They hope that the HER2 DNA vaccines might potentially be used in cancer-free women to prevent initial development of such tumors.
HER2 receptors promote normal cell growth, and are found in low amounts on normal breast cells. But HER2-positive breast cells can contain many more receptors than is typical, promoting a particularly aggressive type of tumor that affects 20 to 30 percent of all breast cancer patients.
Currently, therapies such as trastuzumab and lapatinib are used to treat this cancer, however, a greater chunk of patients develop a resistance to them, following which cancer metastasis that is hard to treat.
Lead researcher Wei-Zen Wei, a professor of immunology and microbiology at the Karmanos Cancer Institute, said that the treatment relied on activated, own-immunity to wipe out the cancer,
The vaccine consists of "naked" DNA - genes that produce the HER2 receptor - as well as an immune stimulant.
In the study conducted using mouse model, the researchers used pulses of electricity to deliver the injected vaccine into leg muscles in mice, where the gene produced a huge quantity of HER2 receptors that activated both antibodies and killer T cells.
"The immune response against HER2-positive receptors we saw in this study is powerful, and works even in tumors that are resistant to current therapies," said Wei.
"The vaccine could potentially eliminate the need to even use these therapies."
"While HER2 receptors are not usually seen by the immune system when they are expressed at low level on the surface of normal cells, a sudden flood of receptors alerts the body to an invasion that needs to be eliminated," Wei said.
"During that process, the immune system learns to attack cancer cells that display large numbers of these receptors," she added.
They also used an agent that inhibited the activity of regulatory T cells, which normally keeps the immune system from over-reacting.
In the absence of regulatory T cells, the immune system responded much more strongly to the vaccine. Then, when the researchers implanted HER2-positive breast tumors in the animals, the cancer was eradicated.
"Both tumor cells that respond to current targeted therapies and those that are resistant to these treatments were eradicated," Wei said. "This may be an answer for women with these tumors who become resistant to the current therapies."
The study is reported in the September 15 issue of Cancer Research, a journal of the American Association for Cancer Research.