In at least some cases type 1 diabetes is considered an autoimmune disease as are the other diseases listed in the headline. They're using the "vaccine" to turn off the body's overreaction to a specific antigene. This is huge if this makes it through human trials. There are a lot of people suffering from various autoimmune diseases.

From the article:

"A typical vaccine teaches the human immune system to recognize a virus or bacteria as an enemy that should be attacked. The new “inverse vaccine” does just the opposite: it removes the immune system’s memory of one molecule. While such immune memory erasure would be unwanted for infectious diseases, it can stop autoimmune reactions like those seen in multiple sclerosis, type I diabetes, rheumatoid arthritis, or Crohn’s disease, in which the immune system attacks a person’s healthy tissues."

The rest of the article goes into some details of how it works.

It's usually (70% of the time, or more) caused by the host immune system destroying the beta cells in the pancreas.