Tuberculosis BCG vaccine shows potential to retrain immunity against Alzheimer’s
Worth reading — 1 past UPSC question on this theme (Prelims GS-1 2022).
2-minute summary
A recent study published in Communications Medicine highlights the potential of the century-old Bacillus Calmette-Guérin (BCG) tuberculosis vaccine to mitigate Alzheimer's disease pathology. The mechanism relies on 'trained immunity'—a process where innate immune cells undergo functional and epigenetic reprogramming to mount a broad, heightened response against diverse, non-specific threats rather than generating specific antibodies. In aging brains, chronic low-grade inflammation ('inflammaging') impairs microglia and monocytes, causing toxic amyloid-beta proteins to accumulate into damaging plaques. Researchers observed that administering BCG induced monocytes in the central nervous system to enter an active surveillance state. In pre-symptomatic participants, this reprogramming facilitated the clearance of amyloid-beta from cerebrospinal fluid into the bloodstream. However, this clearance did not occur in participants with advanced Alzheimer's disease due to severe pre-existing neuroinflammation and a compromised blood-brain barrier. Consequently, while BCG offers limited therapeutic reversal for established dementia, it emerges as a promising, low-cost preventive strategy for early intervention.
Why it's in the news
A clinical study from Massachusetts General Hospital demonstrated that the BCG vaccine induces trained immunity in central nervous system monocytes. This mechanism facilitates amyloid-beta clearance in early stages, presenting a viable preventive lead against Alzheimer's disease.
Background and context
The BCG (Bacillus Calmette-Guérin) vaccine, developed in the early 20th century from attenuated Mycobacterium bovis, is primarily used to protect infants against severe forms of tuberculosis (such as tubercular meningitis) and as an immunotherapy agent for non-muscle-invasive bladder cancer. In recent decades, epidemiological observations indicated that BCG recipients exhibited reduced all-cause mortality and lower incidence of age-related neurodegenerative conditions like Alzheimer's disease. Alzheimer's is characterized by the accumulation of extracellular amyloid-beta plaques and intracellular tau neurofibrillary tangles, accelerated by 'inflammaging'—age-related dysregulation of the innate immune system. Understanding how non-specific immune stimulation through BCG crosses into the central nervous system opens up new frontiers in drug repurposing for neurodegenerative disorders.
Constitutional provisions
- Article 47 — Directs the State to regard the improvement of public health as among its primary duties, encompassing preventive healthcare for age-related disorders.
Government schemes
- Universal Immunisation Programme (UIP) — Provides BCG vaccination at birth across India as part of the standard infant immunization schedule.
- National Programme for Health Care of the Elderly (NPHCE) — Addresses health issues of the aging population, including screening and management of neurodegenerative disorders like dementia.
International organisations
- World Health Organization (WHO) — Promotes the Global Action Plan on the Public Health Response to Dementia (2017–2025) and oversees global immunization standards.
Previous UPSC questions on this theme
- Prelims GS-1 2022 — In the context of vaccines manufactured to prevent COVID-19 pandemic, consider the following statements : 1. The Serum Institute of India produced COVID-19 vaccine named Covishield using mRNA platform. 2. Sputnik V vaccine is manufactured using vector based platform. 3. COVAXIN is an inactivated pathogen based vaccine. Which of the statements given above are correct ? (a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3
Mains practice: What is 'trained immunity'? Discuss its significance in drug repurposing and its potential application in preventing age-related neurodegenerative disorders.
Trained immunity refers to the long-term functional and epigenetic reprogramming of innate immune cells (such as monocytes, macrophages, and natural killer cells). Unlike adaptive immunity, which depends on somatic gene rearrangement to create antigen-specific antibodies and memory T cells, trained immunity enhances the non-specific responsiveness of innate cells to secondary, unrelated pathogens and inflammatory challenges.
Significance in Drug Repurposing and Neurodegenerative Disorders:
• Overcoming 'Inflammaging': In aging brains, chronic low-grade neuroinflammation renders immune cells dysfunctional, leading to the accumulation of toxic amyloid-beta plaques in Alzheimer's disease. Repurposing vaccines like BCG (Bacillus Calmette-Guérin) can retrain these cells to regain clearance capabilities.
• Central Nervous System Modulation: Research shows that BCG administration triggers monocytes in the cerebrospinal fluid to adopt an active surveillance phenotype, moving amyloid peptides from the central nervous system into peripheral blood circulation.
• Cost-Effective Prophylaxis: Developing novel central nervous system therapeutics involves prohibitive costs and high failure rates due to the blood-brain barrier. Repurposing widely available, off-patent vaccines like BCG presents an accessible preventive tool.
• Preventive vs. Curative Window: Studies indicate that trained immunity is highly effective in pre-clinical stages but has limited efficacy once severe neurodegeneration and structural blood-brain barrier damage occur.
Conclusion:
Trained immunity bridges the gap between conventional immunology and neurodegenerative interventions. Leveraging existing vaccines for preventative neuro-immunomodulation can significantly lower the public health and economic burdens of dementia in rapidly aging societies.
Prelims practice questions
Q1. With reference to 'Trained Immunity', consider the following statements: 1. It is mediated primarily through epigenetic and metabolic reprogramming of innate immune cells. 2. It provides specific, antibody-driven protection restricted solely to the original pathogen. 3. It can be induced by certain live-attenuated vaccines such as BCG. Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Answer: C. Statement 1 is correct as trained immunity relies on epigenetic modifications and metabolic changes in innate cells (monocytes, macrophages). Statement 2 is incorrect because trained immunity is non-specific and does not rely on antibody production (which is a feature of adaptive immunity). Statement 3 is correct as BCG is a known inducer of trained immunity.
Q2. The Bacillus Calmette-Guérin (BCG) vaccine is prepared from an attenuated strain of which of the following microorganisms?
- Mycobacterium bovis
- Corynebacterium diphtheriae
- Mycobacterium leprae
- Mycobacterium tuberculosis
Answer: A. The BCG vaccine is derived from a live-attenuated strain of Mycobacterium bovis, a bacterium closely related to Mycobacterium tuberculosis that causes tuberculosis in cattle.
Q3. Consider the following statements regarding Alzheimer's disease: 1. It is pathologically characterized by the accumulation of amyloid-beta plaques and neurofibrillary tangles. 2. Cerebrospinal fluid (CSF) biomarkers can assist in identifying the disease before overt clinical symptoms appear. Which of the statements given above is/are correct?
- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
Answer: C. Both statements are correct. Alzheimer's disease is marked by extracellular amyloid-beta plaques and intracellular tau tangles. Cerebrospinal fluid (CSF) analysis allows early detection of these protein biomarkers prior to severe cognitive impairment.
Revision flashcards
- What is 'Trained Immunity'? The epigenetic and functional reprogramming of innate immune cells (like monocytes and macrophages) leading to a heightened, non-specific response against unrelated secondary pathogens or challenges.
- What is 'Inflammaging'? A state of chronic, sterile, low-grade inflammation that develops during physiological aging, contributing to the pathogenesis of age-related conditions including neurodegenerative diseases.
- What is the primary pathological hallmark of Alzheimer's Disease? Extracellular accumulation of amyloid-beta (Aβ) plaques and intracellular aggregates of hyperphosphorylated tau proteins (neurofibrillary tangles) leading to neuronal loss.
- What is the source strain and traditional medical uses of the BCG vaccine? Derived from attenuated Mycobacterium bovis; used globally to prevent severe tuberculosis (especially in infants) and as an immunotherapy instillation for superficial bladder cancer.
- Why did BCG fail to reverse established Alzheimer's disease in clinical trials? In advanced disease, severe pre-existing neuroinflammation, dense plaque deposits, and a damaged blood-brain barrier overwhelm the capacity of retrained immune cells to effect clearance.