Treating Disease With Vaccines

While traditional vaccines are designed to prevent disease, researchers are working on something new: therapeutic vaccines, vaccinations that treat an illness after you have it.

Therapeutic vaccines have the potential to change medical treatment radically and may be able to treat all sorts of scourges, such as:

• HIV
• Herpes
• Alzheimer's disease
• Cancer

"We're at a fascinating crossroads in the development of therapeutic vaccines," says Hildegund C. J. Ertl, MD, program leader in the Immunology Program at the Wistar Institute at the University of Pennsylvania. "We understand so much more about the underlying science."

But Ertl and other experts urge cautious optimism. While therapeutic vaccines seem to be on the horizon, they've seemed that way for a long time.

"I remember when therapeutic vaccines were first developed for skin cancer in the 1960s," says Richard L. Wasserman, MD, PhD, clinical professor in the department of pediatrics at the University of Texas Southwestern Medical School in Dallas. "But forty years later, we still don't have one."

How Do Therapeutic Vaccines Work?

Standard preventative vaccines work by helping your immune system develop immunity to a weakened or dead form of a germ. Then, when you actually come into contact with the live germ, your immune system knows how to fight it off.

Therapeutic vaccines would be used after a person contracts a disease, yet they would still work by boosting your own immune system's response to an illness.

While the immune system works very well most of the time, some illnesses -- like cancer, HIV, and Alzheimer's -- don't trigger an effective immune response. In the case of some cancers, the immune system simply fails to recognize the invading cells. Other viruses, like HIV, can overwhelm the immune system and shut it down before it can work.

Therapeutic vaccines help by forcing the immune system to recognize a virus or cancerous cell. Some specific types of therapeutic vaccines include:

• Antigen vaccines. When an antigen is introduced into the body, it provokes the immune system to create an antibody to fight it. Some researchers are working on vaccines that will use specific cancer antigens to force the immune system into action.
• Dendritic cell vaccines. Dendritic cells are immune cells which prowl your bloodstream, grabbing foreign germs and bringing them to other immune cells, which create antibodies to attack them. Researchers have had some success in removing dendritic cells from a person, "loading" them with dead tumor cells or dead viruses, and then injecting them back into the person. Once the dendritic cells have been "taught" how to recognize the invading cells, they may spur the immune system to attack.
• DNA vaccines. One problem with many therapeutic vaccines is that the effects wear off. After a vaccination, the immune system might be aggressive for awhile, but eventually return to normal. Some researchers hope they can inject bits of DNA into cells, instructing them to keep the immune system revved up and alert.
• Tumor cell vaccines. These vaccines use actual cancer cells that are removed during surgery. The cells are then killed -- so they can't cause cancer growth -- and tweaked in some way, often by adding new genes or chemicals. They are then introduced into the body. The hope is that the modified gene will get the attention of the immune system, which will then target other cancer cells. Some of these vaccines are autologous (using cancer cells from your own body), others are allogeneic (using cells that came from someone else).