S92 Proteomic and transcriptomic analysis of residual steroid-responsive inflammation in mepolizumab treated patients

<h3>Background</h3> Mepolizumab is an anti-interleukin-5 monoclonal antibody for severe eosinophilic asthma (SEA). The additional effects of prednisolone to mepolizumab, on molecular mechanisms in the airways and blood are poorly understood. <h3>Aim</h3> Determine the transcriptomic and proteomic effects of prednisolone versus placebo on the airways and blood in patients with SEA treated with mepolizumab. <h3>Methods</h3> MAPLE was a randomized, double-blind, placebo-controlled crossover trial of prednisolone at stable state in adults with SEA after mepolizumab (Yang F, JACI Pract 2022;10:2925–34.e12). Prednisolone had a minor effect on FEV₁ but not on symptoms. Sputum and blood samples were taken before and after high dose prednisolone and placebo in patients treated with mepolizumab. These underwent O-link expression analysis of 1536 proteins. A paired comparison of normalised protein expression for 1536 proteins in sputum and serum were compared in a linear mixed effects model, with Benjamini-Hochberg correction for multiple testing. Nasal scrape samples were taken for transcriptomic analysis after prednisolone and placebo in patients treated with mepolizumab. RNA was extracted (Qiagen) and good quality samples sequenced (Illumina Novaseq). We identified differentially expressed genes with paired t-tests with Benjamini-Hochberg correction for multiple testing. <h3>Results</h3> 21 participants had paired serum, and 14 had paired sputum, before and after both prednisolone and placebo. Prednisolone significantly downregulated 173 and 229 proteins and upregulated 63 and 140 proteins in sputum and serum respectively. Downregulated proteins in sputum included IL-4, IL-5, IL-13, chemokines, and signatures of mast cells, prostaglandin synthesis, and alternatively activated macrophages. Up-regulated proteins included FKBP5, typical of steroid treatment. 6 people had paired nasal epithelial samples comparing prednisolone to placebo. 28 genes were down-regulated by prednisolone included leukocyte chemotaxis, mast cell tryptase and the 15-lipoxygenase pathway. <h3>Conclusions</h3> Prednisolone in addition to mepolizumab suppresses type-2 pathways unaffected by IL-5 inhibition in the sputum and blood proteome, and nasal transcriptome. These findings support the notion that the type-2 airway epithelium remains active in mepolizumab-treated patients. The relationship of these additional effects to longer term clinical outcome is unknown. Please refer to page A286 for declarations of interest related to this abstract.