The long, low building sandwiched between a railway station and a busy traffic roundabout could be a 1950s American motel. It's anything but. It's the busy DarDar Clinic in central Dar es Salaam, Tanzania. Some 2,000 Tanzanians who are HIV-positive are taking part there in a clinical trial, sponsored by the U.S. National Institutes of Health (NIH), to test an experimental tuberculosis vaccine. More than 8% of the adults in Tanzania—which has a population of 37 million—are infected with HIV, and between 10% and 25% of those with HIV are at risk of developing disseminated tuberculosis.

The principal investigator for the trial is Dr. C. Fordham von Reyn, chief of infectious diseases at Dartmouth. He also heads the overall DarDar Health Project, established in 2000, of which the trial is one part. DarDar is a collaboration between Dartmouth Medical School and Tanzania's Muhimbili University College of Health Sciences (MUCHS) in Dar es Salaam. The project's name was drawn from the first syllables of "Dartmouth" and "Dar es Salaam" and also evokes the Swahili word for sister—"dada."

In addition to the clinical trial, the DarDar Health Project also includes a primary-care clinic for patients who are enrolled in the trial; a pediatric clinic for their children; a training grant, underwritten by the NIH's Fogarty International Center, which allows MUCHS faculty to earn degrees at DMS—master's degrees in public health and Ph.D.'s in basic science disciplines; jointly taught courses on HIV/AIDS and tuberculosis (TB); a faculty exchange program; opportunities for MUCHS students to visit DMS; and an elective that allows Dartmouth medical students to work at the DarDar Clinic and at MUCHS.

The clinical trial of the TB vaccine was the foundation on which all these activities were built. TB is the main cause of death in HIV/AIDS patients in

Tanzania, as in many developing countries. The disease usually affects the lungs, but in immunocompromised individuals it can disseminate, or spread, throughout the bloodstream. In resource-poor settings, disseminated TB often goes unrecognized and untreated. "Part of the DarDar study," explains von Reyn, "is to determine how blood cultures can help diagnose TB cases that are otherwise missed."

A second, even more important part of the study is a double-blind vaccine trial.

Patients get five injections over 12 months of either an experimental TB vaccine (Mycobacterium vaccae) or a placebo; then they report back to the clinic for follow-up visits every three months for three to five years. The treatments are coded so neither the patients nor the researchers giving the treatments know who gets the vaccine and who gets the placebo. "Our strategy in this study is to give a booster vaccine to HIV patients who had the standard TB vaccine, BCG, at birth . . . to help reduce the risk of people with HIV getting

tuberculosis," says von Reyn. The BCG (bacille Calmette-Guerin) vaccine is used in many countries with a high prevalence of TB—though not in the U.S. It is 80 percent effective in preventing childhood forms of the disease but loses its effectiveness by adulthood. "Our hypothesis is that the [experimental] vaccine will reduce the risk of TB by 50 percent," von Reyn adds.

In 2008, the researchers will break the code and evaluate the results to see

whether the experimental vaccine is effective. If it is, "the vaccine can be given to people with HIV on a large scale to reduce the incidence of TB," says von Reyn. In the meantime, faculty and students from MUCHS and from DMS—like von Reyn, who makes several trips a year to Tanzania, and like Cara Mathews, who shares her experiences there in a story that starts on the next page—will continue to travel back and forth, opening doors from one culture to another. From one medical system to another. From one people to another.