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.