Inhalation of recombinant adenovirus expressing granulysin protects mice infected with Mycobacterium tuberculosis

Granulysin is a cytolytic molecule with perforin and granzymes that is expressed by activated human CTLs, NK and gamma delta T cells, and it has broad antimicrobial activity, including to drug-sensitive and drug-resistant Mycobacterium tuberculosis. We hypothesized that approaches facilitating the expression of granulysin in M. tuberculosis-infected host cells in the lung may provide a novel treatment strategy for pulmonary TB. In this study, a recombinant replication-deficient adenovirus serotype 5-based rAdhGLi was constructed that expressed human granulysin in the cytosol of the U937 and RAW264.7 macrophage-like cell lines as confirmed by western blotting and co-localization technology using indirect immunofluorescence staining. Ninety-six hours after both cell lines were infected with M. tuberculosis, acid-fast staining and enumeration demonstrated that rAdhGLi-treated cells had a lower colonyforming units (CFU) of intracellular bacteria than culture medium or AdNull controls. Granulysin was only expressed in the lung and not in other organs following inhalation of rAdhGLi. In particular, immunocompetent BALB/c mice or SCID mice intranasally infected with similar to 200 CFU of virulent M. tuberculosis H37Rv intranasally were treated with rAdhGLi, and they showed decreased bacterial loads in the lung when compared with phosphate-buffered saline or AdNull controls. Importantly, a clear dose-dependent rAdhGLi treatment efficacy was found in infected BALB/c mice, with the most significant reduction in lung bacteria obtained in BALB/c mice treated with 109 plaque-forming units of rAdhGLi without any pathological changes. Our study indicates that rAdhGLi may be used as a novel and efficient treatment strategy with the capability to directly kill intracellular M. tuberculosis.