Vaccine Kills Cancer Cells

A novel vaccine that stimulates the immune system to seek out and destroy tumor cells is showing promise for people with leukemia.

Reporting at the annual meeting of the American Society of Hematology, a Houston researcher says the experimental vaccine produced an immune response in almost two-thirds of the people tested. Of those who responded to the vaccine, overall survival and survival free of cancer were improved compared with those who did not respond.

Even more exciting is the observation that the vaccine is helping people who mount an immune response to live longer — and without any signs of their cancer, says Jeffrey Molldrem, MD, associate professor in the department of blood and marrow transplantation at the University of Texas M.D. Anderson Cancer Center.

Half of the responders are alive and disease-free three years after they got the vaccine, compared with 23 percent of those who did not have a response, Molldrem says.

"Normally, we would have expected these people to live only three to six months," he tells WebMD. "These are very sick people who failed to get better despite our best chemotherapies. Half of them even had bone marrow transplants. They were pretty well along."

There are other signs the vaccine, which was given as a weekly shot, is working, Molldrem says. Four people went into complete remission — meaning their tumor cells were completely wiped out, he says. And when three of the four underwent more testing — even sensitive molecular screening, which detects abnormal cancerous cells — no cancer cells were found.

And in another four patients, blood cell levels, which are normally suppressed in leukemia patients, shot back up to normal, he says.

People who received the vaccine had either active or relapsed acute myelogenous leukemia (AML) or refractory chronic myelogenous leukemia (CML) — forms of leukemia in which there is a dangerous accumulation of immature cells in the bone marrow. The others had myelodysplastic syndrome (MDS), a precancerous disorder of the bone marrow.

Vaccine Targets Leukemia Cancer Cells

Unlike flu and other vaccines, most cancer vaccines under development are not intended to be given to healthy people to prevent disease. Rather, they are being developed to help cancer patients bolster their immune system to better fight the cancer.

In this case, the vaccine targets a specific part of a protein that is present in large amounts on the surface of cancerous leukemia cells. The protein, called PR1, is also present on normal cells, but in very small amounts, Molldrem says.

The vaccine encourages the immune system to seek out and attack only those cells that carry abnormally high amounts of PR1, he says.

Because the vaccine targets only tumor cells, healthy cells are left unscathed. And that means the unpleasant side effects, such as hair loss and nausea, associated with traditional cancer medications are avoided, he notes.

The most frequent adverse reaction: a rash at the site of injection in 12 patients. It went away within two days, Molldrem reports.

"This is the first evidence that a peptide vaccine, with very little toxicity, can put someone with a tumor into molecular remission," he says.

Down the road, he imagines the vaccine will be used in combination with other types of specific drug therapy to keep cancer at bay. Molldrem even hopes the vaccine can help prevent cancer in people at high risk.

John E. Goodwin, MD, a cancer specialist at Loyola University Medical Center in Chicago, says that while the work is early, the approach is noteworthy and worthy of further study.

"What's amazing," he tells WebMD, "is how they got the body to mount an immune response. Usually vaccines target substances that are abnormally expressed on cancer cells. But they are targeting a substance that is present (although in low amounts) even on normal cells. This is a new way of looking at things."

Sources: 46th Annual Meeting of the American Society of Hematology, San Diego, Dec. 2-7, 2004. Jeffrey Molldrem, MD, associate professor, department of blood & marrow transplantation, University of Texas M. D. Anderson Cancer Center, Houston. John E. Goodwin, MD, professor of medicine and pathology, Loyola University Medical Center, Chicago

By Charlene Laino
Reviewed by Brunilda Nazario, MD
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