Kinetics of engraftment of CD34− and CD34+ cells from mobilized blood differs from that of CD34− and CD34+ cells from bone marrow

Objective Mobilized peripheral blood (PB) progenitors are increasingly used in autologous and allogeneic transplantation. However, the short- and long-term engraftment potential of mobilized PB or bone marrow (BM) has not been directly compared. Although several studies showed that BM-derived Lin−CD34− cells contain hemopoietic progenitors, no studies have addressed whether Lin−CD34− cells from mobilized PB contain hemopoietic progenitors. Here, we compared the short- and long-term engraftment potential of CD34+ cells and Lin−CD34− cells in BM and PB of normal donors who received 5 days of granulocyte colony-stimulating factor (G-CSF). Materials and Methods 35 × 103 CD34+ or Lin−CD34− cells from G-CSF mobilized BM and PB of normal donors were transplanted in 60-day-old fetal sheep. Animals were evaluated 2 and 6 months after transplantation for human hemopoietic cells. In addition, cells recovered after 2 months from fetal sheep were serially passaged to secondary and tertiary recipients to assess long-term engrafting cells. Results Mobilized PB CD34+ cells supported earlier development of human hemopoiesis than BM CD34+ cells. When serially transferred to secondary and tertiary recipients, earlier exhaustion of human hematopoiesis was seen for PB than BM CD34+ cells. A similar degree of chimerism was seen for Lin−CD34− cells from PB or BM in primary recipients. We again observed earlier exhaustion of human hemopoiesis with serial transplantation of PB than BM Lin−CD34− cells. Conclusions Differences exist in the short- and long-term repopulating ability of cells in PB and BM from G-CSF mobilized normal donors, and this is independent of the phenotype. Studies are ongoing to examine if this reflects intrinsic differences in the repopulating potential between progenitors from PB and BM, or a lower frequency of long-term repopulating cells in PB than BM CD34+ and Lin−CD34− cells, that may not be apparent if larger numbers of cells are transplanted.