Lamivudine resistant occult HBV: implications for public health?

Occult infection related hepatitis B surface antigen variants showing lowered secretion capacity

AIM: To elucidate the molecular mechanisms underlying hepatitis B virus (HBV) occult infection of genotype C.

METHODS: A total of 10 types of hepatitis B surface antigen (HBsAg) variants from a Korean occult cohort were used. After a complete HBV genome plasmid mutated such that it does not express HBsAg and plasmid encoding, each HBsAg variant was transiently co-transfected into HuH-7 cells. The secretion capacity and intracellular expression of the HBV virions and HBsAgs in their respective variants were analyzed using real-time quantitative polymerase chain reaction assays and commercial HBsAg enzyme-linked immunosorbent assays, respectively.

RESULTS: All variants exhibited lower levels of HBsAg secretion into the medium compared with the wild type. In particular, in eight of the ten variants, very low levels of HBsAg secretion that were similar to the negative control were detected. In contrast, most variants (9/10) exhibited normal virion secretion capacities comparable with, or even higher than, the wild type. This provided new insight into the intrinsic nature of occult HBV infection, which leads to HBsAg sero-negativeness but has horizontal infectivity. Furthermore, most variants generated higher reactive oxidative species production than the wild type. This finding provides potential links between occult HBV infection and liver disease progression.

CONCLUSION: The presently obtained data indicate that deficiency in the secretion capacity of HBsAg variants may have a pivotal function in the occult infections of HBV genotype C.

Occult HBV infection: a faceless enemy in liver cancer development

The hepatitis B virus (HBV) represents a worldwide public health problem; the virus is present in one third of the global population. However, this rate may in fact be higher due to occult hepatitis B virus infection (OBI). This condition is characterized by the presence of the viral genome in the liver of individuals sero-negative for the virus surface antigen (HBsAg). The causes of the absence of HBsAg in serum are unknown, however, mutations have been identified that produce variants not recognized by current immunoassays. Epigenetic and immunological host mechanisms also appear to be involved in HBsAg suppression. Current evidence suggests that OBI maintains its carcinogenic potential, favoring the progression of fibrosis and cirrhosis of the liver. In common with open HBV infection, OBI can contribute to the establishment of hepatocellular carcinoma. Epidemiological data regarding the global prevalence of OBI vary due to the use of detection methods of different sensitivity and specificity. In Latin America, which is considered an area of low prevalence for HBV, diagnostic screening methods using gene amplification tests for confirmation of OBI are not conducted. This prevents determination of the actual prevalence of OBI, highlighting the need for the implementation of cutting edge technology in epidemiological surveillance systems.

Molecular characterization of occult hepatitis B cases in Greek blood donors

The use of sensitive nucleic acid testing for hepatitis B virus in blood donors revealed a number of HBV DNA(+) cases among HBsAg(-) donors, a status known as occult HBV infection. The purpose of this study was the serological and molecular characterization of occult HBV infection in Greek blood donors. A prospective study was undertaken in order to identify occult HBV infection cases in blood donors. As part of the routine screening of blood donations in Greece, blood units were screened individually by a multiplex HIV-1/HCV/HBV nucleic acid assay. Initially reactive samples were retested with discriminatory assays. HBV DNA(+)/HBsAg(-) samples were tested further for HBV serological markers and HBV DNA was quantified by real-time PCR. Molecular characterization was performed by sequencing the envelope and polymerase genes of HBV. Preliminary screening revealed 21 occult cases with the following patterns: anti-HBc only: 7 donors, anti-HBc/anti-HBs: 7 donors, anti-HBc/anti-HBe: 5 donors, anti-HBc/anti-HBs/anti-HBe: 2 donors. In all cases, the HBV DNA load was <351 IU/ml. Sequencing was successful in 10 donors (classified within genotype D) revealing several amino acid substitutions related to diagnostic escape and antiviral resistance. HBsAg diagnostic failure and low viral replication in occult HBV infection carriers could possibly be attributed to multiple changes in envelope and polymerase regions, respectively.

Efficacy of hepatitis B vaccine against antiviral drug-resistant hepatitis B virus mutants in the chimpanzee model

Hepatitis B virus (HBV) mutants resistant to treatment with nucleoside or nucleotide analogs and those with the ability to escape from HBV-neutralizing antibody have the potential to infect HBV-vaccinated individuals. To address this potential serious public health challenge, we tested the efficacy of immunity induced by a commercial hepatitis B vaccine against a tissue culture-derived, clonal HBV polymerase mutant in HBV seronegative chimpanzees. The polymerase gene mutant contained a combination of three mutations (rtV173L, rtL180M, rtM204V), two of which resulted in changes to the overlapping viral envelope of the hepatitis B surface antigen (sE164D, sI195M). Prior to the HBV mutant challenge of vaccinated chimpanzees, we established virologic, serologic, and pathologic characteristics of infections resulting from intravenous inoculation of the HBV polymerase gene mutant and the sG145R vaccine-escape surface gene mutant. Cloning and sequencing experiments determined that the three mutations in the polymerase gene mutant remained stable and that the single mutation in the surface gene mutant reverted to the wild-type sequence. Immunological evidence of HBV replication was observed in the vaccinated chimpanzees after challenge with the polymerase gene mutant as well as after rechallenge with serum-derived wild-type HBV (5,000 chimpanzee infectious doses administered intravenously), despite robust humoral and cellular anti-HBV immune responses after hepatitis B vaccination.

CONCLUSION

Our data showing successful experimental infection by HBV mutants despite the presence of high anti-HBs levels considered protective in the vaccinated host are consistent with clinical reports on breakthrough infection in anti-HBs-positive patients infected with HBV mutants. In the absence of a protective humoral immunity, adaptive cellular immune responses elicited by infection may limit HBV replication and persistence.

Direct detection of lamivudine-resistant hepatitis B virus mutants by a multiplex PCR using dual-priming oligonucleotide primers

Mutations in the YMDD motif of the hepatitis B virus (HBV) polymerase gene increase lamivudine resistance of HBV, highlighting the clinical importance of accurate and sensitive detection of HBV mutants. Using dual-priming oligonucleotide primer technology, an assay that can detect mutations at codons 180 (L528M) and 204 (YVDD, YIDD, and YSDD) by a single-step multiplex PCR was developed. This Seeplex Lami-DR assay was sufficiently sensitive to detect 10(3)HBV/ml and was able to detect minor mutants comprising as little as 2% of the viral population. Mutants were detected in 57 of 65 serum samples (88%) from patients with chronic hepatitis B who had been treated with lamivudine (median, 32 months; range, 1-83 months). The agreement with direct sequencing was only 38.5% (25/65). Discrepancies between these methods resulted from detection of additional mutants by the Seeplex Lami-DR assay, as confirmed by a novel verification analysis. This assay is not only highly accurate and sensitive, but is also simple and cost-effective, requiring no expensive probes, laborious sequencing procedures, or digestion with restriction enzymes. Accordingly, the Seeplex HBV Lami-DR assay should be considered as a first-line, cost-effective tool for detecting viral mutations in patients with chronic hepatitis B receiving lamivudine therapy.

Occult hepatitis B virus infection in patients with chronic liver disease due to hepatitis C virus and hepatocellular carcinoma in Brazil

BACKGROUND

The prevalence and consequences of occult HBV infection in patients with chronic liver disease by HCV remain unknown.

AIMS

To evaluate the prevalence of occult HBV infection in a population of HCV-infected patients with hepatocellular carcinoma.

METHODS

The serum samples were tested for HBV DNA by nested PCR and liver tissue analysis was carried out using the immunohistochemical technique of 66 HBsAg-negative patients: 26 patients with chronic hepatitis by HCV (group 1), 20 with hepatocellular carcinoma related to chronic infection by HCV (group 2) and 20 with negative viral markers for hepatitis B and C (control group).

RESULTS

Occult HBV infection was diagnosed in the liver tissue of 9/46 (19.5%) HCV-infected patients. Prevalence of occult B infection was evaluated in the HCV-infected patients with and without hepatocellular carcinoma, and there were seven (77.7%) of whom from group 2, conferring a 35% prevalence of this group. No serum sample was positive for HBV DNA in the three groups.

CONCLUSION

Occult infection B is frequently detected in liver tissue of HCV-infected patients, especially in cases of hepatocellular carcinoma. However large studies are needed to confirm that co-infection could determine a worse progress of chronic liver disease in this population.

Extended lamivudine therapy against hepatitis B virus infection in hematopoietic stem cell transplant recipients

Lamivudine has demonstrated efficacy in the treatment and prevention of hepatitis B virus (HBV) reactivation after hematopoietic stem cell transplantation (HSCT). However, most of these studies involved short durations of prophylaxis, so there is significant concern regarding lamivudine resistance in these patients. Between March 1984 and November 2002, 71 HBV surface antigen-positive HSCT recipients, including a subgroup of 16 who received pretransplantation lamivudine therapy, which was continued into the posttransplantation period to prevent reactivation hepatitis, were enrolled onto our study. The efficacy of lamivudine therapy was first evaluated for the subgroup of 16 patients in terms of treatment response, lamivudine resistance, and viral recurrence after discontinuation by using virologic assays. Efficacy was then evaluated for all patients in terms of the hazards of lamivudine therapy for reactivation hepatitis after transplantation. During a median lamivudine therapy period of 73 weeks (range, 19-153 weeks), the initial response showed a median reduction of 2.54 log10 in serum HBV DNA (-0.28 to 6.72 range). Lamivudine-resistant mutations were detected in 10 (63%) of 16 patients during therapy, and 1 (12%) of 16 patients finally developed a viral breakthrough. At a median follow-up of 30 months after discontinuation, 3 (27%) of 11 cases had recurrence of HBV infection. Despite the emergence of the mutations, no deaths were due to HBV reactivation or severe cases of hepatitis. In the Cox proportion regression model regarding reactivation hepatitis after transplantation of all enrolled patients, lamivudine therapy was found to be the only favorable factor for the event, with a hazard ratio of 0.122 (95% confidence interval, 0.016-0.908; P = .040). In conclusion, extended lamivudine therapy is safe and effective for the prevention of HBV reactivation in an HSCT setting and significantly decreases reactivation hepatitis after transplantation.

Management of Antiviral Resistance in Patients with Chronic Hepatitis B

A meeting of physicians and scientists involved in the management of chronic hepatitis B (CHB) was held to review current scientific data regarding antiviral resistance in hepatitis B virus (HBV) infection. The goals of the meeting were to describe current treatments for CHB, discuss emerging issues in HBV drug resistance and to delineate patient monitoring, including markers for resistance, during administration of antiviral therapy. The aim of this review article is to provide treating physicians with a framework for the management of CHB in the context of antiviral resistance. Definitions of primary and secondary antiviral treatment failure can be used to aid monitoring and early diagnosis of drug resistance before disease progression occurs as a consequence of viral breakthrough. Primary antiviral treatment failure is defined as failure of a drug to reduce HBV DNA levels by ≥1xlog10 IU/ml within 3 months following initiation of therapy, and secondary antiviral treatment failure as a rebound of HBV replication of ≥1xlog10 IU/ml from nadir in patients with an initial antiviral treatment effect (≥1xlog10 IU/ml decrease in serum HBV DNA). Confirmation of antiviral drug failure can be established by sequencing the HBV DNA polymerase and identifying specific genetic markers of antiviral drug resistance. In addition to virological assays, HBV resistance can be assessed from a clinical perspective including increased serum alanine aminotransferase levels and the development of systemic symptoms or signs of liver failure. Potential strategies to prevent the emergence of resistance and how to manage drug-resistant HBV once it emerges are discussed.