Novel prime-boost immune-based therapy inhibiting both hepatitis B and D virus infections

Preclinical animal models to evaluate therapeutic antiviral antibodies

Despite the availability of effective preventative vaccines and potent small-molecule antiviral drugs, effective non-toxic prophylactic and therapeutic measures are still lacking for many viruses. The use of monoclonal and polyclonal antibodies in an antiviral context could fill this gap and provide effective virus-specific medical interventions. In order to develop these therapeutic antibodies, preclinical animal models are of utmost importance. Due to the variability in viral pathogenesis, immunity and overall characteristics, the most representative animal model for human viral infection differs between virus species. Therefore, throughout the years researchers sought to find the ideal preclinical animal model for each virus. The most used animal models in preclinical research include rodents (mice, ferrets, …) and non-human primates (macaques, chimpanzee, ….). Currently, antibodies are tested for antiviral efficacy against a variety of viruses including different hepatitis viruses, human immunodeficiency virus (HIV), influenza viruses, respiratory syncytial virus (RSV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and rabies virus. This review provides an overview of the current knowledge about the preclinical animal models that are used for the evaluation of therapeutic antibodies for the abovementioned viruses.

Distinct roles of vaccine-induced SARS-CoV-2-specific neutralizing antibodies and T cells in protection and disease

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific neutralizing antibodies (NAbs) lack cross-reactivity between SARS-CoV species and variants and fail to mediate long-term protection against infection. The maintained protection against severe disease and death by vaccination suggests a role for cross-reactive T cells. We generated vaccines containing sequences from the spike or receptor binding domain, the membrane and/or nucleoprotein that induced only T cells, or T cells and NAbs, to understand their individual roles. In three models with homologous or heterologous challenge, high levels of vaccine-induced SARS-CoV-2 NAbs protected against neither infection nor mild histological disease but conferred rapid viral control limiting the histological damage. With no or low levels of NAbs, vaccine-primed T cells, in mice mainly CD8+ T cells, partially controlled viral replication and promoted NAb recall responses. T cells failed to protect against histological damage, presumably because of viral spread and subsequent T cell-mediated killing. Neither vaccine- nor infection-induced NAbs seem to provide long-lasting protective immunity against SARS-CoV-2. Thus, a more realistic approach for universal SARS-CoV-2 vaccines should be to aim for broadly cross-reactive NAbs in combination with long-lasting highly cross-reactive T cells. Long-lived cross-reactive T cells are likely key to prevent severe disease and fatalities during current and future pandemics.

Targeting virus-specific CD8+ T cells for treatment of chronic viral hepatitis: from bench to bedside

INTRODUCTION

More than 350 million people worldwide live with chronic viral hepatitis and are thus at risk for severe complications like liver cirrhosis and hepatocellular carcinoma (HCC). To meet the goals of the World Health Organization (WHO) global hepatitis strategy, there is an urgent need for new immunotherapeutic approaches. These are particularly required for chronic hepatitis B virus infection and - B/D coinfection.

AREAS COVERED

This review summarizes data on mechanisms of CD8+ T cells failure in chronic hepatitis B, D, C and E virus infection. The relative contribution of the different concepts (viral escape, CD8+ T cell exhaustion, defective priming) will be discussed. On this basis, examples for future therapeutic approaches targeting virus-specific CD8+ T cells for the individual hepatitis viruses will be discussed.

EXPERT OPINION

Immunotherapeutic approaches targeting virus-specific CD8+ T cells have the potential to change clinical practice, especially in chronic hepatitis B virus infection. Further clinical development, however, requires a more detailed understanding of T cell immunology in chronic viral hepatitis. Some important conceptual questions remain to be addressed, e.g. regarding heterogeneity of exhausted virus-specific CD8+ T cells.

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.