WASHINGTON A new tuberculosis vaccine has shown promise in animal studies, researchers said on Wednesday, raising hope it might replace the current vaccine that has failed to stop one of the world's top killers.
If all goes well, human trials of the new vaccine with some modifications to make it safer could start in two to three years, said one of the researchers, immunologist Dr. Steven Porcelli of Albert Einstein College of Medicine in New York.
TB, a bacterial infection that usually attacks the lungs, kills about 1.6 million people a year globally. The increasing resistance of the TB organism to drug treatments makes creation of a truly effective vaccine even more crucial, experts say.
The existing BCG vaccine, in use for almost a century despite its limited effectiveness, is based on a live, weakened strain of the bacterium that causes TB in cattle.
Rather than trying to make changes in the BCG vaccine, the researchers decided to take a different path, using a weakened version of the bacterium that causes TB in people.
The idea behind this and other vaccines is to make the body's immune system -- its natural defenses -- better able to fight off invaders like disease-causing bacteria or viruses.
The researchers found a gene in the organism that helps it elude immune system detection, and removed it from the bacterium. That helps the vaccine, using this live, weakened version of the organism, induce a strong immune response.
They tested the new vaccine head-to-head against the existing one. They found that the new one extended the lives of mice and guinea pigs and stimulated stronger immune responses in those animals compared to the existing BCG vaccine.
"It seems to be translating directly into something that might be of great benefit to humanity. So I feel extremely energized and quite optimistic about where this project is leading," Porcelli said in a telephone interview.
"It has some limitations. A major one at this point is that it's still probably too infectious to give to humans. It's only partially attenuated, or weakened, for virulence," he added.
The work appears in the Journal of Clinical Investigation.
Porcelli said the researchers are working to make the vaccine safer by removing additional genes. He said they plan to test it in monkeys. He said if the results continue to be positive, human studies may be possible in two to three years.
"We're very excited because this is the first vaccine strain we've ever seen that is significantly better than BCG," said another researcher, William Jacobs of Albert Einstein College of Medicine and the Howard Hughes Medical Institute.
The TB organism infects roughly a third of the world's population. Most infections remain latent but can become active when the immune system is weakened, for example in people also infected by the virus that causes AIDS. About 10 million people worldwide have active cases of TB.
The existing BCG vaccine protects young children from tuberculosis, but does not do well at preventing the type of TB most adolescents and adults develop.
TB can be treated effectively with drugs in many cases, but the drugs have to be given daily for upward of six months, making treatment complicated and expensive. Many poorer parts of the world lack the medical infrastructure to deliver that kind of treatment, so many experts believe an effective vaccine could be a highly valuable tool in combating the disease.