L6 Hepatitis C Virus Flashcards
What does immune-screening involve?
Using the human antibodies to find the viral proteins
How can Hepatitis C virus (HCV) be transferred?
By transfusion of blood or blood products, as well as non-sterile medical measures
HCV infection can cause…
chronic liver inflammation, leading to cirrhosis and liver cancer
What percentage of infected people can develop a chronic life-long infection?
70-80%
What cancer is commonly associated with HCV infection?
Hepatocellular carcinoma (HCC)
Features of HCC
- highly malignant tumour with poor prognosis
- high levels of anti-HCV present
- 97% have cirrhosis
Which genotype is associated with higher rates of HCV-associated HCC?
Genotype 1b
Briefly explain how erythrocyte destruction can occur when a Rh- woman has given birth to a Rh+ baby
- Erythrocytes from a Rh+ foetus leak into the maternal circulation, usually during birth
- This stimulates the production of anti-Rh antibody of the IgG class postpartum
- During subsequent pregnancies, IgG antibodies are transferred across the placenta into the foetal circulation
- If the foetus is again compatible, the antibodies cause erythrocyte destruction
What can be used to treat Rhesus negative mothers who have had a Rhesus positive baby?
Anti-D immunoglobulin (available since 1970)
It eliminates the Rh+ erythrocytes and prevents sensitisation
Which genotype is the most resistant to therapy?
Genotype 1a
Around how long does an acute HCV infection last?
from 0-24 weeks, often remains undetected
What are the most important causes of mortality in end-stage chronic Hepatitis C (CHC)?
cirrhosis and hepatocellular carcinoma (HCC)
HCV structure
- enveloped virus
- positive-sense ssRNA genome
- capsid
- virus-encoded proteins present in lipid bilayer
HCV is part of which family?
HCV is a Hepacivirus (Flaviviridae family)
What is the IRES in HCV?
IRES = internal ribosomal entry site
Contains regions of dsRNA - used by virus to bind ribosomes and start translation
How does HCV enter the cell?
HCV binds to hepatocyte cell surface protein receptors and enters the cell by receptor-mediated endocytosis
Examples of hepatocyte cell surface receptors to which HCV bind
- LDLRs on the basolateral hepatocyte surface
- CD81
- tight-junction proteins claudins (CLDN-1 and OCLN)
Innate immunity receptors involved in HCV detection
- TLR7: detects ssRNA (endosome)
- TLR3: detects dsRNA in replicating ssRNA viruses
- (RLR) RIG-1 (retinoic acid-inducible gene 1) detects ssRNA (cytoplasm)
- PKR (RLR) detects dsRNA (in HCV genome, it detects dsRNA in IRES at 5’ end)
Detection of HCV RNA leads to?
activation of transcription factors (NF-κβ, IRF3, IRF7), which leads to the production and secretion of cytokines and Interferons (anti-virals)
What is the HCV protease that inhibits the immune system in a number of different ways?
NS3-NS4A
How does NS3-NS4A inhibit the immune system?
- cleaves HCV polyprotein several times to liberate NS proteins
- blocks RIG-1 signalling by cleaving MAVS from intracellular membranes to prevent signals (results in lower IFNs)
- blocks TLR3 signalling by cleavage of TRIF
- NS3-NS4A and E2 protein blocks PKR activity
HCV genotypes
(i) Genotypes 2 and 3: highest IFNα treatment response rates, 70-80%
(ii) Genotypes 1 and 4: only curative in 40-50% of cases
IFN induces the expression of 100s of…
IFN stimulated genes (ISGs), that have anti-viral and immuno-modulatory activities
Genotypes 1 and 4 induce high levels of __ in infected patient’s liver before therapy, resulting in a less effective IFN response.
hepatic ISGs
What is Ribavirin?
a guanosine analog used to stop viral RNA synthesis in HCV infection
What is sustained virologic response (SVR)?
defined as an undetectable level of HCV RNA, 12 weeks after the end of therapy - virological surrogate for clinical cure
What drug was often combined with Ribavirin to initially treat HCV infection?
pegylated Interferon-α (PEG-IFNα)
(usually for 24-48 weeks)
Most individuals that clear HCV do so within the first __ months
6
After how long do CD4+ and CD8+ cells present in the liver of most patients infected with HCV?
4-8 weeks
What factors play a role in disease progession?
- HCV genotypes (viral factors)
- Host factors
- Genetics
- The nature of early hepatocyte immune response to HCV infection
Are side effects common with IFN-α therapy?
Yes
Type 1 vs Type 3 IFNs
Type 1 = IFNα, IFNβ
Type 3 = IFNλ3, IFNλ4
Factors that influence therapy responses to PEG-IFNα
- Viral genotype variation (1&4 vs 2&3)
- The patient’s IFNλ3 & IFNλ4 genotypes
- The activation status of hepatic ISGs before therapy
- Role of patient MHC/HLA and HCV antigen presentation to T cells in clearance of HCV or chronic HCV infection
Which genotypes have the best clinical outcome of IFN treatment?
Genotypes 2 and 3
Which HLA molecules are associated with spontaneous clearance of HCV infection?
HLA-B27, HLA-B57, HLA-A03
What single nucleotide polymorphism, located upstream of the IFNλ3 gene is strongly predictive of HCV clearance?
rs12979860
Individuals carrying a __ __ __ __ __ in IFNλ4 allele are strongly associated with decreased clearance of HCV infection
ΔG frame-shift exonic genetic variant
Where is the HLA-B27 binding epitope located?
within a conserved region of the RNA-dependent RNA polymerase (NS5B 2841-2849)
What is the effect of the HLA-B27 binding epitope?
It puts fitness constraints on HCV’s ability to mutate this locus and avoid peptide presentation by HLA-B27 and detection of epitope by corresponding CD8+ T cells
What amino acid sequence does HLA-B27 bind in NS5B 2841-2849
ARMILMTHF (basically if you have this aa code you will clear the virus, if you don’t have it you will struggle)
HLA-B27 is not protective in which HCV genotype infection?
3
What dictates infection outcome?
Combination of host’s antigen presentation genes/proteins and what HCV genotype the host is infected with
What were the first Interferon-free direct acting antiviral (DAA) treatments that were approved in 2011?
HCV protease inhibitors, Telaprevir (TLV) and Boceprevir (BOC)
The combination of which drugs increased the percentage of patients who showed an SVR to 75%?
PEG-IFNα + Ribavirin + Telaprevir/Boceprevir
HCV NS4A interacts with?
HCV NS3
NS5A plays multiple roles in?
- mediating viral replication
- host cell interactions
- viral pathogenesis
Main targets for DAAs
- NS3/NS4A polymerase
- NS5B polymerase
- NS5A replication complex
What new protease inhibitor (DAA) was approved in 2014 and why?
Simeprevir (SMV) because it was a once daily dose with less toxicity issues. SVR increased to 81% when given with PEG-IFNα + Ribavirin
What was the first NS5B polymerase inhibitor approved?
Sofosbuvir (SOF)
(resistance barrier to SOF much higher compared to PIs)
What drug combination results in a SVR of ~92%?
SOF + SMV
Example of a NS5A inhibitor
Velpatasvir (VEL)
What genotype accounts for ~20% of global HCV?
3
(resistance-associated variants)
