3. The Hallmarks of Cancer

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Development Team

Paper Coordinator : Prof. Anju Shrivastava

Department of Zoology, University of Delhi Principal Investigator : Prof. Neeta Sehgal

Department of Zoology, University of Delhi

Content Writer : Dr. Usha

Gargi College, University of Delhi

Content Reviewer : Prof. Sukhmahendra Singh Banaras Hindu University Co-Principal Investigator : Prof. D.K. Singh

Department of Zoology, University of Delhi Paper : 10 Immunology

Module : 34 Immunity in health and diseases: Cancer immunology

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Description of Module

Subject Name ZOOLOGY

Paper Name Zool 010: Immunology

Module Name/Title Immunity in health and diseases Module ID M34: Cancer immunology

Keywords

Cancer, Hallmarks, tumour antigens, immuno surveillance, immunoediting, immunotherapy, check point blockade, adoptive cell transfer

1. Learning outcomes

After studying this module, you will be able to learn

• Cancer and hallmarks of cancer

• Difference between normal and cancer cells

• Relationship of cancer with immune system

• Role of immune system in tumour growth

• Mechanisms of immune evasion by cancer

• Immunotherapy to treat cancer

2. Introduction

The term cancer was earlier defined by Hippocrates (The father of medicine) as Karkinos (A Greek word which means crab) probably because of the similar appearance of the rounded solid tumour with a crab. Cancer is characterized by unregulated, unlimited cell division and cell growth beyond the cell boundaries so that it can invade the adjoining tissue and spread from one tissue to other. Other common terms used for cancers are, tumours and neoplasms (new growth). There are two types of tumours based on the invasiveness nature: (i) Benigntumour, a tumour which remains only at one site and does not invade the healthy surrounding tissue extensively. (ii) Malignant tumour, a tumour that continues to grow and gradually becomes invasive. Malignant tumours show metastasis; a process in which small populationof cancerous cells extricate from a tumour, invade the blood or lymphatic vessels, and are carried to other tissues, where they establish and start to proliferate (Fig. 1).

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Fig.1 Different types of cells surrounding tumour and invading the other tissues (Douglas Hanahan and Robert A. Weinberg, Cell, 2011).

3. The Hallmarks of Cancer

Essential alterations in cancer cell physiology characterize cancer malignancy which was called as “Hallmarks of cancer” by Hanahan and Weinberg (2000, 2011)(Fig.2).

(i) Self-sufficiency in growth signals: Cancer cells can grow in absence of exogenous growth factors because they are able to produce necessary growth factors or overexpresses growth factor receptors like epidermal growth factors receptor (EGFR).

(ii) Insensitivity to anti-growth signals/growth inhibitory signals: Cancer cells do not respond to tumour suppressor genes such as retinoblastoma (Rb) and p53 which provide inhibitory signals for growth.

(iii) Evasion of apoptosis: Cancer are resistant to apoptosis as these cells produces anti- apoptotic factors such as Bcl-2 or reduces the expression of pro-apoptotic signals Bax and Bak.

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(iv) Replicative immortality. Cancer cells show increased expression of telomerase enzyme which protects tumour cell senescence and apoptosis resulting in unlimited cell proliferation.

(v) Sustained angiogenesis: Cancer cells can increase the angiogenesis by increased expression of vascular endothelial growth factor (VEGF) or vascular endothelial growth factor receptor (VEGFR). Infiltrating leukocytes during malignant cancer also helps in angiogenesis.

(vi) Tissue invasion and metastasis: Cancer cells can migrate, invade and spread to different tissues through blood and lymphatic blood vessels, leading to malignant cancer. Stromal, mesenchymal stem cells and tumour associated macrophages also help in invasion and metastasis.

(vii) Evading immune destruction: Tumour cells evade the immune system by secreting immunosuppressive factors like transforming growth factor-β (TGFβ) or by recruiting regulatory T (Treg) cells which can suppress cytotoxic T lymphocytes (CTLs) function.

(viii) Reprogramming energy metabolism: Cancer cells show increased rates of glycolysis despite the availability of adequate oxygen level (Warburg effect) by the overexpression of hypoxia inducible fctor-1(HIF-1) and glucose transporter (GLUT1).This process provides raw material for other activities and pyruvate can be converted to lactic acid lowering the pH which favours tumour invasion and suppress anti-tumour activity.

(ix) Genomic instability and mutation: Certain mutations generated in tumour cells offer a selective advantage leading to overgrowth of the dominant clone and helps in tumour progression.

(x) Tumour promoting inflammation: Infiltration of inflammatory cells in tumour can provide growth, pro-angiogenic factors and signals for invasion and metastasis.

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Fig. 2: Hallmarks of cancer. (Source: Author)

4. Tumour antigens and mechanism of their formation

4.1. Tumour antigens

Cancer cells can be recognized by the immune cells because of presence of some antigens on their surface called as tumour antigens. Broadly these antigens can be of two types:

(a) Tumour-specific antigens: Those expressed only on tumour cells but not on normal cells(viral induced antigens).

(b) Tumour associated antigens: Those that also expressed on normal tissue (oncofetal antigens). Examples of some important tumour antigens are:

(i) Products of oncogenes, mutated and overexpressed genes: Those proteins produced by the oncogenes and mutated tumour suppressor genes. Tyrosinase, an enzyme over expressed in tumour cells.

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(ii) Antigens of oncogenic viruses: Oncogenic virus product functions as tumour antigens [Epstein-Barr virus (EBV), human papilloma virus (HPV)].

(iii) Oncofetal antigens: Those proteins that are normally expressed in fetus but absent in normal adult tissue. These may have expressed at high level on tumour cells of adult tissues [carcinoembryonic antigen (CEA) and α-fetoprotein (AFP)].

(iv) Altered glycolipid and glycoprotein antigens: Tumour cells overexpress abnormal forms of surface glycoproteins (MUC-1).

(v) Testes-specific antigen: The proteins which are expressed only on testis may expressed by tumour cells (MAGE 1-3).

4.2. Mechanism of conversion of self-antigen to tumour antigen

There are three ways by which a self-antigen becomes tumour antigens:

(1) Mutation: any mutation in the DNA of normal cell leads to production and presentation of abnormal protein on the surface of tumour cell.

(2) Overexpression: a protein which is expressed on normal cell at low concentration because of mutation or some regulatory factor may overexpress on tumour cells.

(3) Post translational modifications: a normal protein may not be properly processed. This abnormal protein may be expressed on tumour cells as tumour antigen (Fig. 2).

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Fig. 2. Three ways of self-antigen to become non-self/tumour antigen: Three self-peptides (yellow, blue, and green) are presented on the cell surface along with MHC molecules as normal self-antigens. A. Mutation:

Mutation in DNA of normal protein (green) leads to formation and presentation of mutated (red) protein on the tumour cell surface as non-self-antigen. B. Overexpression: Normal protein (single green) can be overexpressed (many green) and presented on the cell surface at high level. C. Post-translational modifications: a normal protein may not be processed properly so becomes different from normal and presented on cell surface as non-self (green stripes).

Source:Olivera J. Finn,2008.

5. Cancer and its relationship with immune system

Immune system is known to play important role in cancer prevention because of that there is emergence of a new branch of science called cancer immunology which deals with the study of interaction between the cancer and immune system. It aimed to find out the methods for cancer treatment.

5.1. Microenvironment of cancer

Cancer grows in a complex network of epithelial and infiltrating immune cells and is supplied with blood and lymphatic vessels. Immune cells present in tumour microenvironment include natural killer (NK) cells, macrophages, dendritic cells (DCs),B and T cells [Th1, Th2, Th17, regulatory T (Treg) cells, and cytotoxic T lymphocytes (CTLs)]and myeloid-derived suppressor cells (MDSC)(Fig. 3).These different types of cells help in tumour elimination by different mechanism.

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Fig. 3: Tumour microenvironment containing tumour core and distribution of immunecells. DC, dendritic cells;

MDSC, myeloid-derived suppressor cells; NK cells, natural killer cells; FDS, follicular dendritic cells; TFH, follicular T cells; CTL, cytotoxic T lymphocytes; TLS, tertiary lymphoid structure.

Source: Wolf Herman Fridman, FranckPagès, Catherine Sautès-Fridman and JérômeGalon,Nature reviews, Cancer, 2012).

5.2. Role of immune system in protection of host from cancer

Both innate and adaptive immune system play vital role in eradication of cancer cells.

(A). Role of innate immune system: Important effector cells of the innate immune system, NK cells, macrophages and DCs have the potential to kill the tumour cells by different mechanism. (i) NK cells, the lymphocytes of innate immune system and provide cell mediated defense against tumour cells. NK cells monitor the cell surface for any abnormal expression of MHC class I & stress markers and also recognize natural killer group 2 D ligands (NKG2D) on tumour cells and kill those tumour cells with reduced number of MHC class I molecule by releasing perforins and granzymes, without any prior sensitization. NK cells are also source of some chemokines and cytokines like interferon-γ(IFN-γ) and tumour necrosis factor (TNF)which play role in anti-tumour immunity.

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(ii) Macrophages, important cells of innate immune system capable of both inhibiting and promoting the growth and spread of cancers, depending on their activation state. Based on the activation state, macrophages can be of two types: M1 and M2. M1 are activated by INF- γ and kill the tumour cells by producing reactive oxygen species (ROS), nitric oxide and IL-12.

In presence of IL-4 and IL-13 M1 polarized to M2 (tumour associated macrophages). These cells produce growth factor (EGF), promote angiogenesis and reduce anti-tumour responses.

(iii) Dendritic cells (DCs), known more efficient than other professional antigen presenting cells (APCs) in induction of both arms of adaptive immunity (cell mediated and humoral).These cellsare able to control both immunity and tolerance. DCs cells produce pro- inflammatory cytokines and cross talk with NK cells to mediate the tumour cell killing. DCs also capture antigens from dying cancer cells prime the T cells and stimulate antigen specific T and B cells to enhance anti-tumour activity.

(B). Role of adaptive immune system: Both cell mediated and humoral immune response involve in tumourkilling.

(i) Cell mediated immunity against cancer cells: The main mechanism of cancer cell killing is T cell mediated in which both CD8⁺and CD4⁺ cells are activated through the tumour antigen presented by DCs. T cells secrete cytokines like TNF, INF-γ increasing activation of CTL and macrophages to kill the tumour.

(ii) Humoral immunity against cancer: APCs like DCs activates T cells by cross presentation of tumour antigen, which activates the B cells to produce tumour antigen specific antibodies. Mechanism of tumour cell killing by antibodies can be of two types: (i) Direct killing, mediated by binding of antibody to tumour cell surface activating and leading to apoptosis. (ii) Immune mediated tumour cell killing carried out by phagocytosis, complement activation and antibody-dependent cellular cytotoxiciy (ADDC).

5.3. Cancer immuno surveillance and immunoediting:

Paul Ehrlich (1909) first time suggested the role of immune system in cancer elimination. Later on, Frank Macfarlane Burnet (1959) put forward the theory of

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by which immune system detects and identifies nascent transformed/precancerous cells as abnormal cells of body and eliminates them before they become harmful. On one hand, immune system tries to protect the host from cancer by immune surveillance, on other hand cancer cells tend to suppress the immune system, invade and metastasize to other tissues. Therefore, there exist battle between the immune system and cancer cells, if immune system wins, tumour eliminated and if cancer cells win there is development and progression of tumour.

The interaction of cancer and immune cells in tumour microenvironment initiates cascades of events called immunoediting, a process wherein immune system functions not only as an extrinsic tumour suppressor but also to shape tumour immunogenicity and can be divided into three phases, called as “three E” - Elimination, Equilibrium and Escape (Fig. 4).

5.3.1. Elimination phase: Immune cells play important role in protection and elimination of tumour cells

This phase represents the classical concept of surveillance of tumour cells where immune cells eliminate cancer cells. In this phase both innate and adaptive immune system identifies and destroys the early nascent transformed tumour cells before they become invasive and metastatic. Macrophages (M1) and granulocytes secrete TNF-α, IL-1, IL-12 and ROS creating anti-tumour immunity. DCs take up the tumour antigens from dying cancer cells and cross present to T and NKT cells, these cells produce INF-γ leading to inhibition of tumour cells proliferation and angiogenesis. Effector CD8⁺ and NK cells recognized tumour cells expressing tumour antigens along with MHC I molecules and NKG2D ligands respectively and kill them either by releasing perforin and granzymes or by inducing apoptosis through Fas and TRAIL. Gama-delta(γδ) T cells can also recognize and kill the tumour cells through NKG2D receptor. In elimination phase, tumour is eliminated because of higher anti-tumour immunity. This phase can be referred as complete elimination phase where all the transformed tumour cells are removed or as incomplete elimination/partial elimination whereby only portions of tumour cells are eliminated leaving some tumour cells alive.

5.3.2. Equilibrium phase: Immune induced tumour dormancy

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This phase refers to the period of immune-mediated dormancy after incomplete tumour destruction in the elimination phase. The surviving tumour cells either remain dormant or continue to evolve, by undergoing genetic changes (DNA mutation or gene expression) that can modulate the tumour specific and stress-induced antigens that they express leading to formation of tumour cell variant. In this phase the balance between anti-tumour (IL-12, INF- γ) and tumour promoting (IL-10, IL-13) cytokines is maintained. The functional tumour dormancy is maintained by adaptive immunity. At this stage failure of immune system to clear tumour variants results in selection of those tumour cell variants that are able to resist, avoid, or suppress the anti-tumour immune response. These variants undergo escape phase.

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Fig. 4.Immunoediting: The three phases of cancer immunoediting also knows as three Es (Elimination, equilibrium and elimination). Action of carcinogens, radiations etc, on normal cell leading to transformed/

precancerous cells. Precancerous cells are removed through the intrinsic tumour suppressor mechanism (repair, senescence,or /and apoptosis) before they become cancerous. (1) Elimination phase: This phase is also known as immuno surveillance. Failure of intrinsic tumour suppressor leads to initiation of extrinsic tumour suppressor mechanism. Nascent transformed cells are highly immunogenic as they express tumour antigen which led to recruitment and activation of immune cells. Integrated efforts of both innate and adaptive immune system lead to tumour elimination and protection of host body from tumour. (2) Equilibrium phase:If there is incomplete elimination of transformed cells, surviving tumour variants may enter into the equilibrium phase, where cells and molecules or cytokines of adaptive immunity maintains functional tumour dormancy and prevent tumour outgrowth. (Abbreviations: CTLA-4, cytotoxic T lymphocyte associated protein-4; IDO, indoleamine 2,3- deoxygenase; IFN, interferon; IL, interleukin; M, macrophage; MDSC, myeloid-derived suppressor cells; NK,

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natural killer; NKG2D, NK group 2, member D; PD-L1, programmed cell death 1 ligand 1; TGF-β, transforming growth factor-β; TRAIL, tumour necrosis factor-related apoptosis-inducing ligand; Treg, regulatory T cell; VEGF, vascular endothelial growth factor). Source: Matthew D. Vesely, Michael H. Kershaw, Robert D. Schreiber and Mark J. Smyth; Annual Reviews, Immunology, 2011.

5.3.3. Escape phase: Tumour mediated immunosuppression

This phase refers to the final out growth of the tumour cells that have overcome the anti- tumour immunity in equilibrium phase. During this phase, immune system is no longer able to prevent the tumour growth. Because of reduced immunogenecity, tumour variants start to grow progressively, establish an immunosuppressive situation in tumour microenvironment leading to metastasis. Cancer cells develop mechanisms which allow them to protect from destruction by host immune system (Fig. 5).These mechanisms can broadly be divided into:

A) Intrinsic mechanisms: Tumour cells bring about modulation in their receptor presentation or may secrete immune suppressive molecules to inhibit the immune response.

(1) Loss of MHC expression: Many tumour cells show decreased expression of MHC I molecules to prevent from CD8⁺T cell mediated tumour killing.

(2) Absence or low expression of co-stimulatory or MHC II molecules: Tumour cell reducedCD4⁺T cell response by reducing/absence of co-stimulatory signals and MHC II molecules

(3) Inaccessibility of tumour antigens to immune cells: Tumour antigen may be masked by glycocalyx molecules (mucopolysaccharide) and prevent the interaction of tumour and immune cells.

(4) Inhibition through checkpoints: Tumour cells may increase inhibitory action on immune cells through the expression of checkpoints ligands like cytotoxic T lymphocyte A-4(CTLA-4) and programmed death protein (PD-L1) resulting in sustained T cell inhibitory action.

(5) Anti-apoptotic molecules: Tumour cells prevent their apoptosis by releasing anti- apoptotic molecules like Bcl2.

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(6) Immunosupression through cytokines: Tumour cells secrete cytokines like VEGF, TGF-β, M-CSF which induce the angiogenesis. IL-6 has pro-tumoural role as it is growth- promoting and anti-apoptotic inflammatory cytokine.

(7) Suppression of anti-tumour factors: Tumour cells may secrete immunosuppressive factors like transforming growth factor- β (TGF-β) which inhibit the proliferation and functions of lymphocytes.

B) Extrinsic mechanisms: Tumour cells may modulate or suppress the anti-tumour activity by following mechanisms:

(1) Tumour growth and invasiveness increased by M2 type tumour-associated macrophages (TAM). M2 are characterized by presence of low IL-12 and high IL-10 which may impair T cell activation and effector functions. M2 also produces TGF-β and VEGF, which enhances tumour angiogenesis (2) Cytokines block tumour associated DC maturation: IL-6 and IL-10 block DC maturation leading to prevention of CD8⁺ T cell activation that can cause tumour regression.(3)T cell response suppression through recruitment of T_regin tumour microenvironment: Tumour cells recruit large number of T_regwhich suppress the immune system through following mechanism: (i) By induction of T cell cycle arrest through APCs (ii) Direct killing of T and APCs by activated T_reg by perforin, granzyme release (iii)Suppression of T-cell activation byCTLA-4 and release of IL-10, IL-12 and TGF-β which inhibits expression of MHC (4) MDSCs suppress anti-tumour innate and T cell responses: MDSCs inhibit macrophase activity through IL-10, T cells proliferation and activation through production of indolamine 2,3-dioxygenase (IDO) and generation of peroxynitrite. These cells also help in development of Treg to induce T cell inhibition.

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Fig. 5. Mechanism of tumour escape from immune system: The tumour variants surviving during equilibrium may evolve to tumour variants resistant to anti-tumour factors over the time by acquiring epigenetic and mutational changes in DNA. These cells suppress immune system by various intrinsic and extrinsic mechanisms. Intrinsic alterations in tumour cells includes downregulation of antigen presentation of MHC or co-stimulatory molecules, upregulation of anti-apoptotic molecules (Bcl-XL, FLIP), or excess expression of cell surface molecules ((PD-L1, FasL) leading to direct killing of CD8+ T cell. Tumour secretions like TGF-β, IL- 10, VEGF, LXR-L, IDO and MICA inhibit the effector immune cell functions. Extrinsic factors include the recruitment of T_regcells which produce immunosuppressive cytokines (IL-4, IL-13, GM-CSF, IL-1β, VEGF, or PGE2) leading to further suppression of immune cells function. IL-4 and IL-13 lead to polarization of M1 to M2 which inhibit T cells through expression of TGF-β, IL-10, and PDGF. Treg further inhibit the T cell function through expression of ligands for inhibitor pathways (CTLA-4). In addition to this accumulation of MDSCs also inhibit the T cell function through TGF-β, ARG1 and iNOS.

(Abbreviations: ARG1, arginase 1; Bcl-XL, B cell lymphoma extra-long; CTLA-4, cytotoxic T lymphocyte associated protein-4; DC, dendritic cell; FasL, Fas ligand; FLIP, apoptosis- stimulating fragment-associated protein with death domain-like interleukin-1 converting enzyme-like inhibitory protein; GM-CSF, granulocyte macrophage colony–stimulating factor; IDO, indoleamine 2,3-deoxygenase; IL, interleukin; iNOS, inducible nitric oxide

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major histocompatibility complex; MICA, MHC class I polypeptide-related sequence A;

PDGF, platelet-derived growth factor; PD-L1, programmed cell death 1 ligand 1; PGE2, prostaglandin-E2; TGF-β, transforming growth factor-β; Treg, regulatory T cell; VEGF, vascular endothelial growth factor.)

6. Cancer immunotherapy

The aim of cancer immunotherapy is to make the host immune response strong enough to be able to detect and identify cancer cells as abnormal and mount a defense against them. The immune response against cancer cells can be enhanced by using two types of approach: First, stimulating immune response against cancer cells by using vaccines, cytokines or checkpoints inhibitors. Second, enabling the immune system to fight against cancer through passive immunity whereby tumor specific antibodies and T cells are injected into the patients. Some important cancer immunotherapies are:

(i) Cytokines based immunotherapy: Cytokines stimulates the immune system by activation and proliferation of T cells leading to cell and humoral mediated tumour cell killing. Major Cytokines involved in immunotherapy areIL-2 and IFN-α.

(ii) Cell based immunotherapy: In this therapy, patient’s leukocytes are isolated, manipulated in vitro and then transfer back to the patient. These include vaccines and adoptive cell transfer. For this, monocytes are isolated from patients’s blood, cultured in presence of granulocyte macrophage colony-stimulating factor (GM-CSF), IL-4, loaded with antigens and then reintroduced into the patient.

Adoptive cell therapy is a potential immunotherapy which exploits the anti-tumour properties of lymphocytes to eradicate the cancer cells. In this approach tumour infiltrating lymphocytes (TILs), a mixture of CD4+ and CD8+ T cells collected from patients, cultured, proliferated and reinfused back to patient. AsDCs are known to more efficient in T-cell response induction, therefore attempts have been made to develop vaccines based on these cells (Fig. 6).

(iii) Antibody based immunotherapy: Most successful therapy for treating cancer. The monoclonal antibody can be used to kill the cancer cells by two ways; one is by direct

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killing through the receptor blockade like epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF). Second, by immune mediated tumour killing through activation of phagocytes, T cells or antibody dependent cellular cytotoxicity and inhibition of T cell inhibitory receptors like CTLA-4(Fig. 7).

(iv) Checkpoints blockade: Because tumour induces T cell inhibition by expressing ligands for inhibitory receptors. In this approach, immune inhibitory pathways activated by cancer cells are blocked by using inhibitors(CTLA-4).

Fig. 6: Adoptive cell transfer immunotherapy. Lymphocytes isolated from the blood or tumour infiltrate of a patient are cultured in presence of cytokine interleukin 2 (IL-2) proliferated and reintroduced back into the patient.

Source: Abul K. Abbas (Cellular and molecular immunology, 7^th edition).

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Fig. 7: Antibody mediated tumour cell killing.a. Direct tumour cell killing: Antibody acts as receptor agonist, bind to tumour cell surface activate it leading to tumour cell apoptosis. Antibody can also acts as antagonist, bind to tumour cell surface receptor, block receptor dimerization, enzyme activation and downstream signaling leading to decreased proliferation and apoptosis. b. Immune mediated tumour cell killing: It is through the activation of complement system; induction of phagocytosis and ADCC. T cells can be activated by antibody mediated cross presentation of tumour antigens by DCs; T cell inhibition can be prevented by blocking inhibitory receptors on T cells. Abbreviations: ADCC (Antibody-dependent cellular cytotoxicity), CTLA-4 (cytotoxic T lymphocyte-associated antigen- 4); DC, Dendritic cells.

Source: Andrew M. Scott1, Jedd D. Wolchok and Lloyd J. Old; Nature Reviews, Cancer, 2012.

The immunotherapies are not only advantages but also have some disadvantages (Table 1).

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Table 1: Advantages and disadvantages of immunotherapy. IL-2 (Interleukin 2); IFN-α(Interferon- alpha); CTLA-4(Cytotoxic T lymphocyte-associated protein 4); PD1 (Programmed cell death protein 1); TIL, (Tumour infiltrating lymphocytes).

7. Summary

1. Cancer immunology is the interdisciplinary branch of science that deals with the interaction between cancer and immune system.

2. Cancer is a mass of cells having unregulated, unlimited growth.

Strategy Basic mechanism and major advantages Major disadvantage

I. Cytokines

IL-2 Stimulates the host’s immune system Low response rates and risk of serious systemic

inflammation

IFN-α Stimulates the host’s immune system;durable responses (from a small subset of melanoma patients)

Low response rates; high-dose toxicity

II. Cell based therapies

Vaccines Stimulates the host’s immune system, Minimal toxicity (e.g., sipuleucel-T)

Lack of universal antigens and ideal immunization protocols lead to poor efficacy and response

Adoptive cell transfer therapies

Omits the task of breaking toleranceto tumour antigens, Produces a high avidity in effector T cells, genetic T cell engineering broadens TIL to malignancies other than melanoma

Restricted to melanoma, safety issues, serious adverse effects, and lack of long lasting responses in many patients, requires time to develop the desired cell populations, expensive

III. Immune checkpoints blockade

Anti-CTLA-4 monoclonal antibodies

Unleashes pre-existing anticancer T cell responses and possibly triggers new, exhibits potent antitumor properties,Prolongation of overall survival

Only a relatively small fraction of patients obtain clinical benefit, severe immune-related adverse events have been observed in up to 35 % of patients

Anti-PD1 and anti-PD-L1 antibodies

Sufficient clinical responses which areoften long-lasting Therapeutic responses in patients withina broad range of human cancers;reduced toxicity compared to anti-CTLA-4 antibodies

Only a relatively small fraction of patients obtain clinical benefit

Combination immunotherapy

Improvement of anti-tumour responses/immunity May lead to increases in the magnitude, frequency, and onset of side effects

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3. Hallmarks of cancer are self-sufficiency in growth signals, insensitivity to anti-growth signals, tissue invasion and metastasis, inducing angiogenesis, evading apoptosis/anti- apoptotic, replicative immortality, evading immune system, reprogramming energy metabolism, genomic instability &mutation and tumour promoting inflammation.

4. Tumour antigens are those molecules which are expressed by tumour cells by which these are recognised by the immune system as abnormal or non-self from normal body cells.

5. Tumour specific antigens are unique to tumour cells; whereas tumour associated antigens may also be expressed by normal cells.

6. Self-antigen can become non-self by mutation, overexpression and posttranslational modifications.

7. Tumour microenvironment is a complex network of epithelial cells and infiltrating immune cells, enriched with blood and lymphatic vessels.

8. Immune cells present in tumour microenvironment include macrophages, dendritic cells, natural killer (NK) cells and B & T lymphocytes (Th1,Th2, Th17,Tregand CTLs).

9. Both innate and adaptive immune system act together to prevent the tumour growth.

10. Innate immune system protects the host body from cancer by activating NK cells and antigen presenting cells (macrophages and dendritic cells). These cells eliminate tumour cells either by releasing perforins & granzymes, cytokines or induction of apoptosis of tumour cells through ligand-receptor binding.

11. Both cell mediated and humoral immune response show anti-tumour activity. Cell mediated immunity eliminates tumour cells by activating APCs which activate helper T cells which in turn produce effector CD8⁺ cells and tumour cell killing whereas in humoral immunity, activation of B cells results in antibody mediated tumour cell killing.

12. Cancer immuno surveillance is a mechanism by which immune system detect and destroy the nascent transformed cells before tumour formation.

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13. Cancer immunoediting is a process wherein immune system functions not only as an extrinsic tumour suppressor but also promotes tumour formation and progression by the immunoselection of resistant tumour variants.

14. Immunoediting can be divided into three basic phases called as “three E” elimination, equilibrium and escape phase.

15. In elimination phase, anti-tumour factors are greater than immune suppressor so it eliminates the pre-cancerous cells before they become cancerous.

16. Equilibrium phase is a state of functional tumour dormancy leading to establishment of equilibrium between immune and tumour cells.

17. Escape phase is a state of immune failure to prevent the tumour formation. Immune resistant tumour cells escape from anti-tumour activity by modifying themselves through intrinsic as well as extrinsic mechanisms.

18. Intrinsic mechanism includes loss or low expression of MHCs and co-stimulatory molecules inhibiting cell mediated and humoral immunity against tumour cells.

19. Extrinsic mechanism includes inhibition in activity and killing of immune cells by the secretions of tumour cells, and recruitment of immunnosuppressive cells (T_regand MDSC) or by expressing ligand for inhibitory pathway.

20. Cancer immunotherapy aimed to treat cancer by boosting immune system either by vaccination, cytokines, and antibodies or by adoptive cell transfer.

3. The Hallmarks of Cancer

Development Team

Contents

1. Learning outcomes

2. Introduction

3. The Hallmarks of Cancer

4. Tumour antigens and mechanism of their formation

5. Cancer and its relationship with immune system

6. Cancer immunotherapy

7. Summary