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Towards a small animal model
for hepatitis C
Alexander Ploss & Charles M. Rice
EMBO reports (2009) 10, 1220 - 1227
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Hepatitis C virus
•Hepatitis C virus (HCV) causes chronic liver
diseases.
•Can lead to cirrhosis, liver failure and liver cancer.
•130 million people infected worldwide
•Current Interferon treatment is often ineffective
and poorly tolerated
•No vaccine available till date.
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HCV life cycle
Drawbacks to HCV research
Chimpanzee are the only available
immunocompetent experimental system.
Use limited by ethical constraint, restricted
availability and high costs
Preferred animal model due to easy
availability and handling, economical and
complete genome information available
Approaches towards animal model
Viral adaptation to infect non human cells
Genetic host humanization to adapt the rodent
tissues
Xenotransplation of human tissues
Viral adaptation
Sera inoculated from HCV infected individual resisted due to block in HCV
entry
CD81 and OCLN must be of human origin to permit HCV infection
Expression of mouse CD81 in human hepatoma cells causes very low
infection probably due to reduced affinity
Mouse CD81 is 90% homologous to human; 4 unconserved key residues
HCV can be adapted in vitro to use mouse CD81;
Selection of three mutations in E1 and E2 enhanced mouse CD81
dependent uptake to levels comparable to human orthologue
Viral adaptation
Studies show HCV entry and replication in murine environment; assembly
and release of infectious virions are unclear
Increasing viral replication can allow detection of infectious virus by
expression of cDNA transgene encoding entire HCV genome
Generation of proper 5’ and 3’ ends of HCV genome crucial, production of
infectious HCV from stably HCV cDNA-transfected HepG2 has been
reported
Additional adaptation steps necessary to select for genomes with
assembly competence in a mouse cell environment
Viral adaptation
The efficiency of murine tropic HCV infection to that of human
cells expressing the mouse entry factors is uncertain
Post entry additional restriction might exist, thus virally encoded
replication machinery might not adapt to murine counterpart
Modifications affecting species tropism might have significant
efforts on immune responses and pathogenesis
Xenotranplantation model
Chimeric mice harboring HCV permissive tissue can be obtained,
susceptible to human hepatotropic pathogens
Alb-uPa transgene overexpression results in severe liver damage rescued
by transplanting non transgenic (human) hepatocytes
Xenotransplanted humanized mice are potential for studying drug and
vaccine efficacy as well as pharmacokinetics and toxicity
Application limited by less production, substantial variability and logistical
constraints.
Pathogenesis and immunity studies impeded by absence of functional
immune system-required to avoid xenograft rejection
Xenotransplantation model
Combination of humanized liver model with mice harbouring a human
haematolymphoid system
Generation by engrafting suspensions of human haematopoetic progenitor
stem cells into immunodeficient animals, virus-specific immune response
can be elicited on successful human immune reconstitution
Merging hepatic and haematolymphoid reconstitution in a single recipient
will allow studies of pathogenesis, immune correlates and mechanisms of
persistence of HCV and other human hepatotropic pathogens
The generation of these types of humanized mice requires substantial
infrastructure and advanced technical skills
Host adaptation
An inbred mouse model with inheritable susceptibility to HCV would
overcome the technical difficulties of the xenotransplantation model
Efforts for genetic adaptation of human CD81-transgenic mice were resistant
to HCV infection
Functional cDNA complementation screen approach could identify critical
human factors required for efficient HCV RNA replication in mouse cells.
Liver specific miRNAs- miR122 and miR199a have shown to affect HCV
RNA translation and replication
Dominant-negative restriction factors causing altered innate antiviral
responses or inability of HCV proteins to overcome murine defences could
impair HCV replication in mouse.
Host adaptation
Several genetic adaptations to humanize the murine host are required to
create an inbred mouse model for HCV infection which could be a
platform for further improvements designed to mimic more closely the
clinical features of human hepatitis.
Studies to identify crucial human factors is dubious due to minimal overlap
and relevance of HCV interactions yet to be demonstrated
Sequence divergence of identified factors might reduce the infectious
capacity and affect tropism.
Conclusion
HCV infection aggravated by insufficient therapy and lack of proper
vaccine
A robust animal model easily propagated and reproducing the viral life
cycle would be instrumental in understanding HCV pathogenesis and to
guide drug development
Deciphering the barriers to HCV replication in mouse cells will provide
rich insights into virus host interactions directing towards a sustainable
mouse model of HCV infection.