Mesenchymal stem cells are of recipient origin in pediatric transplantations using umbilical cord blood, peripheral blood, or bone marrow

The cellular composition and function of the bone marrow niche after allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (HCT) is a potentially curative therapy for patients with a variety of malignant and non-malignant diseases. Despite its life-saving potential, HCT is associated with significant morbidity and mortality. Reciprocal interactions between hematopoietic stem cells (HSCs) and their surrounding bone marrow (BM) niche regulate HSC function during homeostatic hematopoiesis as well as regeneration. However, current pre-HCT conditioning regimens, which consist of high-dose chemotherapy and/or irradiation, cause substantial short- and long-term toxicity to the BM niche. This damage may negatively affect HSC function, impair hematopoietic regeneration after HCT and predispose to HCT-related morbidity and mortality. In this review, we summarize current knowledge on the cellular composition of the human BM niche after HCT. We describe how pre-HCT conditioning affects the cell types in the niche, including endothelial cells, mesenchymal stromal cells, osteoblasts, adipocytes, and neurons. Finally, we discuss therapeutic strategies to prevent or repair conditioning-induced niche damage, which may promote hematopoietic recovery and improve HCT outcome.

Analysis of Mesenchymal Stromal Cell Engraftment After Allogeneic HSCT in Pediatric Patients: A Large Multicenter Study

The mesenchymal stem cell (MSC) role after allogeneic hematopoietic stem cell transplantation (HSCT) is still a matter of debate; in particular, MSC engraftment in recipient bone marrow (BM) is unclear. A total of 46 patients were analyzed for MSC and hemopoietic stem cell engraftment after HSCT. The majority of patients had the BM as the stem cell source, and acute leukemia was the main indication for HSCT. Mesenchymal and hematopoietic stem cell chimerism analysis was carried out through specific polymorphic tandemly repeated regions. All patients reached complete donor engraftment; no evidence of donor-derived MSC engraftment was noted. Our data indicate that MSCs after HSCT remain of recipient origin despite the following: (i) myeloablative conditioning; (ii) the stem cell source; (iii) the interval from HSCT to BM analysis; (iv) the underlying disease before HSCT; and (v) the patients' or the donors' age at HSCT.

Autologous Stem Cell Rescue for Graft Failure of Second Allogeneic Stem Cell Transplant After Engraftment of Primary Allogeneic Transplant

Here, we describe a case of primary graft failure with severe sepsis in a boy who experienced frequent relapses of osteosarcoma. The patient had undergone haploidentical bone marrow transplant after engraftment of unrelated cord blood transplant performed 10 months earlier. Considering his severe condition, we transfused autologous peripheral stem cells along with a single dose of etoposide (50 mg/m2). Granulocyte engraftment was confirmed on human leukocyte antigen-microsatellite analysis of bone marrow on day 14. Although the patient died due to respiratory failure, transfusion of autologous hematopoietic stem cells is a reasonable rescue option for graft failure even in patients whose background hematopoiesis is reconstituted by a first donor.

Hematopoietic-to-mesenchymal transition of adipose tissue macrophages is regulated by integrin β1 and fabricated fibrin matrices

Some bona fide adult adipocytes arise de novo from a bone marrow-derived myeloid lineage. These studies further demonstrate that adipose tissue stroma contains a resident population of myeloid cells capable of adipocyte and multilineage mesenchymal differentiation. These resident myeloid cells lack hematopoietic markers and express mesenchymal and progenitor cell markers. Because bone marrow mesenchymal progenitor cells have not been shown to enter the circulation, we hypothesized that myeloid cells acquire mesenchymal differentiation capacity in adipose tissue. We fabricated a 3-dimensional fibrin matrix culture system to define the adipose differentiation potential of adipose tissue-resident myeloid subpopulations, including macrophages, granulocytes and dendritic cells. Our data show that multilineage mesenchymal potential was limited to adipose tissue macrophages, characterized by the acquisition of adipocyte, osteoblast, chondrocyte and skeletal muscle myocyte phenotypes. Fibrin hydrogel matrices stimulated macrophage loss of hematopoietic cell lineage determinants and the expression of mesenchymal and progenitor cell markers, including integrin β1. Ablation of integrin β1 in macrophages inhibited adipocyte specification. Therefore, some bona fide adipocytes are specifically derived from adipose tissue-resident macrophages via an integrin β1-dependent hematopoietic-to-mesenchymal transition, whereby they become capable of multipotent mesenchymal differentiation. The requirement for integrin β1 highlights this molecule as a potential target for controlling the production of marrow-derived adipocytes and their contribution to adipose tissue development and function.

Dopamine mobilizes mesenchymal progenitor cells through D2-class receptors and their PI3K/AKT pathway

As the nervous system exerts direct and indirect effects on stem cells mobilization and catecholamines mobilize hematopoietic stem cells, we hypothesized that dopamine might induce mesenchymal progenitor cells (MPCs) mobilization. We show that dopamine induced in vitro MPCs migration through D2-class receptors, and their alternative phosphoinositide 3-kinase/Akt pathways. Also, administration of catecholamines induced in vivo mobilization of colony-forming unit-fibroblast in mice. In contrast, in vitro and in vivo MPCs migration was suppressed by D2-class receptors antagonists and blocking antibodies, consistent with dopamine signaling pathway implication. In humans, patients treated with L-dopa or catecholaminergic agonists showed a significant increase of a MPC-like population (CD45-CD31-CD34-CD105+) in their peripheral blood. These findings reveal a new link between catecholamines and MPCs mobilization and suggest the potential use of D2-class receptors agonists for mobilization of MPCs in clinical settings.

Ex Vivo Expanded Allogeneic Mesenchymal Stem Cells with Bone Marrow Transplantation Improved Osteogenesis in Infants with Severe Hypophosphatasia

Patients with severe hypophosphatasia (HPP) develop osteogenic impairment with extremely low alkaline phosphatase (ALP) activity, resulting in a fatal course during infancy. Mesenchymal stem cells (MSCs) differentiate into various mesenchymal lineages, including bone and cartilage. The efficacy of allogeneic hematopoietic stem cell transplantation for congenital skeletal and storage disorders is limited, and therefore we focused on MSCs for the treatment of HPP. To determine the effect of MSCs on osteogenesis, we performed multiple infusions of ex vivo expanded allogeneic MSCs for two patients with severe HPP who had undergone bone marrow transplantation (BMT) from asymptomatic relatives harboring the heterozygous mutation. There were improvements in not only bone mineralization but also muscle mass, respiratory function, and mental development, resulting in the patients being alive at the age of 3. After the infusion of MSCs, chimerism analysis of the mesenchymal cell fraction isolated from bone marrow in the patients demonstrated that donor-derived DNA sequences existed. Adverse events of BMT were tolerated, whereas those of MSC infusion did not occur. However, restoration of ALP activity was limited, and normal bony architecture could not be achieved. Our data suggest that multiple MSC infusions, following BMT, were effective and brought about clinical benefits for patients with lethal HPP. Allogeneic MSC-based therapy would be useful for patients with other congenital bone diseases and tissue disorders if the curative strategy to restore clinically normal features, including bony architecture, can be established.

Functional mesenchymal stem cells remain present in bone marrow microenvironment of patients with leukemia post-allogeneic hematopoietic stem cell transplant

Mesenchymal stem cells (MSCs) and their progenies are important supporting cells in the bone marrow (BM) microenvironment. However, the function and kinetics of MSCs post-hematopoietic stem cell transplant (HSCT) remain unknown. In the present study, MSCs were cultured from a total of 76 BM samples from 15 patients receiving HSCT. Colony-forming unit fibroblasts in BM before pre-conditioning and 1, 3, 6 and 9 months post-HSCT were cultured and counted to quantify MSCs. Hematopoiesis-supporting activity of MSCs was observed with long-term culture of hematopoietic progenitors. An inhibitory effect of MSCs on in vitro lymphocyte proliferation was also observed. Results showed that post-HSCT MSCs supported in vitro hematopoiesis and inhibited lymphocyte growth. Moreover, the quantity of MSCs was reduced at an early stage and restored to baseline level 9 months post-transplant. The results indicate that functional MSCs remain present in the BM microenvironment, and these findings shed light on the understanding of BM microenvironment reconstitution post-HSCT.

Chimerism of bone marrow mesenchymal stem/stromal cells in allogeneic hematopoietic cell transplantation: is it clinically relevant?

Multipotent mesenchymal stem/stromal cells (MSCs) have been extensively used as a transplantable cell source for regenerative medicine and immunomodulatory therapy. Specifically in allogeneic hematopoietic stem cell transplantation (HSCT), co-transplantation or post-transplant infusion of MSCs derived from bone marrow (BM) of non-self donors has been implicated in accelerating hematopoietic recovery, ameliorating graft-vs.-host disease, and promoting tissue regeneration. However, irrespective of the use of MSC co-administration, post-transplant chimerism of BM-derived MSCs after allogeneic HSCT has been reported to remain of host origin, suggesting that the infused donor MSCs are immunologically rejected or not capable of long-term engraftment in the host microenvironment. Also, hematopoietic cell allografts currently used for HSCT do not seem to contain sufficient amount of MSCs or their precursors to reconstitute host BM microenvironment. Since the toxic conditioning employed in allo-HSCT may impair the function of host MSCs to maintain hematopoietic/regenerative stem cell niches and to provide a local immunomodulatory milieu, we propose that new directions for enhancing immunohematopoietic reconstitution and tissue repair after allogeneic HSCT include the development of strategies to support functional replenishment of residual host MSCs or to support more efficient engraftment of infused donor MSCs. Future areas of research should include in vivo tracking of infused MSCs and detection of their microchimeric presence in extra-marrow sites as well as in BM.

Alveolar bone regeneration around immediate implants using an injectable nHAC/CSH loaded with autogenic blood-acquired mesenchymal progenitor cells: an experimental study in the dog mandible

BACKGROUND

Lack of osseointegration between a dental implant and the walls of the alveolar bone is a common problem in immediate implantation. Injectable tissue-engineered bone (ITB) may be an effective and minimally invasive solution to the problem. In this study, an injectable bone cement, nHAC/CSH, which consists of nano-hydroxyapatite/collagen (nHAC) and calcium sulfate hemihydrate (CaSO4 .½H2 O; CSH) was investigated as a tissue-engineered scaffold material with blood-acquired mesenchymal progenitor cells (BMPC) as seeding cells.

PURPOSE

The aim of the study was to assess the new bone formation around immediate dental implants using nHAC/CSH loaded with dog blood-acquired mesenchymal progenitor cells (dBMPC) in a canine model.

MATERIALS AND METHODS

dBMPC were first isolated from peripheral blood of healthy adult dogs. Alizarin red and oil red O staining were then used to evaluate the potential of dBMPC to differentiate into bi-lineage mesenchymal tissues in vitro. Four healthy mongrel dogs were used in this study. The alveolar bone defects around immediate implants of dogs were created. Each defect was randomly assigned to one of the following three groups: (1) the ITB group (dBMPC+nHAC/CSH); (2) injectable bone cement nHAC/CSH; or (3) no materials (controls). Methylene blue staining was used to examine the bone formation after 3 months.

RESULTS

Studies in vitro revealed that dBMPC could be induced to osteoblasts and adipocytes. The ITB group (dBMPC+nHAC/CSH) showed significantly more bone-implant contact and bone density than either nHAC/CSH or control groups in the areas with peri-implant defects 3 months after implantation.

CONCLUSION

The results indicate that the ITB composed of nHAC/CSH and dBMPC may represent a useful strategy for the clinical reconstruction of bone defects around immediate implantation. However, further investigation is needed involving the use of human BMPC as well as possible use of stem cells.

Insights into the cellular origin and etiology of the infant pro-B acute lymphoblastic leukemia with MLL-AF4 rearrangement

Infant acute lymphoblastic leukemia (ALL) involving mixed-lineage leukemia (MLL) fusions has attracted a huge interest in basic and clinical research because of its prenatal origin, mixed-lineage phenotype, dismal prognosis and extremely short latency. Over 90% of infant ALLs are pro-B ALL harboring the leukemic fusion MLL-AF4. Despite the fact that major achievements have provided a better understanding about the etiology of infant MLL-AF4+ ALL over the last two decades, key questions remain unanswered. Epidemiological and genetic studies suggest that the in utero origin of MLL rearrangements in infant leukemia may be the result of prenatal exposure to genotoxic compounds. In fact, chronic exposure of human embryonic stem cells (hESCs) to etoposide induces MLL rearrangements and makes hESC more prone to acquire subsequent chromosomal abnormalities than postnatal CD34(+) cells, linking embryonic exposure to topoisomerase II inhibitors to genomic instability and MLL rearrangements. Unfortunately, very little is known about the nature of the target cell for transformation. Neuron-glial antigen 2 expression was initially claimed to be specifically associated with MLL rearrangements and was recently shown to be readily expressed in CD34+CD38+, but not CD34+CD38- cells suggesting that progenitors rather than stem cells may be the target cell for transformation. Importantly, the recent findings showing that MLL-AF4 rearrangement is present and expressed in mesenchymal stem cells from infant patients with MLLAF4+ ALL challenged our current view of the etiology and cellular origin of this leukemia. It becomes therefore crucial to determine where the leukemia relapses come from and how the tumor-stroma relationship is defined at the molecular level. Finally, MLL-AF4 leukemogenesis has been particularly difficult to model and bona fide MLL-AF4 disease models do not exist so far. It is likely that the current disease models are missing some essential ingredients of leukemogenesis in the human embryo/fetus. We thus propose modeling MLL-AF4+ infant pro-B ALL using prenatal hESCs.

Intramarrow injection of beta-catenin-activated, but not naive mesenchymal stromal cells stimulates self-renewal of hematopoietic stem cells in bone marrow

Bone marrow mesenchymal stromal cells (MSCs) have been implicated in the microenvironmental support of hematopoietic stem cells (HSCs) and often co-transplanted with HSCs to facilitate recovery of ablated bone marrows. However, the precise effect of transplanted MSCs on HSC regeneration remains unclear because the kinetics of HSC self-renewal in vivo after co-transplantation has not been monitored. In this study, we examined the effects of intrafemoral injection of MSCs on HSC self-renewal in rigorous competitive repopulating unit (CRU) assays using congenic transplantation models in which stromal progenitors (CFU-F) were ablated by irradiation. Interestingly, naïve MSCs injected into femur contributed to the reconstitution of a stromal niche in the ablated bone marrows, but did not exert a stimulatory effect on the in-vivo self-renewal of co-transplanted HSCs regardless of the transplantation methods. In contrast, HSC self-renewal was four-fold higher in bone marrows intrafemorally injected with beta-catenin-activated MSCs. These results reveal that naive MSCs lack a stimulatory effect on HSC self-renewal in-vivo and that stroma must be activated during recoveries of bone marrows. Stromal targeting of wnt/beta-catenin signals may be a strategy to activate such a stem cell niche for efficient regeneration of bone marrow HSCs.

Treatment of metastatic neuroblastoma with systemic oncolytic virotherapy delivered by autologous mesenchymal stem cells: an exploratory study

Treatment of metastatic tumors with engineered adenoviruses that replicate selectively in tumor cells is a new therapeutic approach in cancer. Systemic administration of these oncolytic adenoviruses lack metastatic targeting ability. The tumor stroma engrafting property of intravenously injected mesenchymal stem cells (MSCs) may allow the use of MSCs as cellular vehicles for targeted delivery. In this work, we study the safety and the efficacy of infusing autologous MSCs infected with ICOVIR-5, a new oncolytic adenovirus, for treating metastatic neuroblastoma. Four children with metastatic neuroblastoma refractory to front-line therapies received several doses of autologous MSCs carrying ICOVIR-5, under an approved preliminary study. The tolerance to the treatment was excellent. A complete clinical response was documented in one case, and the child is in complete remission 3 years after this therapy. We postulate that MSCs can deliver oncolytic adenoviruses to metastatic tumors with very low systemic toxicity and with beneficial antitumor effects.

Cord blood--an alternative source for bone regeneration

Bone regeneration is one of the best investigated pathways in mesenchymal stromal cell (MSC) biology. Therefore strong efforts have been made to introduce tissue engineering and cell therapeutics as an alternative treatment option for patients with bone defects. This review of the literature gives an overview of MSC biology aiming for clinical application including advantages but also specific challenges and problems which are associated with cord blood derived stromal cell (CB-MSC) as a source for bone regeneration. The use of postnatal CB-MSC is ethically uncomplicated and requires no invasive harvesting procedure. Moreover, most data document a high osteogenic potential of CB-MCS and also low immunoreactivity compared with other MSC types. The expression profile of CB-MSC during osteogenic differentiation shows similarities to that of other MSC types. Within the umbilical cord different MSC types have been characterized which are potent to differentiate into osteoblasts. In contrast to a large number of in vitro investigations there are only few in vivo studies available so far.

Role of mesenchymal stem cells in regenerative medicine: application to bone and cartilage repair

BACKGROUND

Mesenchymal stem cells (MSC) are multipotent cells with the ability to differentiate into mesenchyme-derived cells including osteoblasts and chondrocytes.

OBJECTIVE

To provide an overview and expert opinion on the in vivo ability of MSC to home into tissues, their regenerative properties and potential applications for cell-based therapies to treat bone and cartilage disorders.

METHODS

Data sources including the PubMed database, abstract booklets and conference proceedings were searched for publications pertinent to MSC and their properties with emphasis on the in vivo studies and clinical use in cartilage and bone regeneration and repair. The search included the most current information possible.

CONCLUSION

MSC can migrate to injured tissues and some of their reparative properties are mediated by paracrine mechanisms including their immunomodulatory actions. MSC possess a critical potential in regenerative medicine for the treatment of skeletal diseases, such as osteoarthritis or fracture healing failure, where treatments are partially effective or palliative.

Biologic characteristics of mesenchymal stromal cells and their clinical applications in pediatric patients

In the past few years, intensive research in the understanding of the biologic characteristics of the mesenchymal stromal cells has already led to some early clinical applications. The aim of this review is to summarize the latest information from basic science advances and the outcome of their use in clinical practice with a particular focus in pediatric patients. The minimum criteria required to identify mesenchymal stromal cells, their immunosuppressive-nonimmunogenic properties and their attribution in the treatment of graft-versus-host disease, in the acceleration of hematopoietic recovery, in tissue repair/tissue engineering and in the treatment of selected inherited disorders are discussed. Appropriate preclinical models, completion of ongoing and development of new clinical trials will establish the role of these cells in the treatment of both adult and pediatric patients.