To better understand how innate and adaptive immune responses interact with each other, we combined 4-1BB T cell costimulation with specific adjuvants to determine whether these treatments would influence specific T cell expansion and functionin vivo. In the presence of 4-1BB ligation and Toll-like receptor 3 (TLR)3 and/or TLR4 triggering, CD8 T cell clonal expansion and survival was augmented profoundly. Specific T cells primedin vivowith TLR ligands responded normally toin vitrorecall stimulus, but, surprisingly, copriming with 4-1BB costimulation significantly impaired the recall response even though many more specific effector T cells were rescuedin vivo. Here, we demonstrate that the rescued CD8 T cells suppressed CD4 T cell proliferation via a type β transforming growth factor-dependent mechanism. Thus, 4-1BB and TLR ligands induce survival of specific effector CD8 T cells with suppressive recall potential, which may explain the dual role that 4-1BB activation plays in mediating tumor clearance and prevention of autoimmune disease.
