A 40-year-old man from London is believed to have become the second person in the world to be cured of HIV. Adam Castillejo remains free of the virus 30 months after he stopped anti-retroviral therapy, doctors said according to a report by the Independent.

A stem-cell treatment he underwent for cancer also cured him of HIV, according to a study published in the medical journal The Lancet.

The first person cured of HIV was Timothy Brown, initially known only as the “Berlin patient”, in 2011. He received a similar treatment and was found to be free of the virus after three-and-a-half years.

Donors of the stem cells received by Castillejo have an uncommon gene that gives them protection against HIV.

Castillejo, now known in the medical community as the “London patient”, has no detectable active HIV viral load in his blood, semen, or tissue. He was declared free of the virus just over a year ago.

According to scientists, stem cell transplants appear to halt the virus’ ability to replicate itself inside the body by replacing the patient’s own immune cells with donor ones that resist the infection.

Tests carried out on Castillejo suggest 99 percent of his immune cells have been replaced by donor ones.

Lead researcher Professor Ravindra Kumar Gupta, of the University of Cambridge, said:

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.

However, the “high-risk” stem-cell treatment is aggressive and was primarily used to treat the patient’s cancers, not their HIV.

Existing HIV drugs remain highly effective and enable people living with HIV to live long and healthy lives.

Prof Gupta said the treatment is “only used as a last resort for patients with HIV who also have life-threatening hematological malignancies”.

There is also no absolute certainty that Castillejo or Brown’s HIV will never return, as both patients still have remnants of the virus in their bodies.