The Tumour Microenvironment

The tumour microenvironment plays a role in disrupting the cancer immunity cycle

The multicellular composition of the tumour microenvironment includes1:

Tumour cells

Malignant cells that are both aided by and influence the makeup of the tumour microenvironment2,3

Tumour-infiltrating immune cells

Lymphoid and myeloid cells, which can stimulate or inhibit the antitumour immune response2,3

Stromal cells

Tumour-associated fibroblasts and endothelial cells that contribute to the tumour’s structural integrity1


t cells

T cells

Antigen-specific immune cells that carry out cell-mediated adaptive immune responses following activation by dendritic cells. Includes CD8 T cells and CD4 T cells4,5

  • Cytotoxic T cells:
    • CD8+ T cells that specialize in killing other targeted cells
  • T helper cells:
    • CD4+ T cells that support the activity of other immune cells through the release of cytokines
  • Regulatory T cells:
    • immunosuppressive CD4+ T cells that can inhibit T-cell proliferation and cytokine production


B cells

B cells

Antigen-specific immune cells that produce antibodies during an immune response5

natural killer cells

Natural killer cells

Cytotoxic lymphocytes that recognise and kill stressed or malignant cells independent of antigen specificity (unlike T and B cells)3

Myeloid cells

dendritic cells

Dendritic cells

Antigen-presenting cells that capture and process cancer antigens to initiate an immune response6



Phagocytic cells that detect pathogens, secrete cytokines, and present antigens. Types include3,4

  • M1 macrophages, which promote inflammation and antitumour responses3,7

  • M2 macrophages, which reduce inflammation and produce factors that can promote tumour growth3,7

myeloid-derived suppressor cells

Myeloid-derived suppressor cells

Immature myeloid cells, including dendritic cells and macrophage precursors, which have potent immunosuppressive activity on T-cell function8

  1. Nelson D, Fisher S, Robinson B. The “Trojan Horse” approach to tumor immunotherapy: targeting the tumor microenvironment. J Immunol Res. 2014;2014:789069. PMID: 24955376 
  2. Wang T, Liu G, Wang R. The intercellular metabolic interplay between tumor and immune cells. Front Immunol. 2014;5:358. PMID: 25120544 
  3. Goubran HA, Kotb RR, Stakiw J, Emara ME, Burnouf T. Regulation of tumor growth and metastasis: the role of tumor microenvironment. Cancer Growth Metastasis. 2014;7:9-18. PMID: 24926201 
  4. Norvell A. Components of the immune system. In: Prendergast GC, Jaffee EM, eds. Cancer Immunotherapy. 2nd ed. San Diego, CA: Academic Press; 2013:11-24.
  5. Murphy K. Janeway’s Immunobiology. 8th ed. New York, NY: Garland Science; 2012.
  6. Chen DS, Mellman I. Oncology meets immunology: the cancer-immunity cycle. Immunity. 2013;39:1-10. PMID: 23890059 
  7. Martinez FO, Gordon S. The M1 and M2 paradigm of macrophage activation: time for reassessment. F1000Prime Rep. 2014;6:13. Published March 3, 2014. Accessed August 18, 2017. PMID: 24669294 
  8. Gabrilovich DI, Nagaraj S. Myeloid-derived suppressor cells as regulators of the immune system. Nat Rev Immunol. 2009;9:162-174. PMID: 19197294

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