Adam Castillejo is said to have tested negative 30 months after getting off anti-retroviral therapy. [Courtesy, New York Times]

A Briton man has become the second to be cured of HIV.   Adam Castillejo is said to have tested negative 30 months after getting off anti-retroviral therapy.   However, his doctors say what healed him was not the HIV drugs.   Castillejo was being treated for cancer and had a stem-cell procedure.   The Lancet HIV journal reported that donors of those stem cells have an uncommon gene that gives them protection against HIV.   The BBC further reported that in 2011, Berlin patient Timothy Brown was the first person reported 'cured' of HIV.   Brown is also said to have undergone a stem cell procedure.   However, while he was still 18 months free of the HIV virus, researchers insisted it is too early to declare him cured. At the time he had already stopped taking HIV drugs.   How does the stem-cell treatment work?   The Stem-cell transplants stop the virus from replicating and replaces the patient's immune cells with those that resist the drug.   Castillejo, 40, decided to release his identity to the public and become an ambassador of hope.   He has been HIV-free for a year.   University of Cambridge lead researcher Prof Ravindra Kumar Gupta told BBC News "This represents HIV cure with almost certainty.   "We have now had two and a half years with anti-retroviral-free remission.   "Our findings show that the success of stem-cell transplantation as a cure for HIV, first reported nine years ago in the Berlin Patient, can be replicated."   Is there hope for people living with HIV?   Stem-cell treatment is an aggressive therapy meant for cancer patients, not HIV.   Prof Gupta said: "It is important to note that this curative treatment is high-risk and only used as a last resort for patients with HIV who also have life-threatening haematological malignancies.   "Therefore, this is not a treatment that would be offered widely to patients with HIV who are on successful anti-retroviral treatment."   Castillejo still has HIV remnants in his body, and researchers say it is still uncertain whether he may test positive again for HIV.   He told the New York Times: "This is a unique position to be in, a unique and very humbling position. I want to be an ambassador of hope."