TB vaccine gets a needed boost.

An experimental vaccine has proved it can greatly enhance immunity against tuberculosis (TB) in people who were previously vaccinated with the far-from-perfect bacille Calmette-Guerin (BCG) vaccine for TB. BCG was first used more than 80 years ago. It provides some protection in children but not adults.

The scientists gave the new vaccine to 17 volunteers who had received the BCG vaccine in the past--as recently as within a year or as long as 38 years ago. The team also enrolled 25 people who had never received a BCG shot. Of these, 14 received the new vaccine and 11 got a BCG shot.

In the November Nature Medicine, the researchers report that in the group with a history of BCG vaccination, the new vaccine elicited a potent army of immune system T cells that cranked out a compound called interferon-gamma. This protein activates other immune cells, called macrophages, to stand guard against Mycobacterium tuberculosis, the microbe that causes TB.

The volunteers who hadn't received the BCG vaccine in the past had much weaker immune reactions, whether they received the new vaccine or a BCG shot. Their immune responses were only one-thirtieth to one-fifth as strong as those of the people getting the new vaccine on top of a history of BCG vaccination, says study coauthor Helen McShane of the University of Oxford in England.

The new vaccine, called MVA85A by researchers, consists of weakened cowpox virus that has been genetically engineered to make a protein normally found on the surface of M. tuberculosis. Pox viruses "are excellent at boosting previously primed T-cell responses," McShane notes. The research sets the stage for larger trials of the new vaccine, she says.--N.S.