Blood conversion breakthrough could be life-saver for thousands

[cezene]

A life-saving method of converting blood from one group to another has been pioneered by scientists. The breakthrough could potentially mean the end of blood-donor shortages and boost supplies of sought-after group O negative blood.

O negative blood is known as “universal” because it can be given to anyone in a blood transfusion. Giving patients the wrong type of blood can cause severe immune system reactions and can be fatal.

Writing in the journal Nature Biotechnology, an international team of researchers described how they converted blood from group A, B or AB to group O.

The process uses bacterial enzymes found in fungi, which can be used as biological “scissors” to cut sugar molecules from the surface of red blood cells.

People inherit blood type through their parents’ genes, and the system of categorising groups as A, B, AB or O dates back to 1900. Those in groups A and B have blood containing one of two different sugar molecules that can trigger an immune response. People in group O, the most common group, have neither of these “antigens”, while those in group AB have both.

Patients produce antibodies against the antigens they lack. For this reason, AB individuals, who lack neither, can receive blood safely from any group. But group A patients cannot be given a transfusion of group B blood, and vice versa.

Group O patients react badly against A, B or AB blood. However, their own blood, having neither of the sugar antigens, is suitable for people from all the ABO groups. Group O donors are therefore always in demand, and O blood is often in short supply.

A further antigen that can trigger an immune response, a protein called RhD, exists in blood labelled “rhesus positive”. Truly “universal” group O blood is rhesus negative, meaning that it is also missing this antigen, but at the moment this type makes up only 4 per cent of stocks for the National Blood Service (NBS).

The scientists, led by Henrik Clausen, from the University of Copenhagen, screened 2,500 types of fungi and bacteria looking for useful proteins. They found two bacteria, Elizabethingia meningosepticum and Bacterioides fragilis, that yielded enzymes capable of removing A and B antigens from red blood cells.

In tests, the antigens were found to vanish from 200ml samples of A, B and AB blood after an hour’s exposure to the appropriate enzyme. The researchers wrote: “Clinical translation of this approach may allow improvement of the blood supply and enhancement of patient safety in transfusion medicine.”

Group O blood created using the new method will have to be tested on human beings before it can be used in hospitals.

To create supplies of group O negative blood, rhesus negative A, B and AB blood would have to be selected. No way has yet been found to turn rhesus-positive blood into rhesus-negative.

The present system of blood transfusions is wasteful, with 10 per cent of donations in the UK never reaching patients. It is also expensive, with each unit costing more than £120 to extract, screen and store.

The NBS, which serves England and North Wales, holds 40,000 units of blood in stock — enough to last about 5½ days. A unit is a single blood donation, or two thirds of a pint. Red blood cells can be stored for only 35 days, and stocks must be replenished continuously by donors.

Life to the body:Type O blood is the most common group in the world, and is found in 44 per cent of the UK population. About 42 per cent have type A, 10 per cent type B and 4 per cent type AB

— In addition, 83 per cent of Britons are Rh(D) negative, a blood type named after the Rhesus monkey in which it was first detected. This effectively doubles the different blood types to be matched, because you should not mix blood type A+ with blood type A-

— O is the original and oldest of the blood groups, from which the others derived as human populations mingled after the Stone Age

— Group A first appeared between 25,000BC and 15,000BC, when larger human settlements first appeared as farming developed. It is the most common group in Norway, Denmark, Austria, Armenia and Japan

— A quarter of all Chinese or Asian communities are group B, which emerged between 15,000 and 10,000BC

— Group AB appeared as late as 500 years ago, as a response to the mixing of existing blood groups Source: National Blood Service