BCG immunomodulation: From the 'hygiene hypothesis' to COVID-19

Area of Science:

• Immunology
• Vaccinology
• Infectious Diseases

Background:

• The Bacillus Calmette-Guérin (BCG) vaccine, traditionally used for tuberculosis, is gaining attention for its non-specific protective effects against other pathogens.
• These effects are largely mediated by trained immunity, a form of innate immune memory involving epigenetic and metabolic reprogramming of immune cells.

Purpose of the Study:

• To review the immunomodulatory effects of BCG, focusing on trained immunity.
• To explore the relevance of BCG-induced trained immunity in the context of the 'hygiene hypothesis' and its potential applications in autoimmune diseases, allergies, and COVID-19.

Main Methods:

• Literature review of studies on BCG vaccination, trained immunity, the hygiene hypothesis, and COVID-19.
• Analysis of the mechanisms underlying BCG-induced trained immunity.
• Evaluation of potential therapeutic and preventive applications of BCG.

Main Results:

• BCG vaccination induces trained immunity, enhancing innate immune responses against various pathogens.
• BCG holds potential as an immunotherapeutic agent for autoimmune, allergic, neurodegenerative, and neoplastic diseases.
• BCG vaccination is being investigated as a measure against COVID-19 and for developing recombinant vaccines.

Conclusions:

• BCG's ability to induce trained immunity offers a promising avenue for novel therapeutic and preventive strategies.
• Understanding BCG-induced immunomodulation is critical for addressing modern health challenges, including autoimmune diseases and pandemics like COVID-19.