The profile of mutational clusters associated with lamivudine resistance can be constrained by HBV genotypes

Evolution and diversity of the hepatitis B virus genome: Clinical implications

Hepatitis B virus (HBV) infection remains a significant global health burden. The genetic variation of HBV is complex. HBV can be divided into nine genotypes, which show significant differences in geographical distribution, clinical manifestations, transmission routes and treatment response. In recent years, substantial progress has been made through various research methods in understanding the development, pathogenesis, and antiviral treatment response of clinical disease associated with HBV genetic variants. This progress provides important theoretical support for a deeper understanding of the natural history of HBV infection, virus detection, drug treatment, vaccine development, mother-to-child transmission, and surveillance management. This review summarizes the mechanisms of HBV diversity, discusses methods used to detect viral diversity in current studies, and the impact of viral genome variation during infection on the development of clinical disease.

Molecular and Genetic Characterization of Hepatitis B Virus (HBV) among Saudi Chronically HBV-Infected Individuals

The study aimed to characterize the genotype and subgenotypes of HBV circulating in Saudi Arabia, the presence of clinically relevant mutations possibly associated with resistance to antivirals or immune escape phenomena, and the possible impact of mutations in the structural characteristics of HBV polymerase. Plasma samples from 12 Saudi Arabian HBV-infected patients were analyzed using an in-house PCR method and direct sequencing. Saudi patients were infected with mainly subgenotype D1. A number of mutations in the RT gene (correlated to antiviral resistance) and within and outside the major hydrophilic region of the S gene (claimed to influence immunogenicity and be related to immune escape) were observed in almost all patients. Furthermore, the presence of mutations in the S region caused a change in the tertiary structure of the protein compared with the consensus region. Clinical manifestations of HBV infection may change dramatically as a result of viral and host factors: the study of mutations and protein-associated cofactors might define possible aspects relevant for the natural and therapeutic history of HBV infection.

Detection and Genetic Characterization of Hepatitis B and D Viruses: A Multi-Site Cross-Sectional Study of People Who Use Illicit Drugs in the Amazon Region

Hepatitis B (HBV) and delta (HDV) viruses are endemic in the Amazon region, but vaccine coverage against HBV is still limited. People who use illicit drugs (PWUDs) represent a high-risk group due to common risk behavior and socioeconomic factors that facilitate the acquisition and transmission of pathogens. The present study assessed the presence of HBV and HBV-HDV co-infection, identified viral sub-genotypes, and verified the occurrence of mutations in coding regions for HBsAg and part of the polymerase in HBV-infected PWUDs in municipalities of the Brazilian states of Amapá and Pará, in the Amazon region. In total, 1074 PWUDs provided blood samples and personal data in 30 municipalities of the Brazilian Amazon. HBV and HDV were detected by enzyme-linked immunosorbent assay and polymerase chain reaction. Viral genotypes were identified by nucleotide sequencing followed by phylogenetic analysis, whereas viral mutations were analyzed by specialized software. High rates of serological (32.2%) and molecular (7.2%) markers for HBV were detected, including cases of occult HBV infection (2.5%). Sub-genotypes A1, A2, D4, and F2a were most frequently found. Escape mutations due to vaccine and antiviral resistance were identified. Among PWUDs with HBV DNA, serological (19.5%) and molecular (11.7%) HDV markers were detected, such as HDV genotypes 1 and 3. These are worrying findings, presenting clear implications for urgent prevention and treatment needs for the carriers of these viruses.

Mutational characterization of HBV reverse transcriptase gene and the genotype-phenotype correlation of antiviral resistance among Chinese chronic hepatitis B patients

Background and Aims: The drug resistance of hepatitis B virus (HBV) originates from mutations within HBV reverse transcriptase (RT) region during the prolonged antiviral therapy. So far, the characteristics of how these mutations distribute and evolve in the process of therapy have not been clarified yet. Thus we aimed to investigate these characteristics and discuss their contributing factors.

Methods: HBV RT region was direct-sequenced in 285 treatment-naive and 214 post-treatment patients. Mutational frequency and Shannon entropy were calculated to identify the specific mutations differing between genotypes or treatment status. A typical putative resistance mutation rtL229V was further studied using in-vitro susceptibility assays and molecular modeling.

Results: The classical resistance mutations were rarely detected among treatment-naive individuals, while the putative resistance mutations were observed at 8 AA sites. rtV191I and rtA181T/V were the only resistance mutations identified as genotype-specific mutation. Selective pressure of drug usage not only contributed to the classical resistance mutations, but also induced the changes at a putative resistance mutation site rt229. rtL229V was the major substitution at the site of rt229. It contributed to the most potent suppression of viral replication and reduced the in-vitro drug susceptibility to entecavir (ETV) when coexisting with rtM204V, consistent with the hypothesis based on the molecular modeling and clinical data analysis.

Conclusions: The analysis of mutations in RT region under the different circumstances of genotypes and therapy status might pave the way for a better understanding of resistance evolution, thus providing the basis for a rational administration of antiviral therapy.

Key genetic elements, single and in clusters, underlying geographically dependent SARS-CoV-2 genetic adaptation and their impact on binding affinity for drugs and immune control

Objectives

To define key genetic elements, single or in clusters, underlying SARS-CoV-2 (severe acute respiratory syndrome coronavirus-2) evolutionary diversification across continents, and their impact on drug-binding affinity and viral antigenicity.

Methods

A total of 12 150 SARS-CoV-2 sequences (publicly available) from 69 countries were analysed. Mutational clusters were assessed by hierarchical clustering. Structure-based virtual screening (SBVS) was used to select the best inhibitors of 3-chymotrypsin-like protease (3CL-Pr) and RNA-dependent RNA polymerase (RdRp) among the FDA-approved drugs and to evaluate the impact of mutations on binding affinity of these drugs. The impact of mutations on epitope recognition was predicted following Grifoni et al. (Cell Host Microbe 2020;

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671–80.)

Results

Thirty-five key mutations were identified (prevalence: ≥0.5%), residing in different viral proteins. Sixteen out of 35 formed tight clusters involving multiple SARS-CoV-2 proteins, highlighting intergenic co-evolution. Some clusters (including D614G_Spike + P323L_RdRp + R203K_N + G204R_N) occurred in all continents, while others showed a geographically restricted circulation (T1198K_PL-Pr + P13L_N + A97V_RdRp in Asia, L84S_ORF-8 + S197L_N in Europe, Y541C_Hel + H504C_Hel + L84S_ORF-8 in America and Oceania). SBVS identified 20 best RdRp inhibitors and 21 best 3CL-Pr inhibitors belonging to different drug classes. Notably, mutations in RdRp or 3CL-Pr modulate, positively or negatively, the binding affinity of these drugs. Among them, P323L_RdRp (prevalence: 61.9%) reduced the binding affinity of specific compounds including remdesivir while it increased the binding affinity of the purine analogues penciclovir and tenofovir, suggesting potential hypersusceptibility. Finally, specific mutations (including Y541C_Hel + H504C_Hel) strongly hampered recognition of Class I/II epitopes, while D614G_Spike profoundly altered the structural stability of a recently identified B cell epitope target of neutralizing antibodies (amino acids 592–620).

Conclusions

Key genetic elements reflect geographically dependent SARS-CoV-2 genetic adaptation, and may play a potential role in modulating drug susceptibility and hampering viral antigenicity. Thus, a close monitoring of SARS-CoV-2 mutational patterns is crucial to ensure the effectiveness of treatments and vaccines worldwide.

Key mutations in the C-terminus of the HBV surface glycoprotein correlate with lower HBsAg levels in vivo, hinder HBsAg secretion in vitro and reduce HBsAg structural stability in the setting of HBeAg-negative chronic HBV genotype-D infection

Increasing evidences suggest that HBsAg-production varies across HBV-genotypes. HBsAg C-terminus plays a crucial role for HBsAg-secretion. Here, we evaluate HBsAg-levels in different HBV-genotypes in HBeAg-negative chronic infection, the correlation of specific mutations in HBsAg C-terminus with HBsAg-levels in-vivo, their impact on HBsAg-secretion in-vitro and on structural stability in-silico.

HBsAg-levels were investigated in 323 drug-naïve HBeAg-negative patients chronically infected with HBV genotype-D(N = 228), -A(N = 65) and -E(N = 30). Genotype-D was characterized by HBsAg-levels lower than genotype-A and -E (3.3[2.7–3.8]IU/ml; 3.8[3.5–4.2]IU/ml and 3.9[3.7–4.2]IU/ml, P < 0.001). Results confirmed by multivariable analysis correcting for patients’demographics, HBV-DNA, ALT and infection-status.

In genotype-D, specific C-terminus mutations (V190A-S204N-Y206C-Y206F-S210N) significantly correlate with HBsAg<1000IU/ml(P-value from <0.001 to 0.04). These mutations lie in divergent pathways involving other HBsAg C-terminus mutations: V190A + F220L (Phi = 0.41, P = 0.003), S204N + L205P (Phi = 0.36, P = 0.005), Y206F + S210R (Phi = 0.47, P < 0.001) and S210N + F220L (Phi = 0.40, P = 0.006). Notably, patients with these mutational pairs present HBsAg-levels 1log lower than patients without them(P-value from 0.003 to 0.02). In-vitro, the above-mentioned mutational pairs determined a significant decrease in HBsAg secretion-efficiency compared to wt(P-value from <0.001 to 0.02). Structurally, these mutational pairs reduced HBsAg C-terminus stability and determined a rearrangement of this domain.

In conclusion, HBsAg-levels in genotype-D are significantly lower than in genotype-A and -E in HBeAg-negative patients. In genotype-D, specific mutational clusters in HBsAg C-terminus correlate with lower HBsAg-levels in-vivo, hamper HBsAg-release in-vitro and affect its structural stability, supporting their detrimental role on HBsAg-secretion. In this light, genotypic-testing can be a valuable tool to optimize the clinical interpretation of HBsAg in genotype-D and to provide information on HBV-pathogenicity and disease-progression.

High Prevalence of HBV Lamivudine-Resistant Mutations in HBV/HIV Co-Infected Patients on Antiretroviral Therapy in the Area with the Highest Prevalence of HIV/HBV Co-Infection in China

OBJECTIVES

We aimed to determine the prevalence of hepatitis B virus (HBV) drug-resistant mutations in patients co- infected with HBV/human immunodeficiency virus (HIV), including both drug-naïve subjects and those who received antiretroviral therapy (ART) in Guangxi, where the prevalence of HIV/HBV co-infection is highest in China.

METHODS

Two hundred and three subjects co-infected with HBV/HIV were recruited, including 123 drug-naïve patients (group 1) and 80 who received ART (group 2). The polymerase gene of HBV in the serum of all study subjects was analysed.

RESULTS

The results showed that the prevalence of HBV drug-resistant mutations in group 2 (76.5%, 95% CI 56.3-96.7) was significantly higher than that in group 1 (1.4%, 95% CI -1.4 to 4.2; χ2 = 50.955, p < 0.05). The major pattern of lamivudine (3TC)-resistant mutations is L180M+M204I+L80I (35.7%). In total, 95% of subjects with resistant mutations had cross-resistance to telbivudine and entecavir. No putative tenofovir disoproxil fumarate (TDF) resistance change was found. Five subjects (6.5%) in group 2 had HBV viral loads over 10 × 106 copies/mL. Four of them had 3TC-resistant mutations. Multivariate analysis showed that ART was the only factor associated with the development of drug-resistant mutations.

CONCLUSION

Treating HIV in HIV/HBV co-infection with antiretroviral agents may result in a very high prevalence of HBV 3TC-resistant mutations. TDF could not completely suppress HBV replication.

Prevalence of Single and Multiple Natural NS3, NS5A and NS5B Resistance-Associated Substitutions in Hepatitis C Virus Genotypes 1-4 in Italy

Natural resistance-associated substitutions (RASs) are reported with highly variable prevalence across different HCV genotypes (GTs). Frequency of natural RASs in a large Italian real-life cohort of patients infected with the 4 main HCV-GTs was investigated. NS3, NS5A and NS5B sequences were analysed in 1445 HCV-infected DAA-naïve patients. Sanger-sequencing was performed by home-made protocols on 464 GT1a, 585 GT1b, 92 GT2c, 199 GT3a, 16 GT4a and 99 GT4d samples. Overall, 20.7% (301/1455) of patients showed natural RASs, and the prevalence of multiclass-resistance was 7.3% (29/372 patients analysed). NS3-RASs were particularly common in GT1a and GT1b (45.2-10.8%, respectively), mainly due to 80K presence in GT1a (17%). Almost all GTs showed high prevalence of NS5A-RASs (range: 10.2-45.4%), and especially of 93H (5.1%). NS5A-RASs with fold-change >100x were detected in 6.8% GT1a (30H/R-31M-93C/H), 10.3% GT1b (31V-93H), 28.4% GT2c (28C-31M-93H), 8.5% GT3a (30K-93H), 45.5% GT4a (28M-30R-93H) and 3.8% GT4d (28V-30S-93H). Sofosbuvir RAS 282T was never detected, while the 159F and 316N RASs were found in GT1b (13.4-19.1%, respectively). Natural RASs are common in Italian patients infected with HCV-GTs 1-4. High prevalence of clinically-relevant RASs (such as Y93H) supports the appropriateness of HCV resistance-test to properly guide DAA-based therapy.

Immune-escape mutations and stop-codons in HBsAg develop in a large proportion of patients with chronic HBV infection exposed to anti-HBV drugs in Europe

Background

HBsAg immune-escape mutations can favor HBV-transmission also in vaccinated individuals, promote immunosuppression-driven HBV-reactivation, and increase fitness of drug-resistant strains. Stop-codons can enhance HBV oncogenic-properties. Furthermore, as a consequence of the overlapping structure of HBV genome, some immune-escape mutations or stop-codons in HBsAg can derive from drug-resistance mutations in RT. This study is aimed at gaining insight in prevalence and characteristics of immune-associated escape mutations, and stop-codons in HBsAg in chronically HBV-infected patients experiencing nucleos(t)ide analogues (NA) in Europe.

Methods

This study analyzed 828 chronically HBV-infected European patients exposed to ≥ 1 NA, with detectable HBV-DNA and with an available HBsAg-sequence.

The immune-associated escape mutations and the NA-induced immune-escape mutations sI195M, sI196S, and sE164D (resulting from drug-resistance mutation rtM204 V, rtM204I, and rtV173L) were retrieved from literature and examined. Mutations were defined as an aminoacid substitution with respect to a genotype A or D reference sequence.

Results

At least one immune-associated escape mutation was detected in 22.1% of patients with rising temporal-trend. By multivariable-analysis, genotype-D correlated with higher selection of ≥ 1 immune-associated escape mutation (OR[95%CI]:2.20[1.32–3.67], P = 0.002). In genotype-D, the presence of ≥ 1 immune-associated escape mutations was significantly higher in drug-exposed patients with drug-resistant strains than with wild-type virus (29.5% vs 20.3% P = 0.012). Result confirmed by analysing drug-naïve patients (29.5% vs 21.2%, P = 0.032). Strong correlation was observed between sP120T and rtM204I/V (P < 0.001), and their co-presence determined an increased HBV-DNA.

At least one NA-induced immune-escape mutation occurred in 28.6% of patients, and their selection correlated with genotype-A (OR[95%CI]:2.03[1.32–3.10],P = 0.001).

Finally, stop-codons are present in 8.4% of patients also at HBsAg-positions 172 and 182, described to enhance viral oncogenic-properties.

Conclusions

Immune-escape mutations and stop-codons develop in a large fraction of NA-exposed patients from Europe. This may represent a potential threat for horizontal and vertical HBV transmission also to vaccinated persons, and fuel drug-resistance emergence.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3161-2) contains supplementary material, which is available to authorized users.

Naturally occurring hepatitis B virus reverse transcriptase mutations related to potential antiviral drug resistance and liver disease progression

The annual number of deaths caused by hepatitis B virus (HBV)-related disease, including cirrhosis and hepatocellular carcinoma (HCC), is estimated as 887000. The reported prevalence of HBV reverse transcriptase (RT) mutation prior to treatment is varied and the impact of preexisting mutations on the treatment of naïve patients remains controversial, and primarily depends on geographic factors, HBV genotypes, HBeAg serostatus, HBV viral loads, disease progression, intergenotypic recombination and co-infection with HIV. Different sensitivity of detection methodology used could also affect their prevalence results. Several genotype-dependent HBV RT positions that can affect the emergence of drug resistance have also been reported. Eight mutations in RT (rtL80I, rtD134N, rtN139K/T/H, rtY141F, rtM204I/V, rtF221Y, rtI224V, and rtM309K) are significantly associated with HCC progression. HBeAg-negative status, low viral load, and genotype C infection are significantly related to a higher frequency and prevalence of preexisting RT mutations. Preexisting mutations are most frequently found in the A-B interdomain of RT which overlaps with the HBsAg “a” determinant region, mutations of which can lead to simultaneous viral immune escape. In conclusion, the presence of baseline RT mutations can affect drug treatment outcomes and disease progression in HBV-infected populations via modulation of viral fitness and host-immune responses.

High rates of chronic HBV genotype E infection in a group of migrants in Italy from West Africa: Virological characteristics associated with poor immune clearance

Hepatitis B virus (HBV) genotype E almost exclusively occurs in African people, and its presence is more commonly associated with the development of chronic HBV (CHB) infection. Moreover, an epidemiological link has been found between the distribution of HBV genotype E infection and African countries with high incidences of hepatocellular carcinoma. As part of a programme for the health assessment of migrants, we evaluated 358 young African subjects for HBV infection; 58.1% (208/358) were positive for an HBV marker, and 54 (25.5%) had CHB. Eighty-one percent of the CHB subjects were infected with HBV genotype E, with a median serum HBV-DNA of 3.2 (IQR: 2.7-3.6) logIU/ml. All patients had high serum HBsAg titres (10,899 [range 5,359-20,272] IU/ml), and no correlation was found between HBsAg titres and HBV-DNA plasma levels. RT sequence analysis showed the presence of a number of immune escape mutations: strains from all of the patients had a serine at HBsAg position 140; 3 also had T116N, Y100C, and P142L+S143L substitutions; and 1 had a G112R substitution. Six (18%) patients had stop-codons at position 216. In 5 of the 9 (26.5%) CHB patients, ultrasound liver biopsy, quantification of total intrahepatic HBV-DNA and cccDNA, and RT/HBsAg sequencing were performed. The median (IQR) total intrahepatic HBV-DNA was 766 (753-1139) copies/1000 cells, and the median (IQR) cccDNA was 17 (10-27) copies/1000 cells. Correlations were observed for both total intrahepatic HBV-DNA and cccDNA with serum HBV-DNA, while no correlation was found for the HBsAg titres. A difference of 2.5/1,000 nucleotides was found in the HBsAg sequences obtained from plasma and from liver tissue, with 3 cases of possible viral anatomical compartmentalization. In conclusion, a high rate of CHB infection due to the E genotype was demonstrated in a group of immigrants from Western Africa. An analysis of the viral strains obtained showed the virological characteristics of immune escape, which may be the cause of viral replication persistence. Moreover, a fair percentage of stop codon mutations were found. The lack of correlation between HBsAg titres and plasma or intrahepatic HBV-DNA found in these subjects suggests a pathway of virus production that is not linked to HBsAg secretion. Studies with a larger number of patients with CHB due to the E genotype are advisable to corroborate these observations.

Novel HBV recombinants between genotypes B and C in 3'-terminal reverse transcriptase (RT) sequences are associated with enhanced viral DNA load, higher RT point mutation rates and place of birth among Chinese patients

As one of the major global public health concerns, hepatitis B virus (HBV) can be divided into at least eight genotypes, which may be related to disease severity and treatment response. We previously demonstrated that genotypes B and C HBV, with distinct geographical distribution in China, had divergent genotype-dependent amino acid polymorphisms and variations in reverse transcriptase (RT) gene region, a target of antiviral therapy using nucleos(t)ide analogues. Recently recombination between HBV genotypes B and C was reported to occur in the RT region. However, their frequency and clinical significance is poorly understood. Here full-length HBV RT sequences from 201 Chinese chronic hepatitis B (CHB) patients were amplified and sequenced, among which 31.34% (63/201) were genotype B whereas 68.66% (138/201) genotype C. Although no intergenotypic recombination was detected among C-genotype HBV, 38.10% (24/63) of B-genotype HBV had recombination with genotype C in the 3'-terminal RT sequences. The patients with B/C intergenotypic recombinants had significantly (P<0.05) higher serum HBV DNA level than the "pure" B-genotype cohort did. Moreover, the B/C intergenotypic recombinants were prone to more substitutions at several specific residues in the RT region than genotype B or C. Besides, unlike their parental genotypes, the recombinant HBV appeared to display an altered geographic distribution feature in China. Our findings provide novel insight into the virological, clinical and epidemiological features of new HBV B/C intergenotypic recombinants at the 3' end of RT sequences among Chinese CHB patients. The highly complex genetic background of the novel recombinant HBV carrying new mutations affecting RT protein may contribute to an enhanced heterogeneity in treatment response or prognosis among CHB patients.

Mutational analysis of reverse transcriptase and surface proteins of patients with partial virological response during mono and combination antiviral therapies in genotype D chronic hepatitis B

Introduction

The mutational pattern of chronic Hepatitis B virus (HBV) is unclear in patients who show incomplete response to antiviral therapy. The aims of this study were 1) to determine the benefit of combination therapy with adefovir dipivoxil (ADV) and Lamivudine (LAM) versus ADV or LAM alone in maintaining virological, biochemical and histological responses and 2) to investigate the patterns of mutations in the reverse transcriptase and surface proteins of HBV with LAM and/or ADF-resistant in partially-responded chronic hepatitis B (CHB) patients.

Methods

The study group consisted of 186 chronic HBV carriers who were admitted to the Tehran Hepatitis Network from 2010 to 2013. We retrospectively selected 86 patients who partially responded to different nucleoside analogue regimens. After 48 weeks of therapy, five groups of patients were defined including eight Lamivudine (LAM) Group (I), 30 Adefovir (ADV) Group (II), 16 ADV add on LAM Group (III), 32 ADV+LAM Group (IV), and 100 controls (no therapy). Reverse transcriptase (RT) and surface genes were amplified and sequenced for mutational analysis.

Results

All groups showed differences between mean values for age, gender, alanine transaminase (ALT), aspartate transaminase (AST), and HBV DNA levels groups showed significant differences than other groups (p < 0.05). The mutation frequencies for groups were I (1.7%), II (1.39%), III (2.28%), IV (2.0%), and V (0.38%). T54N, L80I/V, I91L/V, L180M, M204I/V, Q215P/S, and F221Y/S showed the highest number of mutations in all groups with different frequencies. Four new, unreported mutations were found.

Conclusion

Those patients who failed to respond in the first 48 weeks, whether they were receiving mono or combination therapy, should be tested genotypically, for the early modification of treatment.

Response to potent anti-HBV agents in chronic hepatitis B and combined effect of HBV reverse transcriptase mutations

BACKGROUND AND AIM

Response to nucleos(t)ide analogue therapy against HBV infection depends on a number of factors. One of them is appearance of drug resistance mutations. The present study aimed to investigate the efficacy of ETV and TDF as anti-HBV agents and to analyze the role of HBV-RT mutations in reducing the efficacy of mentioned drugs.

MATERIAL AND METHODS

Sixty nine treatment naïve CHB patients (mean age 33.8 ± 11.9 years) were enrolled and treated with ETV or TDF for one year. Complete virological response (CVR) was defined as undetectable serum HBV DNA after 12 months of therapy. Amino acid and nucleotide sequence analyses of HBV-RT region were performed using Geno2pheno HBV drug resistance tool. The 3D model of HBV-RT protein was built by I-TASSER server and RMSD was calculated between wild type and mutated HBV-RT protein.

RESULTS

After 12 months of treatment, four CHB patients did not achieve CVR and all of them were with HBV genotype D. HBeAg seroconversion was achieved in 56% HBeAg positive patients after 12 months of antiviral therapy. The HBV-RT amino acid sequences from these four patients were used for in-silico analysis. It was found that the presence of many mutations in HBV-RT region of HBV isolated from these patients led to a high degree of variation in configuration of atoms of HBV-RT protein and also caused displacement of active site of this protein.

CONCLUSION

The efficacy of antiviral drugs in inhibiting HBV replication may be reduced by combined effect of many HBV-RT mutations; however, an in vitro study is needed to validate the findings.

Nucleotide analogue-resistant mutations in hepatitis B viral genomes found in hepatitis B patients

Chronic hepatitis B (CHB) is treated with nucleos(t)ide analogues (NAs). The reverse transcriptase (RT) region in the hepatitis B virus (HBV) genome mutates to resist NA treatment, yet the RT mutations have not been well characterized. Furthermore, the HBV genotype might influence RT sequence evolution, NA resistance (NAr) mutation patterns and drug resistance development. We examined 42 NAr mutation sites in 169 untreated and 131 NA-treated CHB patient samples. Patients were identified with HBV-B and HBV-C genotype infections, with a higher prevalence and mutation frequency of HBV-C than HBV-B. Seventeen reported NAr mutation sites and 13 novel mutations were detected. NAr-related mutation prevalence was significantly higher in NA-treated versus untreated patients. Primary antiviral-resistant mutants only existed in NA-treated patients. Sequencing data revealed seven HBV-C-specific mutations and three HBV-B-specific mutations. In conclusion, NA treatment and HBV genotype might constitute the selection basis and promote NA-resistant HBV strain evolution under antiviral therapy.

Specific mutations in the C-terminus domain of HBV surface antigen significantly correlate with low level of serum HBV-DNA in patients with chronic HBV infection

BACKGROUND

To define HBsAg-mutations correlated with different serum HBV-DNA levels in HBV chronically-infected drug-naive patients.

METHODS

This study included 187 patients stratified into the following ranges of serum HBV-DNA:12-2000 IU/ml, 2000-100,000 IU/ml, and >100,000 IU/ml. HBsAg-mutations were associated with HBV-DNA levels by applying a Bayesian-Partitional-Model and Fisher-exact test. Mutant and wild-type HBV genotype-D genomes were expressed in Huh7 cells and HBsAg-production was determined in cell-supernatants at 3 days-post-transfection.

RESULTS

Specific HBsAg-mutations (M197T,-S204N-Y206C/H-F220L) were significantly correlated with serum HBV-DNA <2000 IU/ml (posterior-probability>90%, P < 0.05). The presence of Y206C/H and/or F220L was also associated with lower median (IQR) HBsAg-levels and lower median (IQR) transaminases (for HBsAg:250[115-840] IU/ml for Y206C/H and/or F220L versus 4300[640-11,838] IU/ml for wild-type, P = 0.023; for ALT:28[21-40] IU/ml versus 53[34-90] IU/ml, P < 0.001). These mutations were localized in the HBsAg C-terminus, known to be involved in virion and/or HBsAg secretion. The co-occurrence of Y206C + F220L was found significant by cluster-analysis, (P = 0.02). In addition, in an in-vitro model Y206C + F220L determined a 2.8-3.3 fold-reduction of HBsAg-amount released in supernatants compared to single mutants and wt (Y206C + F220L = 5,679 IU/ml; Y206H = 16,305 IU/ml; F220L = 18,368 IU/ml; Y206C = 18,680 IU/ml; wt = 14,280 IU/ml, P < 0.05).

CONCLUSIONS

Specific HBsAg-mutations (compartmentalized in the HBsAg C-terminus) correlated with low-serum HBV-DNA and HBsAg-levels. These findings can be important to understand mechanisms underlying low HBV replicative potential including the inactive-carrier state.

Hepatitis B virus reverse transcriptase mutations in treatment Naïve chronic hepatitis B patients

Mutations in the reverse transcriptase (RT) region of the hepatitis B virus (HBV) genome lead to decreased susceptibility to nucleos(t)ide analogs approved for treatment of HBV infection. The aim of this study was to detect and analyze pre-existing HBV RT mutations in treatment naïve patients with chronic hepatitis B. Seventy one chronic HBV treatment naïve patients were enrolled from January 2009 to June 2011. HBV RT sequence analysis was done by using direct bidirectional sequencing of semi-nested PCR products. HBV genotypes were determined by multiplex PCR. Genotype D was found in 64 patients (90.1%) followed by genotype C and A which were present in 5 (7.0%) and 2 (2.8%) patients respectively. The results of the RT sequence analysis showed mutations in 34 (47.9%) patients. The rtH248N mutation was the most common mutation, accounting for 47.1% patients. Other common mutations included rtD263E/S, rtM129L, rtF122L/V/I, rtS135Y/H, rtQ149K, rtL91I, rtH126R, rtC256S/G, rtY257W, rtS259T and rtE271D, which were present in 26.5% (9/34), 29.4% (10/34), 20.6% (7/34), 20.6% (7/34), 20.6% (7/34), 17.6% (6/34), 14.7% (5/34), 14.7% (5/34), 11.8% (4/34), 11.8% (4/34) and 11.8% (4/34) patients respectively. The known primary drug resistance mutations were found in 3 (8.8%) patients. The present study shows the presence of RT amino acid substitutions in treatment-naïve patients with chronic hepatitis B, which may decrease susceptibility to available oral antiviral drugs. On the basis of the finding of this study, genotypic testing is recommended before the start of therapy in naïve patients, so that suitable antiviral drugs can be prescribed.

Amino acid similarities and divergences in the small surface proteins of genotype C hepatitis B viruses between nucleos(t)ide analogue-naïve and lamivudine-treated patients with chronic hepatitis B

Entire C-genotype small hepatitis B surface (SHBs) sequences were isolated from 139 nucleos(t)ide analogues (NA)-naïve and 74 lamivudine (LMV)-treated chronic hepatitis B (CHB) patients. The conservation and variability of total 226 amino acids (AAs) within the sequences were determined individually, revealing significant higher mutant isolate rate and mutation frequency in LMV-treated cohort than those in the NA-naïve one (P=0.009 and 0.0001, respectively). Three absolutely conserved fragments (s16-s19, s176-s181 and s185-s188) and seven moderately conserved regions (a few AA sites acquiring increased variability after LMV-treatment) were identified. The significant mutation rate increase after LMV-treatment occurred primarily in major hydrophilic region (except 'a' determinant) and transmembrane domain 3/4, but not in other upstream functional regions of SHBs. With little influence on immune escape-associated mutation frequencies within 'a' determinant, LMV-monotherapy significantly induced classical LMVr-associated mirror changes sE164D/rtV173L, sI195M/rtM204V and sW196L/S/rtM204I, as well as non-classical ones sG44E/rtS53N, sT47K/A/rtH55R/Q and sW182stop/rtV191I outside 'a' determinant. Interestingly, another newly-identified truncation mutation sC69stop/rtS78T decreased from 7.91% (11/139) in NA-naïve cohort to 2.70% (2/74) in LMV-treated one. Altogether, the altered AA conservation and diversity in SHBs sequences after LMV-treatment in genotype-C HBV infection might shed new insights into how LMV-therapy affects the SHBs variant evolution and its antigenicity.

Anti-HBV treatment induces novel reverse transcriptase mutations with reflective effect on HBV S antigen

INTRODUCTION

The identification of novel reverse-transcriptase (RT) drug-resistance mutations is critical in predicting the probability of success to anti-HBV treatment. Furthermore, due to HBV-RT/HBsAg gene-overlap, they can have an impact on HBsAg-detection and quantification.

METHODS

356 full-length HBV-RT sequences from 197 drug-naive patients and 159 patients experiencing virological-breakthrough to nucleoside/nucleotide-analogs (NUCs) were analyzed. Mutants and wild-type HBs-antigens were expressed in HuH7-hepatocytes and quantified in cell-supernatants and cell-lysates by Architect HBsAg-assay.

RESULTS

Ten novel RT-mutations (rtN53T-rtS78T-rtS85F-rtS135T-rtA181I-rtA200V-rtK212Q-rtL229V/F-rtM309K) correlated with specific NUC-treatments and classical drug-resistance mutations on divergent evolutionary pathways. Some of them reduced RT-binding affinity for anti-HBV drugs and altered S-antigen structure. Indeed, rtS78T (prevalence: 1.1% in drug-naïve and 12.2% in adefovir-failing patients) decreased the RT-affinity for adefovir more than the classical adefovir-resistance mutations rtA181 T/V (WT:-9.63 kcal/mol, rtA181T:-9.30 kcal/mol, rtA181V:-7.96 kcal/mol, rtS78T:-7.37 kcal/mol). Moreover, rtS78T introduced a stop-codon at HBsAg-position 69, and completely abrogated HBsAg-quantification in both supernatants and cell-lysates, indicating an impaired HBsAg-secretion/production. Furthermore, the HBsAg-mutation sP217L, silent in RT, significantly correlated with M204V/I-related virological-breakthrough and increased HBsAg-quantification in cell-lysate.

CONCLUSIONS

Mutations beyond those classically known can affect drug-binding affinity of mutated HBV-RT, and may have potential effects on HBsAg. Their cumulative effect on resistance and HBV-pathogenicity indicates the importance of preventing therapeutic failures.

Characterization of antiviral resistance mutations among the Eastern Indian Hepatitis B virus infected population

Background

Antiviral therapy using nucleos(t)ide analogues (NAs) is an effective control measure of chronic hepatitis B virus (HBV) infection; however they need long term treatment. Presence of drug-resistance mutations may get in the way of the efficacy of antiviral therapy. Our study was aimed at defining the prevalence of HBV drug-resistance in HBVrt region in a population of 147 HBsAg positive patients.

Findings

HBV/D has shown multiple types of HBVrt mutations both among treatment naïve (65.0%, 13 of 20 HBV/D) and treated patients (56.2%, 9 of 16 HBV/D). In additional, several mutations, with a suggested role in drug resistance, were detected among the treatment naïve as well as the treated patients. The mutations reported to be involved in reduction of drug effectiveness, was common among non-responders to therapy as well as among the naïve patients. Notably, classical antiviral resistance mutations (rtL80I/V-rtI169T-rtV173L-rtL180M-rtA181T/V/S-rtT184A/S/G/C-rtA194T-rtS202C /G/I -rtM204V/I-rtN236T-rtM250V) were not detected.

Conclusion

The prevalence of putative NAr mutations among non responders to therapy suggests that they might have role in reduced efficacy of currently available antivirals and requires further investigations.

Antiviral therapy against chronic hepatitis B in Brazil: high rates of lamivudine resistance mutations and correlation with HBV genotypes

The effectiveness of antiviral treatments of chronic hepatitis B has been poorly studied in Brazil. Here, hepatitis B virus (HBV) DNA positivity, drug resistance mutations and their association with HBV genotypes were evaluated in chronically HBV-infected patients under different drug regimens in Brazil. The study involved 129 patients under interferon or nucleos(t)ide analogue therapy for a median treatment time of 12 months. One hundred and five (81%) of these patients were treated with lamivudine (LAM), either in monotherapy or in combination with newer drugs, such as entecavir (ETV) or tenofovir (TDF). High (37.5-100%) rates of HBV DNA positivity were observed with all but one drug regimen (LAM + ETV). However, patients that were treated with ETV alone, TDF alone or with LAM combination therapies had a mean viral load that was 3-4 log lower than patients treated with LAM monotherapy. Of the patients treated with LAM, 47% developed resistance mutations. HBV genotypes A (59.1%), D (30.3%) and F (9.1%) were found. There was no association between the presence of LAM resistance mutations and genotypes, HBeAg status or treatment duration. Nevertheless, the rtM204V mutation was observed more frequently (12/13, 92%) in genotype A than in the others (p = 0.023). Six out of nine isolates that contained the rtM204I mutation belonged to genotype D and half of them displayed a single mutation. Genotype D isolates with the rtM204V variant preferentially displayed a triple mutation, while genotype A preferentially displayed a double mutation (p = 0.04).

Factors influencing inadequate or suboptimal response to adefovir with or without genotypic resistance

The aim of the study was to explore the factors in inadequate-responders to treatment with adefovir (ADV) with or without genotypic resistance. The reverse-transcriptase (RT) gene of hepatitis B virus (HBV) was sequenced in 161 patients with inadequate-response to ADV and analyzed for HBV genotypes using a phylogenetic approach. Seventy-six patients (47.2%) were found to carry the rtA181V/T/S or rtN236T residue substitution, and most of them had viral rebound. In the patients with viral rebound and ADV genotypic resistance, 19 (25.7%) showed rtA181V/T/S + rtN236T substitutions. In the other patients, it was found that HBV genotypes and cirrhosis influenced the selection of ADV-resistant positions by univariate analysis and multiple logistic regression analysis. The rtN236T was more frequent in patients with genotype B, and the rtA181V/T/S was more common in patients with genotype C (χ(2)  = 11.543, P = 0.001). Multiple logistic regression analysis showed that the rtN236T and time resistant strains occurred during ADV-treatment were statistically significant for influencing rtA181 variation types (P = 0.007 and P = 0.024, respectively), and the occurrence of rtA181T was found to be significantly earlier than rtA181V. In conclusion, genotypic resistance was not detected in the majority of primary nonresponders to ADV when compared to the patients with viral rebound. The different HBV genotypes influence the selection of ADV-resistant mutation positions. The rtA181T occurs more frequently in patients with the rtN236T and it occurs earlier when compared to the rtA181V. These findings suggest that early judgment of adequate response and making a decision for interference in patients treated with ADV are of importance in clinical practice.

Discrepancy of potential antiviral resistance mutation profiles within the HBV reverse transcriptase between nucleos(t)ide analogue-untreated and -treated patients with chronic hepatitis B in a hospital in China

Little is known about the discrepancy of the potential antiviral resistance mutation profiles within the hepatitis B virus (HBV) reverse transcriptase (RT) between nucleos(t)ide analogue (NA)-untreated and -treated patients with chronic hepatitis B. Full-length HBV RT sequences from 59 NA-treated and 105 NA-untreated Chinese patients were amplified and sequenced. Forty-two potential NA resistance (NAr) mutation sites were screened within these 164 RT sequences. The NAr mutation prevalence and frequency in the NA-treated group were significantly higher than those in the NA-untreated one (P < 0.001, respectively). The classical primary drug resistance and secondary/compensatory mutations were only detected at seven sites (rtL80, rtI169, rtL180, rtA181, rtT184, rtM204, and rtN236) in NA-treated patients. The non-classical putative NAr and pre-treatment mutations were observed at 22 sites (rtT38, rtN/S53, rtL82, rtL/I91, rtN/Y124, rtH126, rtT128, rtN/D134, rtN139, rtR153, rtV191, rtV207, rtS213, rtV214, rtE218, rtY/F221, rtV/I224, rtL229, rtI233, rtN/H238, rtR242, and rtS/C256) in both groups. Substitutions at seven non-classical mutation sites were of interest due to either detection only in patients with virologic breakthrough (rtL82 and rtV214), or potential ties with HBV genotypes (rtV191 and rtL229), or coexistence with rtM204I/V (rtL229), or increased mutation trends after NA-treatment (rtT128, rtV207, and rtN/H238). In conclusion, NA treatment not only constitutes a major selection factor for the primary and secondary/compensatory NAr mutations but also drives the changes of some of the putative NAr mutation sites, most of which are the genotype-independent RT sites (rtL82, rtT128, rtV191, rtV207, rtV214, rtL229, and rtN/H238). Their antiviral resistance potential calls for further investigations.

rtL180M mutation of hepatitis B virus is closely associated with frequent virological resistance to adefovir dipivoxil therapy

BACKGROUND AND AIM

We intended to investigate the effects of pre-existing mutations at reverse transcriptase region of hepatitis B virus (HBV) on the occurrence of virological breakthrough (VB) to adefovir dipivoxil (ADV) in patients with lamivudine (LAM)-resistant chronic hepatitis B (CHB).

METHODS

Ninety-seven patients with LAM-resistant CHB were treated with ADV at a dose of 10 mg daily, and were followed for a median period of 13 months. Just before the initiation of ADV therapy, the whole length of reverse transcriptase region of serum HBV-DNA was sequenced using direct sequencing.

RESULTS

All patients had genotype C HBV and mutations in the YMDD motif, specifically, YIDD (65%), YVDD (28%), or both (7%). The rtL180M and rtL80V/I mutations were identified in 68% and 69%, respectively. The cumulative probability of VB was 19% and 27% at 1 and 2 years, respectively. There was no difference in the occurrence of VB with regard to types of YMDD mutation or rtL80V/I. However, interestingly, patients carrying rtL180M experienced VB during ADV monotherapy more frequently than those not carrying rtL180M (2-year cumulative probability of VB: 37% vs 3% at 2 years, P < 0.01). On multivariate Cox proportional hazards analysis, rtL180M (hazard ratio [HR]: 8.62, 95% confidence interval: 1.08-69.09, P = 0.042) and decrease in HBV-DNA for 1 year of treatment (HR: 0.69, 95% CI: 0.51-0.95, P = 0.024) are independently associated with VB.

CONCLUSIONS

The rtL180M mutation of HBV, as well as a small decrease in HBV-DNA after 1 year of treatment might be closely associated with frequent occurrence of virological resistance to ADV in patients with LAM-resistant CHB.

Human papillomaviruses 53 and 66: clinical aspects and genetic analysis

Variants of HPV types may have different oncogenic potential. While HPV 16 and 18 variants have been extensively studied, little is known on the less frequent high-risk types such as HPV 53 and 66. Here, we analyzed the genetic variability of HPV 53 and 66 by sequencing the E6, E7, L1 genes and the Long Control Region (LCR) sequences of HPV 53 and HPV 66 from infected women. Fisher's exact-test was performed to correlate viral variants with cervical lesions. Higher-order interactions among identified mutations were analyzed by co-variation and cluster analyses. Antigenic-index alterations following L1 mutations were predicted by Jameson-Wolf algorithm. In HPV53, novel variants were identified in L1 (N=9) and E6 (N=1) genes. The novel L1 mutation P432L was statistically associated with L-SIL lesions (P=0.04) and its development reduced the L1 predicted antigenicity (up to -2.3 for Glu433). HPV 53 E6 and L1 sequences clustered phylogenetically into two main clades. In HPV 66, novel polymorphisms were identified in L1 (N=4) and E6 (N=4) genes. The L1 protein mutations S405P and D458N were exclusively found in patients with L-SILs. Seven E7 variants and 10 LCR variants were for the first time analyzed. Novel HPV 53 and 66 variants were identified in this study. Some of these mutations were significantly associated with L-SIL lesions and affected the antigenic index of the L1 protein with possible interesting implications in vaccine design.

Profile of HBV antiviral resistance mutations with distinct evolutionary pathways against nucleoside/nucleotide analogue treatment among Chinese chronic hepatitis B patients

BACKGROUND

Antiviral drug-resistant HBV mutants under a variety of treatment protocols are complex and only partly understood. Here, a population-based cross-sectional study was performed to analyse the profile of resistance mutations in distinct evolutionary pathways refractory to different nucleoside/nucleotide analogues (NAs).

METHODS

Serum samples of 199 chronic hepatitis B patients undergoing NA treatment from five hospitals in four northern cities of China were obtained between January 2007 and July 2009. The genotypic resistance of HBV in these samples was characterized. The full-length HBV reverse transcriptase region was amplified, sequenced and analysed with particular focus on the following NA-resistant changes: rtL80, rtI169, rtV173, rtL180, rtA181, rtT184, rtA194, rtS202, rtM204, rtN236 and rtM250.

RESULTS

Among 199 HBV isolates, 30 (15.08%) and 169 (84.92%) were genotypes B and C, respectively, and 65 (32.66%) harboured NA-resistant mutations. The prevalence of mutations at rtM204 was 34.33% in 134 patients who had received or who had been exposed to lamivudine-based therapy. Five cases of rtN236 mutations were detected exclusively among 75 patients receiving adefovir-dipivoxil-based therapies. A total of 19 cases of multidrug resistance rtA181 mutations were observed in those with lamivudine-, adefovir-dipivoxil- or telbivudine-based treatment (186 cases), but not in those undergoing entecavir treatment (13 cases). Mutations were not found at rtI169, rtT184, rtA194 or rtS202. rtM204 mutations (27 rtM204I, 15 rtM204V and 5 rtM204I/V cases) were detected at the highest frequency among 65 mutants (72.30% [47/65]) and found to display 16 combination mutation patterns, in which rtM204I and rtM204V were significantly associated with rtL80I/V and rtL180M, respectively (P<0.01).

CONCLUSIONS

One-third of the studied population harboured NA-resistant HBV with complicated mutation patterns. Monitoring HBV genotypic resistance mutation markers and patterns is therefore shown to be beneficial for optimizing antiviral therapies and for avoiding clinical deterioration.

Antiviral treatment including entecavir plus tenofovir disoproxil fumarate for HBV reactivation following a rituximab-based regimen

Entecavir and tenofovir disoproxil fumarate are potent and effective antiviral drugs that now represent recommended treatment options for chronic HBV infection. However, no or very limited clinical evidence is currently available on these drugs for the management of HBV reactivation in patients with haematological malignancies. Herein, we report a case of HBV reactivation in a patient with non-Hodgkin's lymphoma following a rituximab-based regimen, and who was successfully treated with a combination antiviral treatment including entecavir and tenofovir disoproxil fumarate.

Lamivudine-resistance mutations can be selected even at very low levels of hepatitis B viraemia

OBJECTIVE

To investigate lamivudine (LAM)-resistance profiles of hepatitis B virus (HBV) at the early stages of virological breakthrough (serum HBV-DNA 12-345IU/ml) or when HBV-DNA is undetectable.

METHODS

Sixty-four HBV-mono-infected patients were enrolled: 25 had virological breakthrough with serum HBV-DNA ranging from 12 to 345IU/ml during first-line LAM-monotherapy; 24 were on LAM-monotherapy, and 15 were on LAM+adefovir dipivoxil (ADV) with undetectable serum HBV-DNA (<12IU/ml).

RESULTS

HBV-reverse transcriptase was successfully sequenced in 22 (88.0%) LAM-treated patients with HBV-DNA between 12 and 345IU/ml, and in 12 (30.8%) patients receiving LAM (±ADV) with HBV-DNA<12IU/ml. Drug-resistance mutations were observed in 17 (77.2%) LAM-treated patients with virological breakthrough: 8 M204V, 7 M204I, 1 M204I/V, and 1 A181T. One or ≥2 compensatory mutations were found in 10 (58.8%) and in 4 (23.5%) patients. Drug-resistance mutations were present also in patients with undetectable serum HBV-DNA: M204I was detected in 2 patients receiving LAM-monotherapy, and V84M in 1 patient receiving LAM+ADV.

CONCLUSION

Overall findings support the existence of drug-resistance mutations even at very low levels of viral replication. The persistence of low-level HBV replication and consequent drug-resistance emergence should be considered when choosing therapeutic strategies.

Factors affecting the changes in molecular epidemiology of acute hepatitis B in a Southern Italian area

To explore changes in molecular epidemiology of acute viral hepatitis B (AVH-B), hepatitis B virus (HBV) genotypes were determined by direct sequencing of the Pre-S-S region in 123 consecutive patients, with AVH-B observed in Naples or its surroundings in the last decade (group AVH-B) and in 123 HBV chronic carriers [chronic carrier of HBV (CC-B) group] from the same areas, who had been hepatitis B surface antigen-positive for more than 10 years. Genotype D was less frequently detected in patients with AVH-B than in those in the CC-B group (76.4%vs 97.5%, P < 0.0001). In the AVH-B group, intravenous drug addiction (IVDA) was the prevalent risk factor (55.3%) for acquiring HBV in the 94 patients with HBV genotype D, but it was rarely recorded (6.9%) in the 29 patients with genotypes non-D (P < 0.0001); unsafe sexual intercourse was prevalent in patients with genotype non-D (72.3%) and less frequent in those with genotype D (28.8%, P < 0.005). In the AVH-B group, the prevalence of non-D genotypes increased during the observation period from 11.1% in 1999-2003 to 41.1% in 2004-2008 (P < 0.0005), paralleling the increase in the prevalence of patients with unsafe sexual intercourse; similarly, the progressive decrease in IVDA paralleled the decrease in the prevalence of genotype D (from 88.3% in 1999-2003 to 11.7% in 2004-2008). The prevalence of HBV non-D genotypes recorded in the last 10 years in AVH-B in this area shows a progressive increase, most probably because of recent changes in HBV epidemiology, namely, the HBV mass vaccination campaign and increased immigration from areas with high HBV endemicity.

Characterization of potential antiviral resistance mutations in hepatitis B virus reverse transcriptase sequences in treatment-naïve Chinese patients

Full-length hepatitis B virus (HBV) reverse transcriptase (RT) sequences were amplified and sequenced among 192 nucleos(t)ide analogue (NA)-naïve Chinese patients with chronic hepatitis B. Deduced amino acids (AAs) at 42 previously reported potential NA resistance (NAr) mutation positions in RT region were analyzed. Patients were found with either B-genotype (28.65%) or C-genotype (71.35%) infections. Rt53, rt91, rt124, rt134, rt221, rt224, rt238 and rt256 were identified as B- and C-genotype-dependent polymorphic AA positions. AA substitutions at 11 classical NAr mutation positions, i.e. rt80, rt169, rt173, rt180, rt181, rt184, rt194, rt202, rt204, rt236 and rt250, were not detected. However, potential NAr mutations were found in 30.73% (59/192) isolates, which involved 18 positions including rt53, rt207, rt229, rt238 and rt256, etc. The concomitant AA changes of HBsAg occurred in 16.67% (32/192) isolates including sG145R mutation. One-third of mutation positions were located in functional RT domains (e.g. rt207 and rt233), A-B interdomains (overlapping HBsAg 'a' determinant and showing most concomitant immune-associated mutations) and non-A-B interdomains (e.g. rt191 and rt213), respectively. Genotypes B and C each showed several preferred positions to mutate. These results might provide insights into understanding the evolution and selection basis of NAr HBV strains under antiviral therapy.