I've heard of this a few times but I still don't quite get it..

It's just the only hard enough part of the body that won't be rejected but won't the autoimmune issues persist?

It's really incredible this has been around since the 60's and I would love to have a chat with the first person who said "let's try a tooth"

The guy didn't have an auto immune issue. It was a reaction to some medicine he got as a teenager.