14. Cancer Immunology 1 Flashcards
1
Q
Why is it hard to gain an overview of the cancer immunology field?
A
Because it is a new and very dynamic field
2
Q
What are the key influences in cancer immunology?
A
- Cytotoxic T cells.
- Myeloid cells like macrophages and dendritic cells.
- The tumour micro-environment
- Inhibitory receptors.
3
Q
What is the role of cytotoxic T cells in tumour immunology?
A
- Cytotoxic CD8+ T cells do most of the killing in tumours.
- They are the cells the have the strongest effects on eliminating tumour cells.
- NK cells can help them
- They need to be activated by innate immune cells.
4
Q
What is the role of myeloid cells in tumour immunology?
A
- Macrophages and dendritic cells.
- They are the innate components that activate cytotoxic and other T cells.
- They contribute to and shape the tumour microenvironment.
- They don’t eliminate tumour cells themselves.
- They shape the environment where T cells works and influence their function.
5
Q
What is the role of the tumour microenvironment in tumour immunology?
A
- It is a suppressive environment.
- It suppresses cytotoxic T cells and other immune cells.
- This is a key factor that needs to be overcome for any cancer therapeutic.
6
Q
What is the role of inhibitory receptors in tumour immunology?
A
- Inhibitory receptors function across many cell types including cytotoxic T cells and myeloid cells.
- They are upregulated on persistent immune cell stimulation and attenuate immune cell function.
- There to limit the immune response and prevent damage.
- Mostly PD-1 and CTLA-4
7
Q
What are the key concepts of the anti-tumour response?
A
- How do tumours activate the innate immune response.
- What in tumours do T cell recognise during antigen presentation
- How do innate and adaptive immune cells get into tumours.
- How does the TME interact with the immune cells.
8
Q
How do tumours interact with the draining lymph node?
A
- Dendritic cells leave the tissues the tumour is resident in and go to the tumour draining lymph node.
- This is the communication between the tumour and activation of the T cells.
- Antigens from tumour are being presented to T cells to activate adaptive immunity
9
Q
What is the cycle of activating the anti-tumour response?
A
- Activating innate immunity
- This primes adaptive immunity
- Cells are recruited to the TME.
- The cells can adapt to the TME.
- This cycle underpins that anti tumour response
10
Q
What are the key principles of tumour immunity?
A
- The immune system is complex
- Immune cells interact
- Immune cells have different states that are dynamic
- Tumour cells are dynamic
- Any immune response need to be understood at the systems level
11
Q
How is the immune system complex?
A
- There are lots and lots of cell types.
- You cannot understand tumour immunity by looking at 1 cell type.
- It is a complex system that interacts between cells and tissues.
- This makes treatment difficult.
12
Q
How do different immune cell states effect immunity?
A
- T cells are not just T cells there are many different sub-types.
- Different sub-types have different roles and we need to understand the role of each.
- If you target T cells you usually target all T cells from Tregs to effector cells. You can’t focus treatment that specifically.
- These states are dynamic and can change and be influenced by the TME.
- Other cells like DCs can also have subtypes
13
Q
How are tumour cells dynamic?
A
- Tumours are usually a mix of cells with lots of different genetic variants.
- This means they are heterogenous.
- The composition of cells are change over time due to selection from the immune system.
14
Q
What are the 3 “stages” of tumour immunity?
A
- Elimination
- Equilibrium
- Escape
15
Q
What is tumour elimination?
A
- The 1st stage of tumour immunity
- Without the immune regulators the immune system is very good at eliminating initial cancerous cells or tumours.
- The immune system gets rid of most tumours.
16
Q
What is tumour equilibrium?
A
- The 2nd stage of tumour immunity.
- As tumours are heterogenous due to mutation, you get elimination of some cells and selection and escape of others.
- This creates an equilibrium.
- Parts of the tumour is killed and parts grow and this lasts in balance for a while.
- The immune system creates a severe selection pressure on the tumour to evolve.
- Some tumour win the battle and cause immune escape.
17
Q
What is tumour escape?
A
- The 3rd and final stage of tumour immunity.
- Some of the tumour can evade the immune system and grow.
- This causes clinical problems and this is the point cancers are detected and patients present in clinic.
- This means treatment begins when the tumour has spent a long time subverting the immune system.
- These are difficult tumours to deal with as they are the best at escaping immunity
- This dynamic selection of tumours as the immune system is really good at getting rid of other tumours.
18
Q
What are the key experimental approaches for studying tumour immunity in mice?
A
- Immunocompetent mice
- Immunodeficient mice
19
Q
How are immunocompetent mice used to study tumours?
A
- You inject murine tumour cell lines into mice and do genetic manipulation to drive efficient tumourigenesis.
- The immunity is the endogenous to the mouse.
- The advantage is the experimental access and genetic variants of mouse.
- Disadvantages are you don’t really get spontaneous tumour generation of tumours which is an important stage of development.
- Also the mice are sterile so they have altered immune function so it is hard to translate experiments from mice to humans.
- Can modify them to express defined tumour antigens and T cells to see what T cells are doing what in tumours.
- Most of our understanding of tumours come from these models.
20
Q
How are immunodeficient mice used to study tumours?
A
- You inject human tumour cell lines and allow them to develop.
- The immunodeficient mice have no immune system so allow the tumour to develop.
- Transfer in human T cells.
- These are used to study human T cell interactions with human tumours without the rest of immunity.
- The advantage is human cells.
- The disadvantage is having only T cells limits immunity.
21
Q
What are most tumour immunity experiments now done in?
A
Human models
22
Q
What are the key experimental approaches for studying tumour immunity in humans?
A
- System characterisation of human tumour biopsies.
- Tumour organoids
- In vitro tumour models
23
Q
How is system characterisation of human tumour biopsies used to study tumours?
A
- You look what is in the tumour using Omics approaches.
- The tumour generation and immune response are endogenous human responses.
- You take samples of tumours and look what cells are there and what they express.
- This is driven by Omics development like proteomics, RNA-seq, HD tissue staining etc.
- Advantage: It shows exactly what happens in the tumour and endogenous tumour and immunity as it happens.
- Disadvantage is its hard to manipulate
- Can be applied to clinical trials to see what’s happening.
24
Q
How are tumour organoids used to study tumours?
A
- You take a whole tumour biopsy and preserve it in vitro.
- It contains the human immune cells
- Endogenous tumour generation and immune response.
- Advantages: endogenous human immunity and can manipulate the organoid to aid mechanistic understanding.
- Disadvantages: It is very hard to maintain the immune cells in the organoid.
25
Why are tumour organoids hard to maintain in vitro?
1. The tumour loses the interaction with the tumour draining lymph node to maintain the immune cell population.
2. It is more like a snapshot of immunity at the moment the tumour is removed from the body.
26
How are in vitro tumour models used to study tumours?
1. You take an elements of tumour biology and remake them in vitro.
2. Spheroids and organs on a chip
3. Mostly tumour cell lines with added immune cells.
4. Advantages: Experimental access and ease of manipulation not endogenous generation.
5. Disadvantages: Hard to validate finding as you are building your own tumour. You need to check any observations actually will happen in vivo
27
How do tumours activate innate immunity?
1. The tumour induced changes in the tissue are recognised by detecting DAMPs.
2. The DAMPs are recognised by tissue resident immune cells through pattern recognition.
3. Tumours are not sterile so MAMPs can also trigger innate cells.
4. This causes tissue damage which leads to repair or chronic inflammation.
28
What role do bacteria play in tumours?
1. Most tumours are not sterile.
2. They often have their own microbiota.
3. This causes damage and releases MAMPs and more DAMPs
4. This activates innate immunity and can be processed by APC and trigger an adaptive response in the tumour.
29
What is an example of a DAMP that activates tumour immunity?
Cytoplasmic dsDNA which activates cGAS-STING
30
How does cytoplasmic dsDNA activate tumour immunity?
1. dsDNA and other molecules are released from dying tumour cells and get taken up into the cytoplasm of innate immune cells.
2. This is detected through pattern recognition and activates cGAS-STING.
3. cGAS is cyclic GMP-AMP synthase and it generates cGAMP.
4. cGAMP activates STING which leads to the generation of of IRF3 and NF-kB which leads to generation of type 1 interferons.
5. This activates dendritic cells in the TME which translocate to the draining lymph node and then activates T cells.
31
What other DAMPs released from tumours to activate immunity?
1. ATP which triggers the inflammasome
2. RNA which triggers TLR3
3. Extracellular F-actin triggers DNGR1 on cDC1
32
How can synthetic STING activation promote anti-tumour immunity?
1. Use a synthetic compound to find a STING agonist which activates STING more efficiently and activates dendritic cells and prime adaptive immunity.
2. MSA-2 does this
3. Dimerisation of MSA-2 is required for STING binding
4. Dimerisation is restricted to low pH environments like the TME
5. This restricts drug action to the site of the tumour to enhance DC activation only in the TME.
6. This required constant administration in mouse models to get the anti tumour response to last long enough.
33
How does sustained dendritic cell activation promote anti-tumour immunity?
1. You needs to maintain continuous activation of dendritic cells in the anti-tumour response needs to last for months.
2. Activating DCs once doesn’t really help.
3. You need to keep activating new DCs.
4. cDC1 function in priming CD8 T cells diminishes over time.
5. You can restore this cDC1 function with anti-CD40 and Flt3 to maintain continuous activation of the dendritic cells and extend the response.
34
What is a key player in shaping the TME?
1. Macrophages
2. Especially their initial activation
35
What do macrophages recruit when they are activated?
1. They recruit more neutrophils and monocytes to the tumour.
2. More phagocytes
3. These are then activated and recruit more phagocytes creating a cycle.
36
How does macrophage phenotype change in tumours?
1. Continuous low level macrophage activation in metabolically competitive establishes a immunosuppressive phenotype that extends to the new monocytes recruited.
2. These macrophages recruited develop into myeloid-derived suppressor cells and tumour associated macrophages.
3. These are continuously generated in response to the tumour.
4. It also leads to upregulation of inhibitory receptors like PD-1 and the generation of ROS which adds to the immunosuppressive macrophage phenotype.
5. This suppresses T cell function and supports tumour cell growth.
37
What is the tumour-associated macrophage phenotype similar to?
1. Tissue regeneration subtype
2. Help promotes growth and angiogenesis
3. This makes cancers hard to treat
38
Can the bacteria in tumour influence the outcome of treatment?
1. Any tumour you look at has lots of bacteria associated with it.
2. There are epidemiological associations with different bacteria.
3. Bacteria are in tumours, processed by tumours and change the immune response to tumours.
4. We don’t really understand how this effects outcomes.
39
What are the main innate immunity system components in tumours?
1. Activation and persistance of dendritic cells.
2. cGAS STING
3. Macrophages suppress immunity
4. Bacteria are present
40
What do T cells recognise in tumours?
1. They can recognise various antigens.
2. Tumour associated antigens.
3. Tumour specific antigens
41
What are tumour associated antigens?
1. These are endogenous self proteins.
2. They are unmutated.
3. They are normally endogenous proteins that are normally restricted in their expression.
4. They are self proteins so they are subject to partial tolerance.
5. This means immune responses are weak to them and there is some on-target toxicity
6. These antigens are shared between patients so targeting these can treat a large number of patients.
42
What are some examples of tumour associated antigens?
1. CGA (cancer germline antigens) which are normally only expressed in the foetus but also in lots of cancer. Eg. NY-ESO-1
2. HERV - endogenous retroviruses
3. TDA (tissue differentiation antigens) like MART-1
4. Over expressed antigens like Her2 and carcinoembryonic antigen
43
What are tumour specific antigens?
1. These are neoantigens generated in tumour cell transformation.
2. They are mutated proteins that look like new proteins.
3. They are not subject to any tolerance so the generated a very strong immune response against them.
4. They are patient specific so treatment has to be patient specific. This requires large throughput sequencing.
44
How many neoantigens do tumours generate?
1. There are 1000s of mutations and neoantigens in some tumours.
2. But there is massive variation
3. There is lots for T cells to see and recognise
45
Do tumours interact with immunity in the same way?
1. No
2. There are lots of different tumours and lots of different cell interactions.
3. Normally 6 principle immune cell signatures in tumours.
4. Diverse tumour types and different patients cause different outcomes for survival.
5. Different tumour type have different immunological challenges
46
What tumour immune signature provide better survival outcomes?
1. Highly inflammatory tumours with lots of lymphocytes generates strong immune responses and have better chances of survival.
2. This is compare to immunologically quiet tumours.
47
Is the same tumour the same in every patient?
1. No
2. Tumour and immune interactions are different in every patient
3. This patient to patient variability makes treatment very hard.
48
How can immune cell infiltrate tumours?
1. The immune cells can be segregated from the tumour cells which makes a bad anti tumour response.
2. The immune cells can be integrated into the tumour which makes a better anti tumour response
49
What are the main determinants of tumour immune interactions?
1. Tumour type
2. Immune cells present
3. Immune cell phenotype
4. How the immune cells are present
5. The specific patient
50
What different T cell phenotypes are present in tumours?
1. A single cell RNA-seq study of 400,000 T cells in 21 cancer types.
2. It found 21 different CD4 T cell subtypes.
3. It found 16 different CD8 T cell subtypes.
51
What are the main CD8+ T cell subtypes found in tumours?
1. Effector memory T cells
2. Tissue-resident memory T cells.
3. Effector memory T cells expressing CD45RA.
4. Exhausted T cells
(also Naive T cells, Central memory cells, NK-like T cells.)
52
What do effector memory T cells do?
1. They carry out the effector function
2. They generate new T cells.
3. They are very beneficial in tumours.
53
What do Tissue resident memory T cells do?
1. They are important for generating new T cells.
2. They cannot move through the body.
3. They have stem cell like properties and are important for generating new T cells.
54
What makes up the majority of T cells in tumours?
Exhausted T cells.
55
What are the main CD4+ T cell subtypes found in tumours?
1. Regulatory T cells
(also naive T cells, memory T cells, Th1/2/17)
56
What are the key drivers of the cytotoxic T cell anti-tumour response?
Exhausted T cells
57
What are the 3 stages of exhausted cytotoxic T cells?
1. Early/precursor exhausted T cells.
2. Exhausted T cells with remaining effector function
3. Terminal exhausted T cells.
58
What are early/precursor exhausted T cells?
1. They are defined by the TCF1+ transcription factor.
2. They have variable inhibitory receptor expression.
3. They maintain proliferation.
4. They drive the T cell anti tumour response.
5. They are precursor cells that drive active cells.
6. Lots of precursor exhausted T cells = a good prognosis.
59
What are exhausted T cells with remaining effector function?
1. These are the majority of exhausted cells in tumours.
2. They are TOXhi.
3. They do most of the killing and make up the bulk of T cells in the TME.
4. Make IFNy, granzymes, and perforin
5. Cannot proliferate
6. Upregulate inhibitory receptors.
7. Need the precursors to keep generating these as once they die they are dead.
60
What are terminal exhausted T cells?
1. TOXhi
2. Highly express inhibitory receptors
3. No proliferation
4. They don’t really do anything.
61
What are the key principles of the TME?
1. The TME can be immune rich or immune poor.
2. In immune rich tumours immune cells can mix with tumour cells or be separated.
3. There is a wide variety of immune cells in the TME.
4. Anti-tumour immune effectors and suppressive immune cells commonly co-infiltrate and the ratio between these is very important.
5. There are distinct subtypes for most immune cell types.
6. Key cytotoxic subtypes are memory, effector and exhausted.
7. Even exhausted cytotoxic T cells have subtypes.
62
What does immune therapy for tumours aim for?
1. Efficient immune infiltration
2. Efficient mixing of immune cells with tumour cells
3. Favourable balance of effector to regulatory cells.
4. Generating cytotoxic T cells with proliferative potential over exhaustion
63
What is the point on tumour immune evasion?
1. The immune system creates a severe selection pressure on the tumour cells.
2. This forces the tumour to adapt and evade the immune system.
3. The tumour and immunity co-evolve to create the immunosuppressive TME.
64
What are the key mechanisms of immune suppression in tumours?
1. The TME
2. Suppressive cell types
3. Receptor involved in T cell activation
65
How does the TME suppress immunity?
1. Immune exclusion
2. Metabolic competition
3. Suppressive soluble mediators
66
What suppressive cell types are found in the TME?
1. Tregs
2. Myeloid derived suppressive cells (MDSC)
67
What is immune exclusion?
1. Keeping immune cells out of the tumour
2. If the immune cells are not in the tumour you cannot mount an effective anti tumour immune response.
3. the TME can do this passively of actively
68
How does the TME exclude immune cells?
1. Passively using the ECM
2. More actively by altering lipid metabolism, TGFß induced fibrosis, nutrient depletion, hypoxia.
69
How does metabolic competition suppress immune cells in tumours?
1. Tumour cells proliferate very quickly.
2. This needs lots of energy and substrates.
3. This is the same as macrophages and T cells.
4. These 3 cells are basically fighting for these resources within the TME.
5. If you deprive macrophages and T cells of the key metabolic precursors you impair their function.
6. This competition is an important part of immunosuppression.
70
What key metabolic processes are important for replication and function?
1. Glucose to lactate to generate moderate amounts of ATP and lots of anabolic precursors. Useful in low oxygen environments like the TME and leads to the acidification of the TME.
2. Glutamine to TCA and used to make nucleotides and amino acids.
3. Leucine to make other amino acids.
71
What are the key metabolic limitations for immune cells in the TME?
1. Low glucose
2. High lactate
3. Low glutamine
Low oxygen doesn’t bother T cells.
72
What are some suppressive soluble mediators in the TME?
1. Prostaglandin E2 production
2. Tryptophan depletion
3. Adenosine production
73
How does prostaglandin E2 suppress immunity?
1. It is produced by tumour cells.
2. It is heavily researched in Bristol.
3. It is generated by COX (cyclo-oxygenase)
4. Aspirin and NSAIDs can inhibit prostaglandin production
5. Acts on myeloid cells (MDSC).
74
How does tryptophan depletion suppress immunity?
1. An enzyme called IDO is produced by tumour cells and myeloid cells.
2. It depletes tryptophan from the extracellular space and prevents tumour and immune cells metabolism.
3. It regulates availability of amino acids
75
What is IDO?
Indoleamine 2,3-dioxygenase
76
How is adenosine produced in the TME?
1. ATP is released as a DAMP on necrotic cell death.
2. CD39 and CD73 are expressed on Tregs in the TME.
3. CD39 converts ATP to AMP and CD73 converts AMP to adenosine.
77
How does ATP activate immunity?
1. ATP is a DAMP
2. When it is released it can activate the inflammasome and produce IL-1ß
3. A strong inflammatory response = a strong immune response.
78
How does adenosine suppress immunity in the TME?
1. It removes ATP so reduces the inflammatory response.
2. It turns the potent activator of ATP into the suppressor adenosine.
3. Adenosine can bind to a series of inhibitory adenosine receptors.
4. Adenosine 2A receptor is highly expressed on T cells binds the adenosine and inhibits T cells.
79
Could the generation of adenosine be prevented and used as a cancer treatment?
1. Inhibition of the generation and action of adenosine could promote the ATP anti tumour immune response.
2. This could be done using blocking antibodies against CD73 or the adenosine 2A receptor.
80
How can the generation of adenosine be prevented to treat cancer?
1. Blocking CD72 and adenosine 2A receptor independently doesn’t work.
2. This is a classic problem as the treatment causes a selection pressure and causes treatment failure.
3. both mechanisms can compensate for each other.
4. Both need to be targeted to suppress the function and generation of adenosine and overcome compensation.
81
How did the CD73 and adenosine 2A receptor compensate for each other to stop treatment working?
1. When CD73 was blocked there was FcR mediated expansion of myeloid suppressive cells.
2. Knockout of the receptor causes compensatory CD73 production as only 1 of 4 receptors were knocked out.
82
How do Tregs contribute to tumour progression?
1. They impede monitoring of tumours in healthy people.
2. They diminish the anti tumour response in tumour patients.
3. This can result in progression and tumorgenesis
83
How can Tregs support tumour cell survival?
1. By releasing growth factors
2. Interacting with Stromal cells.
84
Can Tregs have anti-tumour effects?
1. Yes
2. potentially through multiple mechanisms like producing inflammatory cytokines or becoming Th-like Tregs.
3. In CRC and gastric cancer there is a positive correlation between Treg infiltration and prolonged survival.
