Characterization of CD34+HLA-DR-CD38+ and CD34+HLA-DR-CD38- progenitor cells from human umbilical cord blood

Genome-wide comparison of the transcriptomes of highly enriched normal and chronic myeloid leukemia stem and progenitor cell populations

The persistence leukemia stem cells (LSCs) in chronic myeloid leukemia (CML) despite tyrosine kinase inhibition (TKI) may explain relapse after TKI withdrawal. Here we performed genome-wide transcriptome analysis of highly refined CML and normal stem and progenitor cell populations to identify novel targets for the eradication of CML LSCs using exon microarrays. We identified 97 genes that were differentially expressed in CML versus normal stem and progenitor cells. These included cell surface genes significantly upregulated in CML LSCs: DPP4 (CD26), IL2RA (CD25), PTPRD, CACNA1D, IL1RAP, SLC4A4, and KCNK5. Further analyses of the LSCs revealed dysregulation of normal cellular processes, evidenced by alternative splicing of genes in key cancer signaling pathways such as p53 signaling (e.g. PERP, CDKN1A), kinase binding (e.g. DUSP12, MARCKS), and cell proliferation (MYCN, TIMELESS); downregulation of pro-differentiation and TGF-β/BMP signaling pathways; upregulation of oxidative metabolism and DNA repair pathways; and activation of inflammatory cytokines, including CCL2, and multiple oncogenes (e.g., CCND1). These data represent an important resource for understanding the molecular changes in CML LSCs, which may be exploited to develop novel therapies for eradication these cells and achieve cure.

Regulation of human hematopoietic stem cell self-renewal by the microenvironment's control of retinoic acid signaling

The high expression of aldehyde dehydrogenase 1, also known as retinaldehyde dehydrogenase, by hematopoietic stem cells (HSCs) suggests an important role for retinoic acid (RA) signaling in determining the fate of these cells. We found that primitive human bone marrow-derived CD34(+)CD38(-) cells not only highly express aldehyde dehydrogenase 1, but also the RA receptor α. Despite the up-regulation of early components of RA signaling, the downstream pathway remained inactive in the primitive CD34(+)CD38(-) cells. Primitive hematopoietic cells rapidly undergo terminal differentiation when cultured away from their microenvironment; however, we found that inhibition of RA signaling maintained their primitive phenotype and function, and promoted their self-renewal. HSCs reside in a complex microenvironment that enforces the balance between self-renewal and differentiation. The exact physiologic mechanisms by which the niche controls HSC fate remain elusive. The embryonic gonadal microenvironment has recently been shown to determine germ-cell fate by degrading RA through expression of the P450 retinoid-inactivating enzyme CYP26B1. We found that the bone marrow microenvironment similarly can control primitive hematopoietic cell fate via modulation of retinoid bioavailability. Accordingly, we found that bone marrow stromal cell CYP26 was also able to inactivate retinoids in serum, preventing RA signaling. Thus, primitive hematopoietic cells appear to be intrinsically programmed to undergo RA-mediated differentiation unless prevented from doing so by bone marrow niche CYP26. Modulation of RA signaling also holds promise for clinical HSC expansion, a prerequisite for the wide-scale use of these cells in regenerative medicine and gene therapy.

Cord blood banking for clinical transplantation

Cord blood (CB) stem and progenitor cells from related donors have been transplanted for past 20 years and from unrelated donors issued by public CB banks for 16 years. This brief look at public CB banking highlights aspects of its current status to suggest that accomplishing the currently required tasks, though no small undertaking, is not enough: much remains to be contributed. CB banking started in the 1930s, collecting blood for transfusion and showed that CB could be effectively collected, stored and administered intravenously without negative consequences. The realization that it contains hematopoietic 'stem' cells (actually, colony-forming units) followed discoveries elsewhere in hematopoiesis research, while HLA and unrelated BMT were being investigated. Progress in the exploration of ethnically stratified HLA allele frequencies, together with plausible neonatal (partial) immunological tolerance, seemed to predict initially frequent, unavoidable, but sufficiently tolerable HLA mismatching with CB grafts. Gluckman et al. and Boyse et al. proved that HLA-identical sibling CB grafts led to definitive engraftment. Technical developments in processing and freezing enabled public banks to accumulate large inventories and to supply grafts that could succeed despite major HLA incompatibility and low cell doses and provide hope for universal access to unrelated-donor transplantation. Public CB banking has thrived worldwide. Regulation and accreditation defined Good Tissue Practice in the CB banking environment and provided accepted do's, don't's and how to's. Startling advances continue to be made, not only technical, but including the description of molecular regulation in the function of natural killer and other cells involved in allogeneic recognition that will have dramatic effects and will permit further improvement in CB selection and use.

Immobilized DNA aptamers used as potent attractors for porcine endothelial precursor cells

Because of their insufficient biocompatibility and high thrombogenicity, small diameter artificial vascular prostheses still do not show a satisfactory patency rate. In vitro endothelialization of artificial grafts before implantation has been established experimentally years ago, but, this procedure is extremely time consuming and expensive. This study deals with the coating of graft surfaces with capture molecules (aptamers) for circulating endothelial progenitor cells (EPCs), mimicking a prohoming substrate to fish out EPCs from the bloodstream after implantation and to create an autologous functional endothelium. Using the SELEX technology, aptamers with a high affinity to EPCs were identified, isolated, and grafted onto polymeric discs using a blood compatible star-PEG coating. A porcine in vitro model that demonstrates the specific adhesion of EPCs and their differentiation into vital endothelial-like cells within 10 days in cell culture is presented. We suggest that the rapid adhesion of EPCs to aptamer-coated implants could be useful to promote endothelial wound healing and to prevent increased neointimal hyperplasia. We hypothesize that future in vivo self-endothelialization of blood contacting implants by homing factor mimetic capture molecules for EPCs may bring revolutionary new perspectives towards clinical applications of stem cell and tissue engineering strategies.

Identification of stem cells from human umbilical cord blood with embryonic and hematopoietic characteristics

We identified stem cells from the umbilical cord blood, designated cord blood-stem cells (CB-SC). CB-SC displayed important embryonic stem (ES) cell characteristics including expression of ES-cell-specific molecular markers including transcription factors OCT-4 and Nanog, along with stage-specific embryonic antigen (SSEA)-3 and SSEA-4. CB-SC also expressed hematopoietic cell antigens including CD9, CD45 and CD117, but were negative for CD34. CB-SC displayed very low immunogenicity as indicated by expression of a very low level of major histocompatibility complex (MHC) antigens and failure to stimulate the proliferation of allogeneic lymphocytes. CB-SC could give rise to cells with endothelial-like and neuronal-like characteristics in vitro, as demonstrated by expression of lineage-associated markers. Notably, CB-SC could be stimulated to differentiate into functional insulin-producing cells in vivo and eliminated hyperglycemia after transplantation into a streptozotocin-induced diabetic mouse model. These findings may have significant potential to advance stem-cell-based therapeutics.

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.

Punish the parent not the progeny

Chronic myeloid leukemia (CML) is sustained by a rare population of primitive, quiescent, BCR-ABL+ cells and represents an excellent example of a malignancy in which tumor-initiating cells represent the key to disease eradication. CML is also the first malignancy for which targeted therapy has replaced conventional chemotherapy. Within a vast excess of proliferating progenitor cells that express breakpoint cluster region-abelson (BCR-ABL) and are exquisitely sensitive to the tyrosine kinase inhibitor imatinib mesylate (IM) resides a small population of quiescent leukemic cells that, despite higher levels of BCR-ABL transcripts, exhibits innate insensitivity to IM. These cells remain after IM therapy, even when apparently complete responses are achieved, and they probably explain molecular disease persistence. Although it can be argued that patients may survive for many years with low levels of leukemia still present, it is possible to achieve disease clearance at the molecular level following an allogeneic stem cell transplantation. The emergence of drug resistance with IM monotherapy also argues in favor of complete disease eradication that we believe should remain the ultimate therapeutic goal in CML. New approaches to the elimination of these primitive CML cells may thus be crucial to the development of curative strategies.

New developments in pediatric plastic surgery research

Pediatric plastic surgery research is a rapidly expanding field. Unique in many ways, researchers in this field stand at the union of multiple scientific specialties, including biomedical engineering, tissue engineering, polymer science, molecular biology, developmental biology, and genetics. The goal of this scientific effort is to translate research advances into improved treatments for children with congenital and acquired defects. Although the last decade has seen a dramatic acceleration in research related to pediatric plastic surgery, the next 10 years will no doubt lead to novel treatment strategies with improved clinical outcomes.

Selective in vitro expansion and efficient retroviral transduction of human CD34+ CD38- haematopoietic stem cells

Ex vivo expansion of primitive human haematopoietic stem cells (HSC) is clinically relevant for stem cell transplantation and gene therapy. Here, we demonstrate the selective expansion of CD34+CD38- cells from purified CD34+ cells upon stimulation with Flt3-ligand, stem cell factor and thrombopoietin. Over a 100-fold (range 80 to 128-fold) expansion of CD34+CD38- cells was observed with bone marrow and cord blood (CB). The expanded CD34+CD38- cells remained negative for lineage-specific markers and could be induced to differentiate into granulocytes, monocytes, megakaryocytes, erythrocytes, and T and B-lymphocytes in vitro. Lineage differentiation assays with single CD34+CD38- cells showed no loss of multilineage potential of expanded cells after ex vivo culture. We also demonstrated that the increase in frequency of CD34+CD38- cells was not as a result of the downregulation of CD38 expression during the culture. Quantitative analysis showed that the number of 6 week cobblestone area forming cells (CAFCwk6), a measure of proliferating HSC, in cytokine-stimulated CD34+ cells were increased by 20-fold. Expanded CD34+CD38- cells could be transduced efficiently with retroviruses encoding the low affinity nerve growth factor receptor (LNGFR) marker gene (17% to 44%, mean 27%), resulting in long-lasting expression of retroviral-encoded genes in progeny HSC and differentiated progenitors. We conclude that the combination Flt3-ligand (FL), stem cell factor and thrombopoietin (TPO) induced strong ex vivo proliferation of CD34+CD38- cells and that the absolute number of expanded cells with stem cell activity increased substantially in this population.

Hoechst dye efflux reveals a novel CD7+CD34− lymphoid progenitor in human umbilical cord blood

A novel Hoechst 33342 dye efflux assay was recently developed that identifies a population of hematopoietic cells termed side population (SP) cells. In the bone marrow of multiple species, including mice and primates, the SP is composed primarily of CD34−cells, yet has many of the functional properties of hematopoietic stem cells (HSCs). This report characterizes SP cells from human umbilical cord blood (UCB). The SP in unfractionated UCB was enriched for CD34+ cells but also contained a large population of CD34− cells, many of which were mature lymphocytes. SP cells isolated from UCB that had been depleted of lineage-committed cells (Lin− UCB) contained CD34+ and CD34− cells in approximately equivalent proportions. Similar to previous descriptions of human HSCs, the CD34+Lin− SP cells were CD38dimHLA-DRdimThy-1dimCD45RA−CD71−and were enriched for myelo-erythroid precursors. In contrast, the CD34−Lin− SP cells were CD38−HLA-DR−Thy-1−CD71−and failed to generate myelo-erythroid progeny in vitro. The majority of these cells were CD7+CD11b+CD45RA+, as might be expected of early lymphoid cells, but did not express other lymphoid markers. The CD7+CD34−Lin− UCB SP cells did not proliferate in simple suspension cultures but did differentiate into natural killer cells when cultured on stroma with various cytokines. In conclusion, the human Lin− UCB SP contains both CD34+ multipotential stem cells and a novel CD7+CD34−Lin− lymphoid progenitor. This observation adds to the growing body of evidence that CD34− progenitors exist in humans.

Hoechst dye efflux reveals a novel CD7+CD34− lymphoid progenitor in human umbilical cord blood

A novel Hoechst 33342 dye efflux assay was recently developed that identifies a population of hematopoietic cells termed side population (SP) cells. In the bone marrow of multiple species, including mice and primates, the SP is composed primarily of CD34−cells, yet has many of the functional properties of hematopoietic stem cells (HSCs). This report characterizes SP cells from human umbilical cord blood (UCB). The SP in unfractionated UCB was enriched for CD34+ cells but also contained a large population of CD34− cells, many of which were mature lymphocytes. SP cells isolated from UCB that had been depleted of lineage-committed cells (Lin− UCB) contained CD34+ and CD34− cells in approximately equivalent proportions. Similar to previous descriptions of human HSCs, the CD34+Lin− SP cells were CD38dimHLA-DRdimThy-1dimCD45RA−CD71−and were enriched for myelo-erythroid precursors. In contrast, the CD34−Lin− SP cells were CD38−HLA-DR−Thy-1−CD71−and failed to generate myelo-erythroid progeny in vitro. The majority of these cells were CD7+CD11b+CD45RA+, as might be expected of early lymphoid cells, but did not express other lymphoid markers. The CD7+CD34−Lin− UCB SP cells did not proliferate in simple suspension cultures but did differentiate into natural killer cells when cultured on stroma with various cytokines. In conclusion, the human Lin− UCB SP contains both CD34+ multipotential stem cells and a novel CD7+CD34−Lin− lymphoid progenitor. This observation adds to the growing body of evidence that CD34− progenitors exist in humans.

Immunophenotypic characterization of human bone marrow endosteal cells

In order to determine the relationship between bone marrow (bm) endosteal cells (EDC) and hemopoietic progenitors, we have analyzed the immunophenotype of EDC using various antibodies (Ab) against mesenchymal antigens. The Ab were applied on paraffin sections of normal bm (iliac crest, n=17; talus, n=1; phalanx, n=1), myeloregenerative bm (after chemotherapy), and hematologic disorders (acute myeloid leukemia (AML), n=8; chronic myeloid leukemia (CML), n=6; myelodysplastic syndromes (MDS), n=14; severe aplastic anemia (SAA), n=4; essential thrombocythemia (ET), n=2; idiopathic (primary) osteomyelo-fibrosis (IMF), n=1; polycythemia vera (PV), n=1). In normal bm, EDC were found to react with Ab against vimentin, tenascin, alpha-smooth muscle actin, osteocalcin, CD51, and CD56, but did not react with Ab against CD3, CD15, CD20, CD34, CD45, CD68, or CD117. An identical phenotype of EDC was found in AML, MDS, SAA, ET, IMF, PV, myeloregenerative bm, and peripheral bones lacking active hemopoiesis (talus, phalanx). In patients with CML, EDC reacted with Ab to CD51, but did not react with Ab to CD56. Based on their unique antigen profile, EDC were enriched from normal bm by enzyme digestion and cell sorting. However, these enriched cells (CD56+, CD45-, CD34-) did not give rise to hemopoietic cells under the culture conditions used, i.e. in the presence of the growth factors IGF-1, bFGF, SCF, IL-3, and GM-CSF Together, our data do not support the hypothesis that EDC are totipotent mesenchymal progenitors giving rise to hemopoietic cells.

Fetal cord blood as an alternative source of hematopoietic progenitor cells: immunophenotype, maternal cell contamination, and ex vivo expansion

The present study was performed to investigate the character of hematopoietic progenitor cells in fetal cord blood (CB). Thirty blood samples from fetuses at a median of 24 weeks of gestation (range 19-29) and 30 neonatal CB samples were analyzed for their immunophenotype by three-color flow cytometry and examined for the presence of female cells by fluorescence in situ hybridization (FISH). We tested the effects of different cytokine combinations (rhIL-1beta, rhIL-3, rhIL-6, rh erythropoietin [rhEPO], rhGM-CSF plus rhSCF, and rhSCF plus rhflt3-ligand) on the differentiation of 100 CD34+-enriched neonatal CB cells for up to 21 days. Ex vivo expansion of 32 unselected fetal blood samples cells was performed in the presence of rhSCF and rhflt3-ligand. The percentage of CD34+ cells in fetal blood was significantly higher compared with neonatal CB (1.24%+/-0.82% versus 0.33%+/-0.18%, p = 0.0001) and inversely correlated with the age of gestation. The contamination of fetal and neonatal CB with maternal cells was low (1.72%+/-0.89%, range 1.0%-4.0%). By using rhflt3-ligand we were able to expand committed progenitor cells while maintaining cells with stem cell function. The use of expanded fetal immature progenitors might have implications for in utero transplantation and autologous gene therapy.