Targeting of the IL-5 pathway in severe asthma reduces mast cell progenitors.

Background: Therapies targeting interleukin-5 (IL-5) or its receptor (IL-5Rα) are currently used to treat patients with severe eosinophilic asthma.

Objective: To investigate the impact of anti-IL-5 and anti-IL-5Rα biological therapies on mast cells (MCs) and their progenitors.

Methods: Surface IL-5Rα expression was investigated on MCs and their progenitors in mouse lungs and bone marrow, and in human lungs and blood. Isolated human MC progenitors cultured in the presence or absence of IL-5 were analyzed in vitro. Circulating MC progenitors were quantified in patients with severe asthma, before and after anti-IL-5 (mepolizumab) or anti-IL-5Rα (benralizumab) therapy. Gene expression analysis of MC progenitors was performed before and after anti-IL-5Rα therapy.

Results: Approximately 50% of the human primary lung MCs, and 30% of the human MC progenitors from individuals with allergic asthma expressed IL-5Rα. In patients with mild-to-moderate allergic asthma and mice with acute allergic airway inflammation, the fraction of IL-5Rα ⁺ MC progenitors was elevated. Additionally, IL-5 promoted the proliferation and/or survival of isolated human MC progenitors. Further, patients with severe asthma from two independent cohorts demonstrated a reduction of blood MC progenitors after anti-IL-5 or anti-IL-5Rα treatment. This was associated with improved asthma control, as well as a decline in both blood eosinophils and Th2 cells. Finally, the blood MC progenitors remaining after anti-IL-5Rα (benralizumab) treatment exhibited a downregulated expression of genes involved in growth and proliferation.

Conclusion: This study introduces the possibility that the clinical effects of targeting IL-5/IL-5Rα in severe asthma also may involve reduction of MC populations.