BCG: A throwback from the stone age of vaccines opened the path for bladder cancer immunotherapy

It is 40 years since the initial documentation of the efficacy of bacille Calmette-Guérin (BCG) in the management of non-muscle invasive bladder cancer (NMIBC) and probably an opportune a time as any to retrace the origins of this development and to reflect on the progress that has occurred on the use of immune modifiers in the treatment of NMIBC.

A PubMed search for publications on the history of BCG was conducted, and those related to the development of the vaccine for protection against tuberculosis as well as those published in the last 40 years related to its use for treatment for NMIBC were selected for review. A manual search was also carried out for recent articles on immunotherapy for NMIBC failing to respond to BCG. Publications were selected for their usefulness in exemplifying the development of BCG as an antineoplastic agent, elucidating its mechanisms of action of BCG or introducing significant modifications in treatment regimens resulting in enhancement of its efficacy. Alternative innovative immunotherapeutic approaches were chosen to illustrate current trends in the management of this disease.

Well thought-out modifications of the original protocol resulted in enhanced efficacy of the vaccine, which currently ranks as the best-known and most-used and investigated agent for high risk NMIBC. Despite its efficacy, a considerable number (30%-40%) of these tumors fail to respond to BCG. In addition, as a live bacterium it carries the potential for serious adverse effects and some patients are unable to tolerate it. These shortcomings have created the need for new agents. These range from other mycobacteria and viruses to monoclonal antibodies alone or in combination with other agents currently at various stages of development.

After 4 decades of use, BCG remains the most effective agent against high risk NMIBC, but it still holds substantial drawbacks. The enduring use of immunotherapy for NMIBC has created a propitious environment to search for better alternatives. There are an increasing number of promising in vitro, animal and early human clinical trials to anticipate a significant therapeutic alternative in the foreseeable future.