Vaccine- and hepatitis B immune globulin-induced escape mutations of hepatitis B virus surface antigen

Mutation spectra of the surface-protein-coding region of the HBV genome in HBV-vaccinated and non-vaccinated individuals in Hungary

Hepatitis B virus (HBV) infection has a major effect on health care systems, with about one-third of the world's population currently infected with the virus. There is an effective vaccine against HBV, which contains a recombinant "surface antigen" produced in an expression vector. Vaccination has proved to be successful in Hungary: the number of acute HBV cases has decreased in the past 10 years. Although an increasing number of publications report on "vaccine-escape" HBV variants which can infect HBV-vaccinated individuals, such mutant HBV strains have not yet been detected in Hungary. We therefore surveyed two risk groups for vaccine-escape or immunoglobulin-escape HBV mutations in Hungary: 28 actively and/or passively HBV-immunized children of HBV carrier mothers who proved to be HBsAg and/or anti-HBc positive and 40 symptomless HBV carrier pregnant women (presumably carrying genotype B or C). We focused on the coding sequences of the "a" immundominant region of the surface protein. We could not detect the G145R amino acid substitution associated with vaccine escape mutant virus. However, we could map other mutations potentially affecting the immunodominant "a" region of the HBV surface protein.

Multiple surface antigen mutations in five blood donors with occult hepatitis B virus infection

Occult hepatitis B virus (HBV) infection is characterized by the presence of HBV DNA while the HBV surface antigen (HBsAg) remains undetectable. The HBV genomes in five asymptomatic blood donors with occult HBV infection and low viremia (<10 to 1,000 HBV DNA copies/mL, genotype D) were studied. An unusually large number of amino acid mutations was present in the immunodominant a-determinant of HBsAg (respectively 3, 6, 7, 10, and 10 mutations). Comparison of the HBV genomes in two donors to a consensus HBV genotype D sequence showed a most prominent hotspot of genetic variation in HBV nucleotides 480-570, encoding the HBsAg a-determinant. The phylogenetic comparison of separate donor HBV genes to the HBV genes of 11 reference strains (genotypes A-H) showed the donor HBV surface genes to form an outgroup, while the HBV polymerase, core and X genes closely cluster with the HBV genotype D reference strain. Maybe the HBV strains in this study represent a natural end-stage of seemingly cleared HBV infection, in which HBV maintains a low level of possibly non-infectious replication, after sacrificing its immunologically offending surface antigen, thus avoiding final clearance by the immune system.

Hepatitis B caused by a hepatitis B surface antigen escape mutant

Amino acid substitutions within the S gene involving the major antigenic a determinant of the hepatitis B virus (HBV) surface antigen (HBsAg) have been detected in cases of failure of immunization against the virus. Our report showed development of clinical hepatitis in presence of antibody to HBsAg in a healthy individual. A single amino acid substitution (G145R) within the a determinant of the HBsAg was determined by sequencing of the isolated HBV strain. Lamivudine treatment efficiently cleared the peripheral HBV DNA, HBsAg, and hepatitis B e antigen. In conclusion, the immune escape mutant in the S gene can cause hepatitis despite pre-existing naturally acquired immunity.

Hepatitis B virus vaccine switch program for prevention of de novo hepatitis B virus infection in pediatric patients

The principal objective of this study was to evaluate the feasibility of Hepatitis B virus (HBV) vaccine switch program after 1-year Hepatitis B immunoglobulin (HBIG) for the prevention of de novo HBV (DNHBV) infection in pediatric recipients of hepatitis B core antibody (anti-HBc)-positive grafts. In this study, we enrolled pediatric recipients (n = 14), who had undergone living donor liver transplantation with anti-HBc-positive grafts between July 2000 and July 2005 and were followed up for over 24 months after transplantation. HBIG was given daily during the first week and intermittently in order to maintain anti-hepatitis B surface antigen (anti-HBs) titers greater than 200 IU/l until 12 months post-transplantation. Then the HBV vaccine was given intermittently as a substitute for HBIG when anti-HBs titer fell below 200 IU/l. The median follow-up duration after vaccination was 26.5 months, and a median of 2.03 doses of vaccine per year was required for the maintenance of anti-HBs titers greater than at least 100 IU/l. Two of the patients did not start the HBV vaccine due to sustained high anti-HBs titer. Eleven completed the HBV switch, whereas 1 was ongoing. With the HBV vaccine switch program, anti-HBs titers greater than 100 IU/l could be maintained conveniently and effectively.

Management of hepatitis B in liver transplant recipients

Advances in hepatitis B virus (HBV) antiviral prophylaxis have dramatically improved graft and patient survival for patients undergoing liver transplantation for hepatitis B related end-stage liver disease. In particular, the availability of hepatitis B immune globulin (HBIg) in combination with nucleos(t)ide analogues such as lamivudine and adefovir, have transformed outcomes. The availability of newer antivirals such as adefovir, tenofovir and entecavir either as monotherapy or in combination offer an increasing number of antiviral options. Despite these advances, significant challenges remain. Factors that affect the efficacy of anti-viral therapy include detectable HBV viraemia at the time of transplant and emergence of HBV mutants (especially in patients with prior exposure to lamivudine). HBV prophylaxis protocols are expensive especially with use of high-dose HBIg and newer nucleos(t)ide analogues. This review summarizes current HBV prophylaxis protocols and management of recurrent disease post-transplantation. There is an increasing need for individualization of therapy based on prior drug exposures, level of HBV DNA at time of transplantation and type of prophylaxis used.

Prevalence of hepatitis B, C, and delta virus infections among children in Mongolia: progress in childhood immunization

Mongolia is highly endemic for hepatitis B virus (HBV), hepatitis C virus (HCV), and hepatitis delta virus (HDV) infections among apparently healthy adults. However, the age-specific prevalence of ongoing HBV, HCV, and HDV infections among children in Mongolia remains unknown. Therefore, samples obtained from a total of 655 apparently healthy children of 0.3-15 years of age (307 boys and 348 girls; age, mean +/- standard deviation [SD], 8.4 +/- 4.2 years) living in Mongolia, between October 2005 and January 2006, were tested for serological and molecular markers of HBV, HCV, and HDV infections. Although 88.7% of the 655 children studied were immunized against hepatitis B, 64 (9.8%) tested positive for hepatitis B surface antigen (HBsAg) and/or HBV DNA and 13 (2.0%) for HDV RNA. Twenty-seven children (4.1%) had detectable HCV RNA. Collectively, 82 (12.5%) were viremic for one or more of these viruses, including eight children with dual viremia of HBV/HCV and one child with triple HBV/HCV/HDV viremia. When children without anti-HBc, anti-HCV and anti-HDV IgG (n = 510) served as a control, a history of hospitalization was significantly associated with HBV viremia (P < 0.0001), anti-HBc positivity (P < 0.0001), and HCV viremia (P = 0.0001). HBsAg mutation was found in 18 (31.6%) of the 57 children with viremia, including those at amino acid position 126, 127, 129, 131, 134, 143 or 144. There were no significant differences in the frequency of HBsAg mutation in relation to age, sex, and hepatitis B vaccination status of the children, suggesting that HBsAg mutation plays a limited role in failure of vaccination in Mongolia.

The amino Acid residues at positions 120 to 123 are crucial for the antigenicity of hepatitis B surface antigen

The major hydrophilic region (MHR) of hepatitis B surface antigen (HBsAg) harbors conformational B-cell epitopes and is the major target of neutralizing antibodies to HBsAg (anti-HBs). Mutant HBsAg (mtHBsAg) with amino acid substitutions such as G145R is known to affect the binding of specific anti-HB antibodies and their detection by conventional diagnostic assays. In the present study, we focused on the role of the amino acid positions 120 to 123, which are around MHR 2 according to the spectrum of recently identified, naturally occurring mtHBsAg. Strikingly, the amino acid substitution K122I abolished the reactivity of HBsAg in all immunoassays tested so far. Also, mtHBsAg G145R could be clearly detected with four different enzyme-linked immunosorbent assays that were based on monoclonal anti-HB antibodies (MAbs) with high affinity. Positive immunofluorescence staining of mtHBsAg K122I was achieved only by polyclonal anti-HBs, while all MAbs tested failed. mtHBsAg T123N showed a low reactivity in immunoassays and appeared to be secretion defective. The amino acid substitution P120T reduced the binding of anti-HBs but did not completely prevent the detection of mtHBsAg by anti-HB MAbs. The testing of naturally occurring mtHBsAg confirmed that the presence of amino acid substitutions within the region of 120 to 123 is strongly associated with impaired detection in immunoassays. In conclusion, MHR 2 is essential for HBsAg antigenicity, a fact that has not been recognized before.

Clinical and virological significance of the co-existence of HBsAg and anti-HBs antibodies in hepatitis B chronic carriers

The co-existence of hepatitis B surface antigen (HBsAg) and anti-HBs antibodies (HBsAb) in serum of hepatitis B virus (HBV)-chronic carriers has been previously associated with HBsAg-amino acid (aa) substitutions. However, the aa pattern of HBV-reverse transcriptase (RT) and the clinical settings associated with this serological profile remain largely unknown. We studied thirteen HBsAg-positive/HBsAb-positive patients. Newly diagnosed HBsAg-positive/HBsAb-negative patients (n=51) served as controls. HBsAg/RT sequences were obtained using in-house protocols. HBsAg-positive/HBsAb-positive patients were predominantly immunosuppressed (69%). Five presented advanced liver fibrosis. HBV DNA >5.0 log(10) copies/ml was significantly more frequent than in controls. A significantly higher aa variability was observed versus controls within HBsAg major hydrophilic region (MHR), especially the a-determinant, and within RT for regions overlapping the MHR, the a-determinant, and HBsAg C terminal region where drug resistance mutations occur. Further studies are needed to determine whether this higher HBsAg/HBV-RT variability might favor dissemination of anti-HBsAb escape HBV mutants and concomitantly alter nucleos(t)ide analogs efficacy.

Selection for functional diversity drives accumulation of point mutations in Dr adhesins of Escherichia coli

Immune escape is considered to be the driving force behind structural variability of major antigens on the surface of bacterial pathogens, such as fimbriae. In the Dr family of Escherichia coli adhesins, structural and adhesive functions are carried out by the same subunit. Dr adhesins have been shown to bind decay-accelerating factor (DAF), collagen IV, and carcinoembryonic antigen-related cell adhesion molecules (CEACAMs). We show that genes encoding Dr adhesins from 100 E. coli strains form eight structural groups with a high level of amino acid sequence diversity between them. However, genes comprising each group differ from each other by only a small number of point mutations. Out of 66 polymorphisms identified within the groups, only three were synonymous mutations, indicating strong positive selection for amino acid replacements. Functional analysis of intragroup variants comprising the Dr haemagglutinin (DraE) group revealed that the point mutations result in distinctly different binding phenotypes, with a tendency of increased affinity to DAF, decreased sensitivity of DAF binding to inhibition by chloramphenicol, and loss of binding capability to collagen, CEACAM3 and CEACAM6. Thus, variability by point mutation of major antigenic proteins on the bacterial surface can be a signature of selection for functional modification.

Hepatitis B virus genetic variability and evolution

Hepatitis B virus has been evolving gradually over a long period of time, resulting in a large amount of genetic diversity, despite the constraints imposed by the complex genetic organization of the viral genome. This diversity is partly due to virus/host interactions and partly due to parallel evolution in geographically distinct areas. Recombination also appears to be an important element in HBV evolution. Also, human intervention in the form of mass vaccination and antiviral treatment will reduce the burden of HBV-related liver disease but may also be accelerating evolution of the virus.

A new hepatitis B virus vaccine escape mutation in a renal transplant recipient

Surface antigen mutations of hepatitis B virus (HBV) may lead to immune escape and cause failure of immunization. In this report, the development of a chronic HBV infection in a vaccinated renal transplant recipient with pre-existing anti-HBs antibody is documented. The sequencing data showed that the HBV strain carried five amino acid substitutions in the major hydrophilic region of the S protein, one (sS143L) located at the "a" determinant. A commercial HBsAg assay failed to detect the mutant antigen.

Detection of HBsAg mutants in a population with a low prevalence of hepatitis B virus infection

Two independent studies were conducted to evaluate performance of two HBsAg immunoassay products performed on the Abbott ARCHITECT and Bayer ADVIA Centaur immunoassay analyzers. One was a retrospective study of 484 stored samples and the second was a prospective study of 349 samples from random population. In the process of the evaluation, a number of discordant samples from HBsAg-positive patients were found which led to the discovery of a number of HBsAg mutants in the general Australian population. Following viral DNA sequencing, these were identified as HBsAg escape mutants. Whilst the existence of HBsAg mutants has been well documented in various regions of the world, this is surprising in an area of low endemicity and demonstrates the necessity of an HBsAg assay to detect mutants reliably in a diagnostic situation where HBsAg is used as the only marker to detect an HBV infection. These studies demonstrate the ability of the Abbott ARCHITECT and AxSYM HBsAg immunoassays to detect these HBsAg mutations which were not detected by the Bayer ADVIA Centaur.

Novel mutations in the respiratory syncytial virus G gene identified in viral isolates from a girl with severe combined immune deficiency treated with intravenous immune globulin

BACKGROUND

Respiratory syncytial virus (RSV) can cause prolonged infections in individuals with compromised immunity.

OBJECTIVES

To investigate whether RSV evolves during prolonged infection in an immunocompromised host.

STUDY DESIGN

We sequenced the envalope glycoprotein genes of RSV obtained at three time points during a 59-day period from a 4-year-old female with severe combined immune deficiency (SCID) treated with intravenous immunoglobulin (IVIG).

RESULTS

Sporadic silent mutations were found in the SH, G and F genes among three RSV samples collected at days 0, 19 and 59. Premature stop codons at amino acid positions 257 and 278 were present in the RSV G glycoprotein gene sequenced from each time point. None of the 48 RSV G sequences available on GenBank or any of 50 genetically diverse clinical isolates of RSV contained these mutations. These premature stop codon mutations occurred at the same positions of the G glycoprotein gene as those described in in vitro monoclonal-antibody resistant mutants reported elsewhere.

CONCLUSION

Our patient was most likely infected with a single RSV strain that did not mutate during the study period. This strain contains unique mutations that may have previously evolved in this individual who had prolonged infection and was treated with monthly IVIG.

Neutralization epitope responsible for the hepatitis B virus subtype-specific protection in chimpanzees

Neutralizing monoclonal antibody (BX-182) directed against the d determinant of hepatitis B virus (HBV) surface antigen protected chimpanzees from infection by HBV subtype adw but not by subtype ayw, as demonstrated by intravenously inoculating a mixture of the antibody with the respective subtype of the virus. To elucidate the mechanism underlying the subtype-specific protection, a combinatorial approach of screening random peptide phage libraries, bioinformatics, and structure analysis was used in this study to identify the neutralization epitope responsible for the observed protection. The epitope was mapped at the N terminus of the pre-S1 region of the hepatitis B surface antigen between residues 17 and 21, of which the residues Val-18/Pro-19 were critical for antibody binding. Alignment of amino acid sequences derived from diverse genetic variants of HBV revealed that the epitope was present in ad subtypes and in their corresponding genotypes A, B, C, F, and H. By contrast, this epitope was not found in a majority of ay subtypes or in genotypes D, E, and G, where the antigenic residues Val-18/Pro-19 within the epitope were replaced by Thr/Ser, Thr/Thr, or Ala/Ser, respectively, resulting in a drastic conformational change of the epitope. These data indicate that, by binding discriminately to the subtype "d" epitope in the pre-S1 region, neutralizing antibody BX-182 protects chimpanzees from HBV infection in a subtype-specific manner, suggesting a potential escape mechanism for HBV genetic variants.

Prevention and treatment of recurrent Hepatitis B after liver transplantation: the current role of nucleoside and nucleotide analogues

The Hepatitis B virus (HBV) is a DNA virus that can cause both acute and chronic liver disease in humans. Approximately 350–400 million people are affected worldwide and up to one million deaths occur annually from cirrhosis and hepatocellular carcinoma. When cirrhosis and liver failure develop, the definitive treatment of choice remains orthotopic liver transplantation (OLT). In the past, an unacceptable HBV recurrence rate with a high rate of graft loss was noted. The use of Hepatitis B immunoglobulin (HBIG) has resulted in improved patient and graft survival rates. The addition of the nucleoside analog Lamivudine (LAM) to HBIG has improved these survival curves to an even greater degree. Prolonged use of LAM will almost invariably lead to the development of viral mutations resistant to the drug. There are now several other nucleoside and nucleotide analogs (Adefovir, Entecavir, Tenofovir, and Truvada) available for the clinician to utilize against these resistant strains. It should be possible to prevent recurrence in most, if not all, post-transplant patients and also to significantly reduce viral loads with normalization of transaminases in those who have developed recurrent infection. The antiviral regimen should be robust and minimize the risk of breakthrough mutations. A prudent approach may be the implication of combination antiviral therapy. This review summarizes the efficacy of previous regimens utilized to prevent and treat recurrent HBV following OLT. Particular attention will be paid to the newer nucleoside and nucleotide analogs and the direction for future strategies to treat HBV in the post transplant setting.

Coexistence of hepatitis B surface antigen (HBs Ag) and anti-HBs antibodies in chronic hepatitis B virus carriers: influence of "a" determinant variants

In chronic hepatitis B (CHB), the persistence of hepatitis B surface antigen (HBs Ag) is sometimes associated with antibodies (Ab) to HBs (anti-HBs). To assess the hypothesis of the selection of HBs Ag immune escape variants in CHB patients, the variability of the HBV S gene was determined for patients persistently carrying both HBs Ag and anti-HBs antibodies and patients solely positive for HBs Ag. We selected 14 patients who presented both markers (group I) in several consecutive samples and 12 patients positive for HBs Ag only (group II). The HBs Ag-encoding gene was amplified and cloned, and at least 15 clones per patient were sequenced and analyzed. The number of residue changes within the S protein was 2.7 times more frequent for group I than for group II patients and occurred mostly in the "a" determinant of the major hydrophilic region (MHR), with 9.52 versus 2.43 changes per 100 residues (P = 0.009), respectively. Ten patients (71%) from group I, but only three (25%) from group II, presented at least two residue changes in the MHR. The most frequent changes in group I patients were located at positions s145, s129, s126, s144, and s123, as described for immune escape variants. In CHB patients, the coexistence of HBs Ag and anti-HBs Ab is associated with an increase of "a" determinant variability, suggesting a selection of HBV immune escape mutants during chronic carriage. The consequences of this selection process with regard to vaccine efficacy, diagnosis, and clinical evolution remain partially unknown.

Antigenicity and immunogenicity of the immunodominant region of hepatitis B surface antigen displayed on bacteriophage T7

The immunodominant region of hepatitis B virus (HBV) located in the viral small surface antigen (S-HBsAg) elicits virus-neutralizing and protective antibodies. In order to develop an easy and inexpensive method to produce this region without the need for extensive purification, amino acid residues 111-156 of S-HBsAg were fused to the C-terminal end of the 10B capsid protein of T7 phage. Western blotting and ELISA confirmed the expression of the recombinant protein on the surface of the phage particles. The recombinant phage exhibited the antigenic and immunogenic characteristics of HBsAg, illustrating its potential as an immunological reagent and vaccine.

Prevalence of naturally occurring surface antigen variants of hepatitis B virus in Korean patients infected chronically

Although Korea is one of the endemic areas of hepatitis B virus (HBV) infection, the prevalence of naturally occurring variants in the major hydrophilic region (MHR) of the surface (S) gene of HBV has not been determined. In the present study, the prevalence of these variants was examined in terms of the clinical state, and HBeAg serostatus in a large series of Korean patients with chronic HBV infection by direct sequencing analysis of part of the S gene containing the MHR of HBV isolated from 101 chronic HBV patients (51 HBeAg-positive and 50 HBeAg-negative): 37 were asymptomatic carriers, 21 had chronic hepatitis, 20 had liver cirrhosis, and 23 had hepatocellular carcinoma (HCC). Forty-seven MHR variants (46.5%) of the 101 patients were detected, involving a total of 59 amino acid substitutions at 12 positions inside and 14 position outside the 'a' determinant, and 33 'a' determinant variants (32.7%). A total of 17 novel variants and 14 novel mutation patterns were detected. The prevalence of MHR variants in HBeAg-negative patients tended to be higher than in HBeAg-positive patients (54.0% vs.39.2%) and the prevalence of MHR variants in HCC and liver cirrhosis tended to be higher than in asymptomatic carriers (65.2% vs. 40.5% and 50.0% vs. 40.5%, respectively). In conclusion, three important findings were found in the present study. First, an unexpectedly high prevalence of naturally occurring MHR variants was found in Korean chronic patients. Second, several novel variants associated with mutations outside the 'a' determinant were detected. Finally, a higher prevalence of MHR variants was associated with HBeAg-negative serostatus and severe liver disease, particularly HCC.

Mutant hepatitis B virus surface antigens (HBsAg) are immunogenic but may have a changed specificity

Mutant hepatitis B virus with substitutions within the coding region for HBV surface antigen (HBsAg) has been found naturally in chronic carriers. It is therefore important to clarify whether the identified substitutions within the HBsAg have impact on the antigenicity and immunogenicity of HBsAg. A total of nine mutated HBV s-genes with single representative mutations were generated by site-directed mutagenesis and subcloned into an expression vector. The binding of polyclonal and monoclonal antibodies to these mutant HBsAg (mtHBsAg) was tested by immunofluorescence (IF) staining of cells transfected with the expression vectors. The amino acid (aa) substitutions like G145R, F134S, and C147W affected the binding of anti-HBs antibodies to corresponding mtHBsAg to different extents. The impact of aa substitutions G145R and F134S on the immunogenicity was accessed by genetic immunization of mice with vectors expressing middle HBsAg with the corresponding mutations. The immunized mice developed antibodies to recombinant HBsAg containing the HBV preS region and HBsAg-specific cytotoxic T-cell. However, the development of antibody response to wild-type small HBsAg was significantly impaired by the aa substitutions in HBsAg. Based on this fact, we further investigated whether the mtHBsAg with the aa substitution G145R is able to induce mutant-specific antibody responses. Strikingly, serum samples from mice immunized with mtHBsAg with G145R recognized plasma-derived mtHBsAg. Two mouse MAbs specific to mtHBsAg were generated. One MAb recognized mtHBsAg with G145R but not wild type and other mtHBsAg. We conclude that HBsAg with aa substitutions are immunogenic but may have a changed fine specificity.

Incidence of HBV variants with a mutation at nt551 among hepatitis B patients in Nanjing and its neighbourhood

AIM: To investigate the epidemiology of hepatitis B virus (HBV) strains with a mutation at nt551 in surface gene among hepatitis B patients in Nanjing and its neighbourhood.

METHODS: By using mutation-specific polymerase chain reaction (msPCR) established by our laboratory for amplifying HBV DNAs with a mutation at nt551, 117 serum samples taken from hepatitis B patients were detected.

RESULTS: The results showed that 112 samples were positive for nt551A, 4 samples were positive for nt551G. One sample was positive for nt551T. No nt551C of HBV DNA was found. The incidence of HBsAg mutants with G, C, T, A at nt551 among 117 samples was 3.42%, 0%, 0.85%, 95.73%, respectively.

CONCLUSION: In Nanjing and its neighbourhood, hepatitis B patients are mainly infected with wild genotype HBV. The incidence of mutants with a mutation at nt551 in HBV genome is significantly lower than that in wild genotype HBV DNA (P<0.01). The necessity of adding components of HBsAg mutants to HBV vaccine needs further investigation.

Antigenic and immunogenic changes due to mutation of s gene of HBV

AIM: To investigate the change of immunological characteristics of HBsAg caused by the mutation at codon 145 of HBsAg using DNA-based immunization.

METHODS: Plasmids expressing mutant and wild type envelope antigens were transfected into human hepatocellular carcinoma cellsviaelectrotransformation. The antigenicity of HBsAg was studied with EIA and immunocytochemical staining. Then plasmids were used to immunize 5 C57BL/6 mice. Sera of mice were detected for anti-HBs and anti-preS2 with ELISA.

RESULTS: The mutant HBsAg could be detected by native antibody in EIA and immunocytochemical study. But the A_{(450 nm)} value of the mutant HBsAg in the supernatant was apparently lower than that of the wild-type. Both mutant and native HBsAg expression plasmid could stimulate a strong humoral immune response to HBsAg and preS2 antigen in mice. Protective antibodies against HBsAg elicited by the native HBsAg occurred earlier than that elicited by the mutant HBsAg about one to two weeks. The occurrence of protective antibodies against preS2 antigen was one to two weeks earlier than that of anti-HBs.

CONCLUSION: The amino acid substitution causes changes of the antigenicity and immunogenicity of HBsAg, but mutant HBsAg can still induce a protective humoral immune response in mice.

Replication and gene expression of mutant hepatitis B virus in a transgenic mouse containing the complete viral genome with mutant s gene

AIM: To establish the transgenic mouse line harbouring complete hepatitis B virus (HBV) genome with mutant s gene (adr subtype).

METHODS: Transgenic mice were generated by microinjecting HBV genome into fertilized eggs. Integration, expression, replication of HBV gene and histological changes in transgenic mice were estimated by genomic DNA PCR, serum DNA PCR, Southern blot, ELISA, HE staining, immunohistochemistry and transmission electron microscopy. Transgenic mice with HBsAg positive in serum were bred and analyzed.

RESULTS: A total of 288 eggs survived from microinjections were transplanted into the oviducts of 13 pseudopregnant mice and 49 pups were produced. Twenty-six mice were identified to have the integrated HBV gene. Serum HBsAg and HBeAg were detected in 2 of 43 mice. HBsAg and HBcAg in cytoplasm or nuclei of hepatocytes were detected in 10 mice. Founders with HBsAg in serum were named lineages G145R-15 and G145R-18. Of the 16 F1 offsprings generated by G145R-15 founder, 12 were positive for HBV genome with PCR, 10 were positive for HBsAg and HBcAg with immunohistochemistry and 7 were positive for HBsAg and HBeAg with ELISA. Only 1 of 8 F1 offsprings generated by G145R-18 founder was survived and it was detected positive for HBV genome, HBsAg, HBcAg and HBeAg. Both of the two lineages had some pathological characteristics of mild chronic hepatitis B in the liver, such as swelling of hepatocytes and focal hepatocellular necrosis and parenchymal lymphomononuclear cell infiltrate.

CONCLUSION: Transgenic mice harbouring HBV with mutant s gene can be generated. The HBV genes are integrated in the transgenic mice genome and can be expressed, replicated, packaged and excreted. HBV DNA can be stably transmitted in the transgenic mice.

Yeast expression and DNA immunization of hepatitis B virus S gene with second-loop deletion of α determinant region

AIM: Immune escape mutations of HBV often occur in the dominant epitope, the second-loop of the a determinant of hepatitis B surface antigen (HBsAg). To let the hosts respond to the subdominant epitopes in HBsAg may be an effective way to decrease the prevalence of immune escape mutants. For this reason, a man-made clone of HBV S gene with the second-loop deletion was constructed. Its antigenicity was evaluated by yeast expression analysis and DNA immunization in mice.

METHODS: HBV S gene with deleted second-loop, amino acids from 139 to 145, was generated using splicing by overlap extension. HBV deleted S gene was then cloned into the yeast expression vector pPIC9 and the mammalian expression vector pcDNA3 to generate pHB-SDY and pHB-SD, respectively. The complete S gene was cloned into the same vectors as controls. The deleted recombinant HBsAg expressed in yeasts was detected using Abbott IMx HBsAg test kits, enzyme-linked immunoadsorbent assay (ELISA) and immune dot blotting to evaluate its antigenicity in vitro. The anti-HBs responses to DNA immunization in BALB/c mice were detected using Abbott IMx AUSAB test kits to evaluate the antigenicity of that recombinant protein in vivo.

RESULTS: Both deleted and complete HBsAg were successfully expressed in yeasts. They were intracellular expressions. The deleted HBsAg could not be detected by ELISA, in which the monoclonal anti-HBs against the α determinant was used, but could be detected by Abbott IMx and immune dot blotting, in which multiple monoclonal anti-HBs and polyclonal anti-HBs were used, respectively. The activity of the deleted HBsAg detected by Abbott IMx was much lower than that of complete HBsAg (the ratio of sample value/cut off value, 106 ± 26.7 vs 1814.4 ± 776.3, P < 0.01, t = 5.02). The anti-HBs response of pHB-SD to DNA immunization was lower than that of complete HBV S gene vector pHB (the positive rate 2/10 vs 6/10, 4.56 ± 3.52 mIU/mL vs 27.60 ± 17.3 mIU/mL, P = 0.02, t = 2.7).

CONCLUSIONS: HBsAg with deleted second-loop of the α determinant still has antigenicity, and can also raise weak anti-HBs response in mice to DNA immunization, suggesting that it is possible to develop a subdominant vaccine for preventing infections of immune escape mutants of HBV.

The hepatitis B virus polymerase mutation rtV173L is selected during lamivudine therapy and enhances viral replication in vitro

Therapy of chronic hepatitis B virus (HBV) infection with the polymerase inhibitor lamivudine frequently is associated with the emergence of viral resistance. Genotypic changes in the YMDD motif (reverse transcriptase [rt] mutations rtM204V/I) conferred resistance to lamivudine as well as reducing the in vitro replication efficiency of HBV. A second mutation, rtL180M, was previously reported to partially restore replication fitness as well as to augment drug resistance in vitro. Here we report the functional characterization of a third polymerase mutation (rtV173L) associated with resistance to lamivudine and famciclovir. rtV173L was observed at baseline in 9 to 22% of patients who entered clinical trials of adefovir dipivoxil for the treatment of lamivudine-resistant HBV. In these patients, rtV173L was invariably found as a third mutation in conjunction with rtL180M and rtM204V. In vitro analyses indicated that rtV173L did not alter the sensitivity of wild-type or lamivudine-resistant HBV to lamivudine, penciclovir, or adefovir but instead enhanced viral replication efficiency. A molecular model of HBV polymerase indicated that residue rtV173 is located beneath the template strand of HBV nucleic acid near the active site of the reverse transcriptase. Substitution of leucine for valine at this residue may enhance polymerization either by repositioning the template strand of nucleic acid or by affecting other residues involved in the polymerization reaction. Together, these results suggest that rtV173L is a compensatory mutation that is selected in lamivudine-resistant patients due to an enhanced replication phenotype.

Pre-s1 antigen-dependent infection of Tupaia hepatocyte cultures with human hepatitis B virus

The susceptibility of the tree shrew Tupaia belangeri to human hepatitis B virus (HBV) has been demonstrated both in vivo and in vitro. In this study, we show that purified HBV infects primary T. belangeri hepatocyte cultures in a very specific manner, as detected by HBV covalently closed circular DNA, mRNA, HBV e antigen, and HBsAg production. A monoclonal antibody (MAb), MA18/7, directed against the pre-S1 domain of the large HBs protein, which has been shown to neutralize infectivity of HBV for primary human hepatocytes, also blocked infection of primary Tupaia hepatocytes. MAbs against the pre-S2 domain of HBs inhibited infection only partially, whereas an S MAb and polyvalent anti-HBs antibodies neutralized infection completely. Thus, both pre-S1 and S antigens are necessary for infection in the tupaia. Using subviral particles, >70% of primary Tupaia hepatocytes are capable of specific binding of pre-S1-rich HBsAg, showing localization in distinct membrane areas. The data show that the early steps of HBV infection in Tupaia hepatocyte cultures are comparable to those in the human system.

Induction of antibodies to the PreS region of surface antigens of woodchuck hepatitis virus (WHV) in chronic carrier woodchucks by immunizations with WHV surface antigens

BACKGROUND/AIMS

One goal of therapeutic vaccinations against chronic hepatitis B virus infection is to stimulate the B-cell responses to viral surface antigens in chronic carriers. Here we investigated the induction of antibody responses to hepadnaviral surface antigens in the woodchuck model, with emphasis on the vaccination of woodchucks chronically infected with woodchuck hepatitis virus (WHV).

METHODS

Naive and chronically WHV-infected woodchucks were immunized with plasma-derived WHV surface antigens (p-WHsAg) containing the S and PreS sequences. Antibody responses to WHsAg and the WHV PreS region and viral load in immunized woodchucks were monitored.

RESULTS

After repeated immunizations with WHsAg, 17 of 18 chronic WHV carriers developed a persistent antibody response to WHsAg. These antibodies were mainly directed to epitopes within the PreS region and detectable by Western blotting. However, neither WHV DNA nor WHsAg concentrations in these woodchucks changed significantly by immunizations and during the follow up. Sequence analysis of WHV genomes showed that no WHV mutants emerged after the induction of anti-WHs/anti-WHpreS antibodies. No immunopathological changes in livers of immunized animals were recognized thus far.

CONCLUSIONS

Our study demonstrated that the immunological unresponsiveness of chronically WHV-infected woodchucks to WHsAg can be partially overcome by repeated immunizations with WHsAg.

A novel stop codon mutation in HBsAg gene identified in a hepatitis B virus strain associated with cryptogenic cirrhosis

AIM: HBsAg is the most important serological marker for acute or chronic hepatitis B. Nevertheless, there were reports of HBsAg-negative infection caused by hepatitis B virus in recent years. We had a patient with crytogenic cirrhosis who was negative for HBsAg, positive for anti-HBs and HBeAg. This paper was to explore the pathogenic and molecular basis of the unusual serological pattern.

METHODS: HBV serologic markers were qualitatively and quantitatively determined. HBV DNA in serum was qualitatively tested using routine Polymerase chain reaction(PCR), and the viral level was determined with real-time fluorescence quantitative PCR. HBsAg gene was amplified and cloned. Four clones were sequenced. The new genomic sequences were compared with GenBank on the DNA level as well as the protein level.

RESULTS: The qualitative results of serological markers were HBsAg(-), anti-HBs(+), HBeAg(+), anti-HBe(-) and anti-HBc(+). The quantitative results of serological marker were HBsAg (S/N): 0.77 (cut off of S/N: ≥ 2.00), HBeAg (S/N): 56.43 (cut off S/N: ≥ 2.10), anti-HBc (S/C_O): 2.03 (cut off of S/C_O: ≤ 1.00). The viral level was as high as 1.54 × 10⁹ copies/ml. Sequencing of the HBsAg gene clones revealed a unique point mutation at nucleotide 336 (C to A), which resulted in a novel stop codon at aa 61. The novel HBsAg gene stop mutation had not been described.

CONCLUSION: The lack of detection of HBsAg in the presence of high viral levels of replication may be caused by the existence of viral genomes harboring point mutations which resulted in stop codon upstream of the “a” determinant in HBsAg gene.

Characterization of hepatitis B virus surface antigen and polymerase mutations in liver transplant recipients pre- and post-transplant

We evaluated serum samples from 18 chronic hepatitis B virus (HBV) patients who underwent liver transplantation for the presence of HBV polymerase and S gene mutations and HBV genotype using a new commercially available sequencing assay. All three patients with hepatitis B immune globulin (HBIG) treatment failure followed by nucleoside analogue treatment failure were infected with HBV genotype C; a pre-existing HBV S antigen (HBsAg) mutation (sD144A) was identified in one patient pretransplant, while sG145R mutations emerged in the other two patients post-transplant. These HBsAg mutations persisted for the duration of the study (5-6 years), despite the absence of HBIG administration for a 4-5-year period. Significant viral polymerase mutations (rtL180M and rtM204I/V) also emerged in all of these patients following treatment with lamivudine and/or famciclovir. Four of six patients with HBIG breakthrough without nucleoside analogue treatment failure yielded potentially significant HBsAg mutations post transplant. These data do not support previous reports highlighting the disappearance of HBsAg mutants in liver transplant recipients after discontinuation of HBIG. Determination of HBV genotype, as well as identification of HBV polymerase and S gene mutations in liver transplant candidates may be warranted to optimize HBV management strategies post transplant.

Active immunization against de novo hepatitis B virus infection in pediatric patients after liver transplantation

The shortage of donor organs occasionally mandates the use of hepatic allografts from anti-HBc (+) donors. HBIG and/or lamivudine are recommended for the prevention of de novo HBV infection in naive patients, but there are attendant problems, such as mutant strain emergence and high cost. Active immunization presents a better alternative than the use of HBIG or lamivudine, if it can be proven to be effective. Accordingly, we investigated the outcome of HBV vaccination in pediatric hepatic transplant recipients. Between July 1999 and October 2001, 19 pediatric recipients were administered HBV vaccinations after liver transplantation at Seoul National University Hospital. Nine patients received a graft from anti-HBc (+) donors and 10 from anti-HBc (-) donors. When steroid was withdrawn, recombinant HBV vaccine was administered. The median follow-up period after vaccination was 10.0 +/- 5.2 months. Seventeen of the 19 patients showed a positive response to vaccination. In 9 patients who received grafts from anti-HBc (+) donors, 2 patients showed no response, 4 patients low response (peak HBsAb titer <1,000 IU/L), and 3 patients high response (peak HBsAb titer >/=1,000 IU/L). De novo HBV infection developed in 1 of 2 patients who showed no response to vaccination. In 10 patients who received grafts from anti-HBc (-) donors, 5 showed a low response and 5 a high response. In conclusion, HBV vaccination in pediatric patients after liver transplantation appeared to exhibit some effectiveness at protecting young children that received a graft from anti-HBc (+) donors from de novo HBV infection.

A mutation specific polymerase chain reaction for detecting hepatitis B virus genome mutations at nt551

AIM: The hepatitis B surface antigen (HBsAg) is considered to be one of the best markers for the diagnosis of acute and chronic HBV infection. But in some patients, this antigen cannot be detected by routine serological assays despite the presence of virus. One of the most important explanations for the lack of detectable HBsAg is that mutations which occur within the “a” determinant of HBV S gene can alter expression of HBsAg and lead to changes of antigenicity and immunogenicity of HBsAg accordingly. As a result, these mutants cannot be detected by diagnosis assays. Thus, it is essential to find out specific and sensitive methods to test the new mutants and further investigate their distribution. This study is to establish a method to investigate the distribution of the HBsAg mutant at nt551.

METHODS: A mutation specific polymerase chain reaction (msPCR) was established for amplifying HBV DNA with a mutation at nt551. Four sets of primer pairs, P551A-PPS, P551G-PPS, P551C-PPS and P551T-PPS, with the same sequences except for one base at 3’ terminus were designed and synthesized according to the known HBV genome sequences and the popular HBV subtypes, adr and adw, in China. At the basis of regular PCR method, we explored the specific conditions for amplifying HBV DNAs with a mutation at nt551 by regulating annealing temperature and the concentration of these primers. 126 serum samples from patients of hepatitis B were collected, among which 16 were positive for HBV S DNA in the nested PCR amplification. These 16 HBV S DNAs were detected by using the msPCR method.

RESULTS: When the annealing temperature was raised to 71 °C, nt551A and nt551G were amplified specifically by P551A-PPS and P551G-PPS; At 72 °C and 5 pmole of the primers (each) in reaction of 25 μl volume, nt551C and nt551T were amplified specifically by P551C-PPS and P551T-PPS. 16 of HBV S gene fragments were characterized by using this method. 14 of them were positive for nt551A, one was positive for nt551G, and the other one was positive for nt551T. The results were confirmed by nucleotide sequencing.

CONCLUSION: The mutation specific polymerase chain reaction is a specific and sensitive method for detecting the mutations of HBV genome at nt551.

A novel hepatitis B virus mutant with A-to-G at nt551 in the surface antigen gene

AIM: Hepatitis B surface antigen (HBsAg) mutant of hepatitis B virus (HBV) is one of the important factors that result in immune escape and cause failure of immunization. In this study we reported and characterized a novel HBV mutant with A-to-G at nt551 and intended to provide theoretical data for prevention of HBV infection in China.

METHODS: A methodology comprising polymerase chain reaction (PCR) amplifying, M13 bacteriophage cloning and nucleotide sequencing was used to analyze the sera of the pediatric patient who was hepatitis B (HB) immune failure. Expression plasmids containing the mutant S gene and a wild-type (adr) S gene were constructed respectively and the recombinant HBsAg were expressed in COS-7 cells under the regulation of SV40 early promoter. The recombinant proteins were investigated for their immunological reactivity with different monoclonal antibodies (mAb) against 'a' determinant and vaccine-raised human neutralizing antibodies.

RESULTS: It was found that there was a new point mutation at nt551 of the HBV (adr) genome from A to G, leading to a substitution of methionine (Met) to valine (Val) at position 133 in the 'a' determinant of HBsAg. Compared to the wild-type HBsAg, the binding activity of the muant HBsAg to mAbs (A6, A11 and S17) and to vaccine-raised human anti-hepatitis B surface antibody (anti-HBs) decreased significantly.

CONCLUSION: According to the facts that the patient has been immunized with HB vaccine and that the serum is anti-HBs positive and HBsAg negative, and based on the nucleotide sequence analysis of the mutant HBV S gene and its alteration of antigenicity, the HBV is considered to be a new vaccine-induced immune escape mutant different from the known ones.

Monoclonal antibodies to elongation factor-1alpha inhibit in vitro translation in lysates of Sf21 cells

Elongation factor-1alpha (EF-1alpha) is an enzyme that is essential for protein synthesis. Although EF-1alpha offers an excellent target for the disruption of insect metabolism, agents known to interfere with EF-1alpha activity are toxic to humans. In this article, we describe the development of monoclonal antibodies (MAbs) that can disrupt the activity of insect EF-1alpha without cross-reacting with the human enzyme. MAbs were generated to EF-1alpha from Sf21 cells derived from the fall armyworm, Spodoptera frugiperda, by immunizing mice with EF-1alpha eluted from SDS-PAGE gels. The MAbs reacted with EF-1alpha in eggs and first through fifth instars of the fall armyworm in immunoblots of SDS-PAGE gels, but did not recognize EF-1alpha in human carcinoma cells and normal tissues. MAbs with the ability to recognize EF-1alpha in its native conformation, identified through immunoprecipitation experiments, were added to Sf21 cell lysates to determine whether the antibodies could inhibit incorporation of [(35)S]methionine into newly synthesized in vitro translation products. Of the four EF-1alpha-specific MAbs tested, three significantly inhibited protein synthesis when compared to the negative control antibody (P < 0.001, one-way ANOVA; followed by Dunnett's test, P < 0.05).

Genetic variation of hepatitis B surface antigen coding region among infants with chronic hepatitis B virus infection

Variants in the amino acid composition of the primary antibody-binding site of hepatitis B surface antigen (HBsAg) have been identified in a number of populations with chronic hepatitis B virus (HBV) infection. Direct sequencing of amplified or cloned PCR products, solid phase detection of sequence-specific PCR products (SP-PCR), and limiting dilution cloning PCR (LDC-PCR) were compared to determine their sensitivity in detecting differing concentrations of HBsAg variants. LDC-PCR had the greatest sensitivity and could detect HBsAg variants at a concentration of 0.1% of the total viral population. HBsAg variants were detected in 51% of infants with chronic HBV infection acquired after postexposure prophylaxis, and more than half of the variants were detected only by the most sensitive methods.