For a study, the researchers sought to determine if leukocyte redistribution might have been used as a biomarker of disease heterogeneity and a bioindicator of possible corticosteroids (CS) resistance in individuals with severe asthma. They devised an unbiased clustering approach based on clinical data and flow cytometry results of peripheral blood leukocyte morphologies of 142 patients with severe asthma before and after systemic CS treatment. Investigators identified 2 extreme asthma clusters, which differed in cell frequencies, response to CS, and atopy status, based on differences in blood count eosinophils, neutrophils, and lymphocytes, as well as flow cytometry measurements of primary T cell, B cell, and NK cell subpopulations before and after systemic CS administration. Cluster 1 patients had a greater baseline frequency of blood eosinophils, were less sensitive to allergens, and had improved steroid response, as judged by significant leukocyte redistribution after systemic CS treatment. Cluster 2 patients had a more significant B-cell frequency and a more substantial IgE sensitivity status to several allergens. They also had stronger steroid resistance, which was correlated with the reduced leukocyte redistribution following systemic CS treatment. Flow cytometry-based profiling of the fundamental populations of immune cells in the blood and its characterization before and after systemic corticosteroid administration should have helped patients with severe asthma receive more customized treatment.