactivated by MB plus light below the detection limit already by 1/12 of the full light dose. HCV in PCs was inactivated by UVC irradiation with a reduction factor of more than 5 log. BVDV was less sensitive to the two pathogen reduction methods.

CONCLUSIONS

Functional assays with human HCV offer an efficient tool to directly assess the inactivation capacity of pathogen reduction procedures. Pathogen reduction technologies such as MB plus light treatment and UVC irradiation have the potential to significantly reduce transfusion-transmitted HCV infections.

Infectivity in chimpanzees (Pan troglodytes) of plasma collected before HCV RNA detectability by FDA-licensed assays: implications for transfusion safety and HCV infection outcomes

Serial plasma aliquots (50 mL) obtained from 10 commercial donors who converted from hepatitis C virus (HCV) RNA negative to positive were transfused into 2 chimpanzees to assess infectivity during early HCV infection. Plasma, obtained 4 days before HCV RNA detectability by licensed assays, transmitted HCV infection to chimpanzee X355. The infectious PCR-negative plasma was subsequently shown to be positive in 2 of 23 replicates using a sensitive transcription-mediated amplification (TMA) assay, and estimated to contain 1.2 HCV RNA copies/mL (60 copies/50 mL transfused). Plasma units obtained up to 8 weeks earlier were not infectious in a second susceptible chimp, even when from donors with low-level, intermittent HCV RNA detection. Chimp x355 developed acute viremia with subsequent seroconversion, but cleared both virus and Ab in 17 weeks. When rechallenged 38 months later with 6000 RNA copies/mL from the same donor, X355 was transiently reinfected and again rapidly lost all HCV markers. We conclude that: (1) transfusions can transmit HCV infection before RNA detection, but the interval of test-negative infectivity is very brief; (2) early "blips" of HCV RNA appear noninfectious and can be ignored when calculating residual transfusion risk; and (3) markers of HCV infection can be lost rapidly after exposure to low-dose inocula.

Hepatitis C virus-multispecific T-cell responses without viremia or seroconversion among Egyptian health care workers at high risk of infection

Hepatitis C virus (HCV)-specific cell-mediated immunity (CMI) has been reported among exposed individuals without viremia or seroconversion. Limited data are available regarding CMI among at-risk, seronegative, aviremic Egyptian health care workers (HCW), where HCV genotype 4 predominates. We investigated CMI responses among HCW at the National Liver Institute, where over 85% of the patients are HCV infected. We quantified HCV-specific CMI in 52 seronegative aviremic Egyptian HCW using a gamma interferon (IFN-γ) enzyme-linked immunospot assay in response to 7 HCV genotype 4a overlapping 15-mer peptide pools covering most of the viral genome. A positive HCV-specific IFN-γ response was detected in 29 of 52 HCW (55.8%), where 21 (40.4%) had a positive response for two to seven HCV pools and 8 (15.4%) responded to only one pool. The average numbers of IFN-γ total spot-forming cells (SFC) per million peripheral blood mononuclear cells (PBMC) (± standard error of the mean [SEM]) in the 29 responding and 23 nonresponding HCW were 842 ± 141 and 64 ± 15, respectively (P < 0.001). Flow cytometry indicated that both CD4(+) and CD4(-) T cells produced IFN-γ. In summary, more than half of Egyptian HCW demonstrated strong HCV multispecific CMI without viremia or seroconversion, suggesting possible clearance of low HCV exposure(s). These data suggest that detecting anti-HCV and viremia to determine past exposure to HCV can lead to an underestimation of the true disease exposure and that CMI response may contribute to the low degree of chronic HCV infection in these HCW. These findings could have strong implications for planning vaccine studies among populations with a high HCV exposure rate. Further studies are needed to determine whether these responses are protective.

Occult infection with hepatitis C virus: friend or foe?

Hepatitis C virus (HCV) infection is a global pandemic associated with a growing disease burden due to cirrhosis and the consequent morbidity and mortality. Transmission is largely via blood-to-blood contact. Following primary infection, a minority of individuals clear the infection predominantly via cellular immune mechanisms, whereas the majority become chronically infected. Recent data suggest that a third outcome may also be possible, termed 'occult' infection in which subjects who are known, or suspected to have previously been infected with HCV, no longer have viral RNA in their serum at levels detectable by sensitive commercial assays, but do have virus detected by ultra-sensitive techniques. Occult infection has also been detected in peripheral blood mononuclear cells, which may indicate an extra-hepatic reservoir of the virus. Although the clinical significance of occult infection remains unknown, most authors have raised concerns of recrudescent infection. Here we critically review the published literature, suggest further avenues of investigation and propose that occult infection may be beneficial to the host by maintaining immunological memory to protect against reinfection.

Cellular immune responses and occult infection in seronegative heterosexual partners of chronic hepatitis C patients

It is unknown whether hepatitis C virus (HCV)-specific cellular immune responses can develop in seronegative sexual partners of chronically HCV-infected patients and whether they have occult infection. Thirty-one heterosexual partners of patients with chronic HCV were studied, fifteen of them with HCV transmission risks. Ten healthy individuals and 17 anti-HCV seropositive patients, without viremia, were used as controls. Virus-specific CD4+ and CD8+ T-cell responses were measured by flow cytometry against six HCV peptides, situated within the nonstructural (NS) proteins NS3, NS4 and NS5, through intracellular detection of gamma interferon (IFN-γ) or interleukin 4 (IL-4) production and CD69 expression. Sexual partners had a higher production of IFN-γ and IL-4 by CD4+ cells against NS3-p124 (P = 0.003), NS5b-p257 (P = 0.005) and NS5b-p294 (P = 0.012), and CD8+ cells against NS3-p124 (P = 0.002), NS4b-p177 (P = 0.001) and NS3-p294 (P = 0.004) as compared with healthy controls. We observed elevated IFN-γ production by CD4+ T cells against NS5b-p257 (P = 0.042) and NS5b-p294 (P = 0.009) in the sexual partners with HCV transmission risks (sexual, professional and familial altogether) than in those without risks. RNA was extracted from peripheral blood mononuclear cells (PBMC), and detection of HCV-RNA positive and replicative (negative) strands was performed by strand-specific real-time PCR. In four sexual partners, the presence of positive and negative HCV- RNA strands in PBMC was confirmed. Hence, we found an HCV-specific cellular immune response as well as occult HCV infection in seronegative and aviremic sexual partners of chronically HCV-infected patients.

Acute hepatitis C in Korea: different modes of infection, high rate of spontaneous recovery, and low rate of seroconversion

The epidemiology and clinical outcomes of acute hepatitis C are different geographically. This study aimed to investigate the mode of infection, clinical characteristics, and outcomes of acute hepatitis C in Korea. Forty-seven patients with acute hepatitis C were enrolled consecutively in a study conducted in seven medical centers. The patients with the mean age of 45.8 years had mostly mild symptoms. A healthcare-related procedure was the most common exposure history (42.5%): acupuncture (17%), surgery (10.6%), needle-stick injury (8.5%), and other medical procedures (6.4%). There was no case of intravenous drug use. Twenty-one patients (44.7%) recovered spontaneously. Among the 16 patients who received antiviral therapy (34%), all of the 12 evaluable patients had a sustained virologic response, while 10 patients (21.3%) who did not receive antiviral therapy progressed to chronic infection. The overall seroconversion rate of anti-HCV antibody was 61.7%. The patients who recovered spontaneously had significantly lower rate of seroconversion compared with the patients who did not clear spontaneously the infection. In conclusion, acute hepatitis C in Korea was related to various healthcare procedures, including acupuncture, characterized by high rates of spontaneous recovery and low rates of seroconversion, which may be associated with different modes of infection and ethnic differences. The characteristics of acute hepatitis C in Asian countries warrants further study.

Strong hepatitis C virus (HCV)-specific cell-mediated immune responses in the absence of viremia or antibodies among uninfected siblings of HCV chronically infected children

BACKGROUND

Cell-mediated immune (CMI) responses to hepatitis C virus (HCV) antigens in adults without seroconversion or viremia are biomarkers for prior transient infection. We investigated HCV-specific CMI responses in seronegative children living with HCV-infected siblings.

METHODS

Children 3-18 years of age living with HCV-infected siblings were screened for HCV antibodies and HCV RNA. Peripheral blood mononuclear cells (PBMCs) were evaluated for HCV-specific CMI responses by interferon γ (IFN-γ) enzyme-linked immunospot assay using 3 recombinant HCV protein antigens. Flow cytometry phenotypically characterized IFN-γ-secreting cells.

RESULTS

Forty-five seronegative children and 5 seropositive viremic siblings had functionally viable PBMCs. Among the 45 seronegative siblings, 15 (33.3%) had positive HCV-specific IFN-γ responses, and subsequent RNA testing revealed that 3 were viremic. Compared with the 5 seropositive viremic children, the median number of HCV-specific spot-forming units was significantly higher in the 12 seronegative aviremic children (P = .002) and in the 3 seronegative viremic children (P = .025). Flow cytometric analysis revealed that IFN-γ was synthesized mainly by CD4(+) T cells.

CONCLUSION

Strong HCV-specific CD4(+) T cell responses were detectable in higher frequency among seronegative, aviremic children compared with persistently infected siblings. Further studies are needed to determine whether these immune responses are protective against HCV infection.

Antibody dynamics and spontaneous viral clearance in patients with acute hepatitis C infection in Rio de Janeiro, Brazil

Background

The anti-HCV antibody response has not been well characterized during the early phase of HCV infection and little is known about its relationship to the clinical course during this period.

Methods

We analyzed serial anti-HCV antibodies longitudinally obtained from a prospective cohort of 65 patients with acute HCV infection by using a microparticle enzyme immunoassay AxSYM HCV 3.0 (Abbott Diagnostics) during the first 12 months from HCV acquisition in Rio de Janeiro, Brazil. Spontaneous viral clearance (SVC) was defined as undetectable HCV RNA in serum, in the absence of treatment, for three consecutive HCV PCR tests within 12-months of follow-up.

Results

Baseline antibody values were similar among patient groups with self-limiting HCV evolution (n = 34) and persistent viremia (n = 31) [median (interquartile range) signal/cut-off ratio (s/co) 78.7 (60.7-93.8) vs. 93.9 (67.8-111.9), p = 0.26]. During 12-months follow-up, patients with acute spontaneous resolving HCV infection showed significantly lower serial antibody response in comparison to individuals progressing to chronic infection [median (interquartile range) s/co 62.7 (35.2-85.0) vs. 98.4 (70.4-127.4), p < 0.0001]. In addition, patients with self-limiting HCV evolution exhibited an expeditious, sharp decline of serial antibody values after SVC in comparison to those measured before SVC [median (interquartile range) s/co 56.0 (25.4-79.3) vs. 79.4 (66.3-103.0), p < 0.0001].

Conclusion

Our findings indicate a rapid short-term decline of antibody values in patients with acute spontaneous resolving HCV infection.

Meta-analysis of hepatitis C virus vaccine efficacy in chimpanzees indicates an importance for structural proteins

BACKGROUND & AIMS

Studies in patients and chimpanzees that spontaneously cleared hepatitis C virus (HCV) infections demonstrated that natural immunity to the virus is induced during primary infections and that this immunity can be cross protective. These discoveries led to optimism about prophylactic HCV vaccines, and several studies were performed in chimpanzees, although most included fewer than 6 animals. To draw meaningful conclusions about the efficacy of HCV vaccines in chimpanzees, we performed statistical analyses of data from previously published studies from different groups.

METHODS

We performed a meta-analysis that compared parameters among naïve (n = 63), vaccinated (n = 53), and rechallenged (n = 36) animals, including peak RNA titer postchallenge, time points of peak RNA titer, duration of viremia, and proportion of persistent infections.

RESULTS

Each vaccination study induced immune responses that were effective in rapidly controlling HCV replication. Levels of induced T-cell responses did not indicate vaccine success. There was no reduction in the rate of HCV persistence in vaccinated animals, compared with naïve animals, when nonstructural proteins were included in the vaccine. Vaccines that contained only structural proteins had clearance rates that were significantly higher than vaccines that contained nonstructural components (P = .015).

CONCLUSIONS

The inclusion of nonstructural proteins in HCV vaccines might be detrimental to protective immune responses, and/or structural proteins might activate T-cell responses that mediate viral clearance.

Prospective follow-up of patients with acute hepatitis C virus infection in Brazil

BACKGROUND

The natural outcome of infection with hepatitis C virus (HCV) varies substantially among individuals. However, little is known about host and viral factors associated with a self-limiting or chronic evolution of HCV infection.

METHODS

From 1 January 2001 through 31 December 2008, a consecutive series of 65 patients from Rio de Janeiro, Brazil, with a well-documented diagnosis of acute HCV infection, acquired via various routes, were enrolled in this study. Patients were prospectively followed up for a median of 40 months after the estimated date of HCV infection with serial measurements of serum alanine aminotransferase, HCV RNA, and anti-HCV antibodies. Spontaneous viral clearance (SVC) was defined as undetectable levels of HCV RNA in serum, in the absence of treatment, for 3 consecutive HCV polymerase chain reaction tests within the first 6 months of follow-up. Cox proportional hazards regression was used to identify host and viral predictors of SVC.

RESULTS

The cumulative rate of SVC was 44.6% (95% confidence interval, 32.3%-57.5%). Compared with chronic HCV evolution, patients with self-limiting disease had significantly lower peak levels of anti-HCV antibodies (median, 109.0 vs 86.7 optical density-to-cutoff ratio [od/co]; P<.02), experienced disease symptoms more frequently (69.4% vs 100%; P<.001), and had lower viral load at first clinical presentation (median, 4.3 vs 0.0 log copies; P=.01). In multivariate analyses, low peak anti-HCV level (<93.5 od/co) was the only independent predictor for SVC; the hazard ratio compared with high anti-HCV levels (> or =93.5 od/co) was 2.62 (95% confidence interval, 1.11-6.19; P=.03).

CONCLUSION

Our data suggest that low levels of anti-HCV antibodies during the acute phase of HCV infection are independently related to spontaneous viral clearance.

Risk factors and immune response to hepatitis E viral infection among acute hepatitis patients in Assiut, Egypt

Hepatitis E virus (HEV) infection is a common cause of acute viral hepatitis (AVH) in Egypt. We aimed to identify risk factors of HEV among acute hepatitis cases, measure HEV specific immune response to differentiate between symptomatic and asymptomatic infections. The study included symptomatic acute hepatitis (AH) patients (n = 235) and asymptomatic contacts (n = 200) to HEV cases. They completed a lifestyle questionnaire, screened for common hepatotropic viruses. Blood and serum samples were collected from patients and contacts after onset of disease and follow-up samples collected until convalescence. PBMC were separated and tested for specific HEV T-cell response by INF-gamma ELISPOT assay. Serum samples were tested for IgM and IgG anti-hepatitis E virus by ELISA. IgM antibodies to HAV were detected in 19 patients (8.1%), 37 (15.7%) with HBV, 10 (4.3%) with HCV. HEV infection was identified in 42 (16%) patients with AVH. Of the 200 contacts, 14 (7%) had serological evidence of recent HEV asymptomatic infection, showed stronger CMI responses than HEV infected subjects (2540 +/- 28 and 182 +/- 389 ISCs/106 cells, respectively; P < 0.05). In conclusion, HEV is a major cause of AVH in Egypt. Asymptomatic HEV patients are likely to have stronger immune responses including CMI responses, than symptomatic cases.

Chimpanzees in hepatitis C virus research: 1998-2007

BACKGROUND

Chimpanzees have been widely used in hepatitis C virus (HCV) research, but their endangered status and high financial and ethical costs have prompted a closer review.

METHODS

One hundred and nine articles published in 1998-2007 were analyzed for the number of chimpanzees involved, experimental procedures, objectives and other relevant issues.

RESULTS

The articles described the use of 852 chimpanzees, but accounting for likely multiple uses, the number of individual chimpanzees involved here is estimated to be approximately 500. Most articles addressed immunology and inoculation studies. A significant portion of studies lasted for several months or years. Approximately one half of the individual chimpanzees were each used in 2-10 studies.

CONCLUSIONS

Significant financial and scientific resources have been expended in these chimpanzee HCV studies. Discussion addresses troublesome questions presented by some of the reviewed articles, including statistical validity, repeatability, and biological relevance of this model. These concerns merit attention as future approaches to HCV research and research priorities are considered.

Prospective cohort study of mother-to-infant infection and clearance of hepatitis C in rural Egyptian villages

Although persistent transmission of hepatitis C virus (HCV) from infected mothers to their infants is reported in 4-8%, transient HCV perinatal infection also occurs. This prospective cohort study determined perinatal HCV infection- and early and late clearance-rates in 1,863 mother-infant pairs in rural Egyptian villages. This study found 15.7% and 10.9% of pregnant women had HCV antibodies (anti-HCV) and HCV-RNA, respectively. Among 329 infants born of these mothers, 33 (10.0%) tested positive for both anti-HCV and HCV-RNA 2 months following birth-29 (12.5%) having HCV-RNA positive mothers and 4 (with transient infections) having mothers with only anti-HCV. Fifteen remained HCV-RNA positive at one and/or 2 years (persistent infections), while 18 cleared both virus and antibody by 1 year (transient infections). Among the 15 persistent cases, 7 cleared their infections by 2 or 3 years. At 2- to 6- and at 10- to 12-month maternally acquired anti-HCV was observed in 80% and 5% of infants, respectively. Four perinatally infected and one transiently infected infant were confirmed to be infected by their mothers by the sequence similarity of their viruses. Viremia was 155-fold greater in mothers of infants with persistent than mothers of infants with transient infections. Maternal-infant transmission of HCV is more frequent than generally reported. However, both early and late clearance of infection frequently occurs and only 15 (4.6%) and 8 (2.4%) infants born of HCV-RNA positive mothers had detectable HCV-RNA at one and 2-3 years of age. Investigating how infants clear infection may provide important information about protective immunity to HCV.

Identification of serologically silent occult hepatitis C virus infection by detecting immunoglobulin G antibody to a dominant HCV core peptide epitope

BACKGROUND/AIMS

Occult HCV infection has been described among anti-HCV-HCV RNA-negative individuals with abnormal transaminase values in whom HCV RNA is detected in liver.

METHODS

IgG antibody to an HCVcore-derived peptide (anti-HCVcore) was investigated in 145 patients with serologically silent occult HCV infection.

RESULTS

At the time of the diagnostic biopsy 45/145 (31%) occult HCV-infected patients tested IgG anti-HCVcore-positive but none of the 140 patients with HCV-unrelated liver disease (P<0.001). Among 23 IgG anti-HCVcore-positive patients at baseline, 22 remained antibody-reactive (one became antibody-negative). Similarly, 17/31 baseline anti-HCVcore-negative patients remained non-reactive whereas 14 seroconverted to IgG anti-HCVcore (although transiently in 10 patients). Thus, a total of 59/145 (40.7%) patients with occult HCV infection showed IgG anti-HCVcore reactivity at any time point analyzed, including 14 initially non-reactive patients. By supplemental immunoblot assay 16 sera reacted weakly with an HCVcore-peptide band (indeterminate result) of which 10 (62.5%) reacted in the IgG anti-HCVcore assay. Occult HCV-infected patients who tested anti-HCVcore-positive showed more frequently signs of necro-inflammation (P=0.035) and greater percentages of HCV RNA-positive hepatocytes (P=0.004) compared with those anti-HCVcore-negative.

CONCLUSIONS

This work documents that IgG anti-HCVcore testing identifies occult HCV infection among seronegative, non-viremic patients using screening tests and may be useful in tracking anti-HCV-negative infections.

Hepatitis C virus (HCV)--specific T cell responses in injection drug users with apparent resistance to HCV infection

BACKGROUND

Injection drug users (IDUs) are at risk of acquiring hepatitis C virus (HCV) infection. We have identified a cohort of long-term IDUs who remain uninfected by HCV despite high-risk behavior. We have categorized these subjects as "exposed uninfected" and have sought immunological correlates with this apparent resistance.

METHODS

We studied 40 exposed uninfected subjects testing negative for both HCV antibody and HCV RNA. Details of injection behavior were ascertained by questionnaire. In vitro interferon (IFN)-gamma production by T cells in response to HCV proteins (core, E1, NS3, NS4, and NS5) was quantified by enzyme-linked immunospot assay, and findings were compared with those in 21 healthy control subjects.

RESULTS

All exposed uninfected subjects reported sharing needles or other injection paraphernalia on multiple occasions. The mean duration of injecting was 9.3 years (range, 0.5-26 years), with a median estimated number of injection episodes of 8760. IFN-gamma production in response to HCV proteins was found in 23 (58%) of 40 exposed uninfected subjects versus 4 (19%) of 21 control subjects (P = .004), with 14 exposed uninfected subjects responding to multiple antigens, compared with none of the control subjects (P = .001).

CONCLUSIONS

The majority of long-term IDUs who remain uninfected by HCV despite their high-risk behavior have HCV-specific T cell responses. These responses were frequently found for multiple HCV proteins, making cross-reactivity to other homologous antigens unlikely. These responses may represent an immunological footprint of HCV exposure that has not resulted in viremia or HCV antibody seroconversion. The potential role played by these responses in protection from HCV infection is of clinical importance.

Occult hepatitis B virus and hepatitis C virus infections

Occult HBV infection is a well-recognised clinical entity characterised by the detection of HBV-DNA in serum and/or in liver in the absence of detectable hepatitis B surface antigen (HBsAg). Occult HBV infection has been described not only in patients who have resolved an acute or chronic HBV infection but also in patients without any serological markers of a past HBV infection. Occult HBV infection in patients with chronic HCV infection may induce more severe liver disease and lower response rate to interferon treatment. The existence of occult HCV infections has been also reported more recently. Occult HCV infection is characterised by the presence of HCV-RNA in liver and peripheral blood mononuclear cells in the absence of detectable serum HCV-RNA. Occult HCV infection may occur under two different clinical situations: in hepatitis C antibody-(anti-HCV) negative and serum HCV-RNA-negative patients with abnormal liver function tests and in anti-HCV-positive patients who have no detectable serum HCV-RNA and who have normal liver enzymes. The clinical relevance of occult HCV infections is still under investigation.

Characterization of hepatitis E-specific cell-mediated immune response using IFN-gamma ELISPOT assay

In developing countries, hepatitis E (HEV) and hepatitis A (HAV) are the major causes of acute viral hepatitis with similar feco-oral modes of transmission. In contrast to the high seroprevalence of hepatitis A infection, a low seroprevalence of HEV among children in endemic areas has been reported. These data suggest the possibility that silent HEV infection is undiagnosed by the current available methods. Many of the serological tests used for HEV diagnosis have poor specificity and are unable to differentiate among different genotypes of HEV. Moreover, the RT-PCR used for HEV isolation is only valid for a brief period during the acute stage of infection. Cell-mediated immune (CMI) responses are highly sensitive, and long lasting after sub-clinical infections as shown in HCV and HIV. Our objective was to develop a quantitative assay for cell-mediated immune (CMI) responses in HEV infection as a surrogate marker for HEV exposure in silent infection. Quantitative assessment of the CMI responses in HEV will also help us to evaluate the role of CMI in HEV morbidity. In this study, an HEV-specific interferon-gamma (IFN-gamma) ELISPOT assay was optimized to analyze HEV-specific CMI responses. We used peripheral blood mononuclear cells (PBMC) and sera from experimentally infected chimpanzees and from seroconverted and control human subjects to validate the assay. The HEV-specific IFN-gamma ELISPOT responses correlated strongly and significantly with anti-HEV ELISA positive/negative results (rho=0.73, p=0.02). Moreover, fine specificities of HEV-specific T cell responses could be identified using overlapping HEV ORF2 peptides.

Verletzungen mit Hepatitis-C-Virus-kontaminierten Nadeln

The risk of infection after injury with a needle contaminated with hepatitis C virus (HCV) is thought to be about 3%, but this assumption is mainly based on studies published in the 1990's, which were limited by small sample sizes and insensitive HCV-RNA assays. We therefore investigated needle injuries at the Hannover Medical School over a period of 6 years and performed a systematic review of the literature identifying 22 studies with a total of 6,956 injuries with HCV contaminated needles. Between 2000 and 2005, 1,431 occupational injuries were reported at our institution and two-thirds were needle injuries. Index patients were known to be HCV infected in 166 cases but there were no cases of HCV seroconversion during follow-up. Analysis of published data showed seroconversion rates of 0-10.3% with a mean of 0.75% (52/6,956). The risk of acute HCV infection was lower in Europe with 0.42% compared to Eastern Asia with 1.5% of cases where an HCV viremia was reported during follow-up. In summary, the risk of acquiring an HCV infection after a needlestick injury is lower than frequently reported. Worldwide differences in HCV seroconversion rates suggest that genetic factors might provide some level of natural resistance against HCV. Future studies should address not only the frequency of acute hepatitis but also factors associated with a higher risk of becoming HCV infected.

In vivo study of the HC-TN strain of hepatitis C virus recovered from a patient with fulminant hepatitis: RNA transcripts of a molecular clone (pHC-TN) are infectious in chimpanzees but not in Huh7.5 cells

Both viral and host factors are thought to influence the pathogenesis of hepatitis C virus (HCV) infection. We studied strain HC-TN (genotype 1a), which caused fulminant hepatic failure in a patient and, subsequently, severe hepatitis in a chimpanzee (CH1422), to analyze the relationship between disease severity, host immune response, viral evolution, and outcome. A second chimpanzee (CH1581) was infected from CH1422 plasma, and a third chimpanzee (CH1579) was infected from RNA transcripts of a consensus cDNA of HC-TN (pHC-TN). RNA transcripts of pHC-TN did not replicate in Huh7.5 cells, which were recently found to be susceptible to infection with another fulminant HCV strain (JFH1). The courses of viremia were similar in the three animals. However, CH1581 and CH1579 developed a less severe acute hepatitis than CH1422. CH1579 and CH1422 resolved the infection, whereas CH1581 became persistently infected. CH1579 and CH1581, despite their differing outcomes, both developed significant intrahepatic cellular immune responses, but not antibodies to the envelope glycoproteins or neutralizing antibodies, during the acute infection. We analyzed the polyprotein sequences of virus recovered at five and nine time points from CH1579 and CH1581, respectively, during the first year of follow-up. High mutation rates and high proportions of nonsynonymous mutations suggested immune pressure and positive selection in both animals. Changes were not selected until after the initial decrease in virus titers and after the development of immune responses and hepatitis. Subsequently, however, mutations emerged repeatedly in both animals. Overall, our results indicate that disease severity and outcome of acute HCV infection depend primarily on the host response.

Induction of hepatitis C virus (HCV)-specific T cells by needle stick injury in the absence of HCV-viraemia

BACKGROUND

The risk of hepatitis C virus (HCV) infection after occupational exposure is low with seroconversion rates between 0 and 5%. However, factors associated with natural resistance against HCV after needle stick injury are poorly defined. HCV-specific T-cell responses have been described in cross-sectional studies of exposed HCV-seronegative individuals.

MATERIALS AND METHODS

In this study, we prospectively followed 10 healthcare professionals who experienced an injury with an HCV-contaminated needle. Blood samples were taken on the day or the day after the event and at different time points during follow-up for up to 32 months. HCV-specific T-cell responses were investigated directly ex vivo and in T-cell lines.

RESULTS

None of the individuals became positive for HCV-RNA in serum tested with the highly sensitive transcription-mediated amplification (TMA)-assay or in peripheral blood mononuclear cells (PBMC). All of them remained anti-HCV negative throughout follow-up. At the time of injury, HCV-specific CD4+ T-cell responses were already detectable in two individuals and became detectable thereafter in three additional persons. Transient HCV-specific CD8+ T-cell responses developed in two HLA-A2 positive patients, which became negative until the most recent follow-up after 5 and 17 months, respectively.

CONCLUSION

We demonstrate the development of HCV-specific T cells in HCV-exposed individuals after needle stick injury indicating subinfectious exposure to HCV. T-cell immunity against HCV may contribute to the low prevalence of HCV in medical healthcare professionals in Western countries.