Toll-like receptors (TLRs) are a family of ten evolutionarily conserved receptors expressed either on the cell surface or in intracellular endocytic vesicles or organelles, and which collectively recognize a diverse range of microbial ligands. Recognition by TLRs triggers the rapid, orchestrated production of chemokines, cytokines, and other inflammatory mediators that leads to the generation of cellular immune responses.

Activation of the innate immune response in humans is, therefore, regulated in part by TLRs. In addition, increasing evidence supports an added critical role for TLRs in orchestrating the development of adaptive immune responses. Due to their central role in inducing and modulating immune responses, Toll-like receptors have been the focus of drug development in a variety of clinical indications, including oncology, infectious disease, allergy, and as vaccine adjuvants.