Circulating CD34+ cells in cord blood and mobilized blood have a different profile of adhesion molecules than bone marrow CD34+ cells

Abstract: The expression of adhesion molecules was studied on CD34+ hematopoietic precursors in cord blood, bone marrow and mobilized blood. The samples were labeled in a double immunofluorescence procedure with a CD34 monoclonal antibody and with antibodies against maturation and differentiation antigens and adhesion molecules. Myeloid precursors formed the majority of the CD34+ cells in all samples. In bone marrow a separate cluster of B-cell precursors with low forward scatter was present. Nearly all CD34+ cells in normal bone marrow expressed VLA-4 and VLA-5, PECAM-1, LFA-3 and HCAM. The majority of the CD34+ cells also had LFA –1 and L-selectin on the surface membrane. A small subset was VLA-2, VLA-3, ICAM-1 or Mac-1 positive. CD34+ cells expressing the vitronectin receptor or the CD11c antigen were rare. Cord blood and mobilized blood CD34+ cells had a lower expression of VLA-2, VLA-3 and VLA-5 and a higher expression of LFA-1, ICAM-1 and L-selectin than bone marrow CD34+ cells. Except for LFA-1, this was not due to the presence of more myeloid precursors in these samples. Low β₁ integrin expression may lead to less adhesion to the extracellular matrix. High expression of L-selectin may facilitate interaction with endothelial cells. Therefore, this phenotype may favour mobilization.     

Growth factor receptor profile of CD34 cells in normal bone marrow, cord blood and mobilized peripheral blood

Growth factors regulate the proliferation and differentiation of hemopoietic cells. Their effect on hemopoietic precursors differs according to the ontogenic source of the cells. Cord blood and mobilized blood CD34(+) cells have a higher sensitivity for growth factors than bone marrow CD34(+) cells. This could be due to a higher expression of growth factor receptors. Therefore, we examined the expression of receptors for stem cell factor (SCF), interleukin-6 (IL-6), IL-3, granulocyte colony-stimulating factor (G-CSF) and IL-7 on the CD34(+) cells of cord blood, mobilized peripheral blood and bone marrow. The receptors were detected with monoclonal antibodies and flow cytometry. The majority of the CD34(+) cells in bone marrow clearly expressed SCFR; they showed a moderate positivity for IL-3Ralpha and a weak staining for G-CSFR and IL-6 Ralpha. Less than 10% of the cells were IL-7R positive. Cord blood CD34(+) cells showed a higher expression of SCFR and a lower positivity for G-CSFR and IL-6Ralpha. Mobilized blood CD34(+) cells showed a lower expression of SCFR and G-CSFR, and a higher positivity for IL-3Ralpha. This was not solely due to the presence of more myeloid precursors in mobilized blood, as the growth factor receptor profile did not correspond to that of early or late myeloid CD34(+) precursors in normal bone marrow. Changes induced by the mobilization procedure occurred as well. In conclusion, the higher sensitivity for growth factors of hemopoietic precursors in cord blood and mobilized blood cannot be explained by a general increase of the growth factor receptor expression on the CD34(+) cells.     

Hematopoietic capability of CD34+ cord blood cells: a comparison with CD34+ adult bone marrow cells

The characteristics of hematopoietic progenitor and stem cell (HPC/HSC) populations in mammals vary according to their ontogenic stage. In humans, HPC/HSCs from umbilical cord blood (CB) are increasingly used as an alternative to HPC/HSCs from adult bone marrow (BM) for the treatment of various hematologic disorders. How the hematopoietic activity of progenitor and stem cells in CB differs from that in adult BM remains unclear, however. We compared CD34+ cells, a hematopoietic cell population, in CB with those in adult BM using phenotypic subpopulations analyzed by flow cytometry, the colony-forming activity in methylcellulose clonal cultures, and the repopulating ability of these cells in NOD/Shi-scid (NOD/SCID) mice. Although the proportion of CD34+ cells was higher in adult BM than in CB mononuclear cells, the more immature subpopulations, CD34+ CD33- and CD34+ CD38- cells, were present in higher proportions in CD34+ CB cells. Clonal culture assay showed that more multipotential progenitors were present in CD34+ CB cells. When transplanted into NOD/SCID mice. CD34+ adult BM cells could not reconstitute human hematopoiesis in recipient BM, but CD34+ CB cells achieved a high level of engraftment, indicating that CD34+ CB cells possess a greater repopulating ability. These results demonstrated that human hematopoiesis changes with development from fetus to adult. Furthermore, CD34+ CB cells contained a greater number of primitive hematopoietic cells, including HSCs, than did adult BM, suggesting the usefulness of CD34+ CB cells not only as a graft for therapeutic HSC transplantation but also as a target cell population for ex vivo expansion of transplantable HSCs and for gene transfer in gene therapy.     

Platelet characteristic antigens of CD34+ cells in cryopreserved cord blood: a study of platelet-derived microparticles in transplant processing

BACKGROUND AND OBJECTIVES: In previous studies, we found that platelet microparticles (PMPs) bind to cord blood (CB) CD34+ cells and transfer adhesion molecules to them, which enhances their engraftment. Before applying this phenomenon in actual transplants, we investigated the effect of PMPs on cryopreserved CD34+ cells in CB. MATERIALS AND METHODS: We cryopreserved 18 CB units, then evaluated the binding of PMPs to CD34+ cells after thawing, by varying the expression of platelet characteristic antigens (CD41a, CD61, CD62P and CXCR4) on these cells. Adherence of the CD34+ cells, coated with freeze/thaw-induced PMPs, to endothelium and fibronectin was also studied, as were the effects of thrombin-induced PMPs from both fresh and preserved CB platelets. RESULTS: PMPs induced by freezing and thawing adhered less well to CD34+ cells than did those from fresh CB, and cells coated with these PMPs had poor adherence. However, thrombin-induced PMPs from both fresh and preserved CB platelets bound equally well to cryopreserved CD34+ cells and improved their adhesion properties. CONCLUSIONS: PMPs could be a useful tool for enhancing engraftment after CB transplantation.     

T-lymphoid differentiation potential measured in vitro is higher in CD34+CD38-/lo hematopoietic stem cells from umbilical cord blood than from bone marrow and is an intrinsic property of the cells

Background

Human bone marrow and umbilical cord blood are sources of allogeneic hematopoietic stem cells for transplantation, which is a life-saving treatment in a variety of diseases but is burdened by delayed T-cell reconstitution. Observational studies evaluating T-cell reconstitution in post-transplant recipients suggest that cord blood hematopoietic stem cells have a more effective capacity for T-cell reconstitution. This study focuses on the comparison of the capacity of cord blood and bone marrow hematopoietic stem cells to generate T cells in vitro.

Design and Methods

Hematopoietic stem cells were cultured in OP9-delta-like-1 and OP9-green fluorescent protein co-cultures to estimate T and myeloid generation capacity, respectively. Phenotypic markers of T-lineage or myeloid differentiation were measured by flow cytometry and used to analyze their kinetics as a function of culture time. Hematopoietic stem cells were labeled with carboxyfluorescein diacetate succinamidyl ester and analyzed after culture to track their phenotypic progression in consecutive generations. Mixed OP9-delta-like-1 co-cultures were done with either carboxyfluorescein diacetate succinamidyl ester-labeled bone marrow and unlabeled cord blood hematopoietic stem cells, or vice versa, to evaluate their mutual influence on T-lineage differentiation. The T-cell potential of hematopoietic stem cells was addressed quantitatively by limiting dilution analysis.

Results

Bulk cultures showed faster and more extensive T-cell differentiation by cord blood hematopoietic stem cells. Furthermore, the T-lymphoid differentiation capacity of cord blood and bone marrow hematopoietic stem cells can be discriminated very early based on the coordinated expression of CD34 and CD7. Mixing experiments with cord blood hematopoietic stem cells and bone marrow hematopoietic stem cells showed that these differences are cell intrinsic. Quantitative clonal analyses demonstrated that CD34⁺CD38^−/lo hematopoietic stem cells from cord blood contained a two-fold higher T-lineage generation capacity than CD34⁺CD38^−/lo bone marrow hematopoietic stem cells, whereas the myeloid differentiation was similar.

Conclusions

Our data shows that cord blood hematopoietic stem cells have higher T-lymphoid differentiation potential than bone marrow hematopoietic stem cells and that this property is cell autonomous.     

脐血造血干细胞向巨核细胞诱导分化的研究

目的:建立脐血CD34+造血干细胞向巨核细胞诱导分化的体系,探讨最佳的扩增方法。方法:免疫磁珠法分离获得CD34+细胞培养在无血清无基质培养液中,采用TPO加SCF加IL-3加IL-6、TPO加SCF加IL-3、TPO加SCF3种不同因子组合对其诱导分化及扩增。收集3、7、10、14d的扩增产物,运用荧光显微镜检测巨核细胞的表面标志;流式细胞术(FCM)检测巨核细胞的凋亡;并对巨核细胞形成单位(CFU-MK)及DNA含量进行检测。结果:分离获得的CD34+细胞在体外可以有效扩增,随培养时间的延长CD34+/CD41+细胞数第7天达最高值,之后逐渐下降;而CD41+、CD42b+、CD61+细胞随培养时间的延长表达量逐渐增高。加入IL-3和IL-6后,Annexin Ⅴ阳性细胞由(8.26±2.49)%降至(3.51±1.24)%。CFU-MK的数量在第10天时最高,且8倍体及8倍体以上的巨核细胞所占的的百分比增加,即成熟产板型巨核细胞增加。结论:脐血CD34+造血干细胞在体外可向巨核细胞诱导分化及有效扩增。3种因子组合中TPO加SCF加IL-3加IL-6组扩增效率最高。     

Increased number of peripheral blood CD34+ cells in lithium-treated patients

Eight adult patients with bipolar disorder were prospectively examined to find whether lithium carbonate increased their peripheral blood CD34⁺ haemopoietic stem cells. Following lithium therapy for 3–4 weeks their neutrophil counts increased by a mean of 88% (from 4625 ± 1350 × 10⁹/l, mean ± SD pretreatment, to a peak of 8300 ± 3910 × 10⁹/l). Concommitantly, there was a significant increment in their CD34⁺ cells (from 0.11 ± 0.01% to a peak of 0.18 ± 0.08%). There was a significant correlation between the rise in neutrophil count and that of the CD34⁺ cells ( r  = 0.795, P  = 0.019). Lithium therapy may be used to mobilize peripheral blood CD34⁺ cells for marrow transplantation.     

In vitro differentiation of natural killer T cells from human cord blood CD34+ cells

Natural killer T (NKT) cells are involved in innate immune defence and also in the regulation of adaptive immune responses. However, the development of NKT cells in vitro has not been fully characterized and culture conditions have not been fully optimized. In the present study, we found that an NKT cell fraction developed during the in vitro culture of cord blood (CB) CD34+ cells, and this was subsequently characterized both phenotypically and morphologically. CD34+ cells purified from 10 human CB were cultured in the presence of several cytokines and analysed by flow cytometry, light microscopy and electron microscopy. The NKT cell fraction, defined phenotypically (CD3+CD16+CD56+CD94+) as expressing the invariant T-cell receptor Valpha24 and Vbeta11, appeared in the CD56hi fractions. Intracytoplasmic staining demonstrated that interferon-gamma and interleukin 4 (IL-4) were detected in the CD56hi fractions. IL-15 was essential and, in combination with either flt3-ligand (FL) or stem cell factor (SCF), was sufficient to induce the development of NKT cells. The phenotype of the NKT cell fraction was CD45RO+CD45RA- and CD4+CD8alpha+. Morphologically, they were very large, with either round or oval nuclei, moderately condensed chromatins, voluminous weakly basophilic cytoplasm and various cytoplasmic granules such as dense core granules, multivesicular bodies, and intermediate form granules. When CD34+ cells purified from bone marrow (BM) were compared with those from CB, the latter were consistently more efficient at generating CD56hi NKT cell fractions. In conclusion, IL-15 in combination with FL and/or SCF can induce the differentiation of NKT cells from human CB CD34+ cells.     

Cytokine mediated expansion of human umbilical cord blood CD34+ cells: comparison of the use of partially purified and pure CD34+ target cells

To determine the optimal cell population for cytokine mediated expansion, we compared the use of Magnetic Cell Sorting (MACS) system enriched CD34+ human umbilical cord blood (HUCB) cells with that of MACS enriched, flow purified CD34+ HUCB cells. Both MACS enriched CD34+ cells and MACS enriched, flow purified CD34+ cells (mean starting purity of CD34+ SC 51.27 ± 7.6% and 96.36 ± 1.34% respectively n = 6) were incubated for seven days with Interleukin-1 (IL-1)+IL-3+Stem Cell Factor (SCF) and showed a fold increase in the number of nucleated cells (10.02 ± 2.6 and 18.23 ± 4.73 respectively) and a reduction in the percentage of CD34+ cells (5.55 ± 1.23% and 12.21 ± 3.29% respectively). An increase in the absolute numbers of CD34+ cells (4.8 × 10⁴ ± 2.3 × 10⁴) was observed with MACS enriched CD34+ cells as compared to no change (1.3 × 10⁵ ± 8.8 × 10⁴) with MACS enriched, flow purified CD34+ cells. An increase in IL-3+GM-CSF+SCF responsive colony forming unit (CFU) (1.7 × 10⁴ ± 9.4 × 10³ and 1.6 × 10⁵ ± 7.7 × 10⁴ respectively) was also observed as compared with input values (1.5 × 10⁴ ± 1 × 10⁴ and 2.3 × 10⁴ ± 8.9 × 10³ respectively). We conclude that MACS enriched, flow sorted CD34+ HUCB cells have greater cytokine mediated expansion potential as measured by progenitor expansion, than MACS enriched CD34+ HUCB cells.     

CD34~+ CD38~-细胞对异基因造血干细胞移植的影响研究

目的观察CD34+CD38-细胞对异基因造血干细胞移植术后造血重建和移植物抗宿主病(GVHD)的影响。方法分析2004年1月至2009年12月河南省人民医院血液科全相合异基因外周血干细胞造血干细胞移植78例,CD34+、CD34+CD38-细胞输入量与血缘全相合异基因外周血造血干细胞移植术后造血重建及GVHD发生率间的相关性。结果粒细胞、血小板恢复时间与CD34+CD38-细胞输入量呈负相关(r分别为-0.521、-0.448,P<0.01),与CD34+细胞输入量也呈负相关(r分别为-0.405、-0.371,P<0.05)。急性GVHD、慢性GVHD的发生与CD34+、CD34+CD38-、CD3+、CD4+、CD8+细胞输入量无相关性。结论输入高数量的CD34+CD38-细胞有利于移植术后的粒细胞、血小板快速恢复;对于预测术后造血恢复,CD34+CD38-细胞亚群输入量可能优于CD34+细胞总数。     

Lack of DNA synthesis among CD34+ cells in cord blood and in cytokine-mobilized blood

Flow cytometric DNA analysis was performed in combination with three-colour immunological staining of cell surface antigens on density-separated mononuclear cells (MNC) obtained from peripheral blood (PB) before, during and after cytokine stimulation of healthy adults. The aim of the study was to determine the cell-cycling status of haemopoietic progenitor cells mobilized into the blood of healthy volunteers during a 5 d treatment period with 5 μg per kg body weight of either granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF). Despite considerably increasing numbers of CD34⁺ PB MNC, the latter were not found to be in S/G₂M phase, whereas, among the CD34^? MNC, the proportion of cells in S/G₂M phase increased from <0.1% to 0.75 ± 0.4% (GM-CSF) and to 1.34 ± 0.75% (G-CSF) and dropped again after discontinuation of the cytokine stimulation. These cells expressed CD33 but were negative for CD45RA, CD3, CD19 and CD14 and were thus considered granulopoietic cells. Analogous results were obtained from analyses of cord blood (CB). In contrast, CD34⁺ cells from bone marrow (BM) were partially (between 9% and 15%) found to be in S/G₂M phase. The non-cycling status of PB and CB progenitor cells was confirmed by the analysis of CD34⁺ cells enriched from the two cell sources. However, in vitro stimulation of these progenitor cells using IL3, GM-CSF, erythropoietin and steel factor (SF) revealed that, after 48 h in suspension culture, up to 30% of the CD34⁺ cells were in S/G₂M phase. The fact that cycling CD34⁺ cells are only detectable in BM but not in PB or CB may suggest different adhesive properties of migrating/mobilized ‘stem cells’ which may require the BM micro-environment for adequate proliferation in vivo     

Caspase-3在脐血CD34+造血干/祖细胞中的表达及意义

目的：探讨脐血CD34^＋干／祖细胞在不同细胞因子支持下的体外扩增过程中Caspase-3表达及意义，方法：采用RT－PCR、Wester blot和流式细胞仪分析技术测定脐血CD34^ 细胞在体外扩增过程中的生物学特性及Caspase-3的表达。结果：Caspase-3 mRNA在新鲜分离的脐血CD34^ 细胞中低水平表达，在细胞因子支持下体外增养3d，扩增的CD34^ 细胞中Caspase-3 mRNA和蛋白质表达上调，但在该两种细胞中仅能检测到分子量为32000的无活性酶原形式的Caspase-3，随着体外培养时间的延长，在IL－3、IL－6和GM－CSF组合条件下，Caspase-3被激活，可检测到分子量为20000的裂解片段。结论：虽然造血干细胞的凋亡是个复杂的过程，但在脐血CD34^ 干／祖细胞体外扩增过程中，Caspase-3参与了凋亡事件并发挥着重要的作用。     

Human G-CSF-mobilized CD34-positive peripheral blood progenitor cells can stimulate allogeneic T-cell responses: implications for graft rejection in mismatched transplantation

To investigate mechanisms of stem cell graft rejection we studied the allo-stimulatory potential of G-CSF mobilized peripheral blood progenitor cells (PBPC). CD34+ cells were purified (>95%) in a two-step procedure using immunoaffinity columns for CD34 selection and T-depletion. The capacity of CD34+ cells to stimulate allogeneic T-cell responses was compared with other cells from the same individual. CD34+ cells induced potent proliferative responses at stimulator:responder ratios of 1:20, but were approximately 50-fold less efficient compared to dendritic cells. Furthermore, CD34+ cells primed responses from partially matched allogeneic T cells in bulk cultures. Dual-colour flow cytometry showed that the co-stimulatory molecules B7.1, CD40 and ICAM-1 were absent on resting CD34-positive progenitor cells, but were induced during incubation with allogeneic lymphocytes due to a cytokine-mediated effect. Up-regulation of accessory molecules on CD34+ cells was reproduced by incubation with interferon-gamma or GM-CSF which enhanced the allo-stimulatory activity of CD34+ cells. Blocking studies with inhibitory antibodies suggested co-stimulatory functions for B7.2, ICAM-3, CD40 and LFA-3. CD34+ cells were more efficient in inducing allogeneic T-cell responses when compared to the unprocessed leukapheresis products. The reduced allo-stimulatory ability of G-CSF mobilized PBPC could be explained by the presence of CD3+ 4+ and CD3+ 8+ lymphocytes with suppressor activity. We conclude that current methods of stem cell selection for transplantation do not avoid allosensitization of the recipient and that further graft manipulation with add-back of lymphocytes or selection of subsets of CD34+ cells with reduced allo-stimulatory ability may reduce graft rejection.     

流式细胞术分析冻存前后脐血CD34+细胞的分布

目的探讨低温冻存对脐血CD34+细胞的影响.方法采用流式细胞仪分析冻存前后脐血CD34+细胞百分率、CD45+细胞和CD34+细胞的荧光强度变化及死细胞群的分布情况.结果冻存后CD34+细胞占CD45+细胞的百分率[(0.84±0.39)%]明显高于冷冻前[(0.51±0.24)%](P<0.01),冻存前后CD34+细胞绝对数无明显变化[(9.372±6.072) ×106/L和(9.246±6.132)×106/L](P>0.05),冻存前后CD34+细胞百分率呈正直线相关(r=0.564, P<0.01).冻存后CD45+细胞荧光强度减弱(P<0.01),CD34+细胞荧光强度无明显变化(P>0.05);中性粒细胞比例下降,淋巴细胞和单核细胞比例增高.死细胞组分中以中性粒细胞为主,占81.52%;活细胞组分中以淋巴细胞为主,占59.44%.结论冻存后CD34+细胞占CD45+细胞的百分率增高,但低温冻存对CD34+细胞绝对数量影响不大.死细胞主要为较成熟的粒细胞,冻存后CD34+细胞的分析需排除死细胞的干扰.     

Apoptotic bone marrow CD34+ cells in cirrhotic patients

AIM: To access the frequency and level of apoptotic CD34+ cells isolated from the marrow fluid of patients with post-hepatitis cirrhosis. METHODS: The frequency of bone marrow CD34+ cells and apoptotic bone marrow CD34+ cells in 31 inpatients with post-hepatitis cirrhosis (cirrhosis group), and 15 out-patients without liver or blood disorders (control group) was calculated by flow cytometry. Parameters were collected to evaluate liver functions of patients in cirrhosis group. RESULTS: The percentage of norm...     

Exclusive expression of G-CSF receptor on myeloid progenitors in bone marrow CD34+ cells

Although granulocyte colony-stimulating factor (G-CSF) has been reported to act on cells of neutrophilic lineage, the administration of G-CSF to induce the mobilization of various haematopoietic progenitors into the circulation. We analysed the expression of receptors for G-CSF (G-CSFR) on human bone marrow and G-CSF-mobilized peripheral blood CD34+ cells, and examined the proliferation and differentiation capabilities of sorted CD34+G-CSFR+ and CD34+G-CSFR- cells using methylcellulose clonal culture. Flow cytometric analysis showed that G-CSFR was expressed on 14.9 +/- 4.9% of bone marrow CD34+ cells, most of which were included in CD34+CD33+ and CD34+CD38+ cell fractions. In clonal cultures, CD34+G-CSFR+ cells produced only myeloid colonies, whereas CD34+G-CSFR- cells produced erythroid bursts, megakaryocyte and multilineage colonies. When incubated with the cytokine cocktail for 5 d, CD34+G-CSFR- cells generated CD34+G-CSFR+ myeloid progenitors. In G-CSF-mobilized peripheral blood, CD34+ cells contained 10.8 +/- 5.8% of G-CSFR+ cells, most of which were also myeloid progenitors, although CD34+G-CSFR- cells contained a substantial number of myeloid progenitors. These results indicated that the expression of G-CSFR on CD34+ cells is restricted to myeloid progenitors, suggesting that the specific activity of G-CSF on myelopoiesis depends on the exclusive expression of its receptor on myeloid progenitors, and that the mobilization of various haematopoietic progenitors is not a direct effect of G-CSF in humans.     

Influence of the different CD34+ and CD34- cell subsets infused on clinical outcome after non-myeloablative allogeneic peripheral blood transplantation from human leucocyte antigen-identical sibling donors

Currently, no information is available regarding the influence of the different CD34+ cell subsets infused on the haematopoietic recovery, following non-myeloablative allogeneic peripheral blood stem cell transplantation (allo-PBSCT). We have explored, in a group of 13 patients receiving non-myeloablative allo-PBSCT from human leucocyte antigen-identical sibling donors, the influence of the total dose of CD34+ haematopoietic progenitor cells (HPC) infused, compared with that of the different CD34+ HPC and CD34- leucocyte subsets in the leukapheresis samples, on both engraftment and clinical outcome. The overall numbers of total CD34+ HPC (P = 0.002) and myelomonocytic-committed CD34+ HPC infused (P = 0.0002) were strongly associated with neutrophil recovery (> 1 x 109 neutrophils/l), the latter being the only independent parameter influencing neutrophil recovery. Regarding long-term engraftment, only the number of immature CD34+ HPC infused/kg correlated with the duration of hospitalization in the first 2 years after discharge (r = -0.75, P = 0.005). Both the overall amount of CD34+ HPC and the number of myelomonocytic CD34+ HPC infused showed a significant influence on the risk of graft-versus-host disease (GVHD). Thus, the overall probability of GVHD was 100%vs 25% for patients receiving >/= 5 x 106 CD34+ HPC or >/= 3.5 x 106 of myelomonocytic-committed CD34+ HPC vs lower doses (P = 0.013). None of the other CD34+ and CD34- cell subsets analysed correlated with development of GVHD. In summary, our results suggest that in non-myeloablative allo-PBSCT, high numbers of CD34+ HPC, especially the myelomonocytic-committed CD34+ progenitors, lead to rapid neutrophil engraftment. However, they also strongly impair clinical outcome by increasing the incidence of GVHD.     

An in situ study of CD34(+) cells in human fetal bone marrow

The purpose of this study was to characterize the spatial distribution, number and size of CD34(+) cells in fetal bone marrow. Thin sections of normal fetal bone marrow from lumbar vertebrae were stained using CD34 antibody QBend/10. Sections were used under light microscopy with various eyepiece graticules to make measurements of CD34(+) cells in situ. Results showed that at mid- and late gestation, approximately 2% and 0.5% of fetal bone marrow cells were CD34(+) respectively. The mean distance of CD34(+) cells from the nearest trabecular bone surface was 61 +/- 4 and 46 +/- 4 microm, respectively, for mid- and late gestation. The mean distance to the nearest neighbour was 46 +/- 5 and 105 +/- 15 microm, and the mean distance to the nearest blood vessel was 13 +/- 1 and 17 +/- 2 microm respectively. The concentration of CD34(+) cells in the peripheral region was 6.5 times greater than that at the centre of the sections. Overall, the percentage number of CD34(+) cells decreased with gestational age. The cellular and nuclear diameters of CD34(+) cells remained unchanged throughout mid- and late gestation at 5.4 +/- 0.1 and 3.8 +/- 0.1 microm respectively. This information will be used to calculate the natural background alpha-radiation dose to haemopoietic stem cells.     

Short-term phytohaemagglutinin-activated mononuclear cells induce endothelial progenitor cells from cord blood CD34+ cells

Endothelial progenitor cells (EPCs) were recently demonstrated to exist in human cord blood. Phytohaemagglutinin (PHA), a potent mitogen for mononuclear cells was used to induce EPCs from unsorted cord blood mononuclear cells (CBMCs). Adherent cells in clusters appeared approximately 24 h after CBMCs were cultured in plain Roswell Park Memorial Institute media containing 10% fetal bovine serum (culture media) and PHA. Adherent cells were further propagated for 1 week in plain culture media. Flow cytometry and Di-I staining analyses showed that CD45-, CD34+, Flk-1+, CD31+ or VE-cadherin+ EPCs were induced and that they were mainly from the CD34+ cell compartment. When enriched CD34+ cells alone were stimulated with culture supernatant of the PHA-activated CBMCs, they neither proliferated readily nor induced EPCs. Because EPCs first appeared within the clustering cells that expressed high levels of fibronectin and vascular endothelial growth factor (VEGF), our data suggest that both cell-cell/cell-matrix interaction and the local VEGF action are important in the induction of EPCs. Thus, we demonstrate for the first time that EPCs are induced from human cord blood stem cell populations that interact with neighbouring PHA-activated CBMCs. This finding may have a significant implication in inflammatory cell-mediated vasculogenesis and angiogenesis in vivo.