A gene therapy method, which until recently would have seemed like science fiction, has allowed British medical scientists to save several patients in an experimental group from a previously incurable and highly aggressive form of blood cancer—T-cell acute lymphoblastic leukemia (T-ALL).

The approach involves editing the DNA of white blood cells, or leukocytes, turning them into a “living medicine” that attacks cancer cells.

The first patient to receive this treatment was a girl named Alyssa Tapley, whose story was covered by the BBC in 2022. No new cancer cells have appeared in her body since. Alyssa, who would have otherwise faced certain death, is now healthy and aspires to become a doctor to treat cancer patients.

Now, a team of scientists and physicians from two London hospitals—Great Ormond Street Hospital for Children and University College London Hospital—has published a report in the New England Journal of Medicine detailing the results of experimental treatment on Alyssa and ten other patients: eight children and two adults.

According to the report, nine of the eleven patients achieved deep remission, allowing them to undergo bone marrow transplants.

For seven patients, no signs of the disease were detected between three months and three years after treatment.

One major risk of this therapy, noted by the authors, is infection during the period when patients are temporarily left without an immune system.

In two of the eleven cases, both cancer cells and the modified donor T-cells lost the CD7 antigen marker, allowing them to “hide” from treatment.

“Given how aggressive this form of leukemia is, these clinical results are remarkable, and I am, of course, delighted that we were able to give hope to patients who would otherwise have lost it,” said Dr. Robert Kieza from the Bone Marrow Transplant Unit at Great Ormond Street Hospital.

The therapy modifies genes in T-cells, a type of lymphocyte that normally protects the body by fighting infections, but in T-ALL attacks the body itself.

Patients who agreed to experimental therapy had already not responded to chemotherapy or bone marrow transplants. Without this treatment, the only remaining option was palliative care.

Three years ago, doctors removed Alyssa’s immune system and regrew it from scratch. Now, there are no signs of cancer in her body, and she only needs an annual check-up.

The method relies on precise editing of DNA bases—adenine (A), cytosine (C), guanine (G), and thymine (T)—the building blocks of our genetic code. Scientists can target specific parts of the genome and change one base into another, altering genetic instructions.

Using this technique, the medical team engineered donor T-cells to track and kill cancerous T-cells in the patient’s body. This required careful programming to ensure that the “living medicine” would not attack itself.