Advances in stem cell treatment give hope to millions with 'incurable' diseases

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Here's what to know about the landmark case.

Experts universally hailed the case, even as they cautioned that the procedure that resulted in the likely cure - a bone marrow transplant to treat blood cancer - is too risky and costly to be applied as a general treatment for HIV, which can today easily be managed, though not cured, with pills. In 2007, Brown received a hematopoietic stem cell transplantation from a donor with two genetic copies of the CCR5 receptor, then had another transplant a year later following a relapse.

Doctors say they'll need to keep monitoring the London patient to see how his condition develops from here, and point out that this treatment would not necessarily work with all patients - not to mention that the donated stem cells used in this case are very rare, owing to the specific CCR5 mutation involved.

However, news that a second person may have been "cured" demonstrates that the Berlin Patient was not an anomaly.

Brown stopped taking ART after the transplant and has now been free of readily detectible virus for 12 years-meaning: he is cured. The unusual situation is one reason why this way of treating HIV is not done more often.

Professor Ravindra Gupta is a virologist at University College London. "Is that a cure?" This makes it a tricky and unfeasible option as a treatment for other HIV-positive patients in the near future. That's when it can also mutate to evade drugs.

This means the virus can not penetrate cells in the body that it normally infects.

"They used a reduced intense conditioning regimen but I think that had no influence on the outcome", he said.

This latest development is obviously big news for researchers hoping to cure HIV on a larger scale, but this particular case was extremely unique.

Could the patient's HIV come back?

But the virus is clever and comes in another form that can use a different, side entrance into cells through another receptor called CXCR4.

A mutation in the door's CCR5 gene stops HIV entering. "Everybody believed after the Berlin patient that you needed to almost die basically to cure H.I.V., but now maybe you don't".

That didn't happen with the London patient.

He was diagnosed with the disease in 1995 and started antiretroviral treatment.

This is the second known case of HIV going into long term remission. Worldwide, an estimated 36.9 million people were living with HIV at the end of 2017.

Bone marrow transplant is a high-risk, life-threatening procedure.

This is the second time a person has been cleared of HIV following a bone marrow transplant from a donor with this genetic mutation. CCR5 is also the gene that Chinese researcher He Jiankui tweaked in embryos to give them a genetically-engineered resistance to HIV infection throughout their lifetimes.

Brown, though, had undergone more severe treatment than the London patient and for a while researchers believed that his near-death experience was key to curing HIV.

Still, Fauci is hopeful that such approaches will eventually be available for HIV patients.

"I am an optimist because I'm a scientist and vice versa", Henrich said. The new patient, treated by doctors in Europe and nicknamed "the London patient" for anonymity, mirrors a similar case from over a decade ago, which scientists have spent years trying to replicate.