There's a potential cure for autoimmune diseases like multiple sclerosis, type 1 diabetes, and rheumatoid arthritis; transplant rejection; and many kinds of allergies, actively in development!
Typical vaccines work by training your immune system to see something as a threat, so your body will attack harmful bacteria and viruses before they can get established or do serious damage.
"Tolerogenic vaccines", also called "inverse vaccines", do the opposite, and teach your immune system that something isn't a threat and therefore it shouldn't be attacked. At the moment, the only way to stop someone's immune system from attacking one thing is to suppress it entirely, which makes that person vulnerable to many other infections.
Tolerogenic vaccines could be a huge help for illnesses where your immune system has started attacking your own body, like multiple sclerosis (attacking nerve cells), type 1 diabetes (attacking insulin-producing pancreatic cells), and rheumatoid arthritis (attacking joints).
They could also be used to tell a person's immune system not to attack a transplanted organ. Right now, anyone who gets a transplant can expect to need to take immunosuppressants for the rest of their life, just to prevent their immune system from killing the transplant. Inverse vaccines could change that!
And of course, allergies occur when your immune system misidentifies, say, peanuts as a threat, and then overreacts to any exposure to the allergen. Tolerogenic vaccines could cure people of allergies to foods, medicines, and common pets!