Expansion of human cord blood CD34+CD38−cells in ex vivo culture during retroviral transduction without a corresponding increase in SCID repopulating cell (SRC) frequency: dissociation of SRC phenotype and function

Advances in ex vivo expansion of hematopoietic stem and progenitor cells for clinical applications

As caretakers of the hematopoietic system, hematopoietic stem cells assure a lifelong supply of differentiated populations that are responsible for critical bodily functions, including oxygen transport, immunological protection and coagulation. Due to the far-reaching influence of the hematopoietic system, hematological disorders typically have a significant impact on the lives of individuals, even becoming fatal. Hematopoietic cell transplantation was the first effective therapeutic avenue to treat such hematological diseases. Since then, key use and manipulation of hematopoietic stem cells for treatments has been aspired to fully take advantage of such an important cell population. Limited knowledge on hematopoietic stem cell behavior has motivated in-depth research into their biology. Efforts were able to uncover their native environment and characteristics during development and adult stages. Several signaling pathways at a cellular level have been mapped, providing insight into their machinery. Important dynamics of hematopoietic stem cell maintenance were begun to be understood with improved comprehension of their metabolism and progressive aging. These advances have provided a solid platform for the development of innovative strategies for the manipulation of hematopoietic stem cells. Specifically, expansion of the hematopoietic stem cell pool has triggered immense interest, gaining momentum. A wide range of approaches have sprouted, leading to a variety of expansion systems, from simpler small molecule-based strategies to complex biomimetic scaffolds. The recent approval of Omisirge, the first expanded hematopoietic stem and progenitor cell product, whose expansion platform is one of the earliest, is predictive of further successes that might arise soon. In order to guarantee the quality of these ex vivo manipulated cells, robust assays that measure cell function or potency need to be developed. Whether targeting hematopoietic engraftment, immunological differentiation potential or malignancy clearance, hematopoietic stem cells and their derivatives need efficient scaling of their therapeutic potency. In this review, we comprehensively view hematopoietic stem cells as therapeutic assets, going from fundamental to translational.

Cytokine secretion in stem cells of cattle infected with bovine leukaemia virus

Introduction

Bovine leukaemia virus (BLV) is a Deltaretrovirus responsible for enzootic bovine leukosis, the most common neoplastic disease of cattle. It deregulates the immune system, favouring secondary infections and changes in the blood and lymphatic tissues. Blood homeostasis depends on functional haematopoietic stem cells (HSCs). Bone marrow is populated by these cells, which express CD34+ and CD35+ surface antigens and produce and release cytokines involved in the maintenance of haematopoiesis. The aim of the study was determination of the profile of cytokine production by CD34+ stem cells of cattle naturally infected with BLV.

Material and Methods

The HSCs were generated from the blood and lymphoid organs of cows infected with BLV and healthy control cows with immunomagnetic separation and anti-CD34+ monoclonal antibodies. Isolated CD34+ cells were cultivated for two weeks with interleukin (IL)-4 and granulocyte-macrophage colony-stimulating factor. The levels of IL-6, IL-10, IL-12p40, IL-12p70, interferon gamma (IFN-γ) and tumour necrosis factor alpha (TNF-α) were determined in culture fluid by flow cytometry.

Results

The expression of IL-6, IL-12p70 and TNF-α in blood HSCs was higher in BLV+ cows than in the control animals. In bone marrow HSCs of infected cows, IL-12, TNF-α and IFN-γ were more concentrated, but in these cows' spleen HSCs only expression of IL-10 was elevated. In HSCs isolated from the lymph nodes of leukaemic cows, only TNF-α secretion was lower than in control cows, the other cytokines being more potently secreted.

Conclusion

Infection with BLV caused statistically significant differences in cytokine expression by HSC CD34+ cells.

Ex vivo hematopoietic stem cell expansion technologies: recent progress, applications, and open questions

Hematopoietic stem cells (HSCs) are a rare but potent cell type that support life-long hematopoiesis and stably regenerate the entire blood and immune system following transplantation. HSC transplantation represents a mainstay treatment for various diseases of the blood and immune systems. The ex vivo expansion and manipulation of HSCs therefore represents an important approach to ask biological questions in experimental hematology and to help improve clinical HSC transplantation therapies. However, it has remained challenging to expand transplantable HSCs ex vivo. This review summarizes recent progress in ex vivo HSC expansion technologies and their applications to biological and clinical problems and discusses current questions in the field.

Ciclopirox ethanolamine preserves the immature state of human HSCs by mediating intracellular iron content

Culture conditions in which hematopoietic stem cells (HSCs) can be expanded for clinical benefit are highly sought after. To elucidate regulatory mechanisms governing the maintenance and propagation of human HSCs ex vivo, we screened libraries of annotated small molecules in human cord blood cells using an optimized assay for detection of functional HSCs during culture. We found that the antifungal agent ciclopirox ethanolamine (CPX) selectively supported immature CD34+CD90+ cells during culture and enhanced their long-term in vivo repopulation capacity. Purified HSCs treated with CPX showed a reduced cell division rate and an enrichment of HSC-specific gene expression patterns. Mechanistically, we found that the HSC stimulating effect of CPX was directly mediated by chelation of the intracellular iron pool, which in turn affected iron-dependent proteins and enzymes mediating cellular metabolism and respiration. Our findings unveil a significant impact of iron homeostasis in regulation of human HSCs, with important implications for both basic HSC biology and clinical hematology.

CEA cell adhesion molecule 5 enriches functional human hematopoietic stem cells capable of long-term multi-lineage engraftment

Hematopoietic stem cell (HSC) surface markers improve the understanding of cell identity and function. Here, we report that human HSCs can be distinguished by their expression of the CEA Cell Adhesion Molecule 5 (CEACAM5, CD66e), which serves as a marker and a regulator of HSC function. CD66e+ cells exhibited a 5.5-fold enrichment for functional long term HSCs compared to CD66e- cells. CD66e+CD34+CD90+CD45RA- cells displayed robust multi-lineage repopulation and serial reconstitution ability in immunodeficient mice compared to CD66e-CD34+CD90+CD45RA-cells. CD66e expression also identified almost all repopulating HSCs within the CD34+CD90+CD45RA- population. Together, these results indicated that CEACAM5 is a marker that enriches functional human hematopoietic stem cells capable of long-term multi-lineage engraftment.

Hematopoietic reconstitution dynamics of mobilized- and bone marrow-derived human hematopoietic stem cells after gene therapy

Mobilized peripheral blood is increasingly used instead of bone marrow as a source of autologous hematopoietic stem/progenitor cells for ex vivo gene therapy. Here, we present an unplanned exploratory analysis evaluating the hematopoietic reconstitution kinetics, engraftment and clonality in 13 pediatric Wiskott-Aldrich syndrome patients treated with autologous lentiviral-vector transduced hematopoietic stem/progenitor cells derived from mobilized peripheral blood (n = 7), bone marrow (n = 5) or the combination of the two sources (n = 1). 8 out of 13 gene therapy patients were enrolled in an open-label, non-randomized, phase 1/2 clinical study (NCT01515462) and the remaining 5 patients were treated under expanded access programs. Although mobilized peripheral blood- and bone marrow- hematopoietic stem/progenitor cells display similar capability of being gene-corrected, maintaining the engineered grafts up to 3 years after gene therapy, mobilized peripheral blood-gene therapy group shows faster neutrophil and platelet recovery, higher number of engrafted clones and increased gene correction in the myeloid lineage which correlate with higher amount of primitive and myeloid progenitors contained in hematopoietic stem/progenitor cells derived from mobilized peripheral blood. In vitro differentiation and transplantation studies in mice confirm that primitive hematopoietic stem/progenitor cells from both sources have comparable engraftment and multilineage differentiation potential. Altogether, our analyses reveal that the differential behavior after gene therapy of hematopoietic stem/progenitor cells derived from either bone marrow or mobilized peripheral blood is mainly due to the distinct cell composition rather than functional differences of the infused cell products, providing new frames of references for clinical interpretation of hematopoietic stem/progenitor cell transplantation outcome.

Living Biomaterials to Engineer Hematopoietic Stem Cell Niches

Living biointerfaces are a new class of biomaterials combining living cells and polymeric matrices that can act as biologically active and instructive materials that host and provide signals to surrounding cells. Here, living biomaterials based on Lactococcus lactis to control hematopoietic stem cells in 2D surfaces and 3D hydrogels are introduced. L. lactis is modified to express C-X-C motif chemokine ligand 12 (CXCL12), thrombopoietin (TPO), vascular cell adhesion protein 1 (VCAM1), and the 7th-10th type III domains of human plasma fibronectin (FN III_7-10 ), in an attempt to mimic ex vivo the conditions of the human bone marrow. These results suggest that living biomaterials that incorporate bacteria expressing recombinant CXCL12, TPO, VCAM1, and FN in both 2D systems direct hematopoietic stem and progenitor cells (HSPCs)-bacteria interaction, and in 3D using hydrogels functionalized with full-length human plasma fibronectin allow for a notable expansion of the CD34⁺ /CD38^- /CD90⁺ HSPC population compared to the initial population. These results provide a strong evidence based on data that suggest the possibility of using living materials based on genetically engineered bacteria for the ex-vivo expansion of HSPC with eventual practical clinical applications in HSPCs transplantation for hematological disorders.

CEACAM1 is a novel culture-compatible surface marker of expanded long-term reconstituting hematopoietic stem cells

CEACAM1 is a novel cell surface marker of ex vivo expanded LT-HSCs.

Sorting umbilical cord blood cells based on CEACAM1 and known HSC marker expression allows purification of LT-HSCs with improved purity.

HLF expression defines the human hematopoietic stem cell state

Hematopoietic stem cells (HSCs) sustain blood cell homeostasis throughout life and can regenerate all blood lineages after transplantation. Despite this clear functional definition, highly enriched isolation of human HSCs can currently only be achieved through combinatorial assessment of multiple surface antigens. Although several transgenic HSC reporter mouse strains have been described, no analogous approach to prospectively isolate human HSCs has been reported. To identify genes with the most selective expression in human HSCs, we profiled population and single-cell transcriptomes of unexpanded and ex vivo cultured cord blood-derived hematopoietic stem and progenitor cells as well as peripheral blood, adult bone marrow, and fetal liver. On the basis of these analyses, we propose the master transcription factor HLF (hepatic leukemia factor) as one of the most specific HSC marker genes. To directly track its expression in human hematopoietic cells, we developed a genomic HLF reporter strategy, capable of selectively labeling the most immature blood cells on the basis of a single engineered parameter. Most importantly, HLF-expressing cells comprise all stem cell activity in culture and in vivo during serial transplantation. Taken together, these results experimentally establish HLF as a defining gene of the human HSC state and outline a new approach to continuously mark these cells with high fidelity.

Mitigating oxygen stress enhances aged mouse hematopoietic stem cell numbers and function

Bone marrow (BM) hematopoietic stem cells (HSCs) become dysfunctional during aging (i.e., they are increased in number but have an overall reduction in long-term repopulation potential and increased myeloid differentiation) compared with young HSCs, suggesting limited use of old donor BM cells for hematopoietic cell transplantation (HCT). BM cells reside in an in vivo hypoxic environment yet are evaluated after collection and processing in ambient air. We detected an increase in the number of both young and aged mouse BM HSCs collected and processed in 3% O2 compared with the number of young BM HSCs collected and processed in ambient air (~21% O2). Aged BM collected and processed under hypoxic conditions demonstrated enhanced engraftment capability during competitive transplantation analysis and contained more functional HSCs as determined by limiting dilution analysis. Importantly, the myeloid-to-lymphoid differentiation ratio of aged BM collected in 3% O2 was similar to that detected in young BM collected in ambient air or hypoxic conditions, consistent with the increased number of common lymphoid progenitors following collection under hypoxia. Enhanced functional activity and differentiation of old BM collected and processed in hypoxia correlated with reduced "stress" associated with ambient air BM collection and suggests that aged BM may be better and more efficiently used for HCT if collected and processed under hypoxia so that it is never exposed to ambient air O2.

Integrin-α3 Is a Functional Marker of Ex Vivo Expanded Human Long-Term Hematopoietic Stem Cells

Transplantation of expanded hematopoietic stem cells (HSCs) and gene therapy based on HSC engineering have emerged as promising approaches for the treatment of hematological diseases. Nevertheless, the immunophenotype of cultured HSCs remains poorly defined. Here, we identify Integrin-α3 (ITGA3) as a marker of cultured human HSCs. Exploiting the pyrimidoindole derivative UM171 to expand cord blood (CB) cells, we show that ITGA3 expression is sufficient to separate the primitive EPCR⁺CD90⁺CD133⁺CD34⁺CD45RA^- HSC population into two functionally distinct fractions presenting mostly short-term (ITGA3^-) and both short-term and long-term (ITGA3⁺) repopulating potential. ITGA3⁺ cells exhibit robust multilineage differentiation potential, serial reconstitution ability in immunocompromised mice, and an HSC-specific transcriptomic signature. Moreover, ITGA3 expression is functionally required for the long-term engraftment of CB cells. Altogether, our results indicate that ITGA3 is a reliable marker of cultured human long-term repopulating HSCs (LT-HSCs) and represents an important tool to improve the accuracy of prospective HSC identification in culture.

On-chip recapitulation of clinical bone marrow toxicities and patient-specific pathophysiology

The inaccessibility of living bone marrow hampers the study of its pathophysiology under myelotoxic stress induced by drugs, radiation or genetic mutations. Here, we show that a vascularized human bone-marrow-on-a-chip supports the differentiation and maturation of multiple blood-cell lineages over 4 weeks while improving CD34+ cell maintenance, and that it recapitulates aspects of marrow injury, including myeloerythroid toxicity after clinically relevant exposures to chemotherapeutic drugs and ionizing radiation as well as marrow recovery after drug-induced myelosuppression. The chip comprises a fluidic channel filled with a fibrin gel in which CD34⁺ cells and bone-marrow-derived stromal cells are co-cultured, a parallel channel lined by human vascular endothelium and perfused with culture medium, and a porous membrane separating the two channels. We also show that bone-marrow chips containing cells from patients with the rare genetic disorder Shwachman–Diamond syndrome reproduced key haematopoietic defects and led to the discovery of a neutrophil-maturation abnormality. As an in vitro model of haematopoietic dysfunction, the bone-marrow-on-a-chip may serve as a human-specific alternative to animal testing for the study of bone-marrow pathophysiology.

Past, present, and future efforts to enhance the efficacy of cord blood hematopoietic cell transplantation

Cord blood (CB) has been used as a viable source of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) in over 35,000 clinical hematopoietic cell transplantation (HCT) efforts to treat the same variety of malignant and non-malignant disorders treated by bone marrow (BM) and mobilized peripheral blood (mPB) using HLA-matched or partially HLA-disparate related or unrelated donor cells for adult and children recipients. This review documents the beginning of this clinical effort that started in the 1980’s, the pros and cons of CB HCT compared to BM and mPB HCT, and recent experimental and clinical efforts to enhance the efficacy of CB HCT. These efforts include means for increasing HSC numbers in single CB collections, expanding functional HSCs ex vivo, and improving CB HSC homing and engraftment, all with the goal of clinical translation. Concluding remarks highlight the need for phase I/II clinical trials to test the experimental procedures that are described, either alone or in combination.

Robust generation of erythroid and multilineage hematopoietic progenitors from human iPSCs using a scalable monolayer culture system

One of the most promising objectives of clinical hematology is to derive engraftable autologous hematopoietic stem cells (HSCs) from human induced pluripotent stem cells (iPSCs). Progress in translating iPSC technologies to the clinic relies on the availability of scalable differentiation methodologies. In this study, human iPSCs were differentiated for 21 days using STEMdiff™, a monolayer-based approach for hematopoietic differentiation of human iPSCs that requires no replating, co-culture or embryoid body formation. Both hematopoietic and non-hematopoietic cells were functionally characterized throughout differentiation. In the hematopoietic fraction, an early transient population of primitive CD235a⁺ erythroid progenitor cells first emerged, followed by hematopoietic progenitors with multilineage differentiation activity in vitro but no long-term engraftment potential in vivo. In later stages of differentiation, a nearly exclusive production of definitive erythroid progenitors was observed. In the non-hematopoietic fraction, we identified a prevalent population of mesenchymal stromal cells and limited arterial vascular endothelium (VE), suggesting that the cellular constitution of the monolayer may be inadequate to support the generation of HSCs with durable repopulating potential. Quantitative modulation of WNT/β-catenin and activin/nodal/TGFβ signaling pathways with CHIR/SB molecules during differentiation enhanced formation of arterial VE, definitive multilineage and erythroid progenitors, but was insufficient to orchestrate the generation of engrafting HSCs. Overall, STEMdiff™ provides a clinically-relevant and readily adaptable platform for the generation of erythroid and multilineage hematopoietic progenitors from human pluripotent stem cells.

Maintenance and enhancement of human peripheral blood mobilized stem/progenitor cell engraftment after ex vivo culture via an HDACi/SALL4 axis (3465)

Currently, there is a growing need for culturing hematopoietic stem/progenitor cells (HSPCs) in vitro for various clinical applications including gene therapy. Compared with cord blood (CB) CD34⁺ HSPCs, it is more challenging to maintain or expand CD34⁺ peripheral blood mobilized stem/progenitor cells (PBSCs) ex vivo. To fill this knowledge gap, we have systematically surveyed 466 small-molecule drug compounds for their potential in cytokine-dependent expansion of human CD34⁺CD90⁺ HSPCs. We found that epigenetic modifiers, especially histone deacetylase inhibitors (HDACis), could preferentially maintain and expand these cells. In particular, treatment of CD34⁺ PBSCs with a single dose of HDACi trichostatin A (TSA) at a concentration of 50 nmol/L ex vivo yielded the greatest expansion (11.7-fold) of CD34⁺CD90⁺ cells when compared with the control (dimethyl sulfoxide [DMSO] plus cytokines) group. Additionally, TSA-treated PBSC CD34⁺ cells had a statistically significant higher engraftment rate than the control-treated group in xenotransplantation experiments. Mechanistically, TSA treatment was associated with increased expression of HSPC-related genes such as GATA2 and SALL4. Furthermore, TSA-mediated CD34⁺CD90⁺ expansion was reduced by downregulation of SALL4 but not GATA2. Overall, we have developed a robust, short-term (5-day), PBSC ex vivo maintenance/expansion culture technique and found that the HDACi-TSA/SALL4 axis is important for the biological process.

Enhancing Lentiviral and Alpharetroviral Transduction of Human Hematopoietic Stem Cells for Clinical Application

Ex vivo retroviral gene transfer into CD34⁺ hematopoietic stem and progenitor cells (HSPCs) has demonstrated remarkable clinical success in gene therapy for monogenic hematopoietic disorders. However, little attention has been paid to enhancement of culture and transduction conditions to achieve reliable effects across patient and disease contexts and to maximize potential vector usage and reduce treatment cost. We systematically tested three HSPC culture media manufactured to cGMP and eight previously described transduction enhancers (TEs) to develop a state-of-the-art clinically applicable protocol. Six TEs enhanced lentiviral (LV) and five TEs facilitated alpharetroviral (ARV) CD34⁺ HSPC transduction when used alone. Combinatorial TE application tested with LV vectors yielded more potent effects, with up to a 5.6-fold increase in total expression of a reporter gene and up to a 3.8-fold increase in VCN. Application of one of the most promising combinations, the poloxamer LentiBOOST and protamine sulfate, for GMP-compliant manufacturing of a clinical-grade advanced therapy medicinal product (ATMP) increased total VCN by over 6-fold, with no major changes in global gene expression profiles or inadvertent loss of CD34⁺CD90⁺ HSPC populations. Application of these defined culture and transduction conditions is likely to significantly improve ex vivo gene therapy manufacturing protocols for HSPCs and downstream clinical efficacy.

A novel method for detecting the cellular stemness state in normal and leukemic human hematopoietic cells can predict disease outcome and drug sensitivity

Acute leukemia is an aggressive blood malignancy with low survival rates. A high expression of stem-like programs in leukemias predicts poor prognosis and is assumed to act in an aberrant fashion in the phenotypically heterogeneous leukemia stem cell (LSC) population. A lack of suitable genome engineering tools that can isolate LSCs based on their stemness precludes their comprehensive examination and full characterization. We hypothesized that tagging endogenous stemness-regulatory regions could generate a genome reporter for the putative leukemia stemness-state. Our analysis revealed that the ERG  + 85 enhancer region can serve as a marker for stemness-state and a fluorescent lentiviral reporter was developed that can accurately recapitulate the endogenous activity. Using our novel reporter, we revealed cellular heterogeneity in several leukemia cell lines and patient-derived samples. Alterations in reporter activity were associated with transcriptomic and functional changes that were closely related to the hematopoietic stem cell (HSC) identity. Notably, the differentiation potential was skewed towards the erythro-megakaryocytic lineage. Moreover, an ERG  + 85^High fraction of AML cells could regenerate the original cellular heterogeneity and was enriched for LSCs. RNA-seq analysis coupled with in silico drug-screen analysis identified 4HPR as an effective inhibitor of ERG  + 85^High leukemia growth. We propose that further utilization of our novel molecular tool will identify crucial determinants of LSCs, thus providing a rationale for their therapeutic targeting.

Functional Integrity and Gene Expression Profiles of Human Cord Blood-Derived Hematopoietic Stem and Progenitor Cells Generated In Vitro

To date, different experimental strategies have been developed for the ex vivo expansion of human hematopoietic stem (HSCs) and progenitor (HPCs) cells. This has resulted in significant advances on the use of such expanded cells in transplantation settings. To this day, however, it is still unclear to what extent those stem and progenitor cells generated in vitro retain the functional and genomic integrity of their freshly isolated counterparts. In trying to contribute to the solving of this issue, in the present study we have selected and purified three different hematopoietic cell populations: HSCs (CD34+ CD38- CD45RA- CD71- Lin- cells), myeloid progenitor cells (CD34+ CD38+ CD45RA+ CD71- Lin- cells), and erythroid progenitor cells (CD34+ CD38+ CD45RA- CD71+ Lin- cells), obtained directly from fresh human umbilical cord blood (UCB) units or generated in vitro under particular culture conditions. We, then, compared their functional integrity in vitro and their gene expression profiles. Our results indicate that in spite of being immunophenotipically similar, fresh and in vitro generated cells showed significant differences, both in functional and genetic terms. As compared to their fresh counterparts, those HSCs generated in our culture system showed a deficient content of long-term culture-initiating cells, and a marked differentiation bias toward the myeloid lineage. In addition, in vitro generated HSCs and HPCs showed a limited expansion potential. Such functional alterations correlated with differences in their gene expression profiles. These observations are relevant in terms of HSC biology and may have implications in UCB expansion and transplantation. Stem Cells Translational Medicine 2018;7:602-614.

EPCR: a novel marker of cultured cord blood HSCs

In this issue of Blood, Fares et al1 demonstrate that endothelial protein C receptor (EPCR) is a reliable marker of human cord blood (CB) hematopoietic stem cells (HSCs), both from uncultured cells and those expanded with UM171, a pyrimidoindole derivative previously shown to expand CB HSCs.2

A Human IPS Model Implicates Embryonic B-Myeloid Fate Restriction as Developmental Susceptibility to B Acute Lymphoblastic Leukemia-Associated ETV6-RUNX1

ETV6-RUNX1 is associated with childhood acute B-lymphoblastic leukemia (cALL) functioning as a first-hit mutation that initiates a clinically silent pre-leukemia in utero. Because lineage commitment hierarchies differ between embryo and adult, and the impact of oncogenes is cell-context dependent, we hypothesized that the childhood affiliation of ETV6-RUNX1 cALL reflects its origins in a progenitor unique to embryonic life. We characterize the first emerging B cells in first-trimester human embryos, identifying a developmentally restricted CD19^-IL-7R⁺ progenitor compartment, which transitions from a myeloid to lymphoid program during ontogeny. This developmental series is recapitulated in differentiating human pluripotent stem cells (hPSCs), thereby providing a model for the initiation of cALL. Genome-engineered hPSCs expressing ETV6-RUNX1 from the endogenous ETV6 locus show expansion of the CD19^-IL-7R⁺ compartment, show a partial block in B lineage commitment, and produce proB cells with aberrant myeloid gene expression signatures and potential: features (collectively) consistent with a pre-leukemic state.

Spheroid Coculture of Hematopoietic Stem/Progenitor Cells and Monolayer Expanded Mesenchymal Stem/Stromal Cells in Polydimethylsiloxane Microwells Modestly Improves In Vitro Hematopoietic Stem/Progenitor Cell Expansion

While two-dimensional (2D) monolayers of mesenchymal stem/stromal cells (MSCs) have been shown to enhance hematopoietic stem/progenitor cell (HSPC) expansion in vitro, expanded cells do not engraft long term in human recipients. This outcome is attributed to the failure of 2D culture to recapitulate the bone marrow (BM) niche signal milieu. Herein, we evaluated the capacity of a novel three-dimensional (3D) coculture system to support HSPC expansion in vitro. A high-throughput polydimethylsiloxane (PDMS) microwell platform was used to manufacture thousands of uniform 3D multicellular coculture spheroids. Relative gene expression in 3D spheroid versus 2D adherent BM-derived MSC cultures was characterized and compared with literature reports. We evaluated coculture spheroids, each containing 25-400 MSCs and 10 umbilical cord blood (CB)-derived CD34⁺ progenitor cells. At low exogenous cytokine concentrations, 2D and 3D MSC coculture modestly improved overall hematopoietic cell and CD34⁺ cell expansion outcomes. By contrast, a substantial increase in CD34⁺CD38^- cell yield was observed in PDMS microwell cultures, regardless of the presence or absence of MSCs. This outcome indicated that CD34⁺CD38^- cell culture yield could be increased using the microwell platform alone, even without MSC coculture support. We found that the increase in CD34⁺CD38^- cell yield observed in PDMS microwell cultures did not translate to enhanced engraftment in NOD/SCID gamma (NSG) mice or a modification in the relative human hematopoietic lineages established in engrafted mice. In summary, there was no statistical difference in CD34⁺ cell yield from 2D or 3D cocultures, and MSC coculture support provided only modest benefit in either geometry. While the high-throughput 3D microwell platform may provide a useful model system for studying cells in coculture, further optimization will be required to generate HSPC yields suitable for use in clinical applications.

EPCR expression marks UM171-expanded CD34+ cord blood stem cells

Publisher's Note: There is an Inside Blood Commentary on this article in this issue.

Human mesenchymal and murine stromal cells support human lympho-myeloid progenitor expansion but not maintenance of multipotent haematopoietic stem and progenitor cells

A major goal in haematopoietic stem cell (HSC) research is to define conditions for the expansion of HSCs or multipotent progenitor cells (MPPs). Since human HSCs/MPPs cannot be isolated, NOD/SCID repopulating cell (SRC) assays emerged as the standard for the quantification of very primitive haematopoietic cell. However, in addition to HSCs/MPPs, lympho-myeloid primed progenitors (LMPPs) were recently found to contain SRC activities, challenging this assay as clear HSC/MPP readout. Because our revised model of human haematopoiesis predicts that HSCs/MPPs can be identified as CD133(+)CD34(+) cells containing erythroid potentials, we investigated the potential of human mesenchymal and conventional murine stromal cells to support expansion of HSCs/MPPs. Even though all stromal cells supported expansion of CD133(+)CD34(+) progenitors with long-term myeloid and long-term lymphoid potentials, erythroid potentials were exclusively found within erythro-myeloid CD133(low)CD34(+) cell fractions. Thus, our data demonstrate that against the prevailing assumption co-cultures on human mesenchymal and murine stromal cells neither promote expansion nor maintenance of HSCs and MPPs.

Semi-automated closed system manufacturing of lentivirus gene-modified haematopoietic stem cells for gene therapy

Haematopoietic stem cell (HSC) gene therapy has demonstrated potential to treat many diseases. However, current state of the art requires sophisticated ex vivo gene transfer in a dedicated Good Manufacturing Practices facility, limiting availability. An automated process would improve the availability and standardized manufacture of HSC gene therapy. Here, we develop a novel program for semi-automated cell isolation and culture equipment to permit complete benchtop generation of gene-modified CD34⁺ blood cell products for transplantation. These cell products meet current manufacturing quality standards for both mobilized leukapheresis and bone marrow, and reconstitute human haematopoiesis in immunocompromised mice. Importantly, nonhuman primate autologous gene-modified CD34⁺ cell products are capable of stable, polyclonal multilineage reconstitution with follow-up of more than 1 year. These data demonstrate proof of concept for point-of-care delivery of HSC gene therapy. Given the many target diseases for gene therapy, there is enormous potential for this approach to treat patients on a global scale.

Polydimethylsiloxane (PDMS) modulates CD38 expression, absorbs retinoic acid and may perturb retinoid signalling

Polydimethylsiloxane (PDMS) is the most commonly used material in the manufacture of customized cell culture devices. While there is concern that uncured PDMS oligomers may leach into culture medium and/or hydrophobic molecules may be absorbed into PDMS structures, there is no consensus on how or if PDMS influences cell behaviour. We observed that human umbilical cord blood (CB)-derived CD34(+) cells expanded in standard culture medium on PDMS exhibit reduced CD38 surface expression, relative to cells cultured on tissue culture polystyrene (TCP). All-trans retinoic acid (ATRA) induces CD38 expression, and we reasoned that this hydrophobic molecule might be absorbed by PDMS. Through a series of experiments we demonstrated that ATRA-mediated CD38 expression was attenuated when cultures were maintained on PDMS. Medium pre-incubated on PDMS for extended durations resulted in a time-dependant reduction of ATRA in the medium and increasingly attenuated CD38 expression. This indicated a time-dependent absorption of ATRA into the PDMS. To better understand how PDMS might generally influence cell behaviour, Ingenuity Pathway Analysis (IPA) was used to identify potential upstream regulators. This analysis was performed for differentially expressed genes in primary cells including CD34(+) haematopoietic progenitor cells, mesenchymal stromal cells (MSC), and keratinocytes, and cell lines including prostate cancer epithelial cells (LNCaP), breast cancer epithelial cells (MCF-7), and myeloid leukaemia cells (KG1a). IPA predicted that the most likely common upstream regulator of perturbed pathways was ATRA. We demonstrate here that ATRA is absorbed by PDMS in a time-dependent manner and results in the concomitant reduced expression of CD38 on the cell surface of CB-derived CD34(+) cells.

Optimizing autologous cell grafts to improve stem cell gene therapy

Over the past decade, stem cell gene therapy has achieved unprecedented curative outcomes for several genetic disorders. Despite the unequivocal success, clinical gene therapy still faces challenges. Genetically engineered hematopoietic stem cells are particularly vulnerable to attenuation of their repopulating capacity once exposed to culture conditions, ultimately leading to low engraftment levels posttransplant. This becomes of particular importance when transduction rates are low or/and competitive transplant conditions are generated by reduced-intensity conditioning in the absence of a selective advantage of the transduced over the unmodified cells. These limitations could partially be overcome by introducing megadoses of genetically modified CD34(+) cells into conditioned patients or by transplanting hematopoietic stem cells hematopoietic stem cells with high engrafting and repopulating potential. On the basis of the lessons gained from cord blood transplantation, we summarize the most promising approaches to date of increasing either the numbers of hematopoietic stem cells for transplantation or/and their engraftability, as a platform toward the optimization of engineered stem cell grafts.

The frequency of multipotent CD133(+)CD45RA(-)CD34(+) hematopoietic stem cells is not increased in fetal liver compared with adult stem cell sources

The cell surface marker CD133 has been used to describe a revised model of adult human hematopoiesis, with hematopoietic stem cells and multipotent progenitors (HSCs/MPPs: CD133(+)CD45RA(-)CD34(+)) giving rise to lymphomyeloid-primed progenitors (LMPPs: CD133(+)CD45RA(+)CD34(+)) and erythromyeloid progenitors (EMPs: CD133(low)CD45RA(-)CD34(+)). Because adult and fetal hematopoietic stem and progenitor cells (HSPCs) differ in their gene expression profile, differentiation capabilities, and cell surface marker expression, we were interested in whether the reported segregation of lineage potentials in adult human hematopoiesis would also apply to human fetal liver. CD133 expression was easily detected in human fetal liver cells, and the defined hematopoietic subpopulations were similar to those found for adult HSPCs. Fetal HSPCs were enriched for EMPs and HSCs/MPPs, which were primed toward erythromyeloid differentiation. However, the frequency of multipotent CD133(+)CD45RA(-)CD34(+) HSPCs was much lower than previously reported and comparable to that of umbilical cord blood. We noted that engraftment in NSG (NOD scid gamma [NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ]) mice was driven mostly by LMPPs, confirming recent findings that repopulation in mice is not a unique feature of multipotent HSCs/MPPs. Thus, our data challenge the general assumption that human fetal liver contains a greater percentage of multipotent HSCs/MPPs than any adult HSC source, and the mouse model may have to be re-evaluated with respect to the type of readout it provides.

Genetic treatment of a molecular disorder: gene therapy approaches to sickle cell disease

Effective medical management for sickle cell disease (SCD) remains elusive. As a prevalent and severe monogenic disorder, SCD has been long considered a logical candidate for gene therapy. Significant progress has been made in moving toward this goal. These efforts have provided substantial insight into the natural regulation of the globin genes and illuminated challenges for genetic manipulation of the hematopoietic system. The initial γ-retroviral vectors, next-generation lentiviral vectors, and novel genome engineering and gene regulation approaches each share the goal of preventing erythrocyte sickling. After years of preclinical studies, several clinical trials for SCD gene therapies are now open. This review focuses on progress made toward achieving gene therapy, the current state of the field, consideration of factors that may determine clinical success, and prospects for future development.

Ex vivo expansion of hematopoietic stem cells

Ex vivo expansion of hematopoietic stem cells (HSCs) would benefit clinical applications in several aspects, to improve patient survival, utilize cord blood stem cells for adult applications, and selectively propagate stem cell populations after genetic manipulation. In this review we summarize and discuss recent advances in the culture systems of mouse and human HSCs, which include stroma/HSC co-culture, continuous perfusion and fed-batch cultures, and those supplemented with extrinsic ligands, membrane transportable transcription factors, complement components, protein modification enzymes, metabolites, or small molecule chemicals. Some of the expansion systems have been tested in clinical trials. The optimal condition for ex vivo expansion of the primitive and functional human HSCs is still under development. An improved understanding of the mechanisms for HSC cell fate determination and the HSC culture characteristics will guide development of new strategies to overcome difficulties. In the future, development of a combination treatment regimen with agents that enhance self-renewal, block differentiation, and improve homing will be critical. Methods to enhance yields and lower cost during collection and processing should be employed. The employment of an efficient system for ex vivo expansion of HSCs will facilitate the further development of novel strategies for cell and gene therapies including genome editing.

Ex vivo expansion of human mobilized peripheral blood stem cells using epigenetic modifiers

BACKGROUND

Epigenetic modifications likely control the fate of hematopoietic stem cells (HSCs). The chromatin-modifying agents (CMAs), 5-aza-2'-deoxycytidine (5azaD) and trichostatin A (TSA), have previously been shown to expand HSCs from cord blood and marrow. Here we assessed whether CMA can also expand HSCs present in growth factor-mobilized human peripheral blood (MPB).

STUDY DESIGN AND METHODS

5azaD and TSA were sequentially added to CD34+ MPB cells in the presence of cytokines, and the cells were cultured for 9 days.

RESULTS

After culture, a 3.6 ± 0.5-fold expansion of CD34+CD90+ cells, a 10.1 ± 0.5-fold expansion of primitive colony-forming unit (CFU)-mix, and a 2.2 ± 0.5-fold expansion of long-term cobblestone-area-forming cells (CAFCs) was observed in 5azaD/TSA-expanded cells. By contrast, cells cultured in cytokines without 5azaD/TSA displayed no expansion; rather, a reduction in CD34+CD90+ cells (0.7 ± 0.1-fold) and CAFCs (0.3 ± 0.1-fold) from their initial numbers was observed. Global hypomethylation corresponding with increased transcript levels of several genes implicated in HSC self-renewal, including HOXB4, GATA2, and EZH2, was observed in 5azaD/TSA-expanded MPB cells in contrast to controls. 5azaD/TSA-expanded MPB cells retained in vivo hematopoietic engraftment capacity.

CONCLUSION

MPB CD34+ cells from donors can be expanded using 5azaD/TSA, and these expanded cells retain in vivo hematopoietic reconstitution capacity. This strategy may prove to be potentially useful to augment HSC numbers for patients who fail to mobilize.

Intercellular network structure and regulatory motifs in the human hematopoietic system

The hematopoietic system is a distributed tissue that consists of functionally distinct cell types continuously produced through hematopoietic stem cell (HSC) differentiation. Combining genomic and phenotypic data with high-content experiments, we have built a directional cell-cell communication network between 12 cell types isolated from human umbilical cord blood. Network structure analysis revealed that ligand production is cell type dependent, whereas ligand binding is promiscuous. Consequently, additional control strategies such as cell frequency modulation and compartmentalization were needed to achieve specificity in HSC fate regulation. Incorporating the in vitro effects (quiescence, self-renewal, proliferation, or differentiation) of 27 HSC binding ligands into the topology of the cell-cell communication network allowed coding of cell type-dependent feedback regulation of HSC fate. Pathway enrichment analysis identified intracellular regulatory motifs enriched in these cell type- and ligand-coupled responses. This study uncovers cellular mechanisms of hematopoietic cell feedback in HSC fate regulation, provides insight into the design principles of the human hematopoietic system, and serves as a foundation for the analysis of intercellular regulation in multicellular systems.

Stem cell programs are retained in human leukemic lymphoblasts

Leukemic lymphoblasts within different immunophenotypic populations possess stem cell properties. However, whether or not the self-renewal program is retained from stem cells or conferred on progenitors by leukemogenic molecules remains unknown. We have addressed the issue in the context of TEL-AML1-associated acute lymphoblastic leukemia (ALL) by profiling a refined program edited from genes essential for self-renewal of hematopoietic stem cells and B-cell development. Bioinformatic analysis shows that ALL populations are loosely clustered and close to the normal population that contains stem and primitive progenitor cells. This finding indicates that immunophenotypes do not reflect maturation stages in ALL and that the self-renewal program may be retained from stem cells. Results of assessing 'first hit' function of TEL-AML1 in different populations of normal cells demonstrate the molecular model. Therefore, the current study shows a leukemogenic scenario of human ALL in which programs of stem cells are sustained in distinct fractions by leukemogenic mutations.

Protective role of functionalized single walled carbon nanotubes enhance ex vivo expansion of hematopoietic stem and progenitor cells in human umbilical cord blood

In this study, carboxylic acid functionalized single walled carbon nanotubes (f-SWCNT-COOH) was shown to support the viability and ex vivo expansion of freeze-thawed, non-enriched hematopoietic stem and progenitor cells (HSPC) in human umbilical cord blood-mononucleated cells (UCB-MNC). Our in vitro experiments showed that f-SWCNT-COOH increased the viability of the CD45(+) cells even without cytokine stimulation. It also reduced mitochondrial superoxides and caspase activity in CD45(+) cells. f-SWCNT-COOH drastically reduced the proportions of CD45(-) cells in the non-enriched UCB-MNC. Phenotypic expression analysis and functional colony forming units (CFU) showed significant ex vivo expansion of HSPC, particularly of CD45(+)CD34(+)CD38(-) population and granulocyte-macrophage (GM) colonies, in f-SWCNT-COOH augmented cultures supplemented with basal cytokines. In vivo data suggested that f-SWCNT-COOH expanded UCB-MNC could repopulate immunodeficient mice models with minimal acute or sub-acute symptoms of graft-versus-host disease (GVHD) and f-SWCNT-COOH dependent toxicity.

FROM THE CLINICAL EDITOR

In this paper a novel method is presented by using single wall functionalized carbon nanotubes to enhance viability and ex vivo expansion of freeze-thawed, non-enriched hematopoietic stem and progenitor cells in human umbilical cord blood -mononucleated cells. Detailed data is presented about enhanced viability, including improved repopulation of immunodeficient mice models with minimal acute or sub-acute symptoms of graft-versus-host disease.

Stem cell bioengineering strategies to widen the therapeutic applications of haematopoietic stem/progenitor cells from umbilical cord blood

Umbilical cord blood (UCB) transplantation has observed a significant increase in recent years, due to the unique features of UCB haematopoietic stem/progenitor cells (HSCs) for the treatment of blood-related disorders. However, the low cell numbers available per UCB unit significantly impairs the widespread use of this source for transplantation of adult patients, resulting in graft failure, delayed engraftment and delayed immune reconstitution. In order to overcome this issue, distinct approaches are now being considered in clinical trials, such as double-UCB transplantation, intrabone injection or ex vivo expansion. In this article the authors review the current state of the art, future trends and challenges on the ex vivo expansion of UCB HSCs, focusing on culture parameters affecting the yield and quality of the expanded HSC grafts: novel HSC selection schemes prior to cell culture, cytokine/growth factor cocktails, the impact of biochemical factors (e.g. O2 ) or the addition of supportive cells, e.g. mesenchymal stem/stromal cell (MSC)-based feeder layers) were addressed. Importantly, a critical challenge in cellular therapy is still the scalability, reproducibility and control of the expansion process, in order to meet the clinical requirements for therapeutic applications. Efficient design of bioreactor systems and operation modes are now the focus of many bioengineers, integrating the increasing 'know-how' on HSC biology and physiology, while complying with the GMP standards for the production of cellular products, i.e. through the use of commercially available, highly controlled, disposable technologies.

Expansion on stromal cells preserves the undifferentiated state of human hematopoietic stem cells despite compromised reconstitution ability

Lack of HLA-matched hematopoietic stem cells (HSC) limits the number of patients with life-threatening blood disorders that can be treated by HSC transplantation. So far, insufficient understanding of the regulatory mechanisms governing human HSC has precluded the development of effective protocols for culturing HSC for therapeutic use and molecular studies. We defined a culture system using OP9M2 mesenchymal stem cell (MSC) stroma that protects human hematopoietic stem/progenitor cells (HSPC) from differentiation and apoptosis. In addition, it facilitates a dramatic expansion of multipotent progenitors that retain the immunophenotype (CD34+CD38-CD90+) characteristic of human HSPC and proliferative potential over several weeks in culture. In contrast, transplantable HSC could be maintained, but not significantly expanded, during 2-week culture. Temporal analysis of the transcriptome of the ex vivo expanded CD34+CD38-CD90+ cells documented remarkable stability of most transcriptional regulators known to govern the undifferentiated HSC state. Nevertheless, it revealed dynamic fluctuations in transcriptional programs that associate with HSC behavior and may compromise HSC function, such as dysregulation of PBX1 regulated genetic networks. This culture system serves now as a platform for modeling human multilineage hematopoietic stem/progenitor cell hierarchy and studying the complex regulation of HSC identity and function required for successful ex vivo expansion of transplantable HSC.

Effect of human parathyroid hormone on hematopoietic progenitor cells in NOD/SCID mice co-transplanted with human cord blood mononuclear cells and mesenchymal stem cells

PURPOSE

We evaluated the effect of human parathyroid hormone (hPTH) on the engraftment and/or in vivo expansion of hematopoietic stem cells in an umbilical cord blood (UCB)-xenotransplantation model. In addition, we assessed its effect on the expression of cell adhesion molecules.

MATERIALS AND METHODS

Female NOD/SCID mice received sublethal total body irradiation with a single dose of 250 cGy. Eighteen to 24 hours after irradiation, 1 × 10(7) human UCB-derived mononuclear cells (MNCs) and 5 × 10(6) human UCB-derived mesenchymal stem cells (MSCs) were infused via the tail vein. Mice were randomly divided into three groups: Group 1 mice received MNCs only, Group 2 received MNCs only and were then treated with hPTH, Group 3 mice received MNCs and MSCs, and were treated with hPTH.

RESULTS

Engraftment was achieved in all the mice. Bone marrow cellularity was approximately 20% in Group 1, but 70-80% in the hPTH treated groups. Transplantation of MNCs together with MSCs had no additional effect on bone marrow cellularity. However, the proportion of human CD13 and CD33 myeloid progenitor cells was higher in Group 3, while the proportion of human CD34 did not differ significantly between the three groups. The proportion of CXCR4 cells in Group 3 was larger than in Groups 1 and 2 but without statistical significance.

CONCLUSION

We have demonstrated a positive effect of hPTH on stem cell proliferation and a possible synergistic effect of MSCs and hPTH on the proportion of human hematopoietic progenitor cells, in a xenotransplantation model. Clinical trials of the use of hPTH after stem cell transplantation should be considered.

PERT: a method for expression deconvolution of human blood samples from varied microenvironmental and developmental conditions

The cellular composition of heterogeneous samples can be predicted using an expression deconvolution algorithm to decompose their gene expression profiles based on pre-defined, reference gene expression profiles of the constituent populations in these samples. However, the expression profiles of the actual constituent populations are often perturbed from those of the reference profiles due to gene expression changes in cells associated with microenvironmental or developmental effects. Existing deconvolution algorithms do not account for these changes and give incorrect results when benchmarked against those measured by well-established flow cytometry, even after batch correction was applied. We introduce PERT, a new probabilistic expression deconvolution method that detects and accounts for a shared, multiplicative perturbation in the reference profiles when performing expression deconvolution. We applied PERT and three other state-of-the-art expression deconvolution methods to predict cell frequencies within heterogeneous human blood samples that were collected under several conditions (uncultured mono-nucleated and lineage-depleted cells, and culture-derived lineage-depleted cells). Only PERT's predicted proportions of the constituent populations matched those assigned by flow cytometry. Genes associated with cell cycle processes were highly enriched among those with the largest predicted expression changes between the cultured and uncultured conditions. We anticipate that PERT will be widely applicable to expression deconvolution strategies that use profiles from reference populations that vary from the corresponding constituent populations in cellular state but not cellular phenotypic identity.

Histone deacetylase 3 modulates the expansion of human hematopoietic stem cells

Epigenetic changes are regarded as emerging major players for hematopoietic stem cell (HSC) biology. Although some histone deacetylase (HDAC) inhibitors, such as valproic acid (VA), induce differentiation and apoptosis in a variety of leukemic cells in vitro, they produce a favorable effect on the expansion of normal HSCs. In this study, we have identified the VA target HDAC3 as a negative regulator of umbilical cord blood HSC expansion. We demonstrate that knockdown of the transcript dramatically improves CD34+ cell expansion, which correlates with a higher potential to generate colony-forming units in functional assays. We show that this effect is mediated at the level of primitive hematopoietic cells and that it is not due to negative effects on specific cell commitment or alterations in the cell cycle. HDAC3 inhibition does not block commitment to the monocytic lineage and the maturation of monocyte precursors, which are the main inhibited pathways in the presence of VA. Therefore, our results identify HDAC3 as a promising target for therapies aiming to expand HSCs.

Stem cell gene therapy: the risks of insertional mutagenesis and approaches to minimize genotoxicity

Virus-based vectors are widely used in hematopoietic stem cell (HSC) gene therapy, and have the ability to integrate permanently into genomic DNA, thus driving long-term expression of corrective genes in all hematopoietic lineages. To date, HSC gene therapy has been successfully employed in the clinic for improving clinical outcomes in small numbers of patients with X-linked severe combined immunodeficiency (SCID-X1), adenosine deaminase deficiency (ADA-SCID), adrenoleukodystrophy (ALD), thalassemia, chronic granulomatous disease (CGD), and Wiskott-Aldrich syndrome (WAS). However, adverse events were observed during some of these HSC gene therapy clinical trials, linked to insertional activation of proto-oncogenes by integrated proviral vectors leading to clonal expansion and eventual development of leukemia. Numerous studies have been performed to understand the molecular basis of vector-mediated genotoxicity, with the aim of developing safer vectors and lower-risk gene therapy protocols. This review will summarize current information on the mechanisms of insertional mutagenesis in hematopoietic stem and progenitor cells due to integrating gene transfer vectors, discuss the available assays for predicting genotoxicity and mapping vector integration sites, and introduce newly-developed approaches for minimizing genotoxicity as a way to further move HSC gene therapy forward into broader clinical application.

Nicotinamide, a SIRT1 inhibitor, inhibits differentiation and facilitates expansion of hematopoietic progenitor cells with enhanced bone marrow homing and engraftment

Strategies that increase homing to the bone marrow and engraftment efficacy of ex vivo expended CD34(+) cells are expected to enhance their clinical utility. Here we report that nicotinamide (NAM), a form of vitamin B-3, delayed differentiation and increased engraftment efficacy of cord blood-derived human CD34(+) cells cultured with cytokines. In the presence of NAM, the fraction of CD34(+)CD38(-) cells increased and the fraction of differentiated cells (CD14(+), CD11b(+), and CD11c(+)) decreased. CD34(+) cells cultured with NAM displayed increased migration toward stromal cell derived factor-1 and homed to the bone marrow with higher efficacy, thus contributing to their increased engraftment efficacy, which was maintained in competitive transplants with noncultured competitor cells. NAM is a known potent inhibitor of several classes of ribosylase enzymes that require NAD for their activity, as well as sirtuin (SIRT1), class III NAD(+)-dependent-histone-deacetylase. We demonstrated that EX-527, a specific inhibitor of SIRT1 catalytic activity, inhibited differentiation of CD34(+) cells similar to NAM, while specific inhibitors of NAD-ribosylase enzymes did not inhibit differentiation, suggesting that the NAM effect is SIRT1-specific. Our findings suggest a critical function of SIRT1 in the regulation of hematopoietic stem cell activity and imply the clinical utility of NAM for ex vivo expansion of functional CD34(+) cells.

Immunophenotyping of hematopoietic progenitor cells: Comparison between cord blood and adult mobilized blood grafts

AIM

To study the immunophenotype of hematopoietic progenitor cells from cord blood (CB) grafts (n = 39) in comparison with adult apheresis grafts (AG, n = 229) and pre-apheresis peripheral blood (PAPB) samples (n = 908) using flow cytometry analysis.

METHODS

First, we performed a qualitative analysis of CD34+ cell sub-populations in both CB and PAPB grafts using the standardized ISHAGE protocol and a wide panel of 20 monoclonal antibodies. Next, we studied some parameters, such as the age of mothers and the weight of newborns, which can influence the quality and the quantity of CD34+ cells from CB.

RESULTS

We found that the percentage of apoptotic cells was high in CB in comparison to PAPB (PAPB: 4.6% ± 2.6% vs CB: 53.4% ± 5.2%, P < 0.001). In CB, the weight of newborn and the age of the mother have the influence on CD34+ cells. The follow-up of Ag CD133 in the ISHAGE double platform protocol in association with CD45, CD34 and the 7'AAD shows an equal rate between the two cell populations CD133+CD45+CD34+ high and CD34+CD45+ high with a higher percentage. So, is the inclusion of Ac CD133 necessary in the present panel included in the ISHAGE method? Last part, we showed a significant presence of interferon γ in CB in comparison to PAPB, the annexin showing the high number of apoptotic cells in CB.

CONCLUSION

This study demonstrates that many different obstetric factors must be taken into account when processing and cryo-banking umbilical CB units for transplantation.

Differential effects of HOXB4 and NUP98-HOXA10hd on hematopoietic repopulating cells in a nonhuman primate model

Expansion of hematopoietic stem cells (HSCs) is beneficial in settings where HSC numbers are limited, such as cord blood transplantation. The human homeobox transcription factor HOXB4 has been shown to enhance stem cell expansion in several experimental models. We have shown previously that HOXB4 overexpression in monkey CD34(+) cells has a dramatic effect on expansion and engraftment of short-term repopulating cells. Here, we wished to compare the effects of HOXB4 and another candidate gene, NUP98-HOXA10hd (NA10hd). We used a competitive repopulation assay in pigtailed macaques to study engraftment of CD34(+) cells modified with gammaretroviral HOXB4YFP or NA10hdGFP. We found that HOXB4YFP contributed more to early hematopoiesis (<30 days), whereas NA10hdGFP contributed more to later hematopoiesis. In each case, we observed two distinct peaks in engraftment of NA10hd-transduced cells, one within 20 days post transplant and another after 5-6 months. Analysis of CD14(+), CD3(+), and CD20(+) subsets confirmed that higher percentages of cells of each lineage were derived from NA10hdGFP(+) progenitors than from HOXB4YFP(+) progenitors. In conclusion, we show that HOXB4 and NA10hd both have a significant impact on hematopoietic reconstitution; however, these effects are differential and therefore may offer complementary strategies for HSC expansion.

Identification of hematopoietic stem cell-specific miRNAs enables gene therapy of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD; also known as Krabbe disease) is an invariably fatal lysosomal storage disorder caused by mutations in the galactocerebrosidase (GALC) gene. Hematopoietic stem cell (HSC)-based gene therapy is being explored for GLD; however, we found that forced GALC expression was toxic to HSCs and early progenitors, highlighting the need for improved regulation of vector expression. We used a genetic reporter strategy based on lentiviral vectors to detect microRNA activity in hematopoietic cells at single-cell resolution. We report that miR-126 and miR-130a were expressed in HSCs and early progenitors from both mice and humans, but not in differentiated progeny. Moreover, repopulating HSCs could be purified solely on the basis of miRNA expression, providing a new method relevant for human HSC isolation. By incorporating miR-126 target sequences into a GALC-expressing vector, we suppressed GALC expression in HSCs while maintaining robust expression in mature hematopoietic cells. This approach protected HSCs from GALC toxicity and allowed successful treatment of a mouse GLD model, providing a rationale to explore HSC-based gene therapy for GLD.

Ex vivo gene transfer and correction for cell-based therapies

Cell-based therapies are fast-growing forms of personalized medicine that make use of the steady advances in stem cell manipulation and gene transfer technologies. In this Review, I highlight the latest developments and the crucial challenges for this field, with an emphasis on haematopoietic stem cell gene therapy, which is taken as a representative example given its advanced clinical translation. New technologies for gene correction and targeted integration promise to overcome some of the main hurdles that have long prevented progress in this field. As these approaches marry with our growing capacity for genetic reprogramming of mammalian cells, they may fulfil the promise of safe and effective therapies for currently untreatable diseases.

Biochemical analysis and quantification of hematopoietic stem cells by infrared spectroscopy

Identification of hematopoietic stem cells (HSCs) in different stages of maturation is one of the major issues in stem cell research and bone marrow (BM) transplantation. Each stage of maturation of HSCs is characterized by a series of distinct glycoproteins present on the cell plasma membrane surface, named a cluster of differentiation (CD). Currently, complicated and expensive procedures based on CD expression are needed for identification and isolation of HSCs. This method is under dispute, since the correct markers' composition is not strictly clear, thus there is need for a better method for stem cell characterization. In the present study, Fourier transform infrared (FTIR) spectroscopy is employed as a novel optical method for identification and characterization of HSCs based on their entire biochemical features. FTIR spectral analysis of isolated mice HSCs reveals several spectral markers related to lipids, nucleic acids, and carbohydrates, which distinguish HSCs from BM cells. The unique "open" conformation of HSC DNA as identified by FTIR is exploited for HSCs quantification in the BM. The proposed method of FTIR spectroscopy for HSC identification and quantification can contribute to stem cell research and BM transplantation.