From Scientific American:
The human body's immune system can quickly track down and kill cells that don't belong. Take certain kinds of bacteria: molecules on their surfaces flag them as foreign invaders, alerting the body's defenders to the breach and drawing a full-fledged attack on anything waving that molecular flag. But sometimes the system mistakenly attacks the body's own cells. The result is autoimmune disease, such as type 1 diabetes, in which the insulin-producing beta cells of the pancreas are attacked and destroyed by T cells.
Scientists have struggled to find ways to treat autoimmune disease without compromising overall immunity. Therapies that suppress the immune system carry the risk of letting infections and even tumors go unchecked. But researchers in Canada have found a way to prevent type 1 diabetes in mice by doing just the opposite—vaccinating to boost the immune system. The approach, published April 8 in Immunity, exploits the immune system's built-in safety mechanism—a group of regulatory T cells whose job is to squelch overactive immune responses.