Bacillus Calmette-Guérin (BCG) (BCG)

Bacillus Calmette-Guérin (BCG) is a live-attenuated strain of Mycobacterium bovis that functions as a potent immunostimulant and biological response modifier. It is primarily utilized as a vaccine for tuberculosis prevention and as a standard-of-care intravesical immunotherapy for non-muscle invasive bladder cancer (NMIBC). The term "Immune system activated by BCG" refers to the complex physiological state induced by the mycobacterium, which stimulates both innate and adaptive immune pathways. By interacting with pattern recognition receptors such as Toll-like receptors (TLR2, TLR4) and NOD2, BCG triggers the release of Th1-type cytokines and the recruitment of macrophages, natural killer (NK) cells, and cytotoxic T-lymphocytes. This localized immune activation is responsible for the destruction of malignant cells in the bladder. Additionally, BCG is a key model for "trained immunity," where it induces long-term epigenetic and metabolic changes in innate immune cells, enhancing their response to subsequent infections (Science, 2016; PubMed, 2017).

Other names

BCG vaccineBacillus of Calmette and GuérinMycobacterium bovis BCGIntravesical BCGLive attenuated Mycobacterium bovis

BCG acts as a biological response modifier by stimulating the innate and adaptive immune systems. Upon administration, the mycobacteria bind to the urothelium via fibronectin and are internalized by macrophages and tumor cells. This triggers pattern recognition receptors (PRRs) such as Toll-like receptor 2 (TLR2), TLR4, and Nucleotide-binding oligomerization domain-containing protein 2 (NOD2), leading to the secretion of pro-inflammatory cytokines (IL-1, IL-6, IL-8, TNF-alpha, IFN-gamma) and the recruitment of T-lymphocytes and natural killer (NK) cells that mediate anti-tumor and anti-mycobacterial activity (StatPearls, 2023; Nature Reviews Urology, 2014).