Trained Immunity, BCG and SARS-CoV-2 General Outline and Possible Management in COVID-19

Area of Science:

• Immunology
• Vaccinology
• Infectious Diseases

Background:

• The Bacillus Calmette-Guérin (BCG) vaccine, used for over a century, primarily prevents severe tuberculosis.
• Emerging evidence suggests BCG confers broader protection against various pathogens.
• This phenomenon is attributed to trained immunity, a non-specific immune response.

Purpose of the Study:

• To review the current understanding of molecular mechanisms underlying trained immunity induced by BCG.
• To identify scientific challenges in studying trained immunity.
• To explore the potential application of trained immunity in the context of the SARS-CoV-2 pandemic.

Main Methods:

• Literature review of studies on BCG, trained immunity, and molecular mechanisms.
• Analysis of existing data on BCG's off-target effects.
• Discussion of potential therapeutic strategies involving trained immunity.

Main Results:

• BCG vaccination induces epigenetic and metabolic reprogramming in innate immune cells, enhancing their response.
• Trained immunity involves long-lasting, non-specific protection mediated by myeloid and NK cells.
• Evidence suggests BCG may offer partial protection against viral infections, including coronaviruses.

Conclusions:

• Trained immunity is a key mechanism explaining BCG's broader protective effects beyond tuberculosis.
• Further research is needed to fully elucidate the molecular pathways and optimize its clinical application.
• Harnessing trained immunity could be a valuable strategy for controlling infectious disease outbreaks, including COVID-19.