A single-center observational study assessing response to mepolizumab in severe eosinophilic asthma

<b>Background:</b> Mepolizumab reduces blood and sputum eosinophils and can reduce exacerbations in severe eosinophilic asthma (SEA). However only 50% of prednisolone-dependent SEA patients are able to reduce their maintenance prednisolone. <b>Method:</b> We measured sputum and blood eosinophil counts and asthma control test (ACT) in 6 SEA patients on monthly Mepolizumab injection at baseline, 3, 6 and 12month of treatment. Suboptimal treatment responsiveness is defined as sputum eosinophil counts &gt; 3% after 4 months of treatment and at least one of the following: (1) ACT score &lt; 20 2) reduction in prednisolone dosage by &lt;50% 3) ≥1 exacerbation requiring prednisolone burst. <b>Results:</b> Four out of the 6 SEA patients are prednisolone-dependent (medium dose 5mg daily); the remaining 2 are on fluticasone &gt; 500mcg daily. Good treatment response was present in 3 patients and only 1 was prednisolone-dependent (table 1). Though they were able to reduce exacerbations by 66-83%, their maintenance prednisolone dose was reduced by only 0-33%. Sputum lymphocyte differential count increased in all 6 patients despite the decrease in blood and sputum eosinophil counts (Table 1). In patients with suboptimal response, their sputum showed an increase in total IgG, IgG2, anti-eosinophil peroxidase and anti-nuclear antibody, suggesting the development of an autoimmune response in severe prednisolone-dependent patients hindering treatment response.