If found to be safe and effective on a large scale, the discovery would greatly expand the supply of available blood and might even make shortages a thing of the past, experts said.

"The Red Cross is very interested in and supports this science and looks forward to seeing the clinical data on this," said Dr. Richard Benjamin, chief medical officer at the American Red Cross in Washington, D.C.

The findings were published Sunday in the online edition of the journal Nature Biotechnology.

Most people are born with one of four blood types: A, B, A/B or O. At the cellular level, types A and B red blood cells are characterized by distinct sugar molecules lying on their surfaces, while A/B carries both the A and B surface molecules. These molecules are "antigens" that can trigger lethal immunological reactions -- for example, if a type B person is transfused with type A blood.

Luckily, about one-quarter of the population also carries a form of blood without these surface antigens that's called type O. This means their donated blood can be safely used by any recipient. Type O blood is especially useful in emergency situations, when doctors don't have time to determine a patient's blood group.

"For this reason, hospitals use a lot more group O blood than they do type A or B," Benjamin said. "When you hear about 'blood shortages' in the press, we are really talking about the fact that we don't have enough type O."

One way to end these shortages would be to find a biochemical means of stripping away the A and B surface antigens from red blood cells, turning them into O. Molecules called enzymes can do this, but it has been tough to find enzymes that target only the A and B antigens and leave the rest of the cell alone.

The company behind the new research, ZymeQuest of Beverly, Mass., "had previously tried this with enzymes purified from things like coffee beans," Benjamin said. Those enzymes were effective, he said, "but what the clinical trials showed was that even if you have removed 99 percent of the group B (antigens), the human immune system can still see the remaining 1 percent and respond to it."

But the new research -- as yet tested only in a lab -- has achieved an efficiency that is many times "better than that prior work," Benjamin said.

The new effort was led by Dr. Henrik Clausen of Harvard Medical School and the University of Copenhagen. His team combed through an exhaustive database of bacteria and fungi looking for enzymes highly specific to the A and B surface antigens. They found two families of bacterial enzymes called glycosidases that target and remove the sugar molecules.

"This is big," said Dr. Louis M. Katz, executive vice president of medical affairs at America's Blood Centers, which oversees 77 regional blood centers serving more than 180 million people nationwide. "It clearly needs to be pushed forward toward clinical trials."

But Katz cautioned that crucial questions remain. "Do these enzymes change anything else on the red blood cell? We might now develop immune reactions to enzyme-treated red cells, for example," he said. Miniscule "residual" levels of the enzyme itself, left behind in the blood, might also cause immune problems, he said.

Finally, Katz said, how much would enzyme-based processing of A and B blood cost? In the research paper, the study authors said processing could be "efficient and cost-effective." Benjamin said the American Red Cross has been talking closely with ZymeQuest, and "I do know that they are trying to develop machines that could process multiple units at a time and get it down to an economic proposition."

But Katz, who also directs the Mississippi Valley Regional Blood Center in Davenport, Iowa, was somewhat more skeptical.

"The real question is whether the resources needed to scale up to this kind of thing would be better put toward better (blood) donor recruitment," he said. "Right now, five percent of the population donates per year. If we made that seven percent, the issue of availability would probably go away."

More information

Find out more about the blood supply, and where you can donate blood, at the American Red Cross.

SOURCES: Richard Benjamin, M.D., Ph.D., chief medical officer, American Red Cross, Washington, D.C.; Louis M. Katz, M.D., executive vice president of medical affairs, America's Blood Centers, Washington, D.C.; April 1, 2007, Nature Biotechnology, online