Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is one of the most deadly infectious diseases, with approximately two million people dying of TB annually. An effective therapeutic method for activating dendritic cells (DCs) and driving Th1 immune responses would improve host defenses and further the development of a TB vaccine. Given the importance of DC maturation in eliciting protective immunity against TB, we investigated whether Rv0315, a newly identified Mtb antigen, can prompt DC maturation. We found that Rv0315 functionally activated DCs by augmenting the expression of the co-stimulatory molecules CD80 and CD86 as well as MHC class I/II molecules. Moreover, it increased DC secretion of the pro-inflammatory cytokines IL-6, IL-1β, and TNF-α. Unlike LPS, however, Rv0315 induced the secretion of IL-12p70, but not IL-10. In addition, Rv0315-treated DCs accelerated the proliferation of CD4(+) and CD8(+) splenic T cells from Mtb-infected mice, with increased levels of IFN-γ, in syngeneic and allogeneic mixed lymphocyte reactions, indicating that Rv0315 contributes to Th1 polarization of the immune response. Importantly, both mitogen-activated protein kinases and nuclear factor κB signaling mediated the expression of DC surface markers and cytokines. Taken together, our results indicate that Rv0315 is a novel DC maturation-inducing antigen that drives T cell immune responses toward Th1 polarization, suggesting that Rv0315 plays a key role in determining the nature of the immune response to TB.

Effective activation of dendritic cells (DCs) toward T helper (Th)-1 cell polarization would improve DC-based antitumor immunotherapy, helping promote the development of immunotherapeutic vaccines based on T-cell immunity. To achieve this goal, it is essential to develop effective immune adjuvants that can induce powerful Th1 cell immune responses. The pathogenic organism Mycobacterium tuberculosis includes certain constitutes, such as heparin-binding hemagglutinin (HBHA), that possess a strong immunostimulatory potential. In this study, we report the first clarification of the functions and precise mechanism of HBHA in immune stimulation settings relevant to cancer. HBHA induced DC maturation in a TLR4-dependent manner, elevating expression of the surface molecules CD40, CD80, and CD86, MHC classes I and II and the proinflammatory cytokines IL-6, IL-12, IL-1β, TNF-α, and CCR7, as well as stimulating the migratory capacity of DCs in vitro and in vivo. Mechanistic investigations established that MyD88 and TRIF signaling pathways downstream of TLR4 mediated secretion of HBHA-induced proinflammatory cytokines. HBHA-treated DCs activated naïve T cells, polarized CD4(+) and CD8(+) T cells to secrete IFN-γ, and induced T-cell-mediated cytotoxicity. Notably, systemic administration of DCs that were HBHA-treated and OVA(251-264)-pulsed ex vivo greatly strengthened immune priming in vivo, inducing a dramatic regression of tumor growth associated with long-term survival in a murine E.G7 thymoma model. Together, our findings highlight HBHA as an immune adjuvant that favors Th1 polarization and DC function for potential applications in DC-based antitumor immunotherapy.