Radiotherapy-induced immunogenic effects in bladder cancer.

418 Background: Many patients with bladder cancer (BC) undergo radiotherapy (RT) during the course of their treatment. There is emerging evidence that RT can cause immune stimulatory changes within the tumour microenvironment (TME), potentially contributing to its efficacy. We aimed to determine if RT induces immunogenic changes in murine BC cell lines, and develop a pre-clinical model of BC with a TME reflective of de novo tumours in order to test this premise in vivo. Methods: Immunogenic effects of RT were determined using murine vaccination studies with irradiated tumour cells. RT-induced immuno-phenotypic changes in surface antigen expression on tumour cells were ascertained using flow cytometry. An orthotopic BC model was established using MBT2 cells instilled intravesically in C3H/Hen mice, and resulting tumours monitored with ultrasound (US). We used immunohistochemical (IHC) staining to determine the immune contexture of the TME within developing orthotopic tumours. Results: C57BL/6 mice inoculated with irradiated MB49 cells demonstrated improved survival compared to control mice after subsequent rechallenge with viable tumour cells. This effect was not seen in C3H mice implanted with irradiated MBT2 cells. RT led to upregulation of immune stimulatory molecules CD80, MHC I, and Fas on MB49 but not MBT2 cells. Tumours developed in 80% of mice following catheter implant, and visible on US 3-4 weeks after instillation. Profiling of the TME with IHC demonstrated that tumours contained few CD8+ T-cells, but high numbers of myeloid cells. Conclusions: RT induces immune stimulatory effects on murine BC cells, including upregulation of several surface proteins. In future work, we will determine the effects of RT on the TME in the orthotopic model, and correlate these with the expression of various immunogenic cell surface proteins. This may lead to the discovery of a biomarker to predict which patients with BC would benefit from combination of an immunomodulatory agent with RT.