A bacterial flagellin in combination with proinflammatory cytokines activates human monocyte-derived dendritic cells to generate cytotoxic T lymphocytes having increased homing signals to cancer.

Flagellin, the cognate ligand for toll-like receptor 5, has potent adjuvant activity in various vaccines. However, its efficacy in generating dendritic cells (DCs) remains contentious. This study assessed how efficaciously Vibrio vulnificus FlaB (v-FlaB) could be used in generating a potent DC to induce antigen-specific cytotoxic T lymphocytes (CTLs). Mature DCs (mDCs) induced by the combination of v-FlaB/TNFα/IFNα were significantly more potent in inducing specific anticancer immune responses compared with the standard DCs that were maturated by the conventional cytokine cocktail of TNFα/IL-1β/IL-6/PGE(2). The potent mDCs produced a higher level of interleukin (IL)-12p70 and polarized naive CD4(+) T cells more towards Th1-type cells, markedly increased antigen-specific CD8(+) T-cell number and significantly enhanced the induction of lytic enzymes in antigen-specific CD8(+) CTLs and sensitized CD3(+) T cells to produce higher number of interferon (IFN)γ-secreting cells. As a result, the mDCs produced more potent antigen-specific CTLs against the MART-1 and expressed higher levels of homing receptors CCR5 and CXCR3. More importantly, the v-FlaB/TNFα/IFNα-DCs generated from melanoma patients produced strong autologous CTLs with efficient cytotoxic activities. In conclusion, v-FlaB combined with tumor necrosis factor (TNF)α and IFNα can generate potent DCs which produce functionally active CTLs and that may have potential as a potent cancer vaccine.