Bacillus Calmette-Guerin (BCG) is a vaccine traditionally used to immunize newborn babies against tuberculosis. BCG is also used as a form of immunotherapy against bladder cancer.1
A weakened form of this bacteria is injected into the bladder using a catheter to elicit an immune response versus cancer cells. The BCG solution entering through the urethra is allowed to reach all areas of the bladder for about two hours, following which the catheter is unclamped following a predetermined time to drain out the liquid. Additional information on immunotherapy can be found here
1. O. Fuge, et al., "Immunotherapy for Bladder Cancer," Res Rep Urol
7: 65-79, 2015.