An HIV sufferer who came off medication 15 years ago is still living with the virus but her immune system is keeping it under control.

This, say experts in Spain, makes the woman – referred to only as the ‘Barcelona patient’ – an “exceptional” case in the world.

Her case – presented at the 24th International AIDS Conference in Montreal, Canada – is different from other high-profile cases that have seen sufferers completely cured of AIDS after receiving stem cell transplants to treat the blood diseases they were suffering from.

It was more than 15 years ago when the Barcelona patient was diagnosed with an acute HIV infection – the earliest stage of HIV infection – and was put on a clinical trial consisting of antiretroviral therapy for nine months and several doses of the immunosuppressant medication cyclosporine A.

It was revealed at the conference that she still harbours viable HIV but her immune system has controlled replication of the virus over the years.

Experts at the Hospital Clinic de Barcelona will now attempt to replicate the woman’s immunological mechanisms in other infected patients.

Antiretroviral therapy – the standard for keeping AIDS under control – is effective in suppressing viral replication within the body and blocking transmission to others, leaving the patient with such a low level of HIV in the blood that it becomes undetectable in a conventional analysis.

But the virus persists in reservoirs, so if the therapy is stopped, it has the ability to replicate and can attack the patient again.

However, a very small group of people, such as the Barcelona patient, are ‘post-treatment controllers’ and, after coming off medication, manage to maintain undetectable viral loads.

Josep Mallolas – head of the HIV unit at the Hospital Clinic de Barcelona – said the woman’s case “is exceptional not only because there are very few people with long-term post-treatment control (15 years), but also because of her HIV control mechanism, which is different from that described in ‘elite controller’ patients and other cases documented so far.”

‘Elite controller’ patients are people who are infected with HIV but never develop symptoms and require no medication due to an extremely rare natural response.