Although years away from clinical trials in humans, the discovery could lead to the development of a new weapon in the fight against cancer.

The scientists, from The Scripps Research Institute in La Jolla, said the vaccine leads only to a reduction in blood vessels leading into tumors, and that it may prove most effective in stopping residual tumors after treatment, or the recurrence of tumors after remission.

"That is certainly a window where immune therapy might be applied the most effectively," said Dr. Andreas G. Niethammer, a research associate at Scripps and a co-author of the study, published online yesterday in the journal Nature Medicine. It will appear in print next month.

Tumors cannot grow without their own blood supply, and in recent years scientists have tried to design drugs that inhibit the development of blood vessels that feed tumors, a process called angiogenesis.

The scientists at Scripps are the first to develop a vaccine that triggers an immune response against a tumor's blood supply.

Previous studies have shown that specific proteins, called vascular-endothelial growth factor receptor-2, or VEGF receptor 2, are found on the blood vessel cells that feed cancer tumors. The Scripps vaccine triggers an immune response that attacks these proteins.

"What Dr. (Ralph) Reisfeld has done here is use a vaccine approach, and he's asked a body to mount an immune response against that . . . VEGF receptor," said Dr. Jeffrey Schlom, chief of the Laboratory of Tumor Immunology at the National Cancer Institute in Bethesda, Md.

"This is what's new."

Since the 1990s, high hopes have been placed on a new class of drugs called angiogenesis inhibitors, which are designed to attack a variety of molecular targets that drive the development of blood vessels in tumors.

But results have been mixed. Also, existing angiogenesis inhibitors often must be administered repeatedly, and sometimes at very high doses, to be effective at all, said Reisfeld, a Scripps immunology professor who conducted the study with Niethammer.

The vaccine the Scripps team developed, by contrast, protected mice from cancer 10 months after their last dose. The Scripps researchers tested the animals' immune response to lung, colon and skin cancer.

The vaccine posed one side effect, however. Angiogenesis is a natural process in wound repair, and the vaccine was found to delay the healing of wounds in mice.

"One is going to have to do a series of animal studies to make sure that this approach is safe," said Schlom.

The article was authored by Niethammer, Rong Xiang, Jurgen C. Becker, Harald Wodrich, Ursula Pertl, Gabriele Karsten, Brian P. Eliceiri and Reisfeld.

The study was supported by the National Institutes of Health, the American Heart Association, the Tobacco-Related Disease Research Program Grant, the Department of Defense, Lexigen Pharmaceuticals, Inc., and by fellowships through Deutsche Krebshilfe and Deutsche Forschungsgemeinschaft.