The majority of severe exacerbations of asthma and need for hospitalizations are triggered by infection with respiratory viruses. Of these, rhinovirus is the most commonly implicated virus. Furthermore, there is evidence that viral infections exert synergistic effects with other stimuli to provoke asthma symptoms such as exposure to allergens and air pollutants. Experimental HRV infection studies have yielded important insights into the underlying disease mechanisms of viral-induced asthma exacerbations, and have been integral to identifying candidates for the development of new therapies. These studies have been safely conducted in both healthy and susceptible populations (those with underlying airway disease such as asthma and chronic obstructive pulmonary disease (COPD)), for more than 60 years.
Much of the understanding of the clinical course of HRV infection is derived from experimental infections of healthy human volunteers. In these studies, subjects were inoculated intranasally with up to 10,000 \[tissue culture infectious dose (TCID)\] TCID50 of HRV, the most commonly used strains being HRV-16 and HRV-39. Experimental HRV infection produces the hallmark clinical features of the common cold including rhinorrhea and nasal obstruction. Respiratory symptoms typically develop 1-2 days after inoculation. Cold symptom scores generally peak 2-4 days post infection and return to baseline within 1 week in most infected subjects. HRV infection induces changes in inflammatory cell recruitment, nasal cytokine levels, and gene expression, which occur concurrently with clinical symptoms.
While the symptoms of HRV infection are typically limited to the upper respiratory tract in healthy subjects, those with underlying airway disease such asthma and COPD are more likely to exhibit an augmented and prolonged response to HRV infection with lower airway involvement. HRV is the leading viral cause of exacerbations of asthma and COPD; therefore, the response of these populations to HRV infection has been the focus of a number of studies. Although most studies in asthmatics have been performed in inhaled corticosteroid-naïve subjects, a recent study performed in subjects whose asthma was well controlled with inhaled corticosteroids demonstrates the safety of experimental HRV infection in this population. This model has also been employed in conjunction with other exposure models such as allergen challenge and pollutant exposure. There are several ongoing and recently completed clinical trials registered with ClinicalTrials.gov that utilize the HRV infection model. Of these, several employ the HRV-16 strain (ClinicalTrials.gov Identifiers: NCT01769573, NCT01466738, NCT01823640, NCT03073837, NCT03296917, NCT01704040, NCT02910401) being used in this study. Both healthy and asthmatic volunteers are represented in these clinical trials.
In summary, the experimental HRV infection model has proven to be a safe and valuable tool for examining various aspects of HRV biology. Due to the limitations associated with animal models of asthma and COPD, and the lack of animal species that are permissive for HRVs, experimental infection of humans with HRV has been integral for examining the pathophysiology of virus-induced exacerbations of asthma and COPD. Although experimental HRV-infection results in a reduction in lung function for some asthmatics and COPD patients, no serious adverse events have been reported using this model.
The goal of this study is to establish the experimental HRV-infection model in this research center using a viral inoculum referred to as RG-HRV-16. This strain was used in a recently-completed safety and dosing study (NCT01769573). Our study would provide the pilot data needed for the design of subsequent studies evaluating innate immune responses to HRV infection in asthmatics, modulation of HRV-induced responses by inhaled pollutants, and efficacy of novel therapeutic agents.
