Transcript 04 M401 Host Defense 2012 - Cal State LA

Host Defense:
Vaccine,
Interferon,
Antiviral Drugs
Combating Infectious
Diseases
• Prevention by Public Health:
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Epidemiology
Control
Education
Vaccines
• Treatment by Medical Science:
– Supportive
– Corrective
– Drugs
• Which is preferred?
• More cost effective?
Vaccination and Immunity
• The process of using inactivated or
attenuated pathogen (or portion) to induce
immune response in individual prior to
exposure of pathogen
• Humoral Immunity (antibody, complement)
• Cell-Mediated Immunity (macrophage, T
lymphocytes)
Killed-Virus Vaccine
• Virulent wild type virus
• Made noninfectious by chemical
treatment (formalin,
betapropiolactone)
• Salk inactivated poliovirus (IPV)
Salk Inactivated
Poliovirus Vaccine (IPV)
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Efficacy – High
Route – Intramuscular injection
Dose / Cost – High
Antibody – IgG
CMI – Poor
Heat labile – No
Interference by other viruses – No
Revert to virulence - No
Use in immune compromised patient - Yes
Live-Virus Vaccine
• Avirulent – mild or no disease
– Vaccinia virus (cowpox?)
• Attenuated – mutated wild type virus
no longer pathogenic
– Sabin oral poliovirus (OPV), not able to
get into CNS
Live - Sabin Oral
Poliovirus Vaccine (OPV)
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Efficacy – High
Route – Oral (natural transmission, infection)
Dose / Cost – Low
Antibody – IgG, IgA
CMI – Good
Heat labile – Yes
Interference by other viruses – Yes (other
Enterovirus infections)
• Revert to virulence – Yes (rare, 1/300,000 doses)
• Use in immune compromised patient - No
Subunit Vaccine
• A viral protein or
glycoprotein that elicits
protective immunity
• May be isolated from virion
– Influenza vaccine (HA, NA),
grow virus in chick embryo,
isolate viral proteins
• May be made in recombinant
expression vector
– HBV vaccine (HBsAg
glycoprotein), grow vector in
yeast cells
Experimental
Recombinant Vaccine
• Recombinant Virus –
introduce viral gene
into another virus by
gene recombination
i.e., HIV gp120 gene
into Vaccinia virus
Experimental DNA Vaccine
• Direct intramuscular injection of
viral DNA gene
• Gene expression and viral protein
synthesis
Experimental Plant Vaccine
• Insert viral gene into plants (potato,
tomato, banana)
• Oral vaccine ingested, elicit immune
response
Experimental HIV Vaccine:
Neutralizing (Blocking) Ab
Interferon: Cell
Antiviral Defense
• 1957 – Isaacs & Lindenmann studying
influenza virus in chick embryo
• Identify soluble substance in allantoic
fluid that blocks influenza virus infection
in chick embryo
• Inhibitor termed “interferon”
• Now known to be a cell cytokine (signal
transducer)
Properties of Interferon
• Species specific
• Induced soon (hours) following virus
infection
• Inhibits various viruses
• Acts indirectly – induces antiviral effector
molecules (AVEM)
• Inhibits cell division
• Activates immune system
• Induces fever
Classes of Interferon
(IFN)
• IFN-α made by leukocytes
• IFN-β made by fibroblasts
• IFN-γ made by T lymphocytes
Inducers of Interferon
• RNA viruses
• dsRNA (synthetic
poly I-C)
• Intracellular MO’s
(protozoa,
rickettsia)
• Bacterial endotoxin
Activity of Interferon
• IFN made and
secreted from virus
infected cell
• Binds to specific cell
receptor that triggers
a signal transduction
cascade
• Prepares the cell to
combat virus infection
by expressing three
proenzymes termed
antiviral effector
molecules (AVEM)
Antiviral State In Cell
(AVEM): Three Proenzymes
• 1) 2’,5’-oligoA
synthetase (OAS)
• 2) dsRNAdependent protein
kinase (PKR)
• 3) RNAse-L
• Proenzymes, when
activated, inhibit
viral replication
OAS-Activated Cell
• Viral infection (dsRNA) activates the
proenzyme OAS
• 2’,5’-oligoA is maded
• 2’,5’-oligoA activates proenzyme RNAse-L,
which cleaves mRNA
• No mRNA, translation STOPPED
PKR-Activated Cell
• Viral infection (dsRNA) activates the
proenzyme PKR
• Ribosome translation initiation factor
(eIF2) is phosphorylated by activated PKR
• No ribosome initiation complex
• No ribosome formation, translation &
protein synthesis STOPPED
Clinical Use of
Interferon: Antiviral
• Available in adequate amount since 1980s
by recombinant DNA technology
• Life threatening infections – rabies,
hemorrhagic fevers, encephalitis due to
arboviruses
• Persistent chronic infections - hepatitis B
hepatitis C, papilloma, herpesvirus, HIV
Clinical Use of
Interferon: Anti-Cancer
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Leukemia / lymphoma
Multiple myeloma
GI tumors
Kidney, Bladder cancer
Mesothelioma (lung cancer)
AIDS-related Kaposi’s sarcoma
(Human Herpes Virus-8)
Interferon: Toxic
Side-Effects
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Fever
Chills
Headache
Nausea & vomiting
Anorexia
Rash, dry skin
CNS – depression, dizziness, confusion
Current Use of
Interferon
• Combination with other antivirals
• Lipid formulation
– Not as readily degraded
– Better delivery to target cell
– Less toxicity
Antiviral Drugs
• Virus & host cell replication closely
related
• Antiviral requires
– Low toxicity for host cell
– Selective toxicity for virus
Testing For Safety of
Antiviral
• Laboratory: Cell culture & animal
testing
• Clinical Trials in Humans:
– Phase 1 test for safety
– Phase 2 test for efficacy
– Phase 3 test for efficacy in a large
population
Therapeutic Index (T.I.)
for Antiviral
• Measure tolerated dose (not
toxic/lethal)
• Measure curative dose (decrease
disease or death)
• Therapeutic Index = tolerated dose /
curative dose
– T. I. = 1/1 = ≤ 1 (toxic)
– T. I. = 1/<1 = >1 (safe)
Antivirals: Nucleoside Analogues
Acyclovir & Herpesvirus
• Nucleoside analogue
• Target viral enzymes
in DNA synthesis
• Herpesvirus
thymidine kinase
activates acyclovir
• Viral DNA polymerase
incorporates acyclovir
into growing DNA
chain
• DNA synthesis
STOPPED due to
chain termination
Rimantadine (Flumadine) Influenza A Virus
• Synthetic cyclic amine
compound
• Stops virus
Uncoating/Maturation
• Prevents acid pH required
for membrane fusion, by
blocking viral M2 (ion
channel) protein
• CNS side effects:
dizziness, ataxia, insomnia,
convulsions
Neuraminidase Inhibitor
(Zanamvir) - Influenza Virus A, B
• Drug blocks neuramindase
(NA), virus release
STOPPED
• During budding, virus
hemagglutinin (HA) readily
binds to neuraminic acid
(sialic acid)
• NA cleaves sialic acid to
insure release of virus from
cell
• NA inhibitors are sialic acid
analogues
• Competitive inhibitor of
virus NA enzyme
Neuraminidase Inhibitors
• Oseltamvir (Tamiflu) – oral, pill
• Zanamivir (Relenza) – nasal, inhaler
• Need to be given within 48 hr.
infection
Antivirals Against HIV
• Reverse
transcriptase (RT)
nucleoside inhibitors
– Azidothymidine
• RT non-nucleoside
inhibitors
– ddC, ddI
• Protease inhibitors
– Saquinavir
• Entry inhibitors
– Enfuvirtide
• DNA Integrase
inhibitor
– Raltegravir
Protease Inhibitor
This picture shows the HIV protease (purple
and green) complexed with the inhibitor
(spacefill). This prevents the substrate from
reacting with the protease and thus, the
polypeptides are not cleaved.
Current Treatment for HIV
• “Cocktail” – combination of four or more
drugs
• Decease virus load (# progeny virus) in
blood
• Clinical “latency”
• Prolong life
• High cost
• HIV reservoir in lymphoid tissue (replicate
in low #)
Experimental Antiviral:
Antisense Oligonucleotide
• ssRNA or
ssDNA
complimentary
to viral mRNA
made
• Will combine
with viral mRNA
and prevent
translation
• Essential viral
protein
STOPPED and
virus replication
stopped
Reading & Questions
• Chapter 8: Strategies to Protect
Against and Combat Viral Infections
(omit Question 1)
QUESTIONS???
Class Discussion – Lecture 4
• 1. How is virus replication stopped in
interferon-treated cells?
• 2. Is a cell treated with interferon able
to make interferon if it is infected by a
virus?
• 3. At what steps are current antivirals
effective in stopping virus replication?
• 4. Why is the antiviral drug, acyclovir,
more selective for herpesvirus? How does
it stop herpesvirus replication?