stalking a killer: respiratory syncytial virus
TRANSCRIPT
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Stalking a Killer: Respiratory Syncytial Virus
Mark E. Peeples, Ph.D.
Center for Vaccines & ImmunityThe Research Institute at Nationwide Children’s [email protected]
ProfessorDepartment of PediatricsOSU College of MedicineCenter for Microbial Interface BiologyPublic Health Preparedness for Infectious Diseases
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Goals for Today• Describe the ‘life’ of a virus• Discuss RSV and the disease it causes• Explore
– Attempts at treatments and prophylaxis – Why we don’t have a vaccine to protect us– What we are doing to
• Understand RSV better• Solve the RSV problem
• What the heck does ‘syncytial’ mean?
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What is a virus?• Very small• Has no life of its own
– A freeloader, a parasite • Gets inside one of your cells and takes over• Produces 100’s of identical viruses
– These viruses infect more of your cells, and so on• Until your immune system stops it
– Or they are spewed onto your friends (or whomever)
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My “measles birthday” 1958
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How is RSV spread?
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Lower
Upper
Respiratory TrRSV infects the upper respiratory tract 1st
• If the immune system stops infection: common cold (most of us)
• If it moves to the lower respiratory tract, RSV can cause disease• Infants (no immunity)• Elderly (losing
immunity)
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RSV as a Public Health Problem
• RSV is the #1 cause for hospitalization at children’s hospitals
• Only present November-March
• Worse for premies
RSV is second only to influenza virus as cause of “excess deaths” of the elderly
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RSV Prevention/Treatment• No vaccine
– Attempt in the 1960’s was disastrous• Killed vaccine
– Since then, focus on live, attenuated virus vaccine• Goal: prevent lower respiratory tract infection
• No effective antiviral agents• Prophylaxis for premature infants
– Synagis (MedImmune/AZ): monoclonal antibody • Expensive
– But less than treatment in the PICU
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Respiratory Syncytial Virus• Single strand RNA virus
– Negative sense• Paramyxoviridae family
– Pneumovirinae subfamily• 10 genes encoding 11 proteins
3’ 5’
Leader
NS1 NS2 N P M SH G F M2-1 L
Trailer
GFP Gene
GSGE
M2-2
Suppress the immune system
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P protein
N protein
L protein
Glycoproteins:
M protein
F (fusion)
G (attachment)
Lipid membraneGenome(RNA)
M2-1 protein
RSV virion
SH
Virion’s goal: Deliver the virus genome to the next cell
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Initiation of RSV Infection• Its G protein binds to a “receptor” on the cell
surface• Only cells expressing the receptor are susceptible to
RSV infection• Its F protein causes the virion membrane to fuse
with the target cell membrane• Result: the guts of the virus are spilled into the
cytoplasm of the target cell• The virus begins to replicate
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Transcription
Genome (-)
Uncoating
Adsorption
ribosome
ER
nucleus
Golgi
Respiratory Syncytial Virus Life Cycle
ER
nucleus
TranslationN P M2-1 L
Golgi
F
G
Assembly
Budding
Progeny virions
Antigenome (+)
Genome ( - )
Replication
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RSV infection of immortalized (HeLa) cells
Syncytia
(We have built the GFP gene into RSV)
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What is the natural target cell for RSV?
• NOT HeLa cells (from a cervical tumor)• (But they are easy to study)
• Human airway epithelial cells• Not so easy to study• Essential for understanding RSV
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Lower
Upper
Respiratory Tract
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Primary Well Differentiated Human Airway Epithelial (HAE) Cultures
Zhang, et al, 2002
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Zhang, et al, 2002
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2 days 8 days 14 days
Zhang, et al, 2002
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RSV Infects the Apical Ciliated Cells
Zhang et al., 2002
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Zhang, et al, 2002
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Does the Cell Source of RSV Matter?
0.01
0.1
1
10
100
1000
10000
rgRSV-SGF rgRSV-F rgRSV-SF rgRSV-GF rgRSV259 rgRSV30
Num
ber o
f Inf
ecte
d C
ells
Virus from HeLa on HEp-2
Virus from HeLa on HAE
Virus from HAE on HEp-2
Virus from HAE on HAE
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Things We’ve Learned that May Improve the Attenuated Vaccine
• Problem: can’t grow enough attenuated RSV vaccine to make it economically feasible– Must grow in a WHO-approved cell line (Vero)
• We have found that: – This vaccine is 1,000 times less infectious for HAE cells than the same
virus produced in HAE cells• The RSV G protein is destroyed in Vero cells• The RSV G protein is not modified properly in any cell line
• If we can fix both of these problems, we should be able to boost vaccine production 1,000 times, easily making it economically feasible
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Adult Vaccine: RSV F Protein• A live attenuated virus vaccine might cause disease if
– A weakened immune system• A protein vaccine would not have that problem
– Would ‘remind’ the adult immune system • It probably would not be used in infants
– Fear: infants might react as they did to the killed virus vaccine• Previous attempts to immunize adults with F protein
– Not toxic– But, not very potent
• Since that time we have learned…
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Pretriggered Posttriggered
RSV F protein has two forms
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Movie Time!
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Pretriggered Posttriggered
We have been able to produce a soluble version of the F protein in its pretriggered form• What causes it to
trigger?
Reduced salt concentration
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Pretriggered Soluble F Protein
• Better vaccine for adults?– Induce better antibodies than previous F vaccines?– We are working to stabilize the pretriggered form
• Supported by a pharmaceutical company
• I was recently appointed to a Board – Funded by the Bill and Melinda Gates Foundation – Produce a vaccine for financially restricted countries– Vaccinate pregnant women
• Transfer of protective antibodies across the placenta
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Pretriggered Soluble F Protein
• Use to test antiviral drugs– Do the drugs cause triggering?
• Or do they prevent triggering?
• Use the F protein model to design better drugs– Crystallize the F protein, determine its exact
structure– We are working with a different pharmaceutical
company
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Summary of a Killer Virus: RSV
• Virus ‘life’ begins at infection– After fusion of the viral membrane with the
cellular membrane
• RSV causes disease in the youngest and oldest– Can’t stop movement of the virus to the lower
respiratory tract• Major burdens on the health care system in US• Major cause of death in the developing world
– Common cold in the rest of us
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Summary of a Killer Virus: RSV• Treatments/Prevention
– Antibody treatment protects premies (expensive)– No vaccine yet
• Killed vaccine trial was a disaster (1960’s)• Attenuated virus is being explored for infants
– Can’t produce enough vaccine to be economically viable– Our lab has discovered 2 problems in the G protein
» Solutions could increase vaccine production by 1,000-fold• F protein vaccine is being explored for the elderly
– Our lab has produced the F protein in the pretriggered form– Does it induce better immunity than the posttriggered F?
– No small molecule antiviral drug yet• We are using our pretriggered F protein and triggering
conditions: Do drugs prevent or cause triggering?• ‘Syncytia’ are giant cells, fused by the RSV F protein
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AcknowledgementsPeeples Lab at Nationwide Children’s
– Supranee (Koi) Chaiwatpongsakorn– Heather Costello– Sara Johnson– Sara Mertz– Zack Risch– Olga Malykhina– Steve Kwilas– Anna Kwilas– Louay Hallak– Mark Yednak– John Manaloor– Barb Newton– Arife Unal– Lenora Yambao
Funding– NIH P01 HL051818 – NIH R01 AI047213– Apath, LLC– MedImmune, LLC– Johnson & Johnson (Tibotec)– Cystic Fibrosis Foundation Therapeutics– Nationwide Children’s Hospital
Collaborators– Peter Collins, NIH– Ray Pickles, UNC
• Liqun Zhang, Rachel Leisman– Will Ray, TRINCH– Richard Epand, McMaster – Ed Walsh, U Rochester– Paul Olivo, Apath; Diagnostic Hybrids– Octavio Ramilo, TRINCH– Asun Mejias, TRINCH– Emilio Flano, TRINCH
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Target cell
6-helix bundle
Target cell
Virion
F protein mediated fusion
pre-HRA
HRB
Target cell
Virion
Straightens out
Fusion peptide inserts
Target cell
Virion
Pretriggered Prehairpinintermediate
Posttriggered(6HB)
Infection/Syncytia
Triggering Fold-BackMembrane
fusion
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A B
Site A
Site B
Site C
Site B
Site A
Site C
C
Site C
S3
S1
Site AS1
Site C
S1
S2
Site BS1
Head
Head
PrePost Pretriggered
Trimer
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Pre-triggered form Top view
Model of RSV F Protein Trimer Will Ray