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Health Protocols

Cancer Immunotherapy

Background

What Does the Immune System Do?

The immune system’s goal is simple: protect the body from viruses, bacteria, malignant cells, and other dangers without damaging normal cells. Several types of immune cells work together to achieve this goal (Table 1).

Cells of the innate immune system are the body’s first line immune responders against foreign and potentially harmful substances and microbial invaders. Cells of the adaptive or acquired immune system, including T cells and B cells, attack invaders that the body has previously encountered (Chaplin 2010).  

Cancer Cells and the Immune System

Cancer cells’ DNA changes as they become increasingly malignant. These changes affect the proteins on the surface of the cancer cells, which are exposed to the immune cells (Pio 2014). Most of the time, cells from the innate and adaptive immune systems recognize these surface protein changes and destroy the cancer cells (Janeway 2001b). Natural killer cells, or NK cells, are one type of immune cell responsible for detecting these changes and destroying the cancer cells (Waldhauer 2008).

However, cancer cells often acquire the ability to evade immune detection (Schreiber 2011). Cancer cells typically use two main methods for avoiding detection by the immune system. First, the cells alter the proteins on their surfaces so that immune cells can no longer recognize them as foreign (Kim, Emi 2007). Second, cancer cells alter their surrounding environment to suppress immune cell function (Menon 2016). In people suffering from immune senescence—the general decline of immune function that accompanies aging—tumors may escape immune detection more easily (Turner 2017).

Table 1: Key Cells for Immunotherapy

Branch of Immune System

Cell Type

Function

Innate

Neutrophil

  • Abundant white blood cell
  • Phagocyte* that responds early to infection

Monocyte

  • A large phagocyte in blood that can differentiate into a macrophage or dendritic cell in tissues

Macrophage

  • A phagocyte with the primary function of ridding the body of debris and microorganisms
  • Can also present antigens to T and B cells and stimulate other immune cells

Dendritic cell

  • A phagocyte that patrols the body to identify pathogens
  • Primary function is to present antigens to T and B cells

Natural killer cell

  • A lymphocyte (white blood cell of the lymphatic system) that directly and rapidly kills tumor and virus-infected cells
  • Releases toxic chemicals that cause the target cell to die

Adaptive

T lymphocyte (T cell)

Cytotoxic (CD8+)

  • Directly and rapidly kills tumor and virus-infected cells
  • Expresses T-cell receptors that are specific for one antigen

Helper (CD4+)

  • Modulates the activity of other immune cells with cytokine signaling
  • Expresses T-cell receptors that are specific for one antigen

Regulatory

  • Immunosuppressive cell; suppresses other immune cells
  • Expresses T-cell receptors that are specific for one antigen

B lymphocyte
(B cell)

  • Expresses B-cell receptors that are specific for one antigen
  • Differentiates into plasma cells that produce antibodies specific for the antigen

(Abbas 2009; Delves 2017)

*A phagocyte is any type of cell that can engulf harmful invaders such as bacteria and malignant cells. After the phagocyte engulfs the invader, it may destroy it or alert other cells to the presence of invaders in the body.