Pilot study of the safety and effect of intranasal delipidated acid-treated Mycobacterium vaccae in adult asthma.

Objective: There is epidemiological and experimental evidence that exposure to mycobacteria has the potential to suppress the development of atopy and/or asthma. Delipidated, deglycolipidated and arabinogalactan-depleted autoclaved Mycobacterium vaccae (delipidated acid-treated M. vaccae) has been shown to suppress allergen-induced airway eosinophilia in mice.

Methodology: Thirty-seven adults with stable moderately severe asthma who were skin prick test-positive to house dust mite were randomized to receive two doses 2 weeks apart of delipidated acid-treated M. vaccae (first dose 0.4 mg and second dose 0.8 mg) or phosphate buffered saline, given as drops intranasally. Safety, tolerability and markers of asthma severity (including peak flow, FEV1, major and minor exacerbations, symptom scores and beta-agonist use), and nasal symptom scores, blood eosinophil and IgE levels were monitored for 8 weeks.

Results: Delipidated acid-treated M. vaccae was safe and well tolerated although there was an occasional mild local reaction. There were no statistically significant differences between the treatment group and placebo for any of the outcome variables.

Conclusions: There is a requirement to elucidate the reasons why mycobacterial-based vaccines have not shown equivalent efficacy in human trials compared with animal models. The role of factors such as duration of disease, route of administration and the active component of mycobacteria need to be addressed.