Dendritic Cells Can Be Primed to Concurrently Activate Both Unconventional Gamma/delta and Conventional alpha/beta T Cells.

Vgamma9/Vdelta2 (gamma/delta) T cells represent the major subset of unconventional T cells circulating in the peripheral blood. Gamma/delta T cells play a major role in immune defenses against microbes, stressed cells and tumor cells. This property is based on their capability to naturally recognize phosphoantigens (pAgs), which are produced via the mevalonate (Mev) or the DOXP pathway in mammalian and nonmammalian cells, and induced self-ligands, which are de novo expressed or upregulated on the surface of stressed or tumor cells. Interestingly, gamma/delta T cells can also be activated by aminobisphosphonates (ABP)-treated monocytes. We have previously shown that ABP specifically target the Mev pathway of monocytes and induce the accumulation of phosphorylated Mev metabolites naturally recognized by gamma/delta T cells. The aim of this work was to determine whether ABP-treated dendritic cells (DC) can also activate gamma/delta T cells and whether this activation, if any, is detrimental or beneficial to the generation of antigen (Ag)-specific MHC-restricted immune responses mediated by conventional alpha/beta T cells. To this end, we have generated highly purified immature (iDC) and mature DC (mDC) from peripheral blood monocytes of healthy donors and incubated with zoledronic acid (Zol) for 24 hours. Zol is the most potent ABP currently available for clinical use. Zol treatment did not affect the phenotype and immunostimulatory properties of iDC and mDC. Zol-treated iDC and mDC induced a rapid and vigorous expansion of central memory and effector memory gamma/delta T cells. Zol-treated iDC were more potent inducers of gamma/delta T-cell activation than mDC and monocytes. Activated gamma/delta T cells displayed antitumor activity and expressed on the cell surface the appropriate antigen repertoire to target secondary lymphoid organs and exert costimulatory activity on conventional alpha/beta T cells. Indeed, an in vitro model showed that antigen-specific MHC-restricted immune responses againt the influenza matrix peptide were significantly improved by the concurrent activation of gamma/delta T cells. This is the first report showing that: 1) DC can simultaneously be primed to activate both gamma/delta and alpha/beta T cells; 2) the former act as cellular adjuvants for the development of adaptive immune responses. In conclusion, large numbers of gamma/delta T cells with effector and costimulatory activities can rapidly be generated by Zol-treated iDC/mDC. This strategy is worth of further investigation to improve adoptive cell therapy and vaccine interventions against tumors and infections.