TLR3 agonists and proinflammatory antitumor activities

Although tumor growth leads to inflammatory responses, the immune system develops tolerance to cancer. One way to break host tolerance to tumors is to activate key immune effector activities. Toward this end, various adjuvants are under investigation in an effort to harness the immune system to overcome tolerance to tumor-associated self-antigens. There is enthusiasm for the use of specific ligands for toll-like receptor 3 (TLR3) that play a key role in the innate immune system. TLR3 agonists serve as immune adjuvants because they potently induce innate immune responses by activating dendritic cell ( DC) maturation and inflammatory cytokine secretion. These activities facilitate the bridge between the innate and adaptive immune systems promoting the expansion of cytotoxic T lymphocytes (CTL) that destroy cancer cells. TLR3 agonists either alone or in combination with tumor antigens have shown success in terms of enhancing immune responses and eliciting antitumor activity in preclinical models. However, TLR3 agonists can also impact regulatory cells that dampen immune responses. Thus, immune strategies that utilize TLR3 agonists should consider the relative induction of suppressive as well as beneficial antitumor immune activities. Herein, we summarize the TLR3 agonists that will hopefully come to clinical fruition.