Remission in any disease means that you are now living disease-free. No more treatment – your immune system has it all under control once more. Remission is the news that all cancer patients hope for. It isn’t a path that HIV patients thought was open to them.
But then the Berlin patient went into viral remission following a stem cell transplant in 2009. 10 years later, the London patient also went into viral remission following a stem cell transplant.
So, does that mean that stem cells could be the answer to curing HIV?
Not so fast.
10 years ago the Berlin patient, an HIV patient, had his HIV go into ‘remission’ after receiving a stem cell transplant to treat his leukemia. And then in March this year it happened again – a second HIV patient had their HIV go into ‘remission’ – the London patient, following a similar stem cell transplant to treat his Hodgkin lymphoma – a form of blood cancer.
Not that scientists can agree exactly what ‘going into remission’ for HIV means, because they just don’t know enough about the dormant HIV virus and what the future holds for patients who stop taking their antiretroviral therapy (ART) drugs long term. But for these two patients, the HIV viral load was undetectable after the patients had ceased their HIV treatment – 10 years and counting for the Berlin patient, 18 months for the London patient
But before the celebrations can begin heralding a cure for HIV, let’s back up.
Current HIV treatment
The HIV virus attacks and infects the body’s immune cells and so the current HIV treatment involves the long term use of ART drugs. The drugs are designed to keep the virus at low levels, and under control, but they can’t eradicate it from a patient’s cells entirely.
If HIV patients opt to stop taking their ART drugs for whatever reason, the virus will come back within just a few weeks.
Is it possible for HIV to go away?
But both the Berlin patient and the London patient had ceased taking ART drugs, and the virus has remained at negligible levels ever since.
Both patients during the course of their stem cell treatment received stem cells from donors to repopulate their own immune cell numbers. They both had to use a donor because their own stem cells weren’t a viable option – doctors typically prefer to harvest a patient’s own stem cells as it increases the chances of success and reduces the chances of complications including the patient’s body rejecting the donor stem cells, but in both these cases the patients had developed immune-cell cancer, so their own stem cells couldn’t be used.
Is a stem cell transplant a potential treatment for HIV?
Well, in both cases the stem cell transplants were intended to generate healthy new blood cells in the recipient, in order to fight the cancer, not the HIV virus. It just so happened that one of the advantageous side effects turned out to be HIV remission.
Both patients received a stem cell transplant from donors who had a natural mutation in both copies of the gene CCR5 – the gene that encodes a receptor protein on the immune cells that the HIV virus binds to during infection.
The mutation that the donors had meant that there was an absence of functional CCR5 proteins on the immune cells’ surface, making them resistant to the strains of HIV virus that depends on the CCR5 to infect immune cells. And both patients had been infected by a form of the HIV virus that depend on the CCR5 protein to gain entry into immune cells.
After the success of the Berlin patient, doctors had tried (unsuccessfully) for years to replicate their findings with other HIV patients with similar cancers, but their efforts yielded nothing. Until the London patient.
The fact that the treatment has worked twice has researchers hoping they could be onto something and are working hard to figure out just what the key was with both of these patients. Because by replicating treatment, it could help prevent almost 1,000,000 people being killed by this disease every year.
But hope is all HIV patients have to hold onto at this stage, because HIV remission after a stem cell transplant is not something that happens in every patient with HIV who receives a stem cell transplant.
In fact there have been reports of the adverse effect occurring – the same treatment that the Berlin and London patients received was given to a person with the exact strain of HIV they had, but a donor stem cell transplant caused their levels of HIV virus to rise rapidly in their bloodstream on ceasing the ART drugs. This rise was caused by a pool of dormant virus that used a different protein, CXCR4, not the CCR5, to gain entry into immune cells, and these strains of HIV are renowned for their drug resistance.
As well as differing strains of HIV complicating the process, stem cell transplants from donors are expensive, risky and each treatment needs to be specifically tailored to each individual patient, meaning stem cell transplant as a treatment is not easily scalable. Essentially replacing the current treatment of taking a couple of pills each day with a procedure that might result in further disease or even death, just isn’t a viable option. Presently.
Yes the transplant worked for these two patients, but to counter the media reports that ‘gene editing could end HIV’, there is nothing in either of their two cases of HIV remission that suggest gene editing could be the answer.
The world’s media hopped on this exciting story, understandably, but this recent case of HIV remission is just that, a solitary case report of one individual’s disease and outcome. It doesn’t mean that the patient’s situation is applicable to the wider population. Yes it is a step forward in HIV research, a significant one that offers hope to the millions of people living with HIV, but that is all it can offer currently, hope, not a cure.