A British teenage girl has been successfully cured of leukemia using a new type of therapy called base editing. All other treatments for 13-year-old Alyssa had failed, so doctors at the renowned Great Ormond Street Children’s Hospital in London essentially created a new drug for her. Six months later, no cancer cells have been found in her body, although Alyssa is still under medical supervision.
In May of last year, Alice was diagnosed with T-cell acute lymphoblastic leukemia. Under normal conditions, T-cells are defenders of the organism, but in Alyssa’s case, their activity went out of control and became dangerous. Alice had a very aggressive form of cancer. Neither chemotherapy nor a bone marrow transplant helped. “At the end of the day, I would have died,” Alissa says. Her mother, Kiona, says she was dreading Christmas last year, thinking it was the last time they would be together, and just cried on her daughter’s birthday in January.
What happened next was unimaginable a few years ago. The team at Great Ormond Street has been using gene editing technology, which is only six years old. Nitrogenous bases are organic compounds that are part of nucleic acids. The four types of bases – adenine (A), cytosine (C), guanine (G), and thymine (T) – are the building blocks of our genetic code. Like the letters of the alphabet, the billions of bases in our DNA provide instructions for the human body. Editing the bases allows scientists to select a specific part of the genetic code and then change the molecular structure of just one base, transforming it into another and altering the genetic instructions.
The team of doctors and scientists used this tool to create a new type of T-cell capable of targeting and killing cancerous T-cells in Allison’s body. Healthy donor T cells were used for this purpose. In the final stage of genetic engineering, the T cells were given instructions to hunt down all cells containing the CD7 protein in order to destroy all the T cells in her body, including the cancerous ones. A second bone marrow transplant was expected to restore Alyssa’s immune system, including T cells. Alyssa remained susceptible to infections because both her cancerous T-cells and her disease-fighting T-cells were attacked during this treatment.
After one month, Alyssa went into remission and underwent a second bone marrow transplant to restore her immune system. Alyssa spent 16 weeks in the hospital, during which time she was protected from possible infections. After the examination, three months later, the doctors were concerned again because the girl showed signs of cancer. However, two subsequent scans showed a complete absence of cancer cells.
Alissa decided to donate her hair when she found out she was going to lose it anyway after chemotherapy. “Alyssa is the first patient to be treated with this technology,” said Professor Vazim Kasim of the University of California and Great Ormond Street Hospital. According to him, such genetic manipulation is a rapidly developing field of science with enormous potential for treating a wide range of diseases. However, the technology used to treat Alice is only a small fraction of what can be achieved by applying basic editing. Dr. David Liu of the Broad Institute, one of the inventors of the method, finds it amazing and unusual that the new method is being used to treat people just six years after it was developed. In the therapy developed for Alyssa, each base editing involved destroying part of the genetic code so that it would no longer function. But the technology can be applied more subtly and selectively – for example, instead of turning off a bad instruction, you can fix it. For example, sickle cell anemia is caused by a single base mutation that can be corrected. Scientists are already experimenting with editing the bases of sickle cell anemia, inherited high cholesterol and beta thalassemia (a blood disorder).