"People have been wondering how long we can freeze and store these cells," Hal Broxmeyer, a researcher at the Indiana University School of Medicine, said Monday. "Our paper says it is highly likely that they can be stored for at least 15 years."
In a study appearing this week in the Proceedings of the National Academy of Sciences, Broxmeyer and his co-author report that human cord blood frozen in 1985 and 1986 was able to grow in laboratory cultures with the same vigor as fresh cord blood. When put into mice, the defrosted cells thrived in the laboratory animals' bone marrow.
"We showed we could take the cells after defrosting and have them expand extremely well - as well as if we had used fresh cord blood," said Broxmeyer, a professor of microbiology and immunology and a pioneer in the freezing of cord blood.
He said cells frozen for five years have been used successfully in patients. While the new study suggests the period of viability can extend to 15 years, he cautioned that 100 percent certainty will come only when the older cells are used in human patients.
Other researchers said the new study may encourage doctors to use long-frozen cord blood for patients who are in desperate need and have no other option.
Blood extracted from the umbilical cord after birth contains stem cells that can develop into bone marrow cells. Since 1989, cord blood has been used to restore the bone marrow of cancer and leukemia patients whose natural bone marrow was destroyed by radiation and chemotherapy treatments.
When compatible bone marrow transplants are available, doctors can use stronger drugs and radiation to attack the cancer and thus are more likely to arrest the disease. Restoring bone marrow using cord blood transplant has been performed more than 2,000 times worldwide, and experts say the success rate is comparable to compatible bone marrow transplants.
Dr. Celso Bianco of America's Blood Centers, an organization of blood and bone marrow banking companies, said the research finding by Broxmeyer is very important for expanding the availability of material for bone marrow transplants.
"Only in recent years have institutions started collecting cord blood to restore the bone marrow of patients," Bianco said. "As these repositories grow, you'll have more chances of finding a match" for patients.
Lengthening the time when frozen cord blood can be used from five years to about 15, he said, would substantially expand the inventory of transplantable cells.
Bianco cautioned that the Broxmeyer study is experimental, and 15-year-old cells will have to prove themselves in clinical use before such lengthy preservation by freezing is accepted by other experts in the field.
In the study, Broxmeyer's team, along with two researchers from the National Institutes of Health, thawed 15-year-old frozen cord blood and tested it for viability. They found the cells could be grown in laboratory culture, and specimens could be removed from that culture and grown into a new colony. This procedure, called replating, is considered a key test for the viability of frozen stem cells.
The researchers also put defrosted cells into laboratory mice that had been bred to have a flawed bone marrow system and no immune system. Broxmeyer said the long-frozen human cord blood cells thrived in the mice and grew bone marrow cells.
"We were able to get engraftment in those mice as good as we get from fresh cord blood samples," he said.
The cells also matched up well with fresh samples when compared in a series of experiments testing whether the cells could grow and expand in number in the laboratory.
By Paul Recer