What is immunotherapy?
Immunotherapy, also called biological therapy, is a type of treatment that uses
the body’s immune system to fight cancer. The therapy mainly consists of
stimulating the immune system to help it do its job more effectively.
Immunotherapy is a comparatively new type of therapy in the fight against many
cancers. Much of this therapy is still in clinical trials.
To help understand the role that biological agents play in
cancer treatment, some understanding of how the normal immune system works is helpful.
How the immune system works
The immune system is a complex network of cells and organs that work together to
defend the body against foreign substances (antigens), such as bacteria,
viruses, and cancer cells. When the body discovers such a substance, several
kinds of cells go into action in what is called an immune response. Below is a
description of some of the cells that are part of the immune system:
- Macrophages — Macrophages are the body’s first line of defense and
have many roles. They are the first cells to recognize and engulf antigens.
They break down these substances and present the smaller proteins to the T
lymphocytes. (T cells are programmed to recognize, respond to, and remember
antigens). Macrophages also produce substances called cytokines that help to
regulate the activity of lymphocytes.
- Lymphocytes — Lymphocytes are one of the main types of immune cells.
They are divided mainly into B and T cells. B lymphocytes produce
antibodies – proteins (gamma globulins) that recognize antigens and attach
themselves to the substances. Each B cell is programmed to make one specific
antibody. When a B cell comes across its triggering antigen, it gives rise
to many large cells known as plasma cells. Each plasma cell is essentially a
factory for producing an antibody. An antibody matches an antigen much like
a key matches a lock. Whenever the antibody and antigen interlock, the
antibody marks the antigen for destruction. B cells are powerless to
penetrate the cell, so the job of attacking these target cells is left to T
lymphocytes.
- T lymphocytes are cells that are programmed to recognize, respond
to, and remember antigens. T cells contribute to the immune defenses in two
major ways. Some direct and regulate the immune responses. When stimulated
by the antigenic material presented by the macrophages, the T cells make
lymphokines that signal other cells. Other T cells are able to destroy
targeted cells on direct contact.
- Dendritic cells — Dendritic cells are known as the most efficient
antigen-presenting cell type, with the ability to interact with T cells and
initiate an immune response. Dendritic cells are receiving increasing
scientific and clinical interest because of their key role in the immune
response and potential use with tumor vaccines.
- Granulocytes — There are three types of white blood cells, known as
granulocytes, which are part of the immune response. Neutrophils are
the most common white blood cells in the body. With an infection, their
number increases rapidly. They are the major components of pus and are found
around most common inflammations. Their job is to eat and destroy foreign
material. Basophils and eosinophils interact with certain
foreign materials. Their increased activity may lead to an allergic
reaction.