Dartmouth professor of medicine Ford von Reyn and his research team recently found that a new tuberculosis vaccine, namely Mycobacterium vaccae (MV), is effective in helping prevent tuberculosis (TB) in HIV-infected individuals. The vaccine is particularly effective in those HIV-infected individuals with childhood Bacille Calmette-Guérin (BCG) immunization, the currently existing TB vaccine. The findings were published last month in AIDS.

HIV infection is a major contributor to the global TB epidemic which continues to grow with an estimated 9.3 million new cases and 1.3 million deaths in 2007. Currently, neither antiretroviral therapy (ART) nor isoniazid preventive therapy (IPT) is entirely effective in reducing this risk. Since TB is the major cause of death in regions where TB and HIV coexist, there is great need to prevent TB in HIV-infected individuals.

The DarDar Health study led by von Reyn is named for Dartmouth and Dar es Salaam, Tanzania where the researchers found that MV immunization reduced the rate of definite TB by 37 percent among 2,013 HIV-infected patients. The researchers found that the administration of a multiple-dose series of MV to HIV-infected adults with childhood BCG immunization is safe and is associated with significant protection against definite tuberculosis.

The DarDar study was carried in an outpatient facility in Dar es Salaam. It was a randomized, placebo-controlled, doubleblind study where participants were HIV-infected patients with CD4 cell counts of at least 200 cells/ml and a BCG scar. The participants were randomized, approximately half to MV and the other half to placebo and followed every three months for around 3.3 years.

During the approximately three-year follow-up period, the researchers observed 207 cases of active TB and 20 cases of disseminated TB where the disease spreads from the lungs to other regions of the body. The researchers also identified 33 cases of confirmed TB among the group receiving the vaccine and 52 cases of confirmed TB among the placebo group, indicating a vaccine efficacy of 37%. Immunization was tolerated well, with no adverse effect on CD4 cell count or HIV viral load, and no increase in the rate of serious adverse events. In fact, the trial was so successful that it had to be terminated early due to significant protection against definite TB.

Von Reyn said to the press that if 50% of HIV-positive people in Tanzania are to receive the vaccine, TB incidence in the country can decline by about 3,300 new cases annually. According to the article, a remaining challenge for the vaccine will be to examine its effects among HIV-positive people with CD4 counts fewer than 200 cells/ml.

“We are optimistic that the DarDar trial will lead to further development and eventual licensing of MV for use in the developing world,” said von Reyn in an email to DUJS.