Leading the Biomedical Revolution

Dr. Kiran Musunuru (M.D. ’04, Ph.D), on left, and Dr. Rebecca Ahrens-Nicklas (Ph.D. ’10, M.D. ’11), holding baby KJ Muldoon

Dr. Kiran Musunuru (M.D. ’04, Ph.D.) and Dr. Rebecca Ahrens-Nicklas (Ph.D. ’10, M.D. ’11) made headlines earlier this year when they collaborated on a revolutionary therapy that changed the life of an infant with a rare genetic disorder at Children’s Hospital of Philadelphia (CHOP).

For the family of baby KJ Muldoon, it was nothing short of a miracle. And for the two physician-scientists, it was a victory with profound implications for the future of customized medicine.

Dr. Ahrens-Nicklas, a pediatric geneticist at CHOP who cares for children with rare diseases, first learned of KJ’s case shortly after his birth in August 2024. KJ had been diagnosed with a liver disorder that causes a buildup of toxic ammonia in the bloodstream. Without quick intervention, he would not survive.

Dr. Ahrens-Nicklas reached out to Dr. Musunuru, a cardiologist who performs research in gene editing for cardiovascular disease. The pair hoped to create a customized treatment that would use CRISPR-based gene editing to correct KJ’s genetic mutation.

The doctors’ academic partners and industry collaborators expedited production and testing of the drug. And the FDA approved administration of the therapy a month ahead of schedule.

Both physicians were in the room when 6-month-old KJ received his first infusion in February 2025.

“We were watching every breath he took, every noise he made, and he just slept through it and didn’t seem bothered by it at all,” says Dr. Ahrens-Nicklas.

“Hundreds of adult patients had received a gene-editing therapy without any serious issues,” says Dr. Musunuru. “So, part of my job was just keeping everyone’s anxiety levels down.”

KJ had two additional infusions of the therapy and is currently at home and doing well. The case is detailed in a study published by The New England Journal of Medicine.

Both doctors credit their training at Weill Cornell Medicine’s Tri-Institutional MD-PhD program with helping them bring the latest research to patients. Dr. Musunuru earned his doctorate in biomedical sciences from The Rockefeller University; Dr. Ahrens-Nicklas received hers in physiology and biophysics from Weill Cornell Medicine.

“Because of our combined training at Weill Cornell, we knew the common languages of basic science, clinical medicine and translational medicine, and we were able to talk to all the collaborators we had to convince to help us,’’ says Dr. Ahrens-Nicklas. “This absolutely would not have happened without the Tri-I program.”

The methodology of the pair’s pathbreaking treatment has laid the groundwork for the deployment of customized gene editing for a range of conditions that affect both children and adults, they say.

“There are so many diseases — especially in the rare pediatric disease space — where, if we correct genetic changes in the liver, there are limitless opportunities to benefit patients,’’ says Dr. Ahrens-Nicklas.

“This treatment gives you a sense of what’s possible,’’ adds Dr. Musunuru. “It has the potential to transform the practice of medicine for the entire spectrum of disease.”