Hepatitis D virus: Improving virological knowledge to develop new treatments

Hepatitis delta virus (HDV), a satellite of hepatitis B virus (HBV), possesses the smallest viral genome known to infect animals. HDV needs HBV surface protein for secretion and entry into target liver cells. However, HBV is dispensable for HDV genome amplification, as it relies almost exclusively on cellular host factors for replication. HBV/HDV co-infections affect over 12 million people worldwide and constitute the most severe form of viral hepatitis. Co-infected individuals are at higher risk of developing liver cirrhosis and hepatocellular carcinoma compared to HBV mono-infected patients. Bulevirtide, an entry inhibitor, was conditionally approved in July 2020 in the European Union for adult patients with chronic hepatitis delta (CHD) and compensated liver disease. There are several drugs in development, including lonafarnib and interferon lambda, with different modes of action. In this review, we detail our current fundamental knowledge of HDV lifecycle and review antiviral treatments under development against this virus, outlining their respective mechanisms-of-action. Finally, we describe the antiviral effect these compounds are showing in ongoing clinical trials, discussing their promise and potential pitfalls for managing HDV infected patients.

[Bulevirtide as the first specific agent against hepatitis D virus infections-mechanism and clinical effect]

Die Blockade des Zelleintritts von Krankheitserregern ist ein geeigneter Ansatz, um Neuinfektionen zu verhindern. Der therapeutische Einsatz von Eintrittsinhibitoren bei chronisch infizierten Patienten war jedoch bisher nur begrenzt erfolgreich. Zur Behandlung von chronischen Hepatitis-D-Virus-(HDV-)Infektionen wurde im Juli 2020 mit Bulevirtide (BLV) ein vielversprechender Wirkstoff bedingt zugelassen, der auf diesem Wirkprinzip beruht. Zuvor hatten für HDV keine gezielte Medikation zur Verfügung gestanden und die Behandlung beruhte auf dem Off-Label-Einsatz von Interferon-Alpha/Peginterferon-Alpha (IFNα/Peg-IFNα). In diesem Beitrag wird ein Überblick über die Grundlagen des Wirkmechanismus von BLV gegeben und bisher vorliegende klinische Daten werden zusammengefasst.

Eine HDV-Infektion manifestiert sich als Ko- oder Superinfektion bei Hepatitis-B-Virus-(HBV-)Infektionen und betrifft 4,5–15 % der HBV-Patienten weltweit. HDV nutzt die Hüllproteine von HBV zur Verbreitung. BLV wirkt, indem es den HBV/HDV-Rezeptor natriumtaurocholat-co-transportierendes Polypeptid (NTCP) blockiert und so den Eintritt von HBV/HDV in Hepatozyten verhindert. BLV senkt die HDV-Serum-RNA-Spiegel und führt bei HBV/HDV-infizierten Personen zur Normalisierung der Alanin-Aminotransferase-(ALT-)Werte. Es hat ein ausgezeichnetes Sicherheitsprofil, selbst wenn es über 48 Wochen in hohen Dosen (10 mg täglich) verabreicht wird. In Kombination mit Peg-IFNα zeigt BLV synergistische Effekte auf die Senkung der HDV-RNA im Serum, aber auch auf die Hepatitis-B-Oberflächenantigen-(HBsAg‑)Spiegel. Dies führte bei einer Untergruppe von Patienten zu einer funktionellen Heilung, wenn 2 mg BLV plus Peg-IFNα verabreicht wurden. Der Mechanismus dieser wahrscheinlich immunvermittelten Eliminierung wird in Folgestudien untersucht.

Novel Therapies of Hepatitis B and D

Hepatitis B virus (HBV) infection is a global public health issue and is a major cause of cirrhosis and hepatocellular carcinoma (HCC). Hepatitis D virus (HDV) requires the hepatitis B surface antigen (HBsAg) to replicate. The eradication of HBV, therefore, can also cure HDV. The current therapies for chronic hepatitis B and D are suboptimal and cannot definitely cure the viruses. In order to achieve functional or complete cure of these infections, novel therapeutic agents that target the various sites of the viral replicative cycle are necessary. Furthermore, novel immunomodulatory agents are also essential to achieve viral clearance. Many of these new promising compounds such as entry inhibitors, covalently closed circular DNA (cccDNA) inhibitors, small interfering RNAs (siRNAs), capsid assembly modulators and nucleic acid polymers are in various stages of clinical developments. In this review article, we provided a comprehensive overview of the structure and lifecycle of HBV, the limitations of the current therapies and a summary of the novel therapeutic agents for both HDV and HBV infection.

Reliable quantification of plasma HDV RNA is of paramount importance for treatment monitoring: A European multicenter study

OBJECTIVES

Quantification of plasma hepatitis D virus (HDV) RNA is the essential tool for patient management under antiviral therapy. The aim of this European multicenter study was to improve the comparability of quantitative results reported by different laboratories using the CE/IVD-labeled RoboGene HDV RNA Quantification Kit 2.0 (Roboscreen GmbH) with different manual or automated nucleic acid extraction protocols/platforms and amplification/detection devices.

METHODS

For harmonization of HDV RNA concentrations obtained by different protocols, correction factors (CF) were determined using the 1st WHO International Standard for HDV RNA. The limit of detection (LOD) and accuracy were determined for each protocol by using reference material. Furthermore, clinical samples were analyzed and results compared.

RESULTS

The CF ranged from 20 to 1,870 depending on the protocol used. The LOD was found between 4 and 450 IU/ml. When accuracy was tested, external quality control (EQC) samples containing low HDV RNA concentrations were not detected by those protocols with higher LODs. For EQC samples, the maximum standard deviation of HDV RNA concentrations was found to be 0.53 log₁₀ IU/ml, for clinical samples 0.87 log₁₀ IU/mL.

CONCLUSION

To ensure reliability in quantification of HDV RNA, any modification of the extraction and amplification/detection protocol validated by the manufacturer requires revalidation. With the 1st WHO International Standard for HDV RNA, the CF could easily be calculated leading to harmonization of quantitative results. This warrants both accurate monitoring of response to existing anti-HDV treatment and comparability of study results investigating novel anti-HDV drugs.