T-cells Definition

Function of T-Cells and Their Role in Cancer

Artistic rendering of a cancer cell surrounded by smaller T-cells, or T-lymphocytes..

Definition: T Cells

T-cells are a subtype of white blood cells which play a key role in the immune system and fighting cancer. 

Let's break down the immune system into parts to make it easier to understand. 

There are 2 primary types of white blood cells (leukocytes) - lymphocytes and granulocytes.

Lymphocytes, in turn, are broken down into:

  • T cells (thymus-derived cells)
  • B cells (bone marrow-derived cells)

Type of Immunity

Our bodies have 2 primary types of acquired immunity:

  • Cell mediated immunity
  • Humoral immunity

T cells are part of the body's cell-mediated immunity, the part of the immune system which you can envision as directly killing bacteria, viruses, and cancer cells.  The other type - humoral immunity - protects our bodies from these invaders by making antibodies.

Types of T-Cells

There are several types of T cells including:

  • Cytotoxic T cells - Cytotoxic T cells find and directly attack foreigners such as bacteria, viruses, and cancer cells.
  • Helper T cells - Helper T cells recruit other immune cells and organize an immune response.
  • Regulatory T cells - Regulatory T cells suppress the immune system so it doesn't overreact (as it does in autoimmune diseases), in other words, they are like dimmer switches on a light.
  • Natural killer T cells - Natural killer T cells are different than natural killer cells.
  • Memory T cells - Memory T cells remember markers on the surface of bacteria, viruses, or cancer cells that they have seen before.

Production, Storage, and Availability

After they are produced in the bone marrow, T cells spend some time maturing and developing in an organ in the chest called the thymus -- this is why they are named T-cells, which stands for thymus-derived cells.

After maturation, T-cells are present in the blood and in lymph nodes.

T-Cell Function in Cancer

T cells play a large role in our fight against cancer.  It can be very confusing to talk about T cells, especially when talking about cancers such as lymphoma, so we'll look at ways that T cells work to fight cancer and how they may be affected by cancer.  To get rid of a cancer, even if there are enough T cells, they first have to see the cancer.

Ways in Which T Cells Work to Fight Cancer

T cells work in both direct and indirect ways to fight cancer. 

  • Killer T cells kill cancer cells directly - These cells first find cancer cells and can also be stimulated to kill cancer cells.
  • Helper T cells fight cancer indirectly - These cells organize and orchestrate the fight against cancer.

Ways in Which T Cells are Affected by Cancer

  • Direct involvement in cancer - In cancers such as T-cell lymphoma, the T cells themselves are cancerous.
  • Direct depletion  of T cells - In HIV, the infection infects and then depletes T cells.
  • Bone marrow takeover - Lymphomas and other cancers which spread to the bone marrow crowd out healthy stem cells in the bone marrow (precursors of T cells) resulting in the depletion of T cells.
  • Destruction due to chemotherapy - Chemotherapy can directly deplete T cells and other white blood cells.

Immunotherapy

A newly emerging research therapy involves re-engineering a patient’s T-cells so that they can recognize and kill cancer cells. This type of therapy has shown promising preliminary results in lymphoma.

The Cancer-Immunity Cycle

T cells are part of what is known as the cancer-immunity cycle.

As cancer cells die, they release antigens, substances that can be recognized by the immune system. Antigens from the cancer cells are then taken up and presented on the cell surface of special immune cells called antigen-presenting cells (APCs) so that other immune cells can “see” the antigens of interest. In the lymph nodes, the APCs activate the T-cells and teach them to recognize the tumor cells. The T-cells then travel via the blood vessels to reach the tumor, infiltrate it, recognize the cancer cells and kill them.

To understand further how the immune system works to fight cancer, and how newer immunotherapy treatments are effective against cancer, check out the Cancer-Immunity Cycle.

Sources:

American Cancer Society. What’s New in Cancer Immunotherapy Research? Updated 11/05/15. http://www.cancer.org/treatment/treatmentsandsideeffects/treatmenttypes/immunotherapy/immunotherapy-whats-new-immuno-res

Chen, D., and I. Mellman. Oncology Meets Immunology: The Cancer Immunity Cycle. Immunity. 2013. 39(1):1-10,25.

Chen, D., Irving, B., and F. Hodi. Molecular Pathways: Next Generation Immunotherapy – Inhibiting Programmed Death-Ligand 1 and Programmed Death-1. Clinical Cancer Research. 2012. Doi:10.1158/1078-0432.CCR-12-1362.

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