Introduction
Airflow limitation represents one of the most important and treatable characteristics in asthma. Together with other traits such as inflammation, the level of airflow limitation triggers the risk of asthma attack (Pavord et al., 2018). Airflow limitation is mainly due to repeated contraction of airway smooth muscle (ASM), inflammatory oedema of the airway wall and intraluminal factors (Pavord et al., 2018). Airway hyperresponsiveness (AHR) is a central abnormality in patients with asthma that induces enhanced sensitivity to a wide variety of stimuli, leading to an increased narrowing of the airways in vivo (Rabe, 1998).
In the recent years passive sensitization, a validated procedure that reproduces ex vivo the AHR typical of asthmatic airways in vivo (Mitchell et al., 1997; Rabe, 1998; Schaafsma et al., 2006; Schmidt et al., 1999), has been extensively applied to pharmacologically characterize the impact of several medications recommended in Step 1 – 4 therapy of asthma (Calzetta et al., 2018b; Cazzola et al., 2016b; Rogliani et al., 2020). Interestingly, passive sensitization has been used also to assess the effect of omalizumab, a monoclonal antibody (mAb) recommended in Step 5 therapy of asthma, on the contractile tone of human hyperresponsive isolated bronchi (Berger et al., 2007). Interleukin-5 (IL-5) plays a pivotal role in modulating AHR in vivo in animal models of airway sensitization and asthma (Hamelmann et al., 1997; Leckie et al., 2000), and passive sensitization of ASM cells elicits sequential autocrine and paracrine release of IL-5 resulting in altered contractility (Damera et al., 2011; Gounni et al., 2005).
Benralizumab, a humanized anti-IL-5 receptor α (IL-5Rα) mAb, blocks IL-5 signaling and hence type-2 inflammation while inducing antibody-dependent cell-mediated cytotoxicity (ADCC) of eosinophils and basophils (European Medicines Agency, 2018; US Food and Drug Administration, 2017). On the other hand mepolizumab, a humanized anti-IL-5 mAb that prevents IL-5 from binding its receptor on the surface of eosinophils and basophils, modulates type-2 inflammation occurring in approximately 50% of patients with asthma (European Medicines Agency, 2015; Farne et al., 2017; US Food and Drug Administration, 2015). The treatments with benralizumab and mepolizumab are recommended in Step 5 therapy of asthma and have been shown to induce clinical improvement in patients suffering from severe eosinophilic disease (Bleecker et al., 2016; FitzGerald et al., 2016; Nair et al., 2017; Ortega et al., 2014).
Indeed, robust evidence generated by clinical trials consistently indicated that benralizumab (Bleecker et al., 2016; FitzGerald et al., 2016) is effective in improving lung function expressed as forced expiratory volume in 1st second (FEV1). Conversely, conflicting data are available with respect to the impact of mepolizumab on lung function, with some studies reporting no effect on FEV1 (Flood-Page et al., 2007; Haldar et al., 2009) and others showing some improvement in FEV1 (Ortega et al., 2014; Pavord et al., 2012) that however was generally smaller than that induced by benralizumab (Bleecker et al., 2016; FitzGerald et al., 2016). A greater numerical effect of benralizumab compared to mepolizumab on FEV1was reported also by a Cochrane analysis (Farne et al., 2017).
Beyond the effect of anti-IL-5 and anti-IL-5Rα mAbs on lung function, although it is recognized that IL-5 itself may modulate AHR, further inconsistent data are currently available also concerning the real efficacy of targeting IL-5 pathway in preventing AHR, at least in animal models of asthma. In this respect, while some studies indicated that acting on IL-5 pathway may inhibit AHR (Mauser et al., 1995; Nag et al., 2003; Shardonofsky et al., 1999), others failed to report any effect on abnormal ASM contractility (Eum et al., 2005; Mathur et al., 1999; Tanaka et al., 1998).
In this scenario the difference between targeting IL-5 or IL-5Rα in modulating AHR remains to be fully established. Therefore, also considering that unlike omalizumab (Berger et al., 2007) neither benralizumab nor mepolizumab have been pharmacologically characterized in human hyperresponsive airways, the aim of this study was to compare the efficacy and potency of benralizumab and mepolizumab in passively sensitized human airways, and to identify whether acting on the IL-5/IL-5Rα axis may protect against AHR by increasing the tissue synthesis of cyclic adenosine monophosphate (cAMP).