MESENCHYMAL STEM- AND STROMAL CELLS IN BONE MARROW AND OSTEOSARCOMA

Primary mesenchymal stem cells (MSC) play a central role in bone marrow (BM) and during haematopoiesis. Yet, the exact phenotype and spatial distribution of primary MSC in the human BM are unknown. Their cultured progeny are promising candidates for clinical applications. MSC cultures however, are heterogeneous and, while critical for clinical applications, their exact composition is not known. We have therefore analysed the phenotype of primary MSC in the BM and found that mesenchymal progenitors were highly enriched in the lin-/CD271+/CD45- fraction. Interestingly, CD146 expression pertained to the in-vivo localization of primary MSC in the human bone marrow (perivascular/endosteal) while CD146 expression in-vitro was oxygen level dependent. Cultured MSC were analysed after carboxyfluorescein succinimidyl ester (CFSE) staining for cell division tracking. Sorting for slowly dividing and rapidly dividing sub-populations and global gene expression analysis yielded 102 differentially expressed genes. Two of these genes translated into proteins that enabled for the prospective identification of a VCAM+/ FMOD+ sub-population, with low progenitor activity and a limited differentiation potential. On the other hand, MSC support tumour growth and metastasis and have even been suggested as osteosarcoma (OS) stem cells. We therefore analysed MSC in OS (OS-MSC) and compared them with BM-MSC. OS samples contained very high frequencies of mesenchymal progenitor cells. OS-derived MSC (OS-MSC) did not show chromosomal aberrations, had normal MSC morphology and expressed the typical MSC surface marker profile. A global gene expression analysis yielded a set of genes differentially expressed between OS- and BM-MSC. Of these, 3 genes responsible for membrane-associated proteins were analysed: CD142, LY6H, and OSS3* were 24.9- , 7.2- , and 66.4-fold higher expressed in OS-MSC. The OSS3-protein was expressed in all analysed primary OS samples and only OSS3 identified the majority of mesenchymal progenitor cells in uncultured tumour samples. Taken together, we propose here a marker combination for a highly enriched primary MSC population and show that CD146 expression relates to the perivascular (versus endosteal) localization of primary human MSC. This is of importance to further studies of the haematopoietic environment. We also show the presence of sub-populations within MSC cultures and propose markers for the isolation of a functionally impaired population. This is important for safe and efficient clinical application of cultured MSC. Furthermore we could demonstrate high numbers of colony forming mesenchymal progenitors in OS, suggesting that MSC are a major constituent of the OS stroma and consequently represent a target for therapy. Finally the above data show that a sub-population of OS cells expresses OSS3 and we furthermore demonstrate that OSS 3 identifies the majority of colony forming mesenchymal progenitors within OS. Presumably, these cells are the origin of a considerable part of the CAF population within the tumour and they should therefore be considered a target for therapy. Experiments investigating the use of OSS3 antibodies in an antibody-dependent cell-mediated cytotoxicity-based approach are currently underway. *Due to a possible patent application, we were advised to substitute the original gene name with an alias

Anti-endotoxic and antibacterial effects of a dermal substitute coated with host defense peptides.

Biomaterials used during surgery and wound treatment are of increasing importance in modern medical care. In the present study we set out to evaluate the addition of thrombin-derived host defense peptides to human acellular dermis (hAD, i.e. epiflex(®)). Antimicrobial activity of the functionalized hAD was demonstrated using radial diffusion and viable count assays against Gram-negative Escherichia coli, Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus bacteria. Electron microscopy analyses showed that peptide-mediated bacterial killing led to reduced hAD degradation. Furthermore, peptide-functionalized hAD displayed endotoxin-binding activity in vitro, as evidenced by inhibition of NF-κB activation in human monocytic cells (THP-1 cells) and a reduction of pro-inflammatory cytokine production in whole blood in response to lipopolysaccharide stimulation. The dermal substitute retained its anti-endotoxic activity after washing, compatible with results showing that the hAD bound a significant amount of peptide. Furthermore, bacteria-induced contact activation was inhibited by peptide addition to the hAD. E. coli infected hAD, alone, or after treatment with the antiseptic substance polyhexamethylenebiguanide (PHMB), yielded NF-κB activation in THP-1 cells. The activation was abrogated by peptide addition. Thus, thrombin-derived HDPs should be of interest in the further development of new biomaterials with combined antimicrobial and anti-endotoxic functions for use in surgery and wound treatment

Mesenchymal stromal cells from primary osteosarcoma are non-malignant and strikingly similar to their bone marrow counterparts.

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 CFU-F assay (median: 1,117 colonies per 10(5) cells, range: 133 - 3,000, n=6). This is considerably higher compared to other human tissues such as normal bone marrow (1.3 ± 0.2 colonies per 10(5) cells, 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 bone marrow 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 bone marrow-derived MSC. © 2010 UICC

CD146 expression on primary nonhematopoietic bone marrow stem cells is correlated with in situ localization

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