Role of Antigens in the Antitumor Immune Response



Antigen release: after tumor cell lysis, danger signals, cytokines, and tumor-derived antigens are released, initiating an inflammatory immune response

Tumors with higher mutational burden potenially harbor immunogenic mutations, resulting in antigens that trigger antitumor immune responses1,2

  • Necrosis is a form of immunogenic cell death caused by stressors4,5
    • This is in contrast to apoptosis, which does not trigger an immune response4
  • Immunogenic cell death stimulates production of proinflammatory cytokines and chemokines, such as IL-10, TNF-α, and IL-81
    • Release of cytokines causes local inflammation, which activates an immune response1
  • Immunogenic cell death also releases DAMPs and tumor-derived antigens, which induce inflammation, recruit innate immune cells, and establish innate and adaptive immune responses2,3

DAMP, damage-associated molecular pattern; IL, interleukin; TNF, tumor necrosis factor.

1. Fadok VA, et al. J Immunol. 2001;166:6847-6854. 2. Rubartelli A, et al. Trends Immunol. 2007;28:429-436. 3. Chen DS, et al. Immunity. 2013;39:1-10. 4. Guo ZS, et al. Front Oncol. 2014;4:74. 5. Krysko DV, et al. Nat Rev Cancer. 2012;12:860-875.

  • Tumor immunogenicity is the ability to induce an antitumor response, which potentially increases with rates of tumor mutations1,2
  • Mutation rates vary across different tumor types and within a specific tumor type1
  • Immunogenic mutation counts are associated with CD8A, PDCD1, and CTLA-4 expression2

CTLA-4, cytotoxic T lymphocyle-associated 4.

1. Lawrence MS, et al. Nature. 2013;499:214-218. 2. Brown SD, et al. Genome Res. 2014;24:743-750. Image reproduced from Lawrence MS, et al. Nature. 2013;499:214-218. With permission from Macmillan Publishers Ltd.

Antigen downregulation: tumor-mediated downregulation of antigen expression contributes to immune evasion

TDA, tumor-derived antigen.

1. Barrow C, et al. Clin Cancer Res. 2006;12:764-771. 2. Dunn GP, et al. Annu Rev Immunol. 2004;22:329-360. 3. Alexandrov LB, et al. Nature. 2013;500:415-425. 4. Urosevic M, et al. Exp Dermatol. 2005;14:491-497.

Phenotypic evolution of tumor-derived antigens (TDA)

Downregulation or loss of antigens

  • Expression patterns for tumor antigens may increase over disease course, while others may decrease or be lost3,4
  • Tumor antigens can be reduced or lost over time due to immunoediting2


2. ANTIGEN presentation

Antigen presentation: danger signals and cytokines released after cell lysis lead to dendritic cell maturation, thereby enabling cross-presentation of tumor-derived anigens to T cells in lymph nodes

  • Immature dendritic cells (DCs) undergo maturation and transformation into antigen-presenting cells (APCs) upon exposure to “danger signals” and inflammatory cytokines provided by tumor cell lysis1
  • Frequent and continual presentation with diverse tumor-derived antigens (TDA) is vital to priming and activating T cells2-4
  • Tumor antigens can exhibit varied expression across different tumors within the same patient5
  • Releasing a large pool of patient-specific TDA may promote a robust antitumor immune response4

APC, antigen-presenting cell; DC, dendritic cell; TCR, T-cell receptor; TDA, tumor-derived antigen.

1. Guermonprez P, et al. Annu Rev Immunol. 2002;20:621-667. 2. den Boer AT, et al. J Immunol. 2004;172:6074-6079. 3. Alexandrov LB, et al. Nature. 2013;500:415-425. 4. Dunn GP, et al. Annu Rev Immunol. 2004;22:329-360. 5. Rubinsteyn A, et al. Poster presented at: 13th Cancer Immunotherapy Annual Meeting; May 11-13, 2015; Mainz, Germany.

Decrease in antigen presentation: multiple mechanisms can contribute to defective antigen presentation

Gene regulatory events

  • Downregulation of gene promoters and regulators that control expression of genes encoding tumor-associated antigens is a major contributor to antigen loss1

Mutation of epitopes recognized by the immune system

  • Changes in gene sequences can result in mutation of epitopes previously recognized by the immune system2,3

HLA class I downregulation

  • Mutations in genes encoding HLA and loss of HLA haplotypes and alleles can lead to downregulation of HLA class I molecules, which increases the tumorigenicity of cancer cells2,4

Secretion of immunosuppressive cytokines

  • Immunosuppressive cytokines, such as IL-10, secreted by cancer cells suppress antigen-specific T-cell responses by downregulation of MHC molecules, decreased expression of proteins involved in antigen presentation, and inhibition of proinflammatory cytokines2

DC, dendritic cell; HLA, human leukocyte antigen; IL, interleukin; MHC, major histocompatibility complex.

1. Kholmanskikh O, et al. Int J Cancer. 2010;127;1625-1636. 2. Rabinovich GA, et al. Annu Rev Immunol. 2007;25;267-296. 3. Vinay DS, et al. Semin Cancer Biol. 2015;35(suppl):S185-S198. 4. Dunn GP, et al. Annu Rev Immunol. 2004;22:329-360.


3. t-cell priming, activation, and memory generation

T‑cell priming, activation, and memory: activation of T cells drives further differentiation and proliferation, helping to magnify the immune response

TDA, tumor-derived antigen.

1. Wherry EJ, et al. J Virol. 2004;78:5535-5545. 2. Kaech SM, et al. Immunity. 2007;27:393-405. 3. Murphy K. Janeway's Immunobiology. 8th ed. New York, NY: Garland Scientific; 2012. 4. Klebanoff CA, et al. Immunol Rev. 2006;211:214-224. 5. Alexandrov LB, et al. Nature. 2013;500:415-425. 6. Dunn GP, et al. Annu Rev Immunol. 2004;22:329-360.

  • Initial exposure to tumor-derived antigens (TDA) induces naive T cells to differentiate into effector T cells and memory cells1,3
  • Effector T cells are equipped to perform downstream immune functions and mount immune responses against tumor antigens.They are lost after completion of the immune response2
  • Under normal conditions, a subset of T cells may survive as a heterogeneous pool of immune memory cells, which may contribute to a more rapid response (than the primary response) to a rechallenge of TDA4
  • Repeated TDA exposure to diverse antigens may expand the pool of immune memory cells, increasing the heterogeneity of the memory T‑cell population4-6 

Decrease in T‑cell activation: decreased expression of costimulatory molecules impairs optimal T‑cell activation

Impaired immune memory: insufficient antigen exposure impairs generation of immune memory

Immunosuppression: suppressor cells and cytokines present in tumor microenvironment diminish T‑cell activation

  • Antigen presentation by MHCs and costimulatory signals such as B7 on antigen-presenting cells are needed for activation of T cells1
  • Tumors are capable of preventing the expression of costimulatory signals on antigen-presenting cells, inhibiting T‑cell activation1
  • Immunosuppressive cytokines (eg, IL-10) have also been shown to reduce induction of expression of costimulatory molecules such as B72

APC, antigen-presenting cell; CTL, cytotoxic T lymphocyte; DC, dendritic cell; IL, interleukin; MHC, major histocompatibility complex; TCR, T‑cell receptor.

1. Kirkwood JM, et al. J Clin Oncol. 2008;26:3445-3455. 2. Ding L, et al. J Immunol. 1993;151:1224-1234.

  • Limited antigen availability can cause
    • Competition between T‑cell subsets1
    • Decreased generation of memory T cells2
    • Decreased survival of memory T cells3

1. Cose S, et al. Int Immunol. 2006;18:1285-1293. 2. Blair DA, et al. Proc Natl Acad Sci U S A. 2007;104:15045-15050. 3. Hataye J, et al. Science. 2006;312:114-116. Image reprinted from Immunity, 27(3), Kaech SM and Wherry EJ, Heterogeneity and cell-fate decisions in effector and memory CD8+ T cell differentiation during viral infection, pp. 393-405. Copyright 2007, with permission from Elsevier.

Immunosuppressive cells

  • Immunosuppressive cells present in the tumor microenvironment can inhibit antitumor immune response by secreting immunosuppressive cytokines or growth factors, or through direct cell-cell contact

Immunosuppressive cytokines

  • Secretion of cytokines, such as IL-10 and TGF-β, from immune cells in the tumor microenvironment (eg, Tregs) can inhibit T‑cell activation, proliferation, and differentiation

IL-10, interleukin 10; MDSC, myeloid-derived suppressor cell; TAM, tumor-associated macrophage; TGF-β, transforming growth factor β; Treg, regulatory T cell.

Rabinovich GA, et al. Annu Rev Immunol. 2007;25:267-296.


4. Migration and 5. Infiltration

T-cell migration and infiltration: after activation, proliferation, and differentiation, activated effector T cells (cytotoxic T lymphocytes) traffic to and infiltrate the tumor bed

  • Chemokines are chemotactic cytokines. Several chemokines, such as CCL2, CCL3, CCL4, CCL5, CXCL9, and CXCL10, are highly expressed in tumor lesions.Chemokines
    • Mediate the migration and infiltration of activated CD8effector T cells into tumor sites1,2
    • Are required for the activation of strong specific immune responses and generation of potential protective immunologic memory3

CTL, cytotoxic T lymphocyte.

1. Gajewski TF. Clin Cancer Res. 2007;13:5256-5261. 2. Harlin H, et al. Cancer Res. 2009;69:3077-3085. 3. Novak L, et al. Mol Cancer Ther. 2007;6:1755-1764.

Key factors affecting antitumor T‑cell migration to and infiltration into tumor site

Interplay between innate and adaptive immune systems provides effective antitumor T‑cell responses

  • Innate immune system regulates adaptive immune system by producing cytokines, inducing interaction between DCs and lymphocytes, and activating complement system1
  • Adaptive immune system regulates innate immune system by producing cytokines and antibodies1

DAMP, damage-associated molecular pattern; DC, dendritic cell; IFN, interferon; NK, natural killer.

Woo S-R, et al. Annu Rev Immunol. 2015;33:445-474.

Activation of oncogenic tumor signaling pathways inhibits T‑cell infiltration

  • Activation of WNT/β-catenin signaling results in T‑cell exclusion from tumor microenvironment, lack of chemokine expression, decreased recruitment of DCs, and resistance to therapy with immune checkpoint inhibitors

CCL4, chemokine ligand 4; DC, dendritic cell; TdLN, tumor-draining lymph node.
Spranger S, et al. Adv Immunol. 2016;130:75-93.

Genetic polymorphisms in key immune regulatory genes can impact the degree of T‑cell infiltration into tumor site1,2

  • Patients with genetic polymorphisms in CCR5 have decreased survival associated with immunotherapy

Composition of host gut microbiota could influence the differentiation of T cells and activation state of innate APCs, impacting priming of systemic immune responses1,3

  • Heterogeneity in composition of host gut microbiota is a potential contributing factor for varied clinical responses to tumor immunotherapy

APC, antigen-presenting cell; CCR5, chemokine receptor 5.

1. Spranger S, et al. Adv Immunol. 2016;130:75-93. 2. Ugurel S, et al. Cancer Immunol Immunother. 2008;57:685-691. 3. Sivan A, et al. Science. 2015;350:1084-1089.


6. Recognition and 7. cell death

T‑cell recognition and killing: after tumor infiltration, effector T cells recognize target cancer cells and induce tumor cell death

Step 6: Recognition

• After infiltration into the tumor, effector T cells recognize the antigen expressed on the tumor cells1

Step 7: Cell death

• Effector T cells eliminate target cancer cells through the release of perforin and granzymes, which permeate the tumor cell membrane, initiating cell death and subsequent release of antigens1,2

CTL, cytotoxic T lymphocyte; MHC, major histocompatibility complex; TCR, T‑cell receptor.

1. Chen DS, et al. Immunity. 2013;39:1-10. 2. Murphy K. Janeway’s Immunobiology. 8th ed. New York, NY: Garland Scientific; 2012.

Multiple immunoinhibitory pathways are present that suppress T‑cell activation and T‑cell–mediated tumor cell death

PD-1/PD-L1 pathway suppresses T‑cell response in various tumor types1

  • Tumor cells overexpressing PD-L1 bind to PD-1 receptors on T cells, inhibiting T‑cell activation, suppressing T‑cell attack, and inducing immune escape1

IDO activation has been demonstrated to generate an immunosuppressive tumor microenvironment2

  • IDO biosynthesis in APCs decreases tryptophan levels, leading to T‑cell anergy, T‑cell apoptosis, and proliferation of Tregs2

APC, antigen-presenting cell; IDO, indoleamine 2,3-dioxygenase; MHC, major histocompatibility complex; PD-1, programmed cell death 1; PD-L1, PD ligand 1; TCR, T‑cell receptor; Treg, regulatory T cell.

1. He J, et al. Sci Rep. 2015;5:13110. 2. Mbongue JC, et al. Vaccines (Basel). 2015;3:703-729.



Tumor-immunosuppressive mechanisms can diminish induction of antitumor immune response, leading to escape and progression of cancer1,2

Tumor immunosuppression present at different stages of the cancer immunity cycle results in the following:

  • Inhibiting induction and propagation of antitumor immune response
  • Blocking tumor-infiltrating T cells
  • Suppressing T-cell–mediated antitumor cytotoxicity

CTLA-4, cytotoxic T lymphocyte–associated 4; MHC, major histocompatibility complex; PD-1, programmed cell death 1; PD-L1, PD ligand 1.

1. Chen DS, et al. Immunity. 2013;39:1-10. 2. Rabinovich GA, et al. Annu Rev Immunol. 2007;25:267-296. 3. Postow MA, et al. J Clin Oncol. 2015;33:1974-1982.

*Oncolytic therapy is defined as agents that cause immunogenic or necrotic cell death (eg, biologics, chemotherapy, radiation, small molecules, vaccines, and viruses).1,3,4,6,11,12

Figure adapted from Chen DS, et al. Immunity. 2013;39:1-10.

Immunotherapy approaches target different steps of the cancer immunity cycle.

Immunotherapy approaches such as anti–CTLA-4, anti–PD-1, anti–PD-L1, and oncolytic therapy are designed to impact the cancer-immune dynamic at specific points in the cycle.

1. Guo ZS, et al. Front Oncol. 2014;4:74. 2. Donnelly OG, et al. Gene Ther. 2013;20:7-15. 3. Anacak Y, et al. Marmara Medical Journal. 2015;28:40-44. 4. Emens LA, et al. Cancer Immunol Res. 2015;3:436-443. 5. Miyamoto S, et al. Cancer Res. 2012;72:2609-2621. 6. Gargett T, et al. Immunol Cell Biol. 2014;92:359-367. 7. Kaufman HL, et al. J Immunother Cancer. 2014;2:11. 8. Weber J. Semin Oncol. 2010;37:430-439. 9. Sim GC, et al. Cytokine Growth Factor Rev. 2014;25:377-390. 10. Pardoll DM, et al. Nat Rev Cancer. 2012;12:252-264. 11. Cheadle EJ, et al. Br J Haematol. 2013;162:842-862. 12. Kwilas AR, et al. Cancer Cell & Microenvironment. 2015;2:e677.

Glossary Terms

Adaptive immune response: induction of an immune response to antigens by antigen-specific lymphocytes, which includes generating immunological memory.

Anergy: an unresponsive state induced in T cells after T-cell receptor engagement in the absence of costimulatory signals.

Chemotactic cytokines: also known as chemokines, which are small proteins that support the migration of inflammatory cells to specific tissue locations.

Damage-associated molecular patterns (DAMPs): nuclear or cytosolic proteins released by dying cells that induce an inflammatory response.

Immunoediting: dynamic process by which tumors evolve to evade the immune system. Immunoediting is hypothesized to include three phases: elimination, equilibrium, and escape.

Immunogenic: ability of a substance (eg, antigen) to induce an immune response.

Immune memory: the capacity of the immune system to remember an encounter with an antigen due to the activation of immune memory cells having specificity for the antigen and to react more swiftly to the antigen by means of these activated cells upon later encounter.

Immunosurveillance: monitoring process of the immune system that detects and destroys cancerous cells and that tends to break down in immunosuppressed individuals.

Innate immune response: an immune response that is initially triggered by pathogenic exposure, leading to the immediate activation of a nonspecific defense mechanism; in contrast, adaptive immune response develops later and requires antigen-specific lymphocytes.