Extensive phenotypic analysis of CD34 subsets in successive collections of mobilized peripheral blood progenitors

Efficient generation of multipotent mesenchymal stem cells from umbilical cord blood in stroma-free liquid culture

Background

Haematopoiesis is sustained by haematopoietic (HSC) and mesenchymal stem cells (MSC). HSC are the precursors for blood cells, whereas marrow, stroma, bone, cartilage, muscle and connective tissues derive from MSC. The generation of MSC from umbilical cord blood (UCB) is possible, but with low and unpredictable success. Here we describe a novel, robust stroma-free dual cell culture system for long-term expansion of primitive UCB-derived MSC.

Methods and Findings

UCB-derived mononuclear cells (MNC) or selected CD34⁺ cells were grown in liquid culture in the presence of serum and cytokines. Out of 32 different culture conditions that have been tested for the efficient expansion of HSC, we identified one condition (DMEM, pooled human AB serum, Flt-3 ligand, SCF, MGDF and IL-6; further denoted as D7) which, besides supporting HSC expansion, successfully enabled long-term expansion of stromal/MSC from 8 out of 8 UCB units (5 MNC-derived and 3 CD34⁺ selected cells). Expanded MSC displayed a fibroblast-like morphology, expressed several stromal/MSC-related antigens (CD105, CD73, CD29, CD44, CD133 and Nestin) but were negative for haematopoietic cell markers (CD45, CD34 and CD14). MSC stemness phenotype and their differentiation capacity in vitro before and after high dilution were preserved throughout long-term culture. Even at passage 24 cells remained Nestin⁺, CD133⁺ and >95% were positive for CD105, CD73, CD29 and CD44 with the capacity to differentiate into mesodermal lineages. Similarly we show that UCB derived MSC express pluripotency stem cell markers despite differences in cell confluency and culture passages.

Further, we generated MSC from peripheral blood (PB) MNC of 8 healthy volunteers. In all cases, the resulting MSC expressed MSC-related antigens and showed the capacity to form CFU-F colonies.

Conclusions

This novel stroma-free liquid culture overcomes the existing limitation in obtaining MSC from UCB and PB enabling so far unmet therapeutic applications, which might substantially affect clinical practice.

CD13 is dispensable for normal hematopoiesis and myeloid cell functions in the mouse

While the myeloid marker CD13 has been implicated in numerous myeloid cell functions, its genetic ablation reveals a nominal contribution of CD13 to these functions.

The robust and consistent expression of the CD13 cell surface marker on very early as well as differentiated myeloid hematopoietic cells has prompted numerous investigations seeking to define roles for CD13 in myeloid cells. To address the function of myeloid CD13 directly, we created a CD13 null mouse and assessed the responses of purified primary macrophages or DCs from WT and CD13 null animals in cell assays and inflammatory disease models, where CD13 has been implicated previously. We find that mice lacking CD13 develop normally with normal hematopoietic profiles except for an increase in thymic but not peripheral T cell numbers. Moreover, in in vitro assays, CD13 appears to be largely dispensable for the aspects of phagocytosis, proliferation, and antigen presentation that we tested, although we observed a slight decrease in actin‐independent erythrocyte uptake. However, in agreement with our published studies, we show that lack of monocytic CD13 completely ablates anti‐CD13‐dependent monocyte adhesion to WT endothelial cells. In vivo assessment of four inflammatory disease models showed that lack of CD13 has little effect on disease onset or progression. Nominal alterations in gene expression levels between CD13 WT and null macrophages argue against compensatory mechanisms. Therefore, although CD13 is highly expressed on myeloid cells and is a reliable marker of the myeloid lineage of normal and leukemic cells, it is not a critical regulator of hematopoietic development, hemostasis, or myeloid cell function.

Early and long-term engraftment after autologous peripheral stem cell transplantation in acute myeloid leukemia patients

This study aimed to identify which subset of CD34+ cells might be the most predictive of early and long-term hematopoietic recovery following autologous peripheral blood stem cell (PBSC) transplantation (PBSCT) in adult acute myeloid leukemia (AML) patients. The relationships between the number of 'mature' subsets of CD34+ cells (CD34+/CD33+, CD34+/CD38+, CD34+/DR+ and CD34+/CD90-) and 'immature' subsets of CD34+ cells (CD34+/CD33-, CD34+/CD38-, CD34+/DR- and CD34+/CD90+) and early and long-term hemoglobin, neutrophil and platelet counts were studied in a homogeneous series (for disease, pre-transplant chemotherapy, mobilization chemotherapy, conditioning regimen) of 26 AML patients after autologous PBSCT. Cell counts were performed before and after cryopreservation, but only after thawing were the cell counts used for correlation with early and long-term engraftment. The number of CD34+/CD38- cells infused correlated with the neutrophil (r = 0.88, p < 0.005) and platelet counts (r = 0.67, p < 0.05) at 12 months after PBSCT. This correlation was better than that for the total CD34+ cell dose at 12 months (r = 0.36, p = 0.09 for neutrophil count and r = 0.48, p = 0.06 for platelets count). The number of CD34+/CD90+ cells was also correlated with the platelet counts at 6 (r = 0.70, p < 0.05) and 12 months (r = 0.80, p = 0.005) after PBSCT. This correlation was better than the total dose of CD34+ cells at 6 (r = 0.31, p = 0.3) and 12 months (r = 0.48, p = 0.06) for the platelet counts. CD34+ subset analysis suggests that for early engraftment the total number of CD34+ cells infused is more strongly correlated than the CD34+ subsets, whereas the CD34+/CD38- and CD34+/CD90+ subsets may be associated with sustained long-term neutrophil and platelet engraftment. These findings may help to predict the repopulating capacity of PBSCs in AML patients after autologous PBSCT, especially when a relatively low number of CD34+ cells is infused.

Phenotypic and Functional Analysis of Human Fetal Liver Hematopoietic Stem Cells in Culture

Steady-state hematopoiesis and hematopoietic transplantation rely on the unique potential of stem cells to undergo both self-renewal and multilineage differentiation. Fetal liver (FL) represents a promising alternative source of hematopoietic stem cells (HSCs), but limited by the total cell number obtained in a typical harvest. We reported that human FL nonobese diabetic/severe combined immunodeficient (NOD/SCID) repopulating cells (SRCs) could be expanded under simple stroma-free culture conditions. Here, we sought to further characterize FL HSC/SRCs phenotypically and functionally before and following culture. Unexpanded or cultured FL cell suspensions were separated into various subpopulations. These were tested for long-term culture potential and for in vivo repopulating function following transplantation into NOD/SCID mice. We found that upon culture of human FL cells, a tight association between classical stem cell phenotypes, such as CD34(+) /CD38(-) and/or side population, and NOD/SCID repopulating function was lost, as observed with other sources. Although SRC activity before and following culture consistently correlated with the presence of a CD34(+) cell population, we provide evidence that, contrary to umbilical cord blood and adult sources, stem cells present in both CD34(+) and CD34(-) FL populations can sustain long-term hematopoietic cultures. Furthermore, upon additional culture, CD34-depleted cell suspensions, devoid of SRCs, regenerated a population of CD34(+) cells possessing SRC function. Our studies suggest that compared to neonatal and adult sources, the phenotypical characteristics of putative human FL HSCs may be less strictly defined, and reinforce the accumulated evidence that human FL represents a unique, valuable alternative and highly proliferative source of HSCs for clinical applications.

Searching for common stem cells of the hepatic and hematopoietic systems in the human fetal liver: CD34+ cytokeratin 7/8+ cells express markers for stellate cells

BACKGROUND/AIMS

The hematopoietic and hepatic systems are intertwined in the liver during fetal life. Cells expressing the hematopoietic stem cell marker CD34 and cytokeratin 7/8 (CK7/8) are hypothesized to be common stem cells for the hematopoietic and hepatic systems. Our aim was to determine if human fetal liver cells expressing CD34 and CK7/8 represent a common stem cell for both the hematopoietic and hepatic systems.

METHODS

CD34+CK7/8+ cells from midgestation livers were analyzed for the expression of various markers by flow cytometry and isolated based on their expression of CD34, nerve growth factor receptor (NGFR) and lack of CD45 expression. CD34+CD38- hematopoietic stem cells were also isolated and cultured in the presence of various hepatopoietins.

RESULTS

CD34+CK7/8+ cells comprised 3.4-8.5% of the erythrocyte-depleted liver. CD34+CK7/8+ cells had unique light-scatter properties compared to hematopoietic precursors and did not express most markers associated with hematopoietic cells. They did stain with CD13, CD59, NGFR, desmin and alpha-smooth muscle actin. In culture, these cells had a stellate appearance. Cultured hematopoietic stem cells failed to generate hepatocytes.

CONCLUSIONS

CD34+CK7/8+ cells are not common stem cells but rather appear to be hepatic stellate cells. A link between the hematopoietic and hepatic systems during fetal life requires further investigation.

Long-term ex vivo expansion of human fetal liver primitive haematopoietic progenitor cells in stroma-free cultures

Successful expansion of haematopoietic cells in ex vivo cultures will have important applications in transplantation, gene therapy, immunotherapy and potentially also in the production of non-haematopoietic cell types. Haematopoietic stem cells (HSC), with their capacity to both self-renew and differentiate into all blood lineages, represent the ideal target for expansion protocols. However, human HSC are rare, poorly characterized phenotypically and genotypically, and difficult to test functionally. Defining optimal culture parameters for ex vivo expansion has been a major challenge. We devised a simple and reproducible stroma-free liquid culture system enabling long-term expansion of putative haematopoietic progenitors contained within frozen human fetal liver (FL) crude cell suspensions. Starting from a small number of total nucleated cells, a massive haematopoietic cell expansion, reaching > 1013-fold the input cell number after approximately 300 d of culture, was consistently achieved. Cells with a primitive phenotype were present throughout the culture and also underwent a continuous expansion. Moreover, the capacity for multilineage lymphomyeloid differentiation, as well as the recloning capacity of primitive myeloid progenitors, was maintained in culture. With its better proliferative potential as compared with adult sources, FL represents a promising alternative source of HSC and the culture system described here should be useful for clinical applications.

Cryopreserved human haematopoietic stem cells retain engraftment potential after extended (5-14 years) cryostorage

Harvesting of stem cells during the early phases of treatment with no immediate intention to perform a stem cell transplant is becoming an increasingly common practice. Such "insurance" harvests are often stored for many years before being needed for transplant in a subsequent relapse. The effect of long-term cryostorage (5-14 years) on the viability and functional capacity of haematopoietic stem cells (HSCs) was investigated in 40 bone marrow and peripheral blood harvests using standard in vitro methods, the colony forming unit-granulocyte/macrophage (CFU-GM) assay and a single platform viable CD34(+) cell absolute count by flow cytometry. Forty percent of harvests had CD34(+) HSC counts of at least 0.7 x 10(6)/kg bodyweight and 85% had CFU-GM counts of at least 1.0 x 10(5)/kg bodyweight, these values representing our institutional minimum requirements for safe transplantation. Based on these results, it appears that HSC collections can remain adequate for safe transplantation after up to 14 years of cryostorage. However, as deterioration of HSC quality and viability may occur, some precautions may be warranted, namely harvesting higher than normal numbers of HSCs in collections intended for long-term storage and repeating in vitro assays on harvests after long-term storage prior to transplantation.

Impact of mobilized blood progenitor cell quality determined by the CFU-GM/CD34+ ratio on rapid engraftment after blood stem cell transplantation

To find a parameter to predict the quality of collected mobilized CD34+ blood as hemopoietic reconstituting cells, the ratio of CFU-GM to CD34+ cells was examined. One hundred six consecutive patients who underwent blood stem cell transplantation at the University of Rochester from 01/01/99 to 12/31/99 were examined retrospectively for the number of days to reach an absolute neutrophil count of 500 or 1000 cells/microl and an absolute platelet count of 20,000 or 50,000 cells/microl without transfusion support as measures of engraftment. Linear regression analyses were conducted to determine factors influencing engraftment. The number of CD34+ cells/kg and CFU-GM/kg correlated highly with the number of nucleated blood cells/kg. In this population, in which 90% of patients received >2 x 10(6) CD34+ cells/kg, neither the number of CD34+ cells/kg nor the number of CFU-GM/kg correlated with the time to engraftment as judged by neutrophil or platelet levels. In contrast, the lower the ratio of CFU-GM to CD34+ cells, the more rapid the reconstitution of platelets to 20,000/microl (P = 0.03) and 50,000/microl (P = 0.02). Thus, a lower ratio of the CFU-GM/CD34+ appended to reflect a greater number of hematopoietic reconstituting cells in the blood cell collection. The CFU-GM/CD34+ ratio is an apparent predictor of earlier platelet engraftment, suggesting that the ratio reflects the engraftment potential of mobilized donor progenitor cells.

CD34+/CD90+ cells infused best predict late haematopoietic reconstitution following autologous peripheral blood stem cell transplantation

This study aimed to identify which graft product subset of cells might be the most predictive of late haematopoietic recovery (three to 12 months) following autologous peripheral blood stem cell transplantation (PBSCT). The relationships between the numbers of reinfused CD34+ cells and their immature subsets such as CD34+/CD90+, CD34+/AC133+, CD34+/CD38- and CD34+/HLA-DR- cells, and haemoglobin, white blood cell (WBC) and platelet counts at 3, 6, 9 and 12 months after PBSCT, were studied in 25 patients with haematological and solid malignancies. The total CD34+ cell number, as well as CD34+/CD90+ and CD34+/AC133+ cell numbers, correlated with platelet counts at 3, 6, 9 and 12 months after PBSCT, but the CD34+/CD90+ cells infused best predicted platelet recovery during the first 12 months after PBSCT (P < 0.0238 at any time-point). The CD34+/AC133+ cell dose also correlated with WBC counts at 3 months post PBSCT. In addition, all patients receiving more than 80 x 10(4) CD34+/CD90+ cells/kg showed platelet counts greater than 100 x 10(9)/l at all points after PBSCT, suggesting that this value of the CD34+/CD90+ cells infused was a threshold dose for durable haematopoietic engraftment after PBSCT.

The phenotypic profile of CD34-positive peripheral blood stem cells in different mobilization regimens

The type of regimen used might result in mobilization of phenotypically and functionally different CD34(+) cells. We compared the phenotype of CD34(+) cells in leukapheresis products of three homogeneous groups: I, healthy individuals treated with granulocyte colony-stimulating factor (G-CSF) alone (n = 13); II, patients mobilized with G-CSF following chemotherapy (n = 16); and III, patients mobilized with G-CSF after high-dose chemotherapeutic pretreatment (n = 24). Multiparameter flow cytometry was performed for CD34(+) subpopulation analysis and focused on adhesion molecules, differentiation markers and megakaryocytic markers relevant for stem cell homing, with special reference to the importance of L-selectin expression. Regimens I and II led to higher numbers of mobilized CD34(+) cells (mean 468 x 10(6) and 491 x 10(6) CD34(+) cells per leukapheresis procedure respectively) than regimen III (mean 41 x 10(6) CD34(+) cells per leukapheresis procedure). Both the expression of L-selectin and CD54 on CD34(+) cells was significantly lower in group III, as was the percentage of megakaryocytic (CD41(+)) progenitors. A higher percentage of primitive (CD38(-) and/or HLA(-)DR(-)) CD34(+) cells was found in group III, correlating with a higher clonogenicity of the CD34(+) cells. However, when comparing the CD34(+)_ subpopulations that were also positive for L-selectin, there was no significant difference between the three regimens. A similar approach for the megakaryocytic CD34+ population resulted in an even worse quality of regimen III: 5.1% of CD34(+) being CD41(+)/L-selectin(+) compared with 9.2% and 8.9% in regimens I and II respectively. We concluded that the phenotypes of the CD34(+) cells in the G-CSF (group I) and G-CSF-chemotherapy (group II) regimens are similar, whereas the phenotype of the CD34(+) cells mobilized in the high-dose regimen (group III) displayed features that might negatively influence homing of the cells. Future studies will be directed towards regimens that will lead to the mobilization of a higher amount of CD34(+) cells with a phenotypically favourable phenotype.

Monoclonal antibodies with neuroblastoma specificity: a flow cytometric analysis of cross-reactivity with CD34+ hematopoietic stem cells

The aim of this study was to evaluate the specificity of a number of monoclonal antibodies (MAbs) used for immunological in vitro purging of stem cell grafts from neuroblastoma patients. The extent of cross-reactivity of 10 neuroblastoma-specific MAbs (NB-MAb) with CD34+ stem cells from 14 leukapheresis products was analyzed. The level of cross-reactivity was analyzed on a Coulter (Fullerton, CA) flow cytometer using biotinylated NB-MAbs. There was a marked difference in the reactivity of the ten NB-MAbs with CD34+ stem cells. The antibodies could be divided into three groups with increasing levels of cross reactivity. Four antibodies (126-4, 5.1 H11, UJ127.11, and 14.G2a) all reacted with median levels of less than 2% (range 0.0 to 5.4) of CD34+ stem cells (median of 14 patients). Another three antibodies reacted with a median of 3.1-4.1% of the stem cells (UJ13A, Ab390, and Ab459) but with a wide range (0.2 to 25.6). Finally, M340, HSAN 1.2, and antiThy-1 reacted with a median of 9-16% of the stem cells (range 0.6 to 51.5). We conclude that there is a significant variation in the proportion of CD34+ stem cells reacting with each of the ten neuroblastoma antibodies investigated in this study. Therefore, to avoid a significant loss of CD34+ cells from the stem cell product, we find it important to carefully consider which antibodies to use for immunomagnetic purging.

Mobilization of hematopoietic stem cells

Hematopoietic stem cell transplantation has been extensively exploited as a therapeutic and research modality and has revolutionized current patient care. At present, more and more medical centers use peripheral blood progenitor cells for transplantation by mobilizing hematopoietic stem cells from bone marrow to peripheral blood because of potential advantages of peripheral blood stem cell transplantation over bone-marrow transplantation. Different effective mobilization regimens have been developed recently with chemotherapeutic agents, hematopoietic growth factors or their combination. This article reviews current developments related to hematopoietic stem cell mobilization including the biology of hematopoietic stem cells, strategies for mobilization, management for mobilization failure, mechanisms of mobilization, and side effects during mobilization. Finally, the Initiation-Amplification-Emigration-Adaptation Model is proposed to help aid understanding of the mechanisms of hematopoietic stem cell mobilization and to stimulate development of novel and optimal mobilization strategies for patient care.

Reduction of intra- and interlaboratory variation in CD34+ stem cell enumeration using stable test material, standard protocols and targeted training. DK34 Task Force of the European Working Group of Clinical Cell Analysis (EWGCCA)

The European Working Group on Clinical Cell Analysis (EWGCCA) has, in preparation for a multicentre peripheral blood stem cell clinical trial, developed a single-platform flow cytometric protocol for the enumeration of CD34+ stem cells. Using this protocol, stabilized blood and targeted training, the EWGCCA have attempted to standardize CD34+ stem cell enumeration across 24 clinical sites. Results were directly compared with participants in the UK National External Quality Assessment Scheme (NEQAS) for CD34+ Stem Cell Quantification that analysed the same specimens using non-standardized methods. Two bead-counting systems, Flow-Count and TruCount, were also evaluated by the EWGCCA participants during trials 2 and 3. Using Flow-Count, the intralaboratory coefficient of variation (CV) was </= 5% in 39% of the laboratories (trial 1), increasing to 65% by trial 3. Interlaboratory variation was reduced from 23.3% (trial 1) to 10.8% in trial 3. In trial 2, 70% of laboratories achieved an intralaboratory CV </= 5% using TruCount, increasing to 74% for trial 3; the interlaboratory CV was reduced from 23.4% to 9.5%. Comparative analysis of the EWGCCA and the UK NEQAS cohorts revealed that EWGCCA laboratories, using the standardized approach, had lower interlaboratory variation. Thus, the use of a common standardized protocol and targeted training significantly reduced intra- and interlaboratory CD34+ cell count variation.