Mobilized peripheral blood stem cells provide rapid reconstitution but impaired long-term engraftment in a mouse model.

In this study, we use competitive repopulation to compare the quality and frequency of stem cells isolated from mobilized blood with stem cells isolated from bone marrow (BM) in a mouse model. Lin(-)Sca-1(+)c-Kit(+) (LSK) cells were harvested from control BM and peripheral blood of mice following granulocyte colony-stimulating factor (G-CSF) administration. LSK cells were used because of their resemblance to human CD34(+) cells. We confirmed that transplantation of phenotypically defined mobilized peripheral blood (MPB) stem cells results in rapid recovery of blood counts. However, in vitro results indicated that LSK cells purified from MPB had lower cobblestone area-forming cell day 35 activity compared to BM. Additionally, evaluation of chimerism after co-transplantation of LSK cells purified from blood and BM revealed that MPB stem cells contained 25-fold less repopulation potential compared to BM stem cells. Competitive repopulating unit frequency analysis showed that freshly isolated MPB LSK cells have 8.8-fold fewer cells with long-term repopulating ability compared to BM LSK cells. Secondary transplantation showed no further decline in contribution of hematopoiesis relative to BM. We conclude that the reduced frequency of stem cells within the LSK population of MPB, rather than poorer quality, causes the reduced repopulation potential.Bone Marrow Transplantation (2007) 39, 401-409. doi:10.1038/sj.bmt.1705601; published online 12 February 2007.

Efficient mobilization of haematopoietic progenitors after a single injection of pegylated recombinant human granulocyte colony-stimulating factor in mouse strains with distinct marrow-cell pool sizes.

We have compared the efficacy of a single injection of SD/01, a newly engineered, pegylated form of recombinant human granulocyte colony stimulating factor (rhG-CSF), with a single injection of glycosylated rhG-CSF (Filgrastim). SD/01 was administered to regular and recombinant inbred strains of mice (AKR, C57L/J, DBA/2, C57BL/6, AKXL) known to have widely distinct marrow-cell pool sizes and proliferation kinetics. A single injection of G-CSF was unable to mobilize granulocyte-macrophage colony-forming units (CFU-GM). In sharp contrast, a single dose of SD/01 resulted in massive mobilization of progenitors and stem cells. Although all mice strains showed qualitatively similar mobilization responses, large interstrain differences remained. C57L and C57BL/6 mice mobilized relatively poorly, whereas AKR and DBA/2 mice showed threefold to tenfold superior responses. In order to explain these different phenotypes, we studied the effects of SD/01 in nine AKXL recombinant inbred strains, derived from well-responding AKR and poorly responding C57L parental strains. The best predictor for SD/01 responsiveness in these strains was marrow cellularity prior to mobilization. Comparison of the AKXL strain distribution pattern for marrow cellularity with loci previously mapped in these strains showed complete concordance with Aat, a serine protease inhibitor mapping to chromosome 12.

Autonomous behavior of hematopoietic stem cells.

Mechanisms that affect the function of primitive hematopoietic stem cells with long-term proliferative potential remain largely unknown. Here we assessed whether properties of stem cells are cell-extrinsically or cell-autonomously regulated. We developed a model in which two genetically and phenotypically distinct stem cell populations coexist in a single animal. Chimeric mice were produced by transplanting irradiated B6D2F1 (BDF1) recipients with mixtures of DBA/2 (D2) and C57BL/6 (B6) day-14 fetal liver cells. We determined the mobilization potential, proliferation, and frequency of D2 and B6 stem and progenitor cells in animals with chimeric hematopoiesis. After granulocyte colony-stimulating factor (G-CSF) administration, peripheral blood D2 colony-forming units granulocyte-macrophage were fourfold to eightfold more numerous than B6 progenitors. We determined that D2 and B6 progenitors maintained their genotype-specific cycling activity in BDF1 recipients. Chimeric marrow was harvested and D2 and B6 cell populations were separated by flow cytometry. Cobblestone area-forming cell (CAFC) analysis of sorted marrow showed that the number of late appearing CAFC subsets within the D2 cell population was approximately threefold higher than within the B6 fraction. We performed secondary transplantation using unfractionated chimeric marrow, which was given in limiting doses to lethally irradiated BDF1 recipients. Comparison of the proportion of animals possessing D2 and/or B6 leukocytes 5 months after transplant revealed that the frequency of D2 LTRA was approximately 10-fold higher than B6 LTRA numbers. Our data demonstrate that genetically distinct stem cell populations, coexisting in individual animals, independently maintain their parental phenotypes, indicating that stem cell properties are predominantly regulated cell-autonomously.