IFN-beta improves BCG immunogenicity by acting on DC maturation

Given the variable protective efficacy provided by Mycobacterium bovis bacillus Calmette-Guérin (BCG), there is an urgent need to develop new vaccines against tuberculosis. As dendritic cells (DC) play a critical role in initiating and regulating a protective T cell response against the pathogens, the comprehension of mycobacterium-induced modulation of DC functions is critical to pinpoint new, immunological strategies. To this end, a comparative analysis of the effect induced by BCG and Mycobacterium tuberculosis (Mtb) infection on the DC immunophenotype indicated that BCG is less efficient in inducing DC maturation than Mtb. In addition, BCG-infected DC poorly expressed IFN-beta and displayed a reduced production of IL-12 as compared with Mtb-stimulated cells. The impaired expression of IL-12p35 and IFN-beta is likely a result of the inability of BCG to induce the activation of the IFN regulatory factor-3. Taking into account these data, we sought to investigate whether the exogenous addition of IFN-beta, a cytokine that exerts important effects on the immune system, could enhance the Th1-polarizing capacity of BCG-infected DC. Interestingly, when DC infected by BCG were pretreated in vitro with IFN-beta, they displayed a fully mature phenotype and released a significant amount of bioactive IL-12p70, which resulted in an enhanced Th1 response. This study demonstrates that IFN-beta potentiates DC immunological functions following BCG infection, thus suggesting IFN-beta as a possible candidate as vaccine adjuvant.