Focus on TILs: Prognostic significance of tumor infiltrating lymphocytes in human bladder cancer.

The idea of generating cytotoxic T-lymphocytes that have anti-tumor activity has been the focus of many clinical trials aimed at delivering effective immunotherapy to cancer patients. We have gained insight into the human immune system in cancer patients as a result of these numerous clinical investigations. It is now clear that although various vaccination methods are capable of inducing tumor antigen-specific T-cells in the circulating blood, these immunological responses are infrequently correlated with clinical responses. Therefore, it appears that priming of a T-cell response is not sufficient for tumor regression and other avenues, downstream of the priming phase, need to be investigated. Mechanisms of immune evasion at the effector phase of the anti-tumor phase are currently under investigation, with an increasing focus on the tumor microenvironment. There is evidence indicating that multiple variables may contribute to immune escape, including: regulatory cells; inhibitory ligands on tumor cells, such as PD-L1 and B7x; soluble factors such as TGF-beta and IL-10; and nutrient-catabolizing enzymes, such as indoleamine-2,3-dioxygenase (IDO). In addition, there are ongoing efforts to assess the presence and function of effector cells within the tumor microenvironment. Tumor infiltrating lymphocytes (TILs) have been observed in patients with melanoma, colon cancer, and ovarian cancer. TILs in these patients have been associated with favorable clinical outcomes. In the clinical setting of bladder cancer, as compared to melanoma, there is limited data regarding TILs. This review will focus on immunological responses to bladder cancer and ongoing studies to identify factors that are amenable to therapeutic manipulation.