Microbial Pathogenicity Antigenic Variation & Vaccine Development

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Microbial PathogenicityAntigenic Variation
Vaccine Development
Kevin Coombs kcoombs_at_cc.umanitoba.ca
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Fields Virology, 2001
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Kinetics of endogenous immune responses
Biron Sen (2007) Fields Virology, Chapter 9
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Viral-induced Signaling pathways
Biron Sen (2007) Fields Virology, Chapter 9
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Summary of innate immune responses
Biron Sen (2007) Fields Virology, Chapter 9
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Fields Virology, 2001
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Class I Antigen Processing
Yewdell et al Nature Immunol 3 1019
Nature Reviews Immunology 2 283-291 (2002)
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Class II Antigen Processing
Nature Reviews Immunology 1 126-134
(2001)CROSS-PRESENTATION IN VIRAL IMMUNITY AND
SELF-TOLERANCE
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Humoral Immunity
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What is antigenic variation ?
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Nucleic acid mutation rates
What contributes to Ag variation ?

• Chromosomal DNA 1 1010 - 1011
• DNA virus 1 108 - 109
• RNA virus 1 104 - 105

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Implications of high mutation rate
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Reoviridae
Orthomyxoviridae
Some viruses have segmented genomes Allows
assortment
T1L T2J T3D
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Segmented Genomes Allow Assortment
X
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Viruses with Segmented Genomes
Influenza (8 genes) 256 possibilities Rotav
irus (11 genes) 2048 possibilities
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RNA viruses with segmented genomes have capacity
to generate altered genomes by both random
mutation (where rates are high) and by assortment
In Orthomyxoviridae random mutation leads to
Genetic drift and assortment leads to Genetic
shift
Influenza pandemics generally result from
assortment of human and avian influenza viruses
in a pig mixing vessel which results in new
virus
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Junction adhesion molecule
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Orthomyxoviridae
SPECIFIC VIRUSES
Current genera
100nm virion Pleomorphic Segmented Genome
(7-8 segments) ss(-) RNA Enveloped
Influenza A Influenza B Influenza
C Thogotovirus Isavirus
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History and Impact

• Epidemics documented since 1173 AD
• 1918 Pandemic Spanish Flu (HINI)
• - Killed 20 50 Million
• 1957 Asian Influenza ( H2N2)
• 1968 Hong Kong Flu (H3N2)
• 1997 - H5N1 outbreak / 18 infected / 6 die
• 2004 - ( H5N1) 408 cases so far Avian Flu
  / 254 deaths (WHO, Feb. 18)
• Yearly Epidemics lead to approx. 2000 deaths in
  Canada, 1M deaths globally

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Bird Flu
An Introduction and Call to Action Jan 3, 2006
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Orthomyxoviruses
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What about Humans?

• 408 people have become infected
• 254 have died
• There have been many more suspected cases not
  tested
• More humans died in 2006 than in the previous 3
  years combined

Cumulative cases as of Feb. 18, 2009 Total
Cases 408 Total Deaths 254 (WHO
database)
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H5N1 Compared to 1918 Flu

• For Both Flu types
• - the virus came directly from birds
• - young and healthy make up most fatalities
• - The human immune system creates
  cytokine storm, filling the
  lungs with fluid

• The 1918 flu had a Case Fatality Ratio of 2.5
• H5N1 has a Case Fatality Ratio of 60

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B
Noda et al., (2006) Nature 439490
Figure 1. Influenza A/PR/8/34 genetic and
structural organization. A. Gene protein coding
assignments characteristics. B. Virus
structure Top, electron micrograph Bottom,
Diagrammatic cartoon of virion, with proteins
designated as in A, middle column.
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Phylogeny of Influenza A H and N Genes
Fields Virology, 2007, Chapter 47
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Fields Virology, 2007, Chapter 48
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CAP SNATCHING
n-n-n-n-n-n-n-n-n
n-n-n-n-n-n-n-n-n
n-n-n-n-n-n Cellular mRNA
A G
n-n-n-n-n-n-n-n-n-n-n-n-
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n-n-n-n-n-n-n-n-n-n-n-n-
A
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Viral RNA (-)
n-n-n-n-n-n-n-n-n-n-n-n-
mRNA ()
5
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• Mediated by PB2
• Essential to terminate with a G residue

Viral RNA (-) template
- position 16

• Mediated by PB1
• Progeny mRNA ()
• TL into proteins

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Influenza Variation
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Influenza virus transmission/assortment
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• The recurring nature of influenza is due to its
  ability
• to vary surface antigen expression

• Antigenic Drift
• Due to subtle changes of the viral genome
• Changes antigenic character of H and N
• Responsible for epidemics

• Antigenic Shift
• Due to rearrangement of viral gene segments when
  two different influenza viruses infect the same
  cell
• Produces major changes in the antigenic nature
• Responsible for epidemics and pandemics

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Pico rnaviridae
Very small
30nm non-enveloped icosahedral particles 60
copies each of VP1, VP2, VP3, VP4 Genome 7-8kb
ss() RNA 5 genera Enteroviruses 111
strains(poliovirus)
Rhinoviruses 105(common cold) Hepatovirus
2(hepatitis A) Aphthovirus 8(Foot and
mouth) Cardiovirus 7(Encephalomyocarditis)
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Overview of picornavirus life cycle
Baltimore Class IV Cytoplasmic Polyprotein
cleavage All proteins amounts No
glycosylation No splicing RNA replication
through full-length (-) strand
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Translation and processing of picornavirus
proteins
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Internal Ribosome Entry Site (IRES)
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Translation and processing of picornavirus
proteins
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Picornavirus receptors
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Anther prototypic Class IV ss() RNA virus (ex.
Coronaviridae)
www.microbiologybytes.com
www.microbiologybytes.com
Different Coronavirus transcripts are produced by
differentially transcribed messages The genome
is copied into a full-length (-) copy, from which
various sub-genomic () are transcribed
www.microbiologybytes.com
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Vaccine Development Considerations

• Which agents should be targeted ?
• Who should be vaccinated ?
• What constitutes a good vaccine ?
• Live vs Dead

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Fields Virology, 2001
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CDC, 2005
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CDC, 2005
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Are all Antibody Responses Good ?
Fields Virology, 2001
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Fields Virology, 2001
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from Ponnuraj et al., J. Gen. Virol. (2001) 82
2663-74
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Fields Virology, 2001
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Polio Eradication Program (WHO)
Year
1988
1997
2003
WHO, 2004
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news.bbc.co.uk/2/low/africa/3725470.stm
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Fields Virology, 2001
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Genetic Relatedness Between Vaccinia Virus and
Variola major Brunham Coombs (1998) CJIDMM