Stable donor chimerism >25% following hematopoietic cell transplantation (HCT) for sickle cell disease (SCD) is linked with resolved SCD-related symptoms, according to a retrospective analysis involving 95 individuals. Meanwhile, hemoglobin S (HbS) level ≥50% predicts recurrent disease. Investigators looked at the link between chimerism, HbS level, and symptomatic disease in participants who underwent HCT and had chimerism reports from day 100, and 1 and 2 years after transplantation. Among the results:

• 35 patients maintained full donor chimerism through 2 years.
• Graft failure occurred in 13 patients during this period.
• The remaining 47 patients had mixed chimerism ranging between 10% and 94%.
• The lowest recorded donor chimerism without symptomatic disease was 26%.
• Of 12 surviving patients with recurrent disease, 2 experienced recurrence prior to graft failure, with donor chimerism ranging between 11% and 17%.
• 3 patients underwent second transplantation for graft failure; none received donor leukocyte infusion.