Severe asthma can lead to hospital treatment
Patients with a type of severe asthma benefit from injections of an antibody, research has shown.
Two teams, in the UK and Canada, found the treatment mepolizumab helped those patients with asthma exacerbated by a condition called eosinophilia.
The drug not only reduced the frequency of severe attacks, but enabled patients to cut back on the use of steroids, which are associated with side effects.
The studies feature in the New England Journal of Medicine.
It is estimated that up to 500,000 people in the UK have severe asthma complicated by eosinophilia.
This is a form of persistent airway inflammation linked to high levels of white blood cells called eosinophils.
Their condition can be so severe that they require regular hospital treatment.
The Canadian study focused on 20 patients who had been taking the steroid prednisone - which is linked to side effects such as weight gain and bone loss - for an average of nine years to control their condition.
Those who were given mepolizumab were able to reduce their use of prednisone significantly without their asthma getting any worse.
In contrast, symptoms deteriorated in patients who were given a dummy drug instead of mepolizumab as they cut back on prednisone.
Analysis showed that mepolizumab reduced the number of eosinophils to the normal range - and kept them there.
Canadian study leader Dr Paul O'Byrne, of McMaster University in Ontario, said: "Mepolizumab works by blocking the production of eosinophils.
"By preventing their production, we were able to improve asthma, reduce the need for prednisone and really show that eosinophils are important in causing asthma symptoms in these patients."
The UK study of 61 patients, led by Professor Ian Pavord at the Institute for Lung Health, produced similar results.
In this case patients continued to take steroids alongside mepolizumab.
Professor Pavord, also chief medical advisor to the charity Asthma UK, said the results suggested mepolizumab could cut severe asthma attacks by up to 50%, as well as enabling patients to reduce their use of steroids.
He added: "The last decade has seen a limited number of alternative treatment approaches become available for asthma, so the possible benefits that mepolizumab could bring to the half a million people with severe asthma in the UK are incredibly exciting."
Lack of facilities
However, he stressed that the therapy would not benefit all patients with severe asthma, and that there were only a handful of centres in the UK with the facilities to be able to assess who would benefit.
"We would urge local health trusts to make obtaining these simple facilities a priority so that the individuals who will benefit the most from this expensive new treatment can be carefully targeted when it becomes available," he said.
Writing in the journal, Dr Sally Wenzel, an expert in pulmonary medicine at the University of Pittsburgh, said eosinophils had been linked to asthma for more than a century - but their role in the condition had remained uncertain until now.
She said: "These studies clearly confirm that in a sub-group of patients with eosinophilic asthma, eosinophils play a role in exacerbations."