Mouse mesenchymal stem cells can support human hematopoiesis both in vitro and in vivo: the crucial role of neural cell adhesion molecule

Knockdown the moyamoya disease susceptibility gene, RNF213, upregulates the expression of basic fibroblast growth factor and matrix metalloproteinase-9 in bone marrow derived mesenchymal stem cells

Moyamoya disease (MMD) is a chronic, progressive cerebrovascular occlusive disease. Ring finger protein 213 (RNF213) is a susceptibility gene of MMD. Previous studies have shown that the expression levels of angiogenic factors increase in MMD patients, but the relationship between the susceptibility gene RNF213 and these angiogenic mediators is still unclear. The aim of the present study was to investigate the pathogenesis of MMD by examining the effect of RNF213 gene knockdown on the expression of matrix metalloproteinase-9 (MMP-9) and basic fibroblast growth factor (bFGF) in rat bone marrow-derived mesenchymal stem cells (rBMSCs). Firstly, 40 patients with MMD and 40 age-matched normal individuals (as the control group) were enrolled in the present study to detect the levels of MMP-9 and bFGF in serum by ELISA. Secondly, Sprague-Dawley male rat BMSCs were isolated and cultured using the whole bone marrow adhesion method, and subsequent phenotypic analysis was performed by flow cytometry. Alizarin red and oil red O staining methods were used to identify osteogenic and adipogenic differentiation, respectively. Finally, third generation rBMSCs were transfected with lentivirus recombinant plasmid to knockout expression of the RNF213 gene. After successful transfection was confirmed by reverse transcription-quantitative PCR and fluorescence imaging, the expression levels of bFGF and MMP-9 mRNA in rBMSCs and the levels of bFGF and MMP-9 protein in the supernatant of the culture medium were detected on the 7th and 14th days after transfection. There was no significant difference in the relative expression level of bFGF among the three groups on the 7th day. For the relative expression level of MMP-9, there were significant differences on the 7th day and 14th day. In addition, there was no statistically significant difference in the expression of bFGF in the supernatant of the RNF213 shRNA group culture medium, while there was a significant difference in the expression level of MMP-9. The knockdown of the RNF213 gene affects the expression of bFGF and MMP-9. However, further studies are needed to determine how they participate in the pathogenesis of MMD. The findings of the present study provide a theoretical basis for clarifying the pathogenesis and clinical treatment of MMD.

Unveiling heterogeneity in MSCs: exploring marker-based strategies for defining MSC subpopulations

Mesenchymal stem/stromal cells (MSCs) represent a heterogeneous cell population distributed throughout various tissues, demonstrating remarkable adaptability to microenvironmental cues and holding immense promise for disease treatment. However, the inherent diversity within MSCs often leads to variability in therapeutic outcomes, posing challenges for clinical applications. To address this heterogeneity, purification of MSC subpopulations through marker-based isolation has emerged as a promising approach to ensure consistent therapeutic efficacy. In this review, we discussed the reported markers of MSCs, encompassing those developed through candidate marker strategies and high-throughput approaches, with the aim of explore viable strategies for addressing the heterogeneity of MSCs and illuminate prospective research directions in this field.

The efficacy of topical insulin application on rat model with burn wounds treated with adipose-derived stem cells

Overall, major burn wounds may require special care and long-term hospitalization as they not only bring complications from the wound itself, but may also compromise the immune system, or even other organs. Previous studies have indicated that topical insulin cream shortened wound closure time in second-degree burns in rats. Transplanted adipose-derived stem cells (AD-MSCs) have been developed as an alternative to treat burns and to accelerate the healing process. The aim of the present study is to investigate the effect of topical insulin gel, associated with AD-MSCs intradermal administration to heal second-degree burn wounds in rat models who were subjected to second-degree dorsal burns. The models were divided into four groups (n = 10 per group): placebo gel (C), topical insulin gel (TI), topical insulin gel and adipose-derived mesenchymal stem cells (TIMSCs) and placebo gel and adipose-derived mesenchymal stem cells (CMSCs). Wounds were assessed on a daily basis and histological evaluations were made on 5 animals from each group on the seventh and fourteenth day. There was a significant macroscopic decrease in burn wound areas in the Control (P = 0.0083), TIMSCs and CMSCs (P = 0.042) groups between the seventh and fourteenth days. The TI treatment did not show any significant change (P > 0.05) throughout this same period. The histological analysis showed significant granulation tissue formation in CMSCs and TIMSCs (P = 0.02235) treatments during the experimental period. According to the results, intradermal administration of allogenic AD-MSCs in experimental second-degree burns for short periods of time in the rat model has contributed to reducing the inflammatory phase duration, improving wound re-epithelialization, tissue granulation and wound contraction, as well as increasing collagen deposition.

The application of mesenchymal stem cells to treat thermal and radiation burns

Mesenchymal stem cells (MSCs) have been developed for a number of indications due to their regenerative and anti-inflammatory phenotypes and their utility is enhanced by the fact that allogeneic transplant is feasible with this cell type. Animal studies and early human cases indicate that this has the potential to be an exciting new therapy for treating chronic non-healing wounds such as diabetic ulcers, burns and cutaneous radiation burns. This review will focus on the use of MSCs to treat thermal and radiation burns. Large, severe burns are difficult to treat and pose a major public health burden worldwide. They are characterized by an extensive loss of the outer protective barrier, delayed wound healing, increased oxidative stress and a heightened inflammatory state. The breakdown of the protective barrier results in increased susceptibility to fluid loss and bacterial sepsis. In the case of radiation burns, chronic inflammation can result in subsequent waves of tissue injury leading to skin breakdown and necrosis. The aim of this review is to summarize the current knowledge on MSCs in treating thermal and radiation burns along with the specific scope of characterizing the biologic function of MSCs that help enhance wound healing in these chronic injuries.

Expression of neural cell adhesion molecule and polysialic acid in human bone marrow-derived mesenchymal stromal cells

BACKGROUND

In order to develop novel clinical applications and to gain insights into possible therapeutic mechanisms, detailed molecular characterization of human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) is needed. Neural cell adhesion molecule (NCAM, CD56) is a transmembrane glycoprotein modulating cell-cell and cell-matrix interactions. An additional post-translational modification of NCAM is the α2,8-linked polysialic acid (polySia). Because of its background, NCAM is often considered a marker of neural lineage commitment. Generally, hBM-MSCs are considered to be devoid of NCAM expression, but more rigorous characterization is needed.

METHODS

We have studied NCAM and polySia expression in five hBM-MSC lines at mRNA and protein levels. Cell surface localization was confirmed by immunofluorescence staining and expression frequency in the donor-specific lines by flow cytometry. For the detection of poorly immunogenic polySia, a fluorochrome-tagged catalytically defective enzyme was employed.

RESULTS

All five known NCAM isoforms are expressed in these cells at mRNA level and the three main isoforms are present at protein level. Both polysialyltransferases, generally responsible for NCAM polysialylation, are expressed at mRNA level, but only very few cells express polySia at the cell surface.

CONCLUSIONS

Our results underline the need for a careful control of methods and conditions in the characterization of MSCs. This study shows that, against the generally held view, clinical-grade hBM-MSCs do express NCAM. In contrast, although both polysialyltransferase genes are transcribed in these cells, very few express polySia at the cell surface. NCAM and polySia represent new candidate molecules for influencing MSC interactions.

Gene-expression and in vitro function of mesenchymal stromal cells are affected in juvenile myelomonocytic leukemia

An aberrant interaction between hematopoietic stem cells and mesenchymal stromal cells has been linked to disease and shown to contribute to the pathophysiology of hematologic malignancies in murine models. Juvenile myelomonocytic leukemia is an aggressive malignant disease affecting young infants. Here we investigated the impact of juvenile myelomonocytic leukemia on mesenchymal stromal cells. Mesenchymal stromal cells were expanded from bone marrow samples of patients at diagnosis (n=9) and after hematopoietic stem cell transplantation (n=7; from 5 patients) and from healthy children (n=10). Cells were characterized by phenotyping, differentiation, gene expression analysis (of controls and samples obtained at diagnosis) and in vitro functional studies assessing immunomodulation and hematopoietic support. Mesenchymal stromal cells from patients did not differ from controls in differentiation capacity nor did they differ in their capacity to support in vitro hematopoiesis. Deep-SAGE sequencing revealed differential mRNA expression in patient-derived samples, including genes encoding proteins involved in immunomodulation and cell-cell interaction. Selected gene expression normalized during remission after successful hematopoietic stem cell transplantation. Whereas natural killer cell activation and peripheral blood mononuclear cell proliferation were not differentially affected, the suppressive effect on monocyte to dendritic cell differentiation was increased by mesenchymal stromal cells obtained at diagnosis, but not at time of remission. This study shows that active juvenile myelomonocytic leukemia affects the immune response-related gene expression and function of mesenchymal stromal cells. In contrast, the differential gene expression of hematopoiesis-related genes could not be supported by functional data. Decreased immune surveillance might contribute to the therapy resistance and progression in juvenile myelomonocytic leukemia.

Kinetics of hematopoietic stem cells and supportive activities of stromal cells in a three-dimensional bone marrow culture system

In the bone marrow, hematopoietic cells proliferate and differentiate in close association with a three-dimensional (3D) hematopoietic microenvironment. Previously, we established a 3D bone marrow culture system. In this study, we analyzed the kinetics of hematopoietic cells, and more than 50% of hematopoietic progenitor cells, including CFU-Mix, CFU-GM and BFU-E in 3D culture were in a resting (non-S) phase. Furthermore, we examined the hematopoietic supportive ability of stromal cells by measuring the expression of various mRNAs relevant to hematopoietic regulation. Over the 4 weeks of culture, the stromal cells in the 3D culture are not needlessly activated and "quietly" regulate hematopoietic cell proliferation and differentiation during the culture, resulting in the presence of resting hematopoietic stem cells in the 3D culture for a long time. Thus, the 3D culture system may be a new tool for investigating hematopoietic stem cell-stromal cell interactions in vitro.

Mouse Dental Pulp Stem Cells Support Human Umbilical Cord Blood-Derived Hematopoietic Stem/Progenitor Cells in Vitro

It is well documented that specialized mesenchymal stem/stromal cells (MSCs) constitute the hematopoietic stem cell (HSC) niche in the bone marrow (BM), and these MSCs support/maintain the HSCs in an undifferentiated state. A number of studies have demonstrated that BM-derived MSCs (BM-MSCs) can support HSCs in vitro. However, it remains unclear whether nonhematopoietic tissue-derived MSC-like cells, such as dental pulp stem cells (DPSCs), have the ability to support HSCs. In this study, we prospectively isolated DPSCs from mouse mandibular incisors by fluorescence-activated cell sorting (FACS) using BM-MSC markers, such as PDGFRα and Sca-1. The PDGFRα and Sca-1 double-positive DPSCs and BM-MSCs showed similar morphologies and expression patterns of MSC markers. The ability of the DPSCs to support hematopoietic stem/progenitor cells (HSPCs) was then analyzed by an in vitro coculture system. Moreover, their HSC-supporting activity was evaluated by in vivo xenotransplantation assays using NOD/Shi-scid/IL-2Rγcnull (NOG) mice. Interestingly, the DPSCs supported human cord blood (CB)-derived CD34-positive (CD34+), as well as CD34-negative (CD34–), HSCs. The supporting activities of DPSCs for human CB-derived CD34+ and CD34– HSCs were comparable to those of BM-MSCs. The results of the present study demonstrated, for the first time, that prospectively isolated murine PDGFRα and Sca-1 double-positive DPSCs could support primitive human CD34+ and CD34– HSCs in vitro.

Prospective isolation and characterization of human bone marrow-derived MSCs

There is an increasing interest in adult stem cells, especially mesenchymal stem/stromal cells (MSCs), in hematology and regenerative medicine because of the simplicity of isolation and ex vivo expansion of these cells. Conventionally, MSCs are functionally isolated from tissue based on their capacity to adhere to the surface of culture flasks. This isolation procedure is hampered by the unpredictable influence of secreted molecules and interactions with co-cultured hematopoietic and other unrelated cells, as well as by the arbitrarily selected removal time of non-adherent cells prior to the expansion of MSCs. Finally, functionally isolated cells do not provide biological information about the starting population. To circumvent these limitations, several strategies have been developed to facilitate the prospective isolation of MSCs based on the selective expression or absence of surface markers. The isolation and ex vivo expansion of these cells require an adequate quality control of the source and product. Here we summarize the most frequently used markers and introduce new targets for antibody-based isolation and characterization of bone marrow-derived MSCs.

Efficacy and safety of mesenchymal stromal cell treatment from related donors for patients with refractory aplastic anemia

BACKGROUND AIMS

This study evaluated the feasibility, safety and immunological effects of the intravenous administration of mesenchymal stromal cells (MSCs) from a related donor in patients with refractory aplastic anemia (AA).

METHODS

A mean of 6 × 10(5)/kg (range, 5.0-7.1 × 10(5)) MSCs were injected intravenously to 18 patients, including 14 patients with nonsevere AA and four patients with severe AA who were refractory to prior immunosuppressive treatment. The outcomes of patients treated with MSCs were evaluated and compared with a historic control cohort, including 18 patients with refractory AA.

RESULTS

Two patients had injection-related adverse events, including transient fever and headache. No major adverse events were reported during the follow-up period. An immunological analysis revealed an increased proportion of CD4(+)CD25(+) FOXP3(+)regulatory T cells in peripheral mononuclear cells. Following up for 1 year, six of 18 patients (33.3%) achieved a complete response or a partial response to MSC treatment. In six patients, two achieved a complete response including a recovery of three hematopoietic cell lines after MSCs therapy at days 88 and 92, two patients achieved only a red cell recovery with hemoglobin levels >100 g/L at days 30 and 48 and two patients had only a platelet recovery with a platelet count of >60 × 10(9)/L at days 54 and 81. In the control cohort, only one patient (5.56%) achieved a partial response during the follow-up period.

CONCLUSIONS

The data from the present study suggest that treatment with MSCs from a related donor may be a promising therapeutic strategy for patients with refractory AA. The trial has been registered at ClinicalTrials.gov: identifier NCT01305694.

Neural stem cells-trends and advances

For many years, accepted dogma held that brain is a static organ with no possibility of regeneration of cells in injured or diseased human brain. However, recent preclinical reports have shown regenerative potential of neural stem cells using various injury models. This has resulted in renewed hope for those suffering from spinal cord injury and neural damage. As the potential of stem cell therapy gained impact, these claims, in particular, led to widespread enthusiasm that acute and chronic injury of the nervous system would soon be a problem of the past. The devastation caused by injury or diseases of the brain and spinal cord led to wide premature acceptance that "neural stem cells (NSCs)" derived from embryonic, fetal or adult sources would soon be effective in reversing neural and spinal trauma. However, neural therapy with stem cells has not been realized to its fullest extent. Although, discrete population of regenerative stem cells seems to be present in specific areas of human brain, the function of these cells is unclear. However, similar cells in animals seem to play important role in postnatal growth as well as recovery of neural tissue from injury, anoxia, or disease.

Impaired endothelial progenitor cell mobilization and dysfunctional bone marrow stroma in diabetes mellitus

Background

Circulating Endothelial Progenitor Cell (EPC) levels are reduced in diabetes mellitus. This may be a consequence of impaired mobilization of EPC from the bone marrow. We hypothesized that under diabetic conditions, mobilization of EPC from the bone marrow to the circulation is impaired –at least partly– due to dysfunction of the bone marrow stromal compartment.

Methods

Diabetes was induced in mice by streptozotocin injection. Circulating Sca-1⁺Flk-1⁺ EPC were characterized and quantified by flow cytometry at baseline and after mobilization with G-CSF/SCF injections. In vivo hemangiogenic recovery was tested by 5-FU challenge. Interaction within the bone marrow environment between CD34⁺ hematopoietic progenitor cells (HPC) and supporting stroma was assessed by co-cultures. To study progenitor cell–endothelial cell interaction under normoglycemic and hyperglycemic conditions, a co-culture model using E4Orf1-transfected human endothelial cells was employed.

Results

In diabetic mice, bone marrow EPC levels were unaffected. However, circulating EPC levels in blood were lower at baseline and mobilization was attenuated. Diabetic mice failed to recover and repopulate from 5-FU injection. In vitro, primary cultured bone marrow stroma from diabetic mice was impaired in its capacity to support human CFU-forming HPC. Finally, hyperglycemia hampered the HPC supportive function of endothelial cells in vitro.

Conclusion

EPC mobilization is impaired under experimental diabetic conditions and our data suggest that diabetes induces alterations in the progenitor cell supportive capacity of the bone marrow stroma, which could be partially responsible for the attenuated EPC mobilization and reduced EPC levels observed in diabetic patients.

Phenotypic and functional heterogeneity of human bone marrow- and amnion-derived MSC subsets

Bone marrow-derived mesenchymal stromal/stem cells (MSCs) are nonhematopoietic cells that are able to differentiate into osteoblasts, adipocytes, and chondrocytes. In addition, they are known to participate in niche formation for hematopoietic stem cells and to display immunomodulatory properties. Conventionally, these cells are functionally isolated from tissue based on their capacity to adhere to the surface of culture flasks. This isolation procedure is hampered by the unpredictable influence of secreted molecules, the interactions between cocultured hematopoietic and other unrelated cells, and by the arbitrarily selected removal time of nonadherent cells before the expansion of MSCs. Finally, functionally isolated cells do not provide biological information about the starting population. To circumvent these limitations, several strategies have been developed to facilitate the prospective isolation of MSCs based on the selective expression, or absence, of surface markers. In this report, we summarize the most frequently used markers and introduce new targets for antibody-based isolation procedures of primary bone marrow- and amnion-derived MSCs.

Neural cell adhesion molecule modulates mesenchymal stromal cell migration via activation of MAPK/ERK signaling

Mesenchymal Stromal Cells (MSCs) represent promising tools for cellular therapy owing to their multipotentiality and ability to localize to injured, inflamed sites and tumor. Various approaches to manipulate expression of MSC surface markers, including adhesion molecules and chemokine receptors, have been explored to enhance homing of MSCs. Recently, Neural Cell Adhesion Molecule (NCAM) has been found to be expressed on MSCs yet its function remains largely elusive. Herein, we show that bone marrow-derived MSCs from NCAM deficient mice exhibit defective migratory ability and significantly impaired adipogenic and osteogenic differentiation potential. We further explore the mechanism governing NCAM mediated migration of MSCs by showing the interplay between NCAM and Fibroblast Growth Factor Receptor (FGFR) induces activation of MAPK/ERK signaling, thereby the migration of MSCs. In addition, re-expression of NCAM180, but not NCAM140, could restore the defective MAPK/ERK signaling thereby the migration of NCAM deficient MSCs. Finally, we demonstrate that NCAM180 expression level could be manipulated by pro-inflammatory cytokine Tumor Necrosis Factor (TNF)-α treatment. Overall, our data reveal the vital function of NCAM in MSCs migration and differentiation thus raising the possibility of manipulating NCAM expression to enhance homing and therapeutic potential of MSCs in cellular therapy.

Human olfactory mucosa multipotent mesenchymal stromal cells promote survival, proliferation, and differentiation of human hematopoietic cells

Multipotent mesenchymal stromal cells (MSCs) from the human olfactory mucosa (OM) are cells that have been proposed as a niche for neural progenitors. OM-MSCs share phenotypic and functional properties with bone marrow (BM) MSCs, which constitute fundamental components of the hematopoietic niche. In this work, we investigated whether human OM-MSCs may promote the survival, proliferation, and differentiation of human hematopoietic stem cells (HSCs). For this purpose, human bone marrow cells (BMCs) were co-cultured with OM-MSCs in the absence of exogenous cytokines. At different intervals, nonadherent cells (NACs) were harvested from BMC/OM-MSC co-cultures, and examined for the expression of blood cell markers by flow cytometry. OM-MSCs supported the survival (cell viability >90%) and proliferation of BMCs, after 54 days of co-culture. At 20 days of co-culture, flow cytometric and microscopic analyses showed a high percentage (73%) of cells expressing the pan-leukocyte marker CD45, and the presence of cells of myeloid origin, including polymorphonuclear leukocytes, monocytes, basophils, eosinophils, erythroid cells, and megakaryocytes. Likewise, T (CD3), B (CD19), and NK (CD56/CD16) cells were detected in the NAC fraction. Colony-forming unit-granulocyte/macrophage (CFU-GM) progenitors and CD34(+) cells were found, at 43 days of co-culture. Reverse transcriptase-polymerase chain reaction (RT-PCR) studies showed that OM-MSCs constitutively express early and late-acting hematopoietic cytokines (i.e., stem cell factor [SCF] and granulocyte- macrophage colony-stimulating factor [GM-CSF]). These results constitute the first evidence that OM-MSCs may provide an in vitro microenvironment for HSCs. The capacity of OM-MSCs to support the survival and differentiation of HSCs may be related with the capacity of OM-MSCs to produce hematopoietic cytokines.

Novel three-dimensional long-term bone marrow culture system using polymer particles with grafted epoxy-polymer-chains supports the proliferation and differentiation of hematopoietic stem cells

Hematopoiesis occurs in the bone marrow, where primitive hematopoietic cells proliferate and differentiate in close association with a three-dimensional (3D) hematopoietic microenvironment composed of stromal cells. We examined the hematopoietic supportive ability of stromal cells in a 3D culture system using polymer particles with grafted epoxy polymer chains. Umbilical cord blood-derived CD34+ cells were co-cultivated with MS-5 stromal cells. They formed a 3D structure in the culture dish in the presence of particles, and the total numbers of cells and the numbers of hematopoietic progenitor cells, including colony-forming unit (CFU)-Mix, CFU-granulocyte-macrophage, CFU-megakaryocyte and burst-forming unit-erythroid, were measured every seven days. The hematopoietic supportive activity of the 3D culture containing polymer particles and stromal cells was superior to that of 2D culture, and allowed the expansion and maintenance of hematopoietic progenitor cells for more than 12 weeks. Various types of hematopoietic cells, including granulocytes, macrophages and megakaryocytes at different maturation stages, appeared in the 3D culture, suggesting that the CD34+ cells were able to differentiate into a range of blood cell types. Morphological examination showed that MS-5 stromal cells grew on the surface of the particles and bridged the gaps between them to form a 3D structure. Hematopoietic cells slipped into the 3D layer and proliferated within it, relying on the presence of the MS-5 cells. These results suggest that this 3D culture system using polymer particles reproduced the hematopoietic phenomenon in vitro, and might thus provide a new tool for investigating hematopoietic stem cell–stromal cell interactions.

A novel role for neural cell adhesion molecule in modulating insulin signaling and adipocyte differentiation of mouse mesenchymal stem cells

Neural cell adhesion molecule (NCAM) has recently been found on adult stem cells, but its biological significance remains largely unknown. In this study, we used bone-marrow-derived mesenchymal stem cells (MSCs) from wild-type and NCAM knockout mice to investigate the role of NCAM in adipocyte differentiation. It was demonstrated that NCAM isoforms 180 and 140 but not NCAM-120 are expressed on almost all wild-type MSCs. Upon adipogenic induction, Ncam(-/-) MSCs exhibited a marked decrease in adipocyte differentiation compared with wild-type cells. The role of NCAM in adipocyte differentiation was also confirmed in NCAM-silenced preadipocyte 3T3-L1 cells, which also had a phenotype with reduced adipogenic potential. In addition, we found that Ncam(-/-) MSCs appeared to be insulin resistant, as shown by their impaired insulin signaling cascade, such as the activation of the insulin-IGF-1 receptor, PI3K-Akt and CREB pathways. The PI3K-Akt inhibitor, LY294002, completely blocked adipocyte differentiation of MSCs, unveiling that the reduced adipogenic potential of Ncam(-/-) MSCs is due to insulin resistance as a result of loss of NCAM function. Furthermore, insulin resistance of Ncam(-/-) MSCs was shown to be associated with induction of tumor necrosis factor α (TNF-α), a key mediator of insulin resistance. Finally, we demonstrated that re-expression of NCAM-180, but not NCAM-140, inhibits induction of TNF-α and thereby improves insulin resistance and adipogenic potential of Ncam(-/-) MSCs. Our results suggest a novel role of NCAM in promoting insulin signaling and adipocyte differentiation of adult stem cells. These findings raise the possibility of using NCAM intervention to improve insulin resistance.

Mesenchymal stem cells secreting angiopoietin-like-5 support efficient expansion of human hematopoietic stem cells without compromising their repopulating potential

Clinical and preclinical applications of human hematopoietic stem cells (HSCs) are often limited by scarcity of cells. Expanding human HSCs to increase their numbers while maintaining their stem cell properties has therefore become an important area of research. Here, we report a robust HSC coculture system wherein cord blood CD34(+) CD133(+) cells were cocultured with mesenchymal stem cells engineered to express angiopoietin-like-5 in a defined medium. After 11 days of culture, SCID repopulating cells were expanded ~60-fold by limiting dilution assay in NOD-scid Il2rg(-/-) (NSG) mice. The cultured CD34(+) CD133(+) cells had similar engraftment potential to uncultured CD34(+) CD133(+) cells in competitive repopulation assays and were capable of efficient secondary reconstitution. Further, the expanded cells supported a robust multilineage reconstitution of human blood cells in NSG recipient mice, including a more efficient T-cell reconstitution. These results demonstrate that the expanded CD34(+) CD133(+) cells maintain both short-term and long-term HSC activities. To our knowledge, this ~60-fold expansion of SCID repopulating cells is the best expansion of human HSCs reported to date. Further development of this coculture method for expanding human HSCs for clinical and preclinical applications is therefore warranted.