Anti-pre-S responses and viral clearance in chronic hepatitis B virus infection

The Hepatitis B Virus Envelope Proteins: Molecular Gymnastics Throughout the Viral Life Cycle

New hepatitis B virions released from infected hepatocytes are the result of an intricate maturation process that starts with the formation of the nucleocapsid providing a confined space where the viral DNA genome is synthesized via reverse transcription. Virion assembly is finalized by the enclosure of the icosahedral nucleocapsid within a heterogeneous envelope. The latter contains integral membrane proteins of three sizes, collectively known as hepatitis B surface antigen, and adopts multiple conformations in the course of the viral life cycle. The nucleocapsid conformation depends on the reverse transcription status of the genome, which in turn controls nucleocapsid interaction with the envelope proteins for virus exit. In addition, after secretion the virions undergo a distinct maturation step during which a topological switch of the large envelope protein confers infectivity. Here we review molecular determinants for envelopment and models that postulate molecular signals encoded in the capsid scaffold conducive or adverse to the recruitment of envelope proteins.

Designing a therapeutic hepatitis B vaccine to circumvent immune tolerance

An effective prophylactic hepatitis B virus (HBV) vaccine has long been available but is ineffective for chronic infection. The primary cause of chronic hepatitis B (CHB) and greatest impediment for a therapeutic vaccine is the direct and indirect effects of immune tolerance to HBV antigens. The resulting defective CD4⁺/CD8⁺ T cell response, poor cytokine production, insufficient neutralizing antibody (nAb) and poor response to HBsAg vaccination characterize CHB infection. The objective of this study was to develop virus-like-particles (VLPs) that elicit nAb to prevent viral spread and prime CD4⁺/CD8⁺ T cells to eradicate intracellular HBV. Eight neutralizing B cell epitopes from the envelope PreS1 region were consolidated onto a species-variant of the HBV core protein, the woodchuck hepatitis core antigen (WHcAg). PreS1-specific B cell epitopes were chosen because of preferential expression on HBV virions. Because WHcAg and HBcAg are not crossreactive at the B cell level and only partially cross-reactive at the CD4⁺/CD8⁺ T cell level, CD4⁺ T cells specific for WHcAg-unique T cell sites can provide cognate T-B cell help for anti-PreS1 Ab production that is not curtailed by immune tolerance. Immunization of immune tolerant HBV transgenic (Tg) mice with PreS1-WHc VLPs elicited levels of high titer anti-PreS1 nAbs equivalent to wildtype mice. Passive transfer of PreS1 nAbs into human-liver chimeric mice prevented acute infection and cleared serum HBV from mice previously infected with HBV in a model of CHB. At the T cell level, PreS1-WHc VLPs and hybrid WHcAg/HBcAg DNA immunogens elicited HBcAg-specific CD4⁺ Th and CD8⁺ CTL responses.

Nanovaccine for immunotherapy and reduced hepatitis-B virus in humanized model

Chronic Hepatitis B Virus (HBV) infections are severe with weak antiviral immune responses. The lack of an appropriate small animal model for chronic hepatitis, a major hurdle for studying the immunotolerance and immunopathogenesis induced by hepatitis B viral (HBV) infection. In this study, for enhancing the antibody production efficiency the prepared polymeric HBsAg-loaded nanoparticles (nanovaccine) will be tested in immune-deficit mice, which suffer from chronic Hepatitis B virus. Vaccination of Balb/c mice by this prepared nanoparticles that were engrafted with peripheral blood mononuclear cells (PBMCs), which was already lethally irradiated and transplanted by the bone marrow of NOD (knockout mice) mice. In the present study, after the vaccination detected the high frequencies of immunoglobulin G (IgG)-secreting B cells and mitogen-responsive interferon-Y (IFN-Y) secreting T cells in serum, determined by specific ELISA technique. During the entire observation period, unvaccinated animals showed lower concentration of specific IgG secreting B cells and IFN-Y secreting T cells found in comparison to vaccinated mice group. Chronic HBV carrier PBMCs transplanted into the chimera failed to produce antigen and increased the antibodies production due to vaccination. Furthermore, another advantage was that the viral gene expression and viral DNA replication was no longer observed in vaccinated group. This prepared nanovaccine formulations is better for the cure of Hepatitis B viral infection carrier. Therefore, specific memory responses were elicited by vaccination with Hepatitis B virus surface (HBsAg) antigen of chimeric mice transplanted with PBMCs derived from HBV donors.

Inhibition of preS1-hepatocyte interaction by an array of recombinant human antibodies from naturally recovered individuals

Neutralizing monoclonal antibodies are being found to be increasingly useful in viral infections. In hepatitis B infection, antibodies are proven to be useful for passive prophylaxis. The preS1 region (21–47a.a.) of HBV contains the viral hepatocyte-binding domain crucial for its attachment and infection of hepatocytes. Antibodies against this region are neutralizing and are best suited for immune-based neutralization of HBV, especially in view of their not recognizing decoy particles. Anti-preS1 (21–47a.a.) antibodies are present in serum of spontaneously recovered individuals. We generated a phage-displayed scFv library using circulating lymphocytes from these individuals and selected four preS1-peptide specific scFvs with markedly distinct sequences from this library. All the antibodies recognized the blood-derived and recombinant preS1 containing antigens. Each scFv showed a discrete binding signature, interacting with different amino acids within the preS1-peptide region. Ability to prevent binding of the preS1 protein (N-terminus 60a.a.) to HepG2 cells stably expressing hNTCP (HepG2-hNTCP-C4 cells), the HBV receptor on human hepatocytes was taken as a surrogate marker for neutralizing capacity. These antibodies inhibited preS1-hepatocyte interaction individually and even better in combination. Such a combination of potentially neutralizing recombinant antibodies with defined specificities could be used for preventing/managing HBV infections, including those by possible escape mutants.

Variations in the S and P regions of the hepatitis B virus genome under immunosuppression in vitro and in vivo

To provide a basis for improved prevention and treatment of hepatitis B virus (HBV) re-infection after liver transplantation, variations in the S and P genes of HBV under immunosuppression in vitro and their association with patient prognosis were investigated. For the in vitro study, HepG2.2.15 hepatocellular carcinoma cells stably producing HBV particles were treated with the immunosuppressants methylprednisolone (MP) and tacrolimus (FK506) at doses found to be non-toxic by the methylthiazolyl tetrazolium (MTT) cell viability assay. MP dose-dependently inhibited HBV DNA expression in HepG2.2.15 cells, while FK506 did not, as determined by quantitative real-time PCR (qRT-PCR). By gene sequencing, both MP and FK506 were found to cause variations in HBV S, P, and S/P overlapping regions. MP- but not FK506-induced mutations were common in the glucocorticoid response element of the P region, while both immunosuppressants caused mutations outside the nucleoside analogue resistance sites. For the in vivo study, 14 patients with HBV-related end-stage liver disease re-infected after liver transplantation, and 20 cases without HBV re-infection as controls, were studied. Seventy-five percent of re-infected recipients showed multi-loci amino acid mutations at different sites besides lamivudine (LAM)-resistant loci in the P region, including in the glucocorticoid response element. Fifty percent of re-infected recipients had mutations in the "a" determinant region and flanking sequences. Re-infection was associated with negative serum hepatitis B immunoglobulin (HBIG), as measured by a microparticle capture enzyme immunoassay. Nucleotide mutations in the S region caused missense or synonymous mutations, which caused synonymous mutations in the overlapping P region. These results showed that effects of immunosuppressants on HBV genes in vitro were different from those in clinical recipients. Positive HBV DNA and gene mutations pre-transplantation were factors affecting re-infection post-transplantation. Multiple mutations found in the P and S genes suggest that the formation of quasispecies contributes to HBV re-infection after liver transplantation.

Expression and purification of the synthetic preS1 gene of Hepatitis B Virus with preferred Escherichia coli codon preference

To produce high levels of hepatitis B virus (HBV) preS1 protein at low cost, a DNA fragment encoding the preS1 region, residues 1-119, of HBV adr subtype was synthesized by overlapping-PCR according to Escherichia coli (E. coli) B preferred codon usage. The synthetic preS1 gene (spreS1) was cloned into the bacterial expression vector pET-30a and transferred into the expression strain E. coli BL21(DE3). Recombinant preS1 protein with an N-terminal His6 tag was expressed at high levels in soluble form, yielding about 44% of the total cellular protein. This technique overcomes problems that existed in previously reported expression systems of preS1 or its epitope, i.e., low-level expression or expression in inclusion bodies. Using this His-tagged preS1 expression system, recombinant protein was purified by single-step affinity chromatography on a Ni-NTA column resulting in a yield was about 28 mg recombinant protein per liter culture. Furthermore, Western blotting and indirect ELISA analysis demonstrate that the reactivity of preS1-specific antibody is comparable between the recombinant and commercialized preS1 protein. Thus, our improved expression system could be used for practical, low-cost large-scale production of recombinant preS1 without refolding steps.

A flexible peptide linker enhances the immunoreactivity of two copies HBsAg preS1 (21-47) fusion protein

PreS1 (21-47) region of HBV large surface protein is hepatocyte receptor binding site and the anti-preS1 (21-47) antibody possesses the virus-neutralizing activity and protective effect. It is important to obtain the peptide with higher immunoreactivity on a large scale for detecting the anti-preS1 (21-47) antibody in the sera from HBV infected patients and future vaccine recipients. The expression vector pGEX SLS, which expressed two copies of the preS1 (21-47) peptide connected by a flexible linker (Gly4Ser3) fused to glutathione S-transferase (GST), was constructed. The fusion protein, named GST-SLS, was highly expressed in E. coli and purified by affinity chromatography. Ninety milligrams purified protein can be obtained from 1l of culture. The data in ELISA analysis showed that the immunoreactivity of GST-SLS was enhanced significantly in comparison with GST-S II, a GST fusion protein with two copies preS1 (21-47) linked directly; GST-S I, another GST fusion protein with one copy preS1 (21-47) and preS1 (21-47) synthesized peptide. In addition, GST-SLS has been tried to use in detecting anti-preS1 (21-47) antibody in the sera from HBV infected patients and a satisfied result was gained. Therefore, GST-SLS may have potential to be developed into a new kit for diagnosis and prognosis of hepatitis B (HB) patients.

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.

Characterization of complex B cell epitopes on woodchuck hepatitis virus surface antigens by using plasmids encoding chimeric proteins and DNA immunization

The conformational nature of the B cell epitopes on the hepadnavirus surface antigens makes its characterization difficult. Here, a new approach by DNA vaccination with plasmids expressing chimeric hepadnavirus surface antigens was explored to determine B cell epitopes on the surface antigens of woodchuck hepatitis virus (WHsAg). A series of chimeric genes consisting of complementary fragments of WHsAg and hepatitis B virus surface antigens (HBsAg) was constructed. These plasmids expressed the following: (i) middle chimeric surface antigens (MCSAgs), including pre-S2 region and small surface antigens; (ii) small chimeric surface antigens (CSAgs); (iii) a mutated WHsAg with two amino acid substitutions, the Leu 136 to Thr and Ala 140 to Asp, within the central immunogenic region. The mutated region from amino acid 135 to 143 within WHsAg mimics the second loop of the HBsAg a-determinant. MCSAgs and CSAgs were expressed in transiently transfected mammalian cells and were reactive to anti-HBsAg and anti-WHsAg, as shown by indirect immunofluorescence staining and ELISA. Vaccination with plasmids encoding MCSAgs induced strong antibody responses to the pre-S2 region. Anti-pre-S2 antibodies were directed to a linear, immunodominant region within the amino-terminal region of the pre-S2 region and were able to precipitate serum WHsAg. Vaccinations with the plasmids expressing the CSAgs led to the conclusion that an extended region aa 116-169 of WHsAg, analogous to the HBsAg a-determinant, was sufficient for the induction of anti-WHsAg antibodies. The mutated WHsAg with the second loop of the HBsAg a-determinant efficiently induced anti-WHsAg antibodies, but also a low titer of anti-HBsAg. Thus, multiple B cell epitopes of a linear and conformational nature are present on WHsAg. We presented an efficient and broadly applicable strategy for analysis of complex immunogenic determinants of natural or mutated viral antigens.

Development of the diagnostic immunoassay to detect anti-PreS1(21-47aa) antibody--a marker suggesting the health improvement of hepatitis B patients

BACKGROUND

A new immunoassay has been developed for the detection of the anti-PreS1(21-47aa) antibody in sera of hepatitis B virus (HBV)-infected patients. Anti-PreS1(21-47aa) antibody involves virus neutralization and is a new marker for diagnosing acute and chronic B hepatitis.

METHODS

The expression plasmids pGEXS I and pGEXS II, which expressed glutathione S-transferase (GST) fusion proteins containing a copy of PreS1(21-47aa) peptide and two orderly joined copies of PreS1(21-47aa) peptide, were constructed. The soluble expression products were purified by affinity chromatography.

RESULTS

The two PreS1(21-47aa) fusion proteins were both successfully applied in the immunoassay based on biotin-protein A and streptavidin-HRP, and could detect the anti-PreS1(21-47aa) antibody with high sensitivity in sera from hepatitis B patients. The anti-PreS1(21-27aa) antibody was detected during the recovery phase of acute hepatitis B patients, but it was found only in few of the chronic carriers by the established conventional system.

CONCLUSIONS

The follow-up study suggested that the presence of the anti-PreS1(21-27aa) antibody correlated well with the recovery of patients from hepatitis and the improvement in health.

Hypermodification and immune escape of an internally deleted middle-envelope (M) protein of frequent and predominant hepatitis B virus variants

Naturally occurring deletions within the human hepatitis B virus (HBV) preS2 region have frequently been identified in patients with hepatocellular carcinoma (HCC), while chronic carriers without cirrhosis and HCC contain no detectable preS2 deletion variants. We have characterized two different preS2 internal deletion variants from two patients. In addition to several weak phenotypes, our study revealed three unexpected strong phenotypes: (1) a paradoxical "hypermodification" phenomenon was observed with significantly increased size heterogeneity and molecular weights of the secreted middle (M) envelope proteins containing a preS2 internal deletion. This phenomenon was observed in transient transfection with a human hepatoma Huh7 cell line as well as in stable transfection with a rodent hepatoma cell line 7777. (2) A significantly increased intracellular accumulation of all three envelope proteins (large, middle, and small) was detected by both Western blot analysis and immunofluorescence microscopy. (3) The middle envelope proteins with a preS2 internal deletion were not recognized in vitro by a putative neutralizing antiserum, suggesting that these variants can evade immune recognition in vivo. To our knowledge, this is the first identification and characterization of the M deletion variant protein in HBV natural infection.

Reduced hepatitis B virus surface antigen-specific Th1 helper cell frequency of chronic HBV carriers is associated with a failure to produce antigen-specific antibodies in the trimera mouse

In chronic hepatitis B virus (HBV) infection weak antiviral immune responses are associated with viral persistence. We studied possible immune deficits underlying the lack of serum antibodies of such patients against the HBV surface antigen (HBsAg) in a novel human/mouse chimeric model. A hepatitis B surface antigen (HBs) vaccination of Balb/c mice engrafted with peripheral blood mononuclear cells (PBMC) of naturally HBV-immunized donors induced high frequencies of human HBsAg-specific B and T helper 1 (Th1) cells. These responses were associated with high serum anti-HBs antibody levels of the subclasses immunoglobulin G1 (IgG1) and IgG2 that are driven by interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). In contrast, PBMC of chronic HBV carriers transplanted into the chimera failed to produce anti-HBs antibodies after vaccination with HBsAg and exhibited a deficit of antigen-specific Th1 cells. A possible influence of HBsAg or viremia was excluded by the lack of viral replication in such chimera. The observed T-cell defect was specific for HBsAg, as the B- and T-cell responses to tetanus toxoid (TT) were fully retained. Thus, our study shows that viral persistence in chronic HBV carriers is associated with an HBsAg-specific Th1 cell defect, which likely is responsible for the insufficient neutralizing anti-HBs-antibody response and is not reversed by HBs vaccination. Alternative approaches to induce HBs-specific Th1 cell responses might represent a future therapeutic option.

DNA-based immunization against the envelope proteins of the hepatitis B virus

Intramuscular injection in mice of DNA expression vectors encoding the envelope proteins of the hepatitis B virus induced humoral responses specific to several antigenic determinants of the viral envelope. The use of different promoter elements in the plasmid vectors influenced the kinetics and specificity of antibodies produced to the envelope proteins. The first antibodies appeared within 1-2 weeks after injection of DNA and included antibodies of the IgM isotype. Over the following weeks, an IgM-to-IgG class switch occurred, indicating helper T-lymphocyte activity. Peak IgG titers were reached by 4 weeks after a single DNA injection and were maintained for at least 6 months without further DNA injections. The antibodies to the envelope proteins reacted with both group- and subtype-specific antigenic determinants of the HBV surface antigen (HBsAg). The nature of the immune response to the envelope proteins provides indirect evidence that the proteins have adopted a native conformation and have probably been assembled into particles after intramuscular expression from the plasmid vectors. These results indicate that it may be possible to rationally design DNA expression vectors to induce a particular type of immune response for vaccination against hepatitis B or other pathogens.

Effect of pre-S1 antigen on human lymphocyte proliferative responses

The peripheral blood mononuclear cells (PBMCs) from patients acutely infected with HBV and recovered completely (n = 20), patients with chronic hepatitis B infection (CHB)- (n = 10) and HBsAg-positive carriers (n = 9) and healthy individuals (n = 8) were studied for their in vitro proliferative response to a synthetic pre-S1(20-49)x4 antigen. PBMCs from convalescents showed significant proliferative response in the presence of synthetic pre-S1 antigen. PBMCs from CHB- and HBsAg-positive exhibited reduced proliferative response not only to Pre-S1 antigen but also to nonspecific mitogens. This study suggests that the immune recognition of pre-S1 antigen and response of PBMCs to the pre-S1 antigen may be an important part of the normal human response to HBV infection. Failure to clear the HBV infection with development of the chronic carrier state may be caused by the lack of an efficient pre-S1 antigen-specific response.

DNA-mediated immunization to the hepatitis B surface antigen in mice: aspects of the humoral response mimic hepatitis B viral infection in humans

Intramuscular injection of plasmid DNA expression vectors encoding the three envelope proteins of the hepatitis B virus (HBV) induced humoral responses in C57BL/6 mice specific to several antigenic determinants of the viral envelope. The first antibodies appeared within 1-2 weeks after injection of DNA and included antibodies of the IgM isotype. Over the next few weeks, an IgM to IgG class switch occurred, indicating helper T-lymphocyte activity. Peak IgG titers were reached by 4-8 weeks after a single DNA injection and were maintained for at least 6 months without further DNA injections. The antibodies to the envelope proteins reacted with group- and subtype-specific antigenic determinants of the HBV surface antigen (HBsAg). Expression vectors encoding the major (S) and middle (preS2 plus S) envelope proteins induced antibodies specific to the S protein and preS2 domain, and preS2 antibodies were prominent at early time points. In general, the expression vectors induced humoral responses in mice that mimic those observed in humans during the course of natural HBV infection.

Quantitative assessment of IgM antibodies towards an immunodominant B-cell epitope within the preS2 domain of HBV in the natural course and during combined prednisone/interferon alpha 2b treatment of chronic hepatitis B virus infection

A direct binding enzyme-linked immunosorbent assay (ELISA) was established for quantitative determination of serum IgM antibodies towards a synthetic peptide corresponding to a selected segment (14-21) of the preS2-gene product containing an immunodominant linear B-cell epitope. The prevalence of IgM anti-preS2 (14-21) antibody titers > 1,000 for hepatitis B e antigen (HBeAg)-positive patients with chronic hepatitis B virus (HBV) infection was 38% (22/58) and 10% (2/21) for HBeAg-negative subjects (P < 0.005). IgM anti-preS2 (14-21) reactivity was detected during the clinical course of chronic HBV infection and IgM anti-peptide antibody titers declined and disappeared before spontaneous HBe/anti-HBe seroconversion. Recombinant interferon (IFN)-alpha 2b with an antecedent short course of corticosteroids was administered to eight Chinese patients with chronic HBV infection. The IgM anti-preS2 (14-21) reactivity was monitored consecutively during treatment and patients were followed for more than 1 year. A close association between the presence of pretreatment IgM anti-preS2 (14-21) in serum and the capacity to respond favorably to the combined prednisone/IFN-alpha 2b therapy was detected. The IgM anti-preS2 (14-21) titers decreased during treatment with subsequent loss of detectable antibodies 8-16 weeks after the initiation of therapy. This decrease was concomitant with an alanine aminotransferase (ALT) augmentation preceding the disappearance of HBV-DNA and anti-HBe seroconversion. Long-term remission was not observed in treated patients who lacked detectable levels of pretreatment IgM anti-preS2 (14-21) in the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and characterization of the multiplied, recombinant preS1 antigen of hepatitis B virus

The amino acid sequence encoded by the preS1 region of hepatitis B virus genome is expressed on the surface of virions and subviral particles. The preS1 region is involved in the recognition of specific receptors responsible for the attachment of HBV to the host cell. The cell receptor binding site was assigned to the preS1 (20-47 aa) fragment. In order to obtain a large quantity of preS1 binding domains of HBV the expression vector pWX4 was constructed. It contains four tandemly joined DNA sequences, each coding for preS1 (20-49 aa), fused with the 3' end of a DNA fragment coding for 450 aa of beta-galactosidase. E. coli cells transformed with this vector produce fusion protein beta-gal-preSlx4 in the form of inclusion bodies. Owing to the specific trypsin digestion, the preSlx4 domain was cleaved from the fusion protein. The resulting product, a 16 kDa protein, was isolated and purified by anion exchange chromatography. The presence of four Asp-Pro bonds in this sequence and the primary structure of the first 28 N-terminal amino acids were determined. Following the confirmation of the antigenic properties, the recombinant preS1 protein was used for detection of the anti-preS1 response in sera from HBV infected patients.

Significance of pre-S region-defective hepatitis B virus that emerged during exacerbation of chronic type B hepatitis

A defective form of the hepatitis B virus has been found in a patient with chronic type B hepatitis. Sequence analysis of the viral DNA after polymerase chain reaction amplification revealed a 117-base pair deletion (nucleotides 3129-53, subtype adr). This deletion includes the initiation codon of the pre-S2 region and a newly created in-frame stop codon in the pre-S1 region (nucleotide 3055) located 230 base pairs downstream from the pre-S1 initiation codon. This virus coexisted with the wild-type virus during the exacerbation period, as evidenced by an elevation of serum transaminase levels. It was not detected in the stable period, and the blood chemistry results were normal. We assayed antibodies against the mutation-related region by enzyme immunoassay in serial serum samples to clarify the mechanism of the emergence of this variant virus. Antibodies against the pre-S2 region were negative; however, the antibody response against the pre-S1 epitopes coincided with the appearance of the variant virus. These findings suggest that an activated T-cell and B-cell response had developed against the pre-S1 region during hepatic inflammation in this patient and that, consequently, selection occurred for a pre-S antigen-defective mutant strain of the virus that might be resistant to such an immune response.

Hepatitis B virus genomes that cannot synthesize pre-S2 proteins occur frequently and as dominant virus populations in chronic carriers in Italy

The heterogeneity of hepatitis B virus (HBV) pre-S sequences coding for envelope proteins was tested by DNA amplification and direct sequencing of viral genomes from sera of 22 unselected chronic carriers resident in Southern Italy. The sequences of the dominant viral genome populations from 15 carriers were very similar to known published "wildtype" HBV genomes and showed no deletions. In contrast, in the HBV populations of six patients, deletions in the pre-S region, mainly clustered at the amino terminal end of the pre-S2 region, were found. Four of these mutant genome populations and those from another patient cannot express pre-S2 proteins due to deletions or a mutation of the translation initiation codon. Emergence of the pre-S mutant viruses either during the natural course of infection or after interferon treatment was found in follow-up sera of one and two patients, respectively. These data indicate a high prevalence of pre-S mutant viruses which cannot express pre-S2 and normal-size pre-S1 proteins. This has important implications for the usefulness of diagnostic pre-S protein assays and possibly for interferon treatment and the efficacy of new vaccines containing pre-S proteins.