Toddler dies after experimental operation

Less than three months after receiving a synthetic windpipe made from her own stem cells, 2-year-old Hannah Warren has passed away.

Warren died Saturday at Children’s Hospital of Illinois, according to a statement from the hospital. She was the youngest patient to undergo the experimental windpipe procedure and the first patient to receive it in the United States. She would have been 3 years old in August.

“Our hearts are broken,” her family wrote on their blog. “We will forever miss her infectious personality and miraculous strength and spirit. … She is a pioneer in stem-cell technology and her impact will reach all corners of our beautiful Earth.”

The Korean-Canadian toddler was born without a trachea – a condition that’s fatal in 99% of cases. She spent every day of her life leading up to the transplant surgery in intensive care, kept alive by a tube that connected her mouth to her lungs.

Dr. Paolo Macchiarini, director of the Advanced Center for Translational Regenerative Medicine at the Karolinska Institute in Stockholm, Sweden, performed Warren’s operation on April 9. Her new windpipe that was created using stem cells from the toddler’s bone marrow and plastic fibers shaped into a tube.

Stem cells are able to develop into different types of body cells and are great at adapting to a new environment. Because of this, the body is less likely to reject organs made from these cells, especially if they come from the patient.

Children make ideal patients for regenerative procedures, since they are naturally better than adults at healing and growing new tissue.

In the months after surgery, Warren’s new trachea was doing well, the family wrote, but her lungs continued to deteriorate. Dr. Mark Holterman, a pediatric surgeon at the hospital, told the New York Times that the trachea operation also involved surgery on the toddler’s esophagus, which never healed properly.

Macchiarini has performed six of these transplants worldwide. Four of the patients are doing well. The fifth was a cancer patient from Baltimore named Christopher Lyles; he died four months after receiving the synthetic trachea in Sweden, according to the Baltimore Sun.

Macchiarini told the Times Sunday that he plans to continue with similar operations, including one he is performing this week in Stockholm.

“Although regenerative medicine remains in the early stages for pediatric patients, progress is being made,” Children’s Hospital of Illinois said in their statement.

“Even at this time of loss and grief, we, and Hannah’s family, take comfort in the knowledge that the efforts of her physicians and the care team working with them will benefit and serve other children and adults in the years to come.”

TIME’s Alexandra Sifferlin contributed to this story.