HIV and AIDS

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HIV and AIDS
Acquired Immunodeficiency Syndrome
Disease caused by an infectious agent:
a retrovirus
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HIV and AIDS
History of an infectious agent
1979 - 5 cases of Pneumocystis carinii pneumonia
In Los Angeles 1967-1978: only two cases of
Pneumocystis carinii pneumonia
All Homosexual
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107 cases of Pneumocystis carinii pneumonia reported in the United States before the AIDS epidemic

AIDS epidemic has resulted in 166,368 cases up to 1999
HIV and AIDS
History of an infectious agent
Pneumocystis pneumonia
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HIV and AIDS
With dissemination to extrapulmonary sites, Pneumocystis carinii tends to produce foci with prominent calcification, as seen in the kidney
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HIV and AIDS
an infectious agent – Kaposi’s Sarcoma

Early 1981 MMWR: 5 cases of Kaposi’s sarcoma
Hitherto: rare (immunocompromization)
Elderly - Non-aggressive
1981 - 26 cases of Kaposi’s sarcoma
Young
Male
San Francisco and New York
All Homosexuals
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Before 1981: 40 - 120 cases per year in United States
HIV and AIDS
an infectious agent – Kaposi’s Sarcoma

1981-1999: 46,684 definite cases in United States
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HIV and AIDS
Two rare diseases in the gay community linked to
IMMUNOSUPPRESSION
OPPORTUNISTIC INFECTIONS
Gay-Related Immune Deficiency
Acquired Immune Deficiency Syndrome (AIDS)
Also
Lymphadenopathy (diffuse, undifferentiated non-Hodgkins lymphoma)
1977- 1980: No cases in the young male (20 - 39 years old) population of the San Francisco area
March 1981 - January 1982: four cases within 10 months
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HIV and AIDS
Little in common but:
Young
White
Male
Large towns
Homosexual community
But not all gay men got the disease
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HIV and AIDS
Clusters of infected men
Apparent concentration within sexually interactive groups
High numbers of sex partners
Distinguishing characteristics
Suggests an infectious agent
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Female sex partners of AIDS-positive IV drug users and hemophiliacs
Not just in the Gay community
More evidence for an infectious agent
Different ways of getting a similar syndrome
Blood transfusions
Intravenous drug use
Hemophilia (clotting factor)
HIV and AIDS
Haitian origin
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HIV and AIDS
1983: The 4H Club
Homosexuality among males
Hemophilia
Heroin use (drug use that may involve shared needles)
Haitian origin
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HIV and AIDS
Obvious agent:
A virus……that is now in the blood supply
Primary route of transmission: Sex
AIDS is a sexually-transmitted viral disease
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HIV and AIDS
The Cellular Picture
In advanced disease: the loss of another cell type
CD8+ cytotoxic killer cells
Loss of one cell type throughout the course of the disease
CD4+ T4 helper cells
A fall in the CD4+ cells always precedes disease
Suggests an infectious agent
A virus
But initially difficult to grow
Rapidly kills cells on which it grows
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AIDS is therefore the end point of an infection that is continuous, progressive and pathogenic

With the prevalence of HIV in the developing world, HIV and its complications will be with us for generations
AIDS Definition
AIDS is currently defined as the presence of one of 25 conditions indicative of severe immunosuppression
OR
HIV infection in an individual with a CD4+ cell count of <200 cells per cubic mm of blood
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Approximately 30,000,000 people in the world are HIV-infected

Approximately 14,000 new HIV infections occur daily around the world
Over 90% of these are in developing countries
1000 are in children less than 15 years of age
Of adult infections, 48% are in women and 15% in individuals 15-25 years
AIDS Statistics
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As of December 2006, 1,106,400 Americans have been reported with AIDS

At least half of them have died

9,101 children under 15
AIDS Statistics
About ONE MILLION persons in the United States are living with HIV infection
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HIV and AIDS
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HIV and AIDS
AIDS
Deaths
Prevalaence
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HIV and AIDS
Black
White
Hispanic
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AIDS Statistics
Sub-Saharan Africa
About 1 million new cases of AIDS per year

At least 20 million people with HIV infection

AIDS is responsible for a decrease in life expectancy and increase in child mortality. Child mortality rates in East Africa will double by 2010 and adult life expectancy has declined in that region
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Botswana
Zimbabwe
Lesotho
Swaziland
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Several countries in sub-Saharan Africa report infection rates of over 25%, especially urban areas

Zimbabwe: 33.7% of adult population infected

90% of truck drivers in Zimbabwe are infected

In Zambia, 1 in 5 urban girls is HIV-positive by the age of 20
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Human Immunodeficiency Virus
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HIV and AIDS
The Virus
The virus only grows on T4 cells that are proliferating in response to an immune stimulus -- Therefore difficult to grow in culture
Reverse transcriptase in
activated T4 cells in blood of patients
with AIDS
Robert Gallo : HTLV-3
Luc Montagnier and
Françoise Barré-Sinoussi: LAV
Human immunodeficiency viral particles are seen at medium magnification in this electron micrograph (CDC)
Human Immunodeficiency
Virus (HIV)
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HIV and AIDS
The cellular and immunological picture - The course of the disease
virus
CD4 cells
antibody
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HIV and AIDS
The cellular and immunological picture - The course of the disease
CD8 cells
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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 per ml blood)
Macrophages infected
Macrophages bring HIV into the body if sexually transmitted
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HIV and AIDS
2. A strong immune response

Virus almost disappears from circulation
Good cytoxic 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
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HIV and AIDS
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
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HIV and AIDS

10 billion HIV particles per day
Virus half life 5.7 hours
100-10 million virions per ml blood (set point)
Small minority of T4 cells are infected
Virus found in lymph nodes
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HIV and AIDS
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 T4 cell counts
do not develop AIDS
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HIV and AIDS
5. Advanced disease - AIDS
CD8+ cells destroy more CD4+ cells
CD4 cell loss means virus and infected
cells no longer controlled
As CD4+ cells fall below 200 per cu mm
virus titer rises rapidly and remaining immune response collapses
CD8+ cell number collapses
Opportunistic infections
Death in ~2 years without intervention

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HIV and AIDS
Good correlation between
number of HIV particles
measured by PCR and
progression to disease
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HIV and AIDS
Viral load predicts
survival time
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HIV and AIDS
CD4 cell count is not a
good predictor of
progression to disease
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Cofactors
Not all cases of Kaposi’s are associated with HIV
Not all HIV infected persons suffer from Kaposi’s
20% of homosexual HIV+ males get Kaposi’s
Few IV drug users or hemophiliacs get Kaposi’s
Kaposi’s sarcoma associated herpes virus
Human herpes virus-8
HIV and AIDS
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HIV and AIDS
So far it seems that >50% of HIV-infected persons have progressed to AIDS
There is NO strong evidence there is any other infectious agent involved than HIV
Three Views of AIDS
Gallo: Infection by HIV is sufficient to cause AIDS
Montagnier: HIV may be harmless in the absence of other co-factors
Duesberg / Mullis: HIV is too silent to be the etiologic agent of AIDS. It is a much maligned by-stander
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HIV - The Virus
Membrane: host derived
Retrovirus
Three genes
GAG – POL – ENV
Three polyproteins
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HIV - The Virus
vaccine problem
Retrovirus
ENV gene
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HIV - The Virus
GAG gene
Group-Specific Antigens
Retrovirus
Polyprotein
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HIV - The Virus
Polymerase (reverse transcriptase – RNA dependent DNA polymerase)
Integrase
Protease (cuts polyproteins)
Enzymes
POL gene
Retrovirus
Polyprotein
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The Genome of HIV
Three structural genes
LTRs
Extra open reading frames are clue to latency
These ORFs code for small proteins - antibodies in AIDS patients
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HIV - The Virus
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HIV - The Virus
A retrovirus
Latency
Specific destruction of CD4+ cells

How does the virus enter the cell?
Life History
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HIV - Life History
Fusion at ambient pH
No need for entry into lysosomes
Syncytia
Profound significance for AIDS progression:
Spread from cell to cell
Profound significance for therapy:
Humoral antibody will not stop spread – need cell-mediated response
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HIV - Life History
Entry into the cell
T4 (CD4+) cells are major target
Human HeLa Cell
Human HeLa Cell transfected with CD4 antigen
NOT INFECTED
INFECTED
But NOT the whole answer since this
does not happen if CD4 is transfected into a MOUSE cell
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HIV - Life History
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
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HIV - Life History
CD4
CD4
CD4
HIV
CCR5
CCR5
chemokine
Mutant CCR5
macrophage
Chemokine receptors are necessary co-receptors along with CD4 antigen
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HIV and AIDS
Some people do not get AIDS
Long term survivors
Exposed uninfected persons
The chemokine receptor story
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HIV and AIDS
Co-receptors and HIV infection
CCR5 is a chemokine receptor
Cells with homozygous mutant CCR5 molecules are not infected by HIV
1 in 100 Caucasians
No Africans
Persons with heterozygous mutant CCR5 molecules progress to AIDS more slowly
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HIV and AIDS
Co-receptors
25% of long term survivors are CCR5 or CCR2 mutants (deletions)
The same CCR5 mutation (called “delta 32”) is thought to be the mutation that rendered some people immune to the plague in the middle ages
Many other chemokine receptors
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Long term non-progressers

People who have been infected with HIV for more than seven years that have stable CD4+ cell counts above 600 per cu mm with no symptoms and no chemotherapy

Many have produced a very good immune response to the virus
HIV and AIDS
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HIV and AIDS

Nairobi prostitutes
Client infection rate more than 25%
Rare HLA antigens
Associations between resistance to infection and their
class I and class II MHC (HLA) haplotypes
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HIV - Life History
GAG POL ENV
HIV is a retrovirus
It carries with it:
Reverse transcriptase
Integrase
Protease
tRNA primer
HIV genes
HIV has no oncogene but could still be oncogenic
vaccine problem
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HIV - Life History
HIV infection is not manifested as disease for years
During apparent clinical latency, virus is being replicated and cleared
Latency – Cellular – The problem of memory T4 cells
Only activated T4 cells can replicate virus
Most infected T4 cells are rapidly lyzed but are replaced
Some T4 cells revert to resting state as memory cells which are long-lived
Memory T4 cells cannot replicate the virus unless they become activated
Clinical Latency
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Dynamics of CD4 T cells in an HIV infection
Cell death
apoptosis etc
Uninfected activated
T cell
Adapted from Saag and Kilby Nat Med 5: 609, 1999
Cell death
immune
destruction
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Long term latent HIV
T4 resting memory cell
It may be impossible to cure the patient of HIV
Even if combination therapy stops HIV replication
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Inexorable decline of CD4+ T4 cells
Of great importance to therapeutic strategy
Why do all of the T4 cells disappear?
At early stages of infection only 1 in 10,000 cells is infected
Late 1 in 40
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But few cells are infected:
Early stage of infection 1:10,000
Late 1:40
Why do all T4 cells disappear?
1. PUNCTURED MEMBRANE
Virus destroys the cell as a result of budding
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But syncytia not common
Most T4 cells are not HIV+
Could “sweep up” uninfected cells
Uninfected CD4 cell
Gp120 negative
Cells Fuse
Killing of CD4 cells
2. Syncytium Formation
Infected CD4 cell
Gp120 positive
Why do all T4 cells disappear? - 2
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Killing of CD4 cells
3. Cytotoxic T cell-mediated lysis
Why do all T4 cells disappear?
BUT: Most cells are not infected
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CD8 cell
(no CD4 antigen)
Macrophage
CXCR4 chemokine receptor
Why do all T4 cells disappear?
Induction of apoptosis
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CD8 cell
Macrophage
CXCR4
Why do all T4 cells disappear?
Induction of apoptosis
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Macrophages may be infected by two routes
CD4
Fc receptor
HIV gp120 binds to macrophage CD4 antigen
Virus is opsonized by anti gp120 antibodies which bind to macrophage Fc receptors - an enhancing antibody
vaccine problem
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Macrophages - The Trojan Horse
Carry virus into different organs (brain)
Non-proliferating mature macrophages sustain HIV production for a long time without being killed by virus
Macrophages form a reservoir outside the blood
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Population Polymorphism
HIV genome 9749 nucleotides
Therefore EVERY new virus has at least one mutation!
Every possible single mutation arises daily
1% of all possible double mutations arise daily
The HIV that infects a patient is very different from that seen by the time AIDS appears
HIV is a retrovirus
Retroviruses use host cell RNA polymerase II to replicate their genome
vaccine problem
Pol II has a high error rate 1:2,000-10,000
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Population Polymorphism
Initial infecting virus is macrophage-tropic (has CCR5 as co-receptor)
These are non-syncytium-inducing strains
(Note: most vaccines have been made against syncytium-inducing T4 cell tropic strains)
As virus mutates, it changes subtypes of cells that it infects as the ability to bind different co-receptors changes
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Population Polymorphism
Early in infection:
Macrophage-tropic
Non-syncytium-inducing
Slowly replicating
Late in infection
T4 cell tropic
Syncytium-inducing
High titer virus
vaccine problem
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Population Polymorphism
The most variable protein is gp120
Amino acid sequence within a single patient varies by 1-6%
Up to 30% in population
Co-infection may result in recombination
Glycosylation masks conserved sites
vaccine problem
vaccine problem
vaccine problem
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Population Polymorphism
Polymorphism due to high mutation rate as a result of lack of proof-reading in reverse transcriptase and RNA pol II
Sub-populations arise with altered cell tropism
drug problem
Variation in reverse transcriptase leads to resistance to nucleoside analogs
Variation in protease leads to resistance to protease inhibitors
drug problem
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Other cells infected by HIV
CD4-
Epithelial cells of bowel and vagina
Endothelial cells of brain
Brains cells : Astroglia, oligodendroglia

Galactocerebroside receptor
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Anti-HIV Strategies
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Anti-HIV Strategies
Highly
Active
Anti-
Retroviral
Therapy
HAART: Two nucleoside analog RT inhibitors and 1 protease inhibitor
Or: Two nucleoside analog RT inhibitors and 1 non nucleoside
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Does HIV Cause AIDS?
Gay San Franciscans
New York I.V. drug users
African heterosexuals
Hemophiliacs
Spouses of hemophiliacs and drug users
Children of hemophiliacs and drug users
Single common factor between:
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Does HIV Cause AIDS?
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Remember!
Education led to leveling off of rate of increase in AIDS
HAART has greatly slowed death rate
The fact that fewer people are dying per year from the infection means that the number of HIV-infected people in the population is rising!
Unless education continues to be successful and unless we can cure infected people of virus, the problem of virus spread is, and will continue to be, with us