L22- Tumour Immunity and Immunotherapy

Question 1

Define immune surveillance

Answer 1

Immune surveillance is a physiologic function of the immune system is to recognize and destroy clones of transformed cells before they grow into tumours and to kill tumours after they are formed.

Question 2

Explain the lymphocytic infiltrates that appear around tumours.

Answer 2

Histopathologic studies show that many tumours are surrounded by mononuclear cell infiltrates composed of T lymphocytes, natural killer (NK) cells, and macrophages, and that activated lymphocytes and macrophages are present in lymph nodes draining the sites of tumour growth

Question 3

The presence of lymphocytic infiltrates in some types of melanoma and carcinomas of the colon and breast is predictive of a better prognosis. T or F?

Answer 3

True

Question 4

How dies the immune response frequently fail to prevent the growth of tumours?

Answer 4

• Many tumours have specialized mechanisms for evading immune responses
• Tumour cells are derived from host cells and resemble normal cells in many aspects – they are weakly immunogenic
• Rapid growth and spread of a tumour may overwhelm the capacity of the immune system to effectively control the tumour

Question 5

Explain the immune response of an inbred mouse that has been exposed to the chemical carcinogen methylcholanthrene (MCA).

Answer 5

• Sarcoma may be induced in an inbred mouse by painting its skin with the chemical carcinogen methylcholanthrene (MCA)
• If the MCA-induced tumour is excised and transplanted into other syngeneic mice, the tumour grows
• In contrast, if cells from the original tumour are transplanted back into the original host, the mouse rejects this transplant and no tumour grows
• The same mouse that had become immune to its tumour is incapable of rejecting MCA-induced tumours produced in other mice
• Immune responses to tumours exhibit the defining characteristics of adaptive immunity: specificity, memory, and the key role of lymphocytes

Question 6

As predicted from the mouse transplantation experiments with MCA, the most effective response against naturally arising tumours appears to be mediated mainly by …?

Answer 6

T lymphocytes

Question 7

Antigens that are expressed on tumour cells but not on normal cells are called …?

Answer 7

Tumour-specific antigens (TSA)

Some are unique to individual tumours, whereas others are shared among tumours of the same type

Question 8

Tumour antigens that are also expressed on normal cells are called …?

Answer 8

Tumour-associated antigens (TAA)

these antigens are normal cellular constituents whose expression is aberrant or dysregulated in tumours

Question 9

Tumour antigens that were defined by the transplantation of carcinogen-induced tumours in animals, called …?

Answer 9

Tumour-specific transplantation antigens

Question 10

Studies with chemically induced rodent sarcomas, (refer to mouse sarcoma/MCA study) established that different rodent tumours, all induced by the same carcinogen, expressed different transplantation antigens. Explain this.

Answer 10

• The tumour antigens identified by such experiments are peptides derived from mutated self proteins and presented in the form of peptide–class I MHC complexes capable of stimulating CTLs
• These antigens are extremely diverse because the carcinogens that induce the tumors may randomly mutagenize any host gene, and the class I MHC antigen-presenting pathway can display peptides from any mutated cytosolic protein in each tumour

Question 11

What is the role of Tyrosinase?

Answer 11

Tyrosinase is an enzyme involved in melanin biosynthesis that is expressed in normal melanocytes and melanomas

Question 12

Which MHC molecules recognize peptides derived from tyrosinase?

Answer 12

Both class I MHC–restricted CD8 +CTL clones and class II MHC–restricted CD4 +helper T cell clones from melanoma patients recognize peptides derived from tyrosinase

Question 13

Why doesn’t the immune system pick up tyrosinase in melanoma quick enough?

Answer 13

Likely explanation is that tyrosinase is normally produced in such small amounts and in so few cells that it is not recognized by the immune system and fails to induce tolerance

• The increased amount produced by melanoma cells is able to elicit immune responses

Question 14

What are cancer/ testis antigens?

Answer 14

Cancer/testis antigens are proteins expressed in immunologically privileged sites such as testes, placenta and foetal ovary, and in many types of cancers but not in normal somatic tissues.

• First identified in melanoma, termed melanoma-associated antigens (MAGE)
• Expressed in other tumours, including carcinomas of bladder, breast, skin, lung, prostate, normal testis
• Abnormal expression of these germline genes in malignant tumours leads to tumour progression and broad immunogenicity

Question 15

What antigens are detected in Human papilloma virus (HPV)?

Answer 15

E6 and E7 proteins

Vaccines use virus like particles from these proteins

Question 16

What are Oncofoetal antigens?

Answer 16

Oncofoetal antigens are proteins that are expressed at high levels in cancer cells and in normal developing foetal but not adult tissues

• Genes encoding these proteins are silenced during development and are de-repressed with malignant transformation
• Oncofetal antigens are identified with antibodies raised in other species, and their main importance is that they provide markers that aid in tumour diagnosis
• expression in adults is not limited to tumours, but is increased in tissues and in the circulation in various inflammatory conditions, and the antigens are found in small quantities even in normal tissues

Question 17

Two best characterized oncofetal antigens are …?

Answer 17

carcinoembryonic antigen (CEA) and α-fetoprotein (AFP)

Question 18

What are Tissue-Specific Differentiation Antigens with B cell as an example?

Answer 18

Tumours may express molecules that are normally expressed only on the cells of origin of the tumours and not on cells from other tissues

• These antigens are called differentiation antigens because they are specific for particular lineages or differentiation stages of various cell types
• Lymphomas may be diagnosed as B cell–derived tumours by the detection of surface markers characteristic of this lineage, such as CD20
• Antibodies against these molecules are also used for tumour immunotherapy; the most successful immunotherapy for non-Hodgkin’s B cell lymphomas is an anti-CD20 antibody (rituximab)

Question 19

Explain how the adaptive immune responses, mainly mediated by T cells, have been shown to control the development and progression of malignant tumours?

Answer 19

The principal mechanism of adaptive immune protection against tumours is killing of tumour cells by CD8 CTLs

• CTLs may perform a surveillance function by recognizing and killing potentially malignant cells that express peptides that are derived from tumour antigens and are presented in association with class I MHC molecules:
• Tumour-infiltrating lymphocytes (TILs), derived from the inflammatory infiltrate in human solid tumors, contain CTLs with the capacity to kill the tumour from which they were derived
• Data from recent clinical trials shows that blocking these inhibitory pathways, and thus removing the brakes on immune responses, leads to the development of strong T cell responses against the tumour
• Some effective therapeutic anti-tumour antibodies that are passively administered to patients likely work by antibody-dependent cell-mediated cytotoxicity

Question 20

Explain how CD8 + T cell responses specific for tumour antigens may require cross-presentation of the tumour antigens by dendritic cells.

Answer 20

• Most tumour cells are not derived from APCs and therefore do not express the co-stimulators needed to initiate T cell responses, or the class II MHC molecules needed to stimulate helper T cells that promote the differentiation of CD8 + T cells.
• Once effector CTLs are generated, they are able to recognize and kill the tumour cells without a requirement for co-stimulation.

Question 21

How would you induce CD8+ T cell response in a patient?

Answer 21

Grow dendritic cells from a patient with cancer, incubate the APCs with the cells or antigens from that patient’s tumour, and use these antigen-pulsed APCs as vaccines to stimulate anti-tumour T cell responses.

Question 22

Explain the role of NK cells in tumour cells

Answer 22

NK cells kill many types of tumour cells, especially cells that have reduced class I MHC expression and express ligands for NK cell–activating receptors

• In vitro, NK cells can kill virally infected cells and certain tumour cell lines, especially hematopoietic tumours
• NK cells respond to the absence of class I MHC molecules because the recognition of class I MHC delivers inhibitory signals to NK cells
• Some tumours lose expression of class I MHC molecules, perhaps as a result of selection against class I MHC–expressing cells by CTLs. This loss of class I MHC molecules makes the tumours particularly good targets for NK cells

Question 23

Which ligands on tumour cells are recognised by NKG2D on NK cells?

Answer 23

Some tumours also express MIC-A, MIC-B, and ULB, which are ligands for the NKG2D activating receptor on NK cells

Question 24

How can NK cells activate ADCC? (Antibody dependent cellular cytotoxicity)

Answer 24

NK cells can be targeted to IgG antibody–coated tumour cells by Fc receptors (FcγRIII or CD16), to mediate ADCC

Question 25

Tumoricidal capacity of NK cells is increased by which cytokines?

Answer 25

interferon-γ (IFN-γ), IL-15, and IL-12, and the anti-tumour effects of these cytokines are partly attributable to stimulation of NK cell activity.

Question 26

What are lymphokine-activated killer (LAK) cells?

Answer 26

There are IL-2 activated NK cells and are derived by culture of peripheral blood cells or tumuor-infiltrating lymphocytes from tumour patients with high doses of IL-2. It results in the development of effector cells which are cytotoxic to tumor cells.

Question 27

Provide some examples how cancers develop mechanisms that allow them to evade anti-tumour immune responses?

Answer 27

Loss of Antigen Expression Class I MHC expression may be downregulated on tumour cells so that they cannot be recognized by CTLs Secreted products of tumour cells may suppress anti-tumour immune responses. An example of an immunosuppressive tumour product is TGF-β Regulatory T cells may suppress T cell responses to tumours -they are increased in tumour-bearing individuals, and can be found in the cellular infiltrates in certain tumours

Question 28

Define Immunoediting

Answer 28

Immunoediting is a dynamic process that consists of immunosurveillance and tumor progression. It describes the relation between the tumor cells and the immune system resulting in the survival and outgrowth of variant tumour cells with reduced immunogenicity. It is made up of three phases: elimination, equilibrium, and escape

Question 29

Explain each phase of Immunoediting (elimination, equilibrium and escape)

Answer 29

Elimination: When tumour cells arise in a tissue, a number of immune cells can recognise and eliminate them Equilibrium: Variant tumour cells arise that are more resistant to killing and over time a variety of different tumour variants arise Escape: Eventually one variant may escape the killing mechanism or recruit regulatory cells to protect it and so spread unchallenged.

Question 30

Explain how tumour vaccines can be used for therapeutic purposes

Answer 30

Immunization of tumour-bearing individuals with tumour antigens may result in enhanced immune responses against the tumour. * Identification of peptides recognized by tumourspecific CTLs and the cloning of genes that encode tumour-specific antigens recognized by CTLs have provided many candidate antigens to include in tumour vaccines * Most tumour vaccines are therapeutic vaccines; they have to be given after the host has encountered the tumour (unlike preventive vaccines for infections), and in order to be effective, they have to overcome the immune regulation that cancers establish.

Question 31

Explain immune checkpoint inhibitor therapies

Answer 31

Immune checkpoint inhibitors promote an antitumour immune response by blocking signalling via either the cytotoxic T lymphocyte antigen 4 (CTLA4) pathway or the programmed cell death protein 1 (PD1) pathway

Question 32

What type of cancers can you use immune checkpoint inhibitors for?

Answer 32

Immune checkpoint inhibitor therapies are a novel group of monoclonal antibodies with proven effectiveness in a wide range of malignancies, including melanoma, renal cell carcinoma, non-small-cell lung cancer, urothelial carcinoma and Hodgkin lymphoma

Question 33

What is one negative example of using immune checkpoint inhibitors therapies?

Answer 33

They are also associated with a substantial risk of immune-related adverse events

Question 34

Explain the normal process of CTLA-4 in immune regulation against tumours

Answer 34

Checkpoint proteins, such as B7-1/B7-2 on antigen-presenting cells (APC) and CTLA-4 on T cells, help keep the body’s immune responses in check. * When the T-cell receptor (TCR) binds to antigen and major histocompatibility complex (MHC) proteins on the APC and CD28 binds to B7-1/B7-2 on the APC, the T cell can be activated. * However, the binding of B7-1/B7-2 to CTLA-4 keeps the T cells in the inactive state so they are not able to kill tumour cells in the body (left panel). * Blocking the binding of B7-1/B7-2 to CTLA-4 with an immune checkpoint inhibitor (anti-CTLA-4 antibody) allows the T cells to be active and to kill tumour cells

Question 35

Explain therapies of CTLA-4

Answer 35

Blocking CTLA-4 with antibodies results in increased immune responses to tumours * CTLA-4 expression is low on most T cells until the cells are activated by antigen, and once expressed CTLA-4 terminates continuing activation of these responding T cells. * CTLA-4 is expressed on regulatory T cells and mediates the suppressive function of these cells by inhibiting the activation of naive T cells.

Question 36

Provide an example of a cancer that you would use CTLA-4 therapy?

Answer 36

Advanced melanoma

Question 37

What is a disadvantage of CTLA-4 therapy?

Answer 37

Some of the treated patients develop manifestations of autoimmunity with inflammation in various organs.

Question 38

What is PD-1 and what does it do?

Answer 38

The checkpoint protein PD-1 is a co-stimulatory molecule expressed on activated T cells, downregulates immune responses * PD-1 ligates PD-L1, expressed on APCs and many other tissue cells [PD-L2 is expressed mainly on APC] * Engagement of PD-1 by either ligand leads to inactivation of T cells, by inhibiting signal transduction from TCR * PD-1 is important in terminating peripheral responses of effector T cells, especially CD8+ T cells

Question 39

How do cancer cells use PD-L1 to their advantage?

Answer 39

The cancer cells sense they are under attack from T cells by recognising IFN-gamma which leads to the reactive expression of PD-L1 which turns off the antitumor T cell response.

Question 40

Explain how PD-1 checkpoint inhibitor can be blocked to allow T cells to kill tumour cells

Answer 40

AntiPD-1 or anti-PD-L1 antibodies can be used as therapy treatment against cancer. The antibodies block PD-1 and PD-L1 allowing cytotoxic CD8+ T cells to kill tumour cells.

Question 41

Explain CAR T cell therapy

Answer 41

Adoptive therapy using T cells expressing chimeric antigen receptors (CARs) has proven successful in some hematologic malignancies, and this approach is in trials for other tumours * Patent’s peripheral blood T cells are isolated, stimulated with anti-CD3 and/or anti-CD28 antibodies, and subjected to gene transduction with CAR-encoding vectors. * The CAR-expressing T cells are then expanded in vitro and injected into the patient. * The transferred T cells undergo further robust proliferation in the patient, in response to tumour antigen recognition by the CAR. * Tumour killing is achieved by both direct cytotoxic and cytokine-mediated mechanisms. * Patients with B cell malignancies, including chronic lymphocytic leukemia and acute lymphoblastic leukemia, have been effectively treated with CARexpressing T cells specific for CD19, a pan–B cell marker also expressed on the tumour cells

Question 42

What is a challenge of CAR T cell therapy?

Answer 42

Challenge: to identify target antigens that are relatively tumour-specific

Question 43

Explain how CAR receptors are different to TCR’s

Answer 43

CARs are synthetic, engineered receptors that can target surface molecules in their native conformation Unlike TCRs, CARs engage molecular structures independent of antigen processing by the target cell and independent of MHC CARs typically engage the target via a single-chain variable fragment (scFv) derived from an antibody

Question 44

What type of protein is selected for most B-cell lymphoid malignancies

Answer 44

Anti-CD19 CD19 CAR: a single chimeric protein that is the recognition domain of a specific antibody against a tumour-associated antigen, and an intracellular signalling domain capable of activating T cells

Question 45

Currently, there are more than 100 different monoclonal antibodies being considered as therapeutic agents for cancer, either in experimental animal studies or in human trials, and a few have been approved for clinical use. What is the purpose of these monoclonal antibodies

Answer 45

Anti-tumour antibodies may eradicate tumours by the same effector mechanisms that are used to eliminate microbes, including opsonization and phagocytosis, activation of the complement system, and antibodydependent cellular cytotoxicity

Question 46

What is a challenge of monoclonal antibody therapy

Answer 46

One of the most difficult problems with the use of anti-tumour antibodies is the outgrowth of antigen loss variants of the tumour cells that no longer express the antigens that the antibodies recognize. One way to avoid this problem may be to use cocktails of antibodies specific for different antigens expressed on the same tumour