ONCOL 320 FINAL

What are the primary functions of the immune system?

immune system attacks:
- foreign infectious agents
- the body's own cells if infected with foreign agents
- the body's own cells if sufficiently abnormal

How are immune responses generated?

based on how the immune response is generated

Define an adaptive immune response

acquired following exposure of an organism to an antigen
generation of antibodies and cytotoxic T-cells

What are advantages of an adaptive immune response?

fast (one established), robust and specific
developed to recognize a specific immune resp

Define an innate immune response

response that occurs in absence of prior exposure to antigen
mediated by natural killer cells, macrophages and intrinsic cellular responses triggered by pathogenic stimuli

What is an advantage of the innate immune response?

does not require prior exposure

What is an antigen?

a foreign (usually) molecule recognized by the immune system

What do antibodies do in the adaptive immune response?

important for clearing extracellular infectious agents, foreign pathogens or cells expressing pathogen-derived or mutated proteins on the cell surface

What are T-cells important for in the adaptive immune response?

controlling the removal of target cells, even if target protein is expressed inside the cell

How are antibodies produced?

proteins produced by B-cell (B-cell lymphocyte) lineage
variable domain produced in response to specific antigen

Describe the structure of an antibody.

- heterotetramer
- two heavy chains, linked to light chains via disulfide bond
- has a variable domain - this has antigen binding domains which would be specific to each Ab
- has a constant domain - has a hinge domain (Fc) and would be the same regardless of Ab

What is a clonotype?

a set of T-cells with the same T-cell receptor

What is a T-cell receptor? purpose?

T-cell receptors lie on the surface of the T-cell, and can bind antigens
They are specific for a single antigen and can be activated to recognize or kill cells

What is CTLA4?

An inhibitory molecule on the surface of a T-cell

What is PD-1?

An inhibitory molecule on the surface of a T-cell

What is CD28?

An activating molecule on the surface of a T-cell

What is a cytotoxic T-cell?

cytotoxic T lymphocyte (CTL)
kills foreign cells

What is a helper T-cell?

helps to activate B-cells and Tc cells when specific for the same antigen

What are regulatory T-cells?

counteract Tc and TH cells to help prevent auto-immunity
Treg suppresses activity of TH and TC cells nearby to where Treg encounters its antigen
Keeps everything in check after Tc/Th cells are done, suppresses further activity of the immune system

What are APCs?

antigen presenting cells
include macrophages and dendritic cells (DCs)

What is the mechanism of APCs?

a viral infection presented on a cell surface is digested by a cell -> APCs take up antigens and process them into oligopeptides -> MHC class II molecules bind the oligopeptides -> MHC class II molecules display the surface proteins of the viral infection on the cell surface for T-cells to recognize

How are helper T cells activated by APCs?

T-cell receptor on TH binds MHC II on DC -> TH cell is activated

How are B-cells activated by APCs?

After TH cells are activated, the TCR on the TH cell can bind MHC II on B-cells -> differentiation of B-cells -> B-cells can release specific Ab

How does a B-cell become an APC?

B-cell absorbs whatever binds to Ab on cell surface -> MHCII binds digested peptides -> MHCII are displayed on the surface of B-cell

Describe the antibody attack of direct neutralization of target.

Ab binds directly to molecules on the surface of virus, bacteria or blood -> blocks infection or inactivates molecule (binds all over, occupying all binding sites, infector can't go/bund anywhere)
Ab binds directly to protein on the surface of infected/cancer cell and inactivates that protein
stops signalling by inhibitory binding

Describe the indirect attack mechanism of antibody attack.

Ab bound to a target on the cell surface acts as a flag to recruit other immune cells or molecules to eliminate target cells

Describe antibody-mediated elimination of target cells by natural killer cells

Ab bind to an target on the cell surface, acting as a flag
NK can bind to the Fc region of Ab
Fc region of Ab is always the same, so all NK cells w/ FC receptors can bind to Ab
Activation of NK causes lysis

Describe antibody-mediated elimination of target cells by complement.

complement cells bind to Abs on a cell surface
creates a signalling cascade eventually resulting in formation of a pore/channel in plasma membrane
loss of membrane integrity/disruption of proton gradient

Why does an organism need more than just antibodies for adaptive defense?

Ab cannot recognize antigens unless antigens are extracellular or on the cell surface - Abs cannot cross the cell membrane
some virus-infected and cancer cells may not be recognized by antibodies

How do cytotoxic T-cells recognize target cells?

based one expression of either extracellular or intracellular proteins

How do T-cells recognize their target proteins?

all normal cells display protein fragments via MHC class I
complex of processed peptide and MHC is recognized by TCR

Describe the mechanism of MHC class I

a protein synthesized in a cell will be diverted to a specialized proteasome, cleaving it into small peptides -> processed peptides bind to MHC class I molecules -> peptide:MHC complex transported to surface

Describe the steps of T-cell mediated attack on target cells

1) Stimulation of immune system w/ specific antigen (ie. viral protein)
2) Activated Tc kills the target cell by one of two mechanisms: (a) activation of the Fas death receptor on the target cell, (b) releasing toxic proteins into the target cells

How are target cells destroyed by cytotoxic granule release?

- TCR on activated Tc binds to a target
- Intracellular cytotoxic granules containing perforin and granzyme B migrate toward synapse w/ target cell
- Granules are released, perforin perforates target cell membrane, granzyme B cleaves caspases in the target cell, inducing apoptosis

How is T-cell attack modulated?

Treg cells act in highly localized, antigen-specific fashion to down-modulate activity and no. of Tc and Th (to prevent autoimmunity)
Co-receptors on T-cells also regulate activity

How are T-cell responses stimulated or inhibited by different cell surface interactions?

use of two signals: (1) TCR engagement, (2) co-receptor engagement

How is it determined if T-cells will be inhibited or stimulated by cell surface interactions?

1. Which co-receptors are expressed on T-cells (Different receptors for different kinetics of expression)
2. Which ligands are present on "partner" cell

What are immune checkpoints?

Signals that inhibit TH and TC responses through negative feedback

What is the purpose of immune checkpoints?

- to ensure T-cell number and activity decrease after infection clears
- to down-modulate T-cell responses activated by chronic pathogenic infection and disease

What is the result of immune checkpoints?

reduces collateral damage to normal tissues (damage = autoimmunity)

Describe basics of innate immunity.

- no previous exposure to antigen
- innate mediators do not respond to a specific antigen, but responds to general features of pathogens (ie. PAMPS, DAMPS, etc) present in/released by infectious agents or abnormal cells
- host cells respond w/ inflammatory response
- complement as well as NK cells are activated by Abs or molecular patterns

What are PAMPs?

pathogen associated molecular patterns
set of molecules associated w/ a group of pathogens

What are DAMPs?

damage associated molecular patterns
molecules associated w/ cell damage

What are natural killer cells?

NK cells
kill cells coated w/ antibodies
display low levels of MHC class I and elevated levels of stress proteins on their surfaces
release cytokines and chemokines to recruit other immune cells

What evidence is there of the immune system protecting us from cancer?

- mice engineered w/ no Tc cells have more spontaneous tumors
- mice w/ no immune system have more spontaneous and chemically induced tumours
- immunocompromised people are more susceptible to cancers than general population

What immune cells (primarily) are at the tumour site?

tumor infiltrating lymphocytes (TILs)

How do the presence of TILs at the tumor site correlate with survival?

Those with TILs in the initial tumor site have increased survival rate
shows TILs can help kill tumor cells

How would the adaptive immune system distinguish cancer cells from normal cells?

recognition of tumor-associated antigens (TAAs)

What are tumour associated antigens and how does the immune system identify them?

normal proteins appear as foreign to immune system if inappropriately expressed
tumor specific proteins can be viral proteins or neo-antigens (products of mutates alleles that arise during tumour progression, includes oncoproteins)

What are neo-antigens?

products of mutated alleles that arise during tumor progression; includes oncoproteins
can help adaptive immune system recognize cancer cells from normal cells

Besides TAA, what other characteristics of cancer cells may the immune system identify?

increased potential for immune recognition when tumors have defects in DNA repair pathways:
- mismatch repair defects result in frameshift mutations; protein after mutation is abnormal -> the more mutations, the more neo-antigens
- some types of cancers are more immunogenic than others (ie. melanoma)

Describe how vitiligo can occur due to cancer.

immune attack on melanoma cells can result in loss of normal melanocytes - due to shared antigens between normal and tumour cells
vitiligo as a marker for improved survival of melanoma patients

Why are tumors not completely eradicated by the immune system?

strongly antigenic tumors are eliminated by the immune system; weakly or non-antigenic tumors expand

selection for tumors w/ other properties that allow them to evade the immune system

How can tumour cells evade the immune system?

1) decreased sensitivity to Tc cells (decreased antigen presentation, anti-apoptotic state is resistant to Tc)

2) suppress the immune response (induce T-cell destruction via FasL, secrete cytokines to prevent immune activity, neutralize complement, block NK cell recognition, attract Treg cells or other suppressive immune cells to tumour site, express PDL-1 that activates PD-1 immune checkpoint receptor on T-cells)

3) hide from immune response (immuno-privileged tissues, tumor architecture)

4) outpace the immune respone

How can a loss of antigen presentation on tumour cells occur?

low TAA expression

loss of MHC class I

What kinds of cancers is the loss of MHC class I proteins associated with?

invasive and metastatic tumors
ex: 50% of aggressive breast cancers lack MHC class I

How can the immune system respond to loss of antigen presentation on tumour cells?

low MHC class I makes cells susceptible to NK attack

How do cancer cells attract Treg cells to suppress the immune response?

chemokine CCL22 is secreted by tumour cells and attracts Tregs to the tumour site

What is the correlation between number of tumour-infiltrating Treg cells and survival?

the lower [Treg], the greater chance for survival

What does a "hot" tumour mean?

the area is inflamed, has pre-existing immunity
large no. of TILs, CD8 T-cells/INFy, PD-L1/checkpoints
great mutational load

What does a "cold" tumour mean?

non-inflamed, no immune cells present

What are the three classes of tumours?

indolent tumours, highly aggressive tumours and tumours of intermediate grade

What is an indolent tumour?

low invasive and metastatic potential and will remain in such a state during the lifetime of patients
benign
-> is treatment necessary? probably not.

What is a highly aggressive tumour?

tumours w/ a tendency to metastasize that have (w/ a high probability) disseminated by the time the primary tumour has been diagnosed

What is a tumour of intermediate grade?

has the potential to disseminate but can be treated before dissemination occurs and life-threatening metastasis are formed
focus for cancer treatment

Define screening

Testing an asymptomatic (lacking symptoms) population for indicators of disease

What are the four key criteria to screen an asymptomatic population?

1\. disease must have detectable preclinical phase (disease present, no symptoms yet)

2\. there must be a benefit to treating before symptoms appear

3\. screening test and follow-up must be acceptable to individuals at risk (minimal invasiveness) and healthcare providers (manageability)

4\. screening methods meets acceptable levels of accuracy and cost

What is lead-time?

the time between detection (by screening) and appearance of symptoms that would lead to a diagnosis

What is lead-time bias?

occurs when an earlier diagnosis does nothing to change the course of the disease
survival rates are inflated by earlier diagnosis, but there is no change in mortality
mortality is a better measure of benefit than survival

What is a better measure of benefit: mortality or survival?

mortality
if they still die at the same time, how is an early diagnosis better?
normalized against age

What is overdiagnosis?

detection of a slow-growing cancer by screening that never would have caused harm or required treatment during a patient's lifetime

What is overdiagnosis bias?

with screening, you have a higher number of people who have a nonprogressive cancer; when it doesn't progress during their lifetime and mortality is not changed, you have inflated survival rates
mortality is a better measure of benefit than survival is

How are new screening methods evaluated?

sensitivity
specificity
is there a potential risk of over-diagnosis?

What is sensitivity?

the ability of a test to correctly identify patients with the disease
minimize false negatives

What is specificity?

the ability of the test to correctly identify patients without the disease
minimize false positives

What is a mammography?

screens for breast cancer
X-ray
recommended every 2 years for women > age 50

Why are younger women not screened for a mammography?

progression of breast cancer is faster for women < age 40
lead time for women < age 40 is too short for cancer to be detected in a screen given every two yeaars

Why not screen younger women more often for breast cancer via mammography?

X-ray test can be damaging to tissue if administered too often; may cause cancer
can the healthcare system afford?

Explain the potential for overdiagnosis relating to breast cancer screening.

increase in incidence of breast cancer relating to the increased detection by screening
many women carry tumours which do not cause harm; they do not die because of the tumour
can result in harm of overdiagnosis for some patients, and benefit of lower risk of breast cancer mortality for other patients
how can we know which tumours are life threatening and which are benign?

Describe methods of colorectal cancer screening?

reduction in colon cancer morbidity and mortality through screening by:

\- detecting and removing polyps

\- detecting early stage adenocarcinomause stool tests or endocscopy of large bowel

Describe methods of cervical cancer screening

pap test detects precurser lesions

\- epithelial cells from cervix examined for abnormal cytologyHPV associated w/ cervical cancer, virus is fairly common and difficult to detect

\-dysplastic lesions more treatable than invasive lesions

How is lung cancer screened for?

patients w/ lung cancer have poor prognosis (easy to metastasize), if detected while localized, have better outcome

can use imaging techniques (CT is sensitive enough, X-ray is not)

How is prostate cancer screened for?

physical exam

blood test for prostate-specific antigen (PSA): test patient serum with antibody against PSA

What are some reasons why prostate cancer is not screened for using a PSA test anymore?

-> high overdiagnosis potential
-> some prostate cancers PSA-negative
-> variable baseline level
-> large randomized clinical trials showed a small reduction in deaths
-> better as predictor of recurrence

What is diagnosis?

diagnosis is the identification of the disease after the patient presents w/ symptoms or positive test results

What is tumor grade?

indicates liklihood that tumour will grow and spread

Based on microscopic appearance of tumour cells, how could you tell the difference between a low grade and a high grade tumor cell?

low grade tumour cells are closer to normal
high grade tumour cells are closer to abnormal

What is tumour stage?

indicates the extent of the disease at the time of diagnosis
- size of primary tumor
- if it has spread to other sites

Define a Grade 1 tumour.

well-differentiated (low-grade); closest to normal structure (in terms of duct formation, nuclear size, no. of mitotic cells)

Define a Grade 2 tumour.

moderately differentiated (intermediate grade)

Define a Grade 3 tumour.

poorly differentiated (high grade)

Define a Grade 4 tumour.

undifferentiated (high grade)

What does tumour staging systems give information about?

primary tumour (size, grade, location)
dissemination to regional sites (lymph nodes) or distant sites of metastases

What is the TNM staging system?

tumour lymph node metastasis
- defines cancer in terms of primary tumour (T) -> numbers T1, T2, T3 and T4 indicate increasing size
- absence or presence of tumour cells in regional lymph nodes (N) -> numbers indicate node-negative (N0) or node-positive (N1), sometimes N2 or N3 for further lymph node involvement
- absence or presence of distal metastases (M) -> numbers indicate met-negative (M0) or met-positive (M1)

What does T indicate in the TNM staging system?

defines cancer in terms of primary tumour (T)
numbers indicate increasing size

What does N indicate in TNM staging system?

absence/presence of tumour cells in regional lymph nodes (N)
numbers indicate node-negative (N0) or node-positive (N1)
for some cancers, also N2 or N3 for more numerous/distal node involvement

What does M indicate in TNM staging system?

absence/presence of distal metastases (M)
numbers indicate met-negative (M0) or met-positive (M1)
for some cancers also M2, M3

What are treatment options for benign or low-grade tumours?

have low invasive and metastatic potential that remain so during the lifetime of a patient
may not need treatment

What are treatment options for highly aggressive tumours?

have propensity to metastasize, high likelihood to have disseminated at time of diagnosis
may not respond to standard treatment

What are treatment options for intermediate grade tumours?

potential to disseminate but may respond to treatment before dissemination occurs or at least before progression to life-threatening metastases
likely to benefit from proper treatment