Project description:Patients with severe uncontrolled asthma represent a distinct endotype with persistent airway inflammation and remodeling refractory to corticosteroid treatment. CD4+ T cells and their canonical effector molecules, like type 2 cytokines, play a central role in orchestrating asthma pathogenesis, and biologic therapies targeting these cytokine pathways have had promising outcomes. However, not all patients respond well to such treatment, and their effects are not always durable nor reverse airway remodeling. This observation raises the possibility that other CD4+ T cell subsets and their effector molecules may drive airway inflammation and remodeling. To address this issue in a hypothesis-free manner, we performed single-cell transcriptome analysis of >50,000 airway CD4+ T cells isolated from bronchoalveolar lavage (BAL) samples from 30 patients with mild and severe asthma. We observed striking heterogeneity in the nature of CD4+ T cells present in asthmatics' airways with tissue-resident memory (TRM) cells making a dominant contribution. Notably, a subset of CD4+ TRM cells (CD103-expressing) was significantly increased, comprising nearly 65% of all CD4+ T cells in the airways of male patients with severe asthma when compared to mild asthma. This subset was enriched for transcripts linked to T cell receptor (TCR) activation (HLA-DRB1, HLA-DPA1, CD40LG) and cytotoxicity (GZMB, GZMH), and following stimulation expressed high levels of transcripts encoding for pro-inflammatory non-TH2 cytokines (CCL3, CCL4, CCL5, TNF, IL-17A, CSF2, LIGHT) that could fuel persistent airway inflammation and remodeling. Furthermore, we found that CD4+ T cells isolated ex vivo from airways of severe asthmatics displayed signatures linked to corticosteroid resistance (FKBP5, DDIT4), as well as reduced expression of transcripts encoding for molecules that dampen TCR signaling and T cell effector functions (CREM, DUSP1, TNFAIP3). Overall, our single-cell transcriptomic analysis highlights the pathogenic properties and clinical associations of airway CD4+ T cell subsets in severe asthmatics, features that can potentially trigger their unrestrained activation, and that these findings were more pronounced in males. These pathways may therefore be crucial for driving disease severity in adult male severe asthmatics.

Project description:Asthma is a progressive inflammatory airways disease that leads to structural airway changes and debilitating symptoms in many severely affected adults. We need novel therapeutic agents that are affordable, can decrease the reliance on steroids, and can improve quality of life. This clinical and mechanistic study has the potential to impact treatment of a subset of adult severe asthmatics and to further our understanding of the mechanisms of L-arginine metabolism and NO biology in the airways of asthmatics. We will pursue a clinical trial in subjects not well controlled on standard drug therapy; this strategy will address whether L-arginine is efficacious in patients receiving standard of care medications. In studies using animal models, we and others have shown that interventions that augment NO levels, through either supplementation of L-arginine or inhibition of arginase, decrease allergic airway inflammation and hyperresponsiveness-the two hallmarks of asthma. Overall, we hypothesize that a responder subset of adult severe asthma patients will derive clinical benefit from supplemental L-arginine therapy and that these patients will have a lower exhaled NO concentrations (<20 ppb) and a higher NOS2/Arg1 mRNA and protein ratio in their airway epithelial cells than non-responders. We aim to: 1) test the hypothesis that uncontrolled, adult severe asthma patients with exhaled breath NO concentrations <20 ppb will have fewer asthma exacerbations over 3 months when treated with L-arginine compared to patients with FeNO > 25, 2) determine the mechanisms by which L-arginine affects the regulation of NOS and arginase enzymes in primary airway epithelial cell cultures from severe asthmatic subjects, and 3) test the hypothesis that inhaled nanoparticle carrier formulations of L-arginine will decrease airway inflammation, airway hyperresponsiveness, and airway fibrosis at lower doses than systemically administered L-arginine. The major impact of our study will be to identify the adult severe asthma cohort that will benefit from supplemental L-arginine therapy. Our ultimate goal is to develop novel therapeutic agents to treat adult severe asthma patients better. PUBLIC HEALTH RELEVANCE: Asthma is a progressive inflammatory airways disease that leads to structural airway changes and debilitating symptoms in many severely affected adults. This clinical study has the potential to improve the care of adult severe asthmatics and to further our understanding of the mechanisms of L-arginine metabolism and nitric oxide biology in the lung. If we demonstrate that L-arginine supplementation can decrease asthma attacks in a subset of severe asthmatics, it will have great implications for future research as well as for the daily lives of patients with asthma.

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Cytotoxic CD4+ tissue-resident memory T cells are associated with asthma severity [single-cell RNA-seq]

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