Detection of hepatitis B virus surface antigen mutants in paraffin-embedded hepatocellular carcinoma tissues

Hepatitis B virus S gene escape mutants

Hepatitis B virus (HBV) can be classified into nine immunological subtypes or eight genotypes. The most prevalent genotypes in Asia are genotypes B and C. HBV is transmitted parenteraly and can produce either asymptomatic or symptomatic disease. Although the consequences of acute hepatitis B can be severe, serious sequelae are associated with chronic infections. HBV seroprevalence ranges from intermediate (2%-7%) to high (≥8%) levels in Asia. Several strategies for the control and prevention of HBV infection have been found to be efficacious. They include vaccination and the administration of HBIG, interferon-a and nucleoside/nucleotide analogues. However, these procedures also apply selective pressures on HBV in infected individuals leading to the generation and accumulation of mutations in the S gene. Most of these mutations occur in the major hydrophilic region (MHR) of the S gene. These mutations create public health concerns as they can be responsible for reactivation of hepatitis B and occult hepatitis B infection. The inability to detect occult infections means that these individuals may become blood donors. This suggests that new strategies for donor evaluation and selection may need to be developed to protect the blood supply.

Tissue microarray for high-throughput analysis of gene expression profiles in hepatocellular carcinoma

AIM: To study the expression profiles of HBsAg, HBcAg, p21^WAF1/CIP1 (p21), Rb genes in hepatocellular carcinoma (HCC) and to investigate their roles in the hepatocar-cinogenesis.

METHODS: HCC tissue microarray containing 120-min tissues of 40 HCC cases was constructed. HBsAg, HBcAg, p21 and Rb proteins were immunohistochemically stained by streptavidin-peroxidase conjugated method (S-P). The expression loss of these genes in cancerous, para-cancerous tissues and adjacent normal liver tissues of 40 HCCs were comparatively examined.

RESULTS: The positive rate of HBsAg expression in cancerous tissues of 40 HCCs was 7.5%, which was lower than that in para-cancerous and adjacent normal liver tissues (χ² =12.774, P<0.01; χ² = 18.442, P<0.01). The positive rate of HBcAg expression in cancerous tissues of 40 HCCs was 20.0%, which was also lower than that in para-cancerous and adjacent normal liver tissues (χ² = 9.482, P<0.01; χ² = 14.645, P<0.01). p21 protein deletion rate in cancerous tissues of 40 HCCs was 27.5%, which was higher than that in para-cancerous and adjacent normal liver tissues (χ² = 7.439, P<0.01; χ² = 11.174, P<0.01). p21 protein deletion correlated remarkably with the pathological grade of HCC (χ² = 0.072, P<0.05). Rb protein deletion rate in cancerous tissues of 40 HCCs was 42.5%, which was also higher than that in para-cancerous and adjacent normal liver tissues (χ² = 10.551, P<0.01; χ² = 18.353, P<0.01). Rb protein deletion rate did not correlate remarkably with tumor size or pathological grade of HCC (χ² = 0.014, P>0.05; χ² = 0.017, P>0.05).

CONCLUSION: Expression deletion of HBsAg, HBcAg, p21 and Rb proteins in HCCs may play important roles in the carcinogenesis of HCC. Tissue microarray is an effective high-throughput technique platform for cancer research.

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.

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.

Molecular characterization of hepatitis B virus surface antigen mutants in Singapore patients with hepatocellular carcinoma and hepatitis B virus carriers negative for HBsAg but positive for anti-HBs and anti-HBc

BACKGROUND AND AIMS

Mutations on the a-determinant of hepatitis B virus surface antigen (HBsAg), capable of escaping detection and vaccination, are identified in HBsAg-positive/anti-HBs-positive vaccinated infants. We studied the prevalence of these mutants in HBsAg-negative/anti-HBc-positive chronic HBV carriers and patients with hepatocellular carcinoma (HCC).

METHODS

DNA sequence coding for the antigenic a-determinant of HBsAg was amplified from either HCC genomic DNA or serum samples of the selected patients and sequenced. The replicative mutant genomes were reconstituted in vitro and their reactivity to commercial kits measured.

RESULTS

Mutations within and/or outside the a-determinant were identified in patients seronegative for HBsAg. They were then reconstituted in vitro and transiently transfected into HepG2 cells. Culture medium containing secreted HBV viral particles was collected and assayed for their binding to commercial kits. Drastic decrease of reactivity to these kits was seen with most of the identified mutations, including those located outside the a-determinant.

CONCLUSION

The existence of a more complex antigenic structure of HBsAg is indicated by the decreased reactivity to detection of mutations, some of which are outside the a-determinant, escape vaccination and may persist in seronegative patients. The high proportion of HBsAg mutants that are integrated in HCC genomes suggests a role of these mutants in hepatocarcinogenesis, possibly leading to mutant HBV-related HCC.