Tumour microenvironment Flashcards by eve caroe

What are the components of the tumour microenvironment?

Stroma (supporting cells, have many pro tumour roles)
Immune cells
Blood vessels
Lymphatic vessels
Fibroblasts

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What antigen presenting cells are important in the tumour microenvironment?

Macrophages and dendritic cells

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What do macrophages and dendritic cells do in the early stages of tumour development?

Microenvironment is less complicated
Growth is recognised as abnormal, get a wound healing response
Involves proinflammataory cytokines (IFNgamma, TNFalpha) to recruit APCs which are phagocytotic and cytotoxic
M and DC are recruited by growth factors secreted by the tumour e.g. VEGF
APCs present tumour antigens to T cells which then produce more immunogenic cytokines to activate other things
Also produce superoxide anions and nitrogen free radicals

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What is the ideal response in early tumour development?

Necrosis/apoptosis in the centre of the tumour results in the pick up of tumour antigens by APCs. These go through lymph to present to T cells which then kill the tumour. Often doesn’t happen properly.

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What is the function of macrophages and dendritic cells in late tumour development?

Can be tumour promoting e.g. producing growth factors
Are poorly phagocytic
Low expression of MHC so can’t present tumour antigen
Low levels of co-immunostimulatory molecules e.g. second signal to T cells doesn’t occur
Express negative signals (PDL 1 or 2 that tell T cells to die
Don’t produce immunogenic factors (do suppressive factors instead)

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What suppressive factors are expressed by macrophages and dendritic cells late in tumour development?

IDO - removes tryptophan from T cells and induces apoptosis
Arginase - T cells don’t respond to antigen and apopsose
IL-10
TGFbeta

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What are the anti-tumour functions of T cells?

Kill tumour cells through cytotoxic granules and receptor engagement (FasL-Fas; PDL1-PD1)
T regulatory cells inhibit CD8 T cells
High ratio of CD8 T cells is associated with a good prognosis

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What are the pro-tumour functions of T cells?

T cells express high levels of PD1 and Fas and are killed by cells expressing the ligands
T cells are exhausted and poorly cytotoxic
T cells are blocked from accessing the tumour due to the stroma.

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What are the functions of blood vessels in tumour development?

Provide nutrients and oxygen to the tumour
Get immune cells to the tumour
Are a route of metastasis

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What are the characteristics of tumour blood vessels

Abnormal, less functional
Grow very quickly
Leaky - cells surrounding aren’t normal
Chaotic - badly organised, not normal branching
Blood doesn’t flow properly - poor perfusion, lots of hypoxia leading to more angiogenesis

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What are some angiogenic factors?

VEGF-A, FGF-2, CXCL12

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What cells stimulate angiogenesis?

Could be hypoxic tumour cells or immune cells (macrophages, neutrophils) and fibroblasts

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How do endothelial cells modulate the immune response?

Express FasL on their surface, killing immune cells (only in the tumour tissue so there are fewer T cells in the tumour)

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What is the function of lymphatic vessels in tumour development?

Collect fluid form leaky blood vessels and take to lymph. Active route of metastasis. Does immune cell trafficking. Are associated with lymph node metastasis and poor patient prognosis

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How is lymphangigogenesis stimulated?

By tumour cells and immune cells and fibroblasts through VEGF-C, VEGF-D, FGF and VEGF-A

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What is the importance of drainage through the lymph for tumour development?

If cells experience flow, cell changes its behaviour - fibroblasts secret growth factors and chemokines such as CCL21 (get a gradient as flow is different across the tumour)

How is the lymph involved in metastasis?

Has an active role and modulates the metastatic environment. Changes cell surface expression to set up new niches

How does the lymph modulate the immune system in cancer?

Expresses PDL-1 and other negative ligands. Can prevent immune cells leaving the tumour to trigger the immune response (control of entry in to lymphatic system, interact with trafficking of APCs).

What is the function of fibroblasts in tumour development?

Very abundant stromal cells
Are scaffold cells and produce extra cellular matrix and growth factors. Emerging theories that they may contribute to immune evasion by secreting factors that modulate the immune response and interacting with and killing T cells

What is the significance of fibroblasts producing ECM in tumour development?

ECM is protein rich gel which surrounds the cell. Composed of collagen and proteoglycans. As tumour grows, more collagen is included so it stiffens. This promotes tumour cell invasion (use as a scaffold to move along). It is remodelled in response to flow (e.g. from lymphatics) and invasive tumour cells use this to move. As the ECM breaks down, growth factors are released as tumour cells escape

What is the source of fibroblasts in the tumour microenvironment?

Tissue resident
Bone marrow
Endothelial cells that have changed to fibroblasts

What is an experiment that shows how ECM stiffness can lead to tumour development?

Breast cancer cells in a soft gel form spheroid structures
In a stiffer gel, spheroid structures fill in
In the stiffest gel, changes occur in the basement membrane which then breaks and cells become more mesenchymal and start to invade

What is the association between lymphatics and fibroblasts?

Fibres of the gel of the ECM are random in static conditions
If add flow, fibroblasts and fibres align perpendicular to the tumour - this begins cross linking and stiffening of the gel
Can be seen in breast cancer; is associated with poor prognosis

How are growth factors released from the ECM?

Growth factors such as VEGF and TGFbeta stick to matrix components which are released when they break down

How do tumour cells use ECM remodelling to their advantage?

Pull on matrix environment to aid leaving of tumour Use matrix as a scaffold to move along ECM changes the way cells behave Fibroblasts make holes for tumour cells to follow (break down matrix and remodel to make tunnels for tumour cells)

How can the supporting cells of tumours be studied?

Can't do in isolation - need a multidiscipline approach with combinations of modelling techniques (in silico, vitro, vivo - mouse models).

How can heterogeneity of fibroblasts be studied?

Makes it very complicated - look on the single cell level. Inject a green mouse with a tumour cell, then remove the tumour and other stromal cell. Use FACS to sort fibroblasts into 96 wells. See a distinct population of the majority of fibroblasts which changes as the tumour develops. Can sequence wells to find out more then look at targeting in vitro and in vivo.

How do fibroblasts modulate the immune response?

Scavenge dead tumour cells - chop up debris and instead of clearing it, they express it on the cell surface in the presence of a negative ligand. Get lots of expression of negative immune regulatory ligands. Fibroblasts end up killing the T cells they encounter, allowing tumour cells to grow better.

What is the role of fibroblasts in pancreatic cancer?

Controversial - one paper showed they restrained then tumour (upon deletion tumour was more aggressive), other showed they protected the tumour by T cell deletion. Difference could be down to the models being different (e.g. 2 types of fibroblasts) or that our models for the tumour microenvironment aren't stringent enough yet

Why is it important to develop models that represent the tumour microenvironment properly?

Often have drugs that work well in vitro and in vivo (immunocompromised mice) but fail in clinical trials. Could be due to the different environment - stiffness of the tissues, cells behaving differently when grown alone

How can the tumour microenvironment be represented in vitro?

In a flask, tumours + supporting cells form clusters | If grow in 3D culture, get more organisation which may be more representative of tumours

What is the effect of Gemcitabine on tumours in mouse models?

Depends on the model - if inject a pancreatic tumour into a mouse, find that gemcitabine reduces tumour growth. However, if tumour has the same mutations but is triggered (and developed properly) instead of injected, then there is no response to gemcitabine - could be due to a properly developed tumour microenvironment.

How can the tumour microenvironment inhibit the intended effects of drugs?

Could be a physical barrier to drugs (is dense) Abnormal vasculature may result in poor delivery Immune cells and fibroblasts may metabolise drugs and release non-toxic break down products (adding fibroblasts reduces effect of chemotherapy) As tumour evolves and molecular profile changes, targeted therapy fails Immune cells can be non-responsive to therapies

How can T cells in the tumour microenvironment be targeted?

Immune check point inhibitors Reactivate T cells by switching off negative signals Engineer T cells to react to tumour antigen

How can antigen presenting cells in the tumour microenvironment be targeted?

Inhibit recruitment of cells Deplete APCs when in tumour e.g. Clodronatae kills cells when it is phagocytksed Reprogram APCs to be anti-tumour (Imiquimod, Vadimezan) Engineer dendritic cells

How can blood vessels in the tumour microenvironment be targeted?

Anti angiogenesis therapies (anti VEGF agents such as bevacizumab, ramucirumab) Inhibit angiogenesis and normalise vessels - has a very small window of opportunity, if get wrong can lead to more angiogenesis and metastasis Nanoparticles to take advantage of leaky properties (improve delivery) Inhibit lymphatic vessels and growth to prevent metastasis

How can fibroblasts and ECM in the tumour microenvironment be targeted?

Stromal targeting agents such as sonic hedgehog inhibitors and matrix destabilisation to prevent cross linking and stiffening Harness stromal proporties e.g. conjugating drugs to increase size and retention in the tumour (Nab paclitaxel)

What recent trials have gone ahead to target the tumour microenvironment?

Targeting checkpoint inhibitors IL-2 to stimulate immune cell proliferation (have to be careful as can get uncontrolled activation) Immune inhibitors e.g. kinase inhibitors Many more