Hepatitis D virus in 2021: virology, immunology and new treatment approaches for a difficult-to-treat disease

Prevalence of Hepatitis D Virus Antibody Positivity in Chinese Patients with Chronic Hepatitis B Virus Infection

Background and Aims

Large-scale data on the hepatitis D virus (HDV)/hepatitis B virus (HBV) co-infection rate is needed to estimate the current epidemiology of HDV in China. This study aimed to estimate the current epidemiology of HDV.

Methods

Patients with chronic HBV infection, with documented serum hepatitis B surface antigen (HBsAg) positivity for more than six months, were enrolled across China. Blood samples were collected at baseline for central evaluations of HDV antibody and HBsAg quantification. Assessments for antibodies of hepatitis A virus, hepatitis C virus, hepatitis E virus, and human immunodeficiency virus, as well as HDV RNA quantification, were performed in patients who tested positive for HDV antibodies.

Results

Of the 5,044 enrolled patients between September 24, 2021, and December 28, 2022, 4,936 patients were included in the analysis. The mean age (±standard deviation) was 42.9 ± 9.9 years, and 69.8% of patients were male. The mean alanine aminotransferase level was 34 ± 58 U/L, and 1,509 (30.6%) patients were hepatitis B e antigen-positive. The mean (standard deviation) HBsAg level at baseline was 3,535 ± 11,292 IU/mL among 4,842 patients who were HBsAg positive. The rate of HBV infection and HDV antibody positivity was 0.24% (95% confidence interval: 0.1-0.4%), and only one patient was HDV RNA positive.

Conclusions

The prevalence of HDV antibody positivity was 0.24% in Chinese patients with chronic HBV infection, and only one patient with both anti-HDV antibody and HDV RNA positivity was observed in this study.

Antiviral therapy for chronic hepatitis delta: new insights from clinical trials and real-life studies

Chronic hepatitis D (CHD) is the most severe form of viral hepatitis, carrying a greater risk of developing cirrhosis and its complications. For decades, pegylated interferon alpha (PegIFN-α) has represented the only therapeutic option, with limited virological response rates and poor tolerability. In 2020, the European Medicines Agency approved bulevirtide (BLV) at 2 mg/day, an entry inhibitor of hepatitis B virus (HBV)/hepatitis delta virus (HDV), which proved to be safe and effective as a monotherapy for up to 144 weeks in clinical trials and real-life studies, including patients with cirrhosis. Long-term BLV monotherapy may reduce decompensating events in patients with cirrhosis. The combination of BLV 2 mg with PegIFN-α increased the HDV RNA undetectability rates on-therapy but not off-therapy, compared with PegIFN monotherapy. However, combination therapy, but not BLV monotherapy, may induce hepatitis B surface antigen (HBsAg) loss in some patients. The PegIFN lambda study has been discontinued due to liver toxicity issues, while lonafarnib boosted with ritonavir showed limited off-therapy efficacy in a phase 3 study. Nucleic acid polymer-based therapy is promising but large studies are still lacking. New controlled trial data come from molecules, such as monoclonal antibodies and/or small interfering RNA, that target HBsAg or HBV RNAs, which demonstrated not only profound HDV suppression, but also HBsAg decline.While waiting for new compounds to be approved as monotherapy or in combination, BLV monotherapy 2 mg/day remains the only approved therapy for CHD, at least in the European Union region.

Frequency, Severity and Impact of Pegylated Interferon Alpha-Associated Flares in Hepatitis D Infection

We analysed the frequency, severity and impact of hepatitis flares in a large Phase 2 study investigating pegylated interferon-alfa-2a (PEG-IFNa) for the treatment of hepatitis D. In the HIDIT-II study, 120 patients were treated for 96 weeks with PEG-IFNa (180 μg weekly) in combination with tenofovir disoproxil fumarate (TDF, 300 mg once daily) or placebo. Hepatitis flares were defined as ALT increases above 10 times the upper limit of normal or increases of more than 2.5-fold above baseline or nadir values. ALT flares occurred in 28 patients (23%) during treatment (< 96) and in 14 patients post-treatment until follow-up Week 24. There were no differences in the flare frequency between the two treatment arms (12 PEG-IFNa + placebo vs. 16 PEG-IFNa + TDF). The frequency of ALT increases did not differ between cirrhotic and noncirrhotic patients. None of the patients with cirrhosis experienced liver decompensation during or after a flare. Fifty-four per cent of the patients with ALT flare experienced a decrease in HDV RNA (> 1 log10 cop/ml) during subsequent study visits. Mean ALT levels early during treatment were higher in patients with HBsAg loss at follow-up Week 24. More than a third of hepatitis D patients undergoing PEG-IFNa therapy may experience ALT flares during or after treatment. ALT flares in this study posed no obvious safety risk to patients and should not lead to premature withdrawal from treatment. If ALT flares may be beneficial in single patients requires further investigation. Clinical Trial Registration: NCT00932971, EudraCT 2008-005560-13.

Comparing methods for plasma HDV RNA quantification in bulevirtide-treated and untreated patients with HDV

Background & Aims

Accurate HDV RNA quantification is crucial for diagnosis and management of chronic hepatitis delta (CHD), yet a significant variability between assays exists. We compared three methods to quantify HDV RNA levels in untreated and bulevirtide (BLV)-treated patients with CHD.

Methods

Frozen plasma from untreated and BLV-treated patients with CHD were tested in a single-center retrospective study using three different assays: Robogene 2.0 HDV RNA Quantification Kit 2.0 (Roboscreen GmbH; limit of detection [LOD] 6 IU/ml on 7500 Fast Real-Time PCR System [Applied Biosystem]), EurobioPlex HDV PCR quantitative kit (Eurobio Scientific; LOD 100 IU/m) on CFX96™ real-time PCR detection system [Bio-Rad]), and AltoStar HDV RT-PCR RUO Kit 1.5 (Altona Diagnostics; estimated LOD <10 IU/ml) on the AltoStar®AM16.

Results

Overall, 431 plasma samples from 130 patients with CHD (69 untreated and 61 BLV-treated) were studied. Compared with Robogene 2.0, EurobioPlex reported higher HDV RNA levels (3.78 [0.70-7.99] vs. 4.69 [2.00-8.19] log IU/ml, p <0.0001), with viremia higher than >0.5 log in 160 (69%). Likewise, HDV RNA levels were higher with AltoStar than with Robogene 2.0 (3.32 [0.70-7.37] vs. 3.91 [0.19-7.54] log IU/ml, p <0.0001), with AltoStar reporting HDV RNA levels >0.5 log in 127 (52%). Although virological response rates (≥2 log decline vs. baseline) at Weeks 24 (Robogene 2.0 vs. EurobioPlex and AltoStar) and 48 (Robogene 2.0 vs. AltoStar) were similar across assays, rates of HDV RNA undetectability significantly differed between the three assays at Weeks 24 and 72 (p = 0.003 and p = 0.02, respectively).

Conclusions

HDV RNA levels quantified by EurobioPlex and AltoStar were 1 and 0.5 logs higher than those quantified by Robogene 2.0, respectively. HDV RNA undetectability rates during BLV treatment were assay-dependent.

Impact and implications

Management and diagnosis of chronic hepatitis delta (CHD) require standardized tests for HDV RNA quantification. Quantification of HDV RNA is significantly influenced by the quantification method, with EurobioPlex detecting approximatively 1 log and AltoStar 0.5 log IU/ml more than Robogene 2.0, respectively. The HDV RNA undetectability rates during BLV monotherapy significantly differed among assays. These findings are of clinical relevance as patients who achieve negative viremia during BLV monotherapy might be entitled to stop therapy successfully.

Assessment of Response and Safety of Bulevirtide Treatment in Patients with Chronic Delta Virus Infection: The ARISTOTLE Pilot Observational Study

INTRODUCTION

Hepatitis D virus (HDV) infection remains a significant global health challenge due to its severity and high risk of progression to cirrhosis and hepatocellular carcinoma (HCC). Bulevirtide, a novel HDV entry inhibitor, has shown promise in managing chronic hepatitis D by blocking viral entry into hepatocytes. This study evaluated the efficacy and safety of bulevirtide in reducing HDV RNA levels and improving liver function in a real-life cohort of Italian patients with HDV infection.

METHODS

This multicenter prospective trial enrolled 108 consecutive patients with chronic HDV infection, from June 2023 to June 2024, who received 2 mg/day of bulevirtide in combination with a nucleoside/nucleotide analogue for hepatitis B virus (HBV) infection. Patients with any stage of liver fibrosis or compensated cirrhosis were included. Data collected included demographic and clinical characteristics, liver function tests, HDV RNA levels, and adverse events at baseline and 6 months.

RESULTS

The virological response was achieved in 54.6% of patients (n = 59), with 36 demonstrating undetectable HDV RNA levels. Among responders, ALT levels decreased significantly from 67.0 U/mL [IQR 44.0-116.3] to 31.5 U/mL [IQR 24.0-36.5, p = 0.001], and AST levels from 66.0 U/mL [IQR 46.5-91.0] to 32.5 U/mL [IQR 28.0-38.0, p = 0.021]. Median HDV RNA dropped from 29,800 IU/mL [IQR 3100-375,000] to 0 IU/mL [IQR 0-291, p < 0.001]. No significant predictors of response emerged. Mild adverse events, including pruritus (5.6%) and injection-site reactions (1.9%) and flu-like syndrome (0.9) were reported, with no treatment discontinuation.

CONCLUSIONS

Bulevirtide effectively reduces HDV RNA levels and improves liver function with a favorable safety profile, offering a promising therapeutic option for chronic hepatitis D. Further large-scale studies are needed to confirm these findings and explore long-term outcomes.

Current and future therapeutic options for chronic hepatitis D virus infection

In the last few years there have been innovations in HDV therapy which have brought new excitement in the scientific community also considering the few therapeutic opportunities. Recently, new molecular targets have been identified, both in monotherapy and in combination with peginterferon alpha (PegIFNα). Evaluating this review of the literature of the last ten years, HDV-related chronic hepatitis seems to have become a potentially curable disease, a statement that was unthinkable a few years ago. There are old and new weapons at our disposal. The old weapons are PegIFNα and recently PegIFN-lambda (PegIFNλ). PegIFNα, for which there are more data, appears to be an excellent combination regimen, if not contraindicated, both for Bulevirtide (BLV), data supported by important clinical trials and real-world studies, and probably for lonarfanib, although in the latter case the results are not yet definitive as the studies are fewer. However, data on long-term follow-up are needed.

Update on the treatment navigation for functional cure of chronic hepatitis B: Expert consensus 2.0

As new evidence emerges, treatment strategies toward the functional cure of chronic hepatitis B are evolving. In 2019, a panel of national hepatologists published a Consensus Statement on the functional cure of chronic hepatitis B. Currently, an international group of hepatologists has been assembled to evaluate research since the publication of the original consensus, and to collaboratively develop the updated statements. The 2.0 Consensus was aimed to update the original consensus with the latest available studies, and provide a comprehensive overview of the current relevant scientific literatures regarding functional cure of hepatitis B, with a particular focus on issues that are not yet fully clarified. These cover the definition of functional cure of hepatitis B, its mechanisms and barriers, the effective strategies and treatment roadmap to achieve this endpoint, in particular new surrogate biomarkers used to measure efficacy or to predict response, and the appropriate approach to pursuing a functional cure in special populations, the development of emerging antivirals and immunomodulators with potential for curing hepatitis B. The statements are primarily intended to offer international guidance for clinicians in their practice to enhance the functional cure rate of chronic hepatitis B.

HDV RNA assays: Performance characteristics, clinical utility, and challenges

Coinfection with HBV and HDV results in hepatitis D, the most severe form of chronic viral hepatitis, frequently leading to liver decompensation and HCC. Pegylated interferon alpha, the only treatment option for chronic hepatitis D for many years, has limited efficacy. New treatments are in advanced clinical development, with one recent approval. Diagnosis and antiviral treatment response monitoring are based on detection and quantification of HDV RNA. However, the development of reliable HDV RNA assays is challenged by viral heterogeneity (at least 8 different genotypes and several subgenotypes), intrahost viral diversity, rapid viral evolution, and distinct secondary structure features of HDV RNA. Different RNA extraction methodologies, primer/probe design for nucleic acid tests, lack of automation, and overall dearth of standardization across testing laboratories contribute to substantial variability in performance characteristics of research-based and commercial HDV RNA assays. A World Health Organization (WHO) standard for HDV RNA, available for about 10 years, has been used by many laboratories to determine the limit of detection of their assays and facilitates comparisons of RNA levels across study centers. Here we review challenges for robust pan genotype HDV RNA quantification, discuss particular clinical needs and the importance of reliable HDV RNA quantification in the context of drug development and patient monitoring. We summarize distinct technical features and performance characteristics of available HDV RNA assays. Finally, we provide considerations for the use of HDV RNA assays in the context of drug development and patient monitoring.

Quantitative Analysis of Hepatitis D Virus Using gRNA-Sensitive Semiconducting Polymer Dots

Hepatitis D virus (HDV) significantly influences the progression of liver diseases. Through clinical observations and database analyses, it has been established that patients coinfected with HDV and hepatitis B virus (HBV) experience accelerated progression toward cirrhosis, hepatocellular carcinoma (HCC), and liver failure compared to those infected solely with HBV. A higher viral load correlates with increased replicative activity, enhanced infectivity, and more severe disease manifestations. In this study, we use HDV gRNA-sensitive semiconducting polymer dots (Pdots) as the nanoprobes for the quantitative analysis of HDV copy number variations. The surface of the Pdots is engineered with a clamp design that includes a pair of reporter sequences, protection sequences, and capture sequences tailored to the conserved sequence length of the HDV genome. The capture sequence, comprising leading and trailing chains, specifically binds to the gRNA of the target virus. The protection sequence shields the Pdots from external interference, while the reporter sequence detects the presence of target gRNA through the degradation of fluorescent dye Cy5.5dt. We demonstrate the effectiveness of this assay in a stably transfected cell line derived from HepG2-HDV cells and its translational application in clinical samples from patients. Additionally, this nanobiosensor can accurately detect gRNA at femtomolar (fM) levels, a sensitivity unachievable by previously reported methods. This novel virus quantification system offers significant potential for clinical and virological applications, enhancing screening, early diagnosis, and personalized treatment strategies.

Hepatitis B virus DNA integration: Implications for diagnostics, therapy, and outcome

Hepatitis B virus (HBV) DNA integration - originally recognised as a non-functional byproduct of the HBV life cycle - has now been accepted as a significant contributor to HBV pathogenesis and hepatitis D virus (HDV) persistence. Integrated HBV DNA is derived from linear genomic DNA present in viral particles or produced from aberrantly processed relaxed circular genomic DNA following an infection, and can drive expression of hepatitis B surface antigen (HBsAg) and HBx. DNA integration events accumulate over the course of viral infection, ranging from a few percent during early phases to nearly 100 percent of infected cells after prolonged chronic infections. HBV DNA integration events have primarily been investigated in the context of hepatocellular carcinoma development as they can activate known oncogenes and other growth promoting genes, cause chromosomal instability and, presumably, induce epigenetic alterations, promoting tumour growth. More recent evidence suggests that HBsAg expression from integrated DNA might contribute to HBV pathogenesis by attenuating the immune response. Integrated DNA provides a source for envelope proteins required for HDV replication and hence represents a means for HDV persistence. Because integrated DNA is responsible for persistence of HBsAg in the absence of viral replication it impacts established criteria for the resolution of HBV infection, which rely on HBsAg as a diagnostic marker. Integrated HBV DNA has been useful in assessing the turnover of infected hepatocytes which occurs during all phases of chronic hepatitis B including the initial phase of infection historically termed immune tolerant. HBV DNA integration has also been shown to impact the development of novel therapies targeting viral RNAs.

Development of a dual channel detection system for pan-genotypic simultaneous quantification of hepatitis B and delta viruses

Hepatitis B virus (HBV) infection remains a major public health problem and, in associated co-infection with hepatitis delta virus (HDV), causes the most severe viral hepatitis and accelerated liver disease progression. As a defective satellite RNA virus, HDV can only propagate in the presence of HBV infection, which makes HBV DNA and HDV RNA the standard biomarkers for monitoring the virological response upon antiviral therapy, in co-infected patients. Although assays have been described to quantify these viral nucleic acids in circulation independently, a method for monitoring both viruses simultaneously is not available, thus hampering characterization of their complex dynamic interactions. Here, we describe the development of a dual fluorescence channel detection system for pan-genotypic, simultaneous quantification of HBV DNA and HDV RNA through a one-step quantitative PCR. The sensitivity for both HBV and HDV is about 10 copies per microliter without significant interference between these two detection targets. This assay provides reliable detection for HBV and HDV basic research in vitro and in human liver chimeric mice. Preclinical validation of this system on serum samples from patients on or off antiviral therapy also illustrates a promising application that is rapid and cost-effective in monitoring HBV and HDV viral loads simultaneously.

Sodium taurocholate cotransporting polypeptide (NTCP) polymorphisms may influence HDV RNA load and early response to bulevirtide

BACKGROUND & AIMS

Genetic polymorphisms in the sodium taurocholate cotransporting peptide (NTCP encoded by SLC10A1) have been described, but their role in untreated and treated patients with chronic hepatitis delta (CHD) remains unknown. Virological response (VR) to the NTCP inhibitor bulevirtide (BLV) was achieved at week 48 by >70% of patients with CHD, but nearly 15% experienced virological non-response (VNR) or partial response (PR). This study aimed to evaluate whether NTCP genetic polymorphisms affect baseline HDV RNA load and response to BLV in patients with CHD.

METHODS

BLV-untreated and -treated patients were enrolled in a retrospective cross-sectional and longitudinal study. Clinical and virological characteristics were collected at baseline and up to 96 weeks in the BLV-treated patients. NTCP genetic polymorphisms were identified by Sanger sequencing.

RESULTS

Of the six NTCP polymorphisms studied in 209 untreated patients with CHD, carriers of the rs17556915 TT/CC (n = 142) compared to CT (n = 67) genotype presented with higher median HDV RNA levels (5.39 vs. 4.75 log10 IU/ml, p = 0.004). Of 209 patients receiving BLV monotherapy at 2 mg/day, 76 were evaluated at week 24 and 40 up to week 96. Higher mean baseline HDV RNA levels were confirmed in TT/CC (n = 43) compared to CT (n = 33) carriers (5.38 vs. 4.72 log10 IU/ml, p = 0.010). Although 24-week VR was comparable between TT/CC and CT carriers (25/43 vs. 17/33, p = 0.565), the former group presented VNR more often than PR (9/11 vs. 9/23, p = 0.02) at week 24. 7/9 TT/CC genotype carriers remained VNR at week 48 of BLV treatment.

CONCLUSIONS

The NTCP rs17556915 C>T genetic polymorphisms may influence baseline HDV RNA load both in BLV-untreated and -treated patients with CHD and may contribute to identifying patients with different early virological responses to BLV.

IMPACT AND IMPLICATIONS

Although several sodium taurocholate cotransporting polypeptide (NTCP) genetic polymorphisms have been described, no data are available on their potential role in modifying HDV RNA load or treatment response to bulevirtide (BLV) in patients with chronic hepatitis delta (CHD). In this study, we demonstrated that patients with CHD, either treated or untreated, carrying NTCP rs17556915 TT/CC, presented higher baseline HDV RNA levels compared to those with the CT genotype. Higher HDV RNA levels in TT/CC carriers compared to CT carriers were also confirmed in patients with CHD treated with BLV monotherapy up to 96 weeks. Furthermore, carriers of TT/CC, compared to CT genotype, more frequently showed viral non-response (VNR) than partial response (PR) at week 24 of BLV treatment, and 7/9 TT/CC genotype carriers remained VNR at week 48 of BLV treatment. This is the first study demonstrating a potential role of NTCP genetic polymorphisms in influencing HDV viral load and early virological response to BLV monotherapy. Since no direct HDV resistance to BLV has been described so far, if confirmed in larger studies, the genetic polymorphisms in NTCP may help identify patients with different patterns of early virological response to BLV.

Chronic Hepatitis D Virus Infection and Its Treatment: A Narrative Review

More than 12 million individuals worldwide are chronically infected with the hepatitis D virus (HDV). HDV infection is the most severe form of viral hepatitis since it requires hepatitis B virus co-infection and accelerates progression to cirrhosis and hepatocellular carcinoma. Therefore, treatment modalities to slow the progression of the disease are essential but not yet available. In addition, no antiviral treatment to date has been shown to reliably eradicate HDV. Pegylated interferon (PEG-IFN) is the only universally used treatment to suppress HDV RNA replication and improve liver inflammation and fibrosis. This treatment can be completed in 12-18 months, but cure rates remain low, and success does not reliably increase with the addition of a nucleos(t)ide analog. PEG-IFN therapy is also limited by poor tolerability and multiple adverse effects, including neutropenia, thrombocytopenia, and neuropsychiatric symptoms. Newer antiviral therapies in development target unique aspects of HDV viral replication and show promising results in combination with PEG-IFN for long-term HDV RNA suppression. These newer antiviral therapies include buleviritide (which blocks HDV entry), lonafarnib (which prevents HDV assembly), and REP-2139 (which prevents HDV export). In this manuscript, we discuss the characteristics of HDV infection and review the new antiviral therapies approved for treatment and those under investigation.

Enrichment Reveals Extensive Integration of Hepatitis B Virus DNA in Hepatitis Delta Virus-Infected Patients

BACKGROUND

Hepatitis B virus (HBV) DNA may become integrated into the human genome of infected human hepatocytes. Expression of integrations can produce the surface antigen (HBsAg) that is required for synthesis of hepatitis D virus (HDV) particles and the abundant subviral particles in the blood of HBV- and HDV-infected subjects. Knowledge about the extent and variation of HBV integrations and impact on chronic HDV is still limited.

METHODS

We investigated 50 pieces of liver explant tissue from 5 patients with hepatitis D-induced cirrhosis, using a deep-sequencing strategy targeting HBV RNA.

RESULTS

We found that integrations were abundant and highly expressed, with large variation in the number of integration-derived (HBV/human chimeric) reads, both between and within patients. The median number of unique integrations for each patient correlated with serum levels of HBsAg. However, most of the HBV reads represented a few predominant integrations.

CONCLUSIONS

The results suggest that HBV DNA integrates in a large proportion of hepatocytes, and that the HBsAg output from these integrations vary >100-fold depending on clone size and expression rate. A small proportion of the integrations seems to determine the serum levels of HBsAg and HDV RNA in HBV/HDV coinfected patients with liver cirrhosis.

Viral Hepatitis: Host Immune Interaction, Pathogenesis and New Therapeutic Strategies

Viral hepatitis is a major cause of liver illness worldwide. Despite advances in the understanding of these infections, the pathogenesis of hepatitis remains a complex process driven by intricate interactions between hepatitis viruses and host cells at the molecular level. This paper will examine in detail the dynamics of these host-pathogen interactions, highlighting the key mechanisms that regulate virus entry into the hepatocyte, their replication, evasion of immune responses, and induction of hepatocellular damage. The unique strategies employed by different hepatitis viruses, such as hepatitis B, C, D, and E viruses, to exploit metabolic and cell signaling pathways to their advantage will be discussed. At the same time, the innate and adaptive immune responses put in place by the host to counter viral infection will be analyzed. Special attention will be paid to genetic, epigenetic, and environmental factors that modulate individual susceptibility to different forms of viral hepatitis. In addition, this work will highlight the latest findings on the mechanisms of viral persistence leading to the chronic hepatitis state and the potential implications for the development of new therapeutic strategies. Fully understanding the complex host-pathogen interactions in viral hepatitis is crucial to identifying new therapeutic targets, developing more effective approaches for treatment, and shedding light on the mechanisms underlying progression to more advanced stages of liver damage.

Safety and efficacy of off-label bulevirtide monotherapy in patients with HDV with decompensated Child-B cirrhosis-A real-world case series

BACKGROUND AND AIMS

Chronic hepatitis D is the most debilitating form of viral hepatitis frequently progressing to cirrhosis and subsequent decompensation. However, the HDV entry inhibitor bulevirtide is only approved for antiviral treatment of patients with compensated disease. We aimed for the analysis of real-world data on the off-label use of bulevirtide in the setting of decompensated liver cirrhosis.

APPROACH AND RESULTS

We conducted a retrospective study in patients with HDV with decompensated liver disease at German, Austrian, and Italian centers. We included 19 patients (47% male, mean age: 51 years) with liver cirrhosis Child-Pugh B. The median MELD score was 12 (range 9-17) at treatment initiation. The median observation period was 41 weeks. Virologic response was achieved in 74% and normal alanine aminotransferase was observed in 74%. The combined response was achieved by 42%. The most relevant adverse events included self-limited alanine aminotransferase flares, an asymptomatic increase in bile acids, and the need for liver transplantation. Despite bile acid increases, adverse events were considered unrelated. Clinical and laboratory improvement from Child-Pugh B to A occurred in 47% (n = 9/19). Improvements in the amount of ascites were observed in 58% of the patients initially presenting with ascites (n = 7/12).

CONCLUSIONS

This report on off-label bulevirtide treatment in patients with decompensated HDV cirrhosis shows similar virologic and biochemical response rates as observed in compensated liver disease. Significant improvements were observed in surrogates of hepatic function and portal hypertension. However, this improvement was not seen in all patients. Controlled trials are needed to confirm the safety and efficacy of bulevirtide in decompensated HDV cirrhosis.

Long-term outcome of hepatitis delta in different regions world-wide: Results of the Hepatitis Delta International Network

BACKGROUND AND AIMS

Chronic hepatitis delta represents a major global health burden. Clinical features of hepatitis D virus (HDV) infection vary largely between different regions worldwide. Treatment approaches are dependent on the approval status of distinct drugs and financial resources.

METHODS

The Hepatitis Delta International Network (HDIN) registry involves researchers from all continents (Wranke, Liver International 2018). We here report long-term follow-up data of 648 hepatitis D patients recruited by 14 centres in 11 countries. Liver-related clinical endpoints were defined as hepatic decompensation (ascites, encephalopathy and variceal bleeding), liver transplantation, hepatocellular carcinoma or liver-related death.

RESULTS

Patient data were available from all continents but Africa: 22% from Eastern Mediterranean, 32% from Eastern Europe and Central Asia, 13% from Central and Southern Europe, 14% from South Asia (mainly Pakistan) and 19% from South America (mainly Brazil). The mean follow-up was 6.4 (.6-28) years. During follow-up, 195 patients (32%) developed a liver-related clinical event after 3.5 (±3.3) years. Liver cirrhosis at baseline and a detectable HDV RNA test during follow-up were associated with a worse clinical outcome in multivariate regression analysis while patients receiving interferon alfa-based therapies developed clinical endpoints less frequently. Patients from South Asia developed endpoints earlier and had the highest mortality.

CONCLUSIONS

The HDIN registry confirms the severity of hepatitis D and provides further evidence for HDV viraemia as a main risk factor for disease progression. Hepatitis D seems to take a particularly severe course in patients born in Pakistan. There is an urgent need to extend access to antiviral therapies and to provide appropriate education about HDV infection.

Prevalence and clinical characterization of hepatitis D virus (HDV) infection among Sudanese patients with hepatitis B virus (HBV): a cross-sectional study

Background

Sudan has a high prevalence of hepatitis B surface antigen, exceeding 8%. The prevalence of hepatitis B varies across different regions of Sudan, ranging from 6.8% in central Sudan to as high as 26% in southern Sudan. Hepatitis D virus (HDV) relies on HBV for replication and can accelerate the progression of HBV-related liver diseases, leading to more severe outcomes. This study aims to determine the prevalence of HDV infection among Sudanese patients with HBV-related liver diseases and to investigate the clinical characteristics of patients with HDV co-infection.

Design/method

This descriptive cross-sectional hospital-based study was conducted in Sudan between June and September 2022. Ninety HBV patients aged 16 years and above were included. Patients were interviewed using a structured questionnaire, and medical histories and examinations were recorded. Investigations included liver function tests, abdominal ultrasounds, and ELISA for Anti-HDV IgG.

Results

In this study of 90 HBV patients, most were male (68.9%) and under 40 years old (58.9%). HDV-IgG antibodies were found in 8 patients (8.9%), all male. Among the HDV-positive patients, one (12.5%) had jaundice and one (12.5%) had ascites. Elevated ALT levels were seen in 50% of HDV-positive patients. One (12.5%) HDV-positive patient had low albumin. Cirrhosis was present in 25% of HDV-positive patients, and HCC was present in 12.5% of HDV-positive patient.

Conclusion

The prevalence of HDV infection among Sudanese patients with HBV-related liver diseases is 8.9%. This highlights the need for enhanced screening and diagnostic measures in Sudanese populations. Further research is needed to develop targeted interventions.

vHDvDB 2.0: Database and Group Comparison Server for Hepatitis Delta Virus

The hepatitis delta virus (HDV) is a unique pathogen with significant global health implications, affecting individuals who are coinfected with the hepatitis B virus (HBV). HDV infection has profound clinical consequences, manifesting either as coinfection with HBV, resulting in acute hepatitis and potential liver failure, or as superinfection in chronic HBV cases, substantially increasing the risk of cirrhosis and hepatocellular carcinoma. Given the complex dynamics of HDV infection and the urgent need for advanced research tools, this article introduces vHDvDB 2.0, a comprehensive HDV full-length sequence database. This innovative platform integrates data preprocessing, secondary structure prediction, and epidemiological research tools. The primary goal of vHDvDB 2.0 is to consolidate HDV sequence data into a user-friendly repository, thereby facilitating access for researchers and enhancing the broader scientific understanding of HDV. The significance of this database lies in its potential to streamline HDV research by providing a centralized resource for analyzing viral sequences and exploring genotype-specific characteristics. It will also enable more in-depth research within the HDV sequence domains.

Characterisation of HBV and co-infection with HDV and HIV through spatial transcriptomics

Background and aims

The intrahepatic processes associated with chronic hepatitis B (CHB), especially in the context of hepatitis delta virus (HDV) and HIV co-infection, require a better understanding. Spatial transcriptomics can provide new insights into the complex intrahepatic biological processes, guiding new personalised treatments. Our aim is to evaluate this method characterising the intrahepatic transcriptional landscape, cellular composition and biological pathways in liver biopsy samples from patients with hepatitis B virus (HBV) and HDV or HIV co-infection.

Method

The NanoString GeoMx digital spatial profiling platform was employed to assess expression of HBV surface antigen and CD45 in formalin-fixed paraffin-embedded (FFPE) biopsies from three treatment-naïve patients with chronic HBV and HDV or HIV co-infection. The GeoMx Human Whole Transcriptome Atlas assay quantified the expression of genes enriched in specific regions of interest (ROIs). Cell type proportions within ROIs were deconvoluted using a training matrix from the human liver cell atlas. A weighted gene correlation network analysis evaluated transcriptomic signatures across sampled regions.

Results

Spatially discrete transcriptomic signatures and distinct biological pathways were associated with HBV infection/disease status and immune responses. Shared features including 'cytotoxicity' and 'B cell receptor signalling' were consistent across patients, suggesting common elements alongside individual traits. HDV/HBV co-infection exhibited upregulated genes linked to apoptosis and immune cell recruitment, whereas HIV/HBV co-infection featured genes related to interferon response regulation. Varied cellular characteristics and immune cell populations, with an abundance of γδT cells in the HDV/HBV sample, were observed within analysed regions. Transcriptional differences in hepatocyte function suggest disrupted metabolic processes in HDV/HBV co-infection potentially impacting disease progression.

Conclusion

This proof-of-principle study shows the value of this platform in investigating the complex immune landscape, highlighting relevant host pathways to disease pathogenesis.

Effect of Peg-IFN on the viral kinetics of patients with HDV infection treated with bulevirtide

Background & Aims

Bulevirtide is a first-in-class entry inhibitor antiviral treatment for chronic hepatitis D. The viral kinetics during bulevirtide therapy and the effect of combining bulevirtide with pegylated-interferon (Peg-IFN) are unknown.

Methods

We used mathematical modelling to analyze the viral kinetics in two French observational cohorts of 183 patients receiving bulevirtide with or without Peg-IFN for 48 weeks.

Results

The efficacy of bulevirtide in blocking cell infection was estimated to 90.3%, whereas Peg-IFN blocked viral production with an efficacy of 92.4%, albeit with large inter-individual variabilities. The addition of Peg-IFN to bulevirtide was associated with a more rapid virological decline, with a rate of virological response (>2 log of decline or undetectability) at week 48 of 86.9% (95% prediction interval [PI] = [79.7-95.0]), compared with 56.1% (95% PI = [46.4-66.7]) with bulevirtide only. The model was also used to predict the probability to achieve a cure of viral infection, with a rate of 8.8% (95% PI = [3.5-13.2]) with bulevirtide compared with 18.8% (95% PI = [11.6-29.0]) with bulevirtide + Peg-IFN. Mathematical modelling suggests that after 144 weeks of treatment, the rates of viral cure could be 42.1% (95% PI = [33.3-52.6]) with bulevirtide and 66.7% (95% PI = [56.5-76.8]) with bulevirtide + Peg-IFN.

Conclusions

In this analysis of real-world data, Peg-IFN strongly enhanced the kinetics of viral decline in patients treated with bulevirtide. Randomized clinical trials are warranted to assess the virological and clinical benefit of this combination, and to identify predictors of poor response to treatment.

Impact and implications

Bulevirtide has been approved for chronic HDV infection by regulatory agencies in Europe based on its good safety profile and rapid virological response after treatment initiation, but the optimal duration of treatment and the chance to achieve a sustained virological response remain unknown. The results presented in this study have a high impact for clinicians and investigators as they provide important knowledge on the long-term virological benefits of a combination of Peg-IFN and bulevirtide in patients with CHD. Clinical trials are now warranted to confirm those predictions.

Assessment of performance and comparison of three commercial HDV RNA detection assays: implications for diagnosis and treatment monitoring

Objectives

Precise HDV-RNA detection and quantification are pivotal for diagnosis and monitoring of response to newly approved treatment. We evaluate the performance of three HDV RNA detection and quantification assays.

Methods

Hepatitis Delta RT-PCR system kit, EurobioPlex HDV assay, and RoboGene HDV RNA Quantification kit 2.0 were used for testing 151 HBsAg-positive samples, 90 HDV-RNA negative and 61 HDV-RNA positive. We also evaluated serial dilutions of the WHO international standard for HDV, PEI 7657/12. All HDV-RNA positive samples were genotyped using a next-generation sequencing strategy.

Results

Qualitative results indicated a 100% concordance between tests. Quantitative results correlated well, r2 = 0.703 (Vircell-vs-Eurobio), r2 = 0.833 (Vircell-vs-RoboGene), r2 = 0.835 (Robogene-vs-Eurobio). Bias index was 2.083 (Vircell-vs-Eurobio), -1.283 (Vircell-vs-RoboGene), and -3.36 (Robogene-vs-Eurobio). Using the WHO IS, Vircell overestimated the viral load by 0.98 log IU/mL, Eurobio by 1.46 log IU/mL, and RoboGene underestimated it by 0.98 log IU/mL. Fifty-nine samples were successfully genotyped (Genotype 1, n=52; Genotype 5, n=7; Genotype 6, n=1), with similar results for correlation and bias.

Conclusion

This study underscores the necessity of using reliable HDV-RNA detection and quantification assays, as evidenced by the high concordance rates in qualitative detection and the observed variability in quantitative results. These findings highlight the importance of consistent assay use in clinical practice to ensure accurate diagnosis and effective treatment monitoring of HDV infection.

Farnesyltransferase inhibitor lonafarnib suppresses respiratory syncytial virus infection by blocking conformational change of fusion glycoprotein

Respiratory syncytial virus (RSV) is the major cause of bronchiolitis and pneumonia in young children and the elderly. There are currently no approved RSV-specific therapeutic small molecules available. Using high-throughput antiviral screening, we identified an oral drug, the prenylation inhibitor lonafarnib, which showed potent inhibition of the RSV fusion process. Lonafarnib exhibited antiviral activity against both the RSV A and B genotypes and showed low cytotoxicity in HEp-2 and human primary bronchial epithelial cells (HBEC). Time-of-addition and pseudovirus assays demonstrated that lonafarnib inhibits RSV entry, but has farnesyltransferase-independent antiviral efficacy. Cryo-electron microscopy revealed that lonafarnib binds to a triple-symmetric pocket within the central cavity of the RSV F metastable pre-fusion conformation. Mutants at the RSV F sites interacting with lonafarnib showed resistance to lonafarnib but remained fully sensitive to the neutralizing monoclonal antibody palivizumab. Furthermore, lonafarnib dose-dependently reduced the replication of RSV in BALB/c mice. Collectively, lonafarnib could be a potential fusion inhibitor for RSV infection.

Hepatocyte Intrinsic Innate Antiviral Immunity against Hepatitis Delta Virus Infection: The Voices of Bona Fide Human Hepatocytes

The pathogenesis of viral infection is attributed to two folds: intrinsic cell death pathway activation due to the viral cytopathic effect, and immune-mediated extrinsic cellular injuries. The immune system, encompassing both innate and adaptive immunity, therefore acts as a double-edged sword in viral infection. Insufficient potency permits pathogens to establish lifelong persistent infection and its consequences, while excessive activation leads to organ damage beyond its mission to control viral pathogens. The innate immune response serves as the front line of defense against viral infection, which is triggered through the recognition of viral products, referred to as pathogen-associated molecular patterns (PAMPs), by host cell pattern recognition receptors (PRRs). The PRRs-PAMPs interaction results in the induction of interferon-stimulated genes (ISGs) in infected cells, as well as the secretion of interferons (IFNs), to establish a tissue-wide antiviral state in an autocrine and paracrine manner. Cumulative evidence suggests significant variability in the expression patterns of PRRs, the induction potency of ISGs and IFNs, and the IFN response across different cell types and species. Hence, in our understanding of viral hepatitis pathogenesis, insights gained through hepatoma cell lines or murine-based experimental systems are uncertain in precisely recapitulating the innate antiviral response of genuine human hepatocytes. Accordingly, this review article aims to extract and summarize evidence made possible with bona fide human hepatocytes-based study tools, along with their clinical relevance and implications, as well as to identify the remaining gaps in knowledge for future investigations.

Risk factors associated with hepatitis D virus infection and preventive strategies in Mongolia

BACKGROUND

Hepatitis D virus (HDV) infection is highly prevalent in Mongolia. We aimed to identify the risk factors associated with HDV infection, propose preventive strategies, and evaluate the outcomes of a 3-year collaborative project between Taiwan and Mongolia.

METHODS

In 2016 and 2018, we conducted onsite visits to Mongolia. Mongolian investigators collected questionnaires focusing on risk factors, demographic characteristics, and serum samples for acute HDV infections. Furthermore, 19 Mongolian seed teachers participated in a 1-week workshop on infection control in Taiwan. Subsequently, these seed teachers trained more than 400 medical personnel in Mongolia. To assess secular changes in acute HDV infection, we reviewed the registration data from the National Center for Communicable Disease (NCCD) in Mongolia between 2011 and 2021.

RESULTS

Among the 194 Mongolian patients, 108 had dual infection with hepatitis B virus (HBV) and HDV, while 86 had acute hepatitis B (AHB). Patients with HBV/HDV dual infections were older (28.6 vs 25.5 years, p = 0.030) and had lower rates of positive hepatitis B e antigen in their sera, lower rates of serum HBV DNA exceeding 2000 IU/mL, and higher rates of having received dental treatment (59.4% vs 40.5%, p = 0.014) and injection therapy (64.2% vs 44.0%, p = 0.009) compared with those with AHB. Analysis of NCCD data revealed that new HDV infection cases were more prevalent between 2011 and 2015 (111.20 ± 29.79 cases/y) and decreased to 54.67 ± 27.34 cases/y between 2016 and 2021 ( p = 0.010).

CONCLUSION

Dental treatment and injections were associated with a higher risk of acute HDV infections in Mongolia. Through collaborative efforts, the incidence rate of HDV infection has declined in recent years.

Association of hepatitis delta virus with liver morbidity and mortality: A systematic literature review and meta-analysis

BACKGROUND AND AIMS

Studies have suggested that patients with chronic hepatitis B, either co- or superinfected, have more aggressive liver disease progression than those with the HDV. This systematic literature review and meta-analysis examined whether HDV RNA status is associated with increased risk of advanced liver disease events in patients who are HBsAg and HDV antibody positive.

APPROACH AND RESULTS

A total of 12 publications were included. Relative rates of progression to advanced liver disease event for HDV RNA+/detectable versus HDV RNA-/undetectable were extracted for analysis. Reported OR and HRs with 95% CI were pooled using the Hartung-Knapp-Sidik-Jonkman method for random-effects models. The presence of HDV RNA+ was associated with an increased risk of any advanced liver disease event [random effect (95% CI): risk ratio: 1.48 (0.93, 2.33); HR: 2.62 (1.55, 4.44)]. When compared to the patients with HDV RNA- status, HDV RNA+ was associated with a significantly higher risk of progressing to compensated cirrhosis [risk ratio: 1.74 (1.24, 2.45)] decompensated cirrhosis [HR: 3.82 (1.60, 9.10)], HCC [HR: 2.97 (1.87, 4.70)], liver transplantation [HR: 7.07 (1.61, 30.99)], and liver-related mortality [HR: 3.78 (2.18, 6.56)].

CONCLUSIONS

The patients with HDV RNA+ status have a significantly greater risk of liver disease progression than the patients who are HDV RNA-. These findings highlight the need for improved HDV screening and linkage to treatment to reduce the risk of liver-related morbidity and mortality.

Addressing hepatitis delta in primary care practices in the US: a narrative review

OBJECTIVE

Infection with the hepatitis delta virus (HDV), a unique RNA virus that requires hepatitis B virus (HBV) antigens for its assembly, replication, and transmission, causes severe viral hepatitis. Compared to HBV monoinfection, HDV infection increases the risk of severe liver disease, necessity for liver transplant, and mortality. Global HDV prevalence estimates vary from 5% to 15% among persons with HBV, but screening guidelines for HDV are inconsistent; some recommend risk-based screening, while others recommend universal screening for all people with HBV. Among primary care providers (PCPs) in the US, there is a lack of awareness and/or insufficient adherence to current recommendations for the screening of HDV infection and management of chronic HDV.

METHODS

Publications were obtained by conducting literature searches between July and August 2022 using the PubMed database and by manual searches of the retrieved literature for additional references. Information was synthesized to highlight HDV screening and management strategies for PCPs. Best practices for PCPs based on current guidelines and comanagement strategies for patients with HBV and HDV infection were summarized.

RESULTS

We recommend universal screening for HDV in patients positive for hepatitis B surface antigen. Confirmed HDV infection should prompt evaluation by a liver specialist, if available, with whom the PCP can comanage the patient. PCPs should counsel patients on the expected course of the disease, lifestyle factors that may influence liver health, need for consistent disease monitoring and follow-up, and risk of disease transmission. Screening is suggested for sexual partners, household contacts, and family members, with HBV immunization recommended for those found to be susceptible. There are currently no US Food and Drug Administration-approved therapies for HDV infection; thus, management is limited to treatments for chronic HBV infection plus long-term monitoring of liver health.

CONCLUSIONS

PCPs can be a valuable point of care for patients to access HDV/HBV screening, HBV immunization, and education, and can comanage patients with HBV and/or HDV infection.

Cell Culture Models for Hepatitis B and D Viruses Infection: Old Challenges, New Developments and Future Strategies

Chronic Hepatitis B and D Virus (HBV and HDV) co-infection is responsible for the most severe form of viral Hepatitis, the Hepatitis Delta. Despite an efficient vaccine against HBV, the HBV/HDV infection remains a global health burden. Notably, no efficient curative treatment exists against any of these viruses. While physiologically distinct, HBV and HDV life cycles are closely linked. HDV is a deficient virus that relies on HBV to fulfil is viral cycle. As a result, the cellular response to HDV also influences HBV replication. In vitro studying of HBV and HDV infection and co-infection rely on various cell culture models that differ greatly in terms of biological relevance and amenability to classical virology experiments. Here, we review the various cell culture models available to scientists to decipher HBV and HDV virology and host-pathogen interactions. We discuss their relevance and how they may help address the remaining questions, with one objective in mind: the development of new therapeutic approaches allowing viral clearance in patients.

Hepatitis Delta Virus and Hepatocellular Carcinoma

The hepatitis D virus (HDV) is a compact, enveloped, circular RNA virus that relies on hepatitis B virus (HBV) envelope proteins to initiate a primary infection in hepatocytes, assemble, and secrete new virions. Globally, HDV infection affects an estimated 12 million to 72 million people, carrying a significantly elevated risk of developing cirrhosis, liver failure, and hepatocellular carcinoma (HCC) compared to an HBV mono-infection. Furthermore, HDV-associated HCC often manifests at a younger age and exhibits more aggressive characteristics. The intricate mechanisms driving the synergistic carcinogenicity of the HDV and HBV are not fully elucidated but are believed to involve chronic inflammation, immune dysregulation, and the direct oncogenic effects of the HDV. Indeed, recent data highlight that the molecular profile of HCC associated with HDV is unique and distinct from that of HBV-induced HCC. However, the question of whether the HDV is an oncogenic virus remains unanswered. In this review, we comprehensively examined several crucial aspects of the HDV, encompassing its epidemiology, molecular biology, immunology, and the associated risks of liver disease progression and HCC development.

Prospective study of hepatitis B and D epidemiology and risk factors in Romania: A 10-year update

BACKGROUND

The global burden of hepatitis D virus (HDV) infection represents a major medical challenge and a public health crisis worldwide. However, there is a lack of accurate data on the epidemiology and risk factors for HDV. Hepatitis B virus (HBV) and HDV coinfection causes the most severe form of viral hepatitis, leading to a higher cumulative incidence of liver-related events compared with HBV monoinfection, including the need for liver transplantation and death.

AIM

To investigate the epidemiology, natural history, risk factors and clinical management of HBV and HDV coinfection in Romanian patients.

METHODS

This prospective study was conducted between January and July 2022 in six tertiary gastroenterology and hepatology referral centres in Romania. All consecutive adults admitted for any gastroenterology diagnosis who were HBV-positive were enrolled. Patients with acute hepatitis or incomplete data were excluded. Of the 25390 individuals who presented with any type of gastroenterology diagnosis during the study period, 963 met the inclusion criteria. Testing for anti-HDV antibodies and HDV RNA was performed for all participants. Demographic and risk factor data were collected by investigators using medical charts and patient questionnaires. All data were stored in an anonymized online database during the study.

RESULTS

The prevalence of HBV was 3.8%; among these patients, the prevalence of HBV/HDV coinfection was 33.1%. The median age of the study population was 54.0 years, and it consisted of 55.1% men. A higher prevalence of HBV/HDV coinfection was observed in patients 50-69 years old. Patients with HBV/HDV coinfection were significantly older than those with HBV monoinfection (P = 0.03). Multivariate multiple regression analysis identified female gender (P = 0.0006), imprisonment (P < 0.0001), older age at diagnosis (P = 0.01) and sexual contact with persons with known viral hepatitis (P = 0.0003) as significant risk factors for HDV.

CONCLUSION

This study shows that HDV infection among those with HBV remains endemic in Romania and updates our understanding of HDV epidemiology and associated risk factors. It emphasizes the need for systematic screening for HDV infection and collaborative initiatives for controlling and preventing HBV and HDV infection.

Towards Understanding and Identification of Human Viral Co-Infections

Viral co-infections, in which a host is infected with multiple viruses simultaneously, are common in the human population. Human viral co-infections can lead to complex interactions between the viruses and the host immune system, affecting the clinical outcome and posing challenges for treatment. Understanding the types, mechanisms, impacts, and identification methods of human viral co-infections is crucial for the prevention and control of viral diseases. In this review, we first introduce the significance of studying human viral co-infections and summarize the current research progress and gaps in this field. We then classify human viral co-infections into four types based on the pathogenic properties and species of the viruses involved. Next, we discuss the molecular mechanisms of viral co-infections, focusing on virus-virus interactions, host immune responses, and clinical manifestations. We also summarize the experimental and computational methods for the identification of viral co-infections, emphasizing the latest advances in high-throughput sequencing and bioinformatics approaches. Finally, we highlight the challenges and future directions in human viral co-infection research, aiming to provide new insights and strategies for the prevention, control, diagnosis, and treatment of viral diseases. This review provides a comprehensive overview of the current knowledge and future perspectives on human viral co-infections and underscores the need for interdisciplinary collaboration to address this complex and important topic.

Clinical diagnosis of viral hepatitis: Current status and future strategies

Viral hepatitis (VH) is a significant public health issue with tremendous potential to aggravate into chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Recent decade has witnessed remarkable uprising in the drug development and effective treatment of VH. An upsurge is seen in identification of antiviral therapies with low rates of viral resistance, the improvement of Hepatitis B Virus (HBV) vaccination and the development of direct-acting antivirals for Hepatitis C Virus (HCV). But unfortunately, the "2030 worldwide eradication" objective of World Health Organization (WHO) is still unmet. It can be largely attributed to the deficit faced by the healthcare system concerning screening and diagnosis. A timely, accurate and comprehensive screening; encompassing maximum population coverage is essential to combat this disease. However, advancements in VH diagnostics remain inadequate and with a marginal use in routine practice. This paper deliberates upon the lacunae in traditional and prevailing diagnostic methodology of viral hepatitis, especially their inadequacy in meeting the unique situations prevailing low- and middle-income countries (LMIC).

JAK1 promotes HDV replication and is a potential target for antiviral therapy

BACKGROUND & AIMS

Chronic co-infection with HBV and HDV leads to the most aggressive form of chronic viral hepatitis. To date, no treatment induces efficient viral clearance, and a better characterization of virus-host interactions is required to develop new therapeutic strategies.

METHODS

Using loss-of-function strategies, we validated the unexpected proviral activity of Janus kinase 1 (JAK1) - a key player in innate immunity - in the HDV life cycle and determined its mechanism of action on HDV through various functional analyses including co-immunoprecipitation assays.

RESULTS

We confirmed the key role of JAK1 kinase activity in HDV infection. Moreover, our results suggest that JAK1 inhibition is associated with a modulation of ERK1/2 activation and S-HDAg phosphorylation, which is crucial for viral replication. Finally, we showed that FDA-approved JAK1-specific inhibitors are efficient antivirals in relevant in vitro models including primary human hepatocytes.

CONCLUSIONS

Taken together, we uncovered JAK1 as a key host factor for HDV replication and a potential target for new antiviral treatment.

IMPACT AND IMPLICATIONS

Chronic hepatitis D is the most aggressive form of chronic viral hepatitis. As no curative treatment is currently available, new therapeutic strategies based on host-targeting agents are urgently needed. Here, using loss-of-function strategies, we uncover an unexpected interaction between JAK1, a major player in the innate antiviral response, and HDV infection. We demonstrated that JAK1 kinase activity is crucial for both the phosphorylation of the delta antigen and the replication of the virus. By demonstrating the antiviral potential of several FDA-approved JAK1 inhibitors, our results could pave the way for the development of innovative therapeutic strategies to tackle this global health threat.

Ergosterol peroxide blocks HDV infection as a novel entry inhibitor by targeting human NTCP receptor

Hepatitis D virus (HDV), which co-infects or superinfects patients with hepatitis B virus, is estimated to affect 74 million people worldwide. Chronic hepatitis D is the most severe form of viral hepatitis and can result in liver cirrhosis, liver failure, and hepatocellular carcinoma (HCC). Currently, there are no efficient HDV-specific drugs. Therefore, there is an urgent need for novel HDV therapies that can achieve a functional cure or even eliminate the viral infection. In the HDV life cycle, agents targeting the entry step of HDV infection preemptively reduce the intrahepatic viral RNA. Human sodium taurocholate co-transporting polypeptide (hNTCP), a transporter of bile acids on the plasma membrane of hepatocytes, is an essential entry receptor of HDV and is a promising molecular target against HDV infection. Here, we investigated the effect of ergosterol peroxide (EP) on HDV infection in vitro and in vivo. EP inhibited HDV infection of hNTCP-expressing dHuS-E/2 hepatocytes by interrupting the early fusion/endocytosis step of HDV entry. Furthermore, molecular modeling suggested that EP hinders LHBsAg binding to hNTCP by blocking access to S267 and V263. In addition, we generated hNTCP-expressing transgenic (Tg) C57BL/6 mice using the Cre/loxP system for in vivo study. EP reduced the liver HDV RNA level of HDV-challenged hNTCP-Cre Tg mice. Intriguingly, EP downregulated the mRNA level of liver IFN-γ. We demonstrate that EP is a bona fide HDV entry inhibitor that acts on hNTCP and has the potential for use in HDV therapies.

Prevalence of hepatitis D virus infection in Central Italy has remained stable across the last 2 decades with dominance of subgenotypes 1 and characterized by elevated viral replication

OBJECTIVES

Here we investigate Hepatitis D virus (HDV)-prevalence in Italy and its fluctuations over time and we provide an extensive characterization of HDV-infected patients.

METHODS

The rate of HDV seroprevalence and HDV chronicity was assessed in 1579 hepatitis B surface antigen (HBsAg)+ patients collected from 2005 to 2022 in Central Italy.

RESULTS

In total, 45.3% of HBsAg+ patients received HDV screening with an increasing temporal trend: 15.6% (2005-2010), 45.0% (2011-2014), 49.4% (2015-2018), 71.8% (2019-2022). By multivariable model, factors correlated with the lack of HDV screening were alanine-aminotransferase (ALT) less than two times of upper limit of normality (<2ULN) and previous time windows (P <0.002). Furthermore, 13.4% of HDV-screened patients resulted anti-HDV+ with a stable temporal trend. Among them, 80.8% had detectable HDV-ribonucleic acid (RNA) (median [IQR]:4.6 [3.6-5.6] log copies/ml) with altered ALT in 89.3% (median [IQR]:92 [62-177] U/L). Anti-HDV+ patients from Eastern/South-eastern Europe were younger than Italians (44 [37-54] vs 53 [47-62] years, P <0.0001), less frequently nucleos(t)ide analogs (NUC)-treated (58.5% vs 80%, P = 0.026) with higher HDV-RNA (4.8 [3.6-5.8] vs 3.9 [1.4-4.9] log copies/ml, P = 0.016) and HBsAg (9461 [4159-24,532] vs 4447 [737-13,336] IU/ml, P = 0.032). Phylogenetic analysis revealed the circulation of HDV subgenotype 1e (47.4%) and -1c (52.6%). Notably, subgenotype 1e correlated with higher ALT than 1c (168 [89-190] vs 58 [54-88] U/l, P = 0.015) despite comparable HDV-RNA.

CONCLUSIONS

HDV-screening awareness is increasing over time even if some gaps persist to achieve HDV screening in all HBsAg+ patients. HDV prevalence in tertiary care centers tend to scarcely decline in native/non-native patients. Detection of subgenotypes, triggering variable inflammatory stimuli, supports the need to expand HDV molecular characterization.

Molecular determinants within the C-termini of L-HDAg that regulate hepatitis D virus replication and assembly

Background & Aims

Hepatitis D virus (HDV) is the causative agent of chronic hepatitis delta, the most severe form of viral hepatitis. HDV encodes one protein, hepatitis delta antigen (HDAg), in two isoforms: S- and L-HDAg. They are identical in sequence except that L-HDAg contains an additional 19-20 amino acids at its C-terminus, which confer regulatory roles that are distinct from those of S-HDAg. Notably, these residues are divergent between different genotypes. We aimed to elucidate the molecular determinants within the C-termini that are essential for the regulatory role of L-HDAg in HDV replication and assembly.

Methods

Northern blot, reverse-transcription quantitative PCR, and a newly established HDV trans-complementary system were used in this study.

Results

C-termini of L-HDAg, albeit with high sequence variation among different genotypes, are interchangeable with respect to the trans-inhibitory function of L-HDAg and HDV assembly. The C-terminus of L-HDAg features a conserved prenylation CXXQ motif and is enriched with proline and hydrophobic residues. Abolishment of the CXXQ motif attenuated the inhibitory effect of L-HDAg on HDV replication. In contrast, the enrichment of proline and hydrophobic residues per se does not modify the trans-inhibitory function of L-HDAg. Nevertheless, these residues are essential for HDV assembly. Mechanistically, prolines and hydrophobic residues contribute to HDV assembly via a mode of action independent of the prenylated CXXQ motif.

Conclusions

Within the C-terminus of L-HDAg, the CXXQ motif and the enrichment of proline and hydrophobic residues are all essential determinants of L-HDAg's regulatory roles in HDV replication and assembly. This intrinsic viral regulatory mechanism we elucidated deepens our understanding of the unique life cycle of HDV.

Impact and implications

Hepatitis D virus (HDV) encodes one protein, hepatitis delta antigen (HDAg), in two isoforms: S- and L-HDAg. They are identical in sequence except that L-HDAg contains an additional 19-20 amino acids at its C-terminus. This C-terminal extension in L-HDAg confers regulatory roles in the HDV life cycle that are distinct from those of S-HDAg. Herein, we found that C-termini of L-HDAg, although with high sequence variation, are interchangeable among different HDV genotypes. Within the C-terminus of L-HDAg, the prenylation motif, and the enrichment of proline and hydrophobic residues are all essential determinants of L-HDAg's regulatory roles in HDV replication and assembly.

[Delta hepatitis in Africa: epidemiological and clinical particularities]

In 2022, the World Health Organization (WHO) estimated that hepatitis B virus (HBV) infections caused 1.5 million deaths, mostly attributable to complications from chronic infections, cirrhosis and hepatocellular carcinoma (HCC). Despite the availability of a vaccine, 296 million people were chronically infected in 2019. Asia and Africa are the continents most affected by this infection, with around 100 million people infected in Africa as a whole.Hepatitis Delta or D virus (HDV), which is a "satellite" virus of HBV, is often misunderstood and its diagnosis remains neglected. However, it is associated with acute fulminant forms and chronic forms of hepatitis leading to a more rapid evolution towards cirrhosis and HCC than during HBV mono-infection. Research on these two viruses HBV and HDV has progressed a lot in recent years, and new treatments are currently in development.In people living with the human immunodeficiency virus (PlHIV), liver disease is a major cause of morbidity and mortality. Due to common modes of transmission, dual or triple HIV/HBV or HIV/HBV/HDV infections are relatively common, particularly in HBV endemic regions such as Africa. However, while today most co-infected patients benefit from effective treatment against both HIV and HBV, the latter is not active against HDV. In Africa, hepatitis B and D have already been the subject of several studies. However, the frequency and clinical consequences of these co-infections have been little studied in the general population and in PlHIV.This review seeks to update the epidemiological and clinical data and the therapeutic perspectives of HDV co-infections or triple infections (HIV-HBV-HDV) in Africa.

Hepatitis D: A Review

Importance

Hepatitis D virus (HDV) infection occurs in association with hepatitis B virus (HBV) infection and affects approximately 12 million to 72 million people worldwide. HDV causes more rapid progression to cirrhosis and higher rates of hepatocellular carcinoma than HBV alone or hepatitis C virus.

Observations

HDV requires HBV to enter hepatocytes and to assemble and secrete new virions. Acute HDV-HBV coinfection is followed by clearance of both viruses in approximately 95% of people, whereas HDV superinfection in an HBV-infected person results in chronic HDV-HBV infection in more than 90% of infected patients. Chronic hepatitis D causes more rapidly progressive liver disease than HBV alone. Approximately 30% to 70% of patients with chronic hepatitis D have cirrhosis at diagnosis and more than 50% die of liver disease within 10 years of diagnosis. However, recent studies suggested that progression is variable and that more than 50% of people may have an indolent course. Only approximately 20% to 50% of people infected by hepatitis D have been diagnosed due to lack of awareness and limited access to reliable diagnostic tests for the HDV antibody and HDV RNA. The HBV vaccine prevents HDV infection by preventing HBV infection, but no vaccines are available to protect those with established HBV infection against HDV. Interferon alfa inhibits HDV replication and reduces the incidence of liver-related events such as liver decompensation, hepatocellular carcinoma, liver transplant, or mortality from 8.5% per year to 3.3% per year. Adverse effects from interferon alfa such as fatigue, depression, and bone marrow suppression are common. HBV nucleos(t)ide analogues, such as entecavir or tenofovir, are ineffective against HDV. Phase 3 randomized clinical trials of bulevirtide, which blocks entry of HDV into hepatocytes, and lonafarnib, which interferes with HDV assembly, showed that compared with placebo or observation, these therapies attained virological and biochemical response in up to 56% of patients after 96 weeks of bulevirtide monotherapy and 19% after 48 weeks of lonafarnib, ritonavir, and pegylated interferon alfa treatment.

Conclusions and Relevance

HDV infection affects approximately 12 million to 72 million people worldwide and is associated with more rapid progression to cirrhosis and liver failure and higher rates of hepatocellular carcinoma than infection with HBV alone. Bulevirtide was recently approved for HDV in Europe, whereas pegylated interferon alfa is the only treatment available in most countries.

Prevalence of hepatitis D virus infection among patients with chronic hepatitis B infection in a tertiary care centre in Thailand

Knowledge about the epidemiology of hepatitis D virus (HDV) is essential for effective screening and management. Our study aimed to update the prevalence of HDV infection among patients with hepatitis B virus (HBV) infection at hepatology clinics in Thailand. We enrolled HBV-infected patients from hepatology clinics at King Chulalongkorn Memorial Hospital, Bangkok, Thailand, between June 2022 and November 2023. Demographic, biochemical characteristics, and liver-related complications (LRC), including cirrhosis and hepatocellular carcinoma, were reviewed. The competitive enzyme and chemiluminescence immunoassays were used to detect anti-HDV antibodies. Real-time polymerase chain reaction (RT-PCR) was used to test for HDV RNA in anti-HDV-positive patients. The HDV genotype was identified in detectable HDV RNA samples. Of the 702 enrolled patients, four (0.6%) had positive and equivocal for both anti-HDV tests. Two (50.0%) of the four patients tested positive for HDV RNA and genotype 1 was identified; one had multiple risk factors. Anti-HDV seroprevalence was not significantly different between patients with and without LRC. In conclusion, HDV co-infection is less common in Thailand than globally. Additionally, our study identified genotype 1, the predominant HDV genotype worldwide, and observed co-infection even without LRC.

Clinical long-term outcome of hepatitis D compared to hepatitis B monoinfection

BACKGROUND AND AIMS

Hepatitis D virus (HDV) infection causes the most severe form of chronic viral hepatitis. However, it is still unclear to what extent the underlying cirrhosis may contribute to disease progression. The aim of this study was to compare the long-term outcome of HDV infection with HBV monoinfection in a single-center cohort of both non-cirrhotic and cirrhotic patients.

METHOD

We retrospectively studied 175 patients with chronic hepatitis D (CHD) who were followed for at least 6 months (median of 6.3 (0.6-23.6) years). In addition, we selected 175 patients with HBV monoinfection (CHB) who were matched for gender, age, region of origin, HBeAg status, and bilirubin. Liver-related clinical end points were defined as hepatic decompensation (ascites, encephalopathy, variceal bleeding), liver transplantation, HCC, or liver-related death.

RESULTS

Clinical complications developed earlier (4.6 vs. 6.2 years) and more frequently (35.4% vs. 12.6%, p < 0.01) in CHD patients. In a multivariate Cox regression, HDV infection was independently associated with the development of end points (p < 0.01; HR: 3.0; 95% CI 1.4-6.4). However, in cirrhotic patients there were no significant differences between HBV and HDV in the development of end points. Besides, CHB patients with cirrhosis developed more frequently HCC (35.5%) than CHD patients with cirrhosis (18.5%).

CONCLUSION

Our results confirmed that HDV leads to a faster progression to cirrhosis compared to HBV. However, once cirrhosis is present, not HDV but the underlying cirrhosis is the dominate intrinsic risk factor for the development of liver-related end points and for the progression to HCC.

State of the Art: Test all for Anti-Hepatitis D Virus and Reflex to Hepatitis D Virus RNA Polymerase Chain Reaction Quantification

Diagnosis of HDV exposure is based on clinical assays of anti-hepatitis D antibody and current infection with hepatitis D RNA PCR. The role of hepatitis D antigen testing is not yet defined. RT-qPCR is the gold standard for measuring HDV RNA viral load, which is used to assess response to the treatment of HDV infection. Gaps in testing include poor sensitivity of antigen testing and quantitative HDV RNA accuracy can be affected by the genotypic variability of the virus and variation in laboratory techniques. There is also a limitation in HDV testing due to access, cost, and limited knowledge of testing indications. Droplet digital PCR promises to be a more accurate method to quantify HDV RNA. Also, the recent development of a rapid HDV detection test could prove useful in resource-limited areas.

Potent broadly neutralizing antibody VIR-3434 controls hepatitis B and D virus infection and reduces HBsAg in humanized mice

BACKGROUND & AIMS

Chronic hepatitis B is a global public health problem, and coinfection with hepatitis delta virus (HDV) worsens disease outcome. Here, we describe a hepatitis B virus (HBV) surface antigen (HBsAg)-targeting monoclonal antibody (mAb) with the potential to treat chronic hepatitis B and chronic hepatitis D.

METHODS

HBsAg-specific mAbs were isolated from memory B cells of HBV vaccinated individuals. In vitro neutralization was determined against HBV and HDV enveloped with HBsAg representing eight HBV genotypes. Human liver-chimeric mice were treated twice weekly with a candidate mAb starting 3 weeks post HBV inoculation (spreading phase) or during stable HBV or HBV/HDV coinfection (chronic phase).

RESULTS

From a panel of human anti-HBs mAbs, VIR-3434 was selected and engineered for pre-clinical development. VIR-3434 targets a conserved, conformational epitope within the antigenic loop of HBsAg and neutralized HBV and HDV infection with higher potency than hepatitis B immunoglobulins in vitro. Neutralization was pan-genotypic against strains representative of HBV genotypes A-H. In the spreading phase of HBV infection in human liver-chimeric mice, a parental mAb of VIR-3434 (HBC34) prevented HBV dissemination and the increase in intrahepatic HBV RNA and covalently closed circular DNA. In the chronic phase of HBV infection or co-infection with HDV, HBC34 treatment decreased circulating HBsAg by >1 log and HDV RNA by >2 logs.

CONCLUSIONS

The potently neutralizing anti-HBs mAb VIR-3434 reduces circulating HBsAg and HBV/HDV viremia in human liver-chimeric mice. VIR-3434 is currently in clinical development for treatment of patients with chronic hepatitis B or D.

IMPACT AND IMPLICATIONS

Chronic infection with hepatitis B virus and co-infection with hepatitis D virus place approximately 290 million individuals worldwide at risk of severe liver disease and cancer. Available treatments result in low rates of functional cure or require lifelong therapy that does not eliminate the risk of liver disease. We isolated and characterized a potent human antibody that neutralizes hepatitis B and D viruses and reduces infection in a mouse model. This antibody could provide a new treatment for patients with chronic hepatitis B and D.

Broad-spectrum activity of bulevirtide against clinical isolates of HDV and recombinant pan-genotypic combinations of HBV/HDV

Background & Aims

Bulevirtide (BLV) is a small lipopeptide agent that specifically binds to the sodium taurocholate cotransporting polypeptide (NTCP) bile salt transporter and HBV/HDV receptor on the surface of human hepatocytes and inhibits HDV and HBV entry. As a satellite virus of HBV, HDV virions are formed after assembly of HDV RNA with the HBV envelope proteins (HBsAg). Because both viruses exist as eight different genotypes, this creates a potential for high diversity in the HBV/HDV combinations. To investigate the sensitivity of various combinations of HBV/HDV genotypes to BLV, clinical and laboratory strains were assessed.

Methods

For the laboratory strains, the different envelopes from HBV genotypes A through H were combined with HDV genotypes 1-8 in cotransfection assays. Clinical plasma isolates were obtained from clinical studies and academic collaborations to maximise the diversity of HBV/HDV genotypes tested.

Results

The mean BLV EC50 against HDV laboratory strains ranged from 0.44 to 0.64 nM. Regardless of HBV and HDV genotypes, the clinical isolates showed similar sensitivities to BLV with mean values that ranged from 0.2 to 0.73 nM.

Conclusions

These data support the use of BLV in patients infected with any HBV/HDV genotypes.

Impact and implications

This study describes the potent activity of BLV against multiple laboratory strains spanning all HBV/HDV A-H/1-8 genotype combinations and the most diverse collection of HDV clinical samples tested to date, including HBV/HDV genotype combinations less frequently observed in the clinic. Overall, all isolates and laboratory strains displayed similar in vitro nanomolar sensitivity to BLV. This broad-spectrum antiviral activity of BLV has direct implications on potential simplified treatment for any patient infected with HDV, regardless of genotype, and supports the new 2023 EASL Clinical Practice Guidelines on HDV that recommend antiviral treatment for all patients with CHD.

Triple Threat: HDV, HBV, HIV Coinfection

Hepatitis delta virus (HDV) only infects patients with hepatitis B virus (HBV) due to its reliance on HBV surface proteins to form its envelope. With shared routes of transmission, HDV coinfection is estimated to occur in 15% of patients with HIV and HBV. However, HDV is often underdiagnosed and may be missed particularly in people living with HIV (PLWH) who are already on antiretroviral therapy with anti-HBV activity and coincidental HBV suppression. At the same time, HDV causes the most severe form of chronic viral hepatitis and leads to faster progression of liver disease and hepatocellular carcinoma. Thus, increased recognition and effective treatment are paramount, and as novel treatment options approach global markets, the study of their efficacy in PLWH should be pursued.

Hepatitis delta: Epidemiology to recent advances in therapeutic agents

Hepatitis D virus (HDV) was first described in 1977 and is dependent on the presence of hepatitis B surface antigen (HBsAg) for its entry into cells and on the human host for replication. Due to the envelopment with the hepatitis B virus (HBV) envelope, early phases of HDV entry resemble HBV infection. Unlike HBV, HDV activates innate immune responses. The global prevalence of HDV is estimated to be about 5% of HBsAg positive individuals. However, recent studies have described a wide range of prevalence between 12 to 72 million individuals. Infection can occur as super-infection or co-infection. The diagnosis of active HDV infection involves screening with anti HDV antibodies followed by quantitative PCR testing for HDV RNA in those who are HBsAg positive. The diagnostic studies have evolved over the years improving the validity and reliability of the tests performed. HDV infection is considered the most severe form of viral hepatitis and the HDV genotype may influence the disease course. There are eight major HDV genotypes with prevalence varying by geographic region. HDV treatment has been challenging as HDV strongly depends on the host cell for replication and provides few, if any viral targets. Better understanding of HDV virology has led to the development of several therapeutic agents currently being studied in different phase II and III clinical trials. There is increasing promise of effective therapies that will ameliorate the course of this devastating disease.

Analysis of Hepatitis D Virus in Minor Salivary Gland of Sjögren's Disease

Hepatitis delta virus (HDV) has been detected in the minor salivary gland (MSG) tissue of Sjögren's disease (SjD) patients in the absence of a hepatitis B virus (HBV) coinfection. Previous research has shown that HDV antigen (HDAg) expression can trigger an SjD-like phenotype in vivo, demonstrating a potential cause-and-effect relationship. We hypothesize that if HDV plays a role in the development of SjD, then HDV profiles may be correlated with disease manifestations. This retrospective study characterized HDV in a cohort of 48 SjD MSG samples collected between 2014 and 2021. Analyses of HDAg expression, including cell type and subcellular localization, in situ hybridization of HDV RNA, and comparative analyses with associated SjD and viral hepatitis clinical features, were conducted. HDAg was detected in MSG acinar, ductal, myoepithelial, and adipose cells and localized with the nuclei, cytoplasm, and mitochondria. In situ hybridization detected HDV genomic RNA localization in the MSG nuclei. A significant negative correlation was found between HDAg intensity and focal lymphocytic inflammation and in patients with both anti-SSA/Ro-52 and anti-SSA/Ro-60. In analyzing autoimmune disease comorbidities with SjD, it was found that SjD patients diagnosed with autoimmune thyroiditis and/or hypothyroidism were significantly more represented in the high HDAg intensity group compared to the negative and moderate HDAg intensity groups. No significant associations were detected between MSG-localized HDAg and liver enzymes or an evident HBV coinfection. This study has further confirmed that there is a nonhepatic reservoir for chronic HDV persistence in SjD-affected salivary gland tissue in a third independent SjD patient cohort. In addition, this study describes the unique colocalization of HDAg with mitochondria. The detection of HDV antigen and sequence within SjD-affected salivary gland tissue, and in the absence of an evident current or past HBV coinfection, warrants further investigation.

Interferon-Free Regimens and Direct-Acting Antiviral Agents for Delta Hepatitis: Are We There Yet?

Chronic delta hepatitis is a global health problem. Although a smaller percentage of chronic HBV-infected patients are coinfected with the hepatitis delta virus, these patients have a higher risk of an accelerated progression to fulminant "delta hepatitis", cirrhosis, hepatic decompensation, and hepatocellular carcinoma, putting a financial strain on the healthcare system and increasing the need for a liver transplant. Since its discovery, tremendous efforts have been directed toward understanding the intricate pathogenic mechanisms, discovering the complex viral replication process, the essential replicative intermediates, and cell division-mediated viral spread, which enables virion viability. The consideration of the interaction between HBV and HDV is crucial in the process of developing novel pharmaceuticals. Until just recently, interferon-based therapy was the only treatment available worldwide. This review aims to present the recent advancements in understanding the life cycle of HDV, which have consequently facilitated the development of innovative drug classes. Additionally, we will examine the antiviral strategies currently in phases II and III of development, including bulevirtide (an entry inhibitor), lonafarnib (a prenylation inhibitor), and REP 2139 (an HBsAg release inhibitor).

No virologic resistance to bulevirtide monotherapy detected in patients through 24 weeks treatment in phase II and III clinical trials for chronic hepatitis delta

BACKGROUND & AIMS

Bulevirtide (BLV) is a HDV/HBV entry inhibitor that is associated with virologic response (responders, HDV-RNA undetectable or ≥2 log10 IU/ml decrease from baseline) in >50% of patients after a 24-week treatment. However, some patients only achieve a <1 log10 IU/ml decline in HDV-RNA after the 24-week treatment (non-responders). Here, we report a viral resistance analysis in participants receiving BLV monotherapy who were non-responders or experienced virologic breakthrough (VB, i.e., two consecutive increases in HDV-RNA of ≥1 log10 IU/ml from nadir or two consecutive HDV-RNA detectable results if previously undetectable) from the phase II MYR202 and phase III MYR301 study.

METHODS

Deep-sequencing of the BLV-corresponding region in HBV PreS1 and of the HDV HDAg gene, as well as in vitro phenotypic testing, were performed for the participant with VB (n = 1) and non-responders (n = 20) at baseline (BL) and Week 24 (WK24).

RESULTS

No amino acid exchanges associated with reduced susceptibility to BLV within the BLV-corresponding region or within HDAg were identified in isolates from any of the 21 participants at BL or at WK24. Although variants (HBV n = 1; HDV n = 13) were detected at BL in some non-responders or in the participant with VB, none were associated with reduced sensitivity to BLV in vitro. Furthermore, the same variant was detected in virologic responders. A comprehensive phenotypic analysis demonstrated that the BLV EC50 values from 116 BL samples were similar across non-responders, partial responders (HDV RNA decline ≥1 but <2 log10 IU/ml), and responders regardless of the presence of HBV and/or HDV polymorphisms.

CONCLUSIONS

No amino acid substitutions associated with reduced sensitivity to BLV monotherapy were detected at BL or WK24 in non-responders or the participant with VB after 24-week BLV treatment.

IMPACT AND IMPLICATIONS

This is the first study investigating the development of resistance in patients treated with BLV. Excluding resistance to BLV as an explanation for an insufficient decrease in HDV-RNA levels during BLV therapy is an important finding for patients, clinicians, and researchers. It demonstrates that BLV has a high barrier to resistance, indicating it is safe and suitable for long-term treatment, although long-term surveillance for resistance should be performed. Our results hint at other still unknown mechanisms as an explanation for the persistence of serum HDV-RNA during inhibition of viral entry.

CLINICAL TRIAL NUMBERS

NCT03546621 and NCT03852719.