BMSC-derived extracellular vesicles intervened the pathogenic changes of scleroderma in mice through miRNAs

Abstract Background Systemic sclerosis (SSc) is a disease that features severe fibrosis of the skin and lacks effective therapy. Bone marrow mesenchymal stem cell (BMSC)-derived extracellular vesicles (EVs) are potential stem cell-based tools for the treatment of SSc. Methods BMSCs were isolated from the bone marrow of mice and identified with surface markers according to multilineage differentiation. EVs were isolated from the BMSC culture medium by ultracentrifugation and identified with a Nanosight NS300 particle size analyzer, transmission electron microscopy (TEM), and western blot. The microRNAs (miRNAs) of BMSC-derived EVs (BMSC-EVs) were studied via miRNA sequencing (miRNA-seq) and bioinformatic analysis. An SSc mouse model was established via subcutaneous bleomycin (BLM) injection, and the mice were treated with BMSCs or BMSC-derived EVs. Skin tissues were dissociated and analyzed with H&E staining, RNA sequencing (RNA-seq), western blot, and immunohistochemical staining. Results Evident pathological changes, like fibrosis and inflammation, were induced in the skin of BLM-treated mice. BMSCs and BMSC-EVs effectively intervened such pathological manifestations and disease processes in a very similar way. The effects of the BMSC-EVs were found to be caused by the miRNAs they carried, which were proven to be involved in regulating the proliferation and differentiation of multiple cell types and in multiple EV-related biological processes. Furthermore, TGF-β1-positive cells and α-SMA-positive myofibroblasts were significantly increased in the scleroderma skin of BLM-treated mice but evidently reduced in the scleroderma skin of the EV-treated SSc group. In addition, the numbers of mast cells and infiltrating macrophages and lymphocytes were evidently increased in the skin of BLM-treated mice but significantly reduced by EV treatment. In line with these observations, there were significantly higher mRNA levels of the inflammatory cytokines Il6, Il10, and Tnf-α in SSc mice than in control mice, but the levels decreased following EV treatment. Through bioinformatics analysis, the TGFβ and WNT signaling pathways were revealed to be closely involved in the pathogenic changes seen in mouse SSc, and these pathways could be therapeutic targets for treating the disease. Conclusions BMSC-derived EVs could be developed as a potential therapy for treating skin dysfunction in SSc, especially considering that they show similar efficacy to BMSCs but have fewer developmental regulatory requirements than cell therapy. The effects of EVs are generated by the miRNAs they carry, which alleviate SSc pathogenic changes by regulating the WNT and TGFβ signaling pathways.

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BMSC-Derived Exosomes Intervened the Pathogenic Changes of Scleroderma in Mouse Through Its microRNAs

10.21203/rs.3.rs-222441/v1 ◽

2021 ◽

Author(s):

Jiahui Jin ◽

Qingjian OU ◽

Zhe Wang ◽

Haibin Tian ◽

Jingying Xu ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Signaling Pathways ◽

Disease Process ◽

Cell Types ◽

Bioinformatic Analysis ◽

Similar Efficacy ◽

Mrna Levels ◽

Lineage Differentiation ◽

Mirna Sequencing

Abstract BackgroundSystemic sclerosis (SSc) is a disease with severe fibrosis of the skin without effective therapy. While bone marrow mesenchymal stem cell (BMSC) derived exosome was a potential stem cell-based candidate in treatment of SSc.MethodsBMSCs were isolated from the bone marrow of mouse and identified with the surface markers and multi-lineage differentiation. The exosomes were isolated from the BMSCs culture medium with ultracentrifugation and identified with NTA, TEM and western blot. The miRNAs of the BMSC-derived exosomes (BMSC-EXOs) were studied via miRNA sequencing and bioinformatic analysis. The SSc model was established in mice by bleomycin (BLM) subcutaneous injection and the mice were treated with BMSCs or BMSC-derived exosomes. The skin tissues were dissociated and analyzed with H&E staining, RNA sequencing and immunohistochemical staining.ResultsEvident pathological changes like fibrosis and inflammation induced in the skin of BLM-treated mice. Both BMSCs and BMSC-EXOs effectively intervened such pathological manifestations and disease process, in a very similar way. The effects of the BMSC-EXOs were tracked to their microRNAs, which were proved to be involved in regulating the proliferation and differentiation of multiple cell types and in multiple biological processes when the EXOs functioned. Furthermore, the TGF-β1 positive cells and α-SMA positive myofibroblasts were significantly increased in the scleroderma skin of BLM-treated mice, but evidently reduced in the EXO-treated SSc group. Meanwhile, the number of mast cells as well as the infiltrated macrophages and lymphocytes were evidently increased in the skins of the BLM-treated mice, but significantly reduced by the EXO treatment. Such observations were confirmed by the data of the detected inflammatory cytokines that significantly higher mRNA levels of Il6, Il10 and Tnf-α were found in SSc mice, but reduced following the EXO treatment. Through bioinformatics analysis, TGFβ and WNT signaling pathways were revealed to be closely involved in the pathogenic changes in mouse SSc and could be the main targets for treating the disease.ConclusionsBMSC-derived exosomes could be developed as a potential therapy for treating the dysfunction of the skin in SSc, especially for its similar efficacy with BMSCs but less regulated as compared to cell therapy. Its mechanisms are involved in its microRNAs which alleviate the SSc pathogenic changes through regulating WNT and TGFβ signaling pathways.

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Comparison of the Proliferation and Differentiation Potential of Human Urine-, Placenta Decidua Basalis-, and Bone Marrow-Derived Stem Cells

Stem Cells International ◽

10.1155/2018/7131532 ◽

2018 ◽

Vol 2018 ◽

pp. 1-11 ◽

Cited By ~ 7

Author(s):

Chengguang Wu ◽

Long Chen ◽

Yi-zhou Huang ◽

Yongcan Huang ◽

Ornella Parolini ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Mesenchymal Stem Cells ◽

Stem Cell ◽

Stem Cell Differentiation ◽

Cell Types ◽

Stem Cell Marker ◽

Differentiation Potential ◽

Multipotent Stem Cells ◽

Decidua Basalis

Human multipotent stem cell-based therapies have shown remarkable potential in regenerative medicine and tissue engineering applications due to their abilities of self-renewal and differentiation into multiple adult cell types under appropriate conditions. Presently, human multipotent stem cells can be isolated from different sources, but variation among their basic biology can result in suboptimal selection of seed cells in preclinical and clinical research. Thus, the goal of this study was to compare the biological characteristics of multipotent stem cells isolated from human bone marrow, placental decidua basalis, and urine, respectively. First, we found that urine-derived stem cells (USCs) displayed different morphologies compared with other stem cell types. USCs and placenta decidua basalis-derived mesenchymal stem cells (PDB-MSCs) had superior proliferation ability in contrast to bone marrow-derived mesenchymal stem cells (BMSCs); these cells grew to have the highest colony-forming unit (CFU) counts. In phenotypic analysis using flow cytometry, similarity among all stem cell marker expression was found, excluding CD29 and CD105. Regarding stem cell differentiation capability, USCs were observed to have better adipogenic and endothelial abilities as well as vascularization potential compared to BMSCs and PDB-MSCs. As for osteogenic and chondrogenic induction, BMSCs were superior to all three stem cell types. Future therapeutic indications and clinical applications of BMSCs, PDB-MSCs, and USCs should be based on their characteristics, such as growth kinetics and differentiation capabilities.

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Application of Stem Cell-Derived Extracellular Vesicles as an Innovative Theranostics in Microbial Diseases

Frontiers in Microbiology ◽

10.3389/fmicb.2021.785856 ◽

2021 ◽

Vol 12 ◽

Author(s):

Hani Keshavarz Alikhani ◽

Bahare Shokoohian ◽

Sama Rezasoltani ◽

Nikoo Hossein-khannazer ◽

Abbas Yadegar ◽

...

Keyword(s):

Stem Cell ◽

Infectious Diseases ◽

Extracellular Vesicles ◽

Cell Types ◽

The Other ◽

Microbial Pathogens ◽

Microbial Diseases ◽

Clinical Complications ◽

Set Up ◽

Novel Therapeutic Strategies

Extracellular vesicles (EVs), as nano-/micro-scale vehicles, are membranous particles containing various cargoes including peptides, proteins, different types of RNAs and other nucleic acids, and lipids. These vesicles are produced by all cell types, in which stem cells are a potent source for them. Stem cell-derived EVs could be promising platforms for treatment of infectious diseases and early diagnosis. Infectious diseases are responsible for more than 11 million deaths annually. Highly transmissible nature of some microbes, such as newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), drives researcher’s interest to set up different strategies to develop novel therapeutic strategies. Recently, EVs-based diagnostic and therapeutic approaches have been launched and gaining momentum very fast. The efficiency of stem cell-derived EVs on treatment of clinical complications of different viruses and bacteria, such as SARS-CoV-2, hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), Staphylococcus aureus, Escherichia coli has been demonstrated. On the other hand, microbial pathogens are able to incorporate their components into their EVs. The microbe-derived EVs have different physiological and pathological impacts on the other organisms. In this review, we briefly discussed biogenesis and the fate of EVs. Then, EV-based therapy was described and recent developments in understanding the potential application of stem cell-derived EVs on pathogenic microorganisms were recapitulated. Furthermore, the mechanisms by which EVs were exploited to fight against infectious diseases were highlighted. Finally, the deriver challenges in translation of stem cell-derived EVs into the clinical arena were explored.

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Human Heart Explant-Derived Extracellular Vesicles: Characterization and Effects on the In Vitro Recellularization of Decellularized Heart Valves

International Journal of Molecular Sciences ◽

10.3390/ijms20061279 ◽

2019 ◽

Vol 20 (6) ◽

pp. 1279 ◽

Cited By ~ 4

Author(s):

Amanda Leitolis ◽

Paula Suss ◽

João Roderjan ◽

Addeli Angulski ◽

Francisco da Costa ◽

...

Keyword(s):

Wound Healing ◽

Stem Cell ◽

Mesenchymal Stem Cell ◽

Extracellular Vesicles ◽

Tissue Regeneration ◽

Human Heart ◽

Heart Valves ◽

Enrichment Analysis ◽

Cell Types

Extracellular vesicles (EVs) are particles released from different cell types and represent key components of paracrine secretion. Accumulating evidence supports the beneficial effects of EVs for tissue regeneration. In this study, discarded human heart tissues were used to isolate human heart-derived extracellular vesicles (hH-EVs). We used nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) to physically characterize hH-EVs and mass spectrometry (MS) to profile the protein content in these particles. The MS analysis identified a total of 1248 proteins. Gene ontology (GO) enrichment analysis in hH-EVs revealed the proteins involved in processes, such as the regulation of cell death and response to wounding. The potential of hH-EVs to induce proliferation, adhesion, angiogenesis and wound healing was investigated in vitro. Our findings demonstrate that hH-EVs have the potential to induce proliferation and angiogenesis in endothelial cells, improve wound healing and reduce mesenchymal stem-cell adhesion. Last, we showed that hH-EVs were able to significantly promote mesenchymal stem-cell recellularization of decellularized porcine heart valve leaflets. Altogether our data confirmed that hH-EVs modulate cellular processes, shedding light on the potential of these particles for tissue regeneration and for scaffold recellularization.

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Mesenchymal stem cell-derived extracellular vesicles may promote breast cancer cell dormancy

Journal of Tissue Engineering ◽

10.1177/2041731418810093 ◽

2018 ◽

Vol 9 ◽

pp. 204173141881009 ◽

Cited By ~ 4

Author(s):

Jake Casson ◽

Owen G Davies ◽

Carol-Anne Smith ◽

Matthew J Dalby ◽

Catherine C Berry

Keyword(s):

Breast Cancer ◽

Bone Marrow ◽

Cell Proliferation ◽

Stem Cell ◽

Mesenchymal Stem Cell ◽

Cancer Cells ◽

Cancer Cell ◽

Extracellular Vesicles ◽

Breast Cancer Cells ◽

Cell Dormancy

Disseminated breast cancer cells have the capacity to metastasise to the bone marrow and reside in a dormant state within the mesenchymal stem cell niche. Research has focussed on paracrine signalling factors, such as soluble proteins, within the microenvironment. However, it is now clear extracellular vesicles secreted by resident mesenchymal stem cells into this microenvironment also play a key role in the initiation of dormancy. Dormancy encourages reduced cell proliferation and migration, while upregulating cell adhesion, thus retaining the cancer cells within the bone marrow microenvironment. Here, MCF7 breast cancer cells were treated with mesenchymal stem cell–derived extracellular vesicles, resulting in reduced migration in two-dimensional and three-dimensional culture, with reduced cell proliferation and enhanced adhesion, collectively supporting cancer cell dormancy.

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Stem Cell-Derived Extracellular Vesicles for Treating Joint Injury and Osteoarthritis

Nanomaterials ◽

10.3390/nano9020261 ◽

2019 ◽

Vol 9 (2) ◽

pp. 261 ◽

Cited By ~ 18

Author(s):

Jiao Li ◽

Elham Hosseini-Beheshti ◽

Georges Grau ◽

Hala Zreiqat ◽

Christopher Little

Keyword(s):

Stem Cell ◽

Extracellular Vesicles ◽

Cell Types ◽

Current Evidence ◽

Therapeutic Effects ◽

Joint Injury ◽

Direct Cell ◽

Almost All ◽

New Treatments

Extracellular vesicles (EVs) are nanoscale particles secreted by almost all cell types to facilitate intercellular communication. Stem cell-derived EVs theoretically have the same biological functions as stem cells, but offer the advantages of small size, low immunogenicity, and removal of issues such as low cell survival and unpredictable long-term behaviour associated with direct cell transplantation. They have been an area of intense interest in regenerative medicine, due to the potential to harness their anti-inflammatory and pro-regenerative effects to induce healing in a wide variety of tissues. However, the potential of using stem cell-derived EVs for treating joint injury and osteoarthritis has not yet been extensively explored. The pathogenesis of osteoarthritis, with or without prior joint injury, is not well understood, and there is a longstanding unmet clinical need to develop new treatments that provide a therapeutic effect in preventing or stopping joint degeneration, rather than merely relieving the symptoms of the disease. This review summarises the current evidence relating to stem cell-derived EVs in joint injury and osteoarthritis, providing a concise discussion of their characteristics, advantages, therapeutic effects, limitations and outlook in this exciting new area.

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NG2 as an Identity and Quality Marker of Mesenchymal Stem Cell Extracellular Vesicles

Cells ◽

10.3390/cells8121524 ◽

2019 ◽

Vol 8 (12) ◽

pp. 1524 ◽

Cited By ~ 5

Author(s):

Mario Barilani ◽

Valeria Peli ◽

Alessandro Cherubini ◽

Marta Dossena ◽

Vincenza Dolo ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Mesenchymal Stem Cell ◽

Cord Blood ◽

Extracellular Vesicles ◽

Therapeutic Potential ◽

Antigen Expression ◽

Quality Parameter ◽

Proliferative Effect ◽

Quality Marker

The therapeutic potential of mesenchymal stem cell (MSC) extracellular vesicles (EV) is currently under investigation in many pathological contexts. Both adult and perinatal MSC are being considered as sources of EV. Herein, we address antigen expression of cord blood and bone marrow MSC and released EV to define an identity and quality parameter of MSC EV as a medicinal product in the context of clinical applications. The research focuses on EV-shuttled neural/glial antigen 2 (NG2), which has previously been detected as a promising surface marker to distinguish perinatal versus adult MSC. Indeed, NG2 was significantly more abundant in cord blood than bone marrow MSC and MSC EV. Ultracentrifuge-isolated EV were then challenged for their pro-angiogenic properties on an xCELLigence system as quality control. NG2+ cord blood MSC EV, but not bone marrow MSC EV, promote bFGF and PDGF-AA proliferative effect on endothelial cells. Likewise, they successfully rescue angiostatin-induced endothelial cell growth arrest. In both cases, the effects are NG2-dependent. These results point at NG2 as an identity and quality parameter for cord blood MSC EV, paving the way for their clinical translation.

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Annexin II Mediates Plasminogen-Dependant Matrix Invasion by Adult Human Mesenchymal Stem Cells.

Blood ◽

10.1182/blood.v104.11.2326.2326 ◽

2004 ◽

Vol 104 (11) ◽

pp. 2326-2326

Author(s):

Paul B. Bolno ◽

Doris A. Morgan ◽

Mahesh Sharma ◽

Martin Lazorik ◽

Andrew S. Wechsler ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Extracellular Matrix ◽

Mesenchymal Stem Cells ◽

Stem Cell ◽

Western Blot ◽

Human Mesenchymal Stem Cells ◽

Angiogenic Factors ◽

Annexin Ii ◽

Adult Human

Abstract Background: Annexin II (ANX2) is a fibrinolytic receptor that serves as a binding site for plasminogen and tissue plasminogen activator, facilitating the generation of plasmin. ANX2 is present on a wide variety of cells including vascular endothelial cells as well as macrophages. ANX2 has been shown to play a key role in extracellular matrix degradation, cellular migration, and invasion. This degradation of extracellular matrix may also cause the release of matrix-bound angiogenic factors such as VEGF and FGF. We hypothesized that adult human mesenchymal stem cells (hMSCs) express ANX2 and utilize this receptor for plasmin generation to facilitate basement membrane invasion. Methods: Primary hMSCs were isolated from the sternal bone marrow of patients undergoing median sternotomy. Stem cell surface markers were characterized via immuno-fluorescence. The presence of ANX2 protein by hMSCs was established via western blot. ANX2 mediated plasminogen activation and plasmin generation was quantified using chromozyme-P as a colorimetric substrate. Invasion assays were performed in dual-chamber culture wells containing matrigel inserts. hMSCs were plated into upper chambers containing: serum-free medium (SFM), SFM + Plasminogen, or SFM + Plasminogen + epsilon-aminocaproic acid (e-ACA inhibits binding of plasminogen to ANX2). After 24 hours, invasive cells were isolated and counted. Results: Sternal bone marrow derived hMSCs expressed the membrane phenotype CD34 (−), CD14 (−), CD44 (+), CD105 (+), CD106 (+). The presence of ANX2 was confirmed by western blot analysis. hMSCs generated 1.95 units of plasmin per milligram of protein. There was a 20% (p 0 .004) increase in hMSC invasion in the wells containing plasminogen as compared to SFM alone. When e-ACA was introduced there was a decrease in hMSC invasion back to control values. Conclusion: Our observations establish for the first time the presence and functional activity of ANX2 in hMSCs. These data suggest that mesenchymal stem cell expression of ANX2 facilitates plasminogen-mediated hMSC trans-endothelial invasion, migration and the release of pro-angiogenic factors from within the extracellular matrix, promoting stem cell directed repair and angiogenesis.

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Human Embryonic Stem Cell-Derived Mesenchymal Stroma Cells (hES-MSC) Share Basic Properties with Bone Marrow MSC, They Have Potent Stroma Support Capacities but Lack Immune-Modulatory Function. Implications for off-the Shelf ES-MSC Therapies.

Blood ◽

10.1182/blood.v116.21.3858.3858 ◽

2010 ◽

Vol 116 (21) ◽

pp. 3858-3858 ◽

Cited By ~ 1

Author(s):

Ou Li ◽

Ariane Tormin ◽

Jan Claas Brune ◽

Berit Sundberg ◽

Johan Hyllner ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Human Embryonic Stem Cell ◽

Embryonic Stem ◽

Cell Types ◽

Es Cell ◽

Nsg Mice ◽

Mesenchymal Stroma ◽

Mesenchymal Stroma Cells

Abstract Abstract 3858 Mesenchymal stroma cells (MSC) have a high potential for novel cell therapy approaches in clinical transplantation due to their intriguing properties, e.g. high proliferation and differentiation capacity, stromal support and immune-modulation. Commonly, bone marrow-derived MSC (BM-MSC) are used for clinical MSC cell therapies. However, BM-derived MSC have a restricted proliferative capacity and cultured BM-MSC are heterogeneous and thus difficult to standardize. Human embryonic stem cell-derived mesenchymal stroma cells (hES-MSC) have recently been developed and might represent an alternative and unlimited source of hMSCs. We therefore aimed to characterize human ES-cell-derived MSC, i.e. the hES-MSC line hES-MP002.5 (Cellartis) and compare its properties with normal human bone marrow (BM) derived MSC. We found that hES-MP cells have lower yet reasonable CFU-F capacity when compared with BM-MSC (6+3 vs 25+1 CFU-F per 100 cells). hES-MP cells showed similar immunophenotypic properties compared with BM-MSC (flow cytometry): Both cell types were positive for CD105, CD73, CD166, HLA Class I, CD44, CD146 and CD90, and cells were negative for surface markers such as CD45, CD34, CD14, CD31, CD19, and HLA-DR. hES-MP, like BM-MSC, could be differentiated into adipocytes, osteoblasts and chondrocytes upon induction in vitro. In order to test whether MSC were capable of homing to the bone marrow after intravenous injection, hES-MP and BM-MSC were markerd with GFP, and sorted GFP-positive cells were injected intravenously into NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice. GFP-positive cells were not detected in the bone marrow 24 hours after injection, neither when hES-MP cells were injected, nor - and as expected - when cultured BM-MSC were used. Intra-femoral transplantation into NSG mice using GFP expressing hES-MP and BM-MSC on the other hand demonstrated successful long-term engraftment (8 weeks) for both cell types. Morphology and intra-femoral localization of hES-MP were similar compared to BM-MSC. LTC-IC and co-transplantation experiments with cord blood CD34+ hematopoietic cells demonstrated furthermore that hES-MP, like BM-MSC, possess potent stroma support function both in vitro and in vivo. However, hES-MP showed no or only little activity in mixed lymphocyte cultures and PHA lymphocyte stimulation assays. In summary, our data demonstrate that MSC derived from hES cells have biological properties and potent stroma functions similar to conventional BM-MSC. Thus, ES-cell derived MSC might be an attractive and reliable alternative and unlimited source for obtaining MSC for clinical cell therapy. However, hES-MP probably have no or only little immuno-modulative capacity, which may limit their potential clinical use. Disclosures: Hyllner: Cellartis AB: Employment.

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Leukemia-Induced Alterations in Bone Marrow Cytokine and Chemokine Levels Contribute to Altered Stem Cell Lodgment and Impairment of Normal Stem Cell Growth in CML

Blood ◽

10.1182/blood.v118.21.962.962 ◽

2011 ◽

Vol 118 (21) ◽

pp. 962-962

Author(s):

Bin Zhang ◽

Yin Wei Ho ◽

Tessa L. Holyoake ◽

Claudia S Huettner ◽

Ravi Bhatia

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Mouse Model ◽

Hematopoietic Stem Cell ◽

Stromal Cells ◽

Research Funding ◽

Mrna Levels ◽

Hematopoietic Stem ◽

Tnf Α ◽

Selective Impairment

Abstract Abstract 962 Specialized bone marrow (BM) microenvironmental niches are essential for hematopoietic stem cell (HSC) lodgment and maintenance. However microenvironmental interactions of leukemia stem cells (LSC) are poorly understood. Although chronic myelogenous leukemia (CML) results from HSC transformation by the BCR-ABL gene, the role of the microenvironment in modulating leukemia development is not known. We employed the SCL-tTA-BCR/ABL mouse model of CML to investigate the LSC interactions with the BM microenvironment. In this model, targeted expression of the BCR-ABL gene in murine HSC via a tet-regulated SCL promoter results in development of a chronic phase CML-like disorder. We have reported that LSC capacity is restricted to BCR-ABL+ cells with long-term hematopoietic stem cell (LTHSC) phenotype(LSK Flt3-CD150+CD48-) (Blood 2010 116:1212A). LSC numbers are reduced in the BM but increased in the spleen of CML mice compared with LTHSC from control mice, suggesting that LSC have altered niche interactions. LSC also demonstrate altered trafficking with significant reduction in homing of IV injected LSC to BM, and markedly increased egress of intrafemorally injected LSC to the spleen, potentially related to reduced CXCL12 levels in the BM of CML mice. In addition, levels of several chemokines and cytokines, including MIP1α, MIP1β, MIP2, IL-1α, IL-1β, TNF-α, G-CSF and IL-6, were increased in CML BM, related to increased production by malignant hematopoietic cells. We investigated whether altered chemokine and cytokine expression was associated with altered capacity of the CML BM microenvironment to support LTHSC engraftment. LTHSC from control mice or LSC from CML mice were transplanted into irradiated CML or control recipients. There was reduced engraftment of both control LTHSC and CML LSC in the BM of CML compared to control recipients at 2 weeks after transplantation, associated with reduced homing to CML BM, potentially related to low BM CXCL12 levels. The numbers of control LTHSC in the BM of CML recipient mice remained low at 4 weeks post-transplantation, whereas the numbers of CML LSC increased to numbers similar to those seen in the BM of control recipients. Culture with CML BM supernatants (SN) resulted in impaired growth of control LTHSC compared to control BM SN. In contrast the growth of CML LSC was similar following culture with CML and control BM SN. Culture with individual factors at concentrations similar to those observed in CML BM (16ng/ml MIP1α, 8ng/ml MIP1β, 2.5ng/ml IL-1α, 3.5ng/ml IL-1β, 0.05ng/ml TNF-α) resulted in significantly reduced growth of normal LTHSC compared with CML LSC. These results indicate that diffusible factors produced by leukemic cells in the CML BM environment selectively inhibit normal LTHSC compared to CML LSC growth. Exposure of a murine stromal cell line to CML BM SN resulted in reduced CXCL12 mRNA levels compared to BM SN from control mice. The cytokine G-CSF, which was increased in CML BM SN, has been reported to reduce CXCL12 transcription. We observed significant reduction of CXCL12 mRNA levels in stromal cells cultured with G-CSF (0.2ng/ml), supporting a potential role for increased G-CSF production by leukemia cells in reduced CXCL12 production by CML BM stromal cells and reduced LSC retention in the BM. We evaluated whether defects in microenvironmental function in CML were affected by imatinib treatment. Treatment of CML mice with imatinib (200mg/kg/day, 2 weeks) led to reduction in MIP1α, MIP1β, IL-1β, and IL-6 levels in BM cells. Engraftment of normal LTHSC was significantly enhanced in BM of CML recipients pre-treated with imatinib. Results obtained with the mouse model were validated using specimens obtained from CML patients. CXCL12 mRNA levels were significantly reduced in human CML compared to normal MNCs, whereas expression of MIP1α, MIP-2, IL-1α and IL-1β were increased in CML MNCs, consistent with results obtained with the mouse model. Coculture with CML MNC conditioned medium (CM) resulted in selective impairment of growth of normal CD34+CD38- primitive progenitors compared to CM from normal MNC, but did not inhibit growth of CML progenitors. We conclude that leukemia-induced alterations in BM cytokine and chemokine levels contribute to altered LSC lodgment and to selective impairment of growth of normal LTHSC in the CML BM microenvironment, leading to a relative growth advantage for CML LSC over normal LTHSC and expansion of the leukemic clone. Disclosures: Holyoake: Novartis: Research Funding; Bristol Myers Squibb: Research Funding.

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