BCG Vaccine Shifts CSF Amyloid-Beta Levels in Amyloid-Negative Adults Over 12 Months

Mass General Brigham investigators administered BCG to 12 participants with and 11 without biomarker evidence of Alzheimer's disease, sampling CSF and blood at multiple time points over one year. The vaccine enhanced ex vivo immune responses to unrelated stimuli without elevating inflammatory cytokines. Amyloid-beta redistribution occurred only in the amyloid-negative cohort, consistent with possible enhancement of glymphatic clearance or peripheral sink mechanisms.

Prior BCG work at the same institution has shown metabolic and infectious off-target effects in type 1 diabetes and COVID-19 trials. The current findings extend trained-immunity observations from blood to the central nervous system compartment and indicate that disease-stage timing may determine whether biomarker change occurs. The absence of effect in already-pathological participants suggests a narrow prevention window.

These results connect occupational immunology findings on mycobacterial training to Alzheimer's prevention, an area rarely examined in depth by mainstream reporting. The split amyloid response aligns with earlier epidemiological signals of lower dementia incidence in BCG-exposed populations yet supplies the first direct CSF data.

Larger placebo-controlled prevention trials are required to test whether the observed 12-month biomarker shift translates into delayed cognitive decline or reduced incidence. Such studies must stratify by baseline amyloid status and include longitudinal PET imaging to confirm mechanism.