What is the immunologic rationale for intravesical BCG therapy in bladder cancer?

• A. It stimulates local innate and adaptive immune responses to kill cancer cells.
• B. It directly targets cancer cells with toxins.
• C. It reduces bladder inflammation.
• D. It acts as a vaccine against TB only.

Answer: (C)

The immunologic rationale is to stimulate local innate and adaptive immune responses inside the bladder that target and kill cancer cells. When BCG is instilled into the bladder, immune cells in the urothelium and resident antigen-presenting cells recognize the mycobacterial components, triggering a pro-inflammatory cascade. This includes activation of macrophages, dendritic cells, and NK cells, with production of cytokines that favor a Th1-type response (such as IL-12 and IFN-γ). The result is enhanced cytotoxic activity against tumor cells by T cells and NK cells, as well as better presentation of tumor antigens and recruitment of additional immune effectors. The therapy thus creates a local, immune-driven attack on bladder cancer cells rather than relying on direct toxin-mediated killing, and it is not simply a vaccine against TB.