Distinct disease features in chimpanzees infected with a precore HBV mutant associated with acute liver failure in humans.

Transmission to chimpanzees of a precore hepatitis B virus (HBV) mutant implicated in acute liver failure (ALF) in humans did not cause ALF nor the classic form of acute hepatitis B (AHB) seen upon infection with the wild-type HBV strain, but rather a severe AHB with distinct disease features. Here, we investigated the viral and host immunity factors responsible for the unusual severity of AHB associated with the precore HBV mutant in chimpanzees. Archived serial serum and liver specimens from two chimpanzees inoculated with a precore HBV mutant implicated in ALF and two chimpanzees inoculated with wild-type HBV were studied. We used phage-display library and next-generation sequencing (NGS) technologies to characterize the liver antibody response. The results obtained in severe AHB were compared with those in classic AHB and HBV-associated ALF in humans. Severe AHB was characterized by: (i) the highest alanine aminotransferase (ALT) peaks ever seen in HBV transmission studies with a significantly shorter incubation period, compared to classic AHB; (ii) earlier HBsAg clearance and anti-HBs seroconversion with transient or undetectable hepatitis B e antigen (HBeAg); (iii) limited inflammatory reaction relative to hepatocellular damage at the ALT peak with B-cell infiltration, albeit less extensive than in ALF; (iv) detection of intrahepatic germline antibodies against hepatitis B core antigen (HBcAg) by phage-display libraries in the earliest disease phase, as seen in ALF; (v) lack of intrahepatic IgM anti-HBcAg Fab, as seen in classic AHB, but at variance with ALF; and (vi) higher proportion of antibodies in germline configuration detected by NGS in the intrahepatic antibody repertoire compared to classic AHB, but lower than in ALF. This study identifies distinct outcome-specific features associated with severe AHB caused by a precore HBV mutant in chimpanzees, which bear closer resemblance to HBV ALF than to classic AHB. Our data suggest that precore HBV mutants carry an inherently higher pathogenicity that, in addition to specific host factors, may play a critical role in determining the severity of acute HBV disease.

Role of humoral immunity against hepatitis B virus core antigen in the pathogenesis of acute liver failure.

Hepatitis B virus (HBV)-associated acute liver failure (ALF) is a dramatic clinical syndrome leading to death or liver transplantation in 80% of cases. Due to the extremely rapid clinical course, the difficulties in obtaining liver specimens, and the lack of an animal model, the pathogenesis of ALF remains largely unknown. Here, we performed a comprehensive genetic and functional characterization of the virus and the host in liver tissue from HBV-associated ALF and compared the results with those of classic acute hepatitis B in chimpanzees. In contrast with acute hepatitis B, HBV strains detected in ALF livers displayed highly mutated HBV core antigen (HBcAg), associated with increased HBcAg expression ex vivo, which was independent of viral replication levels. Combined gene and miRNA expression profiling revealed a dominant B cell disease signature, with extensive intrahepatic production of IgM and IgG in germline configuration exclusively targeting HBcAg with subnanomolar affinities, and complement deposition. Thus, HBV ALF appears to be an anomalous T cell-independent, HBV core-driven B cell disease, which results from the rare and unfortunate encounter between a host with an unusual B cell response and an infecting virus with a highly mutated core antigen.

Next-generation sequencing of the intrahepatic antibody repertoire delineates a unique B-cell response in HBV-associated acute liver failure.

Hepatitis B virus (HBV) is a major cause of acute liver failure (ALF) worldwide. While liver damage in classic acute hepatitis B is believed to be T-cell mediated, the pathogenesis of HBV-associated ALF remains largely unknown. Access to liver specimens from well-characterized patients with HBV-associated ALF provided us with the opportunity to perform next-generation sequencing (NGS) of the entire VH repertoires of IgM and IgG from the livers of four ALF patients, a control liver donor and a patient with chronic HBV infection. We found that ALF is not associated with expansion of specific B-cell lineages. However, NGS showed that the intrahepatic VH repertoires from ALF patients were characterized by the abundant presence of antibodies in germline configuration in contrast to their marginal prevalence in controls. Moreover, NGS identified a large number of VH genes in germline configuration with identical VDJ sequences in the IgM and IgG repertoires in all four ALF patients, indicating that isotype switch from IgM to IgG had occurred without somatic hypermutation. The results of this study indicate that the presence of intrahepatic antibodies in unmutated germline configuration is a broad phenomenon in the global antibody repertoire generated from total RNA derived from whole-liver tissue that is strongly associated with ALF, suggesting a major role of T cell-independent humoral immunity in the pathogenesis of ALF.

Hepatitis E Virus Seroprevalence and Correlates of Anti-HEV IgG Antibodies in the Rakai District, Uganda.

A cross-sectional study was conducted of 500 human immunodeficiency virus (HIV)-infected adults frequency matched on age, sex, and community to 500 HIV-uninfected individuals in the Rakai District, Uganda to evaluate seroprevalence of anti-hepatitis E virus (HEV) IgG antibodies. HEV seroprevalence was 47%, and 1 HIV-infected individual was actively infected with a genotype 3 virus. Using modified Poisson regression, male sex (prevalence ratios [PR] = 1.247; 95% confidence interval [CI], 1.071-1.450) and chronic hepatitis B virus infection (PR = 1.377; 95% CI, 1.090-1.738) were associated with HEV seroprevalence. HIV infection status (PR = 0.973; 95% CI, 0.852-1.111) was not associated with HEV seroprevalence. These data suggest there is a large burden of prior exposure to HEV in rural Uganda.

The role of hepatitis E virus infection in adult Americans with acute liver failure.

Acute hepatitis E virus (HEV) infection is a leading cause of acute liver failure (ALF) in many developing countries, yet rarely identified in Western countries. Given that antibody testing for HEV infection is not routinely obtained, we hypothesized that HEV-related ALF might be present and unrecognized in North American ALF patients. Serum samples of 681 adults enrolled in the U.S. Acute Liver Failure Study Group were tested for anti-HEV immunoglobulin (Ig) M and anti-HEV IgG levels. Subjects with a detectable anti-HEV IgM also underwent testing for HEV RNA. Mean patient age was 41.8 years, 32.9% were male, and ALF etiologies included acetaminophen (APAP) hepatotoxicity (29%), indeterminate ALF (23%), idiosyncratic drug-induced liver injury DILI (22%), acute hepatitis B virus infection (12%), autoimmune hepatitis (12%), and pregnancy-related ALF (2%). Three men ages 36, 39, and 70 demonstrated repeatedly detectable anti-HEV IgM, but all were HEV-RNA negative and had other putative diagnoses. The latter 2 subjects died within 3 and 11 days of enrollment whereas the 36-year-old underwent emergency liver transplantation on study day 2. At admission, 294 (43.4%) of the ALF patients were anti-HEV IgG positive with the seroprevalence being highest in those from the Midwest (50%) and lowest in those from the Southeast (28%). Anti-HEV IgG+ subjects were significantly older, less likely to have APAP overdose, and had a lower overall 3-week survival compared to anti-HEV IgG- subjects (63% vs. 70%; P = 0.018). CONCLUSION: Acute HEV infection is very rare in adult Americans with ALF (i.e., 0.4%) and could not be implicated in any indeterminate, autoimmune, or pregnancy-related ALF cases. Past exposure to HEV with detectable anti-HEV IgG was significantly more common in the ALF patients compared to the general U.S. POPULATION: (Hepatology 2016;64:1870-1880).

Immunoglobulin with High-Titer In Vitro Cross-Neutralizing Hepatitis C Virus Antibodies Passively Protects Chimpanzees from Homologous, but Not Heterologous, Challenge.

The importance of neutralizing antibodies (NAbs) in protection against hepatitis C virus (HCV) remains controversial. We infused a chimpanzee with H06 immunoglobulin from a genotype 1a HCV-infected patient and challenged with genotype strains efficiently neutralized by H06 in vitro. Genotype 1a NAbs afforded no protection against genotype 4a or 5a. Protection against homologous 1a lasted 18 weeks, but infection emerged when NAb titers waned. However, 6a infection was prevented. The differential in vivo neutralization patterns have implications for HCV vaccine development.

Cross-neutralizing human anti-poliovirus antibodies bind the recognition site for cellular receptor.

Most structural information about poliovirus interaction with neutralizing antibodies was obtained in the 1980s in studies of mouse monoclonal antibodies. Recently we have isolated a number of human/chimpanzee anti-poliovirus antibodies and demonstrated that one of them, MAb A12, could neutralize polioviruses of both serotypes 1 and 2. This communication presents data on isolation of an additional cross-neutralizing antibody (F12) and identification of a previously unknown epitope on the surface of poliovirus virions. Epitope mapping was performed by sequencing of antibody-resistant mutants and by cryo-EM of complexes of virions with Fab fragments. The results have demonstrated that both cross-neutralizing antibodies bind the site located at the bottom of the canyon surrounding the fivefold axis of symmetry that was previously shown to interact with cellular poliovirus receptor CD155. However, the same antibody binds to serotypes 1 and 2 through different specific interactions. It was also shown to interact with type 3 poliovirus, albeit with about 10-fold lower affinity, insufficient for effective neutralization. Antibody interaction with the binding site of the cellular receptor may explain its broad reactivity and suggest that further screening or antibody engineering could lead to a universal antibody capable of neutralizing all three serotypes of poliovirus.

An Epidemiologic Investigation of a Case of Acute Hepatitis E.

Hepatitis E virus (HEV) is considered a zoonotic infection in developed nations. A case of acute hepatitis E in a researcher following a scalpel injury while working on a pig prompted a seroepidemiologic study to identify potential modes of transmission and determine the seroprevalence of HEV among animal handlers at the institute. Sera from personnel (n = 64) in two animal facilities and age/sex-matched blood donors (n = 63) as controls were tested for IgG anti-HEV and, if positive, for IgM anti-HEV and HEV RNA. Sera and stool from pigs aged 6 to 12 weeks from the breeding farm and older pigs from animal facilities were tested similarly. The median age of personnel was 36 years, 74% were white, 56% were male, and 74% had direct exposure to pigs. The prevalence of anti-HEV was 3.1% among personnel compared to 3.2% among blood donors; none were positive for IgM anti-HEV or HEV RNA. IgG anti-HEV was detected in sera from 10% of pigs aged 6 to 8 weeks, 80% aged 10 weeks, 100% aged 12 weeks, and 76% aged >12 weeks. HEV RNA was detected in stool but not sera from three 12-week-old pigs. Sequencing revealed HEV genotype 3 with ∼10% difference between the patient and pig sequences. Parenteral transmission is a potential mode of acute HEV infection. The low and similar seroprevalence of anti-HEV between the at-risk group and age-matched blood donors suggests low transmission risk with universal precautions among animal handlers.

Declining prevalence of hepatitis E antibodies among Danish blood donors.

BACKGROUND: The increasing incidence of reported hepatitis E cases in Europe has focused attention on hepatitis E virus (HEV) and the risk of transfusion-transmitted hepatitis E. The aim of this study was to investigate the prevalence of antibodies to HEV (anti-HEV) among Danish blood donors in 2013 and to compare it to previous studies in Denmark. In addition we wanted to compare the relative reactivity of two different assays. STUDY DESIGN AND METHODS: Samples from 504 blood donors were collected and analyzed for anti-HEV with an in-house assay developed at the National Institutes of Health (NIH). In addition the samples were analyzed with the Wantai anti-HEV assay. Demographic information and possible HEV exposure was collected by self-administered questionnaire. RESULTS: Using the NIH assay the prevalence of anti-HEV among Danish blood donors was 10.7% and with the Wantai assay the prevalence of anti-HEV was 19.8% (p < 0.001). In both cases the presence of anti-HEV was significantly correlated with increasing age. In addition, anti-HEV as measured by the Wantai test was significantly associated with contact with children (p = 0.01), but in multivariate analysis only age was associated with anti-HEV in both assays. By the NIH assay, the prevalence had declined from 20.6% in 2003 to 10.7% in 2013. CONCLUSIONS: Anti-HEV prevalence had decreased by half among Danish blood donors over 10 years, but was still highly prevalent. The difference in reactivity of the two assays demonstrates the importance of using the same assay when comparing the anti-HEV prevalence in populations over time.

Highly efficient full-length hepatitis C virus genotype 1 (strain TN) infectious culture system.

Chronic infection with hepatitis C virus (HCV) is an important cause of end stage liver disease worldwide. In the United States, most HCV-related disease is associated with genotype 1 infection, which remains difficult to treat. Drug and vaccine development was hampered by inability to culture patient isolates representing HCV genotypes 1-7 and subtypes; only a recombinant 2a genome (strain JFH1) spontaneously replicated in vitro. Recently, we identified three mutations F1464L/A1672S/D2979G (LSG) in the nonstructural (NS) proteins, essential for development of full-length HCV 2a (J6) and 2b (J8) culture systems in Huh7.5 cells. Here, we developed a highly efficient genotype 1a (strain TN) full-length culture system. We initially found that the LSG substitutions conferred viability to an intergenotypic recombinant composed of TN 5' untranslated region (5'UTR)-NS5A and JFH1 NS5B-3'UTR; recovered viruses acquired two adaptive mutations located in NS3 and NS4B. Introduction of these changes into a replication-deficient TN full-length genome, harboring LSG, permitted efficient HCV production. Additional identified NS4B and NS5B mutations fully adapted the TN full-length virus. Thus, a TN genome with 8 changes (designated TN cell-culture derived, TNcc) replicated efficiently and released infectious particles of ∼5 log(10) focus-forming units per mL; passaged TNcc did not require additional changes. IFN-α and directly acting antivirals targeting the HCV protease, NS5A, and NS5B, each inhibited full-length TN infection dose-dependently. Given the unique importance of genotype 1 for pathogenesis, this infectious 1a culture system represents an important advance in HCV research. The approach used and the mutations identified might permit culture development for other HCV isolates, thus facilitating vaccine development and personalized treatment.

Profibrogenic chemokines and viral evolution predict rapid progression of hepatitis C to cirrhosis.

Chronic hepatitis C may follow a mild and stable disease course or progress rapidly to cirrhosis and liver-related death. The mechanisms underlying the different rates of disease progression are unknown. Using serial, prospectively collected samples from cases of transfusion-associated hepatitis C, we identified outcome-specific features that predict long-term disease severity. Slowly progressing disease correlated with an early alanine aminotransferase peak and antibody seroconversion, transient control of viremia, and significant induction of IFN-γ and MIP-1ß, all indicative of an effective, albeit insufficient, adaptive immune response. By contrast, rapidly progressive disease correlated with persistent and significant elevations of alanine aminotransferase and the profibrogenic chemokine MCP-1 (CCL-2), greater viral diversity and divergence, and a higher rate of synonymous substitution. This study suggests that the long-term course of chronic hepatitis C is determined early in infection and that disease severity is predicted by the evolutionary dynamics of hepatitis C virus and the level of MCP-1, a chemokine that appears critical to the induction of progressive fibrogenesis and, ultimately, the ominous complications of cirrhosis.

Robust full-length hepatitis C virus genotype 2a and 2b infectious cultures using mutations identified by a systematic approach applicable to patient strains.

Hepatitis C virus (HCV) infection is a leading cause of chronic liver diseases worldwide, but treatment options are limited. Basic HCV research required for vaccine and drug development has been hampered by inability to culture patient isolates, and to date only the JFH1 (genotype 2a) recombinant replicates spontaneously in hepatoma cells and releases infectious virus. A JFH1 chimera with the 5' end through NS2 from another genotype 2a strain, J6, had enhanced infectivity. However, the full-length J6 clone (J6CF), which we previously found to be fully functional in vivo, was replication incompetent in vitro. Through a systematic approach of culturing J6 with minimal JFH1 sequences, we identified three mutations in NS3, NS4A, and NS5B that permitted full-length J6 propagation and adaptation with infectivity titers comparable to JFH1-based systems. The most efficient recombinant, J6cc, had six adaptive mutations and did not accumulate additional changes following viral passage. We demonstrated that HCV NS3/NS4A protease-, NS5A- and NS5B polymerase-directed drugs respectively inhibited full-length J6 infection dose dependently. Importantly, the three J6-derived mutations enabled culture adaptation of the genetically divergent isolate J8 (genotype 2b), which differed from the J6 nucleotide sequence by 24%. The most efficient recombinant, J8cc, had nine adaptive mutations and was genetically stable after viral passage. The availability of these robust JFH1-independent genotype 2a and 2b culture systems represents an important advance, and the approach used might permit culture development of other isolates, with implications for improved individualized treatments of HCV patients and for development of broadly efficient vaccines.

Development of Norwalk virus-specific monoclonal antibodies with therapeutic potential for the treatment of Norwalk virus gastroenteritis.

Passive immunoprophylaxis or immunotherapy with norovirus-neutralizing monoclonal antibodies (MAbs) could be a useful treatment for high-risk populations, including infants and young children, the elderly, and certain patients who are debilitated or immunocompromised. In order to obtain antinorovirus MAbs with therapeutic potential, we stimulated a strong adaptive immune response in chimpanzees to the prototype norovirus strain Norwalk virus (NV) (genogroup I.1). A combinatorial phage Fab display library derived from mRNA of the chimpanzees' bone marrow was prepared, and four distinct Fabs reactive with Norwalk recombinant virus-like particles (rVLPs) were recovered, with estimated binding affinities in the subnanomolar range. Mapping studies showed that the four Fabs recognized three different conformational epitopes in the protruding (P) domain of NV VP1, the major capsid protein. The epitope of one of the Fabs, G4, was further mapped to a specific site involving a key amino acid residue, Gly365. One additional specific Fab (F11) was recovered months later from immortalized memory B cells and partially characterized. The anti-NV Fabs were converted into full-length IgG (MAbs) with human γ1 heavy chain constant regions. The anti-NV MAbs were tested in the two available surrogate assays for Norwalk virus neutralization, which showed that the MAbs could block carbohydrate binding and inhibit hemagglutination by NV rVLP. By mixing a single MAb with live Norwalk virus prior to challenge, MAbs D8 and B7 neutralized the virus and prevented infection in a chimpanzee. Because chimpanzee immunoglobulins are virtually identical to human immunoglobulins, these chimpanzee anticapsid MAbs may have a clinical application.

Human monoclonal antibody HCV1 effectively prevents and treats HCV infection in chimpanzees.

Hepatitis C virus (HCV) infection is a leading cause of liver transplantation and there is an urgent need to develop therapies to reduce rates of HCV infection of transplanted livers. Approved therapeutics for HCV are poorly tolerated and are of limited efficacy in this patient population. Human monoclonal antibody HCV1 recognizes a highly-conserved linear epitope of the HCV E2 envelope glycoprotein (amino acids 412-423) and neutralizes a broad range of HCV genotypes. In a chimpanzee model, a single dose of 250 mg/kg HCV1 delivered 30 minutes prior to infusion with genotype 1a H77 HCV provided complete protection from HCV infection, whereas a dose of 50 mg/kg HCV1 did not protect. In addition, an acutely-infected chimpanzee given 250 mg/kg HCV1 42 days following exposure to virus had a rapid reduction in viral load to below the limit of detection before rebounding 14 days later. The emergent virus displayed an E2 mutation (N415K/D) conferring resistance to HCV1 neutralization. Finally, three chronically HCV-infected chimpanzees were treated with a single dose of 40 mg/kg HCV1 and viral load was reduced to below the limit of detection for 21 days in one chimpanzee with rebounding virus displaying a resistance mutation (N417S). The other two chimpanzees had 0.5-1.0 log(10) reductions in viral load without evidence of viral resistance to HCV1. In vitro testing using HCV pseudovirus (HCVpp) demonstrated that the sera from the poorly-responding chimpanzees inhibited the ability of HCV1 to neutralize HCVpp. Measurement of antibody responses in the chronically-infected chimpanzees implicated endogenous antibody to E2 and interference with HCV1 neutralization although other factors may also be responsible. These data suggest that human monoclonal antibody HCV1 may be an effective therapeutic for the prevention of graft infection in HCV-infected patients undergoing liver transplantation.

Transfusion-associated hepatitis before the screening of blood for hepatitis risk factors.

BACKGROUND: The true incidence of transfusion-associated hepatitis (TAH) before blood screening is unknown. Our aims were to reevaluate blood recipients receiving unscreened blood and analyze hepatitis viruses circulating more than 45 years ago. STUDY DESIGN AND METHODS: Cryopreserved serum samples from 66 patients undergoing open heart surgery in the 1960s were reevaluated with modern diagnostic tests to determine the incidence of TAH and its virologic causes. RESULTS: In this heavily transfused population receiving a mean of 20 units per patient of predominantly paid-donor blood, 30 of 66 (45%) developed biochemical evidence of hepatitis; of these, 20 (67%) were infected with hepatitis C virus (HCV) alone, four (13%) with hepatitis B virus (HBV) alone, and six (20%) with both viruses. Among the 36 patients who did not develop hepatitis, four (11%) were newly infected with HCV alone, nine (25%) with HBV alone, and one (3%) with both viruses. Overall, 100% of patients with hepatitis and 39% of those without hepatitis were infected with HBV and/or HCV; one patient was also infected with hepatitis E virus. The donor carrier rate for HBV and/or HCV was estimated to be more than 6%; contemporaneously prepared pooled normal human plasma was also contaminated with multiple hepatitis viruses. CONCLUSION: TAH virus infections were a larger problem than perceived 50 years ago and HCV was the predominant agent transmitted. All hepatitis cases could be attributed to HCV and/or HBV and hence there was no evidence to suggest that an additional hepatitis agent existed undetected in the blood supply.

Pre- and postexposure protection against virulent anthrax infection in mice by humanized monoclonal antibodies to Bacillus anthracis capsule.

One of the two essential virulence factors of Bacillus anthracis is the poly-γ-D-glutamic acid (γDPGA) capsule. Five γDPGA-specific antibody antigen-binding fragments (Fabs) were generated from immunized chimpanzees. The two selected for further study, Fabs 11D and 4C, were both converted into full-length IgG1 and IgG3 mAbs having human IgG1 or IgG3 constant regions. These two mAbs had similar binding affinities, in vitro opsonophagocytic activities, and in vivo efficacies, with the IgG1 and IgG3 subclasses reacting similarly. The mAbs bound to γDPGA specifically with estimated binding affinities (K(d)) of 35-70 nM and effective affinities (effective K(d)) of 0.1-0.3 nM. The LD(50) in an opsonophagocytic bactericidal assay was ≈10 ng/mL of 11D or 4C. A single 30-µg dose of either mAb given to BALB/c mice 18 h before challenge conferred about 50% protection against a lethal intratracheal spore challenge by the virulent B. anthracis Ames strain. More importantly, either mAb given 8 h or 20 h after challenge provided significant protection against lethal infection. Thus, these anti-γDPGA mAbs should be useful, alone or in combination with antitoxin mAbs, for achieving a safe and efficacious postexposure therapy for anthrax.

Cross-species infections of cultured cells by hepatitis E virus and discovery of an infectious virus-host recombinant.

The RNA virus, hepatitis E virus (HEV) is the most or second-most important cause of acute clinical hepatitis in adults throughout much of Asia, the Middle East, and Africa. In these regions it is an important cause of acute liver failure, especially in pregnant women who have a mortality rate of 20-30%. Until recently, hepatitis E was rarely identified in industrialized countries, but Hepatitis E now is reported increasingly throughout Western Europe, some Eastern European countries, and Japan. Most of these cases are caused by genotype 3, which is endemic in swine, and these cases are thought to be zoonotically acquired. However, transmission routes are not well understood. HEV that infect humans are divided into nonzoonotic (types 1, 2) and zoonotic (types 3, 4) genotypes. HEV cell culture is inefficient and limited, and thus far HEV has been cultured only in human cell lines. The HEV strain Kernow-C1 (genotype 3) isolated from a chronically infected patient was used to identify human, pig, and deer cell lines permissive for infection. Cross-species infections by genotypes 1 and 3 were studied with this set of cultures. Adaptation of the Kernow-C1 strain to growth in human hepatoma cells selected for a rare virus recombinant that contained an insertion of 174 ribonucleotides (58 amino acids) of a human ribosomal protein gene.

Chimpanzees as an animal model for human norovirus infection and vaccine development.

Noroviruses are global agents of acute gastroenteritis, but the development of control strategies has been hampered by the absence of a robust animal model. Studies in chimpanzees have played a key role in the characterization of several fastidious hepatitis viruses, and we investigated the feasibility of such studies for the noroviruses. Seronegative chimpanzees inoculated i.v. with the human norovirus strain Norwalk virus (NV) did not show clinical signs of gastroenteritis, but the onset and duration of virus shedding in stool and serum antibody responses were similar to that observed in humans. NV RNA was detected in intestinal and liver biopsies concurrent with the detection of viral shedding in stool, and NV antigen expression was observed in cells of the small intestinal lamina propria. Two infected chimpanzees rechallenged 4, 10, or 24 mo later with NV were resistant to reinfection, and the presence of NV-specific serum antibodies correlated with protection. We evaluated the immunogenicity and efficacy of virus-like particles (VLPs) derived from NV (genogroup I, GI) and MD145 (genogroup II, GII) noroviruses as vaccines. Chimpanzees vaccinated intramuscularly with GI VLPs were protected from NV infection when challenged 2 and 18 mo after vaccination, whereas chimpanzees that received GII VLPs vaccine or a placebo were not. This study establishes the chimpanzee as a viable animal model for the study of norovirus replication and immunity, and shows that NV VLP vaccines could induce protective homologous immunity even after extended periods of time.

Specificity of an anti-capsid antibody associated with Hepatitis B Virus-related acute liver failure.

Previously, the livers of patients suffering from acute liver failure (ALF), a potentially fatal syndrome arising from infection by Hepatitis B Virus (HBV), were found to contain massive amounts of an antibody specific for the core antigen (HBcAg) capsid. We have used cryo-electron microscopy and molecular modeling to define its epitope. HBV capsids are icosahedral shells with 25Å-long dimeric spikes, each a 4-helix bundle, protruding from the contiguous "floor". Of the anti-HBcAg antibodies previously characterized, most bind around the spike tip while one binds to the floor. The ALF-associated antibody binds tangentially to a novel site on the side of the spike. This epitope is conformational. The Fab binds with high affinity to its principal determinants but has lower affinities for quasi-equivalent variants. The highest occupancy site is on one side of a spike, with no detectable binding to the corresponding site on the other side. Binding of one Fab per dimer was also observed by analytical ultracentrifugation. The Fab did not bind to the e-antigen dimer, a non-assembling variant of capsid protein. These findings support the propositions that antibodies with particular specificities may correlate with different clinical expressions of HBV infection and that antibodies directed to particular HBcAg epitopes may be involved in ALF pathogenesis.

Occult hepatitis B virus infection in chacma baboons, South Africa.

During previous studies of susceptibility to hepatitis B virus (HBV) infection, HBV DNA was detected in 2/6 wild-caught baboons. In the present study, HBV DNA was amplified from 15/69 wild-caught baboons. All animals were negative for HBV surface antigen and antibody against HBV core antigen. Liver tissue from 1 baboon was immunohistochemically negative for HBV surface antigen but positive for HBV core antigen. The complete HBV genome of an isolate from this liver clustered with subgenotype A2. Reverse transcription PCR of liver RNA amplified virus precore and surface protein genes, indicating replication of virus in baboon liver tissue. Four experimentally naive baboons were injected with serum from HBV DNA-positive baboons. These 4 baboons showed transient seroconversion, and HBV DNA was amplified from serum at various times after infection. The presence of HBV DNA at relatively low levels and in the absence of serologic markers in the baboon, a nonhuman primate, indicates an occult infection.