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Mepolizumab provide great clinical benefits for severe eosinophilic asthma (SEA) patients by neutralizing IL-5, but the exact mechanism of this drug is still unclear. We aim to assess if mepolizumab provide its clinical benefits through exerting functional changes on peripheral blood mononuclear cells (PBMCs) and to determine gene profile that is able to predict response to mepolizumab treatment. PBMCs were isolated from healthy control and severe eosinophilic asthma (GINA 5) at different time point of mepolizumab treatment including baseline (visit 1), 16 weeks (visit 2), and 52 weeks (visit 3). Then, PBMCs were activated by either T cell receptor stimulus (aCD3/CD28) or lipopolysaccharide (LPS) in the absence and presence of dexamethasone at different doses (10-10-10-6). With the use of immunoassay techniques, we quantified the basal and induced levels of different TH2 and non-TH2 cytokines. Also, we divided severe eosinophilic asthma subjects into responders and non-responders to mepolizumab based on NICE guidance and RNA samples were isolated and sent for RNA sequencing. We found out that mepolizumab treatment had impacted the production of some cytokines such as IL-17A, GM-CSF, IL-2, and IL-10 after 52 weeks of treatment. In RNA sequencing we show a specific gene expression associated with responders to mepolizumab including that FMN1, THBS1, and TNF. Additionally, gene ontology analysis showed downregulation in protein classes and pathways associated with airway remodelling and airway hyperresponsiveness in responders to mepolizumab. Moreover, we report an upregulation in transcriptional factors that are implicated in regulating inflammatory process. Mepolizumab seems to functionally impact PBMCs by significantly increasing IL-6, IL-10, GM-CSF, and IL-17A and significantly reducing IL-2 following a year of mepolizumab treatment. RNA sequencing revealed possible genes that can predict response to mepolizumab along with a distinct gene profile in responders to mepolizumab that is associated with anti-inflammatory and inflammation regulation processes.