Tuberculosis is the world's deadliest infectious disease, sickening eight million people and killing two million every year. A century-old vaccine prevents childhood forms of the disease. But there's a desperate need for a vaccine that's effective against the adult form of the disease, which is highly contagious and is growing resistant to drug treatment. Renewing hope on this front, two human trials of vaccines that could be protective against the adult form of the disease began in the United States earlier this year.

In one of the trials, Corixa, a biotech firm in Seattle, WA, and GlaxoSmithKline Biologicals of Rixensart, Belgium, are testing the safety of their vaccine on 20 healthy volunteers. Whereas the childhood vaccine consists of live bacteria closely related to the TB-causing germ, the new one is made of two proteins isolated from the TB bacterium using genetic-engineering techniques. Corixa researchers picked these proteins in part by screening the blood of adults who successfully fought off the infection. Because their immune cells-presumably adept at killing tuberculosis germs-most readily recognized these two proteins, it's thought that the proteins will stimulate a stronger and more effective immune response among adults. And because it's not live, the vaccine could be easier to manufacture and store in large quantities, says Christine Sizemore, tuberculosis program officer for the National Institute of Allergy and Infectious Diseases in Bethesda, MD.