According to a news story at sciencedaily.com, Dr. Li Wen and colleagues at Yale University have been able to successfully prevent and treat early type 1 diabetes in mice engineered to express a human antibody (CD20) on immune B cells. I am trying to find the article in the Journal of Clinical Investigation but the story must have been a pre-release, since the December issue isn't available yet online or at pubmed. Anyway, B cells expressing this antibody have been targeted in rheumatoid arthritis, another autoimmune disease, with some success. It took some time to develop the appropriate tools to do this in a model of type 1 diabetes, but it seems like the results are promising. Once the article becomes available, I will try to find some answers to my many questions regarding this research.
Reference from sciencedaily.com: Journal of Clinical Investigation (2007, December 3). Treating Type 1 Diabetes By Eliminating B Cells. ScienceDaily. Retrieved December 3, 2007, from http://www.sciencedaily.com /releases/2007/12/071203190636.htm
Update Dec-06-2007: A link to the article can be found here.