Toll-like receptors in urothelial cells--targets for cancer immunotherapy.

Toll-like receptors (TLRs) have an important role in the activation of both innate and adaptive immunity in response to pathogens and danger signals. These receptors are expressed in immune cells and in some epithelia. They are expressed in the epithelium of the urinary bladder, where they actively participate in the fight against infection by uropathogens. TLR expression is decreased (although still evident) in bladder tumours, especially in non-muscle-invasive tumours. Intravesical immunotherapy with BCG to prevent recurrence of these tumours has been shown to involve the participation of three different TLRs (TLR2, TLR4, and TLR9). However, alternative therapies are needed as BCG fails in some patients and can sometimes cause severe adverse effects that are difficult to tolerate. In recent years, TLR2, TLR4, TLR7, and TLR9 agonists have been tested in vitro and in vivo for their ability to activate an antitumour immune response against bladder cancer. Promising results from these studies have led to the testing of TLR7 and TLR9 agonists in clinical trials.