Monocytes are the likely candidate 'stromal' cell in G-CSF-mobilized peripheral blood

Vascular and perivascular niches, but not the osteoblastic niche, are numerically restored following allogeneic hematopoietic stem cell transplantation in patients with aplastic anemia

Bone marrow (BM) niches, including the osteoblastic, vascular, and perivascular niches, are numerically impaired in patients with aplastic anemia (AA). It remains unclear whether these niches are numerically restored in AA patients after allogenic hematopoietic stem cell transplantation (allo-HSCT). To investigate changes in BM niches, we monitored 52 patients with AA who had undergone allo-HSCT and performed immunohistochemical studies of BM niches using antibodies against CD34, CD146, and osteopontin. After allo-HSCT, patients with AA exhibited a remarkable increase in the number of cellular elements in the BM niches, including the vascular and perivascular cells. However, no significant differences in endosteal cells were detected. We explored the cause of this restoration by analyzing the origin of BM mesenchymal stem cells (BM-MSCs) and the expression of cytokines in BM plasma. STR-PCR revealed that the BM-MSCs were derived from the host, not the donor. In addition, significantly elevated levels of vascular endothelial growth factor (VEGF) were found after allo-HSCT. Our data indicates that vascular and perivascular niches are numerically restored, but the endosteal niche remains numerically impaired in patients with AA after allo-HSCT, and that levels of VEGF, but not donor-derived BM-MSCs, may correlate with the restoration of BM niches.

Recent advances into the understanding of mesenchymal stem cell trafficking

The use of adult stem cells to regenerate damaged tissue circumvents the moral and technical issues associated with the use of those from an embryonic source. Mesenchymal stem cells (MSC) can be isolated from a variety of tissues, most commonly from the bone marrow, and, although they represent a very small percentage of these cells, are easily expandable. Recently, the use of MSC has provided clinical benefit to patients with osteogenesis imperfecta, graft-versus-host disease and myocardial infarction. The cellular cues that enabled the MSC to be directed to the sites of tissue damage and the mechanisms by which MSC then exert their therapeutic effect are becoming clearer. This review discusses the relative therapeutic importance of the ability of MSC to differentiate into multiple cell lineages or stimulate resident or attracted cells via a paracrine mode of action. It also reviews recent findings that MSC home to damaged tissues in a similar, but somewhat distinct, manner to that of leucocytes via the utilisation of adhesion molecules, such as selectins and integrins, and chemokines and their receptors in a manner reminiscent of leucocytes trafficking from the blood stream to inflammatory sites.

Mobilization of bone marrow-derived progenitors

Bone marrow (BM) is a source of various stem and progenitor cells in the adult, and it is able to regenerate a variety of tissues following transplantation. In the 1970s the first BM stem cells identified were hematopoietic stem cells (HSCs). HSCs have the potential to differentiate into all myeloid (including erythroid) and lymphoid cell lineages in vitro and reconstitute the entire hematopoietic and immune systems following transplantation in vivo. More recently, nonhematopoietic stem and progenitor cells have been identified that can differentiate into other cell types such as endothelial progenitor cells (EPCs), contributing to the neovascularization of tumors as well as ischemic tissues, and mesenchymal stem cells (MSCs), which are able to differentiate into many cells of ectodermal, endodermal, and mesodermal origins in vitro as well as in vivo. Following adequate stimulation, stem and progenitor cells can be forced out of the BM to circulate into the peripheral blood, a phenomenon called "mobilization." This chapter reviews the molecular mechanisms behind mobilization and how these have led to the various strategies employed to mobilize BM-derived stem and progenitor cells in experimental and clinical settings. Mobilization of HSCs will be reviewed first, as it has been best-explored--being used extensively in clinics to transplant large numbers of HSCs to rescue cancer patients requiring hematopoietic reconstitution--and provides a paradigm that can be generalized to the mobilization of other types of BM-derived stem and progenitor cells in order to repair other tissues.

Mesenchymal stem cells in stem cell transplant recipients are damaged and remain of host origin

The aim of this study was to investigate the expansion capacity and origin of bone marrow-derived mesenchymal stem cells (MSCs) in 34 patients who received a sex-mismatched stem cell transplant (SCT). Polymerase chain reaction (PCR) analysis of the amelogenin gene (AMEL) was used to detect donor-derived MSCs. Cultured MSCs were hybridized with fluorescence in situ hybridization (FISH) probes for chromosomes X and Y to distinguish cells of donor origin from those of host origin. The MSCs of 31 of the 34 patients showed confluent stroma, and the MSCs from 24 of these 31 patients were successfully passaged more than 5 times and were able to be used for PCR and FISH analyses. The colony-forming unit-fibroblast, confluence time, and passage numbers of the MSCs and the colony-forming capacity of the hematopoietic progenitor cells of the patients were significantly different from those of 30 healthy control subjects. Flow cytometry results showed that the proportion of CD14(+)CD45(+) cells, which are regarded as monocytes/macrophages, in cultured MSCs (fifth passage) was less than 0.04%. PCR and FISH analyses revealed that the MSC-derived cells in all 24 patients were from the host. In conclusion, the expansion capacity of MSCs in patients who receive an SCT is damaged, and the MSCs originate from the host.

G-CSF-primed hematopoietic stem cells or G-CSF per se accelerate recovery and improve survival after liver injury, predominantly by promoting endogenous repair programs

OBJECTIVE

On the basis of the recently recognized potential of bone marrow (BM) cells to give rise to hepatocytes, we investigated the possibility that granulocyte colony-stimulating factor (G-CSF)-mobilized BM cells could home to the injured liver and promote tissue repair. We also examined the origin of cells (endogenous or BM) reconstituting liver after damage.

METHODS

Acute and chronic liver injury models were generated by injecting CCl4 in C57Bl6 mice and G-CSF was administered in hematopoietic stem cell (HSC) mobilization doses. After sex-mismatched BM transplantation into lethally irradiated recipients and treatment with CCl4 +/- G-CSF, sry (sex-determining region for Y chromosome) protein was detected by immunohistochemistry in liver sections. Double immunohistochemistry for sry and ki-67 protein was used to define the origin of proliferating cells reconstituting liver after injury.

RESULTS

In both acute and chronic liver injury model, G-CSF administration ameliorated the histological damage and accelerated the regeneration process. This was accompanied by a strong survival benefit in G-CSF-treated group vs CCl4 group. Quantitative analysis showed higher percentage of BM-origin hepatocytes in the CCl4+G-CSF group compared with the CCl4 group, although the liver engraftment rate still remained rather low. Double staining for ki-67 and sry demonstrated that the recovery acceleration after chemical injury and G-CSF treatment was mainly mediated by increased proliferation of host hepatocytes (ki-67(+)/sry(-)) with less support from BM-origin cells (ki-67(+)/sry(+)).

CONCLUSION

G-CSF treatment significantly improved survival and liver histology in chemically injured mice, predominantly by promoting endogenous repair mechanisms. Therefore, mobilization with G-CSF might offer a novel therapeutic approach for the treatment of acute and chronic liver diseases in humans.

Stem cell therapy of the liver--fusion or fiction?

Various stem cell populations have been described in distinct models of liver regeneration. This review provides an overview of these different stem cell populations aimed at unifying diverse views of liver stem cell biology. Embryonic stem cells, hemopoietic stem cells, mesenchymal stem cells, liver-derived hepatic stem cells, bone marrow-derived hepatic stem cells, and mature hepatocytes (as cells with stemlike properties) are considered separately. In so doing, we seek to clarify the nomenclature of putative liver stem cell types. Experiments that address the question of cellular fusion versus transdifferentiation as explanations for observed liver regeneration are highlighted. This review concludes with a series of open questions that should be addressed in the context of clinical liver disease before attempts at human therapeutic interventions.

Limited engraftment capacity of bone marrow–derived mesenchymal cells following T-cell–depleted hematopoietic stem cell transplantation

The engraftment capacity of bone marrow–derived mesenchymal cells was investigated in 41 patients who had received a sex-mismatched, T-cell–depleted allograft from human leukocyte antigen (HLA)–matched or –mismatched family donors. Polymerase chain reaction (PCR) analysis of the human androgen receptor (HUMARA) or the amelogenin genes was used to detect donor-derived mesenchymal cells. Only 14 marrow samples (34%) from 41 consenting patients generated a marrow stromal layer adequate for PCR analysis. Monocyte-macrophage contamination of marrow stromal layers was reduced below the levels of sensitivity of HUMARA and amelogenin assays (5% and 3%, respectively) by repeated trypsinizations and treatment with the leucyl-leucine (leu-leu) methyl ester. Patients who received allografts from 12 female donors were analyzed by means of the HUMARA assay, and in 5 of 12 cases a partial female origin of stromal cells was demonstrated. Two patients who received allografts from male donors were analyzed by amplifying the amelogenin gene, and in both cases a partial male origin of stromal cells was shown. Fluorescent in situ hybridization analysis using a Y probe confirmed the results of PCR analysis and demonstrated in 2 cases the existence of a mixed chimerism at the stromal cell level. There was no statistical difference detected between the dose of fibroblast progenitors (colony-forming unit–F [CFU-F]) infused to patients with donor- or host-derived stromal cells (1.18 ± 0.13 × 104/kg vs 1.19 ± 0.19 × 104/kg; P ≥ .97). In conclusion, marrow stromal progenitors reinfused in patients receiving a T-cell–depleted allograft have a limited capacity of reconstituting marrow mesenchymal cells.

Limited engraftment capacity of bone marrow–derived mesenchymal cells following T-cell–depleted hematopoietic stem cell transplantation

The engraftment capacity of bone marrow–derived mesenchymal cells was investigated in 41 patients who had received a sex-mismatched, T-cell–depleted allograft from human leukocyte antigen (HLA)–matched or –mismatched family donors. Polymerase chain reaction (PCR) analysis of the human androgen receptor (HUMARA) or the amelogenin genes was used to detect donor-derived mesenchymal cells. Only 14 marrow samples (34%) from 41 consenting patients generated a marrow stromal layer adequate for PCR analysis. Monocyte-macrophage contamination of marrow stromal layers was reduced below the levels of sensitivity of HUMARA and amelogenin assays (5% and 3%, respectively) by repeated trypsinizations and treatment with the leucyl-leucine (leu-leu) methyl ester. Patients who received allografts from 12 female donors were analyzed by means of the HUMARA assay, and in 5 of 12 cases a partial female origin of stromal cells was demonstrated. Two patients who received allografts from male donors were analyzed by amplifying the amelogenin gene, and in both cases a partial male origin of stromal cells was shown. Fluorescent in situ hybridization analysis using a Y probe confirmed the results of PCR analysis and demonstrated in 2 cases the existence of a mixed chimerism at the stromal cell level. There was no statistical difference detected between the dose of fibroblast progenitors (colony-forming unit–F [CFU-F]) infused to patients with donor- or host-derived stromal cells (1.18 ± 0.13 × 104/kg vs 1.19 ± 0.19 × 104/kg; P ≥ .97). In conclusion, marrow stromal progenitors reinfused in patients receiving a T-cell–depleted allograft have a limited capacity of reconstituting marrow mesenchymal cells.