TLR7 in systemic lupus erythematosus: genetics and emerging therapies.

Systemic lupus erythematosus (SLE) is a disease with considerable unmet treatment needs. Endosomal nucleic acid sensing by Toll-like receptor 7 (TLR7) is emerging as a key pathogenic pathway. Gain-of-function mutations in the genes encoding TLR7 and its chaperone UNC93B1 can cause monogenic childhood-onset SLE; rare variants in proteins that regulate ligand availability or downstream signalling proteins also contribute to disease. TLR7 variants can increase the affinity of this receptor for its ligands and can alter binding to endogenous antagonists. Both self RNA-protein complexes and viruses have been implicated in TLR7 activation. Key pathogenic mechanisms include breakdown in B cell tolerance and autoantibody production and type I interferon secretion. Although current therapies such as B cell-depleting chimeric antigen receptor (CAR) T cells and anifrolumab (anti-type I interferon receptor) offer benefit, they are limited by high costs and lack of oral options. In this context, TLR7 has emerged as a promising therapeutic target. Phase II trials of an oral dual TLR7-TLR8 antagonist show durable suppression of the interferon signature in all patients, indicating that TLR7 and TLR8 drive this signature in SLE. This treatment has shown clinical benefit for SLE and cutaneous lupus erythematosus, although the primary endpoint (a dose-response effect) was only met in cutaneous lupus erythematosus. Thus, TLR7-TLR8 antagonists might reshape SLE treatment, alone or in combination with other drugs.