Monday, April 02, 2007

Universal Blood

Researchers have found a way to efficiently convert different human blood types into a neutral type that can be given to any patient.

By Katherine Bourzac

Blood breakthrough: Red blood cells, like those pictured above, can be converted into a universal donor type by bacterial enzymes. Credit: Eye of Science / Photo Researchers, Inc.

When a gunshot victim who has lost a significant amount of blood is rushed to the hospital, doctors must often give him or her a blood transfusion without knowing the appropriate blood type. Only one of the four blood types can safely be given to any patient, so type O, the universal blood type, is in high demand. Now researchers at a Massachusetts startup have found a way to make blood of any type acceptable to any patient by cleaving identifying sugars from the surface of red blood cells. The process is currently in human testing and could be available within five years.

Red blood cells have complex sugars on their surfaces; it is these sugars that determine whether the blood is type A, B, O, or both A and B. People with type A red blood cells carry antibodies against type B blood cells. If they are given a transfusion of type B red blood cells, their body will attack and kill the cells. Similarly, people with type B blood will mount an immune attack against a transfusion of type A blood.

Researchers led by Henrik Clausen of the University of Copenhagen have discovered two enzymes that efficiently chop the A and B sugars off of red blood cells, making them universal. The company ZymeQuest, based in Beverly, MA, has licensed the enzymes and developed a machine that can simultaneously treat eight units of blood with the enzymes in 90 minutes.

Researchers have previously tried a similar strategy. But the A- and B-cleaving enzymes discovered in the past haven't worked very well, says Clausen. He says this is because other researchers have looked for enzymes using simple sugars that don't behave the same way as those on human red blood cells. "We used real substrates from red blood cells," he says. "You have to use these complex, branched sugars to search for enzymes with much better properties."

The two chopping enzymes discovered by Clausen are made by bacteria. They selectively cleave only A or B sugars, leaving other sugars on the red cells' surface intact. The enzymes cleave each of these sugars so that there is no risk of an immune reaction in the patient. And they perform well at a neutral pH. The enzymes discovered previously did not do all these things.

"We don't always have as much type O available as we want," says Laura McDonald, program director for Blood Centers of America, an organization that represents the regional centers that collect and distribute blood. "The ZymeQuest technology is fitting because the product will make all blood cells universally compatible, like type O."

Blood processed by ZymeQuest using the sugar-cleaving enzymes is currently in early phase II clinical trials in the United States. If all goes well, the company expects its blood-processing machines to be on the market in Europe in 2011 and in the United States a few years later.