Multi-lineage expansion potential of primitive hematopoietic progenitors: superiority of umbilical cord blood compared to mobilized peripheral blood

Umbilical cord blood mononuclear cell therapy induces clinical remission of steroid-dependent or -resistant ulcerative colitis patients

To compare the efficacy and safety of umbilical cord blood mononuclear cells (CBMNC) and azathioprine (AZA) in the treatment of patients with steroid-dependent or -resistant ulcerative colitis. One hundred and six patients diagnosed with steroid-dependent or -resistant ulcerative colitis were studied retrospectively, including 36 patients treated with CBMNC and 70 treated with AZA. To reduce confounding bias due to retrospective nature of this study, the propensity score matching system was applied to equipoise the pretreatment data of two groups. After matching, 35 matched pairs (1:1) were created. The ratios of clinical remission, clinical response and endoscopic mucosal healing, Mayo score, and major complications were compared between two groups at weeks 8, 16, and 36 after treatment. The results demonstrated that the ratios of clinical remission (80% vs. 57%, P < 0.05) and mucosal healing (74% vs. 51%, P < 0.05) were significantly higher in CBMNC-treated patients compared with those in AZA-treated patients at week 8. The erythrocyte sedimentation rate was significantly decreased in CBMNC group compared with that in AZA-treated group (14.5 ± 3.9 mm/h vs. 18.0 ± 5.7 mm/h, P < 0.01) at week 8. In AZA group, 2 patients had neutropenia and 3 patients had elevated alanine aminotransferase levels, whereas no obvious side-effects were observed in CBMNC-treated group. Our results reveal that CBMNC therapy appears to be an effective and safe strategy for patients with steroid-dependent or -resistant ulcerative colitis. Further prospective studies are needed to define the potential roles and mechanisms of CBMNC in the treatment of refractory ulcerative colitis.

Generation of Genetically Engineered Precursor T-Cells From Human Umbilical Cord Blood Using an Optimized Alpharetroviral Vector Platform

Retroviral engineering of hematopoietic stem cell-derived precursor T-cells (preTs) opens the possibility of targeted T-cell transfer across human leukocyte antigen (HLA)-barriers. Alpharetroviral vectors exhibit a more neutral integration pattern thereby reducing the risk of insertional mutagenesis. Cord blood-derived CD34+ cells were transduced and differentiated into preTs in vitro. Two promoters, elongation-factor-1-short-form, and a myeloproliferative sarcoma virus variant in combination with two commonly used envelopes were comparatively assessed choosing enhanced green fluorescent protein or a third-generation chimeric antigen receptor (CAR) against CD123 as gene of interest. Furthermore, the inducible suicide gene iCaspase 9 has been validated. Combining the sarcoma virus-derived promoter with a modified feline endogenous retrovirus envelope glycoprotein yielded in superior transgene expression and transduction rates. Fresh and previously frozen CD34+ cells showed similar transduction and expansion rates. Transgene-positive cells did neither show proliferative impairment nor alteration in their lymphoid differentiation profile. The sarcoma virus-derived promoter only could express sufficient levels of iCaspase 9 to mediate dimerizer-induced apoptosis. Finally, the CD123 CAR was efficiently expressed in CD34+ cells and proved to be functional when expressed on differentiated T-cells. Therefore, the transduction of CD34+ cells with alpharetroviral vectors represents a feasible and potentially safer approach for stem cell-based immunotherapies for cancer.

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.

Intraarterial transplantation of human umbilical cord blood mononuclear cells is more efficacious and safer compared with umbilical cord mesenchymal stromal cells in a rodent stroke model

INTRODUCTION

Stroke is the second leading cause of death worldwide, claims six lives every 60 seconds, and is a leading cause of adult disability across the globe. Tissue plasminogen activator, the only United States Food and Drug Administration (FDA)-approved drug currently available, has a narrow therapeutic time window of less than 5 hours. In the past decade, cells derived from the human umbilical cord (HUC) have emerged as a potential therapeutic alternative for stroke; however, the most effective HUC-derived cell population remains unknown.

METHODS

We compared three cell populations derived from the human umbilical cord: cord blood mononuclear cells (cbMNCs); cord blood mesenchymal stromal cells (cbMSCs), a subpopulation of cbMNCs; and cord matrix MSCs (cmMSCs). We characterized these cells in vitro with flow cytometry and assessed the cells' in vivo efficacy in a 2-hour transient middle cerebral artery occlusion (MCAo) rat model of stroke. cbMNCs, cbMSCs, and cmMSCs were each transplanted intraarterially at 24 hours after stroke.

RESULTS

A reduction in neurologic deficit and infarct area was observed in all three cell groups; however, this reduction was significantly enhanced in the cbMNC group compared with the cmMSC group. At 2 weeks after stroke, human nuclei-positive cells were present in the ischemic hemispheres of immunocompetent stroke rats in all three cell groups. Significantly decreased expression of rat brain-derived neurotrophic factor mRNA was observed in the ischemic hemispheres of all three cell-treated and phosphate-buffered saline (PBS) group animals compared with sham animals, although the decrease was least in cbMNC-treated animals. Significantly decreased expression of rat interleukin (IL)-2 mRNA and IL-6 mRNA was seen only in the cbMSC group. Notably, more severe complications (death, eye inflammation) were observed in the cmMSC group compared with the cbMNC and cbMSC groups.

CONCLUSIONS

All three tested cell types promoted recovery after stroke, but cbMNCs showed enhanced recovery and fewer complications compared with cmMSCs.

Mesenchymal stem cell: keystone of the hematopoietic stem cell niche and a stepping-stone for regenerative medicine

Mesenchymal stem cells (MSCs) are self-renewing precursor cells that can differentiate into bone, fat, cartilage, and stromal cells of the bone marrow. Recent studies suggest that MSCs themselves are critical for forming a niche that maintains hematopoietic stem cells (HSCs). The ease by which human MSC-like and stromal progenitor cells can be isolated from the bone marrow and other tissues has led to the rapid development of clinical investigations exploring their anti-inflammatory properties, tissue preservation capabilities, and regenerative potential. However, the identity of genuine MSCs and their specific contributions to these various beneficial effects have remained enigmatic. In this article, we examine the definition of MSCs and discuss the importance of rigorously characterizing their stem cell activity. We review their role and that of other putative niche constituents in the regulation of bone marrow HSCs. Additionally, how MSCs and their stromal progeny alter immune function is discussed, as well as potential therapeutic implications.

Ex vivo differentiation of natural killer cells from human umbilical cord blood CD34+ progenitor cells

Natural Killer (NK)-cells are peripheral blood lymphocytes that represent an important arm of the innate immune system. NK-cells play a critical role in the immune surveillance against tumors and virally infected cells in a major histocompatibiliy complex (MHC)-unrestricted fashion. We have explored such capacities of NK-cells after differentiation from hematopoietic stem and progenitor cells derived from human umbilical cord blood. Several culture conditions have been established supporting proliferation and subsequent differentiation of these cells in terms of receptor expression and specific lysis depending on the growth conditions in the presence and absence of supportive stromal feeders. We show that acquisition of Killer Immunoglobulin Receptor (KIR) as well as NK Cytotoxicity Receptor expressions is independent of culture condition whereas absence of stromal feeders did not support acquisition of CD94/NKG2A expression. Such KIR-positive/NKG2A-negative cells generated under different culture conditions showed strong and specific cytolytic activity which could have impact on further immunotherapeutic strategies.

Harnessing the therapeutic potential of myogenic stem cells

The potential clinical use of stem cells for cell transplantation therapies to replace defective genes in myopathies is an area of intense investigation. Precursor cells derived from non-muscle tissue with myogenic potential have been identified in many tissues, including bone marrow and dermis, although the status of these putative stem cells requires clarification. The incorporation of circulating bone-marrow derived stem cells into regenerating adult skeletal muscle has been demonstrated in mice but the contribution of donor cells is so minimal that it would appear clinically irrelevant at this stage. The possibility of a true stem cell subpopulation within skeletal muscle that replenishes the satellite cells (conventional muscle precursors on the surface of myofibres) is also very attractive as a superior source of myoblasts for muscle construction. A full understanding of the intrinsic factors (i.e. gene expression within the stem cell) and extrinsic factors (i.e. signals from the external environment) which control the commitment of stem cells to the myogenic lineage, and the conditions which favour stem cell expansion in vivo is required before stem cells can be seriously considered for clinical cell therapy.

Hematopoietic cell transplantation with autologous cord blood in patients with severe aplastic anemia: an opportunity to revisit the controversy regarding cord blood banking for private use

The controversy surrounding private banking of umbilical cord blood units (CBU), as a safeguard against future malignancy or other life-threatening conditions, raises many questions in pediatric clinical practice. Recent favorable experiences with autologous transplantation for severe aplastic anemia using privately stored CBU, suggested a possible utility. While private banking is difficult to justify statistically or empirically, there may exist rare cases where autologous transplant of stored umbilical CBU could be beneficial. The reality of privately banked CBU and the possibility for future discovery of additional indications for autologous cord blood transplant, motivated us to re-examine our attitudes towards private cord blood banking.

Stem cell therapy for ischemic heart disease

Stem cell transplantation has emerged as a novel treatment option for ischemic heart disease. Different cell types have been utilized and the recent development of induced pluripotent stem cells has generated tremendous excitement in the regenerative field. Bone marrow-derived multipotent progenitor cell transplantation in preclinical large animal models of postinfarction left ventricular remodeling has demonstrated long-term functional and bioenergetic improvement. These beneficial effects are observed despite no significant engraftment of bone marrow cells in the myocardium and even lower differentiation of these cells into cardiomyocytes. It is thought to be related to the paracrine effect of these stem cells, which secrete factors that lead to long-term gene expression changes in the host myocardium, thereby promoting neovascularization, inhibiting apoptosis, and stimulating resident cardiac progenitor cells. Future studies are warranted to examine the changes in the recipient myocardium after stem cell transplantation and to investigate the signaling pathways involved in these effects.

Heart failure management: the present and the future

Clinical heart failure has been defined for a long time as a clinical syndrome with symptoms and signs including shortness of breath, cyanosis, ascites, and edema. However, in recent years, with the thought of promoting early diagnosis and heart-failure prevention, the concept of heart failure has often been defined simply as a subject with severe LV dysfunction and a dilated left ventricle, or by some, defined by evidence of increased circulating levels of molecular markers of cardiac dysfunction, such as ANP and BNP. Heart failure has been considered an irreversible clinical end point. Current medical management for heart failure only relieves symptoms, slows deterioration, and prolongs life modestly. However, in the recent years, rejuvenation of the failing myocardium began to seem possible as the accumulating preclinical studies demonstrated that rejuvenating the myocardium at the molecular and cellular level can be achieved by gene therapy or stem cell transplantation. Here, we review selected novel modalities that have been shown in preclinical studies to exert beneficial effects in animal models of severe LV dysfunction and seem to have the potential to make an impact in the clinical practice of heart-failure management.

The preferentially expressed antigen in melanoma (PRAME) inhibits myeloid differentiation in normal hematopoietic and leukemic progenitor cells

The preferentially expressed antigen in melanoma (PRAME) is expressed in several hematologic malignancies, but either is not expressed or is expressed at only low levels in normal hematopoietic cells, making it a target for cancer therapy. PRAME is a tumor-associated antigen and has been described as a corepressor of retinoic acid signaling in solid tumor cells, but its function in hematopoietic cells is unknown. PRAME mRNA expression increased with chronic myeloid leukemia (CML) disease progression and its detection in late chronic-phase CML patients before tyrosine kinase inhibitor therapy was associated with poorer therapeutic responses and ABL tyrosine kinase domain point mutations. In leukemia cell lines, PRAME protein expression inhibited granulocytic differentiation only in cell lines that differentiate along this lineage after all-trans retinoic acid (ATRA) exposure. Forced PRAME expression in normal hematopoietic progenitors, however, inhibited myeloid differentiation both in the presence and absence of ATRA, and this phenotype was reversed when PRAME was silenced in primary CML progenitors. These observations suggest that PRAME inhibits myeloid differentiation in certain myeloid leukemias, and that its function in these cells is lineage and phenotype dependent. Lastly, these observations suggest that PRAME is a target for both prognostic and therapeutic applications.

Autologous umbilical cord blood mononuclear cell transplantation preserves right ventricular function in a novel model of chronic right ventricular volume overload

We aimed to evaluate the feasibility and efficacy of autologous umbilical cord blood mononuclear cell (UCMNC) transplantation on right ventricular (RV) function in a novel model of chronic RV volume overload. Four-month-old sheep (n = 20) were randomized into cell (n = 10) and control groups (n = 10). After assessment of baseline RV function by the conductance catheter method, a transannular patch (TAP) was sutured to the right ventricular outflow tract (RVOT). Following infundibulotomy the ring of the pulmonary valve was transected without cardiopulmonary bypass. UCMNC implantation (8.22 +/- 6.28 x 10(7)) in the cell group and medium injection in the control group were performed into the RV myocardium around the TAP. UCMNCs were cultured for 2 weeks after fluorescence-activated cell sorting (FACS) analysis for CD34 antigen. Transthoracic echocardiography (TTE) and computed tomography were performed after 6 weeks and 3 months, respectively. RV function was assessed 3 months postoperatively before the hearts were excised for immunohistological examinations. FACS analysis revealed 1.2 +/- 0.22% CD34(+) cells within the isolated UCMNCs from which AcLDL(+) endothelial cells were cultured in vitro. All animals survived surgery. TTE revealed grade II-III pulmonary regurgitation in both groups. Pressure-volume loops under dobutamine stress showed significantly improved RV diastolic function in the cell group (dP/dt(min): p = 0.043; E(ed): p = 0.009). CD31 staining indicated a significantly enhanced number of microvessels in the region of UCMNC implantation in the cell group (p < 0.001). No adverse tissue changes were observed. TAP augmentation and pulmonary annulus distortion without cardiopulmonary bypass constitutes a valid large animal model mimicking the surgical repair of tetralogy of Fallot. Our results indicate that the chronically volume-overloaded RV profits from autologous UCMNC implantation by enhanced diastolic properties with a probable underlying mechanism of increased angiogenesis.

The HOXB4 homeoprotein differentially promotes ex vivo expansion of early human lymphoid progenitors

The HOXB4 homeoprotein is known to promote the expansion of mouse and human hematopoietic stem cells (HSCs) and progenitors of the myeloid lineages. However, the putative involvement of HOXB4 in lymphopoiesis and particularly in the expansion of early lymphoid progenitor cells has remained elusive. Based on the ability of the HOXB4 protein to passively enter hematopoietic cells, our group previously designed a long-term culture procedure of human HSCs that allows ex vivo expansion of these cells. Here, this method has been further used to investigate whether HOXB4 could cause similar expansion on cells originating from CD34(+) hematopoietic progenitor cells (HPCs) committed at various levels toward the lymphoid lineages. We provide evidence that HOXB4 protein delivery promotes the expansion of primitive HPCs that generate lymphoid progenitors. Moreover, HOXB4 acts on lymphomyeloid HPCs and committed T/natural killer HPCs but not on primary B-cell progenitors. Our results clarify the effect of HOXB4 in the early stages of human lymphopoiesis, emphasizing the contribution of this homeoprotein in the maintenance of the intrinsic lymphomyeloid differentiation potential of defined HPC subsets. Finally, this study supports the potential use of HOXB4 protein for HSC and HPC expansion in a therapeutic setting and furthers our understanding of the mechanisms of the molecular regulation of hematopoiesis.

Co-culture of cord blood CD34(+) cells with human BM mesenchymal stromal cells enhances short-term engraftment of cord blood cells in NOD/SCID mice

BACKGROUND

The major challenge for cord blood transplantation (CBT) is higher rates of delayed and failed engraftment. In an attempt to broaden the application of CBT to more candidates, ex vivo expansion of hematopoietic stem/progenitor cells in CB is a major area of investigation. The purpose of this study was to employ human BM mesenchymal stromal cells (hBM-MSC) as the feeding-layer to expand CB cells ex vivo.

METHODS

In this study, hBM-MSC were isolated and characterized by morphologic, mmunophenotypic and RT-PCR analysis. The hBM-MSC at passage 3 were employed as the feeding-layer to expand CB CD34(+) cells in vivo in the presence of thrombopoietin, flt3/flk2 ligand, stem cell factor and G-CSF. The repopulating capacity of the ex vivo-expanded CB cells was also evaluated in a NOD/SCID mice transplant experiment.

RESULTS

After 1 or 2 weeks of in vitro expansion, hBM-MSC supported more increasing folds of CB in total nucleated cells, CD34(+) cells and colony-forming units (CFU) compared with CB without hBM-MSC. Furthermore, although NOD/SCID mice transplanted with CB cells expanded only in the presence of cytokines showed a higher percentage of human cell engraftment in BM than those with unexpanded CB CD34(+) cells, expanded CB cells co-cultured with hBM-MSC were revealed to enhance short-term engraftment further in recipient mice.

DISCUSSION

Our study suggests that hBM-MSC enhance in vitro expansion of CB CD34(+) cells and short-term engraftment of expanded CB cells in NOD/SCID mice, which may be valuable in a clinical setting.

Stem Cell Therapy for the Heart

Cellular cardiomyoplasty is an expanding field of research that involves numerous types of immature cells administered via several modes of delivery. The purpose of this review is to investigate the benefits of different types of cells used in stem cell research as well as the most efficient mode of delivery. The authors also present data showing that stem cells isolated from bone marrow are present at both 2 weeks and 3 months after engraftment in a myocardial infarction. These cells express muscle markers at both time points, which suggests that they have begun to differentiate into cardiomyocytes. Several questions must be answered, however, before stem cells can be used routinely in the clinic. Once these questions have been addressed, the use of stem cells in clinical practice can be realized.

Human Umbilical Cord Blood-Derived CD133+Cells Enhance Function and Repair of the Infarcted Myocardium

The use of adult stem cells for myocardial tissue repair might be limited in elderly and sick people because their cells are depleted and exhausted. The present study was conducted to explore the potential of human umbilical cord blood (UCB) CD133+ progenitor cells for myocardial tissue repair in a model of extensive myocardial infarction (MI). CD133+ progenitor cells were isolated from newborn UCB. Cells (1.2-2 x 10(6)) or saline (control) was infused intravenously 7 days after permanent coronary artery ligation in athymic nude rats. Left ventricular (LV) function was assessed before and 1 month after infusion by echocardiography. Tracking of human cells was performed by fluorescent in situ hybridization for human X and Y chromosomes or by immunostaining for HLA-DR or HLA-ABC. One month after delivery, LV fractional shortening improved by 42 +/- 17% in cell-treated hearts and decreased by 39 +/- 10% in controls (p = .001). Anterior wall thickness decreased significantly in controls but not in treated hearts. Microscopic examination revealed that the UCB cells were able to migrate, colonize, and survive in the infarcted myocardium. Human cells were identified near vessel walls and LV cavity and were occasionally incorporated into endothelial cells in six of nine cell-treated animals but not in controls. Scar tissue from cell-treated animals was significantly populated with autologous myofibroblasts as indicated by colocalization of HLA-DR and alpha-smooth muscle actin staining. In conclusion, the present work suggests that, after MI, intravenous delivery of human UCB-derived CD133+ cells can produce functional recovery by preventing scar thinning and LV systolic dilatation.

Human umbilical cord blood cells: a new alternative for myocardial repair?

Cell therapy for myocardial disease is a rapidly progressive field. However, present strategies of cell transplantation into the infarcted myocardium have limitations from practical points of view. One of the biggest challenges is to achieve a sufficient number of suitable cells. Umbilical cord blood (UCB), an unlimited source of stem/progenitor cells that could be used for transplantation into the injured heart, is readily available. The aim of our review is to describe the potential and prospect of UCB as a new supplier of cells for myocardial repair. The use of UCB stem cells might be of importance to elderly and sick people in whom the availability of autologous stem cells is limited.

Hematopoietic Progenitor Cells and Cellular Microenvironment: Behavioral and Molecular Changes upon Interaction

Cell-cell contact between stem cells and cellular determinants of the microenvironment plays an essential role in controlling cell division. Using human hematopoietic progenitor cells (CD34+/CD38-) and a stroma cell line (AFT024) as a model, we have studied the initial behavioral and molecular sequel of this interaction. Time-lapse microscopy showed that CD34+/CD38- cells actively migrated toward and sought contact with stroma cells and 30% of them adhered firmly to AFT024 stroma through the uropod. CD44 and CD34 are colocalized at the site of contact. Gene expression profiles of CD34+/CD38- cells upon cultivation with or without stroma for 16, 20, 48, or 72 hours were analyzed using our human genome cDNA microarray. Chk1, egr1, and cxcl2 were among the first genes upregulated within 16 hours. Genes with the highest upregulation throughout the time course included tubulin genes, ezrin, c1qr1, fos, pcna, mcm6, ung, and dnmt1, genes that play an essential role in reorganization of the cytoskeleton system, stabilization of DNA, and methylation patterns. Our results demonstrate directed migration of CD34+/CD38- cells toward AFT024 and adhesion through the uropod and that upon interaction with supportive stroma, reorganization of the cytoskeleton system, regulation of cell division, and maintenance of genetic stability represent the most essential steps.

All-trans retinoic acid (ATRA) enhances maintenance of primitive human hematopoietic progenitors and skews them towards myeloid differentiation in a stroma-noncontact culture system

OBJECTIVE

We have previously shown that hematopoietic progenitor cells (HPCs) from umbilical cord blood (UCB) can be maintained in a cytokine-supplemented stroma-noncontact (SNC) system. Here, we tested if all-trans retinoic acid (ATRA), known to improve expansion of murine hematopoietic stem cells, would enhance human HPC maintenance in a SNC culture system.

METHODS

CD34+CD38-Lin- cells from UCB were cultured in transwells above AFT024 in the presence of Flt-3 ligand (FLT) and thrombopoietin (TPO), with or without ATRA. Total nucleated cells (TNC), colony-forming units (CFUs), long-term culture-initiating cells (LTC-ICs), myeloid-lymphoid initiating cells (ML-ICs) and SCID repopulating cells (SRCs) were evaluated 1 to 5 weeks after culture.

RESULTS

All-trans retinoic acid (1 mumol/L) reduced expansion of CD34+CD38-Lin- TNC and CFUs after 2 to 5 weeks of culture. However, it significantly increased LTC-IC expansion after 1 to 3 and, even more so, 5 weeks of culture. ATRA also increased recovery of more primitive ML-ICs and SRCs. Increased HPC recovery appeared dependent on the presence of stromal cells, as LTC-IC expansion was significantly reduced when ATRA was added to stroma-free cultures.

CONCLUSION

All-trans retinoic acid increases expansion of early HPCs in a stromal cell-dependent fashion.

Cord blood immunology and stem cell transplantation

Allogeneic stem cell transplantation can be curative in a variety of malignant and nonmalignant disorders. Unfortunately, more than 75% of potential recipients lack a matched family donor. Although 50% of these recipients may find a matched unrelated adult stem cell donor from one of the worldwide registries, the other 50% have had no other viable donor alternatives. Cord blood cellular immunity is immature at birth and allows for a greater human leukocyte antigen disparity between a cord blood donor and recipient after an unrelated cord blood transplant. More than 25 cord blood banks have been developed worldwide to support the growing clinical needs of unrelated cord blood transplantation. Standard operating procedures have been developed for maternal donor screening and consent, cord blood collection, processing, cryopreservation, characterization, shipping, and thawing. Cord blood transplantation after myeloablative and reduced-intensity conditioning has been successfully demonstrated, resulting in long-term full donor chimerism, decreased Grade 3/4 acute graft-versus-host disease and improvements in overall survival. Several areas of ongoing research include ex vivo expansion of cord blood hematopoietic progenitor cells to enhance the rapidity of engraftment and isolation and activation of select immune cell populations for prevention or treatment of acute graft-versus-host disease, infectious complications, and tumor reoccurrence.

A multifactorial analysis of umbilical cord blood, adult bone marrow and mobilized peripheral blood progenitors using the improved ML-IC assay

OBJECTIVE

Assays that can evaluate the potential of individual human hematopoietic stem cells (HSC) are still lacking. We previously developed the myeloid-lymphoid initiating cell (ML-IC) assay that enumerates single CD34(+) cells that generate long-term culture-initiating (LTC-IC) and NK-initiating (NK-IC) daughter cells, or single primitive progenitors with multilineage potential. When transplanted in vivo, umbilical cord blood (UCB) has greater repopulating ability than bone marrow (BM) or mobilized peripheral blood (MPB). Whether the greater in vivo repopulating ability is due to an increased frequency of HSC in UCB and generative potential of UCB, BM, and MPB CD34(+) cells is not known.

MATERIALS AND METHODS

Single UCB, BM, and MPB CD34(+)CD38(-)Lin(-) or CD34(+)CD38(-)CD33(-) cells were plated in ML-IC assay and after 2 to 4 weeks, progeny was evaluated for frequency and generative potential of ML-IC. We also tested whether the ML-IC assay could be used to define if increased numbers of primitive progenitors generated by different cytokines in expansion cultures are mediated by recruitment of quiescent cells or by increasing their generative potential.

RESULTS

The frequency of ML-IC in BM, UCB, and MPB was similar, but the generative potential of UCB ML-IC was significantly higher. Substitution of Flt3-L, SCF, and IL-7 with Flt3-L and thrombopoietin significantly increased the generative potential of ML-IC, whereas Flt3-L, SCF, and hyper-IL-6 increased both ML-IC frequency and generative potential.

CONCLUSION

The ML-IC assay demonstrates that the greater repopulating ability of UCB is due to the higher generative ability of HSC in UCB. Furthermore, the ML-IC assay can discriminate between cytokine-mediated expansion of hematopoietic progenitors by enhancing generation of immature daughter cells or by recruiting otherwise quiescent cells.

Preclinical ex vivo expansion of G-CSF-mobilized peripheral blood stem cells: effects of serum-free media, cytokine combinations and chemotherapy

OBJECTIVES

Ex vivo expansion of granulocyte-colony stimulating factor (G-CSF)-mobilized peripheral blood stem cells (PBSC) is a promising approach for overcoming the developmental delay of bone marrow (BM) reconstitution after transplantation. This project investigated the effects of culture duration, serum-free media, cytokine combinations, and chemotherapy on the outcomes of expansion.

METHODS

Enriched CD34+ cells were cultured for 8 or 10 d in serum-free media (QBSF-60 or X-Vivo 10) and four combinations of cytokines consisting of recombinant human pegylated-megakaryocyte growth and development factor, stem cell factor, flt-3 ligand, G-CSF, interleukin (IL)-6, platelet-derived growth factor (PDGF), and IL-1beta.

RESULTS

Eight days of culture in QBSF-60 significantly supported efficient expansions of CD34+ cells, CD34+ CD38- cells, colony-forming units (CFU) of myeloid, erythroid, megakaryocytic, and mixed lineages to 3.76-, 14.4-, 28.3-, 24.0-, 38.1-, and 15.7-fold, respectively. Whilst PDGF or IL-6 enhanced the expansion of early, myeloid, and erythroid progenitors, IL-1beta specifically promoted the megakaryocytic lineage. Engraftment of human CD45+ cells were detectable in all non-obese diabetic/severe-combined immunodeficient mice transplanted with expanded PBSC from donor samples, being 5.80 +/- 3.34% of mouse BM cells. The expansion and engraftment capacity of CD34+ cells from subjects postchemotherapy were significantly compromised across the panel of progenitor cells.

CONCLUSION

Our results provided an optimized protocol for PBSC expansion, applicable to ameliorating neutropenia and thrombocytopenia in post-BM transplant patients by the prompt provision of progenitor cells. For postchemotherapy patients, expansion products might provide committed progenitors for improving short-term engraftment, but not self-renewable stem cells.

Induction of T-cell development from human cord blood hematopoietic stem cells by Delta-like 1 in vitro

The Notch signaling pathway plays a key role at several stages of T-lymphocyte differentiation. However, it remained unclear whether signals induced by the Notch ligand Delta-like 1 could support full T-cell differentiation from a defined source of human hematopoietic stem cells (HSCs) in vitro. Here, we show that human cord blood–derived HSCs cultured on Delta-like 1–expressing OP9 stromal cells undergo efficient T-cell lineage commitment and sustained T-cell differentiation. A normal stage-specific program of T-cell development was observed, including the generation of CD4 and CD8 αβ–T-cell receptor (TCR)–bearing cells. Induction of T-cell differentiation was dependent on the expression of Delta-like 1 by the OP9 cells. Stimulation of the in vitro–differentiated T cells by TCR engagement induced the expression of T-cell activation markers and costimulatory receptors. These results establish an efficient in vitro coculture system for the generation of T cells from human HSCs, providing a new avenue for the study of early T-cell differentiation and function.

Characterization of a lineage-negative stem-progenitor cell population optimized for ex vivo expansion and enriched for LTC-IC

Current hematopoietic stem cell transplantation protocols rely heavily upon CD34+ cells to estimate hematopoietic stem and progenitor cell (HSPC) yield. We and others previously reported CD133+ cells to represent a more primitive cell population than their CD34+ counterparts. However, both CD34+ and CD133+ cells still encompass cells at various stages of maturation, possibly impairing long-term marrow engraftment. Recent studies demonstrated that cells lacking CD34 and hematopoietic lineage markers have the potential of reconstituting long-term in vivo hematopoiesis. We report here an optimized, rapid negative-isolation method that depletes umbilical cord blood (UCB) mononucleated cells (MNC) from cells expressing hematopoietic markers (CD45, glycophorin-A, CD38, CD7, CD33, CD56, CD16, CD3, and CD2) and isolates a discrete lineage-negative (Lin-) cell population (0.10% +/- 0.02% MNC, n=12). This primitive Lin- cell population encompassed CD34+/- and CD133+/- HSPC and was also enriched for surface markers involved in HSPC migration, adhesion, and homing to the bone marrow (CD164, CD162, and CXCR4). Moreover, our depletion method resulted in Lin- cells being highly enriched for long-term culture-initiating cells when compared with both CD133+ cells and MNC. Furthermore, over 8 weeks in liquid culture stimulated by a cytokine cocktail optimized for HSPC expansion, TPOFLK (thrombopoietin 10 ng/ml, Flt3 ligand 50 ng/ml, c-Kit ligand 20 ng/ml) Lin- cells underwent slow proliferation but maintained/expanded more primitive HSPC than CD133+ cells. Therefore, our Lin- stem cell offers a promising alternative to current HSPC selection methods. Additionally, this work provides an optimized and well-characterized cell population for expansion of UCB for a wider therapeutic potential, including adult stem cell transplantation.

Umbilical-cord blood transplantation for the treatment of cancer

Haematopoietic stem-cell transplantation is used to treat many haematological cancers, but is limited by the lack of suitable bone-marrow donors, the risk of graft-versus-host disease (GVHD) and slow immune reconstitution. Umbilical-cord blood is an alternative source of haematopoietic stem cells that has recently been tested in both child and adult cancer patients. These studies have identified several advantages to umbilical-cord cell transplantation, including a lower incidence of GVHD. Umbilical-cord blood is therefore a promising alternative to bone-marrow-derived stem cells.

The symmetry of initial divisions of human hematopoietic progenitors is altered only by the cellular microenvironment

OBJECTIVE

We examined if cellular elements or adhesive ligands were able to alter asymmetric divisions of CD34(+)/CD38(-) cells in contrast to soluble factors at a single cell level.

MATERIALS AND METHODS

After single cell deposition onto 96-well plates, cells were cocultured for 10 days with the stem cell supporting cell line AFT024, fibronectin (FN), or bovine serum albumin (BSA). The divisional history was monitored with time-lapse microscopy. Subsequent function for the most primitive cells was assessed using the myeloid-lymphoid-initiating cell (ML-IC) assay. Committed progenitors were measured using colony-forming cells (CFC).

RESULTS

Only contact with AFT024 recruited significant numbers of CD34(+)/CD38(-) cells into cell cycle and increased asymmetric divisions. Although most ML-IC were still identified among cells that have divided fewer than 3 times, a significant number of ML-IC shifted into the fast-dividing fraction after exposure to AFT024. The increase in ML-IC frequency was predominantly due to recruitment of quiescent and slow-dividing cells from the starting population. Increase in CFC activity induced by AFT024 was found only among rapidly dividing cells.

CONCLUSIONS

For the first time, we have demonstrated that asymmetric divisions can be altered upon exposure with a stem cell-supporting microenvironment. For the primitive subset of cells (ML-IC), this was predominantly due to recruitment into cell cycle and increased rounds of cycling without loss of function. Exposure to AFT024 cells also increased proliferation and asymmetric divisions of committed CFC. Hence direct communication between hematopoietic progenitors with stroma cells is required for maintaining self-renewal potential.

Clinical and experimental uses of umbilical cord blood

Umbilical cord blood (UCB) has been used successfully as an alternative source of haemopoietic stem cells (HSC) in allogeneic stem-cell transplantation for the treatment of acquired and genetic diseases. Advantages of using UCB include: (i) no risk to the donor, (ii) no donor attrition, (iii) minimal risk of viral transmission and (iv) immediate availability. Early results have highlighted differences in engraftment rates and toxicity between UCB and other sources of HSC. These differences relate to the low cell dose in UCB and also to the intrinsic properties of UCB. In this article, the clinical outcome of UCB transplantation (UCBT) will be reviewed with a discussion of the biological characteristics of UCB that may account for some of the clinical outcomes. To overcome the limitations of low cell dose, novel approaches such as ex vivo expansion of HSC are being actively explored, and this will be summarized in the present study. Finally, the success of UCBT has led to the establishment of dedicated UCB banks worldwide and the regulatory issues surrounding this will be briefly discussed.

AC133+ umbilical cord blood progenitors demonstrate rapid self-renewal and low apoptosis

Umbilical cord blood (UCB) provides immediate access to haemopoietic stem/progenitor cells (HSPC) but low cell number restricts use in full adult bone marrow reconstitution. This study investigated early ex vivo expansion kinetics of UCB AC133+ cells (2-4 x 10(4)/ml), mononuclear cells (MNC, 1-2 x 10(6)/ml) and AC133negative cells (AC133(neg), 2-4 x 10(4)/ml) in stroma-free 8 d liquid culture (fetal bovine serum-supplemented Iscove's-modified Dulbecco's medium (IMDM) with either 'K36EG'[c-Kit ligand, interleukin 3 (IL-3), IL-6, erythropoietin, granulocyte colony-stimulating factor] or 'TPOFL' (thrombopoietin, Flt-3 ligand). Cell enumeration, apoptosis assay and AC133/CD34/CD38 antigen immunophenotyping were performed at d 0, 3, 5 and 8. All three cell populations went through a proliferation lag phase between d 3 and d 5. AC133+ cells recovered better from lag phase with significantly higher fold increase (FI) when compared with MNC and AC133(neg) populations (K36EG FI: 15.04 +/- 5.46; TPOFL FI: 8.59 +/- 2.92, P < 0.05). After 8 d, populations lacking AC133+ cells were significantly more inclined to undergo apoptosis under proliferative conditions (P < 0.01). Also, when compared with K36EG, 8 d TPOFL-expanded AC133+ cells encompassed a significantly higher percentage of AC133+ and CD34+ early HSPC (K36EG: 20.50 +/- 2.36; TPOFL: 47.00 +/- 7.69; P < 0.05). In conclusion, TPOFL synergism demonstrated the potential for AC133+ HSPC ex vivo expansion inducing self-renewal, early HSPC maintenance and promoting cell survival status.

Stromal cells from murine embryonic aorta-gonad-mesonephros region, liver and gut mesentery expand human umbilical cord blood-derived CAFC(week6) in extended long-term cultures

The first definitive long-term repopulating hematopoietic stem cells (HSCs) emerge from and undergo rapid expansion in the embryonic aorta-gonad-mesonephros (AGM) region. To investigate the presumptive unique characteristics of the embryonic hematopoietic microenvironment and its surrounding tissues, we have generated stromal clones from subdissected day 10 and day 11 AGMs, embryonic livers (ELs) and gut mesentery. We here examine the ability of 19 of these clones to sustain extended long-term cultures (LTCs) of human CD34(+) umbilical cord blood (UCB) cells in vitro. The presence of in vitro repopulating cells was assessed by sustained production of progenitor cells (extended LTC-CFC) and cobblestone area-forming cells (CAFC). The embryonic stromal clones differed greatly in their support for human HSCs. Out of eight clones tested in the absence of exogenous cytokines, only one (EL-derived) clone was able to provide maintenance of HSCs. Addition of either Tpo or Flt3-L + Tpo improved the long-term support of about 50% of the tested clones. Cultures on four out of 19 clones, ie the EL-derived clone mentioned, two urogenital-ridge (UG)-derived clones and one gastrointestinal (GI)-derived clone, allowed a continuous expansion of primitive CAFC and CFU-GM with over several hundred-fold more CAFC(week6) produced in the 12th week of culture. This expansion was considerably higher than that found with the FBMD-1 cell line, which is appreciated by many investigators for its support of human HSCs, under comparable conditions. This stromal cell panel derived from the embryonic regions may be a powerful tool in dissecting the factors mediating stromal support for maintenance and expansion of HSCs.

Optimization of gene transfer into primitive human hematopoietic cells of granulocyte-colony stimulating factor-mobilized peripheral blood using low-dose cytokines and comparison of a gibbon ape leukemia virus versus an RD114-pseudotyped retroviral vector

Primitive human hematopoietic cells in granulocyte-colony stimulating factor (G-CSF)-mobilized peripheral blood (MPB) are more difficult to transduce compared to cells from umbilical cord blood. Based on the hypothesis that MPB cells may require different stimulation for efficient retroviral infection, we compared several culture conditions known to induce cycling of primitive hematopoietic cells. MPB-derived CD34(+) cells were stimulated in the presence or absence of the murine fetal liver cell line AFT024 in trans-wells with G-CSF, stem cell factor (SCF), and thrombopoietin (TPO) (G/S/T; 100 ng/ml) or Flt3-L, SCF, interleukin (IL)-7, and TPO (F/S/7/T; 10-20 ng/ml), and transduced using a GaLV-pseudotyped retroviral vector expressing the enhanced green fluorescence protein (eGFP). Compared to cultures without stroma, the presence of AFT024 increased the number of transduced colony-forming cells (CFC) by 3.5-fold (with G/S/T), long-term culture-initiating cells (LTC-IC) by 4.6-fold (with F/S/7/T), and nonobese diabetic/severe immunodeficiency disease (NOD/SCID)-repopulating cells (SRC) by 6.8-fold (with F/S/7/T). Similar numbers of long-term culture-initiating cells (LTC-IC) and SRC could be transduced using AFT024-conditioned medium (AFT-CM) or a defined medium that had been supplemented with factors identified in AFT-CM. Finally, using our best condition based on transduction with the gibbon ape leukemia virus (GaLV)-pseudotyped vector, we demonstrate a 33-fold higher level of gene transfer (p < 0.001) in SRC using an RD114-pseudotyped vector. In summary, using an optimized protocol with low doses of cytokines, and transduction with an RD114 compared to a GaLV-pseudotyped retroviral vector, the overall number of transduced cells in NOD/SCID mice could be improved 144-fold, with a gene-transfer efficiency in SRC of 16.3% (13.3-19.9; n = 6).

The role of stem cells in skeletal and cardiac muscle repair

In postnatal muscle, skeletal muscle precursors (myoblasts) can be derived from satellite cells (reserve cells located on the surface of mature myofibers) or from cells lying beyond the myofiber, e.g., interstitial connective tissue or bone marrow. Both of these classes of cells may have stem cell properties. In addition, the heretical idea that post-mitotic myonuclei lying within mature myofibers might be able to re-form myoblasts or stem cells is examined and related to recent observations for similar post-mitotic cardiomyocytes. In adult hearts (which previously were not considered capable of repair), the role of replicating endogenous cardiomyocytes and the recruitment of other (stem) cells into cardiomyocytes for new cardiac muscle formation has recently attracted much attention. The relative contribution of these various sources of precursor cells in postnatal muscles and the factors that may enhance stem cell participation in the formation of new skeletal and cardiac muscle in vivo are the focus of this review. We concluded that, although many endogenous cell types can be converted to skeletal muscle, the contribution of non-myogenic cells to the formation of new postnatal skeletal muscle in vivo appears to be negligible. Whether the recruitment of such cells to the myogenic lineage can be significantly enhanced by specific inducers and the appropriate microenvironment is a current topic of intense interest. However, dermal fibroblasts appear promising as a realistic alternative source of exogenous myoblasts for transplantation purposes. For heart muscle, experiments showing the participation of bone marrow-derived stem cells and endothelial cells in the repair of damaged cardiac muscle are encouraging.

The AFT024 stromal cell line supports long-term ex vivo maintenance of engrafting multipotent human hematopoietic progenitors

The immortalized murine stromal cell line AFT024 has been reported to maintain human hematopoietic progenitors in an undifferentiated state in vitro. In the current studies the beige/nude/xid (bnx) mouse in vivo xenograft model was used to examine the engraftment and multilineage generative potential of human hematopoietic progenitors after 2-3 weeks growth on AFT024 stroma, in comparison to primary stromal monolayers derived from post-natal human bone marrow. Eight to 12 months after transplantation of human CD34+CD38- cells from umbilical cord blood, cultured on AFT024 vs human stroma for 2-3 weeks, the murine bone marrow was harvested and analyzed for the presence of human myeloid and lymphoid cells. The mean percent engraftment of total human hematopoietic cells in the murine marrow was significantly higher after co-cultivation on AFT024 than on human stroma. Human myeloid and lymphoid lineage cells were detected in all mice. However, engraftment of myeloid lineage cells (CD33+), B lymphoid (CD19+), and T lymphoid cells (CD4+and CD8+) were significantly higher after co-cultivation of the human cells on AFT024 than on human stroma, prior to transplantation. Interestingly, the length of time in culture did not significantly affect the engraftment of the myeloid and T lymphoid lineage progenitors, but the percentage of B lymphoid lineage engraftment decreased significantly between 2 and 3 weeks of co-cultivation on both types of stroma. Cells with a primitive phenotype (CD45+/CD34-/CD38- and CD45+/CD34-/lin-) and cells with the capacity to generate secondary human CFU after recovery from the bnx bone marrow were maintained at significantly higher levels during culture on AFT024 stroma than on human stroma. The current studies demonstrate that the AFT024 murine stromal cell line supports the ex vivo survival and maintenance of human hematopoietic progenitors that are capable of long-term multilineage reconstitution for 2-3 weeks ex vivo, to levels superior to those that can be obtained using human stromal cells.

Cord blood G(0) CD34+ cells have a thousand-fold higher capacity for generating progenitors in vitro than G(1) CD34+ cells

We examined the functional differences between G(0) and G(1) cord blood CD34+ cells for up to 24 weeks in serum-free suspension culture, containing Flt-3 ligand, thrombopoietin and stem cell factor. By week 24, there is more than a 1,000-fold difference in granulocyte, macrophage-colony-forming cells (GM-CFC) cumulative production between the two populations, with cultures initiated from G(0) demonstrating an amplification of 1.1 x 10(5)-1.8 x 10(6) of GM-CFC compared to 45-2.7 x 10(3) for the G(1) cells. Cells from the initial G(0) population are able to produce about 250-fold higher numbers of BFU-E than those from G(1) which translates to 3 x 10(3)-1.1 x 10(5)-fold expansion and 25-390-fold expansion for G(0) and G(1), respectively. This amplification of the progenitor cells is reflected in finding that a greater proportion of the progeny of the G(0) population are CD34+, resulting in a 600-fold expansion of CD34+ cells at week 8. As in other in vitro systems, total cell expansion is less discriminatory of stem cell behavior than progenitor cells, and there is no significant difference in total cell numbers between G(0) and G(1) cultures with a mean fold expansion of 2 x 10(7) at 24 weeks.

Purification and ex vivo expansion of postnatal human marrow mesodermal progenitor cells

It is here reported that mesenchymal stem cells known to give rise to limb-bud mesoderm can, at the single-cell level, also differentiate into cells of visceral mesoderm and can be expanded extensively by means of clinically applicable methods. These cells were named mesodermal progenitor cells (MPCs). MPCs were selected by depleting bone marrow mononuclear cells from more than 30 healthy human donors of CD45(+)/glycophorin-A (GlyA)(+) cells. Cells were cultured on fibronectin with epidermal growth factor and platelet-derived growth factor BB and 2% or less fetal calf serum. It was found that 1/5 x 10(3) CD45(-)GlyA(-) cells, or 1/10(6) bone marrow mononuclear cells, gave rise to clusters of small adherent cells. Cell-doubling time was 48 to 72 hours, and cells have been expanded in culture for more than 60 cell doublings. MPCs are CD34(-), CD44(low), CD45(-), CD117 (cKit)(-), class I-HLA(-), and HLA-DR(-). MPCs differentiated into cells of limb-bud mesoderm (osteoblasts, chondrocytes, adipocytes, stroma cells, and skeletal myoblasts) as well as visceral mesoderm (endothelial cells). Retroviral marking was used to definitively prove that single MPCs can differentiate into cells of limb bud and visceral mesoderm. Thus, MPCs that proliferate without obvious senescence under clinically applicable conditions and differentiate at the single-cell level not only into mesenchymal cells but also cells of visceral mesoderm may be an ideal source of stem cells for treatment of genetic or degenerative disorders affecting cells of mesodermal origin.

Stromal support augments extended long-term ex vivo expansion of hemopoietic progenitor cells

Current technology to numerically expand hemopoietic stem/progenitor cells (HSPC) ex vivo within 1 to 2 weeks is insufficient to warrant significant gain in reconstitution time following their transplantation. In order to more stringently test the parameters affecting HSPC expansion, we followed ex vivo cultures of CD34+-selected umbilical cord blood (UCB) HSPC for up to 10 weeks and investigated the effects of stromal support and cytokine addition. The cytokine combinations included FL + TPO, FL + TPO plus SCF and/or IL6, or SCF + IL6. To identify the HSPC in uncultured and cultured material, we determined the number of colony-forming cells (CFC), cobblestone area forming cells (CAFC), the NOD/SCID repopulating ability (SRA), and CD34+ subsets by phenotyping. The highest fold-increase obtained for CD34+ and CD34+ CD38- cell numbers was, respectively, 1197 and 30,937 for stroma-free and 4066 and 117,235 for stroma-supported cultures. In general, CFC generation increased weekly in FL + TPO containing groups up to week 5 with a 28- to 195-fold expansion whereafter the weekly CFC output stabilized. Stroma support enhanced the expansion of CAFC week 6 maximally 11-fold to 89-fold with FL + TPO + IL6. Cultures stimulated with at least FL + TPO gave an estimated 10- to 14-fold expansion of the ability of CD34+ UCB cells to multilineage engraft the BM of sublethally irradiated NOD/SCID mice at 2 weeks of stroma-free and stroma-supported cultures, while at week 5 and later the estimated SRA decreased to low or undetectable levels in all groups. Our results show that stroma and FL + TPO but also inclusion of bovine serum albumin, greatly increase the long-term generation of HSPC as measured by in vitro assays and is indispensable for long-term expansion of CD34+ CD38- CXCR4+ cells. However, the different surrogate methods to quantify the HSPC (CD34+ CD38-, CFC, CAFC week 6 and SRA) show increasing incongruency with increasing culture time, while especially the phenotypic analysis and the CFC generation greatly overestimate the CAFC and SRA expansion in 10-week cultures.

Human natural killer cells with polyclonal lectin and immunoglobulinlike receptors develop from single hematopoietic stem cells with preferential expression of NKG2A and KIR2DL2/L3/S2

The stage of progenitor maturation and factors that determine the fate and clonal acquisition of human natural killer (NK) cell receptors during development are unknown. To study human NK cell receptor ontogeny, umbilical cord blood CD34(+)/Lin(-)/CD38(-) cells were cultured with a murine fetal liver line (AFT024) and defined cytokines. In the absence of lymphocyte-stimulating cytokines or when contact with AFT024 was prohibited, NK cell progeny were killer immunoglobulinlike receptor (KIR) and CD94 lectin receptor negative. In contrast, efficient NK cell differentiation and receptor acquisition was dependent on direct contact of progenitors with AFT024 and the addition of interleukin-15 (IL-15) or IL-2 but not IL-7. To address the question of whether receptor acquisition was determined at the stem cell level, single CD34(+)/Lin(-)/CD38(-) progenitors were studied. More than 400 single cell progeny were analyzed from cultures containing IL-15 or IL-2 and NK cells were always polyclonal, suggesting that receptor fate is determined beyond an uncommitted progenitor and that receptor-negative NK cells acquire class I-recognizing receptors after lineage commitment. KIR2DL2/L3/S2 was expressed more than KIR2DL1/S1 or KIR3DL1, and NKG2A was the dominant CD94 receptor, independent of whether the stem cell source contained the respective major histocompatibility complex class I ligand, suggesting a nonrandom sequence of receptor acquisition. The conclusion is that NK receptor fate is determined after NK cell commitment, does not require stromal presentation of human class I alleles, and is clonally stable after expression but dynamic because new receptors are acquired over time. (Blood. 2001;98:705-713)

Umbilical cord blood cells capable of engrafting in primary, secondary, and tertiary xenogeneic hosts are preserved after ex vivo culture in a noncontact system

This report describes stroma-based and stroma-free cultures that maintain long-term engrafting hematopoietic cells for at least 14 days ex vivo. Umbilical cord blood (UCB) CD34(+) cells were cultured in transwells above AFT024 feeders with fetal-liver-tyrosine-kinase (FL) + stem cell factor (SCF) + interleukin 7 (IL-7), or FL + thrombopoietin (Tpo). CD34(+) progeny were transplanted into nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice or preimmune fetal sheep. SCID repopulating cells (SRC) with multilineage differentiation potential were maintained in FL-SCF-IL-7 or FL-Tpo containing cultures for up to 28 days. Marrow from mice highly engrafted with uncultured or expanded cells induced multilineage human hematopoiesis in 50% of secondary but not tertiary recipients. Day 7 expanded cells engrafted primary, secondary, and tertiary fetal sheep. Day 14 expanded cells, although engrafting primary and to a lesser degree secondary fetal sheep, failed to engraft tertiary recipients. SRC that can be transferred to secondary recipients were maintained for at least 14 days in medium containing glycosaminoglycans and cytokines found in stromal supernatants. This is the first demonstration that ex vivo culture in stroma-noncontact and stroma-free cultures maintains "long-term" engrafting cells, defined by their capacity to engraft secondary or tertiary hosts. (Blood. 2001;97:3441-3449)

A model of human p210(bcr/ABL)-mediated chronic myelogenous leukemia by transduction of primary normal human CD34(+) cells with a BCR/ABL-containing retroviral vector

Most insights into the molecular mechanisms underlying transformation by the p210(BCR/ABL) oncoprotein are derived from studies in which BCR/ABL cDNA was introduced into hematopoietic or fibroblast cell lines. However, such cell line models may not represent all the features of chronic myelogenous leukemia (CML) caused by additional genetic abnormalities and differences in the biology of cell lines compared with primary hematopoietic progenitor and stem cells. A primary human hematopoietic progenitor cell model for CML was developed by the transduction of b3a2 BCR/ABL cDNA in normal CD34(+) cells. Adhesion of BCR/ABL-transduced CD34(+) cells to fibronectin was decreased, but migration over fibronectin was enhanced compared with that of mock-transduced CD34(+) cells. Adhesion to fibronectin did not decrease the proliferation of BCR/ABL-transduced CD34(+) cells but decreased the proliferation of mock-transduced CD34(+) cells. This was associated with elevated levels of p27(Kip) in p210(BCR/ABL)-expressing CD34(+) cells. In addition, the presence of p210(BCR/ABL) delayed apoptosis after the withdrawal of cytokines and serum. Finally, significantly more and larger myeloid colony-forming units grew from BCR/ABL than from mock-transduced CD34(+) cells. Thus, the transduction of CD34(+) cells with the b3a2-BCR/ABL cDNA recreates most, if not all, phenotypic abnormalities seen in primary CML CD34(+) cells. This model should prove useful for the study of molecular mechanisms associated with the presence of p210(BCR/ABL) in CML.