Cancer Research News
Peptide Vaccine Fights Off Breast Tumors with Aid of Bacteria-Mimicking Agents
PHILADELPHIA, February 2007 -- With the help of immune
system-stimulating molecules that mimic bacterial components,
researchers have used a type of cancer vaccine to both delay and prevent
breast tumors in mice. The strategy, they say, holds promise for the
future use of peptide vaccines in women who are at high risk for
developing breast cancer.
Researchers from the Mayo Clinic, University of South Florida, and
University of Torino employed substances called toll-like receptor
agonists to help a synthetic peptide vaccine raise the immune system
response against breast cancer tumors. Simultaneously, they used
antibodies to blunt other aspects of the immune system that might
interfere with a strong killer T cell response, improving the
effectiveness of the vaccine.
In the February 1 issue of Cancer Research, the researchers report that
their strategy was effective in preventing spontaneous tumors in
transgenic mouse models for breast cancer, even when the vaccine was
given when the mice already had early stage cancer.
“The challenge is to get a foreign peptide recognized by the immune
system as a threat so it can react and produce anti-tumor immune cells,”
said Esteban Celis, M.D., Ph.D., professor in the department of
interdisciplinary oncology at the H. Lee Moffitt Cancer Center and
Research Institute at the University of South Florida in Tampa. “We’ve
shown that stimulating the immune system using toll-like receptor
agonists is very important to alerting it and producing lymphocytes that
will have an anti-tumor effect.”
According to Celis, the immune system usually doesn’t react as strongly
to a synthetic peptide in a vaccine as it does against an infectious
agent, which is why immune system boosters such as toll-like receptor
agonists, which mimic bacterial DNA, help. They also used anti-CD25
antibodies to tie up immune system T regulatory cells, which often serve
as brakes that can reduce responses to the vaccine.
The researchers studied both normal mice and transgenic mice carrying an
activated HER2/neu oncogene, which has been linked to breast cancer in
humans. In order to get a protective immune response, the transgenic
mice were repeatedly given vaccine in combination with the toll-like
receptor agonist or were given antibodies that blocked their protective
T regulatory cells. Celis and his colleagues found that the peptide
vaccine administered this way could prevent or slow the growth of
injected tumor cells, and showed some benefit against early stage
spontaneous breast tumors.
The vaccine was most effective in preventing spontaneous tumors when it
was given once at week eight – along with anti-CD25 antibodies -- when
most mice have excessive and often precancerous breast tissue growth
called hyperplasia. It completely prevented spontaneous tumors in HER2/neu
mice up to 35 weeks of age. Even without the antibody, tumors took much
longer to develop, and when they did, they grew more slowly.
“This kind of therapy could be applied to women who have a high
likelihood of developing cancer -- women with pre-malignant hyperplasia
or who have a genetic predisposition or make-up that makes them at high
risk,” Celis said.
Although the peptide vaccine was effective in preventing spontaneous
tumors in the HER2/neu mice, Celis cautions that the mice had to be
vaccinated prior to the appearance of measurable tumors and that the
animals had to receive repeated immunizations.
“Once tumors appear, only certain mice respond and there is only a delay
in tumor growth,” he said. “It extends survival but does not cure the
mice. We know that the immune response in these mice is much lower than
in the animals that are younger, and it’s likely that the tumor is
making something that is inhibiting the immune response.”
Source: American Association for Cancer Research
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