Bacillus Calmette-Guérin strain differences as the basis for immunotherapies against bladder cancer.

In the past 40 years, intravesical immunotherapy with Mycobacterium bovis bacillus Calmette-Guérin has been carried out as the most effective treatment for preventing local recurrences and tumor progression of non-muscle-invasive bladder cancer. Bacillus Calmette-Guérin is a family of vaccines derived in 1921 by the in vitro attenuation of Mycobacterium bovis. Subsequently, bacillus Calmette-Guérin seed lots were spread around the world, and both phenotypic and genotypic differences among the strains have been compiled. In recent genomic comparisons, the evolution of the different bacillus Calmette-Guérin substrains has begun to emerge. However, some of these genetic alterations in bacillus Calmette-Guérin strains have yet to be shown to affect the therapeutic effects and/or adverse effects. There are thus ongoing research efforts to assess the effects of these genetic alterations on the properties of bacillus Calmette-Guérin strains, with the ultimate goal of identifying an ideal bacillus Calmette-Guérin strain for treatment of non-muscle-invasive bladder cancer and providing clues for the improvement of bacillus Calmette-Guérin strains. The present review provides a history of bacillus Calmette-Guérin immunotherapy, and discusses the genetic differences among bacillus Calmette-Guérin strains, the different clinical outcomes afforded by bacillus Calmette-Guérin strains and possible future developments.