Clonal composition of human multipotent mesenchymal stromal cells

Stromal Lineage Precursors from Rodent Femur and Tibia Bone Marrows after Hindlimb Unloading: Functional Ex Vivo Analysis

Rodent hindlimb unloading (HU) model was developed to elucidate responses/mechanisms of adverse consequences of space weightlessness. Multipotent mesenchymal stromal cells (MMSCs) were isolated from rat femur and tibia bone marrows and examined ex vivo after 2 weeks of HU and subsequent 2 weeks of restoration of load (HU + RL). In both bones, decrease of fibroblast colony forming units (CFU-f) after HU with restoration after HU + RL detected. In CFU-f and MMSCs, levels of spontaneous/induced osteocommitment were similar. MMSCs from tibia initially had greater spontaneous mineralization of extracellular matrix but were less sensitive to osteoinduction. There was no recovery of initial levels of mineralization in MMSCs from both bones during HU + RL. After HU, most bone-related genes were downregulated in tibia or femur MMSCs. After HU + RL, the initial level of transcription was restored in femur, while downregulation persisted in tibia MMSCs. Therefore, HU provoked a decrease of osteogenic activity of BM stromal precursors at transcriptomic and functional levels. Despite unidirectionality of changes, the negative effects of HU were more pronounced in stromal precursors from distal limb-tibia. These observations appear to be on demand for elucidation of mechanisms of skeletal disorders in astronauts in prospect of long-term space missions.

Multipotent Mesenchymal Stromal Cells from Porcine Bone Marrow, Implanted under the Kidney Capsule, form an Ectopic Focus Containing Bone, Hematopoietic Stromal Microenvironment, and Muscles

Multipotent mesenchymal stromal cells (MSCs) are an object of intense investigation due to their therapeutic potential. MSCs have been well studied in vitro, while their fate after implantation in vivo has been poorly analyzed. We studied the properties of MSCs from the bone marrow (BM-MSC) before and after implantation under the renal capsule using a mini pig model. Autologous BM-MSCs were implanted under the kidney capsule. After 2.5 months, ectopic foci containing bones, foci of ectopic hematopoiesis, bone marrow stromal cells and muscle cells formed. Small pieces of the implant were cultivated as a whole. The cells that migrated out from these implants were cultured, cloned, analyzed and were proven to meet the most of criteria for MSCs, therefore, they are designated as MSCs from the implant-IM-MSCs. The IM-MSC population demonstrated high proliferative potential, similar to BM-MSCs. IM-MSC clones did not respond to adipogenic differentiation inductors: 33% of clones did not differentiate, and 67% differentiated toward an osteogenic lineage. The BM-MSCs revealed functional heterogeneity after implantation under the renal capsule. The BM-MSC population consists of mesenchymal precursor cells of various degrees of differentiation, including stem cells. These newly discovered properties of mini pig BM-MSCs reveal new possibilities in terms of their manipulation.

Hematopoiesis during Ontogenesis, Adult Life, and Aging

In the bone marrow of vertebrates, two types of stem cells coexist-hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs). Hematopoiesis only occurs when these two stem cell types and their descendants interact. The descendants of HSCs supply the body with all the mature blood cells, while MSCs give rise to stromal cells that form a niche for HSCs and regulate the process of hematopoiesis. The studies of hematopoiesis were initially based on morphological observations, later extended by the use of physiological methods, and were subsequently augmented by massive application of sophisticated molecular techniques. The combination of these methods produced a wealth of new data on the organization and functional features of hematopoiesis in the ontogenesis of mammals and humans. This review summarizes the current views on hematopoiesis in mice and humans, discusses the development of blood elements and hematopoiesis in the embryo, and describes how the hematopoietic system works in the adult organism and how it changes during aging.

Functional Characteristics of the Mouse Il1b Promoter in Various Tissues Before and After Irradiation

Interleukin-1 beta (IL1B) is a key inducer of inflammation and an important factor in the regulation of hematopoietic stem cells and mesenchymal stromal progenitors. Irradiation of mice with ionizing radiation has been shown to induce a lasting increase in IL1B concentration in peripheral blood. One of the possible mechanisms may be demethylation of CpG cytosines in the Il1b promoter, which has not been characterized in detail for the mouse. In this study, the methylation level of CpGs located in a region between -3562 and -208 bp upstream of the start of transcription is studied in muscles, bones, liver, thymus, spleen, bone marrow, lymph nodes, lungs, and brain. The methylation level is compared to Il1b expression. Tissue-specific features of CpG methylation are established. It is demonstrated that the region between -2420 and -2406 bp is likely a part of the mouse Il1b promoter/enhancer and may determine the base level of Il1b expression in various tissues. Irradiation at a dose of 6 Gy does not change the methylation profile of most studied CpGs, and therefore, the cause of the stably increased IL1B level after irradiation is unlikely to be a change in the methylation of the studied CpGs in investigated tissues.

Molecular Profiles of Cell-to-Cell Variation in the Regenerative Potential of Mesenchymal Stromal Cells

Cell-to-cell variation in the regenerative potential of mesenchymal stromal cells (MSCs) impedes the translation of MSC therapies into clinical practice. Cellular heterogeneity is ubiquitous across MSC cultures from different species and tissues. This review highlights advances to elucidate molecular profiles that identify cell subsets with specific regenerative properties in heterogeneous MSC cultures. Cell surface markers and global signatures are presented for proliferation and differentiation potential, as well as immunomodulation and trophic properties. Key knowledge gaps are discussed as potential areas of future research. Molecular profiles of MSC heterogeneity have the potential to enable unprecedented control over the regenerative potential of MSC therapies through the discovery of new molecular targets and as quality attributes to develop robust and reproducible biomanufacturing processes. These advances would have a positive impact on the nascent field of MSC therapeutics by accelerating the development of therapies with more consistent and effective treatment outcomes.

Clonal Composition of Human Multipotent Mesenchymal Stromal Cells: Application of Genetic Barcodes in Research

Clonal composition of human multipotent mesenchymal stromal cells (MMSCs) labeled with lentiviral vectors carrying genetic barcodes was studied. MMSCs were transduced with a cloned library of self-inactivating lentiviral vectors carrying 667 unique barcodes. At each cell culture passage, 120 cells were plated one cell per well in 96-well plates. The efficiency of cloning and labeling of the clonogenic cells was determined. DNA was extracted from the cell-derived colonies, and the barcodes were identified by Sanger sequencing. Also, DNA was extracted from the total MMSC population at each passage to analyze the diversity and representation of barcodes by deep sequencing using the Illumina platform. It was shown that the portion of MMSCs labeled with the lentiviral vectors remained stable in the passaged cells. Because of the high multiplicity of infection, the labeling procedure could decrease the proliferative potential of MMSCs. Identification of barcodes in individual cell clones confirmed the polyclonal character of the MMSC population. Clonal composition of MMSCs changed significantly with the passages due to the depletion of proliferative potential of most cells. Large clones were found at the first passage; at later passages, many small clones with a limited proliferative potential were detected in the population. The results of deep sequencing confirmed changes in the clonal composition of MMSCs. The polyclonal MMSC population contained only a small number of cells with a high proliferative potential, some of which could be stem cells. MMSCs with a high proliferative potential were detected more often in the earliest passages. In this regard, we would recommend to use MMSCs of early passages for regenerative medicine applications based on cell proliferation.

Alterations in multipotent mesenchymal stromal cells from the bone marrow of acute myeloid leukemia patients at diagnosis and during treatment

We analyzed multipotent mesenchymal stromal cells (MMSCs) from the bone marrow (BM) of 33 acute myeloid leukemia (AML) patients at diagnosis, after the first course of chemotherapy (day 37), and at days 100 and 180 after diagnosis. All patients were treated according to the AML 01.10 protocol. Cumulative production of MMSCs from AML patients at diagnosis was normal but increased during treatment. Most of the studied genes were upregulated at AML diagnosis, some (IL6, IL1B, LIF) remained upregulated during treatment, and others were downregulated (FGFR1, ICAM1) or normalized. A few genes were normal at diagnosis but decreased during treatment (FGF2, FGFR2, VEGF, SDF1, SOX9, TGFB1). The upregulation of proinflammatory genes both at diagnosis and during remission reflects ongoing inflammation. PDGFRB expression was upregulated in MMSCs from patients in relapse versus those in remission. The AML 01.10 protocol downregulates the expression of genes related to proliferation, differentiation and niche formation.

Investigation of the Mesenchymal Stem Cell Compartment by Means of a Lentiviral Barcode Library

The hematopoietic bone marrow microenvironment is formed by proliferation and differentiation of mesenchymal stem cells (MSCs). The MSC compartment has been less studied than the hematopoietic stem cell compartment. To characterize the structure of the MSC compartment, it is necessary to trace the fate of distinct mesenchymal cells. To do so, mesenchymal progenitors need to be marked at the single-cell level. A method for individual marking of normal and cancer stem cells based on genetic "barcodes" has been developed for the last 10 years. Such approach has not yet been applied to MSCs. The aim of this study was to evaluate the possibility of using such barcoding strategy to mark MSCs and their descendants, colony-forming units of fibroblasts (CFU-Fs). Adherent cell layers (ACLs) of murine long-term bone marrow cultures (LTBMCs) were transduced with a lentiviral library with barcodes consisting of 32 + 3 degenerate nucleotides. Infected ACLs were suspended, and CFU-F derived clones were obtained. DNA was isolated from each individual colony, and barcodes were analyzed in marked CFU-F-derived colonies by means of conventional polymerase chain reaction and Sanger sequencing. Barcodes were identified in 154 marked colonies. All barcodes appeared to be unique: there were no two distinct colonies bearing the same barcode. It was shown that ACLs included CFU-Fs with different proliferative potential. MSCs are located higher in the hierarchy of mesenchymal progenitors than CFU-Fs, so the presented data indicate that MSCs proliferate rarely in LTBMCs. A method of stable individual marking and comparing the markers in mesenchymal progenitor cells has been developed in this work. We show for the first time that a barcoded library of lentiviruses is an effective tool for studying stromal progenitor cells.

Alterations of the bone marrow stromal microenvironment in adult patients with acute myeloid and lymphoblastic leukemias before and after allogeneic hematopoietic stem cell transplantation

Bone marrow (BM) derived adult multipotent mesenchymal stromal cells (MMSCs) and fibroblast colony-forming units (CFU-Fs) of 20 patients with acute myeloid leukemia (AML) and 15 patients with acute lymphoblastic leukemia (ALL) before and during 1 year after receiving allogeneic hematopoietic stem cell transplantation (allo-HSCT) were studied. The growth characteristics of MMSCs of all patients before allo-HSCT were not altered; however, relative expression level (REL) of some genes in MMSCs, but not in CFU-Fs, from AML and ALL patients significantly changed. After allo-HSCT, CFU-F concentration and MMSC production were significantly decreased for 1 year; REL of several genes in MMSCs and CFU-F-derived colonies were also significantly downregulated. Thus, chemotherapy that was used for induction of remission did not impair the function of stromal precursors, but gene expression levels were altered. Allo-HSCT conditioning regimens significantly damaged MMSCs and CFU-Fs, and the effect lasted for at least 1 year.

Analysis of results of acute graft-versus-host disease prophylaxis with donor multipotent mesenchymal stromal cells in patients with hemoblastoses after allogeneic bone marrow transplantation

Allogeneic bone marrow transplantation (allo-BMT) is currently the only way to cure many hematoproliferative disorders. However, allo-BMT use is limited by severe complications, the foremost being graft-versus-host disease (GVHD). Due to the lack of efficiency of the existing methods of GVHD prophylaxis, new methods are being actively explored, including the use of donors' multipotent mesenchymal stromal cells (MMSC). In this work, we analyzed the results of acute GVHD (aGVHD) prophylaxis by means of MMSC injections after allo-BMT in patients with hematological malignancies. The study included 77 patients. They were randomized into two groups - those receiving standard prophylaxis of aGVHD and those who were additionally infused with MMSC derived from the bone marrow of hematopoietic stem cell donors. We found that the infusion of MMSC halves the incidence of aGVHD and increases the overall survival of patients. Four of 39 MMSC samples were ineffective for preventing aGVHD. Analysis of individual donor characteristics (gender, age, body mass index) and the MMSC properties of these donors (growth parameters, level of expression of 30 genes involved in proliferation, differentiation, and immunomodulation) revealed no significant difference between the MMSC that were effective or ineffective for preventing aGVHD. We used multiple logistic regression to establish a combination of features that characterize the most suitable MMSC samples for the prevention of aGVHD. A model predicting MMSC sample success for aGVHD prophylaxis was constructed. Significant model parameters were increased relative expression of the FGFR1 gene in combination with reduced expression levels of the PPARG and IGF1 genes. Depending on the chosen margin for probability of successful application of MMSC, this model correctly predicts the outcome of the use of MMSC in 82-94% of cases. The proposed model of prospective evaluation of the effectiveness of MMSC samples will enable prevention of the development of aGVHD in the maximal number of patients.

Analysis of multipotent mesenchymal stromal cells used for acute graft-versus-host disease prophylaxis

BACKGROUND

Multipotent mesenchymal stromal cells (MSCs) are used for prophylaxis of acute graft-versus-host disease (aGvHD) after allogeneic hematopoietic cell transplantation (allo-HCT). Not all samples of MSC are efficient for aGvHD prevention. The suitability of MSCs for aGvHD prophylaxis was studied.

METHODS

MSCs were derived from the bone marrow (BM) of HCT donor and cultivated for no more than three passages. The characteristics of donor BM samples including colony-forming unit fibroblast (CFU-F) concentration, growth parameters of MSCs, and the relative expression levels (REL) of different genes were analyzed. MSCs were injected intravenously precisely at the moment of blood cell reconstitution.

RESULTS

MSCs infusion induced a significant threefold decrease in aGvHD development and improved overall survival compared with the standard prophylaxis group. In ineffective MSC samples (9.4%), a significant decrease in total cell production and the REL of CSF1, FGFR1, and PDGFRB was observed. In all studied BM samples, the cumulative MSC production and CFU-F concentrations decreased with age. The expression levels of FGFR2, PPARG, and VEGF differed by age.

CONCLUSIONS

A universal single indicator for the prediction of MSC eligibility for aGvHD prophylaxis was not identified. A multiparameter mathematical model for selecting MSC samples effective for the prevention of aGvHD was proposed.

Interleukin-1 beta enhances human multipotent mesenchymal stromal cell proliferative potential and their ability to maintain hematopoietic precursor cells

Multipotent mesenchymal stromal cells (MMSCs) have been demonstrated to produce mature stromal cells and maintain hematopoietic progenitor cells (HPC). It was previously demonstrated that interleukin-1 beta (IL-1 beta) stimulates the growth of the stromal microenvironment in vivo. The aim of this study was to investigate the effect of IL-1 beta treatment of human MMSCs on their proliferative potential, gene expression, immunomodulating properties, and their ability to support HPCs in vitro. Human bone marrow-derived MMSCs were cultivated in standard conditions or with IL-1 beta. The cumulative cell production was assessed for five passages. After withdrawal of IL-1 beta, MMSC clonal efficiency was investigated, and the maintenance of HPCs on top of MMSCs layers was estimated using cobblestone area forming cell (CAFC) and long-term culture initiating cell (LTC-IC) assays. The effect of untreated MMSCs or MMSCs pretreated with IL-1 beta on lymphocyte proliferation was studied by CFSE staining. The relative expression level of various genes by MMSCs was analyzed using RT-qPCR. The administration of IL-1 beta elevated MMSCs clonal efficiency and total cell production but did not affect lymphocyte proliferation. MMSCs pretreatment with IL-1 beta enhanced their ability to maintain HPCs, as detected by CAFC assay, and it altered the expression levels of genes participating in HPC regulation by stromal cells, e.g., adhesion molecules (ICAM1) and growth factors (SDF1). This study revealed the ability of IL-1 beta to stimulate MMSCs proliferation and enhance their potential to maintain HPCs. MMSCs are considered a stromal niche component in vitro. The combined in vitro and previous in vivo data suggest that IL-1 beta is a systemic regulator of the stromal microenvironment.

The mesenchymal stromal cells dilemma--does a negative phase III trial of random donor mesenchymal stromal cells in steroid-resistant graft-versus-host disease represent a death knell or a bump in the road?

The use of cryopreserved unmatched allogeneic mesenchymal stromal cells (MSCs) for treatment of steroid-resistant graft-versus-host disease has become medical practice in many European jurisdictions. The enthusiasm for use of MSCs in transplantation medicine builds on compelling phase II clinical trial data published by European collaborative groups in the past few years. Notwithstanding, it was reported in 2009 that a large multicenter phase III clinical trial (NCT00366145) conducted in the USA examining the use of an industrial MSC product (Prochymal; Osiris Therapeutics, Inc., Columbia, MD, USA) failed to meet its primary clinical endpoint of achieving a significant increase of complete response of steroid-resistant graft-versus-host disease lasting at least 28 days compared with placebo. Although peer-reviewed publication of the trial and its results are not in public domain at the time of this writing, it is worthwhile to reflect on the apparent discrepancy between the European experience and this industry-sponsored phase III study. This review presents a heuristic failure analysis focusing on the potential variables affecting MSCs and their utility as a cellular pharmaceutical.