Youngest Cedars-Sinai Stem Cell Donor Helps Doctors Treat Dad’s Leukemia

In July, Nick Mondek, MD, drove his healthy 9-year-old son Stephen to Cedars-Sinai on an important mission: To donate stem cells that might cure Mondek's deadly blood cancer. Stephen's donation would give Mondek a brand-new immune system-and make Stephen the hospital's youngest-known stem cell donor.

"A donation from a child this young is very rare," said Hoyoung Chung, DO, a critical care pediatrician at Cedars-Sinai Guerin Children's. "Stephen was very brave, and our team made sure everything went perfectly so that this young boy could help his father."

Mondek, an anesthesiologist who works in the Los Angeles area, was first diagnosed with acute myeloid leukemia, a cancer that affects the blood-forming cells in the bone marrow, in 2022. A stem cell transplant from his brother, a perfect genetic match, sent him into remission, but Mondek's cancer returned in April of this year.

"We followed every clinical protocol but the disease still managed to come back, so we had a new problem on our hands," said Ronald Paquette, MD, clinical director of the Stem Cell and Bone Marrow Transplant Program at Cedars-Sinai Cancer. "How could we treat his cancer a second time around and have a better chance that it doesn't return?"

The only chance was another stem cell transplant from a new donor. A search among Mondek's relatives and in the National Bone Marrow Registry failed to turn up a match, but Mondek recalled a close friend with lymphoma who received a transplant from his 18-year-old son.

"How young could you go with a donor?" he asked Paquette.

Paquette confirmed that Stephen, who turned 10 in August, was a possibility. Children receive half of their DNA from each of their parents, so Stephen would be a half-match to Mondek. Stephen would still have to be tested to be sure that his immune system would be compatible with his father's, but Paquette said that if it was, a half-match might make the transplant more effective. A half-matched immune system might more easily recognize and kill the cancer cells in Mondek's bone marrow, and transplants from younger donors tend to be most successful.

"The conversation with Stephen was pretty simple," Mondek said. "I said, 'Hey, Buddy, Dad's sick and they need someone to give me stem cells, and they want to know if you want to get tested to see if you can do it.'"

Stephen's response: "When do we go?"

After testing showed that Stephen was a compatible donor, the care team at Cedars-Sinai Guerin Children's evaluated him to make sure that he understood and was mature enough to agree to the procedure. Then, after several weeks of pre-donation prep, he was admitted to the pediatric intensive care unit for the donation. He had to be placed under general anesthesia so that doctors could insert a catheter into a vein in his neck. Then Stephen spent six hours in a hospital bed while his blood cycled through a centrifuge that separated out the stem cells.

Stephen's mom, Danielle Boyer, his younger brother, John, and Mondek waited anxiously through the catheter placement.

"Being an anesthesiologist, I put people to sleep every day, so I reassured myself that everyone wakes up when they go to sleep under anesthesia," Mondek said. "But during the whole process that I've gone through, those 60 minutes when Stephen was asleep were probably the toughest."

But all was well. Stephen's stem cells were collected and frozen, and the family was back home that night.

A week later it was Mondek's turn. He spent six days at Cedars-Sinai receiving chemotherapy to suppress his immune system so that his body wouldn't reject Stephen's donor cells. Then he was ready for the transplant.

"Transplant day is always dramatic," Paquette said. "The patient knows that they cannot survive without the stem cells, and the delivery of the stem cells into their body is like a rebirth. We call that day their stem cell birthday."

Paquette said that it takes two to three weeks for the newly transplanted stem cells to begin to grow. For Mondek, this meant two more weeks in the hospital-and away from his family-to protect his newborn immune system. But on Aug. 16, Mondek was discharged from the hospital and made it to the final inning of Stephen's Little League game.

"I felt good helping my dad," Stephen said, "and it felt good to have him home."

Paquette said that it could take a year or more to determine whether the new immune system Mondek received from Stephen can beat his leukemia. But he called Mondek "tough" and said that he and Mondek won't accept anything less than a cure.

John Chute MD, director of the Division of Hematology and Cellular Therapy at Cedars-Sinai, said that the Mondek family's experience is an example of the level of personalized, state-of-the-art care that Cedars-Sinai stem cell transplant patients receive.

"Our exceptional patient care is part of the reason that our stem cell transplantation program has enjoyed consecutive top 10 national rankings by the Center for International Blood and Marrow Transplant Registry (CIBMTR) for patient outcomes since 2021," Chute said.

Mondek is optimistic about his particular outcome.

"Everything lined up for this," Mondek said. "Dr. Paquette said the perfect donor for me would be someone who's young and healthy and a 50% match, and we found him. He was right here in front of us."

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