Cavity Vaccine

Saturday, August 01, 1998
The leading cause of cavities is a bacterium, Streptococcus mutans. This microbe feeds on sugars that stick to our teeth and excretes acids as a waste product. These acids erode tooth enamel. Julian Ma, an immunologist at Guy's Hospital in London, has been working on a vaccine against tooth decay for 15 years. He's finally succeeded in creating a novel vaccine made from plants that could end unpleasant visits to the dentist.

Ma created antibodies to S. mutans in his lab, thinking he could apply them directly to the teeth. The antibodies attach themselves to a molecule on S. mutans that the bacteria use to stick to teeth. But creating large amounts of antibody in the lab was expensive, so Ma learned how to transfer genes for antibodies into the dna of tobacco plants. As the plant cells produce proteins necessary for their own growth, they also routinely churn out Ma's antibodies.

"You can grow fields of the stuff, and this is incredibly cheap," he says. "But the other advantage we discovered is that the plants are extremely good at putting these antibodies together. They're very efficient. That started us thinking we could make more complicated and better antibodies."

The antibody Ma needed comes in two different forms: one that circulates in the bloodstream, and a more complex version that's found in secretions like saliva. The latter has a special protein chain that wraps around the rest of the antibody, protecting it from protein-munching enzymes in saliva. No one has ever made large amounts of this complex molecule in the lab, but in the field Ma's tobacco plants produce enormous quantities of it.

Ma extracted antibodies from the plants, mixed them into a solution, and dripped them onto the teeth of volunteers whose mouths had been cleared of bacteria with antibiotics. After a series of applications over three weeks, their mouths remained free of S. mutans for six months. Ma is still perfecting the delivery system. But his work has implications beyond dentistry. "Probably 90 percent of the infections we suffer start at a mucosal surface," says Ma. "The common cold, sore throat, urinary tract infection, chest infectionothey're all at mucosal surfaces where it might be advantageous to put a secretory antibody. Our model can be applied to all sorts of infectious diseases."
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