Why is a tumour microenvironment important in cancer research?
Drugs now target the tME due to the complex cell types present.
Increased CAFs and decreased TILs associated with poor prognosis.
OMIC analyses used to view mutations in malignant cells.
What are the major cell types in the TME?
- CAFs
- Adipocytes
- Vasculature cells
- Immune cells (T, B, NK, Dendritic cells) (TAMs)
What is a fibroblast?
Mesechymal cell type that expresses Vimentin as a marker.
Maintains structural integrity of stroma and produces the ECM.
Involved in inflammatory response and homeostasis.
What is a CAF?
Cancer associated fibroblast
Major stromal cell type in solid cancers.
Secrete a large amount of ECM proteins, growth factors and cytokines.
Generated through TGFB1 signalling.
How does TGFB1 regulate CAF differentiation?
Through a large latent complex, that sits in the ECM until activated by MMPs - cleave it through integrins in cancer cells.
TGFB1 binds TGF receptor - activates SMAD complexes to increase gene transcription and differentiating into CAFs.
Can proteins in the ECM be associated with more aggressive cancers?
Collagen rich CAFs are associated with the worst survival rates and most aggressive cancer forms.
The metastatic process steps (5)
Invasion Intravasation Migration Extravasation Colonisation
How can tumour invasion be studied in the lab?
What is the seed and soil hypothesis?
Tumour invasion can be studied on a protein gel with fibroblasts to see how far the tumour cells can spread.
The brain, bone, lung and liver are the secondary sites seen most often. ‘Seed and Soil’ hypothesis.
Tumour cell - TGFb1 interaction
Tumour cells activate CAF through avB6-dependent activation of TGFb1 – Inhibiting the avB6 cell surface integrin prevents the CAF formation and also prevents invasion.
3 stages of immunoediting
- Elimination – Immunosurveillance. The innate and adaptive immune systems are active, and the cancer cells are being cleared.
- Equilibrium – Persistence. Genetic instability and immunoselection.
- Escape – Progression. Positive selection for cancer cells that can escape the immune system and the final progression of cancer.
CD8+ T-cells - function
How TME escapes detection.
Recognise antigens on MHC class 1
Express perforin, granzyme and granulysin
T-cells infiltrate the site of the tumour, recognise tumour specific antigens and develop cytotoxic t-cells to kill tumours.
TME will evolve to avoid the immune system.
3 ways secondary resistance can be obtained against the immune system.
1 - Insufficient anti-tumour t-cell generation
2 - inadequate anti-tumour t-cell function
3 - impaired formation of t-cell memory
Dysfunction of CD8 cells in tumours
- Hostile environments can deplete nutrients and produce toxic metabolites
- Suppressive molecules or receptors
- MHC down regulation
- Inhibitory t-cell activity receptors (CTLA4)
Regulatory T-cells
A subset of CD4+ t-cells that maintain tolerance to self antigens.
Immunosuppressive - suppress production and proliferation of CD8 t cells.
Can be induced by TGFB1
Cause apoptosis of CD8+ and prevent their co-activation.
TAMs
Professional phagocytes that are either:
M1 - Classical IFNy pro-inflam, cytotoxic
M2 - Anti-inflam, wound healing, angiogenesis, increased TGFB1
M1 is anti-tumour, M2 is pro-tumour
What are the current main targets for cancer immunotherapy on CD8+ cells?
INHIBITORY - CTLA4 & PD1
Activating targets can provide toxic CD8+ effects throughout the body.
Combination therapies of anti-PD1 + anti-CTLA4 drugs have had 58% response rates in patients with metastatic melanomas.
How can we predict whether patients will respond to the anti-PD1 drug?
- The immunohistochemical test: drugs, cut-offs and cell scoring.
- The number of mutations a patient has in their tumours.
More mutations = more possible recognition of neoantigens and more likely response to drugs.
Anti-cancer vaccination strategies
Develop vaccines against cancers - tumour specific antigens unique to tumour cells. (viral antigens or new proteins based on mutations in proteins to be presented)
- tumour associated antigens (misregulated antigens expressed in some cells, where they’re not usually found)
How do tumours evade immunotherapy?
- Vaccines can be developed to target tumour specific antigens, which show a decline in tumour growth. However, experiments show that alterations in the TME such as CAF differentiation, hypoxic mutations and GLUT1 transporters can provide mechanisms to evade immunotherapies.
What is a CAF differentiation regulation mechanism that can be targeted as an immunotherapy?
NOX4 produces ROS. NOX4 inhibitor GKT831 cells reverse back to a normal fibroblast phenotype.
