Enhanced protection against pulmonary mycobacterial challenge by chitosan-formulated polyepitope gene vaccine is associated with increased pulmonary secretory IgA and gamma-interferon plus T cell responses

Induction of local (pulmonary) immunity plays a critical role in preventing dissemination of Mycobacterium tuberculosis (M. tb) during the early infection stage. To induce specific mucosal immunity, chitosan, a natural cationic polysaccharide, was employed as a mucosal gene carrier and complexed with pHSP65pep, our previously constructed multi-epitope gene vaccine, which induces splenic gamma-interferon (IFN-)+ T helper cell 1 responses. The resultant chitosanpHSP65pep was administered intranasally to BALB/c mice with four doses of 50g DNA followed by mycobacterial challenge 4 weeks after the final immunization. It was found that the chitosan formulation significantly induced production of secretory immunoglobulin A (P<0.05) as determined by measuring its concentrations in lung lavage fluid and enhanced pulmonary CD4+ and CD8+IFN-+ T cell responses (P<0.001) compared with naked gene vaccine. Improved protection against Mycobacterium bovis bacillus CalmetteGuerin (BCG) challenge was consistently achieved by the chitosanDNA formulation both as the vaccine alone or in a BCG prime-vaccine boost immunization scenario. Our study shows that mucosal delivery of gene vaccine in a chitosan formulation remarkably enhances specific SIgA concentrations and mucosal IFN-+ T cell response, which correlated positively with immunological protection.