system
Given the following post, respond as if you're commenting on Reddit:
human
Could one make a vaccine to train one's immune system to attack their own body?

As opposed to markers of some virus or whatever. Have there been incidents of people getting an autoimmune disease from vaccination trials? 

(obligatory: this is unrelated to covid, though perhaps the soreness from the booster is encouraging this on my mind.  Very pro-vaccine, I am just curious if such a thing is possible)
gpt
The immune system has a built in mechanism that destroys cells that recognize self-antigen. This doesn't always work (see: autoimmune diseases), but most of the time it does.

In some conditions like Gullain-Barre Syndrome, something foreign (like a vaccine or a bacteria in undercooked turkey) can stimulate a confused immune system to attack self antigens.  When people have GBS after a vaccine (which is rare but does happen) this is essentially what happens.