Timing of specimen collection.

Peripheral blood (20-40 mL) was obtained from all donors before bone marrow harvest or mobilized peripheral blood collection and from recipients before conditioning. Microsatellite analysis was performed on whole blood leukocytes from these samples to allow for subsequent assessment of hematopoietic chimerism in recipients. Donors' neutrophils were isolated, and their telomere length and X-inactivation pattern (when the donor was female) were assessed. HSCT was performed at time zero. All recipients were sampled within 2 weeks of attainment of an ANC more than 0.5 × 10⁹/L after HSCT (represented by the arrow at 1 month). Three recipients (R23, R24, and R25) underwent further peripheral blood sampling on 3 occasions at weekly intervals from the time of engraftment. Nineteen of 20 surviving patients were sampled 6 months after HSCT, and 17 of 18 surviving patients were sampled 12 months after HSCT. In addition, 9 patients were tested 2 months after HSCT, as shown. Complete blood cell counts and differential white blood cell counts, hematopoietic chimerism, neutrophil telomere length, and X-inactivation patterns in neutrophils (when the donor was female) were determined at these times. Bone marrow specimens (5-10 mL) were obtained from 15 donors at the time of bone marrow harvest, and from 4 recipients 2 months after HSCT, 7 recipients 6 months after HSCT, and 10 recipients 12 months after HSCT, as indicated. The proportion of CD34⁺ cells expressing CD90 was determined, and the cell cycle status of CD90^+/−subsets was examined.