Timothy Brown, 46, became the first person in history to be cured of HIV after receiving a blood stem cell transplant from a person resistant to the virus.
Doctors did the breakthrough surgery in 2007 as they treated Brown for the leukaemia that he had been diagnosed with a year earlier.
And now doctors are one step closer to emulating the success of Brown’s surgery to help the estimated 34 million people worldwide who are HIV positive.
Experts hope that umbilical cord blood transplants could provide a similar solution to Brown’s in curing the virus.
Brown – often known as “The Berlin Patient” because he formerly lived in that city – first tested positive for HIV in 1995.
In 2007, when he was still living in Germany, Brown was undergoing extensive treatment for leukaemia.
During the course of his treatment, doctors gave him a bone marrow stem cell transplant from a donor with a genetic mutation that made him immune from HIV.
The mutation, called delta 32, occurs in an estimated 1 percent of people descended from northern Europeans, with Swedes being the most likely candidates.
The percentage is far less in people of other races. In 2007 Brown’s doctors tested nearly 70 donors before they found a match.
Scientists have been studying immunity to HIV since the disease was discovered 30 years ago, as it soon became apparent that a small percentage of people seemed to be naturally resistant.
Researchers eventually homed in on a gene called CCR5. That gene codes for a protein that acts as a “receptor” outside white blood cells – essentially a “lock”.
If that receptor isn’t present, it seems HIV cannot break into the blood cell. That means it cannot begin the infection that eventually leads to Aids.
Scientists believe those who have one copy of the CCR5 gene enjoy some resistance against HIV, but not total immunity.
That seems to be the case in about 10 to 15 percent of those descended from northern Europeans.
Those who inherit two copies of this so-called “immune gene”, one from each parent, seem to have strong immunity to HIV.
Scientists say the gene is really a mutation, and that DNA studies suggest it arose in the Middle Ages.
Some experts have suggested it spread in response to the Black Plague, while others have pointed to smallpox as more likely.
However, stem cell transplant isn’t feasible as a widespread treatment for HIV patients because it is often very difficult to find a matching bone marrow donor, and much harder to find one who also carries the HIV-resistant gene.
Conversely the match between donor and recipient in umbilical cord transplants does not need to be so close, according to Dr Lawrence Petz, medical director of StemCyte, an umbilical cord blood bank.
Petz told ABC News that Brown’s transplant was made more complicated because the blood stem cells came from an adult donor.
“When you do (stem cell transplants) you have to have a very close match between donor and recipient,” Petz told the news station. “With umbilical cord blood, we don’t need such a close match. It’s far easier to find donor matches.”
However, out of 17 000 samples of cord blood, Petz and his colleagues have found only 102 with the genetic HIV-resistant mutation – so the bank needs to be built up over time.
“At the present time, I feel there’s no other way to cure a reasonable number of patients other than using cord blood,” Petz told Fox News.
The first cord blood transplant on an HIV infected patient from the Netherlands was performed a few weeks ago and Petz’s team have another transplant lined up for a patient in Spain later this month.
It will take months before researchers can tell if the treatment has made any difference to the patient’s HIV.
“We don’t know the final outcome yet, but we’re very optimistic that the transplant will be of significant benefit to the patient,” Petz told Fox.
Like in Brown’s case, the transplants aren’t carried out solely to treat Aids: the patients have an additional condition that requires the transplant.
“It can be done. It’s just a matter of time,” Petz said of finding a cure.
Since his transplant Brown’s body has shown no signs of HIV.
“I feel good,” he told ABC News.
“I haven’t had any major illnesses, just occasional colds like normal people.”
Brown, who feels guilty to be the only person to have been cured of the illness, hopes his story will inspire sufferers that a cure is possible.
“I don’t want to be the only person in the world cured of HIV. I want a cure for everyone,” he said. – Daily Mail