By Richard Black
BBC science correspondent
Medical researchers have obtained promising results from a trial of a genetically-engineered allergy vaccine.
Any vaccine would need to 'turn the fires of the immune system down'
During the trial, conducted in Austria, Sweden and France, the vaccine significantly reduced peoples' allergic response to pollen.
The team says it is already developing further GM vaccines to combat other allergies.
The research is reported in the academic journal Proceedings of the National Academy of Sciences.
It is estimated that around a quarter of the world's population is allergic to something. Some allergies, such as asthma, can be life-threatening.
They are caused by the body's immune system over-reacting to a substance which is in fact harmless.
Switch on, switch off
Vaccines against diseases like measles or polio are intended to make the immune system turn on. But an allergy vaccine needs to do the opposite.
In the words of lead researcher Rudolf Valenta from the Medical University of Vienna, it needs to turn the fires of the immune system down.
"What we find in fact is that when people are vaccinated, they have kind of a barrier of antibodies; and apparently these antibodies prevent the oil getting to the fire and heating up the allergic inflammation," he said.
Professor Valenta's team has genetically-engineered the pollen of birch trees so that in the bodies of allergy sufferers it produces antibodies which greatly reduce the immune response.
As an added bonus it also reduces the response to some other types of pollen as well. Treatments are already available for some allergies which use the same principle, immunising with small fragments of the substance in question.
But although these can work well, they can also produce major side-effects.
By using genetic-engineering, this research team has managed to produce the benefit without the side-effects.
They have already developed GM versions of other common allergy-producing substances, and aims to find out whether these can work as vaccines too - either to treat those who are already allergic, or to prevent allergies developing in the first place.
"In the future...we will soon see further applications of these modified allergens, also in patients," said Professor Valenta.