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Leukemia Cells Surprise Researchers

Chronic lymphocytic leukemia cells die off, are reborn at faster rate than believed

THURSDAY, Feb. 10, 2005 (HealthDay News) -- Scientists have long believed that chronic lymphocytic leukemia (CLL) cells don't die, and they proliferate at a very slow rate.

But researchers now say neither belief is true, and that could alter how scientists think about and treat the disease in the future.

The study, which appears in the Feb. 10 online issue of the Journal of Clinical Investigation, found that CLL cells do die off and they're reborn at a much faster rate than researchers previously thought.

"The basic thoughts about the biology of this disease need to be modified," said study author Dr. Nicholas Chiorazzi, director and CEO of the Institute for Medical Research, which is part of the North Shore-Long Island Jewish Health System in Manhasset, N.Y.

"The theory was that leukemic cells don't die, and they don't grow quickly. The gist of our experiment is that these two original thoughts appear to be completely inaccurate," Chiorazzi said.

CLL is a type of cancer that originates in bone marrow cells, according to the Leukemia & Lymphoma Society. Nearly 8,200 people are diagnosed with this disease in the United States each year.

One reason scientists believed that CLL cells didn't die is that many people live for 20 to 30 years with the disease and die from another cause, according to Chiorazzi. Another reason is that the number of cells with CLL seemed to remain constant over time, which suggested not only that cells weren't dying off, but also that new CLL cells were not reproduced quickly.

However, when scientists looked at individual CLL cells to try to learn how these cells had turned off the natural mechanism that induces cell suicide in older cells, they could find no abnormalities in this mechanism. That suggested that the cells were, in fact, dying off as cells are expected to do.

To see if CLL cells were dying off and being reborn, Chiorazzi and his colleagues had to devise a way to mark the CLL cells. To do this, they had 19 people with CLL drink a solution of "heavy" water.

Heavy water is normal water, but the hydrogen is replaced with deuterium, a non-radioactive substance that can mark cells. Since water enters the DNA of cells, water containing deuterium allowed the researchers to track cells.

The study volunteers drank two ounces of the heavy water every day for 84 days. The researchers then took blood samples for another three months, which allowed them to track the death and then birth of CLL cells.

What they found was that CLL cells do, indeed, die. And they are reproduced at a much faster rate than was previously believed, the researchers found.

They also found that people with the faster-progressing form of the disease had even faster reproduction rates.

Chiorazzi said these findings could eventually be used to assess patients early in the course of their disease to see which form of CLL someone has. Those with the very slow progressing form often don't require any treatment. Also, he said, this may give researchers another target for drug therapies. For example, a drug that could interrupt the reproduction of CLL cells could be a possibility.

Dr. Marshall Lichtman, executive vice president of the Leukemia & Lymphoma Society, said, "This is a very thoughtful, complicated study. It provides a better perspective on the pathogenesis of this disease, but in the short term, it won't have a dramatic effect in how the disease is approached."

More information

To learn more about chronic lymphocytic leukemia, visit The Leukemia & Lymphoma Society.

SOURCES: Nicholas Chiorazzi, M.D., director and CEO, Institute for Medical Research, North Shore-LIJ Health System, Manhasset, N.Y.; Marshall Lichtman, M.D., executive vice president, research and medical programs, The Leukemia & Lymphoma Society, White Plains, N.Y.; Feb. 10, 2005, Journal of Clinical Investigation online
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