Nano-Bacillus Calmette-Guérin immunotherapies for improved bladder cancer treatment

Cancer immunotherapy has rapidly become the fourth mainstream treatment alternative after surgery, radiotherapy, and chemotherapy, with some promising results. It aims to kill tumor cells by mobilizing or stimulating cytotoxic immune cells. However, the clinical applications of tumor immunotherapies are limited owing to a lack of adequate delivery pathways and high toxicity. Recently, nanomaterials and genetic engineering have shown great potential in overcoming these limitations by protecting the delivery of antigens, activating targeted T cells, modulating the immunosuppressive tumor microenvironment, and improving the treatment efficacy. Bacillus Calmette-Guérin (BCG) is a live attenuated Mycobacterium bovis vaccine used to prevent tuberculosis, which was first reported to have antitumor activity in 1927. BCG therapy can activate the immune system by inducing various cytokines and chemokines, and its specific immune and inflammatory responses exert antitumor effects. BCG was first used during the 1970s as an intravesical treatment agent for bladder cancer, which effectively improved immune antitumor activity and prevented tumor recurrence. More recently, nano-BCG and genetically engineered BCG have been proposed as treatment alternatives for bladder cancer due to their ability to induce stronger and more stable immune responses. In this study, we outline the development of nano-BCG and genetically engineered BCG for bladder cancer immunotherapy and review their potential and associated challenges.