VentiRx Pharmaceuticals has developed a series of small molecule agonists for TLR8 as well as dual TLR8/7 agonists. The natural ligand for TLR7 and TLR8 is single stranded RNA, hence these receptors play an important role in triggering immune responses to viral infections. TLR7 and TLR8 are structurally similar TLRs, but are expressed on different cell populations. TLR8 is expressed by and appears to function on monocytes, macrophages, and myeloid dendritic cells (mDCs). In contrast, TLR7 is expressed by a restricted population of cells in the blood referred to as plasmacytoid dendritic cells (pDCs).

In addition to the distinct distribution patterns, functional differences have been described for TLR7 and TLR8. TLR7 selective agonists are more potent than TLR8 agonists in eliciting IFNα and IFN-regulated chemokines such as IFN-inducible protein. In contrast, TLR8 agonists are more effective in inducing inflammatory cytokines and chemokines, including TNFα, IL-12,
IL-1Β and MIP-1α.