A man from London is the second person in the world to be cured of HIV. Adam Castillejo, now 40 years old, is still free of the virus more than 30 months after he completed anti-retroviral therapy. What makes the situation even more interesting is that the combination of drugs he was on as part of the therapy was not what actually cured him. Instead, his HIV cured by a stem-cell treatment he received while he was fighting cancer.

Apparently, the donor of the stem cells has a rare gene that protects against HIV, and this gene was transferred to Castillejo. This is actually similar to how the first person, Timothy Brown, was cured of HIV in 2011 after undergoing similar treatment. Researchers are confident that stem cell transplants are a cure for HIV, as it’s successes have now been replicated. But, at the same time, it will not be a regular treatment for people with HIV.

Stem cell treatment is considered a very aggressive therapy, hence why it is used to treat patients’ cancers and not their HIV. With current HIV drugs available to most people, it would be much easier to live long and healthy lives and forgoing stem cell transplants, according to medical professionals. The treatment is high-risk, so it should only be used as a last resort for patients with HIV. However, it does open the door for future developments in finding a cure using gene therapy.

We are not sure if the cure is permanent yet, as the tests suggest that 99% of Castillejo’s immune cells were replaced, meaning that he still has inactive remnants of the virus in his body, which is the same for Brown. Only time will tell if they stay free of HIV, but regardless, it still allows for further research into potentially low-risk, definitive gene therapy cures.