BCG: a vaccine with multiple faces.

Area of Science:

• Immunology
• Vaccinology
• Public Health

Background:

• The Bacillus Calmette-Guérin (BCG) vaccine is primarily recognized for its efficacy against disseminated and meningeal tuberculosis.
• Beyond tuberculosis, the BCG vaccine possesses immunomodulatory properties with potential applications in other health domains.
• Existing reports indicate a significant protective effect of the BCG vaccine against leprosy.

Purpose of the Study:

• To review the diverse applications and newly discovered mechanisms of action of the BCG vaccine.
• To provide new perspectives on the multifaceted and sometimes controversial roles of this established vaccine.

Main Methods:

• A comprehensive review of existing literature and clinical trial data concerning the BCG vaccine.
• Analysis of reported outcomes from studies investigating BCG's efficacy and side effects across various conditions.

Main Results:

• The BCG vaccine shows beneficial heterologous (nonspecific) effects on mortality in certain developing countries.
• BCG immunotherapy is the established gold standard adjuvant treatment for non-muscle-invasive bladder cancer.
• The vaccine has been explored for therapeutic potential in diabetes and multiple sclerosis, and its site erythema is a clue in Kawasaki disease.

Conclusions:

• The BCG vaccine exhibits a wide range of immunomodulatory actions extending beyond its traditional role in tuberculosis prevention.
• New insights into its mechanisms offer novel perspectives on the therapeutic and prophylactic potential of this long-standing vaccine.
• While beneficial effects are noted, BCG administration in immunodeficient patients can lead to severe BCG disease (BCGitis/BCGosis) and autoimmunity.