TWiV 1163: Hepadnaviridae in the Heartland - Exploring Hepatitis B Virus
0:00 Introduction: TWiV podcast records a special episode at the 2024 International HBV Meeting in Chicago, focusing on Hepatitis B Virus (HBV).
1:28 Hosts and Guests: Vincent Racaniello and Rich Condit host the episode with guests Mala Maini from University College London and John Tavis from Saint Louis University.
7:58 HBV Foundation: The episode highlights the HBV Foundation, a patient-focused advocacy group, for its role in research, education, and support for those affected by HBV.
8:57 MicrobeTV: The nonprofit nature of MicrobeTV and its reliance on listener donations is emphasized.
9:28 HBV Overview: Mala Maini provides an overview of HBV, emphasizing the immune system's role in controlling the virus in most adults. The research focus is on understanding liver immunity and developing immunotherapy strategies.
10:49 HBV Research Focus: John Tavis describes his research focus on HBV replication, specifically reverse transcriptase and drug discovery, including developing inhibitors targeting the ribonuclease H activity.
11:37 HBV Disease Overview: Mala Maini outlines the acute and chronic phases of HBV infection. Acute infection is often asymptomatic but can cause liver inflammation. Chronic infection, more common with early-life exposure, can lead to cirrhosis and hepatocellular carcinoma (HCC).
13:08 HCC Risk: The risk of developing HCC from chronic HBV is estimated at 5-10% but varies depending on factors like geographic location and access to antiviral treatment.
14:17 HBV Transmission: HBV transmission routes are discussed, with mother-to-baby transmission during birth being a major route globally. Sexual transmission and contaminated needles are also significant.
15:12 HBV Prevalence: John Tavis details the global prevalence of HBV, with the highest burden in Southeast Asia and Sub-Saharan Africa. The virus is found worldwide, and an estimated 2 billion people have been exposed.
16:38 Public Health Impact: Mala Maini highlights the stigma associated with HBV and its social and psychological impact, including barriers to employment and travel. The importance of education and therapies is emphasized.
18:18 Misinformation: The episode briefly addresses the issue of misinformation surrounding HBV vaccination.
18:46 HBV Virus Particle: John Tavis describes the structure of the HBV particle, including its envelope proteins, capsid, and partially double-stranded DNA genome. Non-infectious subviral particles are also mentioned, which play a role in immune interactions.
20:49 HBV Replication Cycle: The HBV replication cycle is described as similar to a retrovirus but with reverse transcription occurring later. Key steps like receptor binding, nuclear import, CCC DNA formation, transcription, reverse transcription, and non-cytolytic release are discussed.
23:45 Non-Cytopathic Nature: The episode emphasizes the non-cytopathic nature of HBV, meaning the virus doesn't directly kill infected cells but turns them into virus factories.
25:30 Host Cell Specificity: HBV primarily infects hepatocytes (liver cells), with limited evidence of extrahepatic infection in lymphocytes.
26:25 Role of Integration: The role of HBV DNA integration into the host genome in HCC development is explained, including potential mechanisms like insertional mutagenesis, enhancer activation, and the role of the X protein as a tumor promoter.
28:01 Immunology of Acute Infection: Mala Maini discusses the immunology of acute HBV infection, noting a delayed innate immune response and a critical role for CD4 and CD8 T cells in clearing the infection.
30:21 Immunology of Chronic Infection: The episode covers the immune dysfunction observed in chronic HBV, including T cell exhaustion, impaired NK cell function, and the role of the liver's tolerogenic environment in suppressing immune responses.
31:57 Antigen Presentation: The unusual role of hepatocytes in presenting HBV antigens to T cells, potentially contributing to immune tolerance, is highlighted.
36:00 Source of S Antigen: The source of circulating S antigen in chronic infection is discussed, with integrated HBV DNA being the primary source in later stages of infection.
36:31 Importance of Animal Models: John Tavis discusses the challenges and limitations of animal models for HBV research, emphasizing the importance of ducks and woodchucks in understanding the virus.
39:01 Innate Immunity and Disease Severity: The potential impact of interferon defects on HBV infection severity is mentioned as an area of ongoing research.
40:07 Role of Other Immune Cells: The role of NK cells and antibody-mediated functions in HBV control and clearance is explored.
41:07 HBV Therapies: John Tavis gives an overview of HBV therapies, starting with current frontline drugs like nucleoside/nucleotide analogs, which are effective in suppressing viral replication but not curative.
41:45 New Therapeutic Approaches: The episode covers emerging therapies, including capsid assembly modifiers, ribonuclease H inhibitors, and siRNA/antisense oligonucleotides, aimed at achieving a functional cure.
43:27 Standard Therapy: The current standard therapy for chronic HBV is monotherapy with nucleoside analogs, typically initiated after overt liver disease develops.
46:28 Underdiagnosis and Treatment: Mala Maini highlights the significant underdiagnosis and undertreatment of HBV, particularly in resource-limited settings.
48:31 Functional Cure: The concept of a functional cure for HBV is explained, which involves the loss of detectable surface antigen and HBV DNA after treatment withdrawal. This mimics the natural resolution of acute infection, with the immune system controlling residual viral DNA.
50:43 HBV Vaccines: Mala Maini describes preventative and therapeutic HBV vaccines. Preventative vaccines based on the S antigen are highly effective in preventing infection when given to newborns.
51:59 Therapeutic Vaccines: Therapeutic vaccines, designed to stimulate immune responses in chronically infected individuals, are discussed as a promising area of research, often combined with other immunomodulatory approaches.
53:16 Alternative Careers: Mala Maini expresses a desire to pursue creative writing, while John Tavis mentions woodworking as a potential alternative career path.