Dr Waseem Qasim, UCL and Great Ormond Street Hospital
Inventing a cure for cancer, has in many ways, become medicine’s holy grail. Reaching, or finding it, is still a long way off, but one teenage girl’s reprieve, from what medicine has up until now, regarded as an incurable form of the disease, suggests that scientists are assuredly inching towards some form of a cure.
British teenager Alyssa, was diagnosed with T-cell acute lymphoblastic leukaemia. Hers was in a way, a form of leukaemia, where the body had turned in on itself. In a healthy person, T-cells are protective cells, which fight off threats to the body. But in T-cell leukaemia’s case, like Alyssa’s, the cells become a danger to the body they are supposed to protect.
The normal treatment, chemotherapy, bone marrow transplant, were unable to clear the cancer. Doctors at London’s world renowned children’s hospital, Great Ormond Street, informed Alyssa’s parents, that it was a question of making her as comfortable as possible, with palliative care. The doctors had done all they could have done, and the parents were now faced with having to accept that this Christmas, in all likelihood, might be the last with their child.
With no more tried and tested treatments left, doctors turned to a revolutionary, new experimental treatment, base editing. That this is possible at all, owes to the extraordinary advancements made in the study of DNA (Deoxyribonucleic acid) in the last few years. Base editing was discovered only six years ago, by among others, Dr David Liu, of Harvard University.
Bases or base pairs, are nucleotides, a type of molecules, on opposite strands of the DNA double helix, which pair up, forming chemical bonds with one another.
There are four bases in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). One copy of the human genome consists of approximately 3 billion base pairs of DNA. The scientists who have learned how to read them, are able to see everything they need to know about our bodies.
In base editing, scientists have to identify a small part of the molecular structure of just one base, out of billions, and alter it to change the genetic instructions.
The team of doctors and scientists at Great Ormond Street, constructed a new type of T-cell, using cells from a healthy doner. The new T-cell would then go battling and destroying Alyssa’s rogue cancerous T-cells.
But as even non scientists know, to every action, there is a reaction, and so, the slightest alteration of the tiniest part of our DNA, requires managing unintended consequences.
The team had to adapt the healthy T-cells, so they did not attack the patient’s body. All T-cells have a chemical, known as CD7. This was removed. The next edit was to enable the new cells, to effectively hide themselves, from chemotherapy drugs, intended to destroy the cancer, which would have destroyed them too.
DNA Double Helix
Having protected some T-cells, by the removal of CD7, the T-cells were then instructed to seek and destroy whatever was left in Alyssa’ body, with the CD7 chemical marking, including the cancerous cells.
By the end of the treatment, Alyssa would be left at the mercy of every infection, as the cells whose job is to provide our immune system, had been destroyed. A new bone marrow transplant, would restore them, and her immune system. Until then, she had to be isolated from anyone, and anything, that might infect her with any germs, including members of her family.
The most recent tests after the treatment, found Alyssa clear of the cancer. She continues to be monitored, but is now expected to be at many more Christmases and New Year’s celebrations.
Alyssa is the first person to receive this pioneering treatment, but many more patients are expected to follow.
It is, said one of the team leaders in Alyssa’s treatment, Professor Waseem Qasim, from University College London (UCL) and Great Ormond Street hospital, “a very fast moving area of science, with enormous potential.”
With the team already sharing all their findings, in Alyssa’s treatment, with colleagues around the world, base editing is now an exciting area of medicine, expected to be developed for the treatment of other diseases.
