Dr Muiris Houston: Talk of a ‘cure’ for HIV is premature

Headlines around the world this week about a patient “cured” of HIV were suitably cautious. USA Today went with “HIV patient seemingly cured in second remarkable case”, while The Economist offered a careful “A second person has probably been cured of HIV”.

There is a chequered history of inappropriate media headlines when it comes to prematurely announcing cures for human disease. Even in cases where the latest breakthrough occurs in a study involving a small number of rodents, hyperbole is never far from the surface.

So while talk of a “cure” for HIV remains premature, reportage of the case of the “London patient”, published in Nature magazine, was relatively restrained. The case report was written by researchers from University College London, Imperial College London, Cambridge and Oxford universities.

In order to enter cells in the body, HIV latches on to receptors on the cell surface

Following a stem cell transplant, the patient, who was being treated for cancer, has now been in remission from HIV for 18 months and is no longer taking anti-viral drugs.

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The male London patient, who wishes to remain anonymous, was diagnosed with HIV in 2003 and advanced Hodgkin’s lymphoma in 2012. He had chemotherapy to treat the Hodgkin’s cancer. In addition, stem cells were implanted into the patient from a donor with inbuilt resistance to HIV, leading to both his cancer and HIV going into remission. But the primary target of the aggressive treatment was his cancer.

The case mirrors that of Timothy Brown, who 10 years ago received a bone-marrow transplant from a donor with natural immunity to the HIV virus. He too had cancer – a leukaemia – and was given two transplants and radiotherapy in a treatment strategy primarily aimed at his cancer.

Anti-viral drugs

So while the finding will influence the direction of continued research, it does not offer the hope of a new treatment for the millions of people living with HIV. Such aggressive cancer treatments would not be appropriate when we have a broad range of anti-viral drugs capable of suppressing HIV infection – to the point where the virus is undetectable in the blood stream.

Lifelong combination antiretroviral therapy (cART) can prevent the virus being transmitted to others and give people with HIV a near-normal life expectancy.

Prof Eduardo Olavarria from Imperial College London, one of the research team which this week presented its findings at the annual Conference on Retroviruses and Opportunistic Infections in Seattle, US, said: “The treatment is not appropriate as a standard HIV treatment because of the toxicity of chemotherapy, which in this case was required to treat the lymphoma.”

So what is the science behind a stem-cell approach to eradicating HIV?

In order to enter cells in the body, HIV latches on to receptors on the cell surface. CCR5 is the receptor the virus most commonly uses to enter cells.

A small number of people have two mutated copies of the CCR5 receptor which makes them resistant to HIV infection. Both Timothy Brown and the London patient received stem cells from a donor with this specific genetic mutation.

However, a reservoir of cells can still remain in the body (in a resting state) – another reason to be circumspect about the stem-cell technique. Much longer follow- up of the two patients is needed to ensure the virus does not re-emerge at a later stage.

Mutated receptors

What are the chances of a bone marrow transplant from a person with mutated receptors becoming an established treatment for HIV infection?

The International Aids Society said that “although it is not a viable large-scale strategy for a cure”, results from the second patient “reaffirm our belief that there exists a proof of concept that HIV is curable”.

It does suggest the possibility of gene technology or antibody treatments offering a safe treatment in the future.

With the success of cART in turning HIV infection from a death sentence to a chronic, manageable condition, the need for a cure is arguably less urgent. Coupled with the advent of PrEP – pre-exposure prophylaxis – whereby people who are HIV-negative take a pill once a day to reduce the risk of getting infected if they’re exposed to HIV, the spectre of Aids as a devastating illness has dimmed.

PrEP is very effective at preventing HIV infection. When used every day, in combination with condoms, PrEP reduces the risk of HIV infection by up to 99 per cent.

However, neither cART or PrEP can eliminate HIV, which is why scientists will continue to pursue the holy grail of a cure.

But as the early physician Hippocrates wisely observed, a doctor’s realistic aim must be “to cure sometimes, treat often, comfort always”.

A complete cure for most diseases remains a Utopian dream.