Early establishment of hematopoietic chimerism following allogeneic peripheral blood stem cell transplantation in comparison with allogeneic bone marrow transplantation

To characterize the process of the establishment of complete chimerism after allogeneic peripheral blood stem cell transplantation (allo-PBSCT), we determined the origin of leukocytes in peripheral blood (PB) obtained from 23 patients in the very early period after allo-PBSCT using amplification of mini- or microsatellite regions of genomic DNA. Donor-specific alleles were amplified from the PB obtained at day 8 post-transplant for 19 allo-PBSCT patients. Among the 19 patients, 12 showed only donor-specific alleles (complete chimerism) while 7 did both donor and host-specific alleles (mixed chimerism). Although donor specific alleles were amplified in 10 of 12 patients who received allogeneic bone marrow transplantation (allo-BMT) similarly to allo-PBSCT, all of these ten showed mixed chimerism. When the chimeric state was examined in PB samples obtained serially at 2-3-day intervals post-transplant, host-specific alleles in allo-PBSCT patients were not detectable in the PB much earlier than those in allo-BMT patients. These findings indicate that the appearance of donor-derived cells associated with the disappearance of host-derived cells in the circulation occurs earlier after allo-PBSCT as compared with allo-BMT, leading to the rapid establishment of complete chimerism.