Toll-like receptor 7 and 8 (TLR7/8)

Class

Small-molecule dual TLR7/8 agonist

Pathway

innate immune activation (pDC/NK cells) plus adaptive myeloid/mDC priming of tumor-specific T cells

Toll-like receptors 7 and 8 (TLR7/8) are innate immune sensors that normally detect single-stranded RNA, such as viral genetic material, from within endosomal compartments inside certain immune cells. TLR7 is expressed predominantly on plasmacytoid dendritic cells (pDCs) and B cells, while TLR8 is found mainly on monocytes, macrophages, and myeloid dendritic cells (mDCs). A small molecule that activates both receptors simultaneously can therefore engage two complementary arms of innate immunity: TLR7 signaling drives pDCs to secrete large amounts of type I interferon and activate natural killer (NK) cells, while TLR8 signaling activates myeloid cells to mature and present antigens more effectively to T cells. Combining both signals is intended to convert a locally or systemically "unengaged" immune environment into one primed for anti-tumor or anti-pathogen responses, coupling immediate innate activation with longer-term priming of antigen-specific T cells. This dual mechanism is broadly relevant in oncology, where tumors often evade immune detection by keeping innate sensors quiescent, and in contexts requiring vaccine adjuvants that need to stimulate durable, antigen-specific immunity rather than transient inflammation alone.