Risk of hepatocellular carcinoma across a biological gradient of serum hepatitis B virus DNA level

CONTEXT

Serum hepatitis B virus (HBV) DNA level is a marker of viral replication and efficacy of antiviral treatment in individuals with chronic hepatitis B.

OBJECTIVE

To evaluate the relationship between serum HBV DNA level and risk of hepatocellular carcinoma.

DESIGN, SETTING, AND PARTICIPANTS

Prospective cohort study of 3653 participants (aged 30-65 years), who were seropositive for the hepatitis B surface antigen and seronegative for antibodies against the hepatitis C virus, recruited to a community-based cancer screening program in Taiwan between 1991 and 1992.

MAIN OUTCOME MEASURE

Incidence of hepatocellular carcinoma during follow-up examination and by data linkage with the national cancer registry and the death certification systems.

RESULTS

There were 164 incident cases of hepatocellular carcinoma and 346 deaths during a mean follow-up of 11.4 years and 41,779 person-years of follow-up. The incidence of hepatocellular carcinoma increased with serum HBV DNA level at study entry in a dose-response relationship ranging from 108 per 100,000 person-years for an HBV DNA level of less than 300 copies/mL to 1152 per 100,000 person-years for an HBV DNA level of 1 million copies/mL or greater. The corresponding cumulative incidence rates of hepatocellular carcinoma were 1.3% and 14.9%, respectively. The biological gradient of hepatocellular carcinoma by serum HBV DNA levels remained significant (P<.001) after adjustment for sex, age, cigarette smoking, alcohol consumption, serostatus for the hepatitis B e antigen (HBeAg), serum alanine aminotransferase level, and liver cirrhosis at study entry. The dose-response relationship was most prominent for participants who were seronegative for HBeAg with normal serum alanine aminotransferase levels and no liver cirrhosis at study entry. Participants with persistent elevation of serum HBV DNA level during follow-up had the highest hepatocellular carcinoma risk.

CONCLUSION

Elevated serum HBV DNA level (> or =10,000 copies/mL) is a strong risk predictor of hepatocellular carcinoma independent of HBeAg, serum alanine aminotransferase level, and liver cirrhosis.

Hepatitis B virus immunopathogenesis

Approximately 5% of the world population is infected by the hepatitis B virus (HBV) that causes a necroinflammatory liver disease of variable duration and severity. Chronically infected patients with active liver disease carry a high risk of developing cirrhosis and hepatocellular carcinoma. The immune response to HBV-encoded antigens is responsible both for viral clearance and for disease pathogenesis during this infection. While the humoral antibody response to viral envelope antigens contributes to the clearance of circulating virus particles, the cellular immune response to the envelope, nucleocapsid, and polymerase antigens eliminates infected cells. The class I- and class II-restricted T cell responses to the virus are vigorous, polyclonal, and multispecific in acutely infected patients who successfully clear the virus, and the responses are relatively weak and more narrowly focused in chronically infected patients who do not. The pathogenetic and antiviral potential of the cytotoxic T lymphocyte (CTL) response to HBV has been demonstrated by the induction of a severe necroinflammatory liver disease following the adoptive transfer of HBsAg-specific CTL into HBV transgenic mice, and by the noncytolytic suppression of viral gene expression and replication in the same animals by a posttranscriptional mechanism mediated by interferon gamma, tumor necrosis factor alpha, and interleukin 2. The dominant cause of viral persistence during HBV infection is the development of a weak antiviral immune response to the viral antigens. While neonatal tolerance probably plays an important role in viral persistence in patients infected at birth, the basis for poor responsiveness in adult-onset infection is not well understood and requires further analysis. Viral evasion by epitope inactivation and T cell receptor antagonism may contribute to the worsening of viral persistence in the setting of an ineffective immune response, as can the incomplete downregulation of viral gene expression and the infection of immunologically privileged tissues. Chronic liver cell injury and the attendant inflammatory and regenerative responses create the mutagenic and mitogenic stimuli for the development of DNA damage that can cause hepatocellular carcinoma. Elucidation of the immunological and virological basis for HBV persistence may yield immunotherapeutic and antiviral strategies to terminate chronic HBV infection and reduce the risk of its life-threatening sequellae.

Hepatitis B virus biology

Hepadnaviruses (hepatitis B viruses) cause transient and chronic infections of the liver. Transient infections run a course of several months, and chronic infections are often lifelong. Chronic infections can lead to liver failure with cirrhosis and hepatocellular carcinoma. The replication strategy of these viruses has been described in great detail, but virus-host interactions leading to acute and chronic disease are still poorly understood. Studies on how the virus evades the immune response to cause prolonged transient infections with high-titer viremia and lifelong infections with an ongoing inflammation of the liver are still at an early stage, and the role of the virus in liver cancer is still elusive. The state of knowledge in this very active field is therefore reviewed with an emphasis on past accomplishments as well as goals for the future.

Hepatitis B virus infection

Since the introduction of the hepatitis B vaccine and other preventive measures, the worldwide prevalence of hepatitis B infection has fallen. However, chronic infection remains a challenging global health problem, with more than 350 million people chronically infected and at risk of hepatic decompensation, cirrhosis, and hepatocellular carcinoma. An improved understanding of hepatitis B virology, immunology, and the natural course of chronic infection, has identified hepatitis B virus replication as the key driver of immune-mediated liver injury and disease progression. The approval of potent oral antiviral agents has revolutionised hepatitis B treatment since 1998. Conventional and pegylated interferon alfa and nucleoside and nucleotide analogues are widely authorised treatments, and monotherapy with these drugs greatly suppresses virus replication, reduces hepatitis activity, and halts disease progression. However, hepatitis B virus is rarely eliminated, and drug resistance is a major drawback during long term therapy. The development of new drugs and strategies is needed to improve treatment outcomes.

HBx gene of hepatitis B virus induces liver cancer in transgenic mice

The exact role of hepatitis B virus in the development of liver cancer is not known. The recent identification of a viral regulatory gene HBx suggests a possible direct involvement of the virus whereby the HBx protein, acting as a transcriptional transactivator of viral genes, may alter host gene expression and lead to the development of hepatocellular carcinoma. We have tested this possibility of placing the entire HBx gene under its own regulatory elements directly into the germline of mice. Transgenic animals harbouring this viral gene succumbed to progressive histopathological changes specifically in the liver, beginning with multifocal areas of altered hepatocytes, followed by the appearance of benign adenomas, and proceeding to the development of malignant carcinomas. Male mice developed disease and died much earlier than females. This transgenic animal model appears ideal for defining the molecular events that follow the expression of the viral HBx gene and are responsible for the development of liver cancer.

Proteomics identifies new therapeutic targets of early-stage hepatocellular carcinoma

Hepatocellular carcinoma is the third leading cause of deaths from cancer worldwide. Infection with the hepatitis B virus is one of the leading risk factors for developing hepatocellular carcinoma, particularly in East Asia1. Although surgical treatment may be effective in the early stages, the five-year overall rate of survival after developing this cancer is only 50-70%2. Here, using proteomic and phospho-proteomic profiling, we characterize 110 paired tumour and non-tumour tissues of clinical early-stage hepatocellular carcinoma related to hepatitis B virus infection. Our quantitative proteomic data highlight heterogeneity in early-stage hepatocellular carcinoma: we used this to stratify the cohort into the subtypes S-I, S-II and S-III, each of which has a different clinical outcome. S-III, which is characterized by disrupted cholesterol homeostasis, is associated with the lowest overall rate of survival and the greatest risk of a poor prognosis after first-line surgery. The knockdown of sterol O-acyltransferase 1 (SOAT1)-high expression of which is a signature specific to the S-III subtype-alters the distribution of cellular cholesterol, and effectively suppresses the proliferation and migration of hepatocellular carcinoma. Finally, on the basis of a patient-derived tumour xenograft mouse model of hepatocellular carcinoma, we found that treatment with avasimibe, an inhibitor of SOAT1, markedly reduced the size of tumours that had high levels of SOAT1 expression. The proteomic stratification of early-stage hepatocellular carcinoma presented in this study provides insight into the tumour biology of this cancer, and suggests opportunities for personalized therapies that target it.

Molecular pathogenesis of hepatocellular carcinoma in hepatitis B virus transgenic mice

Transgenic mice that overproduce the hepatitis B virus large envelope polypeptide and accumulate toxic quantities of hepatitis B surface antigen (HBsAg) within the hepatocyte develop severe, prolonged hepatocellular injury that initiates a programmed response within the liver, characterized by inflammation, regenerative hyperplasia, transcriptional deregulation, and aneuploidy. This response inexorably progresses to neoplasia. The incidence of hepatocellular carcinoma in this model corresponds to the frequency, severity, and age of onset of liver cell injury, which itself corresponds to the intrahepatic concentration of HBsAg and is influenced by genetic background and sex. Thus, the inappropriate expression of a single structural viral gene is sufficient to cause malignant transformation in this model. These results suggest that severe, prolonged cellular injury induces a preneoplastic proliferative response that fosters secondary genetic events that program the cell for unrestrained growth.

Viruses in human cancers

Viruses may contribute to the development of human tumors by different mechanisms: indirectly by inducing immunosuppression or by modifying the host cell genome without persistence of viral DNA; directly by inducing oncoproteins or by altering the expression of host cell proteins at the site of viral DNA integration. Human cancers associated with papillomavirus, hepatitis B virus, Epstein-Barr virus, and human T cell leukemia-lymphoma virus infections are responsible for approximately 15 percent of the worldwide cancer incidence. Cancer of the cervix and hepatocellular carcinoma account for about 80 percent of virus-linked cancers. Because experimental and epidemiologic data imply a causative role for viruses, particularly in cervical and liver cancer, viruses must be thought of as the second most important risk factor for cancer development in humans, exceeded only by tobacco consumption.

Genotype C hepatitis B virus infection is associated with an increased risk of hepatocellular carcinoma

BACKGROUND

Identification of risk factors for the development of hepatocellular carcinoma (HCC) is important for HCC surveillance in chronic hepatitis B virus (HBV) infection. Our aim was to study the independent risk factors and effect of HBV genotypes on HCC development in a prospective longitudinal cohort of chronic hepatitis B patients.

PATIENTS AND METHODS

Chronic hepatitis B patients recruited since 1997 were prospectively followed up for the development of HCC. HCC was diagnosed by a combination of alpha fetoprotein, imaging, and histology. Liver cirrhosis was defined as ultrasonic features of cirrhosis together with hypersplenism, ascites, varices, and/or encephalopathy.

RESULTS

In total, 426 patients were followed up for 1664 person years; median 225 (range 12-295) weeks. Forty nine (11%) patients had underlying clinical liver cirrhosis. A total of 242 (57%) and 179 (42%) patients had HBV genotypes C and B, respectively. Twenty five patients developed HCC in a median follow up of 121 (range 14-236) weeks. The overall incidence of HCC was 1502 cases per 100 000 person years. On multivariate analysis, clinical liver cirrhosis and HBV genotype C infection were independently associated with HCC development, with an adjusted relative risk of 10.24 (95% confidence interval (CI) 4.39-23.89; p<0.001) and 2.84 (95% CI 1.05-7.72; p = 0.040), respectively. Patient age, sex, hepatitis B e antigen (HBeAg) status, alanine aminotransferase (ALT) levels, and basal core promoter mutations did not predict HCC development. Patients infected with HBV genotype C tended to have persistently positive HBeAg or fluctuating HBeAg status and higher ALT levels during the follow up period.

CONCLUSION

Genotype C HBV infection is an independent risk factor for HCC development in addition to liver cirrhosis.

Molecular viral oncology of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer, but the third leading cause of cancer death, in the world, with more than 500,000 fatalities annually. The major etiology of HCC/liver cancer in people is hepatitis B virus (HBV), followed by hepatitis C virus infection (HCV), although nonviral causes also play a role in a minority of cases. Recent molecular studies confirm what was suspected: that HCC tissue from different individuals have many phenotypic differences. However, there are clearly features that unify HCC occurring in a background of viral hepatitis B and C. HCC due to HBV and HCV may be an indirect result of enhanced hepatocyte turnover that occurs in an effort to replace infected cells that have been immunologically attacked. Viral functions may also play a more direct role in mediating oncogenesis. This review considers the molecular and cellular mechanisms involved in primary hepatocellular carcinoma, using a viral perspective.

The etiology of hepatocellular carcinoma and consequences for treatment

Most patients with hepatocellular carcinoma (HCC) have liver cirrhosis, which develops following long periods of chronic liver disease. Cirrhosis is characterized by a decrease in hepatocyte proliferation, indicating an exhaustion of the regenerative capacity of the liver, and results in an increase in fibrous tissue and a destruction of liver cells, which may ultimately lead to the development of cancerous nodules. Half of all cases of HCC are associated with hepatitis B virus infection, with a further 25% associated with hepatitis C virus. Other risk factors for developing HCC include alcoholic liver disease, nonalcoholic steatohepatitis, intake of aflatoxin-contaminated food, diabetes, and obesity. There are multiple factors involved in the etiology of HCC, all of which have a direct impact on patient characteristics and disease course, and although a causative agent can often be identified, HCC remains an extremely complex condition associated with a poor prognosis. Additionally, the geographic variation in etiology means that information from different countries is needed in order to optimize surveillance methods and develop effective chemoprevention strategies. Unfortunately, there are still many gaps in our current understanding, and further research efforts are needed to fully elucidate the diverse mechanisms involved in the pathogenesis of HCC and offer optimal prevention strategies for those at risk.

HBXIP functions as a cofactor of survivin in apoptosis suppression

Survivin is an anti-apoptotic protein that is overexpressed in most human cancers. We show that survivin forms complexes with a cellular protein, hepatitis B X-interacting protein (HBXIP), which was originally recognized for its association with the X protein of hepatitis B virus (HBX). Survivin-HBXIP complexes, but neither survivin nor HBXIP individually, bind pro-caspase-9, preventing its recruitment to Apaf1, and thereby selectively suppressing apoptosis initiated via the mitochondria/cytochrome c pathway. Viral HBX protein also interacts with the survivin- HBXIP complex and suppresses caspase activation in a survivin-dependent manner. Thus, HBXIP functions as a cofactor for survivin, and serves as a link between the cellular apoptosis machinery and a viral pathogen involved in hepatocellular carcinogenesis.

Pathogenesis of hepatitis B virus-related hepatocellular carcinoma: old and new paradigms

Chronic infection with the hepatitis B virus (HBV) is a major risk factor for development of hepatocellular carcinoma (HCC). The pathogenesis of cancer in HBV infection has been extensively analyzed, and multiple factors appear to play a role. A major factor is chronic inflammation and the effects of cytokines in the development of fibrosis and liver cell proliferation. Also important is the role of integration of HBV DNA into host cellular DNA, which, in some situations, acts to disrupt or promote expression of cellular genes that are important in cell growth and differentiation. In addition, expression of HBV proteins may have a direct effect on cellular functions, and some of these gene products can favor malignant transformation. Several HBV genes have been found in infected tissues more frequently than others, including truncated pre-S2/S, hepatitis B X gene, and a novel spliced transcript of HBV, referred to as the hepatitis B spliced protein. The proteins expressed from these integrated genes have been shown to have intracellular activities that may account for their association with HCC, including effects on cellular growth and apoptosis. Finally, some patients with HCC have no detectable hepatitis B surface antigen in serum but do have low levels of HBV DNA in serum and integrated molecules of HBV DNA in tissue. Occult HBV infection may account for a proportion of cases of HCC that occur in patients without serologic markers for hepatitis B and C and may be a cofactor in HCC in patients with chronic hepatitis C who have coexistent occult HBV infection.

Hydrodynamic injection of viral DNA: a mouse model of acute hepatitis B virus infection

Hepatitis B virus (HBV) is a prototype for liver-specific pathogens in which the failure of the immune system to mount an effective response leads to chronic infection. Our understanding of the immune response to HBV is incomplete, largely due to the narrow host restriction of this pathogen and the limitations of existing experimental models. We have developed a murine model for studying human HBV replication, immunogenicity, and control. After transfection of hepatocytes in vivo with a replication-competent, over-length, linear HBV genome, viral antigens and replicative intermediates were synthesized and virus was secreted into the blood. Viral antigens disappeared from the blood as early as 7 days after transfection, coincident with the appearance of antiviral antibodies. HBV transcripts and replicative intermediates disappeared from the liver by day 15, after the appearance of antiviral CD8 + T cells. In contrast, the virus persisted for at least 81 days after transfection of NOD/Scid mice, which lack functional T cells, B cells, and natural killer (NK) cells. Thus, the outcome of hydrodynamic transfection of HBV depends on the host immune response, as it is during a natural infection. The methods we describe will allow the examination of viral dynamics in a tightly controlled in vivo system, the application of mutagenesis methods to the study of the HBV life cycle in vivo, and the dissection of the immune response to HBV using genetically modified mice whose immunoregulatory and immune effector functions have been deleted or overexpressed. In addition, this methodology represents a prototype for the study of other known and to-be-discovered liver-specific pathogens.

Analysis of liver disease, nuclear HBcAg, viral replication, and hepatitis B virus DNA in liver and serum of HBeAg Vs. anti-HBe positive carriers of hepatitis B virus

Nine HBeAg+ and 24 anti-HBe+ subjects with chronic hepatitis B virus (HBV) infection were studied for HBV DNA in the serum by molecular hybridization, for HBcAg in the liver by immunofluorescence, and for histologic evidence of liver disease. All HBeAg+ patients had underlying chronic liver disease (chronic persistent hepatitis, chronic active hepatitis, or cirrhosis with or without hepatocellular carcinoma), and all were found positive for both HBV DNA in the serum and HBcAg in the nucleus of hepatocytes. Of the 24 anti-HBe+ individuals, 18 had various forms of chronic liver disease. Six HBsAg+/anti-HBe+ patients had normal liver histology except for numerous "ground-glass" hepatocytes with abundant cytoplasmic HBsAg. All six were negative for nuclear HBcAg and serum HBV DNA, but three showed HBV DNA which appeared to be integrated into unique sites in host liver DNA by hybridization analysis. In contrast, 14/18 (78%) of HBsAg+/anti-HBe+ patients with chronic liver disease were positive for nuclear HBcAg, serum HBV DNA, or both of these markers of HBV replication. It is suggested that in long-term HBsAg carriers with serum anti-HBe and normal liver histology, viral replication is suppressed or inactive and HBV potential infectivity is presumably very low or absent. However, when viral replication is present in HBsAg+/anti-HBe+ carriers (as demonstrated by serum HBV DNA and/or nuclear HBcAg), active liver disease is often found. In these individuals, active chronic liver disease appears to be related to continued replication and secretion of HBV and may occur in a much higher proportion of HBsAg+/anti-HBe+ carriers than was previously suspected.

Epidemiology and natural history of hepatitis B

Hepatitis B virus (HBV) is a common viral pathogen that currently infects an estimated 4 million people worldwide, including 400 million who have chronic infection. Persons with chronic HBV infection are at a lifelong risk of developing hepatocellular carcinoma (HCC) or cirrhosis, or both. Many persons with HBV are unaware that they carry the infection, and, of those who are chronically infected, only a minority receives routine, scheduled follow-up to monitor their disease status. Persons from high-risk populations, especially immigrants from nations where hepatitis B is highly endemic, should be tested for HBV seromarkers and should be vaccinated if they are found to be negative. The natural history of chronic HBV is a dynamic one: patients can fluctuate between periods of active liver inflammation and periods of inactive disease. Disease progression is influenced by various factors, including viral genotype and specific mutations, demographic features, concurrent viral infections, and social and environmental factors. Recent data suggest that antiviral therapy can decrease the risk of liver decompensation and liver-related death and reduce the risk of HCC in selected individuals with active liver disease and severe fibrosis. Persons identified with chronic HBV infection need lifelong, regular monitoring for the development of active liver disease and HCC.

Hepatitis B virus genotypes: Global distribution and clinical importance

At least 600000 individuals worldwide annually die of hepatitis B virus (HBV)-related diseases, such as chronic hepatitis B (CHB), liver cirrhosis (LC), and hepatocellular carcinoma (HCC). Many viral factors, such as viral load, genotype, and specific viral mutations, are known to affect disease progression. HBV reverse transcriptase does not have a proofreading function, therefore, many HBV genotypes, sub-genotypes, mutants, and recombinants emerge. Differences between genotypes in response to antiviral treatment have been determined. To date, 10 HBV genotypes, scattered across different geographical regions, have been identified. For example, genotype A has a tendency for chronicity, whereas viral mutations are frequently encountered in genotype C. Both chronicity and mutation frequency are common in genotype D. LC and progression to HCC are more commonly encountered with genotypes C and D than the other genotypes. Pathogenic differences between HBV genotypes explain disease intensity, progression to LC, and HCC. In conclusion, genotype determination in CHB infection is important in estimating disease progression and planning optimal antiviral treatment.

The toxicology of aflatoxins as a basis for public health decisions

Aflatoxins have been extensively studied with respect to their mechanisms of toxicity. An understanding of metabolism, DNA adduct induction, mutagenicity and carcinogenicity has been paralleled by the development of biomarkers of aflatoxin exposure and biological effects (e.g. mutations) applied to human populations. The improvements in exposure assessment and their application in prospective epidemiological studies and the demonstration of a specific mutation in the TP53 gene in hepatocellular carcinomas from areas of high aflatoxin exposure have contributed significantly to the classification of aflatoxins as human carcinogens. In addition to establishing the carcinogenicity of aflatoxins in humans, understanding molecular mechanisms of action has provided the scientific rationale for prevention strategies, including primary and chemoprevention approaches. Overall, integrated, multidisciplinary research on aflatoxins has provided the platform on which to base decisions regarding acceptable exposures and priorities for interventions to reduce human risk in a public health context.

Environmental factors and risk for hepatocellular carcinoma

Chronic infections with hepatitis B virus (HBV) and hepatitis C virus (HCV) are the most important risk factors for the development of hepatocellular carcinoma (HCC) in humans. HBV is the primary cause of HCC in high-risk areas including China and Africa, whereas in developed countries such as the United States, HCV plays a more prominent role and is at least partially responsible for the increase in HCC incidence in this country. Humans are exposed to hepatocarcinogenic aflatoxins through ingestion of moldy foods, a consequence of poor storage of susceptible grains. Highly exposed populations are primarily in sub-Sahara Africa and Asia, where dietary aflatoxins significantly enhance the carcinogenic effects of viral hepatitis. Heavy, long-term alcohol use is a risk factor for HCC, whereas moderate use (1-3 drinks/day) is not. Constituents of cigarette smoke are hepatic carcinogens in animals, and there is mounting evidence that the liver is an organ susceptible to tobacco carcinogenicity. Diabetic patients are at risk for HCC probably as a result of the hepatic injury, fibrosis, and eventual cirrhosis resulting from fatty liver disease. Given the current epidemic of obesity and diabetes in the United States, this risk factor will be increasingly important. Increased risk for HCC is evident in young noncirrhotic users of oral contraceptives in the United States and Europe. In summary, risk factors for HCC are identifiable in most patients and primarily are associated with chronic hepatic injury.

Natural history and prognosis of hepatitis B

The natural history of hepatitis B virus (HBV) infection is complex and variable and is greatly influenced by the age at infection, the level of HBV replication, and host immune status. Chronic HBV infection generally consists of an early replicative phase with active liver disease (hepatitis B e antigen [HBeAg]-positive chronic hepatitis) and a late low or nonreplicative phase with HBeAg seroconversion and remission of liver disease (inactive carrier state). After HBeAg seroconversion, some patients may have active hepatitis due to HBV variants not expressing HBeAg (HBeAg-negative chronic hepatitis). Morbidity and mortality are linked to development of cirrhosis and hepatocellular carcinoma. Survival is reasonably good (about 85% probability at 5 years) in compensated cirrhosis but very poor in decompensated cirrhosis. Both cirrhotic and noncirrhotic patients with sustained reduction of HBV replication and normalization of aminotransferase after interferon alfa therapy have a reduced risk for liver-related complications.

The woodchuck hepatitis virus X gene is important for establishment of virus infection in woodchucks

All mammalian hepadnaviruses possess a gene, termed X, that encodes a protein capable of transactivating virus gene expression. The X gene overlaps the polymerase and precore genes as well as two newly identified open reading frames (ORFs) termed ORF5 and ORF6. In this investigation, we examined whether ORF5, ORF6, and the X gene were important for the replication of woodchuck hepatitis virus (WHV) in susceptible woodchucks. First, we investigated whether proteins were produced from ORF5 and ORF6 by in vitro translation of appropriate viral transcripts, searched for antibodies against the putative proteins in the sera of animals infected with wild-type virus, and looked for an antisense WHV transcript, necessary for expression of a protein from ORF6, in the livers of acutely or chronically infected woodchucks. All such experiments yielded negative results. Next, we used oligonucleotide-directed mutagenesis to introduce termination codons into ORF5 and ORF6 at two locations within each ORF. Adult woodchucks in groups of three were transfected with one of the four mutant genomes. All of these woodchucks developed WHV infections that were indistinguishable from those of animals transfected with the wild-type WHV recombinant. Polymerase chain reaction amplification and direct DNA sequencing confirmed that reversion of the mutants to a wild-type genotype did not occur. Taken together, these data indicate that ORF5 and ORF6 are not essential for virus replication and are unlikely to represent authentic genes. Finally, we generated five WHV X-gene mutants that either removed the initiation codon for protein synthesis or truncated the carboxyl terminus of the protein by 3, 16, 31, or 52 amino acids. Groups of three adult woodchucks were transfected with one of the five X-gene mutants. Only the mutant that possessed an X gene lacking 3 amino acids from the carboxyl terminus was capable of replication within the 6-month time frame of the experiment. In contrast, all seven woodchucks transfected with wild-type WHV DNA developed markers consistent with viral infection. Thus, it is likely (P < 0.01) that the WHV X gene is important for virus replication in the natural host.

Efficient inhibition of hepatitis B virus infection by acylated peptides derived from the large viral surface protein

The lack of an appropriate in vitro infection system for the major human pathogen hepatitis B virus (HBV) has prevented a molecular understanding of the early infection events of HBV. We used the novel HBV-infectible cell line HepaRG and primary human hepatocytes to investigate the interference of infection by HBV envelope protein-derived peptides. We found that a peptide consisting of the authentically myristoylated N-terminal 47 amino acids of the pre-S1 domain of the large viral envelope protein (L protein) specifically prevented HBV infection, with a 50% inhibitory concentration (IC50) of 8 nM. The replacement of myristic acid with other hydrophobic moieties resulted in changes in the inhibitory activity, most notably by a decrease in the IC50 to picomolar concentrations for longer unbranched fatty acids. The obstruction of HepaRG cell susceptibility to HBV infection after short preincubation times with the peptides suggested that the peptides efficiently target and inactivate a receptor at the hepatocyte surface. Our data both shed light on the molecular mechanism of HBV entry into hepatocytes and provide a basis for the development of potent hepadnaviral entry inhibitors as a novel therapeutic concept for the treatment of hepatitis Beta.

Human mesenchymal stem cell transfusion is safe and improves liver function in acute-on-chronic liver failure patients

Acute-on-chronic liver failure (ACLF) is a severe, life-threatening complication, and new and efficient therapeutic strategies for liver failure are urgently needed. Mesenchymal stem cell (MSC) transfusions have been shown to reverse fulminant hepatic failure in mice and to improve liver function in patients with end-stage liver diseases. We assessed the safety and initial efficacy of umbilical cord-derived MSC (UC-MSC) transfusions for ACLF patients associated with hepatitis B virus (HBV) infection. A total of 43 ACLF patients were enrolled for this open-labeled and controlled study; 24 patients were treated with UC-MSCs, and 19 patients were treated with saline as controls. UC-MSC therapy was given three times at 4-week intervals. The liver function, adverse events, and survival rates were evaluated during the 48-week or 72-week follow-up period. No significant side effects were observed during the trial. The UC-MSC transfusions significantly increased the survival rates in ACLF patients; reduced the model for end-stage liver disease scores; increased serum albumin, cholinesterase, and prothrombin activity; and increased platelet counts. Serum total bilirubin and alanine aminotransferase levels were significantly decreased after the UC-MSC transfusions. UC-MSC transfusions are safe in the clinic and may serve as a novel therapeutic approach for HBV-associated ACLF patients.