Donor stromal cells from human blood engraft in NOD/SCID mice

Syngeneic transplantation of newborn splenocytes in a murine model of neonatal ischemia-reperfusion brain injury

OBJECTIVE

Neonatal hypoxic-ischemic encephalopathy (HIE) is caused by brain injury that occurs in a developing fetus or infant. Stem cell transplantation can reportedly induce functional recovery in animal models of HIE. Murine neonatal splenocytes are enriched with immature blood stem cells and are used for the investigation of murine models of syngeneic transplantation. The aim of this study was to investigate the therapeutic potential of newborn splenocytes in a murine model of neonatal ischemia-reperfusion brain injury.

METHODS

C57BL/6N mice (postnatal day 7) underwent right common carotid artery occlusion with an aneurysm clip. Following hypoxic exposure, reperfusion was achieved by unclamping the artery. Newborn splenocytes were transplanted intravenously at 3 weeks after injury.

RESULTS

The splenocytes transplanted group tended to show an improvement in behavioral tests, but it was not significantly different compared with the control groups. The transplanted cells were localized in various organs including injured brain tissue over 3 weeks. In the penumbra region of the brain, vascular endothelial growth factor (VEGF) expression was upregulated after transplantation.

CONCLUSIONS

These results showed that syngeneic transplantation of newborn splenocytes achieved the long-term survival of the grafts and exerted influence the microenvironment in the injured brains of mice.

Homing pathways of mesenchymal stromal cells (MSCs) and their role in clinical applications

Mesenchymal stromal cells (MSCs) have come into focus for an increasing number of cellular therapies. Since most clinical protocols use intravenous application of MSCs, it has become important to understand their trafficking in the bloodstream. Moreover, since relatively little is known where the transplanted MSCs might locate, a better understanding of involved homing mechanisms will likely shed light on how MSCs exert their therapeutic effects. This review focuses on the current knowledge of homing pathways of transplanted MSCs. We describe regulatory signalling molecules and receptors involved. An outlook is given on significance of these findings for the future use of MSCs as a cellular therapeutic.

Hematopoietic stem cell origin of connective tissues

Connective tissue consists of "connective tissue proper," which is further divided into loose and dense (fibrous) connective tissues and "specialized connective tissues." Specialized connective tissues consist of blood, adipose tissue, cartilage, and bone. In both loose and dense connective tissues, the principal cellular element is fibroblasts. It has been generally believed that all cellular elements of connective tissue, including fibroblasts, adipocytes, chondrocytes, and bone cells, are generated solely by mesenchymal stem cells. Recently, a number of studies, including those from our laboratory based on transplantation of single hematopoietic stem cells, strongly suggested a hematopoietic stem cell origin of these adult mesenchymal tissues. This review summarizes the experimental evidence for this new paradigm and discusses its translational implications.

Umbilical cord blood mesenchymal stromal cells are neuroprotective and promote regeneration in a rat optic tract model

Exploitation of the ability of stem cells to protect damaged neuronal tissue may be a more viable strategy than cell replacement for repair of the central nervous system (CNS). In this study we assessed the capacity of human umbilical cord blood (hUCB)-derived mesenchymal stromal cells (MSCs) to protect and promote regeneration of axotomised neurons within the rat optic system. The optic tract of neonatal rats was transected at the level of the lateral geniculate nucleus, and MSCs were introduced into the lesion site. MSCs survived well up to 2 weeks after grafting, and did not migrate significantly or differentiate. In the presence of MSC grafts, host axonal processes were found to be present in the lesion site, and there was stimulation of an endogenous neural precursor population. Four weeks after grafting, retrograde tracer experiments demonstrated that grafted MSCs, as well as cells of a human fibroblast line, exerted a neuroprotective effect, rescuing a significant percentage of axotomised retinal ganglion cells (RGCs). Further experiments with retrograde and anterograde tracers strongly indicated that MSCs could also promote re-growth of axotomised RGCs to their target, the superior colliculus (SC). Further analysis showed that hUCB-derived MSCs secreted several immunomodulatory and neurotrophic factors in vitro, including TGFbeta1, CNTF, NT-3 and BDNF, which are likely to play a role in neuroprotection. Our data indicate that hUCB-derived MSCs may be an easily accessible, widely available source of cells that can contribute towards neural repair through rescue and regeneration of injured neurons.

Characterization of mesenchymal stromal cells derived from full-term umbilical cord blood

BACKGROUND

Multipotent mesenchymal stromal cells (MSC) are of interest for their potential to repair bone and cartilage, and also their immunosuppressive properties. Umbilical cord blood (UCB) is reported to contain MSC, and therefore may be a useful source of these cells for clinical applications.

METHODS

We evaluated protocols for isolating MSC from UCB and characterized the surface phenotype, differentiation potential and immunoregulatory properties of the cells obtained.

RESULTS

Ten of 25 UCB units processed yielded MSC-like colonies, with depletion of lineage+ cells providing a higher efficiency. Only two of the cultures could be expanded satisfactorily; the remainder failed to proliferate. One culture generated transformed lines that were grossly aneuploid, had up-regulated TERT transcripts and had lost CD90 expression and the capacity to differentiate. The two propagated UCB-MSC lines were similar to those from bone marrow but were not identical to each other, with differences seen in expression of surface markers and cytoskeletal proteins. Both underwent osteogenesis, but at different rates and to different degrees, while neither generated adipocytes. When added as a third party to a mixed lymphocyte culture, both suppressed proliferation.

DISCUSSION

MSC-like cells can be isolated from UCB, but at low efficiencies, and they exhibit a variety of morphologies, growth rates and differentiation potentials and can transform in culture.

Mesenchymal stem cells display coordinated rolling and adhesion behavior on endothelial cells

To explore the initial steps by which transplanted mesenchymal stem cells (MSCs) interact with the vessel wall in the course of extravasation, we studied binding of human MSCs to endothelial cells (ECs). In a parallel plate flow chamber, MSCs bound to human umbilical vein ECs (HUVECs) similar to peripheral-blood mononuclear cells (PBMCs) or CD34(+) hematopoietic progenitors at shear stresses of up to 2 dynes/cm(2). This involved rapid extension of podia, rolling, and subsequent firm adhesion that was increased when ECs were prestimulated with TNF-alpha. MSC binding was suppressed when ECs were pretreated with function-blocking anti-P-selectin antibody, and rolling of MSCs was induced on immobilized P-selectin, indicating that P-selectin was involved in this process. Preincubation of HUVECs with anti-VCAM-1 or of MSCs with anti-VLA-4 antibodies suppressed binding of MSCs to HUVECs but did not enhance inhibition by anti-P-selectin, indicating that both P-selectin and VCAM-1 are equally required for this process. Intravital microscopy demonstrated the capacity of MSCs to roll and adhere to postcapillary venules in vivo in a mouse model in a P-selectin-dependent manner. Thus, MSCs interact in a coordinated fashion with ECs under shear flow, engaging P-selectin and VCAM-1/VLA-4.

Hematopoietic origin of fibroblasts/myofibroblasts: Its pathophysiologic implications

Tissue fibroblasts/myofibroblasts play a key role in growth factor secretion, matrix deposition, and matrix degradation, and therefore are important in many pathologic processes. Regarding the origin of tissue fibroblasts/myofibroblasts, a number of recent in vivo transplantation studies have suggested the bone marrow as the source of fibroblasts/myofibroblasts in liver, intestine, skin, and lung. Because bone marrow cells are thought to contain 2 types of stem cells (ie, hematopoietic stem cells [HSCs] and mesenchymal stem cells), it is important to determine which type of stem cells is the source of fibroblasts/myofibroblasts. To address this issue, we have carried out a series of studies of tissue reconstitution by single HSCs. By transplanting clones derived from single HSCs expressing transgenic enhanced green fluorescent protein, we found that fibroblasts/myofibroblasts in many organs and tissues are derived from HSCs. This brief note summarizes these findings and discusses clinical and experimental perspectives generated by this newly identified differentiation pathway of HSCs.

Multipotential mesenchymal stem cells are mobilized into peripheral blood by hypoxia

MSCs constitute a population of multipotential cells giving rise to adipocytes, osteoblasts, chondrocytes, and vascular-smooth muscle-like hematopoietic supportive stromal cells. It remains unclear whether MSCs can be isolated from adult peripheral blood under stationary conditions and whether they can be mobilized in a way similar to hematopoietic stem cells. In this report, we show that MSCs are regularly observed in the circulating blood of rats and that the circulating MSC pool is consistently and dramatically increased (by almost 15-fold) when animals are exposed to chronic hypoxia. The immunophenotype and the adipocytic, osteoblastic, and chondrocytic differentiation potential of circulating MSCs were similar to those of bone marrow MSCs. Hypoxia-induced mobilization appears to be specific for MSCs since total circulating hematopoietic progenitor cells were not significantly increased. Our data provide an in vivo model amenable to analysis of MSC-mobilizing factors.

Engraftment capacity of mesenchymal cells following hematopoietic stem cell transplantation in patients receiving reduced-intensity conditioning regimen

The engraftment ability of mesenchymal cells was investigated in 26 patients receiving allogeneic transplantation from HLA-identical siblings with reduced-intensity conditioning (RIC). The stem cell source was bone marrow (BM) in eight patients and G-CSF-mobilized peripheral blood hematopoietic cells in 18 cases. A total of 32 patients engrafted very quickly and the chimerism evaluation (both on myeloid and on lymphoid subsets) showed that they were full donor by day 60. At the time of the study they were in complete hematological remission and displayed a full donor hematopoiesis. Two patients showed early disease progression while one did not engraft. Forty-eight out-marrow samples harvested from the 26 patients generated a marrow stromal layer adequate for the chimerism evaluation. Monocyte-macrophage contamination of marrow stromal layers was always reduced below 2% by repeated trypsinizations and treatment with the leucyl-leucine (leu-leu) methyl ester. The chimerism evaluation was performed by PCR analysis of STRs microsatellites and the amelogenin locus, by using capillary electrophoresis (CE) and by FISH analysis in case of the sex mismatch. In eight patients, a partial donor origin of stromal cells was shown (7-86% cells of donor). The source of hematopoietic cells was BM in three patients and mobilized peripheral blood in the other five.

Erythropoietin-independent erythroid colony formation by bone marrow progenitors exposed to interleukin-11 and interleukin-8

OBJECTIVE

Endogenous erythroid colonies (EECs), formed in vitro without erythropoietin (EPo) or other exogenous cytokines, are characteristic of Polycythemia vera (PV). Our aim was to identify specific conditions of culture of bone marrow (BM) progenitors allowing formation of erythroid colonies without EPo.

METHODS

BM mononuclear cells (BMMCs), purified CD34+ cells, and purified CD36+ erythroid progenitors were cultured in serum-free media without and with cytokines: EPo, stem cell factor (SCF), and interleukin (IL)-11 and IL-8, produced by BM stromal cells and found elevated in PV.

RESULTS

EECs were formed in PV cultures of either BMMCs or CD34+ cells, which include cytokine-secreting cells, but not in cultures of purified CD36+ erythroid progenitors (EP). Despite expression of V617F JAK-2, no constitutive activation of JAK-2, Stat-5, or Erk-1/2 was detected in erythroblasts issued from PV CD36+ progenitors. However, when SCF was provided, PV CD36+ progenitors formed erythroid colonies without EPo. The ability to form erythroid colonies with SCF alone was conferred to BM progenitors of healthy donors and secondary erythrocytosis by exposure to IL-11 and IL-8. Both IL-11 and IL-8 enhanced formation of erythroid colonies in response to EPo and interfered with the activation of Erk-1/2 and Stat-5 induced, respectively, by SCF and EPo in erythroblasts. Anti-IL-11 antibody inhibited formation of erythroid colonies by PV BMMCs and CD34+ cells.

CONCLUSION

The data indicate that PV erythroid progenitors remain cytokine-dependent and that normal BM progenitors exposed to IL-11 and IL-8 can acquire the ability to form erythroid colonies without EPo.

Transplantation of human acute myeloid leukemia (AML) cells in immunodeficient mice reveals altered cell surface phenotypes and expression of human endothelial markers

To better characterize acute myeloid leukemia (AML) development in non-obese diabetic (NOD)/severe combined immunodeficiency (SCID) mice, we transplanted samples from patients with AML or KG-1 and EOL-1 cell lines. We found 9/12 primary AML samples and both cell lines to engraft within 2-8 weeks, with 5-80% human cells in bone marrow. Compared with freshly isolated AML cells, percentages of human CD33+, CD38+, CD31+ CD13+ or CD15+ subpopulations increased after transplantation, whereas percentages of CD34+ cells decreased. Engrafted mice frequently showed expression of human endothelial cell markers. Thus, transplantation of human AML into NOD/SCID mice reveals expression of hematopoietic and endothelial differentiation markers.

Replacement of recipient stromal/mesenchymal cells after bone marrow transplantation using bone fragments and cultured osteoblast-like cells

Abstract We present our experience on treatment of three children with potentially fatal diseases using a unique protocol for non-myeloablative bone marrow transplantation. The protocol was designed to promote engraftment of bone marrow stromal/mesenchymal cells (SC/MSCs) based on the knowledge from preclinical models over the last three decades. Accordingly, our protocol is the first to test the use of bone fragments as an ideal vehicle to transplant such cells residing in the bone core. Because of the paucity of knowledge for optimum transplantation of SC/MSCs in humans, we used a multifaceted approach and implanted bone fragments both intraperitoneally and directly into bone on day 0 of BMT. We also infused cultured donor osteoblast-like cells intravenously post-BMT. We were able to achieve high levels of stroma cell engraftment as defined by molecular analyses of bone biopsy specimens.

Cell therapy for bone disease: a review of current status

Bone marrow is a reservoir of pluripotent stem/progenitor cells for mesenchymal tissues. Upon in vitro expansion, in vivo bone-forming efficiency of bone marrow stromal cells (BMSCs) is dramatically lower in comparison with fresh bone marrow, and their in vitro multidifferentiation potentials are gradually lost. Nevertheless, when BMSCs are isolated and expanded in the presence of fibroblast growth factor 2, the percentage of cells able to differentiate into the osteogenic, chondrogenic, and adipogenic lineages is greater. Osteogenic progenitors are not exclusive to skeletal tissues. We could also think of cells in different adult tissues as potentially capable of following an osteochondrogenic differentiation pathway, but, under normal physiological conditions, they are inhibited in this process by the environment and/or the adjacent cell populations. When, for some reason such as pathology, the environment changes dramatically and the inhibiting condition is removed, these cells could become osteoblasts. Bone is repaired via local delivery of cells within a scaffold. Bone formation was first assessed in small animal models. Large animal models were successively developed to prove the feasibility of the tissue engineering approach in a model closer to a real clinical situation. Eventually, pilot clinical studies were performed. Extremely appealing is the possibility of using mesenchymal progenitors in the therapy of genetic bone diseases via systemic infusion. There is experimental evidence to suggest that mesenchymal progenitors delivered by this route engraft with a very low efficiency and do not produce relevant and durable clinical effects. Under some conditions, where the local microenvironment is either altered (i.e., injury) or under important remodeling processes (i.e., fetal growth), engraftment of stem and progenitor cells seems to be enhanced. A better understanding of their engraftment mechanisms will, hopefully, extend the field of therapeutic applications of mesenchymal progenitors.

Interleukin-3 promotes proliferation and differentiation of human hematopoietic stem cells but reduces their repopulation potential in NOD/SCID mice

In the present study we explored systematically the influence of human interleukin-3 (IL-3) on the cord blood (CB) cell-derived production of human hematopoietic cells in the bone marrow, blood, and spleen of chimeric nonobese/severe combined immunodeficient mice ((NOD/SCID) mice. CB mononuclear cells and MACS-enriched CB CD34(+) cells were injected into irradiated NOD/SCID mice. The mice were additionally transplanted with a stably transfected rat fibroblast cell line expressing the human IL-3 gene (Rat-IL-3) constitutively, or with the nontransfected rat fibroblast cell line as a control (Rat-1). Rat-IL-3 mice displayed a higher engraftment of human hematopoietic cells in bone marrow, spleen, and peripheral blood compared with mice with Rat-1 cotransplantation. When we transplanted their total bone marrow cell population into secondary mice, surprisingly, mice transplanted with bone marrow cells from Rat-1 mice displayed a higher proportion of human hematopoietic cells compared with Rat-IL-3 mice. As expected, bone marrow cultures (BMCs) from Rat-IL-3 mice contained a higher proportion of human cells than Rat-1 bone marrow cells. However, when BMCs were passaged to new flasks, we observed a higher proportion of human cells in BMCs from Rat-1 mice compared with BMCs from Rat-IL-3 mice. IL-3 promotes the proliferation and differentiation of hematopoietic stem cells in chimeric bone marrow. In addition, IL-3 may play a role in the depletion of hematopoietic stem cells in chimeric bone marrow. In the absence of IL-3, the hematopoietic stem cells may remain in a quiescent state and proliferation can be induced by stimuli, including secondary transplantation or cell passage.

Bone marrow origin of myofibroblasts in irradiation pulmonary fibrosis

There is a rapid onset of organizing alveolitis/fibrosis at 120-140 d after whole lung irradiation of C57BL/6J mice. To test the hypothesis that circulating cells of bone marrow origin contribute to irradiation fibrosis, irradiated chimeric green fluorescent protein (GFP)+ C57BL/6J mice were followed for GFP+ cells in areas of lung fibrosis. In a second experimental model, C57BL/6J female mice received 20 Gy total lung irradiation, and after 60 or 80 d were intravenously injected with cells from a clonal GFP+ male bone marrow stromal cell line or male GFP+ whole bone marrow, respectively. The mice were then followed for the development of pulmonary fibrosis, and the contribution of Y-probe-positive, GFP+ cells to fibrotic areas was quantitated. Bromodeoxyuridine labeling of developing fibrotic areas showed that the cell division occurred predominantly in GFP+, Y-probe-positive, and vimentin-positive cells. Immunohistochemistry demonstrated that these cells were macrophages and fibroblasts, not endothelial cells. Mice that received manganese superoxide dismutase-plasmid/liposome intratracheal injection 24 h before total lung irradiation demonstrated a decrease in GFP+ fibroblastic cells in the lung. Thus, pulmonary irradiation fibrosis contains proliferating cells of bone marrow origin, and gene therapy prevention of this condition acts in part by decreasing the migration and proliferation of marrow origin cells.

Sensitive PCR method for the detection and real-time quantification of human cells in xenotransplantation systems

The sensitive detection of human cells in immunodeficient rodents is a prerequisite for the monitoring of micrometastasis of solid tumours, dissemination of leukaemic cells, or engraftment of haematological cells. We developed a universally applicable polymerase chain reaction method for the detection of a human-specific 850-bp fragment of the alpha-satellite DNA on human chromosome 17. The method allows the detection of one human cell in 10(6) murine cells and could be established as both, a conventional DNA polymerase chain reaction-assay for routine screening, and a quantitative real-time polymerase chain reaction-assay using TaqMan-methodology. It was applied to the following xenotransplantation systems in SCID and NOD/SCID mice: (1) In a limiting dilution assay, cells of the MDA-MB 435 breast carcinoma were injected into the mammary fat pad of NOD/SCID mice. It could be shown that 10 cells mouse(-1) were sufficient to induce a positive polymerase chain reaction signal in liver and lung tissue 30 days after transplantation as an indicator for micrometastasis. At this time a palpable tumour was not yet detectable in the mammary fat pad region. (2) Cells of a newly established human acute lymphatic leukaemia were administered intraperitoneally to SCID mice. These cells apparently disseminated and were detectable as early as day 50 in the peripheral blood of living mice, while the leukaemia manifestation was delayed by day 140. (3) In a transplantation experiment using mature human lymphocytes we wanted to standardise conditions for a successful survival of these cells in NOD/SCID mice. It was established that at least 5 x 10(7) cells given intravenously were necessary and that the mice had to be conditioned by 2 Gy body irradiation to get positive polymerase chain reaction bands in several organs. (4) Engraftment studies with blood stem cells originating from cytapheresis samples of tumour patients or from cord blood were undertaken in NOD/SCID mice in order to define conditions of successful engraftment and to use this model for further optimisation strategies. The polymerase chain reaction method presented allowed a reliable prediction of positive engraftment and agreed well with the results of immunohistochemical or FACS analysis. All together, the polymerase chain reaction method developed allows a sensitive and reliable detection of low numbers of human cells in immunodeficient hosts. In combination with real-time (TaqMan) technique it allows an exact quantification of human cells. As this method can be performed with accessible material of living animals, follow up studies for the monitoring of therapeutic interventions are possible in which the survival time of mice as evaluation criteria can be omitted.

Human hematopoiesis in murine embryos after injecting human cord blood-derived hematopoietic stem cells into murine blastocysts

At different developmental stages, candidate human hematopoietic stem cells (HSCs) are present within the CD34+ CD38- population. By means of xenotransplantation, such CD34+CD38- cells were recently shown to engraft the hematopoietic system of fetal sheep and nonobese diabetic severe combined immunodeficient adult mice. Here it is demonstrated that, after their injection into murine blastocysts, human cord blood (CB)-derived CD34+ and CD34+ CD38- cells repopulate the hematopoietic tissues of nonimmunocompromised murine embryos and that human donor contribution can persist to adulthood. It is further observed that human hematopoietic progenitor cells are present in murine hematopoietic tissues of midgestational chimeric embryos and that progeny of the injected human HSCs activate erythroid-specific gene expression. Thus, the early murine embryo provides a suitable environment for the survival and differentiation of human CB CD34+ CD38- cells.

Bone marrow stromal damage after chemo/radiotherapy: occurrence, consequences and possibilities of treatment

High dose chemotherapy (CT) followed by bone marrow transplant (BMT) is increasingly used for the treatment of both hematological and solid neoplasms, but an understanding of its late consequences on the marrow microenvironment is still only at its beginning. It is in fact known that marrow stroma is damaged by high-dose cytotoxic therapy and by radiation exposure. However little is known on the extent of this damage and on the self-repair ability of the stroma. The damage of the stromal microenvironment affects the long-term stem cell engraftment and the maintenance of hemopoietic functions. Furthermore, marrow stroma also represents a progenitor compartment for endosteal osteoblasts, and therefore its damage implies alterations of bone metabolism. Indeed, osteoporosis has recently been recognized as a consequence, of BMT, but only a few studies have been performed to establish the functional status of the stromal compartment after treatment with cytotoxic drugs with or without total body irradiation (TBI) and its role in post-BMT sequelae.

Interest of cord blood stem cells

Interest in cord blood stem cells was raised because of the possibility, now realised, of their use in clinical transplantation. The availability of only limited numbers of stem cells in cord blood compared to bone marrow or peripheral blood apheresis after cell mobilisation, led to experimental approaches that first aimed to characterise and then manipulate the stem cells present in cord blood. Their phenotypical and functional characteristics are not identical to those of stem cells in the bone marrow or those cells mobilised into the circulation. The cells selected for phenotype plus Go status show the higher capacity to generate progenitor cells in vitro and will offer the opportunity for mechanistic studies of stem cell self-renewal and proliferation. Another important field of exploration is to investigate the capacity of stem cells in cord blood for differentiation to tissues other than haemopoietic and to establish whether haemopoietic and non-haemopoietic lineages originate in truly multipotential cells or in cells coexisting in cord blood, which have already been limited to differentiation into specific tissue.