Nonhematopoietic bone marrow mesenchymal stem cells (BM-MSCs) are of central importance for bone marrow stroma and the hematopoietic environment. However, the exact phenotype and anatomical distribution of specified MSC populations in the marrow are unknown. We characterized the phenotype of primary human BM-MSCs and found that all assayable colony-forming units-fibroblast (CFU-Fs) were highly and exclusively enriched not only in the lin−/CD271+/CD45−/CD146+ stem-cell fraction, but also in lin−/CD271+/CD45−/CD146−/low cells. Both populations, regardless of CD146 expression, shared a similar phenotype and genotype, gave rise to typical cultured stromal cells, and formed bone and hematopoietic stroma in vivo. Interestingly, CD146 was up-regulated in normoxia and down-regulated in hypoxia. This was correlated with in situ localization differences, with CD146 coexpressing reticular cells located in perivascular regions, whereas bone-lining MSCs expressed CD271 alone. In both regions, CD34+ hematopoietic stem/progenitor cells were located in close proximity to MSCs. These novel findings show that the expression of CD146 differentiates between perivascular versus endosteal localization of non-hematopoietic BM-MSC populations, which may be useful for the study of the hematopoietic environment.

Human mesenchymal stromal cells (MSC) are promising candidates for cell therapy because of their intriguing properties (high proliferation and differentiation capacity, microenvironmental function and immune modulation). However, MSC are heterogeneous and a better understanding of the heterogeneity of the cells that form the MSC cultures is critical. Human MSC were generated in standard cultures and stained with carboxyfluorescein succinimidyl ester (CFSE) for cell division tracking. Gene expression profiling of MSC that were sorted based on functional parameters (i.e. proliferation characteristics) was utilized to characterize potential MSC subpopulations (progenitor content and differentiation capacity) and identify potential MSC subpopulation markers. The majority of MSC had undergone more than two cell divisions (79.7 ± 2.0%) after 10 days of culture, whereas 3.5 ± 0.9% of MSC had not divided. MSC were then sorted into rapidly dividing cells (RDC) and slowly/non-dividing cells (SDC/NDC). Colony-forming unit–fibroblast (CFU-F) frequencies were lowest in NDC and highest in RDC with low forward-/side-scatter properties (RDC_lolo). Comparative microarray analysis of NDC versus RDC identified 102 differentially expressed genes. Two of these genes (FMOD and VCAM1) corresponded to cell-surface molecules that enabled the prospective identification of a VCAM1⁺/FMOD⁺ MSC subpopulation, which increased with passage and showed very low progenitor activity and limited differentiation potential. These data clearly demonstrate functional differences within MSC cultures. Furthermore, this study shows that cell sorting based on proliferation characteristics and gene expression profiling can be utilized to identify surface markers for the characterization of MSC subpopulations.

Mesenchymal stromal cells (MSC) are multipotent cells that can be isolated from a number of human tissues. In cancer, MSC have been implicated with tumor growth, invasion, metastasis, drug resistance and were even suggested as possible tumor‐initiating cells in osteosarcoma (OS). However, MSC from OS and their possible tumor origin have not yet been thoroughly investigated. Therefore, primary OS mesenchymal progenitors and OS‐derived MSC were studied. OS samples contained very high frequencies of mesenchymal progenitor cells as measured by the colony‐forming unit fibroblast (CFU‐F) assay (median: 1,117 colonies per 10⁵cells, range: 133–3,000,n= 6). This is considerably higher compared to other human tissues such as normal bone marrow (BM) (1.3 ± 0.2 colonies per 10⁵cells,n= 8). OS‐derived MSC (OS‐MSC) showed normal MSC morphology and expressed the typical MSC surface marker profile (CD105/CD73/CD90/CD44/HLA‐classI/CD166 positive, CD45/CD34/CD14/CD19/HLA‐DR/CD31 negative). Furthermore, all OS‐MSC samples could be differentiated into the osteogenic lineage, and all but one sample into adipocytes and chondrocytes. Genetic analysis of OS‐MSC as well as OS‐derived spheres showed no tumor‐related chromosomal aberrations. OS‐MSC expression of markers related to tumor‐associated fibroblasts (fibroblast surface protein, alpha‐smooth muscle actin, vimentin) was comparable to BM‐MSC and OS‐MSC growth was considerably affected by tyrosine kinase inhibitors. Taken together, our results demonstrate that normal, non‐malignant mesenchymal stroma cells are isolated from OS when MSC culture techniques are applied. OS‐MSC represent a major constituent of the tumor microenvironment, and they share many properties with BM‐derived MSC.

Background Mesenchymal stem cells (MSC) have not only been implicated in the development of lung diseases, but they have also been proposed as a future cell-based therapy for lung diseases. However, the cellular identity of the primary MSC in human lung tissues has not yet been reported. This study therefore aimed to identify and characterise the ‘bona fide’ MSC in human lungs and to investigate if the MSC numbers correlate with the development of bronchiolitis obliterans syndrome in lung-transplanted patients. Methods Primary lung MSC were directly isolated or culture-derived from central and peripheral transbronchial biopsies of lung-transplanted patients and evaluated using a comprehensive panel of in vitro and in vivo assays. Results Primary MSC were enriched in the CD90/CD105 mononuclear cell fraction with mesenchymal progenitor frequencies of up to four colony-forming units, fibroblast/100 cells. In situ staining of lung tissues revealed that CD90/CD105 MSCs were located perivascularly. MSC were tissue-resident and exclusively donor lung-derived even in biopsies obtained from patients as long as 16 years after transplantation. Culture-derived mesenchymal stromal cells showed typical in vitro MSC properties; however, xenotransplantation into non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice showed that lung MSC readily differentiated into adipocytes and stromal tissues, but lacked significant in vivo bone formation. Conclusions These data clearly demonstrate that primary MSC in human lung tissues are not only tissue resident but also tissue-specific. The identification and phenotypic characterisation of primary lung MSC is an important first step in identifying the role of MSC in normal lung physiology and pulmonary diseases.

Bone marrow mononuclear cells (BMCs) are suitable for bone tissue engineering. Comparative data regarding the needs of BMC for the adhesion on biomaterials and biocompatibility to various biomaterials are lacking to a large extent. Therefore, we evaluated whether a surface coating would enhance BMC adhesion and analyze the biocompatibility of three different kinds of biomaterials. BMCs were purified from human bone marrow aspirate samples. Beta tricalcium phosphate (β-TCP, without coating or coated with fibronectin or human plasma), demineralized bone matrix (DBM), and bovine cancellous bone (BS) were assessed. Seeding efficacy onβ-TCP was 95% regardless of the surface coating. BMC demonstrated a significantly increased initial adhesion on DBM andβ-TCP compared to BS. On day 14, metabolic activity was significantly increased in BMC seeded on DBM in comparison to BMC seeded on BS. Likewise increased VEGF-synthesis was observed on day 2 in BMC seeded on DBM when compared to BMC seeded on BS. The seeding efficacy of BMC on uncoated biomaterials is generally high although there are differences between these biomaterials. Beta-TCP and DBM were similar and both superior to BS, suggesting either as suitable materials for spatial restriction of BMC used for regenerative medicine purposesin vivo.