Hematopoietic progenitor cells from allogeneic bone marrow transplant donors circulate in the very early post-transplant period

Despite the therapeutic efficacy of allogeneic bone marrow transplantation (allo-BMT), circulating hematopoietic progenitor cells after bone marrow tr ansplantation have not been well characterized. In the present study, we fo cused on these 'post-transplant circulating progenitor cells (PTCPC)' which may be on their way to bone marrow. We analyzed the number of myeloid prog enitor cells (CFU-GM) per 10 mi of peripheral blood (PB) on days 0 (just be fore transplantation), 1 (8-15 h after the completion of transplantation), 2, 3, 5, 7, 10, 14, 17, 21, 28 and 35 after allo-BMT in five transplant pat ients using a standard methylcellulose assay, In addition, high proliferati ve potential colony-forming cells (HPP-CFC) of the harvested donor bone mar row (BM) and day 1 PB of recipients were assayed in five patients. The orig in of HPP-CFC from day 1 PB was analyzed by polymerase chain reaction of a DNA region containing a variable number of tandem repeats. The replating po tential of these HPP-CFC was evaluated by a secondary colony assay. The pro portion of CD38(negative) cells among CD34(+) cells in the harvested BM and day 1 PB was evaluated by two-color flow cytometric analysis. The number o f CFU-GM on day 1 ranged from 6 to 73/10 mi PB, and became undetectable on day 5, The reappearance of PTCPC was observed on day 14, along with hematop oietic recovery. The proportion of HPP-CFC among myeloid colonies from day 1 PB was significantly higher than that from harvested BM (44.3 +/- 10.4% v s 11.3 +/- 2.1%, respectively, n = 5, P = 0.0030), These HPP-CFC from day 1 PB were confirmed to be of donor origin, More than 90% of these HPP-CFC ha d replating potential. Two-color flow cytometric analysis revealed that the proportion of CD34(+)CD38(negative) cells was significantly higher in day 1 PB than in the harvested Bill (61.0 +/- 16.5% vs 9.3 +/- 3.5%, respective ly, n = 7, P = 0.0002), These observations suggest that both primitive and committed transplanted myeloid progenitor cells may circulate in the very e arly period following allo-BMT.