National Health System
Kirsten M. Williams, MD Photo from Children’s
An imaging agent can safely show engraftment of hematopoietic stem cells (HSCs) just days after transplant, according to research published in The Lancet Haematology.
The agent is 18F-fluorothymidine (18F-FLT), a radio-labeled analogue of thymidine.
Past studies have shown that 18F-FLT is incorporated into HSCs.
With the current study, researchers wanted to determine if 18F-FLT could allow them to safely visualize transplanted HSCs.
Kirsten M. Williams, MD, of Children’s National Health System in Washington, DC, and her colleagues tested 18F-FLT in 23 patients undergoing HSC transplant to treat high-risk hematologic malignancies.
The patients first underwent total body irradiation to destroy their own HSCs and then received donor HSCs.
The patients underwent PET/CT scans 1 day before they were infused with HSCs as well as post-transplant at 5 or 9 days, 28 days, and 1 year.
Results
All patients engrafted, a finding that was reflected in blood tests conducted 2 to 4 weeks after transplant. However, imaging results revealed more details.
“Through the images we took, these patients could see the new cells growing in their bodies,” Dr Williams said. “They loved that.”
The researchers and the patients saw the HSCs take a complex journey as they engrafted.
First, HSCs migrated to the patients’ livers and spleens. Next, the cells went to the thoracic spine, the axial spine, the sternum, and the arms and legs.
By 1 year, most of the HSCs were concentrated in the bones that make up the trunk of the body, including the hip, where most biopsies to assess marrow function take place.
This pathway is the same one HSCs take in the fetus when they first form.
The researchers also found the radiation in 18F-FLT did not adversely affect engraftment.
And imaging could reveal successful engraftment at 5 days post-transplant, “which was up to 20 days before engraftment became clinically evident,” according to the researchers.
Dr Williams and her colleagues believe use of 18F-FLT could potentially help patients avoid bone marrow biopsies or, at the very least, help target those biopsies.
And the agent might be helpful for taking stock of HSCs in conditions such as aplastic anemia.
“What happens with HSCs always has been a mystery,” Dr Williams said. “Now, we can start to open that black box.”