Therapeutic vaccination Flashcards
(89 cards)
1
Q
What is the cancer immunotherapy cycle?
A
- Release of tumour antigens due to tumour cell lysis
- Antigen taken up by DCs
- DCs instruct T-cells to become more activated & attack tumour
- T-cells attack tumour and cause more lysis
- More DC activation -> cycle
2
Q
At which stages can the cancer immunotherapy cycle be targeted?
A
All stages
3
Q
What is the role of DC vaccines in the cancer immunotherapy cycle?
A
Aim: to kickstart the immunotherapy cycle by loading DCs with tumour antigen
4
Q
What is the biggest difference between prophylactic vaccines (against infectious diseases) and therapeutic vaccines?
A
Prophylactic vaccines often aim for a humoral response, therapeutic vaccines for a cellular response
5
Q
In which settings can therapeutic vaccines be used?
A
- Cancer: start/boost cancer immunotherapy cycle
- Chronic infections: overcome exhaustion
6
Q
Which cells are used as APCs in therapeutic vaccination? Why?
A
DCs -> able to present internalized antigens on MHCI (cross-presentation) & MHCII -> induces strong CD4+ and CD8+ T-cell response
7
Q
Which two antigen presentation pathways do DCs have?
A
- Cross-presentation
- Regular presentation
8
Q
Where are antigens that are presented on MHCI usually derived from?
A
Proteins in the cytosol
9
Q
How are proteins in the cytosol processed for presentation on MHCI? (2)
A
- Degradation in proteasome
- Loading onto MHCI in the ER
10
Q
How can external antigens be presented on MHCI? (2)
A
Cross-presentation:
1. Migration of externally derived proteins to the proteasome, where they enter the cytosolic pathway
2. Exchance of peptides in the endosome -> MHCI internalized with the endosome and loaded with external proteins
11
Q
Why is cross-presentation an important feature of any APC used in therapeutic vaccination?
A
A potent CD8+ T-cell response needs to be induced
12
Q
How are externally-derived proteins loaded onto MHCII?
A
- Endocytosed antigens are degraded in the endosome
- The endosome contrains MHCII complexes which can be directly loaded
13
Q
Why is activation of CD4+ T-cells important for a good therapeutic vaccine?
A
Th-help allows for strongly activated CD8+ T-cells
14
Q
Which factor do activated CD4+ T-cells express, by which they influence DCs? What are the effects of this? (2)
A
CD40L -> binds to CD40 on DC
1. Release of IL-12 & IFN-γ by DC
2. Expression of CD70 by DC -> binds to CD27 on CD8+ T-cell
15
Q
What happens in the absence of a CD4+ T-cell response in therapeutic vaccines?
A
Weak and short-lived CD8+ responses
16
Q
What are factors to consider when choosing an antigen for therapeutic vaccines?
A
- Specificity -> antigen only present in tumour tissue
- Must be no central tolerance to the antigen
- Prevalence in multiple patients -> allows for production of off-the-shelve vaccines
17
Q
Which types of target antigens can be considerd for therapeutic anti-cancer vaccines? (2) How can they be subdivided (2&3)?
A
- Tumour-associated antigens
-Overexpressed proteins
-Cancer germline antigens - Tumour-specific antigens
-Oncoviral antigens
-Shared neoantigens
-Private neoantigens
18
Q
What is the downside of using tumour-associated antigens in therapeutic vaccines?
A
They are not tumour-specific -> also present in healthy tissue
19
Q
What are the characteristics of overexpressed proteins as antigens for therapeutic vaccines? (3)
A
- Variable tumour-specificity
- High central tolerance
- Often high prevalence in multiple patients
20
Q
What is an example over overexpressed proteins in tumours?
A
Differentiation antigens
21
Q
What are cancer testis antigens?
A
Antigens mostly expressed in germline/embryonic tissue, but not in mature tissue
22
Q
What are the characteristics of cancer testis antigens as antigens for therapeutic vaccines? (3)
A
- Re-expression in tumour-tissues -> relatively specific (more so than overexpressed antigens)
- Low central tolerance
- Often high prevalence in multiple patients
23
Q
What are oncoviral antigens?
A
Antigens specific to tumour-inducing viruses
24
Q
What are the characteristics of oncoviral antigens as antigens for therapeutic vaccines? (3)
A
- High tumour-specificity
- No central tolerance
- Often high prevalence in multiple patients
25
What are examples of oncoviral antigens? (2)
1. HPV proteins in HPV-derived carcinoma
2. Chronic HBV proteins in HBV-induced HCC
26
What can be a downside of targeting oncoviral antigens in therapeutic vaccines?
Tumours often don't rely on oncoviral antigens for survival -> can be downregulated
27
What are shared neoantigens?
Neoantigens that are commonly found in multiple patients with a specific type of cancer
28
What are the characteristics of shared antigens as neoantigens for therapeutic vaccines? (3)
1. High tumour-specificity
2. No central tolerance
3. Medium-to-high prevalence in multiple patients
29
What are private neoantigens?
Tumour neoantigens specific to one patient
30
What are the characteristics of private antigens as antigens for therapeutic vaccines?
1. High tumour-specificity
2. No central tolerance
3. Not present in multiple patients
31
What is the downside of private antigens as a target antigen for therapeutic vaccines?
Requires individual vaccine production -> expensive & laborious
32
By which mechanisms can shared neoantigens be generated? (2)
1. Insertions & deletions causing frameshift across the whole gene
2. Generation of new HLA-binding motifs by frequently occuring point mutations
33
How long are peptides in MHCI?
~9 amino acids
34
What happens when peptides >9 amino acids are presented on MHCI? What is the effect of this?
Bulging of the peptide -> less immunogenic
35
What are anchor residues?
Dominant positions in the MHCI binding groove that determine which peptides are able to bind. HLA-subtype specific.
36
Where are the anchor residues of MHCI located?
Positions 2 & 9 (mostly)
37
What is the downside of the limited peptide length & anchor residues of MHCI?
Not all peptides are able to bind all MHCI -> requires matching of HLA-type to peptide antigens used in therapeutic vaccines
38
Why is MHCII not HLA-restricted? (at least not as badly as MHCI)
Less limits on peptide length & less dominant anchor residues
39
What are non-cellular vaccine platforms for therapeutic vaccination? (3)
1. DNA vaccines
2. RNA vaccines
3. SLP vaccines
40
What are the advantages of DNA vaccines for therapeutic vaccination? (2)
1. Built-in adjuvants such as CpG, which activates TLR9
2. Can have built-in co-expression of chemokines to target specific DC subsets
41
What is the disadvantage of DNA vaccines for therapeutic vaccination?
Need to be delivered to DCs in vivo -> they need to be the cells presenting the antigens
42
What are the advantages of RNA vaccines for therapeutic vaccination? (2)
1. Built-in adjuvants such as ssRNA & dsRNA
2. IV lipoplex vaccine can access DCs systemically
43
What is the disadvantage of RNA vaccines for therapeutic vaccination?
Need to be delivered to DCs in vivo -> they need to be the cells presenting the antigens
44
What are SLPs?
Synthetic long peptides
45
What are the advantages of using SLP vaccines for therapeutic vaccination? (2)
1. Short peptides can be directly presented on MHC
2. SLPs yield best result with adjuvants and CD4+ T-cell help
46
What is the disadvantage of using SLP vaccines for therapeutic vaccination?
No built-in adjuvants
47
What is the advantage of using SLPs over SSPs (synthetic short peptides) for therapeutic vaccination?
SSPs can directly bind to MHCI on all cell types -> if presented without inflammatory signals this causes tolerance induction to tumour antigens
SLPs require processing and are therefore most efficiently presented by DCs
48
Why is the use of SLPs more efficient than whole protein antigens for therapeutic vaccination?
SLPs only contain the target epitopes -> more concentrated processing & presentation of antigen
49
What is a disadvantage of using SLPs instead of whole protein antigens for therapeutic vaccination?
SLPs have limited processing possibilities -> more MHC-restricted
50
Why can short synthetic peptides be used for ex vivo DC loading for therapeutic vaccinations? What is necessary for this to occur?
Can directly bind to MHCI on DCs
Condition: the HLA-type of the DC must be compatible with the SSP provided
51
What are the options for ex vivo DC loading for therapeutic vaccination? (5)
1. Synthetic short peptides
2. SLPs
3. mRNA/RNA
4. DNA
5. Tumour lysate
52
What are disadvantages of ex vivo DC loading? (2)
1. Ex vivo culture leads to decreased capacity to induce a immune response
2. moDCs can be less functional due to immunosuppressive mechanisms present in cancer patients
53
What are the characteristics of short synthetic peptides (SSP) for therapeutic vaccination? (3)
1. HLA-restricted
2. No cross-presentation required
3. Potential for off-target HLA-binding, leading to tolerance induction
54
What are the characteristics of SLPs for therapeutic vaccination? (4)
1. Efficient HLA-I and HLA-II presentation
2. Less HLA-restricted than SSP
3. Induces CD4+ and CD8+ T-cells
4. Only gives linear epitope B-cell responses
55
Why do SLPs only give linear epitope B-cell responses?
B-cells recognize tertiaire structures of antigens -> lack of this tertiary structure in SLPs leads to absence of meaningful antibody responses
56
What are the characteristics of whole proteins for therapeutic vaccination? (4)
1. Inefficient cross-presentation
2. Lower induction of CD8+ due to low cross-presentation
3. No HLA-restriction
3. Induces CD4+, CD8+ (weak) & B-cell responses
57
What are the characteristics of cell lysates for DC loading for therapeutic vaccination? (4)
1. Contains multiple antigens
2. Likely inefficient cross-presentation
3. No HLA-restriction
4. Induction of CD4+, CD8+ (weak) and B-cell responses
58
What does HLA restriction of DNA/mRNA therapeutic vaccines depend on?
The HLA restriction of the protein encoded by the DNA/mRNA
59
What are the advantages of cellular (DC-based) therapeutic vaccinations? (2)
1. Short peptides can be used without risk of tolerance induction
2. Well-controlled antigen loading & maturation
60
What are the disadvantages of cellular (DC-based) therapeutic vaccinations? (5)
1. Requires personalized vaccine preparation
2. Ex vivo culture may impair DC function
3. Optimal timing & route difficult to establish
4. Natural DC subsets difficult to purify in large numbers
5. Variability in quality
61
What are the advantages of non-cellular therapeutic vaccinations? (5)
1. Generic production possible for shared antigens
2. Stable & easy to manufacture (-> cheap)
3. Good DC quality
4. Scarce DC subsets can be cultured in vivo
5. Optimal timing & route established
62
What is the disadvantage of non-cellular therapeutic vaccinations?
Poorly controlled antigen loading and maturation
63
What are the three signals required for effective T-cell priming?
1. Presentation of antigen by MHC to TCR
2. Costimulatory molecules
3. Cytokines
64
How can the right cytokine & costimulatory environment for T-cell activation for therapeutic vaccines be achieved?
Triggering PRRs on DCs by PAMPs/DAMPs -> use adjuvants
65
What is the result of an absence of a pro-inflammatory cytokine and costimulatory environment on T-cell activation?
Tolerance induction to presented antigen
66
What could be a possible application for antigen-loaded DCs that lack inflammatory costimulatory & cytokine signals?
Tolerance induction in auto-immune disease
67
What is the advantage & disadvantage of the fact that mRNA/DNA vaccines form their own adjuvant?
Advantage: they automatically induce an inflammatory type of DC
Disadvantage: triggering of TLR7 & TLR9 shut down translation -> encoded epitopes less effectively expressed
68
How can non-cellular vaccines be targeted to DCs in vivo, ensuring that antigens are efficiently expressed? (2)
1. Passive targeting: dependent on scavenging & internalization by tissue-resident DCs at injection site
2. Active targeting: conjugating peptides/proteins/mRNA particles to DC-targeting antibodies/ligands
69
What are antigen vehicles that can be used for active targeting of DCs? (5)
1. Biodegradable nanoparticles
2. Antigen-antibody conjugates
3. Antigen-glycan conjugates
4. Antigen-TLR conjugates
5. Micro-organism/micro-organism-like particles
70
What are the advantages of active DC targeting? (5)
1. Targeted delivery
2. Protection of antigen
3. Biodistribution of antigen
4. Controlled release of antigen
5. Allows for specific targeting of DC subsets
71
What are the two methods to assess vaccine-induces immune responses?
1. In vivo: monitoring of cytokines/T-cell activation in patient blood
2. In vitro experiments to assess T-cell capacity
72
What is the downside of measuring T-cell activation to vaccine antigens in vivo? How can this be resolved?
Often low numbers of antigen-specific T-cells -> no reliable data
T-cells can be isolated & expanded in in vitro experiments
73
What is the process of an in vitro experiment to measure T-cell responses to vaccine antigens?
1. PBMCs + moDCs harvested from blood
2. Cells expsoed to vaccine/vaccine components
3. Readouts of cytokine production & cellular responses
74
Which in vitro readouts are frequently used to gauge antigen-specific T-cell responses?
1. Supernatant: IFN-γ ELISA (sometimes other cytokines)
2. ELISPOT IFN-γ to assess cellular function
3. Flow cytometry to check activation markers
75
What is the advantage of ELISA over ELISPOT? What is the advantage of ELISPOT over ELISA?
ELISA = easier to perform, less sensitive
ELISPOT = more difficult to perform, but more sensitive
76
What does enrichment of TCR clonality after antigen exposure in vitro point to?
That these T-cells are specific to the antigen used
77
Why is there a need of a therapeutic HBV vaccine?
There is currently no curative HBV treatment
78
What is the process required to select good SLPs for a therapeutic vaccine? (3)
1. Immunopeptidomics on antigen-loaded DCs
2. Immunopeptidomics on diseased hepatocytes
3. Immunopeptidomics on HBV-expressing cell lines
79
What is an important requirement for SLPs in therapeutic vaccines against chronic viruses?
They need to target conserved regions of the virus to not allow the virus to mutate and escape
80
Which strategies can be used to enhance DC therapy anti-cancer efficacy? (2)
1. Targeting the TAM phenotype
2. Combination with checkpoint blockade
81
What is a TAM?
Tumour-associated macrophage
82
What is the most common phenotype of tumour-associated macrophages?
M2 phenotype -> immunosuppressive
83
How can TAMs be depleted to allow higher efficacy of DC therapy? What are its effect?
CSFR inhibitors -> depletes macrophages
Gives improved anti-tumour effects over DC therapies alone
84
What are immunosuppressive mechanisms of TAMs? (5)
1. Inhibition of DC maturation with IL-10 & TGF-β
2. Amino acid metabolic starvation of T-cells
3. Suppression of effector T-cells with prostaglandins
4. Expression of inhibitory immune checkpoints
5. Induction of Tregs with IL-10 & TGF-β
85
Which inhibitory immune checkpoints are expressed by TAMs?
1. PD-L1 / PD-L2
2. B7-H4
3. VVISTA
86
What is the most commonly used immune checkpoint blockade? How is this achieved?
PD-1/PD-L1 blocking -> blocked with antibodies
87
What is the effect of immune checkpoints on the antigen presentation of DCs to T-cells? What effect could blocking these checkpoints have?
PD-1/PD-L1 can hamper T-cell priming by DCs in the lymph node -> blocking this enhances T-cell priming by DCs
88
What is the disadvantage of ex vivo loading of DCs when it comes to immune checkpoints?
Ex vivo loaded DCs express high(er) PD-L1
89
What are the results of in vivo DC trials for mesothelioma?
Response in only a small subset of patients, but can induce durable responses
