Pandemics (A) Flashcards
HIV
1
Q
What is a Pandemic
A
Global outbreak of infectious disease
2
Q
What are the major current pandemics?
A
HIV/AIDS, Tuberculosis, Malaria
3
Q
HIV/AIDS causes of death globally in 2007 vs 2017
A
2007: 5th, 2017: 13th
4
Q
Global burden of HIV
A
36.7 million people living with HIV globally, 30% don’t know their status
5
Q
When did AIDS related deaths start declining globally? Why?
A
Early 2000s
Because of availability of antiretroviral therapy (ART) through global advocacy and large donor effort, became available in low income countries
50% now have access to treatment, but about 1 mil still die of AIDS per year
6
Q
What is the definition of AIDS?
A
HIV+ve (+ve HIV antibody test) and sick from virus/complications related to the virus
+
Low CD4+ T cell count <200/350
7
Q
HIV/AIDS related deaths are not declining everywhere.
In Eastern Europe and Central Asia, AIDS-related deaths are increasing because:
A
There, HIV is primarily transmitted through drug use - drugs are illegal and clean needles are not available
8
Q
AIDS related deaths decline as treatment coverage increases.
How are low or middle income countries able to access ART?
A
From early 2000s, increasing global effort to fund antiretroviral therapy
Low/middle income countries don’t need to abide by patent laws and can get access to generic versions of ART drugs
9
Q
New HIV infections declining but not quick enough.
A
New HIV infections peaked in mid 90s largely due to uptake in testing
Numbers of new HIV infections are decreasing, but as of last year 1.8mil new HIV infections per year
10
Q
What are the two global targets of reductions of HIV infections?
A
1) Reduce new HIV infections to 500,000 per year by 2020,
2) Global target of 90:90:90
11
Q
Explain 90:90:90
A
90% in country should be tested and aware of their status
90% on treatment
90% on EFFECTIVE treatment = undetectable viral load
12
Q
What is U = U?
A
Once someone is on ART, the virus in their blood declines to undetectable levels by standard assays and you can no longer transmit the virus sexually
Undetectable = untransmissable
The more people that are on treatment, the less transmission in the community
13
Q
Risk factors for HIV: Globally
A
Globally more women than men affected by HIV
Key populations affected by HIV are very different across the globe
- Eastern Europe and Central Asia: 51% People who inject drugs
14
Q
New HIV diagnoses in indigenous and non-indigenous populations are:
A
Very similar, only about 6x higher rates of HIV infections in indigenous people, compared to 100x that of other STDs like Syphillis
15
Q
How do we track number of newly acquired HIV infections by risk category (HIV negative test within 6 months)?
A
Track number of people who have had positive test and also had a negative test in the last 6 months
- tells you who has HIV now, tells us where the virus is being transmitted
16
Q
What is the normal CD4+ T cell count?
A
> 500
17
Q
Late HIV diagnosis and symptoms start at what CD4+ cell count?
A
<350
18
Q
If someone has CD4+ T cell count <350 at diagnosis, they:
A
Have probably already been infected for about 5-10 years, about 50% of new diagnoses are in people who have a late HIV diagnosis.
19
Q
Why is the number of people living with HIV in Australia an aging cohort?
A
Number of people living with HIV dramatically increased over last 2 decades because of ART, allowing people to live a normal long life with normal life expectancy
Growing number of people over 50 living with HIV
20
Q
HIV is a (complex) retrovirus of the ____ family?
A
Lentiviridae
Slow viruses - make you sick slowly
Can be infected and stay healthy (asymptomatic) for 10+ years
21
Q
Retroviruses are:
A
RNA viruses with the capacity to copy itself into host DNA (reverse transcribing via viral reverse transcriptase)
22
Q
Primate retroviruses do not ____
A
make the primates unwell.
The primate retroviruses are non-pathogenic in their own species but are pathogenic in other species.
23
Q
HIV-1 virus originated from:
A
Chimpanzee (SIVcpz)
24
Q
HIV-2 Virus originated from:
A
African Green Monkey (SIVagm)
25
Lentivirus properties:
Retrovirus family
HIV-1, HIV-2
Icosahedral capsid symmetry
Has envelope
Genome is diploid linear 10kb (+ve) sense ssRNA (2 strands of ssRNA)
Virus replicated in nucleus and assembly in cytoplasm
Slow disease onset of AIDS, neurologic, arthritis, pneumonia
26
HIV genome consists of:
```
Structural proteins (gag)
Viral enzymes (pol - polymerase - encodes all viral enzymes)
Envelope glycoproteins (env)
```
All retroviruses share many of these genes
27
A high degree of ___ exists for gag and env proteins
variability
28
HIV and SIV differ by their ___ proteins?
Regulatory proteins - assist the virus to replicate in different settings
29
HIV regulatory proteins:
tat, rev, vpr, vpu, vif, nef
30
Envelope proteins are key to:
allowing the virus to enter the cell
| bilipid layer envelope on the outside of the virus, thats where the env proteins sit within the bilayer like studs
31
The 2 HIV env proteins are:
```
GP 120 (SU-surface; cell attachment)
GP 41 (TM-transmembrane; fusion domain)
```
GP120 is embedded in the viral lipid bilayer by GP41
32
The 3 HIV structural gag proteins are:
p17 (MA-matrix)
p24 (CA-capsid)
p7 (NC-nucleocapsid)
33
The 3 HIV enzyme pol proteins are:
p66/51 (RT-reverse transcriptase)
p32 (IN-integrase)
p11 (PR-protease)
34
The different strains of HIV globally within the HIV-1 group are called:
Clades
| - defined on their genome sequence and how much they differ from other genome sequences
35
Then most globally important HIV-1 strain is:
Clade C (eastern and southern Africa, and India)
36
The most common HIV-1 clade in North America, South America, Europe and Australia is:
Clade B
37
Why are clades important to consider when designing new drugs/vaccines?
We need to design a drug/vaccine that works across all clades
38
Clades are defined by:
Phylogenetic trees
- shows how related sequences are, whether they are close or clustered on a branch
- HIV-1 M group (Clades A-F) have less sequence homology to each other, but as a group are more similar to SIVcpz, which is very different to HIV-2 (SIVagm)
39
List out the HIV life-cycle
1. CD4 Binding
2. Co-receptor binding
3. Fusion (and genomic replication)
4. Budding
5. Maturation
6. New HIV virion
40
Explain: 1. CD4 binding
HIV has to bind to receptor to infect
Main receptor is CD4
HIV mainly infects CD4+ T cells
Binds CD4 via GP120 (env protein)
41
Explain: 2. Co-receptor binding
GP120-CD4 binding leads to conformational change in the receptor which exposes another biding site within the envelope protein which binds a second receptor called a chemokine co-receptor
CCR5 or CXCR4
42
Explain: 3. Fusion
Virus membrane is brought into very close contact with the membrane of the cell, which results in fusion of the 2 membranes.
Viral ssRNA moves into host cell
43
Explain how virus genetic material replicates in host cell
Viral ssRNA moves into host cell (following fusion) and undergoes reverse transcription in cytoplasm to form viral DNA (proviral DNA)
DNA then moves in through nuclear pore into nucleus, and uses viral enzyme integrase to integrate into host genome (absolutely key step in viral life cycle - this is why we cant cure HIV, because the virus becomes part of our own DNA)
Once proviral DNA integrates into host DNA, it can basically be shut down and be silenced
- persist there for long time
- hiv latency (main reason why we cannot cure)
44
Explain: 4. Budding
In the right cell activation state, the latent virus starts to make copies of itself exactly like other genes do
- DNA>RNA>protein
- Packaged together
- Bud from surface of cell
- then undergoes maturation and a new HIV virion is formed to infect other cells
45
The 4 key features of HIV replication are:
1) Rapid
2) Error prone reverse transcriptase (p66/51)
- leads to rapid evolution of multiple quasispecies
- lots of errors every time the RNA is RT-ed into DNA
- advantageous feature for virus because it can lead to rapid evolution in setting of some sort of pressure
- if a single virus manages to cross the mucosal membrane, within weeks you get this expansion and multiple quasispecies
- no virus is identical because every time it copies itself, it makes these errors
- Single drug agent - virus can rapidly develop resistance in about 3 weeks
- immune pressure can also rapidly develop resistance
3) 10 bil particles produced per day
- someone not treated is producing 10bil viral particles per day
- also clearning 10 bil a day
- amt of virus is at steady state, but it doesnt mean virus isnt replicating
4) Impact on host cells
- CD4+ T cells are prime target for HIV
- If cell enters resting state - virus becomes latent, gives it a mechanism to survive indefinitely
- If cell is activated, will die > progressively lose CD4+ T cells in untreated HIV infection
- Monocyte/macrophages also express CD4 receptor
- slightly different life cycle of the virus which leads to long lived slow release of virus
46
Factors involved in attachment, co-receptor binding, and fusion are:
Attachment: Viral gp120 binds to CD4 on host cell
Co-receptor binding: gp120-CD4 complex binds to CCR5 or CXCR4 on host cell
Fusion: Viral lipid bilayer membrane duses with host cell membrane, facilitating viral ssRNA entry
47
R5 viruses are:
CCR5-tropic, virus enters CD4+ T cells via CCR5
(over 90% of HIV viruses use this co-receptor)
- Nearly all infections are caused by R5 viruses (seems to have selective advantage for transmission across mucosal membranes)
- R5 viruses cause less T-cell destruction
48
X4 viruses are:
CXCR4-tropic, virus enters CD4+ T cells via CXCR4
- Rarely transmitted
- Emerge late in the course of infection (almost not seen today because now we treat everyone as soon as they get diagnosed with HIV+ve status, but left untreated, virus will progress from R5 to X4)
- 50% of AIDS patients carry X4 virus
49
D/M viruses are:
HIV viruses that can use either CCR5 or CXCR4 to enter CD4+ T cells (dual-tropic)
Viral populations containing a mixture of R5-tropic, X4-tropic, and/or dual-tropic HIV are called mixed tropic (D/M)
50
The Δ32 mutation in the CCR5 leads to:
deletion of 32bp and no expression of CCR5 on cell surface
- 90% Wild type, 10% CCR5Δ32
51
CCR5 Normal Wt/Wt alleles lead to:
- Normal CCR5 expression
- Progression of HIV
- Normal immune function
52
Heterozygote (Wt/Δ32) alleles lead to:
- Decreased CCR5 expression
- Delayed progression to AIDS/Death
- Normal immune function
- 10-15% of caucasians
53
Homozygote (Δ32/Δ32) alleles lead to:
- No CCR5 expression
- Rare infection by X4
- Normal immune function
54
List the 4 innate anti-viral cellular factors (host proteins) and the HIV proteins that counteract them:
1) APOBEC3G - vif (regulatory protein)
2) TRIM 5alpha - capsid
3) Tetherin - vpu (regulatory protein)
4) LEDGF - Integrase
55
Describe the APOBEC3G-vif interaction
APOBEC3G - function is to edit/destroy foreign RNA
vif - inhibits APOBEC3G
56
Describe the TRIM 5alpha - capsid interaction
TRIM 5alpha - blocks uncoating of retroviruses
capsid - Human TRIM 5alpha is inactive against HIV capsin protein
57
Describe the Tetherin-vpu interaction
Tetherin - blocks budding/release of viral particles
vpu - inhibits tetherin to allow budding/exit of viral particles
58
Describe the LEDGF-Integrase interaction
LEDGF - tethers HIV to host chromatin (virus has taken advantage of this LEDGF to tether itself to our chromatin)
Integrase - facilitates integration of proviral DNA into host DNA
59
How do Antigen presenting cells (APCs) present foreign material, and to which cells?
APCs present foreign antigens to CD4+ T cells in the context of MHC II (major histocompatibility complex) and the T cell receptor (TCR)
- same process for CD8+ T cells and MHC class I
- both CD4 and CD8 make very robust response to HIV, its the over-exuberant immune response that makes people sick
60
Describe the Immune response to HIV
HIV RNA that we can measure in the blood after exposure
- after 2 weeks can start to detect an exponential increase in HIV RNA up to 1mil copies per mL, then immune response kicks in and a decline in HIV RNA as a combination of immune response and HIV runs out of target cells - start to see decline in HIV RNA and HIV reaches a set point
- Rise in HIV-specific CD8+ T cells, and stays at high level, robust but ineffective response
- By 4 weeks can already detect HIV antibodies (diagnostic of HIV +ve status)
61
What is the HIV RNA set point?
- Normal about 10-100,000 copies per mil of blood
- Elite controllers -> undetectable levels of HIV RNA in blood, body produces fantastic immune response to HIV, 1% of people with HIV
- dont bother with set point in diagnosis anymore because anyone with HIV just goes straight onto treatment
62
How does the HIV virus evade the immune response?
| 1) Sequence Variation
1) Sequence variation
- Reverse transcriptase constantly introduces new mutations into virus, allowing it to escape recognition of both CTL (CD8 cytotoxic mediated immune response) and Antibodies
- Antagonism so CD8 T cell can no longer function effectively
63
How does the HIV virus evade the immune response?
| 2) Altered antigen presentation
2) Altered antigen presentation
- down regulation of MHC Class I molecules by Tat, Vpu and Nef (regulatory proteins in HIV)
- Key protein is Nef (negative factor) which allows HIV to persist in presence of immune response
64
How does the HIV virus evade the immune response?
| 3) Loss of effector cells
3) Loss of effector cells
- Clonal exhaustion (continual dividing and expanding and now the cells no longer function properly - a common feature of many chronic viral infections)
- Loss of CD4 T cell help (to have effective CD8 cytotoxic response, you need CD4 help, and HIV kills CD4 which eliminates CD8 response)
- Replicative senescence (cells can no longer divide any further, drop in population of CD4+ cells)
65
How does the HIV virus evade the immune response?
| 4) Latency
4) Latency
- Virus enters and integrates into host genome of a resting T-cell
- Replication cycle is not complete so cell doesn't express any viral proteins, virus hides in DNA and can evade immune response
- Particularly in resting T cells, macrophages and astrocytes
66
How does the HIV virus evade the immune response?
| 5) Privileged sites of viral replication
5) Privileged sites of viral replication
- Sites traditionally not exposed to the immune system
- Brain (BBB prevents T cells moving into brain), Testes (BTB), GIT (no specific barrier, but the volume and amount of HIV replicating there makes it a privileged site for replication)
67
HIV disease: Define "Primary infection"
Acute phase of CD4 depletion, 0-3 weeks
CD4+ lymphocyte count drops to ~ 500 cells/mL
- because of HIV replicating and killing off CD4 cells
HIV RNA copies per mL in plasma spikes to 10^6
68
HIV disease: Define "Acute HIV syndrome"
3-9 weeks post infection
HIV RNA copies spike to 10^6 then drop down to about 10^3/10^4 at the end of 9th week
CD4+ Lymphocyte count reaches 500
Wide dissemniation of virus
Seeding of lymphoid organs
69
HIV disease: Define "Clinical Latency"
Chronic phase of CD4 depletion
Marker of HIV is CD4 T cell count - normal is > 500
Some recovery after initial drop in CD4 levels, but CD4 count doesnt go back to normal levels, but can get back up to about 500, and usually lose about 50 cells per year in absence of ART
Clinical latency is a bad term
- implies nothing is happening, but in fact, while the viral load is at steady state, there is still viral replication going on at the same rate of clearance
70
When do constitutional symptoms of HIV occur?
After about 5-10 years when CD4 level reaches 200, start getting sick with constitutional symptoms of fever and diarrhea, weight loss, may even get opportunistic diseases.
Will eventually die if not treated because this is when HIV RNA copies per ml plasma start increasing again
71
What happens in the gut of a HIV+ patient?
Massive depletion of CD4+ T cells from GIT in acute infection
- GIT is main target for replication and CD4+ depletion, where only 1% of our lymphocytes are circulating
- Depletion of Peyer's Patches in GIT (lymphatic tissue in GIT ileum) - big driver for many complications seen in HIV
72
Explain the Chronology of CD4 T-cell loss and disease
0-10 Weeks
- Primary Infection
- CD4 cell count per uL drops to 500 by 6th week
- Glandular fever like illness, fever, rash, myalgia, myopathy, meningo-encephalitis
0-5 Years
- Early Immune Deficiency
- CD4> 500
- Still number of complications, largely autoimmune because of the dysregulation of immune system in this early phase, even with normal CD4 count
5-10 Years
- Intermediate Immune Deficiency
- 500 > CD4 > 200
- Mix of both autoimmune and infectious disease e.g. Herpes zoster, TB (not AIDS defining diseases but more common in people with impaired T cell function)
10+ Years
- Advanced Immune Deficiency (AIDS)
- CD4 < 200
- PCP, CMV, MAC, Oral candidiasis, Herpes simplex, Hairy leukoplakia
73
Describe CD4+ T-cell Homeostasis
Bone Marrow > Thymus > Lymph Node > Periphery
Bone Marrow
- CD34+ progenitor cells move into thymus
Thymus
- Complex process of positive and negative selection for T cells
Lymph Nodes
- Naive T cells that are not self reactive
- Constant homeostatic proliferation to replenish numbers
Upon exposure to antigen, Naive T cells expand and become
1) Effector T Cells (move into periphery to effect)
2) Central Memory T cells (Once antigen exposure is complete, Effector T cells will revert to Central Memory cells)
74
Causes of CD4+ T-cell decline
1) Increased Destruction
a) Direct Infection
1) Increased destruction of CD4+ T cells
a) Direct infection
- GIT >>> blood
- Incomplete reverse transcription in Naive T-cells (incomplete reverse transcripts can trigger apoptosis of CD4 T cells)
75
Causes of CD4+ T-cell decline
1) Increased Destruction
b) Indirect Effects
1) Increased Destruction
b) Indirect Effects
- Contribute to far more CD4 loss than direct effects
- Syncitium formation
(CD4 cells become coated in HIV antigen which will bind other uninfected CD4 cells to the infected CD4 cells)
- Apoptosis
- Immune activation
(Drives immune activation, CD4 cells constantly replicating and eventually reach end of life and die)
- Lymph node fibrosis
(due to overactive immune response, cannot produce similar numbers of T cells, stop producing IL-7 which limits T-cell proliferation)
76
Causes of CD4+ T-cell decline
| 2) Impaired production
2) Impaired production
- Thymus
- CD34+ progenitor cells
77
Which HLA types indicate good HIV prognosis?
B13, B27, B51, B57
78
Which HLA types indicate rapid disease progression?
A23, B37, B49
79
Infected CD4+ T cells present HIV antigen to CD8+ T cells via ____
MHC Class I
80
Some people have very good immune responses to HIV, which is largely driven by their ___
HLA type
- Certain HLA molecules present HIV epitopes more effectively, which enhances the adaptive immune response
81
Other than CD4+ T cells, what other 4 cells get Depleted/Dysfunctional due to HIV-induced immunopathology?
1) CD8+ Cytotoxic T-Lymphocytes (CTL)
- Abnormally high during acute phase
- Decline at later stages
2) Natural Killer (NK) cells
- Impaired numbers
- Impaired function
3) Monocytes/Macrophages
- Defects in chemotaxis
- Inability to promote T-cell proliferation
- Defects in Fc receptor function
4) B Cells
- HIV doesnt infect B-cells
- Increased production of IgG and IgA = hyperactive B cells
- Hypergammaglobulimia, but decreased antibody responses
82
HIV causes C____ I____ A___
Chronic Immune Activation
- opposite of what you would expect in an immunodeficiency disease
83
Name some markers of immune activation that are elevated in HIV infection (T-cells)
Cellular markers
- HLA-DR (one of the key markers to measure immune activation)
- CD38
Soluble Markers
- sCD26
- sCD30
- sCTLA-4
84
What are the 4 factors that lead to immune activation, despite the knocking out of CD4+ T cells?
1) Mucosal depletion of CD4 T-cells
1) Mucosal depletion of CD4 T-cells
- Increased microbial translocation
(fragments of microbial products can cross GIT wall)
```
- Activation of TLR4 by bacterial products (LPS)
(TLR4 = toll-like receptor class 4, expressed on monocytes and macrophages - leads to chronic activation even without viral infection)
```
85
What are the 4 factors that lead to immune activation, despite the knocking out of CD4+ T cells?
2) Activation of innate immune response (pDCs)
2) Activation of innate immune response (pDCs)
- Plasmacytoid Dendritic Cells
- pDCs express TLR7/8
- HIV ssRNA is a TLR7/8 ligand
- Increased plasma INF-alpha
86
What are the 4 factors that lead to immune activation, despite the knocking out of CD4+ T cells?
3) Cytomegalovirus (CMV)-specific responses
3) Cytomegalovirus (CMV)-specific responses
- characteristic feature of aging and immune activation
- shows dysregulated immune response to other pathogens that people with HIV are infected with
- Expansion of CMV-specific activated CD4+ and CD8+ T-cells
87
What are the 4 factors that lead to immune activation, despite the knocking out of CD4+ T cells?
4) Loss of T regulatory cells
4) Loss of T regulatory cells
- Treg cells also express CD4, usually activated and important in dampening down immune cell response
- HIV knocks them out, and leads to hyperactive immune response
88
What classes of antiviral drugs are used for HIV?
1) Integrase Inhibitors
- few side effects
- prevent proviral dna from integrating into host dna
2) Protease Inhibitors
- Inhibit the HIV protease required to cleave proteins GAG and POL to block maturation of the new virion particle
3) Reverse Transcriptase Inhibitors
- Prevent viral ssRNA from getting transcribed into proviral DNA which would go on to become integrated
4) Fusion/Entry Inhibitors
89
What was the breakthrough idea concerning antiviral HIV drugs?
Using multiple drugs put together
- if you only treat with 1 drug, within 3 weeks the virus will become resistant
- If treat with 3 drugs, you tackle it from different angles and it freezes viral replication
- introduced in 1996
90
Anti-Retroviral Therapy (ART) leads to ______ in HIV RNA and ______
Rapid decline in HIV RNA, and CD4 recovery
- people on ART, HIV RNA drops rapidly to undetectable levels (<20-50 copies per mL)
- Within 4 weeks can go from 1 mil copies of HIV RNA per mL to undetectable
- Virus is always there but it stops virus from replicating, and T cells will recover
- If you start treatment very late, T cell levels may not recover to normal levels
91
What is the START study?
Key study that changed the way we looked at HIV
- Don't wait for CD4 count to drop below 350, just start immediately
- Life expectancy is normal for people who start treatment early, but if you do wait, your life expectancy is reduced
- Risk of serious illness or death reduced by 53% in immediate (CD4>500 cells/uL) vs deferred (CD4<250 cells/uL) ART
- Survival benefit maintained across all subgroups
92
What are the 5 current challenges of ART?
| 1) Life expectancy almost normal
1) Life expectancy almost normal
| - still reduced if treatment started late
93
What are the 5 current challenges of ART?
| 2) Life long adherence
2) Life long adherence
| - New advances in long acting injected ART
94
What are the 5 current challenges of ART?
| 3) Toxicities of medications
3) Toxicities of medications
| - Hyperlipidemia, renal toxicity, bone disease
95
What are the 5 current challenges of ART?
| 4) Drug resistance
4) Drug resistance
- Very rare if adherent
- Looking globally, about 10% of transmitted strains are drug resistant
- It is a problem of implementation i.e. if people stop taking the ART drugs for whatever reason
96
What are the 5 current challenges of ART?
| 5) Persistent immune activation
5) Persistent immune activation
- More common if you start ART late rather than early
- Multiple drivers and consequences
97
HIV causes ______ risk of diseases of aging
Increased
- Stroke, malignancy (non AIDS), renal disease, liver disease, fracture/osteoporosis, dementia, type 2 DM, COPD, Frailty
in an aging cohort globally
- myocardial infarc
(issue around inflammation that drives heart disease)
- Virus-associated cancer
(very common in untreated HIV infection, but rates decline with progression in ART, still 10x more common in people with HIV)
98
T-cell activation on ART is still_____
Higher than without HIV, but lower than without ART
T-cell markers of immune activation are CD38+ and HLA-DR+
99
What mechanisms drive Immune activation on ART?
Drive immune activation:
- microbial translocation
- persistent HIV
- Co-infections: CMV, HCV
- Activation of pDCs
- Altered Treg/Th17
Immune activation
(Off ART >> On ART >> HIV Negative)
100
What mechanisms drive disease on ART?
Drive Disease (due to immune activation)
- Lymph node fibrosis
- T-cell exhaustion
- Local inflammation
Leads to:
- Impaired CD4 T-cell recovery
- End-organ disease e.g. CVD, liver, dementia
- We see less and less of these problems as people start treatment earlier and earlier
101
What are the 3 Key 2020 fast track Global Targets for tackling HIV?
1) 90(aware of HIV status):90(on HIV treatment):90 (virally suppressed)
2) 30 million people on treatment
3) Fewer than 500,000 new HIV infections annually
102
What is the future of ART?
Injections rather than tablets
- 12 injections over a year instead of 365 tablets
- wont suit everyone
103
Explain the concept of the Combination Prevention Toolbox in treating HIV
- Blood Supply Screening
- Condoms
- Education/Behavior modification
- Clean Syringes
- Treatment/Prevention of Drug/Alcohol Abuse
- STI Treatment
- Mainly rely on behavioural compliance
- Over the last few years, seen many new biomedical strategies to prevent HIV - rely on antiviral therapy
104
List the prevention modalities built on antiviral therapy
1) Prevention of mother-to-child transmission
(we now use full ART with pregnant women and dramatically reduce transmission, from 600,000 to 220,000)
2) Pre-exposure prophylaxis
(Preventing getting infected with HIV)
3) Post-exposure prophylaxis
(Treatment early within 72h of exposure can prevent infection)
4) Treatment as Prevention
(when you treat someone who has HIV with ART, their viral load becomes undetectable and they can no longer transmit HIV)
105
Treatment as Prevention (TASP):
ART reduces infectiousness by 96%
- undetectable = untransmissable
106
Pre-exposure Prophylaxis (PREP):
PREP is highly efficacious in MSM
-taken daily
- taken intermittently
- Truvada contains 2 reverse transcriptase inhibitors
- Event driven PREP
(2h before sex and 24 and 48h after > about 95% effective in preventing transmission)
- PREP activity lower in women (probably because takes longer time for antivirals to accumulate in vaginal mucosa)
Adherence, effects on condom use, STIs and cost are the main concerns
107
Reported failures to PREP are _______
Extremely rare
- Over 500,000 people globally on PREP
- 6 reported cases of infection while on PREP (just not 100% effective)
- Infection with drug resistant virus
- Infection with drug sensitive virus
- Inadequate dosing
- Event driven PREP x1
108
Uptake of PREP globally is still _____
Limited
- Most of the world still doesnt have access to PREP
- Costs a lot of money
- Are you better off putting infected on treatment, or preventing infection?
109
How does a Dapivarine Vaginal Ring work?
Dapivarine = non-nucleoside reverse transcriptase inhibitor
- 2 large Phase III studies using the ring monthly
- ASPIRE, 2600 participants, 56% reduction in new infections
- The Ring Study, 1959 participants, 31% reduction
Both studies showed poor effect in young women (18-21) most likely due to poor compliance
110
Circumcisiton reduces the risk of HIV acquisition by 70% becuase
of removal of langerhan cells in the foreskin
- inner foreskin frenulum is a prime area rich with dendritic cells which is a prime first cell that HIV infects
111
Circumcision for HIV prevention
Implemented across many parts of the world as a strategy to reduce HIV transmissions
112
What 2 components are needed for an effective vaccine response to HIV?
1) Develop better CTL (cytotoxic t-lymphocytes) that recognise an infected T-cell and eliminate it
2) Generate antibodies from B cells that will bind and neutralise HIV and prevent cells from ever getting infected
113
The 4 different Vaccine approaches:
| 1) Recombinant proteins
1) Recombinant proteins
- good antibody but poor t-cell responses
- No protection
114
The 4 different Vaccine approaches:
| 2) Live attenuated virus
2) Live attenuated virus
- not possible with HIV because of potential risk of reverting to WT
- potentially unsafe
115
The 4 different Vaccine approaches:
| 3) DNA vaccines
3) DNA vaccines
- we dont have DNA vaccines for any current viruses
- Good t-cell responses but poor antibody responses
116
The 4 different Vaccine approaches:
| 4) Live vectors
4) Live vectors
- not HIV as the vector, but maybe adenovirus or pox viruses or modified vaccinia Ankara (MVA) as good delivery systems for antigens
- Good t-cell responses but poor antibody responses
117
Prime boost vaccine approaches
(a mix of standard vaccine approach strategies)
1) DNA + protein
(e. g. DNA + protein or vector)
1) DNA + protein
(e. g. DNA + protein or vector)
- Thai trial, canary pox live vector + gp120
- reduced risk of HIV acquisition by 30% (only study that showed reduced risk)
- Most agree that you need 60% reduced risk to have an effective impact on the pandemic
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Prime boost vaccine approaches
(a mix of standard vaccine approach strategies)
2) DNA + live vector
2) DNA + live vector
- Non-replicating poxviruses expressing HIV-1 genes > good T-cell responses
- Live vector of Ad5 (adenovirus 5)
- STEP trial 2008
- DNA vaccine + Ad5 boost
- Possibly increased risk of infection because Ad5 induces activation of T cells which gave HIV more targets when person is exposed
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Prime boost vaccine approaches
(a mix of standard vaccine approach strategies)
3) Ad26 vector + Gp140
3) Ad26 vector + Gp140
| - clinical trial underway
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Most promising HIV vaccine approaches:
1) Broadly neutralising antibodies
(only passive administration currently)
2) CMV vectors
(allow persistent antigen presentation)
3) Adenovirus (Ad) vectors
(Ad26 has minimal prior immunity)
- Chimpanzee (Ch) Ad virus
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What are bNABs?
Broadly neutralising antibodies
- antibodies that some individuals make to HIV
- can neutralise a large number of viruses
- are directed against highly conserved regions of envelope that are "hidden"
- Detected after 1-2 years of infection and of limited help to the patient
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If people make these bNABs, why dont they clear their own virus?
Because they make it too late
By the time they make it, the virus has already escaped that bNAB
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What are some bNAB targets?
- N332 Glycan Supersite
- V1 V2 Apex
- CD4 Binding Site
- Trimer Interface
- GP41 (fusion protein) MPER
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How can bNABS be potentially used in HIV treatment, prevention and cure?
>HIV-infected individual who produces bNABs
>clone HIV-specific B cells
>Broadly neutralising anti-HIV antibodies: >200
>Passive transfer of Abs
i.e. if you inject someone with bNABs, can you cure HIV
- HIV prevention
- Direct anti-HIV therapy
- Prolonged suppression of viral rebound following interruption of ART
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Proof of concept of bNABs
Robust protection from SIV infection with multiple bNABs when monkeys were challenged with hybrid virus of SIV with HIV envelope
- serum concentration of bNABs required to provide full protection from infection varies, and determines how we select antibodies to move into clinical trials
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Future directions and challenges for broadly neutralising antibodies as vaccines
- Mono in combination, bi- or tri-specific bNABs enhance efficacy and reduce chance of resistance
- Modification of the Fc tail of a bNAb to increase half life or activate Fc receptors
- The biggest challenge is to generate bNAbs in vivo through vaccination (right now it is giving injections s.c.)
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CMV vectors promising in macaques
- Induction of unusually broad HIV-specific T-cells
- Peptides (in response to CMV vector) presented by HLA-E (instead of HLA-A and B)
- Alternative antigen presentation triggered by CMV itself
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Ad26 virus + gp140 boost in monkeys and humans
- Ad26 (common flu virus that many humans have not been exposed to)
- Vaccine regimen: Ad26 (with mosaic antigen HIV) + gp140 (protein) + MVA
- Immunogenicity in human (n=393) in a randomised double blind placebo controlled study. Identical vaccine in macaques and similar immune response
- SHIV challenge of vaccinated monkeys gave 67% protection
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What happens when ART is stopped?
Rapid rebound in viral load (HIV RNA) within 2-3 weeks (virus is still present at low levels while on ART)
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Explain the two cases of HIV cure:
Berlin and London cases of HIV cure post stem cell transplantation
- We would never use transplantation to cure HIV - high mortality of about 25%, these 2 patients received it because they needed the BM transplant for their blood cancer
- This tells us that if you can knock out CCR5 and replace someone's immune system with T cells that are no longer susceptible for HIV, we have a chance of the virus not coming back and maybe we have a chance of knocking out this receptor via much safer ways e.g. gene therapy to specifically excise the gene for CCR5
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How can we tell if someone is cured or in remission?
Only way to tell is by stopping ART
> viral load will rebound within 2-3 weeks
We can only do this in the context of a clinical trial, not in a clinical setting
post-treatment controller as opposed to an elite controller
Goals of research: can we delay this rebound so it doesnt happen like with the berlin and london patients, or can we extend the rebound delay from 2-3 weeks to 2-3 years?
No biomarker available that can predict time to rebound or post-treatment control
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Rare cases of "remission"
1) Delay in viral rebound (months/years)
1) Delay in viral rebound (months/years)
- Very very early treatment before the reservoir or the latency can be established
(mississippi baby, san fransisco patient)
- Stem cell transplantation (even without the CCR5 mutation, probably due to GVHD)
(boston patients, minnesota patient)
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Rare cases of "remission"
2) Post treatment control (indefinite)
2) Post treatment control (indefinite)
- Early treatment (6 months)
(then after a few years on treatment, treatment stops, a higher number of people seem to be able to generate some post-treatment control)
- Chronic treatment
(melbourne patient, belgium patients)
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What barriers are there to a HIV cure?
1) Latently infected T cells
2) Residual viral replication
3) Anatomical reservoirs
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The two forms of HIV infected T-cells are:
1) Productive infection
- DNA positive (integrated virus)
- RNA positive (virus that comes out of cell)
- HIV protein positive
- DEATH (cell death, daughter virion goes on to infect new cells)
2) Latent infection
- DNA positive
- RNA negative
- HIV protein negative
- SURVIVAL (of host cell)
**its never one state or the other, not all or nothing, its a spectrum of activity between latency and full infection
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Latently infected cells are ____
RARE
- 1 in 1 million T cells are latent
- They dont express specific surface markers so big challenge in the field is to identify a marker to identify a latently infected cell
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How do infected cells survive on ART?
Latent infected cells
- integrated pro-virus
- doesnt express any foreign antigens
- Therefore hidden from the immune system
- gets into a long lived T cell (central memory and and naive t cells - designed to last a lifetime, its here that HIV establishes latency)
- as long as the cell is not activated, it persists
- Once cell becomes activated, active viral replication continues
- Integration into DNA also allows for replication of viral DNA when the latent T-cells undergo proliferation
(clonally expanded infected cells)
- together, this forms the biggest barrier to a HIV cure
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Clonally expanded infected cells
Off ART = random integration
On ART = expanded clones (come from the same infected parent cell)
Can account for 50% of infected cells
Sites of integration may give the infected cell a survival advantage
139
HIV persistence on ART
Residual virus production
"active reservoir"
- Any virus coming out of this cell cannot infect a new cell because this person is on ART
- for some reason, these cells survive and dont die, dribble out low levels of virus, not a problem for someone on treatment, but the moment you stop treatment, there is active virus in the system to rebound
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Concept of Tissue Reservoirs:
Tissues such as lymph nodes, GIT, brain are protected from drugs and immune system -> can find infected cells in lymph nodes and gut
- B cell follicles in lymph node
(HIV virus sits in the B cell follicle which is a sanctuary because cytotoxic T cells cant enter the follicles, and neither can the ART drugs, so B cell follicles seem to be very important source of active virus production)
141
Clinical strategies to achieve remission off ART include:
1) Virus elimination
2) Gene therapy
3) Immunotherapy
4) Vaccines and antibodies
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Latency reversal involves what methods?
Shock and Kill
>latent cell
>use latency reversing agent to activate the cell and cause productive infection
>starts producing HIV daughter virions but they cannot infect new cells because of ART
>immune mediated killing or pro-apoptotic drugs to kill off the productive infection cells
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Latency Reversing Agents (LRAs)
Most potent type of LRAs are the TLR agonists
- Latency reversal possible in vivo
- No induction of cell death (most likely need to combine latency reversal agents with another intervention that mediates cell death)
- Future studies need more potent LRAs and/or combinations
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Permanent silencing: "Block and Lock"
Trying to push the virus into further latency so it will never reactivate
- deep-latency
- Tat-inhibitor or mTOR inhibitor silencing RNAs
- this strategy has not yet reached the clinic
145
Gene therapy to eliminate CCR5
>HIV+ on cART
>Leukapharesis & CD4+ T-cell isolation
(mix of CCR5 pos and neg cells, collect large number of leukocytes)
>ZFN modification of CCR5
(ex-vivo gene scissors (Zinf finger Nucleases) use to excise CCR5 gene)
>CCR5 neg cells expanded ex-vivo and trhen re-introduced into patient
- get 5-15% of cells to be CCR5 negative, but it doesnt seem to be enough to stop the virus coming back
- Other ways looking at modifying stem cells
