Tumour Immunology and Immunotherapy of Cancer Flashcards
what circumstantial evidence is there for immune surveillance (of tumours)?
1) microscopic colonies of cancer cells found in people that are controlled well and do not develop
2) Patients treated for melanoma and are “disease free” become organ donors and induce melanoma in the recipients (donor had immunity to the melanoma)
3) men have a higher chance of dying of cancer than women (who have stronger immune responses)
4) deliberate immunosuppression increases the risk of malignancy
what is a tumour induced auto-immune response?
tumours express antigens that are normally absent (or at certain immunological sites) in human tissue
the immune system detects this and attacks abnormally expressed antigens/tumours
this may lead to auto-immune destruction of normal human tissue
what are the steps in the cancer-immunity cycle?
- Cancer cells release cancer-specific antigens.
- APCs take up the cancer antigens.
- APCs prime the T-cells in the lymph nodes to the antigens.
- T-cells migrate to tumour (CTLs).
- T-cells infiltrate tumour (TIL = Tumour Infiltrating Lymphocytes)
- T-cells recognise tumour.
- T-cells kill tumour.
antigens released again
what effect does the cancer-immunity cycle have on the tumour cells?
exerts an immune selection pressure which can lead to a loss of tumour MHC expression so the lymphocytes cannot recognise the cells
what does tumour growth eventually lead to?
inflammatory signal which recruit dendritic cells, macrophages and natural killer cells in the innate immune response and then eventually the adaptive antigen-specific immunity response
what is the issue with small tumours in terms of sounding the alarm?
they do not cause a lot of inflammation and therefore there is no co-stimulation so there is immune cell anergy
what are the two requirements for an adaptive anti-tumour immune response?
1) local inflammation in tumour
2) expression and recognition of tumour antigens
what are the problems with immune surveillance of cancer?
- It takes a while for a tumour to cause local inflammation.
- Antigenic differences between normal and tumour cells can be very subtle and hard to pick up on by the APCs.
what is the purpose of cancer immunotherapy when immune surveillance is insufficient?
“teach” the adaptive immune response to selectively detect and destroy tumour cells when the requirements for the activation of the anti-tumour immune response are not met
what are the similarities with the cancer immune response to that to viruses?
- cells can detect the health of the cell using MHC molecules.
Most tumour antigens are cytosolic antigens. - Tumour-specific antigens can be separated into viral proteins that cause cancers or mutated cellular proteins.
examples of tumour specific antigens: viral
EBV, HPV
example of tumour specific antigens: mutated cellular proteins
TGF-beta receptor 3
Bcr-abl
in which two groups of people are malignancies of viral origin possible?
in the immunocompromised due to supression (therefore opportunistic) and in the immunocompetent
name examples of opportunistic malignancies of viral origin
o EBV+ Lymphoma – post-transplant immunosuppression.
o HHV8+ Kaposi’s sarcoma – HIV individuals.
name examples of malignancies in the immunocompetent of viral origin
o HTLV1-associated leukaemia/lymphoma.
o HBV- and HCV-associated hepatocellular carcinoma.
o HPV+ genital tumours.
what antigens do tumour cells of HPV induced cervical cancer express?
viral antigen E6 and E7 (intracellular Onco-proteins of HPV)
These can be targeted in vaccine form
when is the HPV vaccine necessary?
in <1% who do not develop immunity to HPV they could develop cervical neoplasia so the vaccine is used as prophylaxis so immune failure wouldn’t lead to neoplasia
what are tumour associated antigens?
these are derived from normal cellular proteins but are aberrantly expressed, not mutated.
Wrong time, wrong place, wrong amount
what is the issue with having TAAs and trying to evoke an immune response?
as they are normal self proteins, tolerance may need to be overcome to allow an immune response to occur
Give examples of tumour associated antigen at an immunopriviledged site
cancer-testes antigens (developmental antigens)
- which are silent in normal adult tissue except male germ cells.
MAGE family – melanoma associated antigens.
TAAs examples
o HER2 – Human Epidermal Growth Factor Receptor 2 – overexpressed in some breast cancers.
o MUC-1 (Mucin-1) – membrane-associated glycoprotein overexpressed in many cancers.
o CEA (Carcinoembryonic antigen) – normally only expressed in foetal/embryo, but overexpressed in cancers.
o Prostate antigens – PSA (prostate-specific antigen), PSMA (prostate-specific membrane antigen), PAP (prostatic acid phosphatase).
how and where does tolerance induction take place?
Tolerance induction is via negative selection in the thymus (central tolerance).
Central tolerance is not perfect and we all have some potential auto-reactive T-cells in our repertoire
what is tyrosinase and what is the problem caused by it?
- Tyrosinase is a differentiation-type antigen.
- people have poor tolerance of Tyrosinase and therefore have T-cells that can recognise peptides from Tyrosinase.
- Tyrosinase is involved in skin pigmentation.
- In treatment of melanoma, the t-cells target cancer cells and Tyrosinase and so there is a loss of skin pigmentation – vitiligo.
therefore immune responser to cancer leads to some autoimmunity symptoms
what are the two problems with targeting tumour associated auto-antigens for T cell mediated IT?
o Auto-immune responses against normal tissues e.g. the case with melanoma
o Overcoming any immunological tolerance
why do tumour antigens induce tolerance?
tumour cells expressing the antigens can induce tolerance as they might not cause inflammation so the presentation of the antigens without co-stimulation could make the T-cells anergic and induce tolerance.
what are the main approaches of immunotherapy?
o Antibody-based therapy. o Therapeutic vaccination. o Immune checkpoint blockade (involves CTLA4 and PDL1) o Adoptive transfer of immune cells. o Combinations of the above 1 to 4
what are the 3 components of antibody based therapy?
1) “Naked” – direct antibody
e. g. Anti-HER2 antibody (Herceptin).
2) “Conjugated”- antibody + radioactive-particle or drug
- radioactive particles e.g. anti-CD20 linked to yttrium-90 (Zevalin)
- drugs e.g. anti-HER2 linked to cytotoxic drugs (Kadcyla)
3) “Bi-specific” antibodies – multiple direct antibodies
engineered to combine 2 specificities e.g. anti-CD3 and anti-CD19.
what example of therapeutic cancer vaccination is used for the treatment of advanced prostate cancer?
Provenge
what are naked antibodies?
direct antibody
e.g. Anti-HER2 antibody (Herceptin).
what are conjugated antibodies?
antibody + radioactive-particle or drug
- radioactive particles e.g. anti-CD20 linked to yttrium-90 (Zevalin)
- drugs e.g. anti-HER2 linked to cytotoxic drugs (Kadcyla)
what are bi-specific antibodies?
multiple direct antibodies
engineered to combine 2 specificities e.g. anti-CD3 and anti-CD19.
what is the action of provenge?
Patient’s own WBCs treated with a fusion protein (of PAP (prostatic acid phosphatase) and cytokine GM-CSF)
this stimulates DC maturation and enhances PAP-specific T-cell responses.
what is immune checkpoint blockade?
Reduces/removes negative regulatory controls of existing T-cell responses so to enhance the response against the cancer
CTLA4 (negates T cell activation)
PD-1 (negates tumour apoptosis)
what does the immune checkpoint blockade target?
Monoclonal antibodies are used to block reactions in the:
o CTLA-4 pathway – expressed on activated T-reg cells, binds to CD80/86 (co-stimulatory molecules on APCs) ligands
CTLA4 is later expressed on activated T cells
o PD-1 pathway – expressed on activated T-cells, binds to PD-L1/L2 (complex patterns of expression) ligands
CTLA-4 and PD-1 are surface molecules on T cells that can bind to ligands leading to inhibitory signals being sent to the cell.
But blocking these reactions will enhance anti-tumour immunity
example of drugs used in immune checkpoint blockade?
Ipilimumab (anti-CTLA-4)
Nivolumab (anti-PD-1).
what are personalised tumour specific cancer vaccines?
- the whole exome is sequenced
- leads to the identification of somatic mutations; expression confirmation of mutated genes and prediction of personal HLA-binding peptides
a vaccine is manufactured using candidate neoantigens
what is adoptive transfer of cells?
extraction of tumour infiltrating lymphocytes which can then be multiplied (in culture) then re-infused into the patient
how can TILs be genetic engineered?
CAR expressing T cells (Chimeric Antigen Receptor)
using scFV (chimeric molecule derived from antibody) is transferred to a T cells cytoplasmic domain so it can bind to antigen and activate the T cell and kill cells
what is the difference between tumour-specific and tumour-associated antigens?
Tumour-specific antigens are expressed via onco-proteins and are not normally found in the body.
Tumour-associated antigens are NORMAL proteins that are aberrantly expressed by tumours.
why is the immune response to cancer less apparent?
tumours don’t causes as much inflammation.
what cell surface protein do Tumour-Infiltrating Lymphocytes predominantly express?
CD3+ (T cells)
what is CTLA-4? what does it bind to and what effect does this have?
a surface protein on T cells that binds to CD80/CD86 on APCs like dendritic cells
this has an inhibitory effect on the T cells so its activation is not promoted (whilst the interaction between TCR and MHC class 2 would)
this is involved in stage 3 of the cancer-immunity cycle
what is PD-1? what does it bind to and what effect does it have?
a surface protein on T cells and binds to PD-L1 on cancer cells
binding will stop T cell mediated apoptosis of the tumour cell (whilst interaction between TCR and MHC class 1 would cause apoptosis)
this is involved in stage 7 of the cancer immunity cycle
