Improving the Effectiveness of Adjuvants: Targeting Innate Immune Receptors with a Special Focus on Toll-like Receptor Agonists

The development of potent and safe adjuvants for generating vaccines capable of inducing protective and long lasting immunity has become an expanding field in vaccine development. At the same time، the discovery of toll-like receptors (TLRs) and other innate immune receptors، which can bridge the innate immune responses and adaptive immunity، is offering unexampled opportunities for using the agonists of these receptors for developing novel adjuvants. TLRs are among the most important receptors that have been studied for identifying and using of their agonists to induce innate immune responses. TLRs agonists are being employed for the treatment of cancer، allergies and viral infections، and as adjuvants for vaccine improvement to prevent or treat cancer and infectious diseases. Here we review approaches to the discovery and development of immunostimulatory compounds and vaccine formulations that target the innate immune responses. After introducing TLRs biology and their involvement in immune activation، the use of their agonists as adjuvants is discussed.