BCG vaccine may slow Alzheimer’s via brain immunity

The BCG vaccine has been used for over a hundred years. It primarily protects against tuberculosis, but researchers have long known it also trains the broader immune system. This effect is called ‘trained immunity’: the innate immune system becomes more responsive to a wide range of threats afterward.

Now two small clinical trials show this effect is visible inside the brain as well. The researchers vaccinated 23 participants aged 55 and older twice with BCG, one month apart. After one year, they analysed immune cells in the cerebrospinal fluid, the fluid surrounding the brain and spinal cord.

Brain and blood react differently

Immune cells in the cerebrospinal fluid showed a distinct activation pattern compared to those in the blood. This points to a separate immune response within the central nervous system. In participants without Alzheimer’s-related changes, levels of amyloid-beta (a protein that clumps into plaques in Alzheimer’s) fell in the cerebrospinal fluid while rising in the blood. This pattern suggests the protein was being cleared from the brain, though the team stresses that larger controlled studies are needed to confirm this.

Too early for strong conclusions

The study was open-label and the group was small: twelve participants without and eleven with Alzheimer’s-related pathology. There was no placebo group. The findings are therefore preliminary and not yet generalisable. The vaccine was well tolerated, with no unexpected side effects.

From a longevity perspective, it is worth noting that the immune system declines with age, a process researchers call immune ageing. If trained immunity via an existing, low-cost vaccine can help correct this decline, it opens a different avenue from conventional amyloid- or tau-targeting therapies. How large that effect would be in bigger groups remains to be seen.

Read the original article