Combined TLR and CD40 triggering induces potent CD8+ T cell expansion with variable dependence on type I IFN

Toll-like receptors are important in the activation of innate immunity, and CD40 is a molecule critical for many T and B cell responses. Whereas agonists for either pathway have been used as vaccine adjuvants, we show that a combination of Toll-like receptor (TLR)7 and CD40 agonists synergize to stimulate CD8(+) T cell responses 10-20-fold greater than the use of either agonist alone. Antigen-specific CD8+ T cells elicited from combination CD40/TLR,7 treatment demonstrated both lyric activities and interferon (IFN)gamma production and an enhanced secondary response to antigenic challenge. Agonists for TLRs 2/6, 3, 4, and 9 also synergized with CD40 stimulation, demonstrating that synergy with the CD40 pathway is a property of TLR,-derived stimuli in general. The CD8(+) T cell expansion induced by CD40/TLR7 triggering was independent of CD4(+) T cells, IFNgamma, and IL-12 but dependent on B7-mediated costimulation and surprisingly on type 1 IFN. These studies provide the rational basis for the use of TLR, and CD40 agonists together as essential adjuvants to optimize vaccines designed to elicit protective or therapeutic immunity.