The proof that Aids can be cured?
The 'Berlin Patient', Timothy Brown, who was once HIV positive, has been in the clear for five years after a bone marrow transplant in 2007 while a student in Germany. The transplant was undertaken to treat a type of blood cancer but in the process it also apparently cured Mr Brown of his HIV infection.
Françoise Barré-Sinoussi the woman who discovered the Aids virus in 1983 believes his story offers hope to millions.
Five years after his transplant, he continues to be free of HIV despite having given up his anti-viral drugs. It is still not clear to scientists why Mr Brown has managed to shrug off his chronic HIV infection so effectively.
Professor Barré-Sinoussi and her colleague Professor Steven Deeks of the University of California, San Francisco, say that Mr Brown has been effectively cured of HIV – the first person in the world to fulfil the strict scientific definition of a cure.
"He has now been free of readily detectable virus in the absence of therapy for more than five years. In other words, he is cured. His experience suggests that HIV infection might one day be curable," they say.
But even if Mr Brown does continue to defy scientific dogma, the method of his cure would never be appropriate for treating the millions of people in the world who are infected with HIV. A bone marrow transplant is not only expensive and difficult to undertake, it is extremely risky – Mr Brown suffers chronic neurological problems as a result of a second bone marrow transplant he had to receive to treat a relapse of his blood cancer.
Professors Barré-Sinoussi and Deeks accept that his case is only a starting point on the long journey towards a possible cure for HIV. "The barriers to curing HIV are real, and they may prove to be insurmountable," they admit.