TLR9 and head and neck squamous cell carcinoma: Here, we perform a meta-analysis of clinical trials of TLR agonists in HNSCC, including motolimod (TLR8 agonist), SD-101 (TLR9 agonist), IMO-2055 (TLR9 agonist), and EMD 1201081 (TLR9 agonist).