Two open-label trials in 23 adults aged 55 and older found two BCG shots triggered persistent trained-immunity-like changes in cerebrospinal-fluid immune cells over 12 months, with no unexpected safety signals.
Single-cell and cytokine analyses showed the CNS response differed from blood: CSF monocytes gained stronger LPS recall responses and immune-metabolic transcriptional programs, while direct heat-killed BCG recall was largely absent in CSF but robust in PBMCs.
In 11 participants without Alzheimer’s-related pathology, CSF amyloid-β42 fell while plasma amyloid-β42 rose, cutting the CSF-to-plasma ratio by 38.2%; those shifts were not seen in participants with AD-related pathology.
CSF cytokines followed a shared downregulatory pattern across groups, while plasma responses were stronger and more phased in AD-pathology participants, underscoring compartment-specific immune remodeling.
Researchers said the findings are hypothesis-generating rather than proof of clinical benefit, because the single-center study was small, exploratory and lacked a placebo control.
Could a century-old vaccine really reprogram our brain's immunity to fight off Alzheimer's disease?
Why might a vaccine help prevent Alzheimer’s, but not work once the disease has already taken hold?
Immune System Reprogramming and Alzheimer’s: Breakthroughs in BCG Vaccine Research (2024–2026)
Overview
Recent breakthroughs from Massachusetts General Hospital and Mass General Brigham have shown that Bacillus Calmette–Guérin (BCG) immunotherapy can reprogram the immune system in ways that may help fight Alzheimer’s disease. As of July 2026, new studies highlight lasting, specific changes in immune cells within the cerebrospinal fluid after BCG treatment, including signs of 'trained immunity' and improved metabolic activity. These findings, based on detailed immune profiling, offer a new framework for understanding how immune-based strategies could help preserve brain health as people age, building on earlier evidence that BCG may lower the risk of Alzheimer’s and related dementia.