RT Journal Article SR Electronic T1 Biologics in severe difficult-to-treat asthma: find the right niche! JF European Respiratory Review JO EUROPEAN RESPIRATORY REVIEW FD European Respiratory Society SP 51 OP 53 DO 10.1183/09059180.00001509 VO 18 IS 112 A1 M. Humbert YR 2009 UL http://err.ersjournals.com/content/18/112/51.abstract AB