Donor-associated clonal hematopoiesis (CH) has been reported in recipients of allogeneic hematopoietic cell transplantation (HCT); however, an inability to detect ultralow-frequency variants has prevented a better understanding of the impact of HCT on clonal dynamics. Here, Ueda Oshima and colleagues used ultrasensitive duplex sequencing to characterize blood samples from a unique cohort of 16 donor-recipient pairs, collected up to 46 years after allogeneic HCT. The average mutation rate per year was similar between donors and recipients after HCT, and only 5.6% of variants shared between paired donors and recipients were substantially expanded in the recipient compared with the donor. Although larger studies with more time points are needed, the data from this unique cohort suggest that preferential expansion of donor CH variants in recipients of HCT is low. —Melissa L. Norton
