Lecture 10 (immunotherapies) Flashcards

1
Q

How can the immune system contribute to the anti-tumour response

A
  1. By destroying viruses that are known to transform cells
  2. By eliminating pathogens to reduce pro-tumour inflammation as 20% of cancers are now thought to be associated with microbial infection
  3. By identifying and destroying cancerous cells which is mediated by immune ‘killer’ cells
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2
Q

A bad tumour immune profile is composed of what cells

A

-M2 macrophages
-myeloid derived suppressor cells (MDSCs)
-Th2 cells
-Treg cells (prevent immune cells from killing cancer cells)

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3
Q

A good tumour immune profile is composed of what cells

A

-cross-presenting APCs
-NK cells
-Th1 (which is more beneficial than Th2)
-CD8+ CTL response

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4
Q

9 tumour escape mechanisms

A
  1. loss of Tumour Antigen
  2. loss of MHC I or NKG2D
  3. loss of IFNg responsiveness (pathway defects)
  4. inhibition of DC maturation/function
  5. loss of costimulatory molecules such as increasing CTLA4
  6. increase Treg activity which dampens down other T cells
  7. MDSC
  8. immunomodulatory molecules such as IL10 which dampens immune response
  9. cancer cells use checkpoints to dampen the immune response
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5
Q

Two classes of tumour antigens

A

Tumour-specific antigens and tumour-associated antigens

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6
Q

Tumour specific antigens

A

-Only occur in neoplastic (tumor) cells.
-They are recognised as non-self by CD8+ CTLs
Examples of TSA:
-Mutated cellular proteins which leads to APC expression of novel peptides presented by MHC class I
-Virally derived antigens such as HPV E6 and E7 proteins which are found in 80% of invasive cervical cancers

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7
Q

Tumour associated antigens

A

Are normal cellular proteins with unique expression patterns, they are only expressed at specific sites or stages of development (eg. foetal) or at low levels in normal cells.
-Reexpression of foetal or embryonic genes are called oncofoetal tumour antigens eg. CEA (carcinoembryonic antigen)
-90% of all patients with advanced CRC have increased CEA in their serum
-May also be oncogenes that are expressed at abnormally high levels such as EGFR and HER2

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8
Q

What is the anti-tumour response shown by NK cells (innate immune cells)

A

-NK cells kill tumour cells by:
1. Showing reduced MHC I expression which is detected by KIRs (killer cell immunoglobulin-like receptors),
2. By killing tumours that overexpress ligands for activating NK receptors
3. By IFNg secretion which stimulates CTL response
4. By being the key mediators of ADCC

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9
Q

NK deficient mice

A

Are known as SKID mice
-They have increased lymphomas/sarcomas

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10
Q

What is the anti-tumour response of macrophages M1 (innate immune cells)

A

-IFNg drives the M1 phenotype ADCC and secrete cytokines (TNFalpha, IL-12, IL23) which exert cytotoxic activity on tumour cells
-High MHC class II/costimulatory molecules (APCs) secrete chemokines that lead to Th1, CTL recruitment, and NK cells

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11
Q

What is the anti-tumour response of T cells

A

-T cells have strong anti-tumour CTL (CD8+) activity which correlates with tumour remission and maintains state of immune mediated neoplastic cell dormancy
-Th1 cells secrete IFNg which promotes M1 macrophage response and increases MHC I expression which facilitates CTL recognition of tumour antigens
-Th17 cells secret IL17 which leads to secretion of pro-angiogenic factors
-TILs are a prognostic indicator

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12
Q

Anti-tumour response of B cells

A

-B cells can secrete anti-tumour antibodies
-ADCC by NK cells and macrophages
-Bad effect is that B cells can block CTL response by masking tumour antigens
-Also tumour cells can evade B cells by chopping them up and excreting them.

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13
Q

How can cancer evade the immune system

A

1- active immunosuppression in tumour environment
2- chronic inflammation
3- evasion of immune recognition and activation
4- tumour cell avoidance of apoptotic signals
5- poor co-stimulatory signals provided by tumour cells
6- expression of co-inhibitory molecules

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14
Q

What are the details of 1- active immunosuppression in tumour environment

A

-Dampening of immune response by M2 macrophages, MDSCs, Tregs, and Th2 cells
-IL4 drives M2 phenotype which release immune dampening cytokine secretion IL10 chemokines which lead to Treg and Th2 recruitment, pro angiogenic factors (VEGF) and growth factors released by M2 macrophages
-NK cells can be defective at tumour site
-Neutrophils secrete VEGF and proteinases elastase and MMP8/9
-MDSCs are immature cells comprised of precursors of macrophages, granulocytes, DCs, and myeloid cells at earlier stages of differentiation
-Tumours secrete factors to promote MDSC expansion as they induce CD8+ T cell tolerance, block NK cytotoxicity, and polarise immunity (push towards pro-tumour rather than anti-tumour immune response, treatment giving to push this balance back)

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15
Q

what are the details of 2- chronic inflammation

A

-Increases cellular stress and genotoxic stress thereby increasing mutation rate
-Growth factors and cytokines released by leukocytes can also lead to tumour growth
-Inflammation is proangiogenic
-Iink between increased cancer risk and people with obesity as these people experience higher levels of chronic inflammation

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16
Q

what are the details of 3- evasion of immune recognition and activation

A

-reduced MHC I/tumour antigen expression on tumour cells
-secretion of TSAs
-defective TAP or b2macroglobulin
-IFNg insensitivity
-NK cells should step in to kill these cells but tumour cells show decreased expression of ligands that bind activating receptors on NK cells

17
Q

what are the details of 4- tumour cell avoidance of apoptotic signals

A

-upregulation of anti-apoptotic mediators (eg. Bcl2)
-down regulation or expression of non functioning FAS receptor on tumour cells
-secretion of soluble form FAS receptor which acts as a decoy for FAS ligand

18
Q

what are the details of 5- poor co-stimulatory signals provided by tumour cells

A

-T cell activation requires 2 signals, tumour cells are self cells so tend to lack costimulatory molecules
-need APCs in the tumour vicinity to activate T cells, recent therapy aims to enhance the costimulation provided to T cells

19
Q

what are the details of 6- expression of co-inhibitory molecules

A

-immune checkpoints are cell surface molecules that regulate immune response (ie. stop immune response from killing the cancer cells)
-ligands on tumour cells can dampen immune response, results in T cell exhaustion

20
Q

Cancer immunotherapy aims to

A

Reactivate the immune system to kill cancer

21
Q

What is the Coley’s toxins approach and how was it discovered

A

It was discovered in 1891 when William Coley injected bacteria into inoperable tumour of one of his remission patients.
-Immunostimulatory molecules in the bacteria toxins had enhanced the anti-tumour response.
-This approach is used today with BCG therapy for bladder cancer (delivered via catheter to activate immune response)

22
Q

2 reasons why are T-cells are immunotherapy targets?

A

-T cells have an exhausted phenotype in the tissue and no longer attack the tumor.
-Immunoregulatory proteins on T cells can halt the immune response.

23
Q

How can the immune response be reactivated.

A

By designing immune checkpoint inhibitors.

24
Q

3 immune checkpoints:

A

-Signal 1: Antigen recognition
-Signal 2: Co-stimulation
-Signal 3: Activation/effector function or exhaustion

25
Q

What are signal 2 and 3 for Tregs:

A

Signal 2: Development (CD28) and suppressive activity (CTLA-4)
Signal 3: Decreased Tfr activity and pTreg induction

26
Q

What is CTL4

A

-CTLA4 is a molecule expressed on activated T cells
-CTLA4 competes with CD28 to bind to CD80/86 on APC cells leading to T cell inhibition
-Once bound to CD80/86 CTLA4 inhibits cell proliferation, cytokine production and cell cycle progress

27
Q

How is CTLA4 targeted in cancer treatment

A

-Monoclonal antibodies are used against CTLA4 to treat metastatic melanoma, kidney cancer, oesophageal cancer etc

28
Q

Example of a monoclonal antibody used against CTLA4

A

-Ipilimumab is a fully humanized mab
-Uses IgG1 to CTLA4
-Tremelimumab is another one

29
Q

CD80 AND CD86 are also know as

A

B7-1 and B7-2

30
Q

What are PD-1 and PD-L1 and how do they cause blockade

A

PD-1 (program death-1) is expressed on T cells, B cells and monocytes
-When PD-1 binds to the ligands PD-L1 and PD-L2 on tumors or APC it results in inhibitory
immune checkpoint

31
Q

Anti PD-1 antibodies

A

Nivolumab and pembrolizumab

32
Q

Anti PD-L1 antibodies

A

Atezolizumab
Durvalumab
Avelumab