Researchers successfully immunize mice against aggressive cancer

March 13, 2000

GAINESVILLE -- Researchers at the University of Florida have successfully immunized laboratory mice against melanoma, one of the more aggressive forms of skin cancer.

So far, immunized mice have survived for as long as 150 days after exposure to active melanoma cells. Unprotected mice died in a matter of weeks, said Howard Johnson, a graduate research professor of microbiology and cell science with UF's Institute of Food and Agricultural Sciences who heads up the project.

"If we just vaccinate mice with inactivated tumor cells, we get very little protection," Johnson said. "But if we vaccinate the mice with inactivated tumor cells and then give them superantigens, we significantly extend the survival of the mice."

Superantigens are proteins that are strong stimulators of the immune system. The researchers use the superantigens to boost the response to a vaccine, in this case an injection of dead melanoma cancer cells, Johnson said.

The results of the UF research will be presented April 2 at the national conference of the American Association for Cancer Research in San Francisco.

The research is based on the same process doctors have been using for years to protect people against illnesses such as polio, whooping cough and the flu, Johnson said.

"The interesting thing about vaccination against infectious diseases is that it's not a miraculous event," Johnson said. "What you basically do is inject a part of the harmful organism into an individual under circumstances that will not allow it to grow or cause disease.

"What you've done is stimulate the immune system of the individual so that it is revved up and is able to kill the infectious agent before it can get a foothold," he said. "Theoretically, one could use a similar approach dealing with cancers."

The problem, according to another UF researcher, is that an individual's immune system doesn't immediately recognize a cancer as something it needs to fight.

"This isn't an invading bacteria or virus, these are your own cells, and the immune system is primed to not mount an immune response against itself," said Barbara Torres, assistant scientist in UF's department of microbiology and cell science. "So when you get immune response against cancer, part of the problem is that it's foreign and yet it's not, so you get a weaker response."

"The superantigen amplifies the immune response so it becomes a very strong response and can eradicate the tumor," she said.

Johnson characterized the battle between the immune system and a cancer as a "tug of war," in which the immune system wants to defend against the cancer but just can't manage it on its own.

"Unfortunately in a significant amount of people, the immune system doesn't respond fast enough to be protective against cancer," Johnson said. "With superantigens, we are trying to simply tip the scale more in favor of the immune system against this cancer."

Johnson said the logical conclusion to be drawn from the research is that someday individuals will be routinely vaccinated against certain cancers.

"We normally vaccinate kids against infectious diseases before they attend school," Johnson said. "We do not have a mind set for vaccinating against cancer.

"But the studies we're doing indicate that in cases where tumors have a clear-cut antigen associated with it, we would immunize people for cancer the way we immunize them to protect against things like polio," he said.

And nothing would please doctors that treat melanoma more than the development of a method of keeping people from coming down with the disease.

"Melanoma is a very aggressive form of skin cancer and prevention or early detection are the two keys to its treatment," said Dr. Robert Skidmore, interim chief of the division of dermatology and cutaneous surgery at Shands at UF health center. "The possibility of preventing this cancer through immunization would be a fantastic way of reducing both morbidity and mortality associated with melanoma.

"It will put me out of business, but that's fine," he said . "I'll find something else to do."

The American Cancer Society predicts that 47,700 people will be diagnosed with melanoma this year and 7,700 of them will die from the disease.

University of Florida

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