Mepolizumab depleted eosinophils exhibit reduced transmigratory capacity.

Severe eosinophilic asthma (SEA) is associated with high blood eosinophil counts and high serum levels of the cytokine IL-5, involved in the maturation and activation of eosinophils. During inflammation, blood eosinophils tether to the endothelium resulting in extravasation mediated by integrins. The biology of blood eosinophils following Mepolizumab (anti-IL5 therapy) mediated depletion is unexplored. <bold>Aim:</bold> Determine adhesion characteristics of eosinophils from SE asthmatics established on the Mepolizumab (n=8) and SE asthmatics not receiving Mepolizumab (n=8). Eosinophils were isolated from whole blood via Percoll gradient and magnetic negative selection. Cell-adhesion was determined using the O-phenylenediamine dihydrochloride assay. Cell surface markers associated with eosinophil attachment, extravasation and activation were determined by flow cytometry. Migration assays were performed using a Boyden-chamber with eotaxin as a chemoattractant. SEA eosinophils show regular smooth cell membranes, in contrast, eosinophils from Mepolizumab patients show membrane irregularity and are smaller. Population of cells expressing IL-5α and IL-3 receptors are significantly reduced in Mepolizumab SEA (p<0.001 and p=0.006). CD62L/L-Selectin (p=0.001), HCAM (p=0.008) and ICAM (p=0.05) expressing population was reduced in Mepolizumab SEA eosinophils. Eosinophils from Mepolizumab patients display a significantly lower adhesion (p<0.001) and migratory capacity (p=0.004). These data suggest the remaining blood eosinophils in patients responding to mepolizumab therapy likely have a reduced activation and implied ability to transmigrate into the lung parenchyma. This supported study is funded by GSK (SCS <ext-link>NCT04463836</ext-link>).