Their study, published in the online journal, Breast Cancer Research, on Nov. 29, 2004, showed that the vaccine protected 86 percent of experimental mice against HER2/neu-associated breast cancer, even though the tumors were implanted directly into mice.
"This is an exciting strategy that seems to elicit a complete immunologic response against HER2/neu," says the study's lead author, Lawrence Lachman, Ph.D., a professor in the Department of Experimental Therapeutics. "Now that we have gone as far as we can in animal studies, I hope this agent might be tested clinically both to treat HER2/neu breast tumors, and to prevent them from spreading."
Up to one-third of human breast cancers are associated with over-expression of the HER2/neu cell surface receptor protein, which continuously "tells" the cancer cell to grow, this producing an aggressive disease that is difficult to stop.
The drug Herceptin treats this kind of breast cancer by "plugging" these receptors with a monoclonal antibody, but this treatment "produces only a passive and transitory immune reaction," Lachman said. "This vaccine, however, like many that treat microbial infections, appears to create a memory in the immune system that produces a lasting protective response." The vaccine used in this study is a "viral-vectored" approach, in which a naturally occurring virus is re-engineered to be propagation defective but still able to function as a delivery system for proteins from the cancer cells that are to be targeted by the animal's immune system.
The basis for this new vaccine is an RNA virus called VEE, for Venezuelan equine encephalitis, which in its natural form can cause disease in horses.