Gene therapy: first of its kind at Sainte-Justine Hospital
Posted May 21, 2025 3:49 pm.
Last Updated May 23, 2025 4:14 pm.
An 18-year-old man is essentially “cured” after becoming the first patient ever treated with ultra-sophisticated gene editing technology, as part of an international clinical trial involving the Sainte-Justine Hospital.
The gene therapy, called “prime editing,” was used to correct, directly in the patient’s hematopoietic stem cells, a genetic mutation responsible for the serious immune system disease he suffers from: chronic granulomatous disease (CGD).
“Within two weeks, we saw that the abnormality was corrected in half of the cells, and after 45 days, in 66 per cent of the cells,” said Dr. Élie Haddad, the principal investigator of the clinical trial for CHU Sainte-Justine. “For us, a disease that corrects itself in 66 per cent of cells, if we did that with a (traditional) bone marrow transplant, we would be very happy with the result.”
“If you tell me tomorrow that I do a bone marrow transplantation and I correct 66% of the cells, I would say, oh, that’s a success,” he added.
If the result is stable, he added, it means the patient is “cured.”
The usual treatment for CGD is similar to that used for certain leukemias: the patient’s bone marrow — where the immune system’s white blood cells are formed — is destroyed with very aggressive chemotherapy, then a healthy donor bone marrow is transplanted.
However, for the patient, this is a very painful treatment that comes with several risks, such as the body rejecting the transplant.
“When we had the results we felt the emotion in the room and from the parents and himself thinking wow maybe im cured now,” said Dr. Haddad. “To say someone is cured, you need follow-up. We are optimistic. Things are doing well. We are 45 days, now 50 days after the transplantation, after the autologous gene therapy, things are doing well. We are optimistic that he’s going to be cured,” Dr. Haddad explained.
The “prime editing” technique avoids some of these problems. Initially, the preparatory chemotherapy, while not pleasant, is a little less “brutal” for the patient. Subsequently, since their own hematopoietic cells are given back to them after gene editing in the laboratory, no rejection is possible. The survival rate should therefore, in theory, increase from 80 per cent or 90 pet cent to 100 per cent.
“We’re very happy, we’re very optimistic, it’s fabulous,” said Dr. Haddad, who is also a professor at the faculty of medicine at the Université de Montréal. “We took his own bone marrow, cured it in a tube, reinjected it, and cured him. It’s fascinating because it opens the door to correcting all kinds of genetic diseases.”
Gene therapy as we knew it until now, explained Haddad, consisted of replacing a defective gene with a new, healthy one. “Prime editing,” he continued, takes it to the next level and can correct virtually any mutation.
“It’s like unzipping a zipper,” he explained. “You end up with the two strands (of DNA) separated from each other, you provide a template to the cell, telling it ‘this is what you need to do now,’ and you literally correct the mutation.”
The reason a patient with CGD was chosen as the first recipient of this therapy, explained Dr. Haddad, is that virtually all those affected by it have the same genetic mutation.
The plan was to treat nine other patients with the same disease. However, financial difficulties forced the American biotechnology firm that developed it, Prime Medicine, to suspend the clinical trial after only one patient.
“We share the bitterness and sadness of the other patients who were on the waiting list to be among the 10 patients who were going to benefit from this treatment and who learned that unfortunately, while it works, they won’t be able to be treated because it’s not profitable for the company or for some other reason,” said Dr. Haddad.
Prime Medicine has thus announced that their technology will be redirected to other diseases, areas that seem more “interesting” to them.
This demonstrates, adds Haddad, that this type of treatment should probably remain in the academic sphere and be managed by public funds, “because when you depend on industry, they can (pull the plug on the project) whenever they want, and it’s fundamentally sad and unfair to the patients who are waiting.”
“It’s very sad still for the other patients and the patients associations are also very bitter about that. It tells us that this type of strategy and treatment should belong to academic centers with public funding.”
That being said, now that “prime editing” has proven its worth with CGD, this “revolutionary” treatment could one day transform the management of rare genetic diseases, he assures.
“I often tell my friends, ‘You have no idea what’s coming, it’s completely crazy,'” concluded Dr. Haddad. “The obstacles we saw are falling one by one, and the future is now.”
–This report by La Presse Canadienne was translated by CityNews
