A teenage girl’s incurable cancer has been cleared from her body in the first use of a revolutionary new type of medicine.
All other treatments for Alyssa’s leukaemia had failed.
So doctors at Great Ormond Street Hospital used “base editing” to perform a feat of biological engineering to build her a new living drug.
Six months later the cancer is undetectable, but Alyssa is still being monitored in case it comes back.
Alyssa, who is 13 and from Leicester, was diagnosed with T-cell acute lymphoblastic leukaemia in May last year.
T-cells are supposed to be the body’s guardians – seeking out and destroying threats – but for Alyssa they had become the danger and were growing out of control.
Her cancer was aggressive. Chemotherapy, and then a bone-marrow transplant, were unable to rid it from her body.
Without the experimental medicine, the only option left would have been merely to make Alyssa as comfortable as possible.
“Eventually I would have passed away,” said Alyssa. Her mum, Kiona, said this time last year she had been dreading Christmas, “thinking this is our last with her”. And then she “just cried” through her daughter’s 13th birthday in January.
What happened next was unimaginable just a few years ago and has been made possible by incredible advances in genetics.
The Great Ormond Street team used a technology called base editing, which had been invented just six years earlier.
Fundamentals are the language of life. Four types of bases – adenine (A), cytosine (C), guanine (G) and thymine (T) – are the building blocks of our genetic code. Just as letters in the alphabet have meaning, the billions of bases in our DNA spell out the instructions for our bodies.
Base editing allows scientists to zoom in on a precise section of the genetic code and then change the molecular structure of just one base, swapping it for another and changing the genetic instructions.
A large team of doctors and scientists used the device to engineer a new type of T cell capable of hunting down and killing Elisa’s cancerous T cells.
They started with healthy T cells that came from a donor and were ready to be modified.
- The first base modification disabled the targeting mechanism of the T cells so that they would not attack Elisa’s body.
- Another removed a chemical marker, called CD7, that is on all T cells.
- The third modification was an invisible coating that prevented the cells from being killed by chemotherapy drugs.
The last step of the genetic modification instructed the T cells to hunt down anything marked with CD7 so that it would destroy every T-cell in his body – including the cancerous ones. So this scar has to be removed by therapy – otherwise it will destroy itself.
If the therapy works, Elisa’s immune system – including T cells – will be rebuilt with another bone marrow transplant.
