Carl June, a leading University of Pennsylvania researcher, called Brown's success "the holy grail" of HIV cure research.
"It was a real tipping point," June said. "I'm sure over the next decade, we're going to see major advances to find case No. 2 and even past that."
Brown was in Philadelphia on Thursday to share his remarkable story at the Prevention and Outreach Summit at the Convention Center. The free event, sponsored by the AIDS services group Philadelphia FIGHT, began at 8:30 a.m.
Human Immunodeficiency Virus (HIV), the virus that causes AIDS, has long been considered incurable. Advances such as the development of combination antiretroviral drugs in the 1990s gave hope to people living under a death sentence.
Those with access to drug therapy now can think of HIV as a chronic but manageable condition, a massive victory; without treatment, AIDS can kill in one year.
Brown's story stands apart from this narrative.
In an interview, he spoke slowly and methodically about his journey. He is graying and balding now. Though his short-term memory has been weakened by years of intensive care, earlier memories retain their charm.
Bored with his banking job in Seattle, Brown moved to Europe in 1991. In Barcelona, he lived in a four-bedroom apartment crammed with three men from Syria, Catalonia, and Germany, and two Japanese women. "My room should have been a closet but it was rented to me as a room," he recalled. The Catalonian had a preference for playing piano naked, which tickled the women and infuriated the Syrian.
He thinks he contracted HIV in the early 1990s from a Spanish lover.
Brown discovered his positive status in 1995, after following another lover to Berlin and beginning preliminary studies for a political science degree.
"It was a huge shock," he said. "At that point, HIV was a death sentence, or we thought it was."
Luckily for Brown the first protease inhibitor drugs - and the lifesaving combination therapies - became available the next year. Soon, he managed his disease and built a life in Berlin working as a translator and market research analyst, remodeling apartments and vacationing throughout Europe with his partner.
Then in 2006, he started feeling fatigue on a trip to New York for a friend's wedding. He thought it was jet lag, but after returning to Berlin, the fatigue worsened until one day his strength while biking dwindled so much that he had to get off and walk. His doctor eventually found he had acute myeloid leukemia.
Weakened by HIV, Brown could not endure the chemotherapy treatment for his leukemia. He developed pneumonia and a blood infection before abandoning the treatment.
When his leukemia relapsed, his German doctor, Gero Hütter, recommended ablation, or the obliteration of the immune system, followed by an infusion of healthy stem cells, replacing the cancerous immune system with a healthy one.
Hütter had heard of research on the CCR5 receptor, a protein on the surface of white blood cells. Many forms of HIV use the CCR5 receptor to gain entry into human cells. Some people with a mutation called CCR5-delta32 have proved resistant to HIV.
Because Hütter wanted to give Brown a bone-marrow transplant for the leukemia, he decided to try to find a marrow donor who carried the mutation.
In February 2007, Brown stopped taking his HIV medicines and had his first bone-marrow transplant. Though his leukemia relapsed and he needed a second transfusion, he remains free of HIV to this day.
His case raises many questions. Bone-marrow transplants are very risky. The transplanted stem cells can attack the host's body or the graft can fail, and a significant minority of patients die.
Brown suffered severe complications from the transplant. He nearly died after his second procedure. He was even released from the hospital and sent home for hospice care.
"They had given up on the experiment, and I was supposed to go home and die," Brown said. He suffered from dementia and incontinence and required nearly a year of rehabilitation to walk.
"I still have physical problems," he said. "Mentally, I feel like I'm on the road to recovery."
Brown's treatment is not viable for most HIV patients. But it brought new attention and money to the quest for a cure.
"Up until my case, people had given up on the word cure," Brown said. "Since my case was released, a lot of scientists are working on the cure."
Scientists are making headway.
Lawrence Petz, chief medical officer of the California blood bank StemCyte, has been collecting cord blood stem-cell samples that have the CCR5-delta 32 mutation. He said he has 102 samples and hopes to expand to 300 samples, so HIV-positive people in need of a stem cell transfusion can search for a match.
Cord blood stem cells function like bone marrow stem cells but are easier to match.
Still, the transplant is risky, so it will likely benefit only HIV-positive people with another life-threatening disease.
StemCyte has recently sent stem cells to a patient in the Netherlands for a transplant. Although they have to wait a couple of months to test for HIV, Petz is optimistic that a second patient could be cured.
Another approach that scientists are exploring is to genetically modify cells to have the CCR5-delta32 mutation, making them HIV-resistant. Scientists including Penn's Carl June are working with "zinc finger nucleases" which act as molecular scissors that can snip the CCR5 receptor. When it fuses back together, the receptor is mutated, blocking access to HIV.
Still other researchers are looking at ways to attack reservoirs of HIV that hide out in the body even during treatment. People with HIV have to keep taking drugs to hold the virus in check. If treatment stops, the virus emerges from its hiding places and runs rampant.
Last week, researchers reported there might be inactive, broken pieces of virus in Brown's blood. It was the first time anyone had found any trace of the virus since his rise to fame. Some scientists questioned the findings, saying they could have been caused by contaminated samples.
Brown thinks the possible remnants of HIV are not important: "I don't have to take medication and the virus isn't doing anything to my body."
He has a "functional cure," which means the immune system functions normally and the virus does not replicate or require treatment. He says the jury is still out on whether he has a "sterilizing cure," in which all traces of the virus are absent from the body.
At first, Brown, who now lives in San Francisco, said he wanted to stay out of the spotlight and was just happy to be cured. But he realized he had a responsibility to do more.
"I've been told by people who were basically suicidal that hearing my story gave people hope and made them want to stay alive," he said. "I started thinking about the fact that I was the only one in the world cured by HIV and I needed to give back to society."
Contact Allyn Gaestel at firstname.lastname@example.org.