retrovirus biology immunology/hiv michael para, md 1
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Retrovirus BiologyImmunology/HIV
Michael Para, MD
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Learning Objectives
Describe the unique features and interrelationship of simple and complex Retroviridae
Identify the major structural components of HIV Describe how HIV replicates Describe and compare the mechanisms of action for the
5 antiretroviral drug classes Describe how HIV becomes drug resistant and how this
is prevented
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better suppression of HIV
PROPERTIES
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GAG PRO
POL
R U5 U3 R -AAA-3’5’-cap-
Simple Retrovirus - ALV
ENV
GAG ENVR U5 U3 R
-AAA-3’5’-cap-
Complex Retrovirus - HTLV
POL
TAX
REX
PRO
Retroviridae are single stranded + sense RNA
4
5
Schematic Diagram of the HIV-1 Viron
GAG PRO ENVR U5 U3 R
-AAA-3’5’-cap-
POL
GAG ENVR U5 U3 R
-AAA-3’5’-cap-
Complex Retrovirus – HIV or HTLV (below)
POL
TAX
REX
PRO
Simple Retrovirus – ALV with 4 genes
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Spliced regulatory genes
oncoviruses
(SIV)
Evolutionary Relationship of Vertebrate Retroviridae
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evolutionary relationships
PROPERTIES
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Schematic Diagram of the HIV-1 Vironenv
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Schematic Diagram of the HIV-1 Viron
matrix
nucleocapsidgag gag
gag
gag
Reverse Transcriptase
env
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Reverse Transcriptase
HIV-1 RT/DNA Complex
thumb
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Mirror image dimer14
HIV Protease with Inhibitor in Active Site
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Genes of HIVStructural and Regulatory - Spliced non-structural
CCR5 on macrophages or CXCR4 in T cells
1.gp120:CD4
binding
2.Conformationalchange of gp120
3.CCR5
Binding
4.gp41:membrane
insertion
5.membrane-env
fusion
gp120
cytoplasm
HIV virus
CD4
gp41
CCR-5
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HIV binding and entry into CD4 cell
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Replication of HIV Video
HIV enzyme function
PROPERTIES
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Live Cycle of HIV-1
Regulatory proteins
Circularizes, Pre-intergration complex
TAT,REV,NEF
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Years
CD
4+ c
ell c
ou
nt
2 4 10 128
1000
800
700
100
200
500
900
300
Death
400
600
AIDS PCP
CMVMAC
acute mono-like illnesslymphadenopathy
acne
folliculitis
tuberculosis
shingles
oral hairy leukoplakia
thrush
tinea
bacterial pneumonia
gingivitis sinusitis
HIVRNA
107
102
103
104
105
Copies/ml
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“Typical” Course of Untreated HIV
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Viral replication
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Zidovudine - AZT
RT with DNA Strands
A closer view of the polymerase active site in the HIV-1 RT/DNA structure. The sites for the commonly occurring resistance mutations for NRTI drugs are indicated.
Nucleoside analogue inserts here causing DNA chain termination
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Mirror image dimer24
HIV Protease with Inhibitor in Active Site
HIV Enzymes
PROPERTIES
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CCR5 on macrophages or CXCR4 in T cells
1.gp120:CD4
binding
2.Conformationalchange of gp120
3.CCR5
Binding
4.gp41:membrane
insertion
5.membrane-env
fusion
gp120
cytoplasm
HIV virus
CD4
gp41
CCR-5
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HIV binding and entry into CD4 cell
Viral Heterogeneity and why resistant mutations develop Genome is ~ 10,000 bases of RNA HIV reverse transcriptase has a high error rate of ~ 1 base
mismatch in every 3-5 x 104 bases So for each replicative cycle viruses differing by 2 bases from the
input virus are produced and leave the cell. With its rapid replication cycle, ~ 1-10 billion new virions/day are
produced In an untreated infected patient, a virus with every possible
mutation is produced at least once every 24 hours. Some mutations allow the virus to escape immune response e.g.
neutralizing antibodies Mutations at enzymatic site may impart drug resistance
Clavel, F. et al. N Engl J Med 2004;350:1023-1035
Panel A HIV-1 Protease Dimer Binding a Protease Inhibitor
Panel B Drug-Sensitive (Wild-Type) Protease Juxtaposed against a Drug-Resistant Protease
protease inhibitor
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65432101
2
3
4
5
6
Single NucleosideDouble Nucleoside2 NRTI+PI or NNRTI
Months of Treatment
Lo
g R
NA
co
pie
s/m
L o
f b
loo
d
Baseline
Lower limit of measurement
ZDV max fall 0.7 log
ZDV+3TC max fall 1.8 log
ZDV+3TC+PI max fall >3 log
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10
10
10
10
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Effect of Treatment on HIV Viral Load
combinations of multiple antiviral drugs
PROPERTIES
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Summary
Simple retroviruses have just 4 genes – 2 structural and 2 enzymes – and complex Retroviridae also have regulatory gene(s).
Envelope, capsid and RNA are major viral structures. The virus binds to cell, fuses viral and cell membranes, transcribes RNA to
ds DNA (reverse transcription), enters nucleus and integrates into cellular DNA. Sometime later cell produces viral mRNA, and genomic RNA and produces viral proteins, assembles and buds off cell.
There are binding inhibitors, membrane fusion blockers, nucleoside and non-nucleoside reverse transcriptase inhibitors, integration inhibitors, and protease blockers.
HIV RNA develops a mutation nearly every time it goes through RT. These mutations can be at site of action of the antivirals making offspring virus resistant to that drug. To prevent the virus resistant to one drug from overgrowing in the presence of the drug, multiple anti-HIV agents are used in combination.
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