Antibody to hepatitis C virus second envelope (HCV-E2) glycoprotein: a new marker of HCV infection closely associated with viremia

Dural Marginal Zone Lymphoma in a Patient With a Hepatitis C Virus Infection

Primary dural marginal zone lymphomas (MZLs) are exceptionally rare, with fewer than 100 cases reported to date. While the association between hepatitis C virus (HCV) infection and lymphoma is well established, it is unclear if this association extends to all anatomic sites. Here we report a case of dural MZL in a 61-year-old woman with an HCV infection. To our knowledge, this is the first report of a dural MZL associated with an HCV infection in an immunocompetent patient and was successfully treated with radiotherapy and rituximab. As such, future cases of primary MZL found in the dura should prompt consideration of co-infection with microbials such as HCV and upfront treatment with anti-virals should be considered.

HCV infection and non-Hodgkin lymphomas: an evolving story

Hepatitis C virus infection represents a global health problem with 3% of population infected worldwide. Several epidemiological studies have shown an increased risk of B cell non-Hodgkin lymphomas in HCV-infected subjects with a wide geographic variability. The observation that HCV eradication by antiviral treatment is associated with successful lymphoma response provided the most convincing evidence for the causal role of HCV in lymphoma's development. According to the most accepted model, HCV-driven chronic antigenic stimulation may represent the major stimulus for lymphoma growth. Several evidences have led to recommend antiviral therapy (in the past interferon-based, now the new direct-acting antiviral agents) in the setting of asymptomatic indolent B cell lymphomas not requiring an immediate systemic treatment. The favourable profile of direct-acting antiviral agents supports the HCV eradication also in the setting of HCV-positive diffuse large B cell lymphoma; however, further studies are needed to assess the appropriate timing of these drugs in the treatment of aggressive lymphomas. Multidisciplinary management involving expert hepatologists is highly warranted.

Hepatitis B and C virus infection and risk of haematological malignancies

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are classified as oncogenic human viruses. Chronic HBV and HCV infections are associated with higher risk of haematological malignancy development. Direct and indirect oncogenic mechanisms have been demonstrated for both HBV and HCV in several studies. HCV and overt/occult HBV infections in patients with oncohaematological disease constitute an impediment and a threat during immunosuppressive chemotherapy treatment. We review the HBV and HCV oncogenic mechanisms and the impact and the safety of antiviral treatment in patients with haematological malignancies.

Hepatitis C virus - Associated marginal zone lymphoma

The link between hepatitis C virus (HCV) infection and the development of B-cell non-Hodgkin lymphoma is now well established and based on a number of epidemiological studies. It is further supported by the observation of lymphoma regression after HCV eradication by antiviral treatment. The far most frequent entities are marginal zone lymphoma (MZL) and diffuse large B-cell lymphoma (DLBCL). MZL usually emerge on a background of mixed cryoglobulinemia, a low-grade lymphoproliferation, and often transform into DLBCL, thereby following a multistep oncogenesis process. The role of HCV in lymphomagenesis is not yet fully understood but several mechanisms have been proposed including (i) chronic external stimulation through the B-cell receptor and other surface receptors, and (ii) direct transformation by intracellular viral proteins, the former being probably predominant in MZL. Regression of HCV-associated MZL can be achieved with antiviral therapy and the novel generation of direct-acting antiviral agents appears highly effective and safe for the treatment of these lymphoma.

Antibodies to the Novel Human Pegivirus 2 Are Associated with Active and Resolved Infections

A novel blood-borne human pegivirus (HPgV), HPgV-2, was recently identified in hepatitis C virus (HCV)-infected individuals and individuals who had received multiple transfusions. Robust serological assays capable of detecting antibodies in HPgV-2-infected individuals are needed to establish global seroprevalence rates and potential disease associations. The two objectives of this study were to determine the utility of mammalian cell-expressed HPgV-2 E2 glycoprotein or bacterium-expressed nonstructural protein 4AB (NS4AB) in detecting past or present infections and to compare the total prevalence (antibody and RNA positive) of HPgV-2 with that of the other human pegivirus, HPgV-1 (GB virus C [GBV-C]). HPgV-2 E2 antibodies were detected in 13 (92.86%) of 14 HPgV-2-viremic cases, and NS4AB antibodies were detected in 8 (57.14%) of 14 cases. The HPgV-2 seroprevalence was significantly higher (P < 0.0001) among HCV-infected individuals (3.31% [24 of 726 samples]) than among non-HCV-infected individuals (0.30% [4 of 1,348 samples]). Of 31 anti-E2-positive samples, 22 had supplemental supporting data; 12 samples were HPgV-2 RNA positive and 10 nonviremic samples were antibody positive for peptides or NS4AB. The total prevalence of HPgV-1 (35.00%) was significantly higher than that of HPgV-2 (1.33%) in all populations tested (P < 0.0001). For HPgV-1, codetection of antibodies to E2 and RNA was infrequent (5.88%). In contrast, antibodies to E2 were detected in most HPgV-2-viremic individuals (92.86%), as is observed among individuals chronically infected with HCV, most of whom are antibody positive for HCV E2. Our studies indicate that HPgV-2 circulates with HCV and displays a profile similar to the serological profile of HCV-infected persons, although the pathogenicity of this virus has yet to be established.

Infectious Aetiology of Marginal Zone Lymphoma and Role of Anti-Infective Therapy

Marginal zone lymphomas have been associated with several infectious agents covering both viral and bacterial pathogens and in some cases a clear aetiological role has been established. Pathogenetic mechanisms are currently not completely understood. However, the role of chronic stimulation of the host immune response with persistent lymphocyte activation represents the most convincing explanation for lymphoproliferation. Gastric MALT lymphoma is strictly associated with Helicobacter pylori infection and various eradicating protocols, developed due to increasing antibiotic resistance, represent the first line therapy for gastric MALT. The response rate to eradication is good with 80% of response at 1 year; this finding is also noteworthy because it recapitulates cancer cured only by the antibacterial approach and it satisfies the Koch postulates of causation, establishing a causative relationship between Hp and gastric MALT lymphoma. Patients with chronic HCV infection have 5 times higher risk to develop MZL, in particular, an association with splenic and nodal MZL has been shown in several studies. Moreover, there is evidence of lymphoma regression after antiviral therapy with interferon+ribavirin, thus raising hope that newly available drugs, extremely efficient against HCV replication, could improve outcome also in HCV-driven lymphomas. Another case-study are represented by those rare cases of MZL localized to orbital fat and eye conjunctivas that have been associated with Chlamydophila psittaci infection carried by birds. Efficacy of antibacterial therapy against C. psittaci are conflicting and generally poorer than gastric MALT. Finally, some case reports will cover the relationship between primary cutaneous B-cell Lymphomas and Borrelia Burgdorferi.

Pathogenetic mechanisms of hepatitis C virus-induced B-cell lymphomagenesis

Hepatitis C virus (HCV) infection is probably the most common chronic viral infection and affects an estimated 180 million people worldwide, accounting for 3% of the global population. Although the liver is considered to be the primary target, extrahepatic manifestations are well recognized among patients with chronic HCV infection. Epidemiological studies have clearly demonstrated a correlation between chronic HCV infection and occurrence of B-cell non-Hodgkin's lymphomas (B-NHL). The clinical evidence that antiviral therapy has a significant role in the treatment at least of some HCV-associated lymphoproliferative disorders, especially indolent B-NHL, further supports the existence of an etiopathogenetic link. However, the mechanisms exploited by HCV to induce B-cell lymphoproliferation have so far not completely clarified. It is conceivable that different biological mechanisms, namely, chronic antigen stimulation, high-affinity interaction between HCV-E2 protein and its cellular receptors, direct HCV infection of B-cells, and "hit and run" transforming events, may be combined themselves and cooperate in a multifactorial model of HCV-associated lymphomagenesis.

Hepatitis viruses and non-Hodgkin lymphoma: epidemiology, mechanisms of tumorigenesis, and therapeutic opportunities

Over the past 2 decades considerable evidence has accumulated on the association between hepatitis C virus (HCV) and hepatitis B virus (HBV) and several hematologic malignancies, most notably B-cell non-Hodgkin lymphoma (NHL). In this review we summarize this evidence, address possible mechanisms whereby hepatitis viruses may contribute to lymphomagenesis, and discuss the therapeutic fallouts from this knowledge. Most of this evidence is on HCV, and this is the main focus of the review. Moreover, we mainly address the association with NHL, the most prevalent hematologic malignancy, and the most extensively investigated with regard to an association with hepatitis viruses. Available evidence on the association with other hematologic malignancies is also addressed briefly.

Antibodies to a novel antigen in acute hepatitis C virus infections

BACKGROUND

Conformational viral proteins potentially play an important role in the immunobiology of acute hepatitis C virus (HCV) infection and may enable earlier antibody detection.

MATERIALS AND METHODS

HCV RNA was detected using nucleic acid testing. Early antibody production was evaluated using three enzyme immunoassays (EIAs) containing antigenic proteins not present in licensed EIAs. Respectively, these contained: (1) multiple-epitope fusion antigen (MEFA) 7.1-NS3/4a, (2) F and Core, and (3) E1/E2 proteins. NS3/4a is a conformational antigen retaining protease and helicase enzymatic activities. MEFA 7.1 contains the linear epitopes used in licenced EIAs, including the latest EIA-3.0, in combination with genotype 1-3 specific epitopes. Forty-two RNA positive, EIA-3.0 negative samples, including two persistently serosilent cases, were used to evaluate these research EIAs. As controls, 54 EIA-3.0 negative/RNA negative and three HCV RNA+/antibody positive specimens were included.

RESULTS

Only the MEFA 7.1-NS3/4a EIA was positive in seven (17%) of the 42 HCV RNA + specimens, in all three EIA-3.0 positive controls but in none of 54 EIA-3.0 negative/HCV RNA negative controls. Notably, six of the seven (86%) specimens had evidence of active hepatitis (ALT > 210 IU/l). The two serosilent cases were research EIA negative.

CONCLUSION

A novel EIA with conformational and linear epitopes detected HCV antibodies in 17% of viraemic specimens missed by the standard reference EIA-3.0. Our research EIA appears to detect HCV antibodies closer to the initiation of acute hepatitis. Given that the average RNA-positive, antibody-negative window period is 56.4 days, this 17% yield would translate into a 10-day earlier detection of antibodies.

Human monoclonal antibodies that react with the E2 glycoprotein of hepatitis C virus and possess neutralizing activity

Active and/or passive immunoprophylaxis against hepatitis C virus (HCV) remain unachieved goals. Monoclonal antibodies might provide one approach to protection. We derived human monoclonal antibodies from the bone marrow of a patient with a well-controlled HCV infection of 22 years duration. Five distinct antibodies reactive with the E2 glycoprotein of the homologous 1a strain of HCV were recovered as antigen-binding fragments (FAbs). They demonstrated affinity constants as high as 2 nanomolar. "Neutralization of binding" titers paralleled the affinity constants. All five FAbs reacted with soluble E2 protein only in nonreducing gels, indicating that the relevant epitopes were conformational. The FAbs could be divided into two groups, based on competition analysis. Three of the FAbs neutralized the infectivity of pseudotyped virus particles (pp) bearing the envelope glycoproteins of the homologous HCV strain (genotype 1a). The three FAbs also neutralized genotype 1b pp and one also neutralized genotype 2a pp. In conclusion, one or more of these monoclonal antibodies may be useful in preventing infections by HCV belonging to genotype 1 or 2, the most medically important genotypes worldwide.

Current issues in the diagnosis of hepatitis B and C virus infections

Diagnostic tests for hepatitis B virus infection are well established, although development of format and components continues. Variants of HBV with amino acid changes in the major antigenic determinant of the surface protein (HBsAg), and which may escape neutralisation by anti-HBs, have been described in many countries. The increasing reliance on monoclonal antibodies in the formulation of new assays for HBsAg raises the question of whether these surface variants may escape detection. The prevalence of variants which are unable to synthesise the e antigen (precor mutants), especially in certain geographical areas, means that the absence of HBeAg in carriers, with or without anti-HBe, does not necessarily indicate clearance of viraemia. The discovery of hepatitis C virus was followed rapidly by evidence of considerable sequence variation among different isolates. At least six major genotypes of HCV are recognised worldwide. Nonetheless, current assays seem reliable for detection of antibodies to this diverse virus. Assays for antigen are not available and diagnosis of viraemia requires sensitive detection of the viral genome, for example using reverse transcription and the polymerase chain reaction (RT-PCR). Evaluation of the efficacy of anti-viral therapy requires quantitative assays, adding a further degree of complexity. Other tests, such as the branch DNA (bDNA) assays are available, but lack sensitivity. Whether different genotypes of HCV vary in their pathogenicity and response to therapy remains contentious and convenient methods for determination of the genotype (or equivalent serotyping assays) are required to resolve this issue.

Evidence for cross-genotype neutralization of hepatitis C virus pseudo-particles and enhancement of infectivity by apolipoprotein C1

The lack of a cell culture system to support hepatitis C virus (HCV) replication has hampered studies of this frequent cause of chronic liver disease. However, pseudotyped retroviral particles (pp) bearing the HCV envelope glycoproteins have provided a different approach to HCV studies. We used genotype 1a pp to detect neutralizing antibodies (NtAb) in eight chimpanzees and four humans infected with 1a strains, and developed pp of genotypes 2a, 3a, 4a, 5a, and 6a to study crossreactivity. NtAb was detected in one of four chimpanzees and none of three humans with acute resolving infection, suggesting that NtAb is not required for HCV clearance. NtAb were detected at high titer in two of four chimpanzees and, in Patient H, all with persistent infection; responses paralleled humoral responses to envelope 1 and 2 proteins and, in some cases, correlate also with antibodies to the hypervariable region 1, previously thought to be the primary site of neutralization. NtAb raised during 1a infections could neutralize HCVpp of genotypes 4a, 5a, and 6a but had only limited reactivity against 2a and 3a. The detection of high-titer NtAb with cross-genotype reactivity has important implications for the development of active and passive immune-prophylaxis strategies against HCV. Finally, we found that HCVpp infectivity was enhanced by human or chimpanzee sera; apolipoprotein C1 alone or as a component of high-density lipoproteins caused this enhancement. Future studies of the in vivo role of apolipoprotein C1 might provide additional insights into the infection process of HCV.

Evidence for cross-genotype neutralization of hepatitis C virus pseudo-particles and enhancement of infectivity by apolipoprotein C1

The lack of a cell culture system to support hepatitis C virus (HCV) replication has hampered studies of this frequent cause of chronic liver disease. However, pseudotyped retroviral particles (pp) bearing the HCV envelope glycoproteins have provided a different approach to HCV studies. We used genotype 1a pp to detect neutralizing antibodies (NtAb) in eight chimpanzees and four humans infected with 1a strains, and developed pp of genotypes 2a, 3a, 4a, 5a, and 6a to study crossreactivity. NtAb was detected in one of four chimpanzees and none of three humans with acute resolving infection, suggesting that NtAb is not required for HCV clearance. NtAb were detected at high titer in two of four chimpanzees and, in Patient H, all with persistent infection; responses paralleled humoral responses to envelope 1 and 2 proteins and, in some cases, correlate also with antibodies to the hypervariable region 1, previously thought to be the primary site of neutralization. NtAb raised during 1a infections could neutralize HCVpp of genotypes 4a, 5a, and 6a but had only limited reactivity against 2a and 3a. The detection of high-titer NtAb with cross-genotype reactivity has important implications for the development of active and passive immune-prophylaxis strategies against HCV. Finally, we found that HCVpp infectivity was enhanced by human or chimpanzee sera; apolipoprotein C1 alone or as a component of high-density lipoproteins caused this enhancement. Future studies of the in vivo role of apolipoprotein C1 might provide additional insights into the infection process of HCV.

Cross-reactive pseudovirus-neutralizing anti-envelope antibodies coexist with antibodies devoid of such activity in persistent hepatitis C virus infection

Most RNA viruses have evolved mechanisms to avoid neutralizing antibody responses, and it is generally believed that variability of envelope-encoding regions is the major molecular basis of this phenomenon. However, it has been hypothesized that other mechanisms can be involved. Recent experimental data indicate that in hepatitis C virus (HCV) infection, the anti-envelope humoral response includes cross-reactive antibody clones able to neutralize vesicular stomatitis virus (VSV) pseudotypes containing HCV E1 and E2 glycoproteins (HCV/VSV pseudotype) as well as other clones devoid of such activity. In this work, we demonstrate that natural infection with a large variety of HCV isolates belonging to different genotypes elicits HCV/VSV pseudotype-neutralizing cross-reactive anti-envelope antibodies together with clones unable to neutralize this pseudovirus. This was shown by designing a novel strategy for quantitation of serum antibodies binding selectively to single viral cross-reactive conformational epitopes. These data can be useful not only for a better understanding of the virus-host interplay in important viral diseases, but also for the development of an effective anti-HCV vaccine.

Quantitative signal of anti-HCV by an automated assay predicts viremia in a population at high prevalence of hepatitis C virus infection

BACKGROUND AND AIMS

The diagnosis of ongoing hepatitis C virus (HCV) infection involves the detection of specific antibodies and of HCV-RNA. We aimed to assess the relationship between these two parameters in a representative sample of a population at high risk for HCV infection.

METHODS

Plasma and serum samples were respectively tested for HCV-RNA by a qualitative PCR (Cobas Amplicor HCV, Roche) and for HCV antibodies by a MEIA screening assay (AxSYM HCV 3.0, Abbott) and an immunoblot (Inno-LIA-III, Innogenetics).

RESULTS AND CONCLUSIONS

Out of 888 samples assayed, 579 (65.2%) were positive for HCV-RNA, while anti-HCV antibodies were detected respectively in 802 sera by AxSYM (90.3%) and in 783 by LIA (706 positive and 77 indeterminate, 88.2%). The anti-core antibodies displayed the best correlation with viremia, since they were present in 97.1% of the PCR+ samples, followed by anti-NS3 (90.2%) and anti-NS4 (89.6%). Only one HCV-RNA positive sample was negative by LIA and MEIA (early seroconversion). The AxSYM sample/cutoff (S/CO) values were directly correlated with the presence of HCV-RNA: a PCR positivity was found in 4.9% of samples with a S/CO < or =10, in 60.8% of samples with a S/CO between 11 and 50 and in 93.6% of cases with a S/CO >50, (P < 0.005). The immunoblot adds little, on a single specimen, to the information yielded by the AxSYM screening test. A suitable diagnostic algorithm for HCV in high-risk settings could be the anti-HCV screening by MEIA and a qualitative assay for HCV-RNA on samples with low reactivity.

In vitro assay for neutralizing antibody to hepatitis C virus: evidence for broadly conserved neutralization epitopes

Our understanding of the humoral immune response to hepatitis C virus (HCV) is limited because the virus can be studied only in humans and chimpanzees and because previously described neutralization assays have not been robust or simple to perform. Nevertheless, epidemiologic and laboratory studies suggested that neutralizing Ab to HCV might be important in preventing infection. We have recently described a neutralization assay based on the neutralization of pseudotyped murine retrovirus constructs bearing HCV envelope glycoproteins on their surface. We have applied the assay to well characterized clinical samples from HCV-infected patients and chimpanzees, confirmed the existence of neutralizing Ab to HCV, and validated most previously reported neutralizations of the virus. We did not find neutralizing anti-HCV in resolving infections but did find relatively high titers (>1:320) of such Ab in chronic infections. Neutralizing Ab was directed not only to epitope(s) in the hypervariable region of the E2 envelope protein but also to one or more epitopes elsewhere in the envelope of the virus. Neutralizing Ab was broadly reactive and could neutralize pseudotype particles bearing the envelope glycoproteins of two different subgenotypes (1a and 1b). The ability to assay neutralizing anti-HCV should permit an assessment of the prospects for successful Ab-mediated passive and active immunoprophylaxis against hepatitis C.

Characterization of secreted and intracellular forms of a truncated hepatitis C virus E2 protein expressed by a recombinant herpes simplex virus

A replication-defective herpes simplex virus type 1 (HSV-1) recombinant lacking the glycoprotein H (gH)-encoding gene and expressing a truncated form of the hepatitis C (HCV) E2 glycoprotein (E2-661) was constructed and characterized. We show here that cells infected with the HSV/HCV recombinant virus efficiently express the HCV E2-661 protein. Most importantly, cellular and secreted E2-661 protein were both readily detected by the E2-conformational mAb H53 and despite the high expression levels, only limited amounts of misfolded aggregates were detected in either the cellular or secreted fractions. Furthermore, cell-associated and secreted E2-661 protein bound to the major extracellular loop (MEL) of CD81 in a concentration-dependent manner and both were highly reactive with sera from HCV-infected patients. Finally, BALB/c mice immunized intraperitoneally with the recombinant HSV/HCV virus induced high levels of anti-E2 antibodies. Analysis of the induced immunoglobulin G (IgG) isotypes showed high levels of IgG2a while the levels of the IgG1 isotype were significantly lower, suggesting a Th1-type of response. We conclude that the HSV-1 recombinant virus represents a promising tool for production of non-aggregated, immunologically active forms of the E2-661 protein and might have potential applications in vaccine development.

Diverging effects of human recombinant anti-hepatitis C virus (HCV) antibody fragments derived from a single patient on the infectivity of a vesicular stomatitis virus/HCV pseudotype

Hepatitis C virus (HCV) is the major causative agent of blood-borne non-A, non-B hepatitis. Although a strong humoral response is detectable within a few weeks of primary infection and during viral persistence, the role played by antibodies against HCV envelope glycoproteins in controlling viral replication is still unclear. We describe how human monoclonal anti-HCV E2 antibody fragments isolated from a chronically HCV-infected patient differ sharply in their abilities to neutralize infection of HepG2 cells by a vesicular stomatitis virus pseudotype bearing HCV envelope glycoproteins. Two clones were able to neutralize the pseudotype virus at a concentration of 10 micro g/ml, while three other clones completely lacked this activity. These data can explain the lack of protection and the possibility of reinfection that occur even in the presence of a strong antiviral antibody response.

Live and killed rhabdovirus-based vectors as potential hepatitis C vaccines

A highly attenuated, recombinant rabies virus (RV) vaccine strain-based vector was utilized as a new immunization strategy to induce humoral and cellular responses against hepatitis C (HCV) glycoprotein E2. We showed previously that RV-based vectors are able to induce strong immune responses against human immunodeficiency virus type I (HIV-1) antigens. Here we constructed and characterized three replication-competent RV-based vectors expressing either both HCV envelope proteins E1 and E2 or a modified version of E2 which lacks 85 amino acids of its carboxy terminus and contains the human CD4 transmembrane domain and the CD4 or RV glycoprotein cytoplasmic domain. All three constructs stably expressed the respective protein(s) as indicated by Western blotting and immunostaining. Moreover, surface expression of HCV E2 resulted in efficient incorporation of the HCV envelope protein regardless of the presence of the RV G cytoplasmic domain, which was described previously as a requirement for incorporation of foreign glycoproteins into RV particles. Killed and purified RV virions containing HCV E2 were highly immunogenic in mice and also proved useful as a diagnostic tool, as indicated by a specific reaction with sera from HCV-infected patients. In addition, RV vaccine vehicles were able to induce cellular responses against HCV E2. These results further suggest that recombinant RVs are potentially useful vaccine vectors against important human viral diseases.

The B-cell receptor of a hepatitis C virus (HCV)-associated non-Hodgkin lymphoma binds the viral E2 envelope protein, implicating HCV in lymphomagenesis

Hepatitis C virus (HCV) infection is associated with extrahepatic B-cell lymphoproliferative disorders. To determine whether a viral antigen drives this B-cell expansion, the B-cell receptors were cloned from HCV-associated lymphomas and were expressed as soluble immunoglobulins. The rescued immunoglobulins were then tested for their ability to bind the HCV-E2 envelope glycoprotein, an antigen that was previously implicated in the pathogenesis of HCV-associated B-cell diseases. One of 2 lymphoma immunoglobulin test cases bound the E2 protein in a manner identical to a bona fide human anti-E2 antibody. Moreover, it bound E2 from multiple viral genotypes, suggesting reactivity with a conserved E2 epitope. These findings support the hypothesis that some HCV-associated lymphomas originate from B cells that were initially activated by the HCV-E2 protein and might explain the association between HCV infection and some B-cell lymphoproliferative disorders.

[Role of neutralizing antibodies and cellular immunity in hepatitis C virus infection]

Hepatitis C virus (HCV) is responsible for the development of a chronic carrier state that can lead to the induction of cirrhosis and liver cancer. These clinical manifestations are believed to be the direct consequence of the viral persistence and the incapacity of the host to develop vigorous and sustained immune responses. Still contradictory data suggest the existence of neutralizing antibodies specifically directed at the second glycoprotein (E2). These antibodies may nonetheless play only a minor role in the control of infection. In contrast, it is now generally recognized that cellular-mediated immune responses, CD4+ and CD8+ mediated, if in place early enough, of a vigorous and polyclonal nature as well as long-lasting, appear by themselves competent enough to control an infection. One of the mechanisms possibly responsible for the establishment and persistence of a chronic infection could be the alteration of the ability of antigen-presenting cells (dendritic cells) to stimulate a T cell response. Such alteration could be the result of a direct infection of these cells by HCV.

Cross-reactivity and clinical impact of the antibody response to hepatitis C virus second envelope glycoprotein (E2)

The genotype of hepatitis C virus (HCV) can profoundly affect the success of antiviral therapy for HCV infection. A possible contributing factor is a varied immune response elicited by infection with different HCV genotypes. In this study, full-length E2 proteins of HCV genotypes 1a, 1b, 2a, and 2b were used to determine the fraction of the humoral immune response to HCV E2 that is genotype specific. Greater than 90% of all infected individuals had serum antibodies to the four E2 proteins. Overall, individuals infected with genotype 1a or 1b were characterized by variable immune responses to HCV E2 with relatively high amounts of cross-reactivity with other E2 proteins. Individuals infected with genotype 2a or 2b exhibited a strong preferential reactivity to genotype 2a and 2b E2 proteins. Individuals with elevated titers to HCV E2 were more likely to be infected with genotype 2a and had a significantly lower median viral load. These findings indicate that the antibody response to HCV E2 is affected by the genotype of the virus and that induction of a strong humoral immune response to HCV E2 may contribute to a decreased viral load.

Cryoprecipitate of patients with cryoglobulinemic glomerulonephritis contains molecules of the lectin complement pathway

Serological and histological studies were carried out to explore the role of the lectin complement pathway in the pathogenesis of cryoglobulinemic glomerulonephritis. Sixteen patients with mixed cryoglobulinemia type II with glomerulonephritis (GN) were enrolled. All cases had hepatitis C virus (HCV) infection. The serum concentration of mannose-binding lectin (MBL) was significantly higher in the GN patients than in the normal controls according to ELISA (P < 0.01). IgG, IgM, C1q, C4d, HCV envelope antigen, MBL, and MBL-associated serine protease-1 (MASP-1) could be visualized in the cryoprecipitate of the 16 patients by Dot blot assay. Renal biopsy specimens obtained from 3 patients were examined by immunohistochemistry, and the glomeruli strongly stained for IgG, IgM, MBL, MASP-1, C4d, C3c, and C3d in a fringe-like pattern. The pattern of HCV constituent deposition was partially fringe-like. The complement profiles of the 16 cases were distinctive; briefly, the serum levels of C1q, C2, and C3 were reduced, although the levels of circulating regulatory proteins (C1-inhibitor, factor H, and factor I) were in the normal range. The serum C4 level was significantly reduced. These results indicate that immune complex formation involves molecules of the lectin pathway and leads to organ damage in cryoglobulinemic glomerulonephritis.

Mapping B-cell epitopes of hepatitis C virus E2 glycoprotein using human monoclonal antibodies from phage display libraries

Clinical and experimental evidence indicates that the hepatitis C virus (HCV) E2 glycoprotein (HCV/E2) is the most promising candidate for the development of an effective anti-HCV vaccine. Identification of the human epitopes that are conserved among isolates and are able to elicit protective antibodies would constitute a significant step forward. This work describes the mapping of the B-cell epitopes present on the surface of HCV/E2, as recognized by the immune system during infection, by the analysis of the reciprocal interactions of a panel of human recombinant Fabs derived from an HCV-infected patient. Three unrelated epitopes recognized by antibodies with no neutralization-of-binding (NOB) activity were identified; a fourth, major epitope was defined as a clustering of minor epitopes recognized by Fabs endowed with strong NOB activity.

Nonneutralizing human antibody fragments against hepatitis C virus E2 glycoprotein modulate neutralization of binding activity of human recombinant Fabs

Evidence from clinical and experimental studies indicates that hepatitis C virus E2 (HCV/E2) glycoprotein is the major target of a putatively protective immune response. However, even in the presence of a vigorous production of anti-HCV/E2 antibodies, reinfection can occur. Dissection of the human immune response against HCV/E2 indicated that blocking of binding of HCV/E2 to target cells [neutralization of binding (NOB) activity] varies widely among antibody clones. Moreover, in vivo, simultaneous binding of antibodies to distinct epitopes can induce conformational changes and synergies that may be relevant to understanding the anti-HCV immune response. In this study, human recombinant Fabs were generated by affinity-selecting a phage display repertoire library with antibody-coated HCV/E2. These Fabs, which share the same complementarity-determining region DNA sequences, had higher affinity than other anti-HCV/E2 Fabs but showed no NOB activity even at the highest concentrations. Binding of Fabs to HCV/E2 caused conformational changes modifying Fab-binding patterns and reducing, with a negative synergistic effect, Fab-mediated NOB activity. These data suggest that some antibody clones have the potential to modify HCV/E2 conformation and that, in this state, binding of this glycoprotein to its cellular target is less prone to inhibition by some antibody clones. This can explain why high anti-HCV/E2 antibody titers do not directly correlate with protection from infection. Information on the interactions among different antibody clones can contribute to understanding virus-host interplay and developing more effective vaccines.

ADAM-HCV, a new-concept diagnostic assay for antibodies to hepatitis C virus in serum

We screened phage libraries using sera from noninfected individuals and patients infected by hepatitis C virus (HCV). By applying different selection and maturation strategies, we identified a wide collection of efficient phage-borne ligands for HCV-specific antibodies. The selected ligands retained their antigenic properties when expressed as multimeric synthetic peptides. Peptides that mimic several immunodominant epitopes of the virus were used to develop a novel type of diagnostic assay which efficiently detects antibodies to HCV in serum. This type of analysis provides a conclusive diagnosis for many patients identified as indeterminate according to presently available serological assays.

Failure to infect rhesus monkeys with hepatitis C virus strains of genotypes 1a, 2a or 3a

The chimpanzee is the only recognized animal model for the study of hepatitis C virus (HCV). However, recently it was reported that rhesus monkeys were susceptible to HCV and developed hepatitis during infection. In the present study, we inoculated two rhesus monkeys each with HCV strain H77 (genotype 1a), strain HC-J6 (genotype 2a) or strain S52 (genotype 3a). Weekly serum samples were tested for liver enzyme values, HCV antibodies and HCV RNA. We did not find evidence of HCV infection in any of the monkeys during 24 weeks of follow-up. Our study demonstrates that rhesus monkeys are not readily infected with HCV and apparently do not represent a useful animal model for the study of HCV.

Hepatitis C virus envelope protein E2 binds to CD81 of tamarins

Since recombinant envelope glycoprotein E2 of hepatitis C virus (HCV) binds to CD81 on human and chimpanzee cells, it has been suggested that CD81 may be a receptor for HCV. Humans and chimpanzees are the only species known to be susceptible to HCV infection. E2 has been reported not to bind to CD81 of the African green monkey, mouse, or rat, suggesting that binding of HCV to CD81 is species specific and may determine susceptibility to infection with HCV. We investigated the interaction between E2 of HCV and CD81 of tamarins, a group of small New World monkeys frequently used for the study of human viruses. Tamarins are not susceptible to HCV infection. Nonetheless, we found that three different forms of HCV E2 (intracellular, secreted, and cell surface-displayed) bound more efficiently to recombinant tamarin CD81 than to human CD81, as determined by ELISA and immunofluorescence. The affinity of the interaction was approximately 10-fold higher for tamarin than for human CD81. Binding of E2 to CD81 on cultured or primary tamarin cells was demonstrated by flow cytometry. In contrast to previous reports, there was also a low-affinity interaction between E2 and African green monkey CD81. Thus, the HCV E2 interaction with CD81 is not limited to humans and chimpanzees and does not predict susceptibility to HCV infection.

Human monoclonal antibodies that inhibit binding of hepatitis C virus E2 protein to CD81 and recognize conserved conformational epitopes

The intrinsic variability of hepatitis C virus (HCV) envelope proteins E1 and E2 complicates the identification of protective antibodies. In an attempt to identify antibodies to E2 proteins from divergent HCV isolates, we produced HCV E2 recombinant proteins from individuals infected with HCV genotypes 1a, 1b, 2a, and 2b. These proteins were then used to characterize 10 human monoclonal antibodies (HMAbs) produced from peripheral B cells isolated from an individual infected with HCV genotype 1b. Nine of the antibodies recognize conformational epitopes within HCV E2. Six HMAbs identify epitopes shared among HCV genotypes 1a, 1b, 2a, and 2b. Six, including five broadly reactive HMAbs, could inhibit binding of HCV E2 of genotypes 1a, 1b, 2a, and 2b to human CD81 when E2 and the antibody were simultaneously exposed to CD81. Surprisingly, all of the antibodies that inhibited the binding of E2 to CD81 retained the ability to recognize preformed CD81-E2 complexes generated with some of the same recombinant E2 proteins. Two antibodies that did not recognize preformed complexes of HCV 1a E2 and CD81 also inhibited binding of HCV 1a virions to CD81. Thus, HCV-infected individuals can produce antibodies that recognize conserved conformational epitopes and inhibit the binding of HCV to CD81. The inhibition is mediated via antibody binding to epitopes outside of the CD81 binding site in E2, possibly by preventing conformational changes in E2 that are required for CD81 binding.

Antibodies against hepatitis C virus-like particles and viral clearance in acute and chronic hepatitis C

We recently described the efficient assembly of hepatitis C virus (HCV) structural proteins into HCV-like particles (HCV-LPs) in insect cells. These noninfectious HCV-LPs have similar morphologic and biophysical properties as putative virions isolated from HCV-infected humans and can induce a broadly directed immune response in animal models. The HCV envelope proteins of HCV-LPs are presumably presented in a native, virion-like conformation and may therefore interact with antienvelope antibodies directed against conformational epitopes. In this study, HCV-LPs were used as capture antigens in an enzyme-linked immunosorbent assay (ELISA) to detect and quantify antibodies against HCV structural proteins in patients with acute and chronic hepatitis C. High titers of anti-HCV-LP antibodies were detected in patients chronically infected with HCV genotypes 1 to 6. In contrast to individuals with chronic hepatitis C, patients with acute self-limited hepatitis C displayed only a transient and weak seroreactivity against HCV-LPs. Patients with chronic HCV infection successfully treated with interferon demonstrated a gradual decline of anti-HCV-LP titers during or subsequent to viral clearance. Sustained interferon responders were characterized by significantly higher pretreatment levels of anti-HCV-LP antibodies as compared with nonresponders (P =.0001). In conclusion, HCV infection is associated with limited humoral immunity against the envelope proteins present on the HCV-LPs. An HCV-LP-based ELISA may be a useful diagnostic tool to distinguish acute hepatitis C from chronic HCV infection with exacerbation, and to predict viral clearance in response to interferon.

Vaccination of chimpanzees with plasmid DNA encoding the hepatitis C virus (HCV) envelope E2 protein modified the infection after challenge with homologous monoclonal HCV

Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. Development of vaccines to prevent HCV infection, or at least prevent progression to chronicity, is a major goal. In mice and rhesus macaques, a DNA vaccine encoding cell-surface HCV-envelope 2 (E2) glycoprotein stimulated stronger immune responses than a vaccine encoding intracellular E2. Therefore, we used DNA encoding surface-expressed E2 to immunize chimpanzees 2768 and 3001. Chimpanzee 3001 developed anti-E2 after the second immunization and antibodies to hypervariable region 1 (HVR1) after the third immunization. Although chimpanzee 2768 had only low levels of anti-E2 after the third immunization, an anamnestic response occurred after HCV challenge. CTL responses to E2 were not detected before challenge, but a strong response was detected after HCV challenge in chimpanzee 2768. An E2-specific CD4+ response was detected in chimpanzee 2768 before challenge and in both chimpanzees postchallenge. Three weeks after the last immunization, animals were challenged with 100 50% chimpanzee-infectious doses (CID(50)) of homologous monoclonal HCV. As a control, a naive chimpanzee was inoculated with 3 CID(50) of the challenge virus. The vaccine did not generate sterilizing immunity because both vaccinated chimpanzees were infected. However, both vaccinated chimpanzees resolved the infection early whereas the control animal became chronically infected. Compared with the control animal, hepatitis appeared earlier in the course of the infection in both vaccinated chimpanzees. Therefore, DNA vaccine encoding cell surface-expressed E2 did not elicit sterilizing immunity in chimpanzees against challenge with a monoclonal homologous virus, but did appear to modify the infection and might have prevented progression to chronicity.

Characterization of modified hepatitis C virus E2 proteins expressed on the cell surface

The envelope proteins of hepatitis C virus (HCV) are the likely targets of neutralizing antibodies and their molecular and functional characterization is relevant for vaccine development. We previously showed that surface-expressed E2 is a better immunogen than intracellular E2 and, therefore, we were interested in exploring more efficient ways to present E2 protein on the cell surface. We found that E2 targeted to the cell surface by replacement of its transmembrane domain did not bring E1 to the surface although E1 could be expressed independently on the cell surface if its transmembrane domain was similarly replaced. FACS analysis suggested that E2 expressed on the cell surface acquired its native conformation more efficiently when truncated at aa 661 than when truncated at aa 715. The shorter form of truncated E2 better retained the ability to bind the second extracellular loop (EC2) of CD81, the putative HCV receptor. Interestingly, deletion of the hypervariable region 1 (HVR1) did not perceptibly alter E2 structure; cell-surface forms of E2 lacking the HVR1 remained reactive with conformation-sensitive MAbs and were able to bind recombinant EC2 of CD81.

Diagnostic tests for hepatitis C

Two categories of virological assays are in practice used for the diagnosis and management of hepatitis C virus (HCV) infection, including serological and molecular biology-based assays. Serological assays include: screening tests based on enzyme immunoassays (EIAs); supplemental "analytical" assays based on immunoblot testing; and serological assays detecting genotype-specific antibodies for the serological determination of HCV genotype, so-called "serotyping" assays. Molecular assays include: qualitative assays, detecting HCV RNA in body fluids; quantitative assays measuring HCV viral load, a parameter that estimates the level of HCV replication in the liver; and tests analyzing the sequence of HCV genomes (genotyping assays).

Quasispecies in viral persistence and pathogenesis of hepatitis C virus

Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. This RNA virus circulates as a quasispecies and its genetic heterogeneity has been implicated in the lack of protective immunity against HCV and in its persistence following infection. HCV might escape from immune surveillance by developing mutations in proteins that are subject to immune pressure.

Viral persistence, antibody to E1 and E2, and hypervariable region 1 sequence stability in hepatitis C virus-inoculated chimpanzees

The relationship of viral persistence, the immune response to hepatitis C virus (HCV) envelope proteins, and envelope sequence variability was examined in chimpanzees. Antibody reactivity to the HCV envelope proteins E1 or E2 was detected by enzyme-linked immunosorbent assay (ELISA) in more than 90% of a human serum panel. Although the ELISAs appeared to be sensitive indicators of HCV infection in human serum panels, the results of a cross-sectional study revealed that a low percentage of HCV-inoculated chimpanzees had detectable antibody to E1 (22%) and E2 (15%). Viral clearance, which was recognized in 28 (61%) of the chimpanzees, was not associated with an antibody response to E1 or E2. On the contrary, antibody to E2 was observed only in viremic chimpanzees. A longitudinal study of animals that cleared the viral infection or became chronically infected confirmed the low level of antibody to E1, E2, and the HVR-1. In 10 chronically infected animals, the sequence variation in the E2 hypervariable region (HVR-1) was minimal and did not coincide with antibody to E2 or to the HVR-1. In addition, low nucleotide and amino acid sequence variation was observed in the E1 and E2 regions from two chronically infected chimpanzees. These results suggest that mechanisms in addition to the emergence of HVR-1 antibody escape variants are involved in maintaining viral persistence. The significance of antibodies to E1 and E2 in the chimpanzee animal model is discussed.

Limited humoral immunity in hepatitis C virus infection

BACKGROUND & AIMS

The extremely high rate of chronicity to hepatitis C virus (HVC) infection suggests an inefficient immune response. The humoral immune response to HCV was evaluated in 60 patients with chronic HCV infection and in 12 patients acutely infected with HCV.

METHODS

A number of recombinant HCV antigens including the core, envelope 2 (E2), nonstructural (NS) 3, NS4, and NS5 proteins, and NS4a and E2-HVR-1 peptides were used in enzyme-linked immunoassays.

RESULTS

Immunoglobulin (Ig) G antibody responses to these viral antigens, except for the HCV core, were highly restricted to the IgG1 isotype. The prevalence of antibodies of the IgG1 isotype specific for the HCV core, E2, E2-HVR1, NS3 (helicase domain), NS4, and NS5 antigens was 97%, 98%, 28%, 88%, 33%, and 68%, respectively. Antibodies of the IgG3 isotype specific for E2, E2-HVR-1, NS3, NS4, and NS5 were detected in a minority of serum samples. The IgG2 and IgG4 isotypes were rarely if ever detected. Furthermore, antibody responses to HCV viral antigens were of relatively low titer and, with the exception of anti-HCV core, were delayed in appearance until the chronic phase of infection.

CONCLUSIONS

The IgG1 restriction, low titer, and delayed appearance of antibody responses elicited during HCV infection suggest that the immunogenicity of HCV proteins is limited in the context of natural infection. Inasmuch as recombinant HCV viral antigens perform as relatively normal immunogens in small animals, we suggest that the defective humoral immune responses during HCV infection may be attributable to an "immune avoidance" strategy.

Characterization of human monoclonal antibodies specific to the hepatitis C virus glycoprotein E2 with in vitro binding neutralization properties

Both linear and conformational determinants of hepatitis C virus (HCV) are believed to be involved in viral neutralization. After immortalization of B cells from HCV chronically infected patients with Epstein-Barr virus, we obtained two polyclonal lymphoblastoid cell lines (LCL) secreting human monoclonal antibodies (HMabs). One clone was derived from a patient infected with a genotype 4 isolate while the second was isolated from a genotype 1b-infected patient. Immunoprecipitation studies, Western blot, and immunofluorescence analysis, peptide scanning, and ELISA studies indicated that the HMabs (1) recognized conformation-dependent determinant(s), (2) were capable of recognizing genotype 1a and 1b derived antigens, and (3) were able to precipitate noncovalently associated E1E2 complexes believed to exist on the surface of virion particles. The HMab derived from the genotype 4-infected patient was in addition shown to neutralize the in vitro binding of recombinant E2 protein onto susceptible cells suggesting a potential for in vivo neutralization. These data indicate that anti-E2 antibodies directed at conserved conformational-dependent determinant(s) exist in chronic HCV infection.

Dissection of human humoral immune response against hepatitis C virus E2 glycoprotein by repertoire cloning and generation of recombinant Fab fragments

Demonstration of antibodies inhibiting key viral functions is the basis for the design of an effective vaccine. Dissection of the human antibody response by repertoire cloning may be a powerful means to address this issue. In this study, a panel of human monoclonal recombinant Fab fragments specific for hepatitis C virus (HCV) E2 envelope protein was generated. The selection procedure was designed to select for cross-genotype reactive antibodies. Sequences coding five different human recombinant Fabs specific for the HCV/E2 protein were cloned and characterized. The ability of the cloned antibody fragments to inhibit adhesion of recombinant envelope E2 protein to target cells was assayed. While affinity of the different antibody fragments appeared similar, activity in inhibiting E2 binding to target cells varied considerably from one Fab fragment to another. Two Fabs were not able to inhibit E2 binding at high concentration (40 microg/mL), while three other Fab clones were active in neutralizing 50% of the E2 binding at concentrations ranging from 3 to 0.35 microg/mL.

HGV: the identification, biology and prevalence of an orphan virus

Hepatitis G virus (HGV) and GB virus C (GBV-C) (both hereinafter referred to as HGV) were independently identified in patients with hepatitis of unknown aetiology. HGV is a positive-sense RNA virus of the family Flaviviridae. The virus can establish both acute and chronic infection and appears to be sensitive to interferon. Horizontal transmission is mainly parenteral, although other routes such as vertical have been well documented. High risk groups include intravenous drug users (i.v.DUs), the multiply transfused, haemodialysis patients and haemophiliacs. Up to 90% of i.v.DUs are positive for either HGV-RNA or antibodies to HGV envelope-2 protein (anti-E2). HGV is frequently detected in patients with HBV and HCV infection. Its link to hepatitis has now become less certain. Only around 3-6% of non-A E hepatitis cases are HGV viraemic, clearly showing that HGV is not the major cause of idiopathic hepatitis as originally hoped. Around 1-5% of volunteer blood donors in developed countries are HGV viraemic, but the prevalence is 10-20% in the general population in some developing countries. At present, it is not known whether HGV is associated with other diseases in humans, is a passenger virus, or only becomes virulent under certain conditions.

Hepatitis C virus structural proteins assemble into viruslike particles in insect cells

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis in the world. The study of HCV has been hampered by the low level of viral particles in infected individuals, the inability to propagate efficiently the virus in cultured cells, and the lack of a convenient animal model. Due to these obstacles, neither the structure of the virus nor the prerequisites for its assembly have been clearly defined. In this report, we describe a model for the production and purification of HCV-like particles in insect cells using a recombinant baculovirus containing the cDNA of the HCV structural proteins. In insect cells, expressed HCV structural proteins assembled into enveloped viruslike particles (40 to 60 nm in diameter) in large cytoplasmic cisternae, presumably derived from the endoplasmic reticulum. Biophysical characterization of viruslike particles by CsCl and sucrose gradient centrifugation revealed biophysical properties similar to those of putative virions isolated from infected humans. The results suggested that HCV core and envelope proteins without p7 were sufficient for viral particle formation. Analysis of particle-associated nucleic acids demonstrated that HCV RNAs were selectively incorporated into the particles over non-HCV transcripts. The synthesis of HCV-like particles in insect cells may provide an important tool to determine the structural requirements for HCV particle assembly as well as to study viral genome encapsidation and virus-host interactions. The described system may also represent a potential approach toward vaccine development.