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How Does Immunotherapy Work? - pg. 2

How Does Immunotherapy Work? - page 2

Cancer Vaccines

The term cancer vaccine refers to a vaccine that treats existing cancer or prevents the development of cancer in certain high-risk individuals. The vaccines that treat existing cancer are known as therapeutic cancer vaccines. Cancer vaccines were first tested in the 1970s on melanoma, but are still considered experimental for the most part.

This section discusses cancer vaccine treatments; to learn more about cancer prevention vaccines please see the section on Infectious Agents .

Tumor cell vaccines

Tumor cell vaccines are made up of actual cancer cells that have been removed from a patient during surgery. The cells are treated in the lab, usually with radiation, so they cannot form more tumors. In most cases, researchers also change the cells in various ways (often by adding chemicals or new genes) to make them more likely to be seen as foreign (or non-self) by the immune system.

These cells are then injected back into the patient. The antigens on the cells are recognized and attacked by the immune system.

  • Autologous (from the same organism) vaccines are made from tumor cells taken from the patient.
Image courtesy of the National Cancer Institute

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  • Allogeneic vaccines use cells of a particular cancer type that originally came from someone other than the patient who will receive them. The cells are often grown in a lab.

Although the FDA has not yet approved any tumor cell vaccines for general use, they are being studied in clinical trials against many types of cancer, including:

  • melanoma
  • kidney cancer
  • ovarian cancer
  • breast cancer
  • colorectal cancer
  • lung cancer
  • prostate cancer
  • non-Hodgkin's lymphoma
  • leukemia
Antigen Vaccines

Antigen vaccines boost the immune system by using only one antigen (or a few), rather than whole tumor cells that contain many thousands of antigens. The antigens are usually proteins or pieces of proteins called peptides. Antigen vaccines may be specific for a certain type of cancer, but they are not made for a unique patient as autologous cell vaccines are.

The challenge has been to find better antigens, as well as to package the antigen in such a way so that they enhance the patient's immune system helping to fight cancer cells that contain the antigen.

Antigen vaccines are being studied for use against these cancer types:

  • breast cancer
  • prostate cancer
  • colorectal cancer
  • ovarian cancer
  • melanoma
  • kidney cancer
  • pancreatic cancer
  • multiple myeloma


Most clinical trials that investigated a cancer vaccine have resulted in failure (the vaccine didn't work). The precise reasons for this failure are unknown, but possible explanations include:

  1. The stage of the disease being treated was too advanced: it is difficult to get the immune system to fight bulky tumor deposits
  2. Cancer vaccines that target just one tumor antigen are likely to be less effective. Tumors are highly heterogeneous and antigen expression differs markedly between types of cancer cells in tumors.
  3. Prior treatments - numerous clinical trials in the past have treated patients who have received numerous cycles of chemotherapy. Chemotherapy is often myelosuppressive and destroys the immune system.
  4. Some tumors progress very rapidly and/or unpredictably; their growth can literally outpace the response of the immune system.

Monoclonal antibodies

Monoclonal antibody therapy uses monoclonal antibodies (or mAb) to bind specifically to target cells. This can then stimulate the patient's immune system to attack those cells.

The idea of a "magic bullet" against cancer was first proposed by Paul Ehrlich who at the beginning of the 20th century postulated that if a compound could be made that selectively targeted a disease-causing organism, a toxin for that organism could be delivered along with the selective agent.

Monoclonal antibodies were first produced in the 1970's, further developed in the 1980's, and approved for specific types of cancer in the 1990's.

Antibodies are proteins that are normally part of the immune system and bind to antigens in the body. Researchers manufacture antibodies outside of the human body that adhere to specific targets in cancer cells.

Targeted immunotherapy drugs are essentially a collection of monoclonal antibodies that have different cellular targets. Targeted therapies provide specific antigens for specific types of cancer in order to generate an immune response. Cancer cells have substances on their outer surfaces that can act as antigens and mark the cells as abnormal.

Image courtesy of the National Cancer Institute

Two Examples:

  1. Herceptin is a monoclonal therapy that is used to destroy malignant tumor cells and prevent tumor growth by blocking specific cell receptors.
  2. Variations of this treatment also exist, such as radioimmunotherapy, in which a dose of radioactivity is focused on a target cell line, and delivers lethal chemical doses to the it.
FDA approved monoclonal antibody therapy
Antibody Brand Name Target Cancer Type
Alemutuzumab Campath CD52 Chronic Lymphocytic Leukemia
Bevacizumab Avastin VEGF Colorectal cancer
Cetuximab Erbitux EGFR Colorectal cancer
Gemtuzumab Mylotarg CD33 Acute myelogenous leukemia
Ibritumomab tiuxetan Zevalin CD20 Non-Hodgkin lymphoma
Panitumumab Vectibix EGFR Colorectal cancer
Rituximab Rituxan CD20 Non-Hodgkin lymphoma
Trastuzumab Herceptin ErbB2 Breast cancer




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