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immunopathology > L12 - Dengue virus immunity and vaccination part 2 (Laura Rivino) > Flashcards

L12 - Dengue virus immunity and vaccination part 2 (Laura Rivino) Flashcards

• To appreciate the challenges around dengue vaccine design • To describe pros & cons of the different vaccine platforms • To evaluate the most suitable vaccine platform for the design of a dengue vaccine • To describe the current landscape for dengue vaccines

1
Q

Why is a holistic approach needed to stop dengue?

A

🌍 Dengue control requires vaccination, vector control, and therapeutic development, including antivirals and host-directed therapies.

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2
Q

Why is vector control crucial for dengue prevention?

A

🦟 Mosquito control helps limit dengue spread, with advances in genetic engineering offering new solutions.

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3
Q

What are host-directed therapies, and why are they promising for dengue?

A

🛡️ Dengue is immune-mediated, so modulating the host immune response may be more effective than targeting the virus, which is transient.

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4
Q

What are the key phases in dengue progression?

A

🩸 Mosquito bite → Fever & viremia → Critical phase (Day 4-5) when severe symptoms may develop.

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5
Q

Why was an antiviral for dengue halted in clinical development?

A

❌ The exact reasons are unclear, but the challenge is that by the time severe symptoms appear, viremia has waned, limiting antiviral effectiveness.

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6
Q

How could targeting the immune response improve dengue treatment?

A

🔄 Since severe dengue occurs after viremia clears, restoring the dysregulated immune response could be more beneficial than antivirals.

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7
Q

why might the late onset of severe dengue be both a challenge and an opportunity

A

🤔 Challenge: Delayed symptoms make treatment harder.
🪟Opportunity: A wider intervention window exists for therapies that target immune regulation rather than the virus itself.

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8
Q

Why is severe dengue difficult to treat?

A

⚠️ Severe dengue manifests late (≥ day 4) and occurs after the virus is cleared, limiting the effectiveness of antiviral treatments.

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9
Q

When does viremia subside in dengue infectin

A

Viremia subsides around day 5, reducing the window for antiviral therapy

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10
Q

What is the therapeutic window for targeting dengue

A

⏳ Antivirals: Before day 5 🦠
Host immunomodulators: Before day 6-7 🛡️

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11
Q

How does the risk of severe dengue change with multiple infections?

A

🔄 Highest risk occurs during a second heterologous infection, medium risk in the first infection, and low risk in subsequent infections.

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12
Q

What is the main goal of dengue vaccination?

A

💉 To induce immunity to all four serotypes, making the person low risk upon real-life dengue exposure.

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13
Q

What is the major challenge of live attenuated dengue vaccines?

A

⚠️ They provide partial, unbalanced immunity, which can put vaccinated individuals at higher risk than those who were dengue-naive.

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14
Q

Why is a tetravalent vaccine necessary for dengue?

A

🛡️ It must generate balanced immunity to all four serotypes, preventing severe disease from any serotype.

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15
Q

What makes it difficult to determine dengue vaccine effectiveness?

A

❓ Correlates of protection are unknown—there is no clear antibody level that guarantees protection.

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16
Q

Why is antibody response measurement complex in dengue?

A

📊 Different serotypes require different antibody titers for protection, complicating tetravalent vaccine design.

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17
Q

💉 What are the three main types of dengue vaccines?

A

1️⃣ Live attenuated vaccines (LAVs): ✅ Broad/sustained immunity ❌ Unbalanced serotype priotection
2️⃣ Virus-vectored vaccines: ✅ Safe, broad immunity ❌ Variable efficacy concerns
3️⃣ Non-infectious vaccines: ✅ Safe, balanced immunity ❌may lack sustained / long term protection

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18
Q

Why does a second heterologous dengue infection pose the highest risk for severe disease?

A

🦠 The first infection provides partial immunity which can enhance viral replication and immune activation upon a second infection with a different serotype leading to severe disease. subsequent infections carry a lower risk due to broader immunity

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19
Q

What is the main challenge of dengue vaccination

A

Achieving balanced immunity to all four serotypes is difficult. Partial or unbalanced immunity from vaccination could increase the risk of severe dengue rather than provide full protection.

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20
Q

What is the main advantage of live attenuated dengue vaccines

A

They replicate in the host mimicking natural infection and eliciting broad and sustained immune responses involving both antibodies and T cells

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21
Q

What is the major disadvantage of live attenuated dengue vaccines

A

⚖️ A competition between the four viral strains in the vaccine can lead to unbalanced immunity where one or more serotypes dominate reducing overal effectiveness

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22
Q

How is virus attenuation achieves in LAVs

A

1️⃣ Passaging the virus in non-human cell lines (e.g., Primary Dog Kidney (PDK) cells) to weaken its ability to cause disease.
2️⃣ DNA recombination technology, introducing specific mutations to reduce pathogenicity while maintaining immunogenicity.

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23
Q

Why was the live attenuated vaccine platform chosen for dengue?

A

Successful live attenuated vaccines exist for other flaviviruses e.g. Yellow fever and Japanese Encephalitis, making it a logical choice for dengue

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24
Q

What is a potential risk of live attenuated vaccines?

A

Although never observed in dengue vaccines, there is a theoretical risk of genetic reversion to a pathogenic form

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25
What are the three main live attenuated dengue vaccines in development?
1️⃣ Dengvaxia® (CYD-TDV) – Developed by Sanofi Pasteur, licensed in 2015. 2️⃣ TAK-003 – Developed by Takeda, licensed in some countries. 3️⃣ TV003/TV005 – Developed by NIAID, in clinical trials with Butantan and Merck.
26
what does NIAID stand for
National Institute of Allergy and Infectious disease (NIAID)
27
What is the key difference in attenuation strategies between Dengvaxia, TAK-003 and TV003/TV005?
👯‍♀️ Dengvaxia®: Uses Yellow Fever 17D as a backbone. 🦴 TAK-003: Uses an attenuated DENV-2 backbone with prM/E proteins from all four serotypes. 🧬TV003/TV005: Uses DNA recombination technology to introduce specific mutations in all four serotypes.
28
What is the commercial name of the first licensed dengue vaccine, and who developed it?
Dengvaxia was developed by Sanofi Pasteur
29
What is the backbone of the Dengvaxia vaccine?
Dengvaxia is based on the yellow fever vaccine backbone with PRM and E proteins substituted from dengue virus serotypes 1-4
30
Why was using the yellow fever vaccine backbone for Dengvaxia potentially problematic?
The nonstructural proteins in Dengvaxia came from yellow fever virus instead of dengue virus, whic may not elicit an effective T cell response against dengue
31
What was the overall vaccine efficacy of Dengvaxia in individuals over 9 years old
📊 65.6% overall, with higher efficacy in seropositive individuals (81.9%) compared to seronegative individuals (52.5%).
32
How effective was Dengvaxia in children under 9 years old?
The efficacy was much lower: 👶 Overall: 44.6% Seropositive children: 70% Seronegative children: Only 14%
33
What alarming trend was observed in vaccinated children under 9 years old durng long - term follow up?
Increased rates of hospitalisation for vaccinated children under 9 years old, especially in year 3 of follow up
34
What did the CYD-14, CYD-15 and CYD-57 clinical trials reveal about hospitalisation rates in young children
More cases of severe dengue occured in the vaccine group copared to the control group, especially in seronegative children under 9 years old
35
What did Scott Halstead warn and what was the WHOs response
Scott Halstead, a dengue researcher, warned about imbalanced immunity leading to enhanced infection, which was later confirmed. But after a vaccine panel, WHO concluded in 2016 that Dengvaxia was safe for children aged 9+
36
What happened in the Phllipines after Denvaxia was rolled out
The government vaccinated 830,000 children, but after 19 vaccinated children died following natural dengue infection the program was halted
37
what did Sanofi Pasteur announce in November 2017
In November 2017 Sanofi Pasteur announced that the vaccine could exacerbate cases of dengue in children never previously infected validating Halstead's concerns and halting the campaign in the Phillipines.
38
What is the current WHO recommendation for Dengvaxia
WHO recommends Dengvaxia only for seropositive individuals aged 9 - 16 years. It should not be given to those without prior dengue infection due to the risk of severe disease
39
What is the backbone of the TAK-003 dengue vaccine?
🦴The backbone of TAK-003 is derived from Dengue serotype 2 (DENV-2) strain PDK-53, which has been attenuated in vitro. This provides all the nonstructural proteins from DENV-2, while the pre-membrane (prM) and envelope (E) proteins are substituted from all four dengue serotypes, making it a tetravalent vaccine.
40
What are the four vaccine groups in the TAK-003 clinical trial
💉 The study tested four different vaccine groups: 1️⃣ Two doses, three months apart (light blue). 2️⃣ One dose (red). 3️⃣ One dose plus a booster one year later (dark blue). 4️⃣ Placebo (green, no vaccine).
41
What did the 18 month interim clinical trial data show about antibody response ( TAK-003 clinical trial)
📊 The vaccine generated neutralizing antibodies against all four dengue serotypes. However, responses were strongest for Dengue 2, particularly in seronegative individuals at baseline. This suggests an imbalance in immunity
42
What was the overall vaccine efficacy (VE) in preventing virologically confirmed dengue (VCD) from years 0-3 for TAK-003
🏥 The overall vaccine efficacy was 62% in preventing virologically confirmed dengue. VE was lower in seronegative individuals (54%) compared to seropositive individuals (65%).
43
How did vaccine efficacy (VE) vary by age group for TAK-003
👶🧑 VE was lower in younger children: 4-5 years old: 42% Older children: Higher efficacy compared to younger children
44
how effective was the TAK-003 vaccine in preventing hospitalisation due to dengue
🚑 The vaccine provided 83.6% protection against dengue-related hospitalization. Protection was lower in 4-5-year-olds (~50%) but reached 89% in older children.
45
How did vaccine efficacy change in year 3 for TAK-003
📉 By year 3, overall vaccine efficacy dropped to 44.7%. The decline was more noticeable in seronegative individuals.
46
What were the serotype specific efficacy rates for TAK-003 against different serotypes
🦠 Dengue 2: 72-84.9% efficacy. 🦠 Dengue 1: Moderate efficacy. 🦠 Dengue 3 & 4: Very low efficacy (9.5% for DENV-3, negative for DENV-4). However, due to limited cases of DENV-3/4 in the study region, statistical conclusions were difficult to draw.
47
What concerns arose about the efficacy against Dengue 3 and 4 for TAK-003
⚠️ Some investigators worried about the potential for antibody-dependent enhancement (ADE) with low efficacy for DENV-3/4. However, due to very few DENV-3/4 cases in the study, more research is needed to determine whether TAK-003 provides adequate protection against these serotypes.
48
What did the clinical trials reveal about protection against hospitalisation over time for TAK-003
🏥 The vaccine maintained strong protection against hospitalization (~70.8%), with higher efficacy in seropositive individuals compared to seronegative ones.
49
What did the WHO's SAGE recommend in 2023 regarding the TAK-003 dengue vaccine?
🌍 The WHO's Strategic Advisory Group of Experts (SAGE) recommended that TAK-003 could be introduced in regions where dengue is highly endemic. Although efficacy is not ideal, the vaccine may still provide benefits.
50
Why is there uncertainty about TAK-003's effectiveness against dengue serotypes 3 and 4?
🔬 There is insufficient data on the vaccine’s efficacy against dengue serotypes 3 and 4. However, the WHO still supports its use in high-transmission regions while awaiting further research.
51
What age group did WHO recomend for TAK-003 vaccination
WHO recommended the vaccine for children aged 6 - 16 years (and vaccine introduction should be accompanied by a well designed communication stretegy and community engagement)
52
What is the dosing schedule for TAK-003
🕒 The recommended dosing schedule consists of two doses with a 3 month interval between doses
53
Why should TAK-003 vaccination program include public engagement?
🗣️ Public engagement is crucial to ensure vaccine recipients understand what they are receiving, including its benefits and potential risks.
54
What is Takeda currently doing post- licensure for TAK-003
🔬 Takeda is conducting large-scale post-licensure clinical trials, particularly in regions where dengue serotypes 3 and 4 are circulating, to gather more efficacy data.
55
Have there been any reports of adverse events linked to TAK-003?
✅ So far, no adverse events have been reported, which is good news, as it suggests the vaccine does not have the same safety concerns as the first dengue vaccine.
56
What is TV003
TV003 is a live attenuated dengue vaccine developed by the national institute of allergy and infectious diseases (NIAID) and later brought forward by various partners including Merck
57
What is the key genetic modification in TV003
🏗️ Scientists introduced 30-nucleotide deletions (Δ30) in the 3’ untranslated region (UTR) of all four dengue serotypes to attenuate the virus.
58
Why was a different approach needed for Dengue 2 in TV003?
🔄 The Δ30 mutation was not sufficient to attenuate Dengue 2, so researchers used a Dengue 4 backbone for the Dengue 2 strain, combining Dengue 4 nonstructural proteins and capsid with Dengue 2 pre-membrane (prM) and envelope (E) proteins.
59
What additional mutation was introduced for Dengue 3 in TV003
🧬 A 31-nucleotide deletion was added to ensure adequate attenuation of Dengue 3.
60
What were the results of the clinical trials for TV003?
✅ The vaccine was well tolerated and induced neutralizing antibodies against all four dengue serotypes. Importantly, it generated a balanced tetravalent T-cell response (CD4+ and CD8+ T cell response)
61
What did research from Alex Sette’s lab reveal about TV003’s immune response?
🧫 Studies showed that TV003 elicited strong T-cell responses, primarily targeting NS3 and NS5 nonstructural proteins, which are highly conserved across dengue serotypes.
62
Why is a conserved T-cell response beneficial for dengue vaccination?
🎯 A highly conserved immune response helps avoid antibody-dependent enhancement (ADE) and original antigenic sin, improving vaccine effectiveness across serotypes.
63
What is a Human Challenge Study?
🔹 A research method where healthy volunteers are deliberately infected with an attenuated pathogen to study immune responses and vaccine efficacy.
64
Why are human challenge studies important
Why are Human Challenge Studies Important? ✅ Speed up vaccine development ✅ Provide early evidence of efficacy ✅ Reduce the need for long, expensive clinical trials
65
What is the Dengue challenge strain
🦠 DENV-2 Δ30 🔹 Originally developed as a vaccine candidate but caused mild symptoms 🔹 Now used to test vaccine effectiveness in human challenge trials
66
How was the Dengue Challenge Study Designed?
👩‍🔬 Participants: 41 healthy individuals 💉 Groups: 21 vaccinated (TV003) 20 unvaccinated (placebo) 🕒 6 months later → All were challenged with DENV-2 Δ30
67
Key Results from the Dengue Challenge Study
Group Viremia Detected? Rash? Neutropenia? Vaccinated (TV003) ❌ 0% (No viremia) ❌ 0% ❌ 0% Placebo (Unvaccinated) ✅ 100% ✅ 80% ✅ 20% Conclusion: TV003 vaccine provided 100% protection against viremia and helped prevent symptoms.
68
what is sterilising immunity
🛡️ Complete prevention of viral replication with no viremia detected or no increase in antibody response (suggesting the immune system was never triggered by live virus)
69
evidence of sterilising immunity in TV003 trial
🔹 12 out of 21 vaccinated individuals showed no increase in neutralising antibodies after being exposed to the dengue challenge strain 🔹 This suggests zero viral replication in these participants
70
evidence of sterlising immunity ++++
Why is This Important? 💡 Normally, if a virus infects someone—even if they don’t get sick—the immune system recognizes the virus and boosts antibody levels in response. 💡 However, in these 12 individuals, antibody levels stayed the same, meaning: ✔️ The virus never replicated enough to trigger an immune response. ✔️ The vaccine completely blocked infection before the immune system even had to fight it. What Does This Suggest? 🛡️ Sterilizing Immunity – The highest level of protection a vaccine can provide. 🛡️ The immune system neutralized the virus immediately, preventing any replication or spread. 🛡️ No detectable viremia (virus in blood) = No risk of transmission. Why Is This a Big Deal? 🚀 Most vaccines don’t achieve sterilizing immunity—they reduce disease severity but don’t always prevent infection entirely. 🚀 This suggests the TV003 vaccine may be highly effective at stopping dengue transmission, not just reducing symptoms. 🚀 If sterilizing immunity is confirmed in larger trials, TV003 could be a game-changer for dengue prevention worldwide.
71
What is the PRNT test?
🔬 Plaque Reduction Neutralization Test (PRNT) ✅ Measures neutralizing antibody levels before & after challenge to see if antibodies increase --> if so virus likely replicated → No sterilizing immunity
72
Key Findings from the Phase 3 Butantan Trial
📍 Conducted in Brazil with 16,000+ participants (ages 2-59) 💉 Single-dose vaccine (major advantage) 🚨 No severe dengue cases or warning signs
73
TV003 Vaccine Efficacy by Serotype
Serotype Overall Efficacy (%) Seropositive (%) Seronegative (%) DENV-1 75.8% 80% 70% DENV-2 59.7% 64.3% 43.6% Total (All Serotypes) 67% 76% 60% 🔹 Higher efficacy in seropositive individuals 🔹 Limited data on DENV-3 and DENV-4 due to low circulatio
74
Why is a Single-Dose Vaccine Important?
✅ Easier to distribute ✅ More cost-effective ✅ Higher compliance (avoids issues with missing booster doses)
75
what are te remaining questions on TV003
❓ How effective is it against DENV-3 & DENV-4? ❓ How long does immunity last? ❓ Will it provide lasting protection in endemic regions?
76
What are the challenges to dengue vaccine development
1️⃣ Four Dengue Serotypes (DENV 1–4) 2️⃣ No Validated Immune Correlates of Protection 3️⃣ Lack of an Accurate Animal Model 4️⃣ Difficulties in Measuring Serotype-Specific Immunity 5️⃣ Large & Long-Term Clinical Trials Required
77
Why does the presence of 4 dengue serotypes make vaccine development difficult
A dengue vaccine must provide balanced immunity against all four serotypes (DENV 1–4). Unequal immunity to different serotypes can lead to Antibody-Dependent Enhancement (ADE), increasing the risk of severe dengue.
78
Why is the lack of validated immune correlates a challenge for dengue vaccine development?
Scientists do not know the exact levels of antibodies or T cells required for full protection. This makes it harder to measure vaccine effectiveness and preduct long term immunity
79
Why is the lack of a suitable animal model a problem for dengue research
Dengue is a human specific virus, meaning common lab animals like mice do not naturally develop the disease. Modified mouse models exist but they do not fully mimic human immunity making vaccine testing more difficult
80
Why is it difficult to measure serotype specific immune responses in dengue?
Dengue antibodies are highly cross-reactive meaning natibodies against one serotype can also recognise others. this makes it challenging to determine if a vaccine is equally protective against all four serotypes
81
Why do dengue vaccines require large and long term clinical trials
Dengue outbreaks are unpredictable, so trials need tens of thousands of participants to gather enough data. long term follow up is required to ensure no adverse effects e.g. ADE appear years after vaccination
82
What are alternative vaccine platforms for dengue, and why are they being explored?
Alternative platforms, such as virus replicon particles (VRPs) are being explored because they may offer different immune responses, improved safety or better protection than traditional vaccines
83
How does E85 VRP dengue vaccine work?
It is based on Venezuelan equine encephalitis virus (VEE) replicon particles
84
VEE replicon particles ( for the VRP dengue vaccine) undergoes ...., contains .... and induces.....
Undergoes only one round of infection but cannot further replicate. Contains dengue envelope (E) proteins from all four serotypes to stimulate immune responses. Induces neutralizing antibodies and T-cell responses in mice and non-human primates.
85
What were the results of testing the E85 VRP vaccine in non-human primates
✅ All vaccinated animals developed antibodies against all four dengue serotypes. Complete protection against viremia for DENV-3 and DENV-4. Transient viremia observed in some animals for DENV-1 and DENV-2, suggesting incomplete protection for these serotypes.
86
What challenges remain for the E85 VRP dengue vaccine?
✅ The vaccine shows unequal protection across serotypes, with weaker protection for DENV-1 and DENV-2. The protective antibody threshold remains unknown. Further human trials are needed to assess effectiveness and long-term immunity.
87
What are the different vaccine platforms for dengue
📌 Live-attenuated vaccines (LAVs) – Weakened virus 🦠 📌 Purified inactivated vaccines (PIVs) – Killed virus ☠️ 📌 Subunit vaccines – Only viral proteins 🎯 📌 Virus-like particle (VLP) vaccines – Virus mimic but no genes 🏴‍☠️ 📌 DNA vaccines – Genetic blueprints 📜 📌 Virus-vectored vaccines – Hitching a ride on another virus 🚌
88
What are non-infectious dengue vaccines?
❌ vaccines that do not replicate at all e.g. Purified Inactivated Vaccines (PIVs) 🏴‍☠️ (Killed virus) Subunit vaccines 🎯 (Viral protein fragments)
89
What is the Purified Inactivated Vaccine (PIV)?
💡 A "dead" virus vaccine developed by Walter Reed Army Institute of Research (USA) & GSL which cannot replicate but still triggers an immune response
90
What’s a Virus-Like Particle (VLP) Vaccine?
🎭 Fake virus, real immune response! 🔗 Uses Envelope Domain III (EDIII) + Hepatitis B surface antigen (HBsAg) 🦠 Tetravalent version created by fusing EDIII domains ✅ Tested in mice & non-human primates 🐭🦧 ✅ Induces neutralizing antibodies & protection 🚀 Still under development!
91
Who developed the tetravalent purified inactivated vaccine (PIV)?
he US Walter Reed Army Institute of Research in partnership with GSK.
92
What antigens are present in the purified inactivated vaccine (PIV)
PRM and E proteins
93
What adjuvants were tested with the PIV vaccine
GSK proprietary adjuvants (Azo 01 and H3) and a classical adjuvant
94
What immune response was observed in non human primartesnon-human primates vaccinated with PIV?
Induction of neutralizing antibodies and reduced viremia after dengue virus challenge.
95
What are the licensed live attenuated dengue vaccines?
Dengvaxia (Sanofi Pasteur) – Based on a yellow fever backbone. Qdenga (Takeda, formerly TAK-003) – Based on a dengue 2 virus backbone.
96
How do live attenuated vaccines differ from non infectious vaccines
Live attenuated vaccines contain weakened viruses with all their components, while non-infectious vaccines contain only selected antigens.
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immunopathology (17 decks)

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