Comparison of myeloid donor chimerism in patients with sustained donor engraftment after reduced-intensity UCBT using either Bu/Flu/TBI or Cy/Flu/TBI conditioning. Achievement of complete donor chimerism was rapid for Bu/Flu/TBI recipients (A), being a median of 100% at day 21 in BM. In contrast, because the Cy/Flu/TBI regimen (B) was less myelosuppressive, myeloid donor chimerism was initially mixed, taking until day 60 to reach a median of 100%.