Basically, Dr Daniell (a researcher at the University of Central Florida) is teaching the body's immune system to stop attacking insulin producing cells. Here is a quote from a news article describing how it works:
In Dr. Daniell's method, the lettuce plant cells help the insulin reach the intestine. Once the plant cells get there, bacteria slowly break down the cell walls and gradually release insulin into the bloodstream. This creates an immune response in the body and teaches it to release its own insulin. "It is the same insulin that is injected, but here what we are doing is instead of injecting it in the blood system, we are presenting it to the immune cells and then asking the immune cells to see that this is your own protein," Dr. Daniell said. "What we have done is to teach the body how to cure this disorder. This is a totally new concept, a new platform to use this oral delivery system to fix this immune disorder."Because Dr. Daniell expects to start testing on people in the next year, I will add this research to the "Preparing for Phase-I Trials" part of my web page. However, here is a blog entry which I did not write, but which pretty much summarizes my opinion of this research right now: http://www.diabetesmine.com/2007/09/lettuce-hope-bu.html
Pay particular attention to the part where Amy points out that giving insulin to mice prevents them from getting type-1 diabetes, but that this same trick doesn't work for people. I'm sure that's why Dr. Daniell is having so much trouble raising the $20 million that he needs.
Here are some news articles covering the research:
I will get excited about this research when it works for the first time on people. This is the kind of thing where mice research doesn't prove much.