FIGURE 3.

Different Tasks of Preventive Versus Therapeutic Vaccines. Therapeutic vaccines need to function despite tumor-induced dysfunction of endogenous dendritic cells (DCs) and in the presence of tumor-induced suppressive cells such as regulatory T cells (T_reg). Their roles go beyond the induction of long-lived memory cells, because cancer is a poor source of proinflammatory alarm signals capable of inducing effector functions and peripheral homing potential in antigen (Ag)-specific T cells. The effectiveness of therapeutic vaccines may require the provision of such signals by the vaccines themselves or by additional factors used in combination with the vaccines. Some tumors show limited production of the chemokines capable of attracting effector cells (cytotoxic T lymphocytes [CTLs], T helper-1 [Th1-], and natural killer [NK] cells), and rather produce T_reg-attracting chemokines. Effective immunotherapies for cancer may benefit from the combination of vaccines with additional modulation of the production of the effector cell-attracting versus T_reg-attracting chemokines within tumor tissues.