4 April 2007

Enzymes may allow universal blood transfusions

Cosmos Online
Two newly discovered bacterial enzymes may be able to safely convert A, B, and AB blood to the universally useful type O, say researchers.
Enzymes may allow universal blood transfusions

Giving someone the wrong blood type can trigger a massive, sometimes fatal immune attack on the transfused cells. The ability to convert all blood to the 'universal' type O could solve this problem. Credit: Jupiterimages

SYDNEY: Two newly discovered bacterial enzymes may be able to safely convert A, B, and AB blood to the universally useful type O, say researchers.

Supplies of type O blood are always in high demand due to the fact that it can be given to anyone, regardless of their blood type.

The new enzymes hold promise for “producing universal red blood cells… which would improve the blood supply while enhancing the safety of clinical transfusions,” wrote researchers behind the discovery in the current issue of British journal Nature Biotechnology.

“If it does what it’s supposed to do, [the technique] could be a leapfrog advance in the way that blood transfusions are conducted across the world,” commented Neelam Dhingra, a spokesperson for the World Health Organisation in Geneva, Switzerland.

Many types of cells in the human body have specialised molecules scattered over their surface. These molecules, called antigens, vary in structure from person to person, and help the body’s immune system distinguish the cells of our own tissues from pathogens and foreign invaders.

Included in the antigens of red blood cells are two sugar molecules known as A and B. Some people have A sugars, some have B sugars, some have both, and some have neither. Those with neither are known as type O.

The immune system only classifies a cell as ‘foreign’ and initiates an immune attack when it detects the presence of the wrong type of antigen. This means that the blood of people with neither antigen – type O – can be given to anyone. Giving someone the wrong type can trigger a massive, sometimes fatal attack on the transfused cells by the host’s immune system.

After sifting through more than 2,500 compounds from bacteria and fungi, biologists led by Henrik Clausen of the University of Copenhagen in Denmark, have now found a pair of enzymes that can rapidly and efficiently break down the A and B molecules, leaving cells as type O. One came from the bacteria Elizabethkingia meningosepticum, and the other from the species Bacteroides fragilis.

Using enzymes – molecular-scale protein machines that speed up biochemical reactions – to deconstruct blood antigens has been floated as an idea since the 1980s, and a coffee bean enzyme that could break down type B antigens was tested clinically the late 1990s. However, until now the technique has been expensive and no enzyme has been able to break down type A sugars.

“Enzyme conversion technology would substantially increase the availability of suitable red blood cells,” commented experts Geoff Daniels of the British Institute for Transfusion Sciences in Bristol, England and Stephen Withers of the University of British Columbia in Canada, in a commentary that appeared in Nature Biotechnology alongside the research.

The next phase will be to subject the enzymes to animal and human clinical trials before they can be used in blood banks, they said.

The WHO’s Dhingra cautioned that the technology could take between five and 10 years to emerge from such an exhaustive battery of tests for safety and effectiveness.

More information:

Blood types, Wikipedia

with Agençe France-Presse

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