before powerful antiviral medicines became available, Kai Brothers lost his partner and many friends to AIDS. Thinking he was next, he quit his job, emptied his $401,000 and waited to die. Nothing happened.

It has been 16 years since Brothers learned he was HIV-positive. Since then, he has never taken AIDS drugs or had any illnesses associated with the disease. Despite his good fortune, Brothers says he feels isolated. “I don’t identify with people who are HIV-negative because I’m not,” he said. “I could infect someone. I don’t identify with the positive people, because I don’t have to deal with my health and medications and the things they have to worry about.”

Once a month Brothers visits the laboratory of Jay Levy, a professor at the University of California, San Francisco, who is director of the university’s laboratory for tumour and AIDS virus research. Since the epidemic began in 1981, Levy has been trying to understand why Brothers and others who are HIV-positive can remain medicine-free yet fit for decades, while the average person with HIV progresses to AIDS within 10 years, if untreated.

An answer to that question can help in the development of a vaccine. As a long-term survivor, also known as a long-term nonprogressor, Brothers, 42, is a much sought-after anomaly. Levy believes that about five per cent of people with HIV are medicine-free and still healthy after 10 years.

Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, defines nonprogressors as treatment-free people with HIV who have so little virus in their blood that it cannot be routinely detected. He suggests their numbers are far smaller, more like 0.2 to 0.4 per cent.

Long-term survivors have been around for a long time, said Mike McCune, senior investigator at the Gladstone Institute of Virology and Immunology. “We just don’t know why they do what they do,” McCune said. Martin Delaney, founder of the Project Inform, an HIV information and advocacy organisation based in San Francisco, said: “The disappointing thing is that there’s no consensus about what the long-term nonprogressors do. Different things explain it in different people.”

For many years, Brothers said, he carried a sense of guilt. Before his infection was discovered, his church encouraged him to donate blood four times a year. The blood bank discovered that one of its donors was HIV-positive and asked that Brothers, too, be tested. Reluctant to learn the truth, he refused and quit donating blood. In retrospect, Brothers, who had a flu-like illness in 1981, an early symptom of infection with the virus, believes he was HIV-positive before he began donating blood. “This is something I contributed to and could possibly have meant dozens of people contracting the virus and dying,” he said in an interview.

For years, he wanted to be part of a study. Five years ago, friends told him about Levy’s research. Even when AIDS was a death sentence, Levy, a virologist, knew that every virus had its survivors. He believed he could learn from those whose bodies had kept the virus in check.

Raising hope: A nurse talks to a HIV-positive woman in Papua New Guinea

Some of Levy’s subjects have been HIV-positive for 27 years, longer than there has been an epidemic. The dates of infection were confirmed by the San Francisco Department of Public Health, which in 1978 began a hepatitis B study of 6,704 gay men, whose blood was preserved. Over time, some of these nonprogressors have turned into slow-progressors, dying of AIDS. But there remain a dozen who are infected but have stayed healthy for more than 20 years without treatment.

In 1986, Levy discovered that in survivors, the white blood cells known as CD8 cells secreted minuscule amounts of an antiviral factor that blocked replication of viruses in cells but did not kill them. The better the antiviral activity of those cells, the healthier the individual. Levy has devoted his career to trying to determine what that factor is. “It is the hardest thing I’ve ever had to do,” he said.

Over the years, Fauci said, many people have grown skeptical. “I have tried to find the factor, and I can’t find what it is,” Fauci said. “I can demonstrate the phenomenon, but I can’t isolate the factor.”

Ten years ago, Dr Robert C. Gallo, a co-discoverer of the AIDS virus and the director of the Institute of Human Virology and Division of Basic Science at the University of Maryland Biotechnology Institute, said he was “fed up” waiting for Levy to reveal the elusive substance.

While searching for it, Gallo, along with Dr Paolo Lusso, discovered three chemicals, called chemokines, in the blood of long-term nonprogressors that inhibit a certain subset of the virus, “like bouncers at a disco,” Gallo said. He did not find Levy’s mysterious factor. But Gallo’s research has opened a new field of therapy.

By 1996, when better treatment became available and people with HIV were living longer, interest in survivors had diminished. But when it became apparent that a vaccine was still sorely needed the interest re-emerged. Dr Eric Rosenberg, an infectious disease doctor and assistant professor at Harvard who focuses on the earliest stages of infection, compares CD4 cells to generals in a bunker. In most people with HIV, he said, the generals quit ordering the CD8 “soldier” cells to kill HIV-infected cells. But in the nonprogressors, the CD4s continue to give their marching orders. Although many survivors attribute their good health to daily exercise, positive thinking, visualisation or eating egg whites, Levy said it was all about genetics. When his subjects ask him why they’re surviving so long, Levy said, he tells them, “You chose the right parents.”

Dr Mark Connors of the Laboratory of Immunoregulation at the infectious disease institute has enlisted 19 subjects from around the country. “Many of these folks are true altruists,” he said. “These are very healthy people,” yet they drop their careers to have blood examined at his laboratory. (NYTNS)