Scientists have found that a variant of an existing vaccine offers stronger protection against both tuberculosis and leprosy.
The currently available vaccine Bacille Calmette-Guerin, or BCG, provides only partial protection against both tuberculosis and leprosy, so a more potent vaccine is needed to combat both diseases.
Researchers from the University of California, Los Angeles found that rBCG30, a recombinant variant of BCG that overexpresses a highly abundant 30 kDa protein of the tuberculosis bacterium known as Antigen 85B, is superior to BCG in protecting against tuberculosis in animal models, and also cross protects against leprosy.
In addition, researchers found that boosting rBCG30 with the Antigen 85B protein, a protein also expressed by the leprosy bacillus, provides considerably stronger protection against leprosy.
"This is the first study demonstrating that an improved vaccine against tuberculosis also offers cross-protection against Mycobacterium leprae, the causative agent of leprosy," said Dr Marcus A Horwitz, professor of medicine and microbiology, immunology and molecular genetics, and the study's senior author.
"That means that this vaccine has promise for better protecting against both major diseases at the same time.
"It is also the first study demonstrating that boosting a recombinant BCG vaccine further improves cross-protection against leprosy," he added.
In one experiment, mice were immunised with either rBCG30 or the old BCG vaccine, or they were given a salt solution.
Ten weeks later, the mice were injected with live leprosy bacteria into their footpads and seven months after that, the number of leprosy bacteria in their footpads was measured.
The researchers found that the mice given BCG or rBCG30 had much fewer leprosy bacteria in their footpads than the mice given the salt solution.
Additionally, mice immunised with rBCG30 had significantly fewer leprosy bacteria than those vaccinated with BCG.
In a second experiment, the mice were first immunised with BCG or rBCG30, and then immunised with a booster vaccine (r30) consisting of the TB bacterium's 30-kDa Antigen 85B protein in adjuvant - that is, in a chemical formulation that enhances the immune response.
The group of mice immunised with rBCG30 and boosted with r30 had no detectable leprosy bacteria in their footpads, in contrast to groups of mice immunised with all other vaccines tested, including BCG and rBCG30 alone and BCG boosted with r30.
The next step in the research will be to test the rBCG30 vaccine for efficacy in humans against TB. If it's effective against TB, then the next step would be to test its effectiveness in humans against leprosy.
The study was published in the journal Infection and Immunity.
