Researchers who designed one experimental breast cancer vaccine say they have fine-tuned the process and come up with a second vaccine they hope will be more effective.

Their new vaccine delivers a cancer-fighting gene into cells, which then produce immune system proteins as well as tumor-destroying cells.

“In our own mind it is a very significant advance because we have put the gene into the cells in the body. The vaccine is produced by your own cells,” Wei-Zen Wei of Wayne State University in Detroit, who led the study, said in a telephone interview. “It is made right in your body.”

The vaccine eliminated tumors in mice from a type of cancer called HER2-positive cancer, they reported in the journal Cancer Research. HER2-positive cancers account for between 20 percent and 30 percent of breast cancers.

It even worked to eliminate HER2 tumors that had developed resistance to drugs designed to fight them, the said.

The HER2/neu protein is over-expressed, meaning it is over-active, in several tumors including breast, colorectal and ovarian cancer.

Herceptin, also known as trastuzumab, an expensive antibody-based drug made by Genentech Inc, can treat these tumors. But many patients eventually acquire what is known as resistance and the tumors start growing again.

ANTIBODIES AND KILLER T-CELLS

Wei’s team made a vaccine using so-called naked DNA from genes that produce the HER2 receptor - the molecular signal for the breast cancer tumors.

They put this DNA, along with an immune system stimulant, into a ring of genetic material, called a plasmid, from a bacterium.

They used a process called electroporation, which employs an electrical pulse, to force the compound through skin and muscle to immunize mice.

Once in the leg muscles, the genes went to cells, which started producing HER2 receptors that activated antibodies and immune cells called killer T-cells, they reported.

“The immune system goes around the body to look for cancer cells,” Wei said.

When they then injected HER2-positive breast tumors into the mice, their bodies eradicated them.

“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.”

It might even be used to prevent cancer from coming back in women who have been successfully treated using Herceptin or other drugs, she said.

Several groups are working on breast cancer vaccines that target HER2, including Seattle-based Dendreon Corp, which calls its vaccine Neuvenge, and privately held Apthera, whose vaccine is called Neuvax.

Breast cancer is the top cause of cancer death among women worldwide, with 1.3 million new cases diagnosed annually and 465,000 deaths, according to the American Cancer Society.

WASHINGTON (Reuters)