Two recent phase III trials in patients with severe eosinophilic
asthma have shown that anti-
interleukin 5 (IL-5)
therapy with
mepolizumab reduces the frequency of
asthma attacks, improves symptoms and allows patients to reduce oral
glucocorticoid use without loss of control of
asthma. An earlier large 616 patient Dose Ranging Efficacy And safety with
Mepolizumab in severe
asthma (DREAM) study had shown that the only variables associated with treatment efficacy were a prior history of
asthma attacks and the peripheral blood eosinophil count. The link between blood eosinophil counts and treatment efficacy is biologically obvious given that
IL-5 has a pivotal role in eosinophil production, proliferation and chemotaxis. It is also clinically relevant as the blood eosinophil count is routinely measured and thus readily available in patients with
asthma. Recognition of the link between airway or blood
eosinophilia and treatment response was also important in the clinical testing of the alternative
IL-5 blocker, such as
reslizumab, which is currently being evaluated in a phase III randomized controlled trial (RCT) after having shown to improve lung function, improve symptom score and reduce sputum
eosinophilia in a smaller phase IIb study. In addition,
benralizumab, an IL-5α receptor blocker, has shown good effects in a phase IIb RCT with patients with severe
asthma that had sputum
eosinophilia and more recently in a phase IIa trial with patients with eosinophilic
chronic obstructive pulmonary disease. Therefore anti-IL-5 treatment seems generally effective in eosinophilic
asthma, either assessed by blood or airway
eosinophilia. This factor together with the impressive clinical efficacy and good safety profile make anti-IL-5 (
mepolizumab,
reslizumab) and
benralizumab (anti-IL-5 receptor α) very promising drugs for the treatment of patients with severe eosinophilic
asthma, a subgroup that is in desperate need of better treatments.