Episode 347: Progress in Hepatitis C (HCV) research?
I’m hesitating to present this chapter, because there are much more knowledgeable specialists in the audience. I would certainly welcome their comments and corrections.
As an introduction and a summary for the non-specialists: both Hepatitis B and C are infamous for their contribution to chronic liver disease, including cirrhosis, liver failure and carcinoma, but they are very different viruses
- Hep B is a DNA virus with reverse transcriptase activity, while Hep C is a positive single stranded RNA virus. Hence HBV can be treated with some nucleoside or nucleotide reverse transcriptase inhibitors such as Tenofovir, but it is not an easy virus to treat, because it can integrate into the host cell. HCV remains in the cytoplasm and therefore can be eliminated by directly acting antivirals (DAA). See below.
- Transmission routes for Hep B and C are similar, but hep C is more linked to IV drug use, while Hep B is more linked to sexual and perinatal transmission.
- Hep C has more tendency to chronicity, cirrhosis and extra-hepatic manifestations.
- The serology of hep B is more straightforward, with anti-Hb S antibodies associated with cure after infection or protection by vaccination. In contrast, there is no clear “protective immunity” defined for hep C; reinfection after cure is possible. As a correlate, the development of HBV vaccine has been straightforward: just using the S protein. For HCV vaccine development is a frustrating exercise, just like it is the case for HIV. No wonder: Hep C is even more variable than HIV….
The literature on hep C (HCV) is enormous and it is impossible to give an exhaustive high-quality in depth review, respecting the format of these “episodes”. What follows is just a very incomplete attempt to a didactic summary that may give you a flavor…
EPIDEMIOLOGY AND TRANSMISSION
Key facts WHO 23 July 2023
- The hepatitis C virus is a bloodborne virus and most infection occur through exposure to blood from unsafe injection practices, unsafe health care, unscreened blood transfusions, injection drug use and sexual practices that lead to exposure to blood.
- Globally, an estimated 58 million people have chronic hepatitis C virus infection, with about 1.5 million new infections occurring per year. There are an estimated 3.2 million adolescents and children with chronic hepatitis C infection.
- WHO estimated that in 2019, approximately 290 000 people died from hepatitis C, mostly from cirrhosis and hepatocellular carcinoma (primary liver cancer).
Abbreviations: CHC = chronic hepatitis C; IFNα = interferon-alpha; ISG = Interferon-stimulated genes
Hepatitis C virus (HCV) enters the liver through the hepatic artery and the portal vein.
Acute HCV infection lasts from 0 to 24 weeks and often remains undetected.
Approximately 70% of HCV-infected individuals develop chronic hepatitis C (CHC). Most patients do not develop substantial liver fibrosis or clinically relevant liver disease. However, in 15–25% of the cases, cirrhosis develops over 10–40 years.
Decompensated cirrhosis and hepatocellular carcinoma are the most important causes of mortality in end-stage CHC. IFN, interferon; ISG, IFN-stimulated gene.
Summary according to Ep 347-1 O’Kane Frontline Gastroenterology 2023
SYMPTOMS OF CIRRHOSIS
Extrahepatic manifestations: a feature of chronic hepatitis C virus (HCV) infection in about 70% of patients and often the first and only clinical sign of infection (!). (Ep 347-2 Mazzaro Viruses 2021)
Pathophysiology of extrahepatic conditions ( Ep 347-3 Fox 2021)
Evolution: Previously: pegylated IFN-α + Ribavirin with success rate of 66% to 87 % (Bernal Cureas Aug 2023)
Now: directly acting antivirals (DAA)à with sustained viral suppression of > 95 or even > 99 %
HOWEVER: - Some DAA are genotype specific (see below)
- Resistance induction is possible
- Reinfection even with same genotype and drug-sensitive HCV is possible: no lasting immunity
IMMUNOLOGY Ep 347-4 Johnasha Stuart Current Opinion in Virology 2021
Acute phase Chronic
Acute phase Chronic
Acute phase Chronic
A) Spontaneous clearance
B) Persistent infection
C) Re- infection
A) Spontaneous clearance: during acute HCV infection (0–6 months), CD4+ T cells (Th1 and Tfh cells) activate HCV-specific CD8+ T and B cells indirectly (via DCs) or directly (via interactions between CD40 and CD40L). Activated CD8+ T cells and B cells enter germinal centers, where they proliferate and differentiate into effector T cells with cytotoxic function or antibody-secreting cells (ASCs), respectively. Cytolytic T cells (CTLs) kill infected hepatocytes, whereas Th1 and Th17 cells release cytokines that promote localized inflammation and potentiate the activities of CTLs. ASCs release antibodies that neutralize autologous HCV.
B) Persistence: activation of B cells and CD8+ T cells by CD4+ T cells (Th1 and Tfh cells) is limited. Treg cells reduce the activity of CTLs, and mutant viruses escape antibody neutralization and killing by T cells. As viremia persists, constant expression of inhibitory molecules (red) results in T-cell exhaustion (EXT), but some CD8+ T cells acquire a memory-like phenotype (TCF1+PD-1+).
C) Re-infection: existing memory CD4+ and CD8+ T cells and memory B cells (MBCs) are rapidly activated and proliferate upon re-exposure to HCV. Activated, HCV-specific T and B cells can undergo further rounds of affinity maturation in germinal centers and/or rapidly differentiate into effector T cells or ASCs, respectively. Cytotoxic activity and nAbs are increased during secondary HCV infection, leading to faster clearance and expansion of memory T and B cells.
Abbreviations: ASC = Antibody-Secreting Cells; CTL = cytolytic T cells; GC = germinal center; mCD4+ = memory CD4+ + T cell; mCD8+ = memory CD8+ + T cell; MTL CD8+ = memory-like CD8+ T cell; Th1 = T helper 1 (IFN-g secreting); Th17 = T helper 17 (Interleukin-17 secreting); Tfh (T follicular helper = stimulate B cells for affinity maturation of Ab; Treg = regulatory (suppressive) T cells.
The issue of variability: Ep 347-5 Justin Bailey Gastroenterology 2019;156:418–430
Hepatitis C (left) shows more genetic variability than HIV (right)
Role of broadly neutralizing antibodies in clearance of HCV infection: Ep 347-6 Valerie Kinchen
Antibodies isolated from humans who spontaneously cleared HCV infection blocked many different HCV strains.
Viruses that evolved resistance to these antibodies lost the ability to replicate, suggesting that antibodies are important
for HCV clearance, and an HCV vaccine may be attainable.
Illustration in Fig 1
A) HCV RNA was measured at initial infection and then periodically for more than 6 years. Dashed line indicates limit of detection (LOD) of the HCV RNA assay.
(B) Neutralizing breadth of longitudinal plasma samples or bNAbs HEPC3 and HEPC98 (isolated from C117), bNAbs HEPC74 and HEPC43 (isolated from C110), or CBH-2 (control bNAb). Values are the number out of 19 HCVpp neutralized at least 50% by a 1:50 dilution of plasma, or by 10 mg/mL mAb, tested in duplicate.
Induction of broadly neutralizing Ab in mice using a secreted form of the hepatitis C virus E1E2 heterodimer: Ep 347-7 Rixue Wang PNAS Nov 2022 e2112008119
Three immunogens compared: membrane-bound E1E2; secreted E1E2LZ and soluble E2 ectodomain
Immunogenicity assessment of antibody inducted in immunized mice at day 56 by ELISA.
(A) Mouse immunization schedule.
(B) Anti-mbE1E2 titer. (C) Anti-sE1E2.LZ titer. (D) Anti-sE2 titer
Breadth of neutralization against all HCV genotypes
Day 56 immunized mice pooled sera were analyzed for neutralization using chimeric HCVcc with H77C (GT1a), J4 (GT1b), Con1 (GT1b), J8 (GT2b), S52 (GT3a), ED43 (GT4a), SA13 (GT5a), HK (GT6a), QC69 (GT7a).
Percent neutralization was calculated using RLU normalized to RLU of supernatant cultured without HCVcc nor serum (100%) and RLU of supernatant cultured with HCVcc without serum (0%). ID50 neutralization was calculated from the
sigmoid curve. Dotted line indicates highest concentration of serum.
Attempts to improve neut Ab and avoid non-neut Ab induction
Hepatitis C E1 and E2 glycoprotein structures: Ep 347-8 Sepulveda-Crespo et al. Journal of Biomedical Science (2020) 27:78
a Linear diagram of HCV E1 (aa192–383) and crystal structures of E1 segments aa192–271 and aa314–324.
b Linear diagram of HCV E2 (aa384–746) and ribbon representation of the E2 crystal structure.
E2 is divided into the following structural components: three hypervariable regions (HVR1, HVR2 and igVR), a front layer, two β-sandwich regions, CD81 binding loop, a back layer followed by the stem region and transmembrane (TM) domain.
The neutralizing face with epitopes I (orange), II (violet) and III (blue) is indicated.
Vaccine design is focusing on these “neutralizing” conserved epitopes and deleting hypervariable regions. (see Ep 347-9 Jonathan Guest Viruses 2021, 13, 837)
A T cell based strategy: targeting more conserved Non-Structural proteins
Phase 1 in healthy volunteers: Ep 347-10 Swadling Sc Trans Med 2014:
Priming with replicative defective simian adenoviral vector (ChAd3) and boosting with modified vaccinia Ankara (MVA) vector encoding the NS3, NS4, NS5A and NS5B proteins of HCV genotype-1b.
Induction of T cell (IFN-g) responses against all components and across genotypes
Induction of various cytokines in both CD4+ and CD8+ T cells
Phase 1-2 in adults at risk for HCV based on recent injection drug use 1:1 to vaccine or placebo on days 0 and 56.
Ep 347-11 Kimberly Page NEJM Feb 2021
Unfortunately: no vaccine efficacy against development of chronic HCV
- Lower geometric mean peak HCV in vaccine group: (1805 ×103 IU versus 152.5×103 IU per milliliter resp.
- Clear T cell response in 78 % of vaccinees
An (incomplete) overview of candidate vaccines: Ep 347-12 Joshua Duncan Vaccines 2020, 8, 90;
Why is it so difficult to develop an HCV vaccine (as compared to HBV vaccine)? Ep 347-13 Zingaretti Clin Microbiol Infect 2014
In summary: high variability, no clear-cut correlate of protection and technical issues….
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