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Leukemia Vaccine Shows Early Promise

Larger studies to begin next year, researchers report

MONDAY, Dec. 6, 2004 (HealthDayNews) -- A leukemia vaccine has been successful enough in its first trials to warrant larger studies that will include hundreds of patients, researchers report.

The vaccine prompted an immune system attack against the overproduced leukemic white blood cells in 20 of 33 people with different forms of the blood cancer, said study leader Dr. Jeffrey Molldrem, an associate professor of medicine at the University of Texas M.D. Anderson Cancer Center.

The most impressive results occurred in the four people with the form of the disease called acute myelogenous leukemia (AML), which affects about 12,000 Americans each year. Three of them had complete remissions that have persisted for several years, and the most delicate test available finds no trace of the disease in two patients, Molldrem said.

The researchers presented their findings Dec. 6 at the American Society of Hematology annual meeting in San Diego.

A multi-center study to include more than 100 AML patients will start in February, Molldrem said. Similar studies that will include patients with another form of the disease, chronic myelogenous leukemia, and a precancerous condition called myelodysplastic syndrome, will also begin early next year, he said.

The vaccine uses a molecule designated PR1 that is overproduced by leukemia cells, Molldrem said. It causes T-cells in the immune system to attack those cells while ignoring normal cells.

"We starting looking about 10 years ago, hoping to find how T-cells recognize leukemic cells," Molldrem explained. "PR1 is overexpressed on the surface of leukemic cells."

He acknowledged that "we were a little surprised at the results. Our primary end point was just to get an immune response, but when we treated these people with the vaccine, they went into remission."

Alan Kinniburgh, senior vice president for research at the Leukemia and Lymphoma Society, called the findings "very exciting." The vaccine seems to provide a much simpler, less traumatic method of achieving the results that now require a bone marrow transplant.

A transplant is done by first using radiation and chemotherapy to wipe out the existing blood cell system. A new system then is established with a transplant. Studies have shown that transplants work by establishing an immune system that has T-cells that do what the old system did not -- attack leukemic cells, Kinniburgh explained.

"We know that the curative effect of a bone marrow transplant is in the immune system," he said. "This [the vaccine] is a procedure that eliminates all the toxic therapy required for a bone marrow transplant."

Molldrem cautioned that the vaccine development is in its early stage and "there is still much more to be done."

Kinniburgh agreed. It's "a little early to talk about wider use" of the vaccine, he said. "I'd like to see a larger study focusing on AML patients to see if this 75 percent response rate holds up," he said.

In another promising development in the fight against leukemia, researchers reported at the same meeting that an experimental drug called BMS-354825 shows promise in treating people with chronic myelogenous leukemia who fail to respond to Gleevec, the standard treatment for the disease.

Data from early clinical trials suggest the drug can overcome Gleevec resistance in people with early stage CML. The 36 patients in the study suffered intolerance or a worsening of their disease when they were treated with Gleevec.

"Our study examined patients in all phases of CML, including the chronic phase, the accelerated phase, and blast crisis. The patients responded quite well to this new compound, and we observed no side effects," study leader Charles L. Sawyers, of the Howard Hughes Medical Institute, said in a prepared statement.

"In fact, the results of this clinical trial match very closely with what we would have predicted the outcome to be based on our earlier studies of this drug in mice," Sawyers said.

More information

Leukemias and their treatment are described by the Leukemia and Lymphoma Society.

SOURCES: Jeffrey Molldrem, M.D., associate professor, medicine, University of Texas M.D. Anderson Cancer Center, Houston; Alan Kinniburgh, Ph.D, senior vice president, research, Leukemia and Lymphoma Society, White Plains, N.Y.: Dec. 5-6, 2004, presentations, American Society of Hematology annual meeting, San Diego
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