Rewriting Medical History》Scientists performed gene editing treatment in the human body for the first time and saved a newborn

For the first time, a Philadelphia team performed gene editing in vivo and saved a boy with a rare disease, setting a record for the world's first "in vivo gene editing" to save a human life. This article originates from a PopularMechanics article and is compiled and compiled by Dongzhu.

It is an absolute biological miracle that life can successfully copy the 3 billion distinct letters in the human genome, but sometimes mistakes are inevitable. Genetic disorders or other birth defects, whether inherited or developed during fetal life, are fairly common, occurring in one in 33 births in the United States, according to the Centers for Disease Control and Prevention (CDC).

Throughout human history, people born with such disorders often had to live with them for life, and depending on the severity of the defect, these lives could be extremely short.

But in 2025, human history changes forever.

In a groundbreaking research announcement published in the New England Journal of Medicine (NEJM), scientists, doctors and experts from top institutions in the United States, including the Children's Hospital of Philadelphia, the University of California, Berkeley, and the University of Pennsylvania School of Medicine, detailed how they successfully saved the life of a newborn named KJ.

In order to accomplish this incredible medical feat, doctors used the world's first customized "in vivo" (i.e. in vivo, not in a petri dish) CRISPR gene therapy. The technology, powered by decades of U.S. government-funded medical research, has the potential to alleviate the suffering of millions of people affected by genetic diseases each year.

“Years of advances in the field of gene editing, as well as close collaboration between researchers and clinicians, have made this moment possible,” study co-author Rebecca Ahrens-Nicklas of Children’s Hospital of Philadelphia said in a press release. "While KJ is a single case, we hope he is the first of many to benefit. This approach can be expanded to meet the specific needs of individual patients."

Real rescue like a medical drama

This astonishing medical intervention was like a TV medical drama, but the stakes were extremely real and serious. A week after KJ was born, doctors noticed something was wrong with him. After ruling out several possibilities, they discovered the brutal answer: a rare genetic disorder called severe methamphetamine synthetase 1 (CPS1) deficiency that affects only one in 1.3 million births.

This disease inhibits the body's ability to eliminate ammonia, a product of protein metabolism. This can have fatal consequences, affecting brain development and wreaking havoc on the liver. Typically, the treatment for this type of disease is a liver transplant, but that was not an option for KJ, who was too young to undergo surgery.

So after her diagnosis, Ahrens-Nicklas contacted Kiran Musunuru, a gene-editing expert at the University of Pennsylvania. “The clock started ticking in my head,” Musunuru later told The New York Times. Ahrens-Nicklas and Musunuru worked with a team of experts across the country for six months to develop a precision-directed gene therapy that targets KJ's specific CPS1 variant.

Meanwhile, KJ was undergoing medical monitoring in the hospital and was being kept alive on a completely protein-free diet. By the time the CRISPR treatment was ready, KJ's weight percentile had dropped to the seventh percentile for his age.

From "Fear" to "Going Home"

On February 25, 2025, the team began to implement treatment. Ahrens-Nicklas and Musunuru describe the process as both exciting and scary.

“One of the scariest moments was when I walked into the room and said, ‘I don’t know if this is going to work, but I promise I’ll do whatever it takes to make it safe,’” Ahrens-Nicklas recalled.

The first infusion took two hours. Within two weeks, KJ was eating protein like a healthy baby. The second dose came 22 days later, and about two weeks ago, KJ received his third treatment.

While it is unclear whether he will still need a liver transplant in the future, doctors can now say with certainty that a man's life has been saved thanks to the world's first "tailor-made" in vivo gene therapy. This is a huge testament to decades of research and experimentation. KJ is now back home with his family.

"We want every patient to have the potential to achieve the same results as this first patient," Musunuru said in the release. "The promise of gene therapies we've heard for decades is coming true, and it will revolutionize the way we approach medicine."