Herceptin, a man-made antibody approved for the treatment of breast cancer, targets these cancers. But after a while, tumor cells often become resistant to Herceptin.
The new vaccine elicits immune responses that kill HER-2 positive breast tumors in mice, whether or not they've become Herceptin resistant, says Wei-Zen Wei, PhD, professor of immunology at Detroit's Karmanos Cancer Institute.
"Regardless of whether tumor cells are resistant, if immune cells are properly primed by immunization we can destroy these cells," Wei tells WebMD.
The vaccine developed by Wei's team uses DNA that carries the genetic code for a key piece of the HER-2 molecule. After injection of the DNA into the skin, a small electric pulse is administered to help cells take up the DNA and produce the protein that elicits immune responses.
Mice given the vaccine made anti-HER-2 antibodies. The vaccine also primed cellular immune responses that attacked breast cancer tumors. These cellular responses alone were enough to kill HER-2 positive cells in mice unable to make antibodies.
A version of the vaccine is now undergoing human safety tests.
However, researchers at San Antonio's Brooke Army Medical Center found that 26 months after vaccination, there was no significant difference in cancer recurrence between vaccinated and unvaccinated women.
Gary Yang, MD, associate professor of radiation medicine at Roswell Park Cancer Institute in Buffalo, N.Y., says these human studies are a major step forward.
"These studies accomplished a lot -- but we need to find out why the immune system cannot sustain this efficacy," Yang tells WebMD.
Yang says that is why Wei's team's work is so important. What's learned in the lab must be tested in patients -- and then more lab work is needed to answer questions raised by human studies.
"The clinical research into breast cancer vaccines is not going to be a home run," he says.
Wei is convinced that in the long run, vaccines will prove to be powerful cancer treatments.
"Ultimately, we will be using the best defense we have to fight cancer -- the human immune system," she says. "It is a very challenging thing to do. We hope we have reached a point where we can make it useful to patients."
Wei and colleagues report their findings in the Sept. 15 issue of Cancer Research.