CRISPR, the groundbreaking and controversial gene-editing technique, has been used in a patient with a debilitating blood disease, scientists revealed today.

The US and Swiss companies behind the venture claim to be the first ever to use CRISPR on a human, disregarding the use of it on cancer patients in China.

The unidentified patient in the clinical trial has beta thalassemia, a hereditary condition that turns off a crucial gene, hampering their ability to make hemoglobin, which is needed to push oxygen around the body.

Sufferers spend their lives on blood transfusions to offset the defect.

But Swiss biotech company CRISPR Therapeutics, backed by Boston's Vertex Pharmaceuticals, has attempted to cure the disease using the experimental DNA-editing technique CRISPR to switch the defective gene back on.

The firms say they are soon to do the same with another patient who has sickle cell anemia, a blood condition that causes excruciating pain.

The scientists hope the treatment - which involves collecting certain stem cells from the blood, editing DNA in the stem cells with CRISPR-Cas 9, and infusing it back into the patient - will be a one-and-done cure.

While it's still too early to tell, the attempt alone sent the company's stock price soaring on Monday afternoon.

The US and Swiss companies behind the venture claim to be the first ever to use CRISPR on a human, disregarding the use of it on cancer patients in China

'Treating the first patient in this study marks an important scientific and medical milestone and the beginning of our efforts to fully realize the promise of CRISPR/Cas9 therapies as a new class of potentially transformative medicines to treat serious diseases,' Samarth Kulkarni, chief executive of CRISPR Therapeutics, said.

Dr David Altshuler, Chief Scientific Officer at Vertex, added: 'Beta thalassemia and sickle cell disease are serious, life-threatening diseases, and we are evaluating ex vivo treatment with CTX001 with the goal of creating a one-time potential curative therapy.'

WHAT IS CRISPR?

CRISPR Cas9 is a powerful tool that can spot defective genes, cut them out, leaving space for a healthy gene to be inserted.

It is a natural tool found inside certain viruses, used to recognize and destroy their enemy: bacteria. These viruses carry 'mugshots' of their nemesis bacteria, and when they see them, they splice them in two, destroying them.

Scientists discovered this in the 1980s, and in the 1990s Jennifer Doudna realized it could be repurposed as a tool for medicine. They could replace the bacteria mugshot with a DNA mugshot, sending the virus to chase and destroy the defect at hand.

Once there's a gap in a chain of DNA, all you need to do is throw a healthy gene in the vicinity, and an army of clean-up enzymes will hurry to slot it into place.

In the case of CTX001, they extract stem cells from the patient, which contain the defective genes. These stem cells are edited using CRISPR, and those edited cells are infused back into the patient.

FROM LAB TO HUMANS - FIRST IN CHINA, AND NOW IN THE U.S.

Once CRISPR-Cas 9 was discovered, it was clear the potential was huge - both positive and sinister.

But until last year, there was general consensus (or, hope) that human applications were a distant prospect.

Regulators banned its use, even in clinical trials, while scientists, theologians and public health officials tried to reach an ethical consensus.

Then it emerged that oncologists in China's Hangzhou Cancer Hospital, just west of Shanghai, were trying it in clinical trials with cancer patients. Scientists across the world were quietly concerned, but intrigued to see the findings.

That calm was derailed when Dr He Jiankui of the Southern University of Science and Technology in Shenzhen told a conference last November that he had used CRISPR-Cas 9 to edit embryos.

In twin girls, Lulu and Nana, he had used the technique to remove the gene CCR5. As a result, he said, they did not inherit their father's HIV. And he said he has more patients lined up.

Predictably, the global medical and science communities panicked. The latest came last week: neuroscientists who study CCR5 found evidence that editing the gene can impact the brain - adding yet more fuel to the fire.

And weeks later, it emerged the Shanghai oncologists had lost track of the patients in their trial - meaning they may never know the long-term impact of their tweaks.

WHY THE NEW CLINICAL TRIAL IS SAFER THAN 'ROGUE' TRIALS

There are two ways you can edit genes: somatic and germ-line.

Somatic gene-editing involves editing one gene, one time, in a way that is not heritable.

Germ-line gene-editing would affect all cells, and would be passed on to future generations.

The fear with Dr He's work is that it could be germ-line, meaning its effects might not be clear for generations, and we may not know how to reverse if the results are disastrous.

The new therapy by CRISPR Therapeutics and Vertex, dubbed CTX001, is somatic, which is regarded as safer and earned the green light from regulators.

News of the new clinical trial sent shares soaring 25 percent on Monday, an injection of relief for investors in the technology after another team, Sangamo Therapeutics, posted disappointing results last week.