It is important to further improve the efficiency of hepatitis B core antigen-pulsed monocyte-derived dendritic cell (core-DC) vaccine in clinical immunotherapy for chronic hepatitis B virus (HBV) infection in humans. Our study shows that CpG-treated plasmacytoid dendritic cells (pDCs) can efficiently promote core-DC terminal maturation and increase interleukin-12 production. These CpG-activated pDCs can act synergistically in vitro with core-DCs in inducing autologous HBV-specific CD8 T-cell proliferation and interferon (IFN)-gamma production. This promotion was mainly dependent on pDC-derived IFN-alpha, because blockade of IFN-alpha nearly completely aborted the effects of pDCs on core-DCs. In addition, the supernatants derived from CpG-treated peripheral blood mononuclear cells can also effectively improve the aforementioned maturation and function of core-DCs. These findings will facilitate a better understanding of how the pDCs regulate myeloid dendritic cell-mediated immune responses, and highlight the notion that manipulating pDCs might have implications in DC vaccine therapy for patients with chronic hepatitis B.