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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Introduction to Retroviruses
Basic Biology of HIV-1
Vivek R. Nerurkar, Ph.D.Professor and Chair
Department of Tropical Medicine, MedicalMicrobiology and Pharmacology
John A. Burns School of Medicine
University of Hawaii at Manoa
Translational Research in
NeuroAIDS and Mental Health
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Retroviridae IntroductionFamily/ClassificationStructure/GenomeLifecycle
HTLVHTLV-1Structure/GenomeLifecycleTransmission
Learning Objectives
HIV IntroductionFamily/ClassificationStructure/GenomeLifecycle/BiologyTransmission/
Pathogenesis
Diagnosis/Treatment Retroviruses and
neurological disorders
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Retroviridae: Introduction
Retro (Latin) = backwards Unique life cycle
Large and diverse group of viruses found in allvertebrates
RNA viruses reverse transcribed into DNAintegrate into host chromosomal DNA (provirus)
template for virus replication and protein expression
Retroviruses are RNA viruses that copy theirgenome into DNA during their replication.
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Retroviridae: Introduction
Provirus:PersistenceVertical transmissionMutagenic
Disease-Immunodeficiency diseases
Leukemia's
Solid tumors
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Alpharetrovirus Avian leukosis virus (ALV)
Rous sarcoma virus (RSV)
Betaretrovirus Mouse mammary tumor virus (MMTV)Mason-Pfizer monkey virus (MPMV)
Gammaretrovirus Murine leukemia virus (MuLV)Feline leukemia virus (FeLV)
Deltaretrovirus Human T-lymphotropic virus (HTLV-1, -2)Simian T-lymphotrophic virus (STLV-1, -2, -3)
Bovine leukemia virus (BLV)
Epsilonretrovirus Walleyedermal sarcoma virus
Lentivirus slow Human immunodeficiency virus (HIV-1, HIV-2)Simian immunodeficiency virus (SIV)
Equine infectious anemia virus (EIAV)Feline immunodeficiency virus (FIV)
Caprine arthritis encephalitis virus (CEAV)Visna/maedi virus
Spumavirus foamy Human foamy virus
Retroviridae: Family
Adapted from Fields Virology, 2007
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Genera:
Simple viruses: encode onlyGag, Pro, Pol, and Env
Alpha Beta Gamma
Complex: encode Gag, Pro,Pol, Env, and an array of small
regulatory proteins
Delta Epsilon Lentiviruses Spumaviruses
Retroviridae: Classification
Fields Virology, 2007
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Simple Retrovirus Retrovirus Genome Organization!
Complex Retrovirus
Structural genes: gag, pol, envRegulatory genes: tat, rev
Accessory genes: vif, vpu, vpr, nef Fields Virology, 2007
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Over 1 million individuals in theUnited States were living with HIV
infection, with 21% undiagnosedinfections (CDC 2006)
Nearly 33 million people world-wide were affected by HIV (United
Nations 2007)
Human Immunodeficiency Virus
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Milestones in HIV-1 Research
2009: Thai Phase III HIV vaccine clinical trial, also known as RV144 ends2008: Nobel Prize in Physiology / Medicine-Franoise Barr-Sinoussi, Luc Montagnier, Harald zur Hausen
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Spherical Enveloped 100-120 nm Cone-shaped,cylindrical core
HIV-1: Structure
Fields Virology, 2007
Current Opinion in Microbiology 2006; 4:437-42
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
HIV-1 Biology
The virus only grows on CD4 cells that are proliferating inresponse to an immune stimulus Therefore it is difficult to growHIV in culture!
Reverse transcriptase in activated CD4 cells in blood of patientswith AIDS !
Robert Gallo : HTLV-3!Luc Montagnier and
Franoise Barr-Sinoussi: !
Lymphoadenopathy virus (LAV)!
Human immunodeficiency viral particles areseen at medium magnification in thiselectron micrograph (CDC)
Human Immunodeficiency
Virus (HIV)
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HIV-1 Immunopathogenesis
Immunol Cell Biol 2007; 1:6-15
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HIV and AIDS: The Cellular and Immunological Picture
The course of the disease!
1. Acute Infection!
High virus titer"Mild symptoms"Fall in CD4+ cells but recovers"Rise in CD8+ cells but recovers
"A high virus titer (up to 10 million viruses/mL"blood)"Macrophages infected!
Macrophages bring HIV into the body if sexually transmitted
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2. A strong immune response!
Virus almost disappears from circulation! Good cytotoxic T cell response! Soluble antibodies appear later against
!both surface and internal proteins!
Most virus at this stage comes from!recently activated (dividing) and
!infected CD4+ cells ! CD4+ cell production compensates for
!loss due to lysis of cells by virus!production and destruction of!infected cells by CTLs!
HIV and AIDS: The Cellular and Immunological Picture
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
3. A latent state" Latency of virus and of symptoms Virus persists in extra-vascular
tissues
Lymph node dendritic cells Resting CD4+ memory cells (last a
very long time - a very stable
population of cells) carry
provirus
HIV and AIDS: The Cellular and Immunological Picture
10 billion HIV particlesper day!
Virus half life 5.7 hours!10-100 million virionsper ml blood (set point)
!
Small minority of T4cells are infected!
Virus found in lymphnodes!
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4. The beginning of disease"
Massive loss of CD4+ cells!
CD4+ cells are the targets of the virus! Cells that proliferate to respond to the virus are
!killed by it!
Dendritic cells present antigen and virus to CD4!cells!
Epitope variation allows more and more HIV to!escape from immune response just as!response wanes!
Apoptosis of CD4+ cells!HIV patients with high CD4 cell countsdo not develop AIDS
HIV and AIDS: The Cellular and Immunological Picture
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
CD4 cell
count is "not a"good
predictor of "progressionto disease"
HIV CD4 Cell Count and AIDS
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
HIV-1: Pathogenesis
Nat Med 2003; 7:847-52
HIV primarily infects CD4 T cells andcells of the macrophage lineage (e.g.,
monocytes, macrophages, alveolarmacrophages of the lung, dendritic
cells of the skin, and microglial cells ofthe brain).
Virus causes lytic infection of CD4 Tcells and persistent low-level
productive infection of macrophage
lineage cells.
Virus causes syncytia formation, with
cells expressing large amounts of CD4antigen (T cells) with subsequent lysis
of the cells.
Virus alters T-cell and macrophage cellfunction.
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Positive-sense, single-stranded RNA genome
HIV-1: Genome
Fields Virology, 2007
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Positive-sense, single-stranded RNA genome
HIV-1: Genome Organization
Main genes gag Group-specific antigen (encodes matrix, capsid, p2,
nucleocapsid, p1 and p6
pol polymerase (encodes p6*, protease, RT, Rnase H, integrase
env envelope
Auxillary genes nef negative regulatory factor
rev regulator of expression of virion proteins
tat transactivator of transcriptionvif virion infectivity factor
vpr viral protein R
vpu viral protion U
Non-coding R repeat sequence
Sequences U3 unique sequence at the 3 end of the genome
U5 unique sequence at the 5 end of the genome
Domains at the TAR trans-acting response element5 end of the Poly-A polyadenylation signal
genome PBS primer-binding site
DIS dimerization initiation site
SD splice donor site
Psi main part of the packaging signal
AUG start codon of the gag gene
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
HIV Life History
A retrovirus"Latency!Specific destruction of
!CD4+ cells !
How does the virus!enter the cell?!
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Entry into the cell
T4 (CD4+) cells are major target
Human HeLa CellHuman HeLa Cell transfectedwith CD4 antigen
NOT INFECTED INFECTED
But NOT the whole answer since this does nothappen if CD4 is transfected into a MOUSE cell"
HIV Life History
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Co-Receptors!CD8+ Cells"
"MIP-1 alpha MIP-1 beta RANTES"
Chemokines""Block HIV infection of macrophages"
Why do CD4-transfected human cells become infected !but CD4-transfected mouse cells do not?!
Human cells must possess a co-factor for infection that mouse cells do not!
HIV Life History
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
HIV-1: Co-receptors
Tropic and biological properties of HIV-1 isolatesChemokineCoreceptor
Used
PBMCReplication
MacrophageReplication
T-cell LineReplication
ReplicativePhenotype
Syncytium-inducing
Phenotype
X4 + _ + Rapid/High ++
R5 + + _ Slow/Low _
R5/X4 + + + Rapid/High +
Adapted from Fields Virology, 2007
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
HIV-1:
Diagnosis andDisease
Progression
Am Fam Physician 2010;10:1239-44
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
HIV-1 Latency and Treatment
Science 2010; 5988:174-80
HDAC Histone deacetylases
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
HIV-1: Evolution of Diversity
N Engl J Med 2008; 18:1965-6
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Features of HIV-1 Pandemic According to
Subtype or Circulating Recombinant Form
N Engl J
Med 2008;18:1965-6!
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Other CD4- cells infected by HIV
Epithelial cells of!bowel and vagina!
Brain endothelial!cells!
Brain macrophage/!microglia,
!astrocytes and!oligodendroglia!
!
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Pacific Center for Emerging Infectious Diseases Research, Asia-Pacific Institute of Tropical Medicine & Infectious Diseases
Structural: gag, env Functional: pr
(protease), pol
(polymerase)
Regulatory: rex, tax Accessory: p12, p30,
p13
Minus strand: HBZ (HTLV-1
basic zip factor):interact with CREB
HTLV-1
transcription
HTLV-1: Genome
Lancet Infectious Diseases 2007; 7:266-81
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Unlike HIV, HTLV predominantly remains as cellassociated provirus
Plasma viral load is very lowDuring early stage cell-to-cell spread throughcontact polyclonal infection of both CD4+ and
CD8+ cells
Late stage when equilibrium with immune systemreached: clonal expansion of infected cells
Hallmark of HTLV-1 infection: spontaneousproliferation of PBMCs in-vitro driven by HTLV-1
tax
HTLV-1: Life cycle
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Mother-to-child Rate:15-25% Intrauterine / peripartum:
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Most common neurological manifestationof HTLV-1
Chronic inflammation of the white andgrey matter of the spinal cord
Manifests clinically by slow progressivespastic paraparesis, neurogenic bladder
disturbances and less conspicuoussensory signs
HTLV-1: HAM/TSP
Lancet Neurology 2006; 5:1068
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HIV: HAND
Ann Neurol 2010; 6:699-714
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