BackgroundMesenchymal stromal cells (MSC) are shown to have a great therapeutic potential in many immunological disorders. Currently the therapeutic effect of MSCs is considered to be mediated via paracrine interactions with immune cells. Umbilical cord blood is an attractive but still less studied source of MSCs. We investigated the production of extracellular membrane vesicles (MVs) from human umbilical cord blood derived MSCs (hUCBMSC) in the presence (MVstim) or absence (MVctrl) of inflammatory stimulus.MethodshUCBMSCs were cultured in serum free media with or without IFN-γ and MVs were collected from conditioned media by ultracentrifugation. The protein content of MVs were analyzed by mass spectrometry. Hypoxia induced acute kidney injury rat model was used to analyze the in vivo therapeutic potential of MVs and T-cell proliferation and induction of regulatory T cells were analyzed by co-culture assays.ResultsBoth MVstim and MVctrl showed similar T-cell modulation activity in vitro, but only MVctrls were able to protect rat kidneys from reperfusion injury in vivo. To clarify this difference in functionality we made a comparative mass spectrometric analysis of the MV protein contents. The IFN-γ stimulation induced dramatic changes in the protein content of the MVs. Complement factors (C3, C4A, C5) and lipid binding proteins (i.e apolipoproteins) were only found in the MVctrls, whereas the MVstim contained tetraspanins (CD9, CD63, CD81) and more complete proteasome complex accompanied with MHCI. We further discovered that differently produced MV pools contained specific Rab proteins suggesting that same cells, depending on external signals, produce vesicles originating from different intracellular locations.ConclusionsWe demonstrate by both in vitro and in vivo models accompanied with a detailed analysis of molecular characteristics that inflammatory conditioning of MSCs influence on the protein content and functional properties of MVs revealing the complexity of the MSC paracrine regulation.

This article is available online at http://www.jlr.org Supplementary key words glycerophospholipid profi le • mesenchymal stem cell • arachidonic acid • docosahexaenoic acid • lipid signaling • mass spectrometry Human mesenchymal stem/stromal cells (hMSC) are currently being studied in a number of clinical applications, for example, to improve the engraftment of hematopoietic stem cell transplant, to promote myocardial repair, and to control immunological responses in graft versus host diseases, autoimmune diseases, and solid organ transplantations ( 1-5 ). In addition to being immunologically privileged, these cells can modulate both innate and adaptive immune responses in vitro and in vivo. hMSCs have been shown to be able to inhibit T-cell proliferation, inhibit dendritic cell maturation ( 6 ), recruit regulatory T-cells ( 7,8 ), and modulate B-cell functions ( 9 ). The mechanisms by which these cells exert their immune modulatory functions are still unclear, but it is likely that both direct cell-cell contacts and the secretion of soluble factors are needed. Several cytokines, growth factors, enzymes, and lipid mediators, such as transforming growth factor ␤ 1, the

Efficient xenofree expansion methods to replace fetal bovine serum (FBS)-based culture methods are strongly encouraged by the regulators and are needed to facilitate the adoption of mesenchymal stromal cell (MSC)-based therapies. In the current study we established a clinically-compliant and reproducible animal serum-free culture protocol for bone marrow-(BM-) MSCs based on an optimized platelet-derived supplement. Our study compared two different platelet-derived supplements, platelet lysate PL1 versus PL2, produced by two different methods and lysed with different amounts of freeze–thaw cycles. Our study also explored the effect of a low oxygen concentration on BM-MSCs. FBS-supplemented BM-MSC culture served as control. Growth kinetics, differentiation and immunomodulatory potential, morphology, karyotype and immunophenotype was analysed. Growth kinetics in long-term culture was also studied. Based on the initial results, we chose to further process develop the PL1-supplemented culture protocol at 20 % oxygen. The results from 11 individual BM-MSC batches expanded in the chosen condition were consistent, yielding 6.60 × 109 ± 4.74 × 109 cells from only 20 ml of bone marrow. The cells suppressed T-cell proliferation, displayed normal karyotype and typical MSC differentiation potential and phenotype. The BM-MSCs were, however, consistently HLA-DR positive when cultured in platelet lysate (7.5–66.1 %). We additionally show that culture media antibiotics and sterile filtration of the platelet lysate can be successfully omitted. We present a robust and reproducible clinically-compliant culture method for BM-MSCs based on platelet lysate, which enables high quantities of HLA-DR positive MSCs at a low passage number (p2) and suitable for clinical use.

Systemic infusion of therapeutic cells would be the most practical and least invasive method of administration in many cellular therapies. One of the main obstacles especially in intravenous delivery of cells is a massive cell retention in the lungs, which impairs homing to the target tissue and may decrease the therapeutic outcome. In this study we showed that an alternative cell detachment of mesenchymal stromal/stem cells (MSCs) with pronase instead of trypsin significantly accelerated the lung clearance of the cells and, importantly, increased their targeting to an area of injury. Cell detachment with pronase transiently altered the MSC surface protein profile without compromising cell viability, multipotent cell characteristics, or immunomodulative and angiogenic potential. The transient modification of the cell surface protein profile was sufficient to produce effective changes in cell rolling behavior in vitro and, importantly, in the in vivo biodistribution of the cells in mouse, rat, and porcine models. In conclusion, pronase detachment could be used as a method to improve the MSC lung clearance and targeting in vivo. This may have a major impact on the bioavailability of MSCs in future therapeutic regimes.

SummaryHuman bone marrow stromal cells, or mesenchymal stem cells (BM-MSCs), need expansion prior to use as cell-based therapies in immunological and tissue repair applications. Aging and expansion of BM-MSCs induce epigenetic changes that can impact therapeutic outcomes. By applying sequencing-based methods, we reveal that the breadth of DNA methylation dynamics associated with aging and expansion is greater than previously reported. Methylation changes are enriched at known distal transcription factor binding sites such as enhancer elements, instead of CpG-rich regions, and are associated with changes in gene expression. From this, we constructed hypo- and hypermethylation-specific regulatory networks, including a sub-network of BM-MSC master regulators and their predicted target genes, and identified putatively disrupted signaling pathways. Our genome-wide analyses provide a broader overview of age- and expansion-induced DNA methylation changes and a better understanding of the extent to which these changes alter gene expression and functionality of human BM-MSCs.