HIV & Stem Cell Therapy

HIV (yellow) infecting a human immune cell (blue).Credit: NIH/SPL

Only two HIV sufferers in the world have been cleared of the virus, but the fact that both received the same treatment is cause for cautious celebration and suggests stem cell therapy could offer a lasting alternative to a lifetime of medication.

The second person with HIV has been cleared of the virus after receiving a stem-cell transplant that replaced their white blood cells with HIV-resistant versions, though researchers warn that it is too early to say that they have been cured. 

In an article published this week in Nature, Matthew Warren discusses the findings and their implications HIV patients.

The anonymous patient has stopped taking antiretroviral drugs, with no sign of the virus returning 18 months later. The stem-cell technique was first used a decade ago to treat Timothy Ray Brown, who is still free of the virus.

Like Brown, the second patient had a form of blood cancer that didn’t respond to chemotherapy and needed a haematopoetic stem cell (HSC) transplant. In this treatment commonly used to treat diseases of the blood and immune system in their advanced stages, the patient’s blood cells are destroyed before being replenished with HSCs from a healthy donor.

This therapy provided an opportunity for the medical team — led by Ravindra Gupta, an infectious-disease physician at the University of Cambridge, UK — to select a donor with two copies of a mutation in the CCR5 gene that gives people resistance to HIV infection.

Gupta’s team report that the transplant successfully replaced the patient’s white blood cells with the HIV-resistant variant. Cells circulating in the patient’s blood stopped expressing the CCR5 receptor, and in the lab, the researchers were unable to re-infect these cells with the patient’s version of HIV.

The team found that the virus completely disappeared from the patient’s blood after the transplant. After 16 months, the patient stopped taking antiretroviral drugs, the standard treatment for HIV. In the latest follow-up, 18 months after stopping his medication, there was still no sign of the virus.

Gupta says that it’s not yet possible to say whether the patient has been cured. Whilst this can only be demonstrated if the patient’s blood remains HIV free for longer, the study does suggest that Brown’s successful treatment ten years ago wasn’t just a one-off.

A breakthrough for HIV?

Gupta says that the latest patient received a less aggressive treatment than Brown to prepare for the transplant. The new patient was given a regimen consisting of chemotherapy alongside a drug that targets cancerous cells, while Brown received radiotherapy across his entire body in addition to a chemotherapy drug.

This suggests that, to be successful, stem-cell transplants in HIV patients would not necessarily need to be accompanied by aggressive treatments that might have particularly severe side effects, says Gupta. “The radiation really does knock the bone marrow and make you very sick.”

Graham Cooke, a clinical researcher at Imperial College London, points out that this kind of treatment wouldn’t be suitable for most people with HIV — who don’t have cancer and so don’t need a bone-marrow transplant, which is a serious procedure that can sometimes have fatal complications. “If you’re well, the risk of having a bone-marrow transplant is far greater than the risk of staying on tablets every day,” he says. Most people with HIV respond well to daily antiretroviral treatment.

But Cooke adds that for those who need a transplant to treat leukaemia or other diseases, it seems reasonable to try and find a donor with the CCR5 mutation, which wouldn’t add any risk to the procedure.

Gero Hütter, who led Brown’s treatment and is now medical director of the stem-cell company Cellex in Dresden, Germany, agrees that this kind of treatment could only ever be used for a small group of patients. But he hopes that the paper will stimulate a renewed interest in gene therapies that target CCR5, which could be applied to a much broader group. “The real breakthrough, we are still waiting for,” he says.

 

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