Abstract :
[en] Eosinophils are key suspects in the pathogenesis of various type 2 immune disorders. Particularly in type 2 asthma, eosinophils contribute to airway inflammation, bronchial hyperresponsiveness, and tissue remodeling. Interleukin (IL)-5 is a cytokine central for promoting the accumulation of eosinophils in blood and tissues, a condition known as eosinophilia. Consequently, precision therapies targeting IL-5 or its receptor have been developed for treating eosinophil-associated diseases. Despite the widespread use of these anti-eosinophil therapies, the exact influence of IL-5 on eosinophils remains incompletely understood. Notably, while anti-IL-5 neutralizing antibodies effectively alleviate eosinophilia, they leave a residual population of eosinophils. It is not yet clear whether these residual, IL-5-deprived eosinophils exhibit different biological activities compared to eosinophils at homeostasis.
In this study, we aimed to investigate the influence of IL-5, or its depletion, on the development of eosinophils in the steady-state and in contexts of eosinophilia in murine models and in patients receiving anti-IL-5 therapy.
In a first study, we combined single-cell proteomics and transcriptomics in humans and mice, generated transgenic IL-5 receptor alpha (Il5ra) reporter mice, and used IL-5 deficient mice as well as mice treated with anti-IL-5 neutralizing antibodies to assess the impact of IL-5 on eosinophilopoiesis. In doing so, we developed an easily transferable toolbox to study human and murine eosinophilopoiesis, which includes thoroughly defined cell surface immunophenotypes and transcriptomes at different stages along the continuum of eosinophil maturation in human and murine bone marrow.
In this same study, we observed that eosinophil lineage expansion during eosinophilia relied on IL-5-dependent transit amplification driven by increased cell cycling activity, prolonged proliferation, and delayed maturation of eosinophil progenitors. On the other hand, deletion or neutralization of IL-5 downregulated eosinophil transit amplification but did not impair their maturation. Additionally, by using our Il5ra reporter mouse strain, we found that Il5ra was only expressed after eosinophil lineage commitment in mice. In human in contrast, IL5RA was already expressed in eosinophil/basophil progenitors, which likely explains the impact of anti-IL-5 and anti- IL5RA biologicals on both lineages in patients.
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In a second study, we assessed the consequences of IL-5 depletion on residual eosinophils. To do so, we compared the transcriptomes of eosinophils arising in IL-5- depleted or IL-5-replete human or murine hosts. In humans, we compared blood eosinophils from patients with severe allergic eosinophilic asthma treated with anti-IL- 5 mepolizumab therapy to those of healthy controls and matched asthma patients receiving anti-IgE omalizumab therapy. In mice, we compared bone marrow eosinophils from mice genetically deficient or sufficient for IL-5.
We observed that the neutralization or complete absence of IL-5 did not cause any detectable transcriptional response in steady state residual eosinophils in mepolizumab-treated patients or IL-5 deficient mice. Likewise, the neutralization or absence of lL-5 influenced only a handful of genes in the response of eosinophil to the alarmin cytokine IL-33 ex vivo. These results indicate that the restriction of IL-5 has no detectable impact on the gene expression programme of steady-state eosinophils, and only minimally influences their response to activation. From a clinical perspective, these findings suggest that treatment with IL-5-neutralising antibodies spares a pool of circulating residual eosinophils resembling those of healthy individuals.
Collectively, our findings support the notion that the major effect of IL-5 on eosinophilopoiesis is promoting eosinophil expansion rather than in influencing their differentiation, maturation, or subsequent response to activation.
In conclusion, this work provides resources, methods and insights for understanding eosinophil ontogeny, the regulation of eosinophil development and numbers in health and disease, as well as the effects of currently used precision therapeutics for severe type 2 asthma.
