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Harnessing the power of the immune system
Although the immune system is programmed to defend the body against invaders such as bacteria or viruses, its ability to fight cancer is limited because it doesn't usually recognize cancer cells as foreign. In fact, some cancers actively suppress the body's immune response.
However, prostate cancer cells do differ from normal cells in some important ways. These differences can be used to harness the immune system's power to destroy cancer cells specifically. For example, proteins made by the cells, called antigens, may be more or less abundant on prostate cancer cells when compared to their normal counterparts.
Therapeutic vaccines combine the body's general immune response, just like one toward a bacterial or viral infection, with an attack on specific prostate cancer antigens.
Another challenge in prostate cancer immunotherapy has been the need to generate large numbers of killer T cells that can specifically recognize, target, and kill prostate cancer cells.
The blood of the cancer patient is collected and enriched to increase the population of dendritic cells. These cells are then grown in the laboratory in the presence of a protein or part of a protein that is present in or on the patient's tumor cells.
The patient's dendritic cells digest the protein and transport tiny pieces of it to the cell surface. When the dendritic cells are put back into the patient, they signal certain populations of killer T cells to destroy all cells with the telltale protein, including cancer cells.
Provenge® (generic drug name sipuleucel-T) is the only cancer therapeutic vaccine that has been approved by the FDA to date. It is approved for use in men with metastatic prostate cancer that does not respond to hormone therapy.
Provenge® uses prostatic acid phosphatase, or PAP, as the key antigen. PAP is highly expressed in nearly all prostate cancers and is largely restricted to prostate cells.
Provenge® is prepared by harvesting the patient's blood and enriching for specialized immune cells, called antigen presenting cells, from that blood.
The role of GM-CSF is to prolong the body's general immune response. The role of PAP is to trigger a specific immune response.
The patient's antigen presenting cells digest the antigen and transport tiny pieces of it to the cell surface. Antigen presenting cells that have taken up and processed the PAP–GM–CSF antigen are then infused back into the patient where they stimulate a specific immune response.
The infused cellular product can activate large numbers of killer T cells that destroy cells expressing the PAP antigen, primarily prostate cancer cells.
- How do therapeutic vaccines work to attack cancer?
- They mount a general immune response.
- They promote a specific immune response to the cancer cell's antigens.
- They make antibodies against the cancer.
- Both A and B.
- Correct answer to Question 1:
- They mount a general immune response. There is a better answer.
- They promote a specific immune response to the cancer cell's antigens. There is a better answer.
- They make antibodies against the cancer. Incorrect. The answer is D (both A and B).
- Both A and B. Correct.