Abstract
Bladder cancer is the most common urinary tract neoplasm globally, with approximately 80% of patients diagnosed with non-muscle invasive bladder cancer (NMIBC). NMIBC represents as a heterogeneous subcategory of urothelial carcinoma, with highly variable treatment outcomes. Bacillus Calmette-Guerin (BCG) immunotherapy has been the gold-standard treatment for NMIBC for decades due to the highly potent antitumour activity. Despite widespread clinical use, BCG therapy fails in up to 40% of patients and there is limited evidence to explain why. Current literature focuses on the innate immune system response to BCG in bladder cancer. Studies on BCG effect in healthy innate and adaptive immune cells would provide vital knowledge on the exact, yet currently unknown mechanisms underlying BCG usage and failure in NMIBC therapy. Gaining a deeper understanding would provide a substantial advancement in improving patient outcomes and predicting response to therapy.
Peripheral blood mononuclear cells were isolated from healthy participants and exposed to BCG in both an inflammatory environment mimicked with the lymphocyte mitogen Concanavalin A, and a non-inflammatory environment. Activation and three different types of exhaustion markers were used to assess shifts in T cell subset frequency, activation, and exhaustion via spectral flow cytometry, using an optimised culturing method and flow cytometry panel within this thesis. T cell subset frequencies, activation and exhaustion were similar between BCG and unstimulated treatment groups and were slightly altered in the inflammatory environment when BCG was present. However, in the Tregs subset, when exposed to BCG in an inflammatory environment, there was a significant increase in activation and exhaustion marker expression, indicating a shift towards a more immunosuppressive and exhausted state.
This is one of the first studies to characterise shifts in frequency, activation, and exhaustion in CD4+ and CD8+ T cell subsets in response to BCG exposure. Effector and memory T cells known to be involved in BCG immunogenic processes in other treatments were not significantly changed in response to BCG in this study. The data supports the concept of BCG-induced Treg exhaustion, an active field of BCG immunotherapy research, and demonstrates that it can occur in healthy immune cells when under inflammatory conditions. This study provides preliminary knowledge for further research on the effects of BCG on T cell exhaustion in the context of NMIBC therapy.