In vitro study of matrix metalloproteinase/tissue inhibitor of metalloproteinase production by mesenchymal stromal cells in response to inflammatory cytokines: the role of their migration in injured tissues

Background aimsThe transmigratory capacity of bone marrow (BM) mesenchymal stromal cells (MSC) through the endothelial cell barrier into various tissues and their differentiation potential makes them ideal candidates for cell therapy. Nevertheless, the mechanisms and agents promoting their migration are not fully understood. We evaluated the effects of several inflammatory cytokines on the migration of BM MSC and matrix metalloproteinase (MMP)/tissue inhibitor of metalloproteinase (TIMP) production.MethodsThe migratory potential of BM MSC was evaluated using a Boyden chamber coated with Matrigel^® in the presence and absence of stromal cell-derived (SDF)-1α, platelet-derived growth factor (PDGF)bb, insulin-like growth factor (IGF)-I and interleukin (IL)-6. The ability of inflammatory cytokines to induce MSC migration was tested in presence of their respective Ab or blocking peptide. We used immunofluorescence to check the expression of cytokine receptors, and MMP/TIMP production was analyzed at the protein (human cytokine array, enzyme-linked immunosorbent assay (ELISA), gelatine zymography and Western blot) and mRNA quantitative real-time polymerase chain reaction (qRT-PCR) levels.ResultsWe have demonstrated that inflammatory cytokines promote the migratory capacity of BM MSC according to the expression of their respective receptors. Higher migration through Matrigel was observed in response to IL-6 and PDGFbb. qRT-PCR and cytokine array revealed that migration was the result of the variable level of MMP/TIMP in response to inflammatory stimuli.ConclusionsOur observations suggest that chemokines and cytokines involved in the regulation of the immunity or inflammatory process promote the migration of MSC into BM or damaged tissues. One of the mechanisms used by MSC to promote their migration though the extracellular matrix is modulation of the production of MMP-1, MMP-2, MMP-13, TIMP-1 and TIMP-2.     

Functional potentials of human hematopoietic progenitor cells are maintained by mesenchymal stromal cells and not impaired by plerixafor

Background aimsMesenchymal stromal cells (MSCs) resemble an essential component of the bone marrow niche for maintenance of stemness of hematopoietic progenitor cells (HPCs). Perturbation of the C-X-C chemokine receptor type 4 (CXCR4)/stromal cell-derived factor-1α (SDF-1α) axis by plerixafor (AMD3100) mobilizes HPCs from their niche; however, little is known about how plerixafor affects interaction of HPCs and MSCs in vitro.MethodsWe monitored cell division kinetics, surface expression of CD34 and CXCR4, migration behavior and colony-forming frequency of HPCs on co-culture with MSCs either with or without exposure to plerixafor.ResultsCo-culture with MSCs significantly accelerated cell division kinetics of HPCs. Despite this, the proportion of CD34⁺ cells was significantly increased on co-culture, whereas the expression of CXCR4 was reduced. In addition, co-culture with MSCs led to significantly higher colony-forming capacity and enhanced migration rate of HPCs compared with mono-culture conditions. The composition of MSC sub-populations—and conversely their hematopoiesis supportive functions—may be influenced by culture conditions. We compared the stromal function of MSCs isolated with three different culture media. Overall, the supporting potentials of these MSC preparations were quite similar. Perturbation by the CXCR4-antagonist plerixafor reduced the cell division kinetics of HPCs on co-culture with MSCs. However, the progenitor cell potential of the HPCs as reflected by colony-forming capacity was not affected by plerixafor.ConclusionsThese results support the notion that the CXCR4/SDF-1α axis is critical for HPC-MSC interaction with regard to migration, adhesion and regulation of proliferation but not for maintenance of primitive progenitor cells.     

Efficient isolation and enrichment of mesenchymal stem cells from bone marrow

Background aimsBone marrow (BM) mesenchymal stromal cells (MSC) have been identified as a source of pluripotent stem cells used in clinical practice to regenerate damaged tissues. BM MSC are commonly isolated from BM by density-gradient centrifugation. This process is an open system that increases the risk of sample contamination. It is also time consuming and requires technical expertise that may result in variability regarding cellular recovery. The BD Vacutainer^® Cell Preparation Tube? (CPT) was conceived to separate mononuclear cells from peripheral blood. The main goal of this study was to verify whether MSC could be isolated from BM using the CPT.MethodsBM was harvested, divided into two equal aliquots and processed using either CPT or a Ficoll-Paque? PREMIUM density gradient. Both methods were compared regarding cell recovery, viability, proliferation, differentiation capacities and the presence of MSC progenitors.ResultsSimilar numbers of mononuclear cells were isolated from BM when comparing the two methods under study. No differences were found in terms of phenotypic characterization, viability, kinetics and lineage differentiation potential of MSC derived by CPT or Ficoll. Surprisingly, a fibroblast–colony-forming unit (CFU-F) assay indicated that, with CPT, the number of MSC progenitors was 1.8 times higher compared with the Ficoll gradient separation.ConclusionsThe CPT method is able to isolate MSC efficiently from BM, allowing the enrichment of MSC precursors.     

Therapeutic effects of menstrual blood-derived endometrial stem cells on mouse models of streptozotocin-induced type 1 diabetes

BACKGROUND Type 1 diabetes(T1D),a chronic metabolic and autoimmune disease,seriously endangers human health.In recent years,mesenchymal stem cell(MSC)transplantation has become an effective treatment for diabetes.Menstrual bloodderived endometrial stem cells(MenSC),a novel MSC type derived from the decidual endometrium during menstruation,are expected to become promising seeding cells for diabetes treatment because of their noninvasive collection procedure,high proliferation rate and high immunomodulation capacity.AIM To comprehensively compare the effects of MenSC and umbilical cord-derived MSC(UcMSC)transplantation on T1D treatment,to further explore the potential mechanism of MSC-based therapies in T1D,and to provide support for the clinical application of MSC in diabetes treatment.METHODS A conventional streptozotocin-induced T1D mouse model was established,and the effects of MenSC and UcMSC transplantation on their blood glucose and serum insulin levels were detected.The morphological and functional changes in the pancreas,liver,kidney,and spleen were analyzed by routine histological and immunohistochemical examinations.Changes in the serum cytokine levels in the model mice were assessed by protein arrays.The expression of target proteins related to pancreatic regeneration and apoptosis was examined by western blot.RESULTS MenSC and UcMSC transplantation significantly improved the blood glucose and serum insulin levels in T1D model mice.Immunofluorescence analysis revealed that the numbers of insulin+and CD31+cells in the pancreas were significantly increased in MSC-treated mice compared with control mice.Subsequent western blot analysis also showed that vascular endothelial growth factor(VEGF),Bcl2,Bcl-xL and Proliferating cell nuclear antigen in pancreatic tissue was significantly upregulated in MSC-treated mice compared with control mice.Additionally,protein arrays indicated that MenSC and UcMSC transplantation significantly downregulated the serum levels of interferonγand tumor necrosis factorαand upregulated the serum levels of interleukin-6 and VEGF in the model mice.Additionally,histological and immunohistochemical analyses revealed that MSC transplantation systematically improved the morphologies and functions of the liver,kidney,and spleen in T1D model mice.CONCLUSION MenSC transplantation significantly improves the symptoms in T1D model mice and exerts protective effects on their main organs.Moreover,MSC-mediated angiogenesis,antiapoptotic effects and immunomodulation likely contribute to the above improvements.Thus,MenSC are expected to become promising seeding cells for clinical diabetes treatment due to their advantages mentioned above.     

In vivo tumour and metastasis reduction and in vitro effects on invasion assays of the ruthenium RM175 and osmium AFAP51 organometallics in the mammary cancer model

We have compared the organometallic arene complexes [(η⁶-biphenyl)M(ethylenediamine)Cl]⁺ RM175 (M = Ru^II) and its isostructural osmium(II) analogue AFAP51 (M = Os^II) for their ability to induce cell detachment resistance from fibronectin, collagen IV and poly-l-lysine, and cell re-adhesion after treatment, their effects on cell migration and cell viability, on matrix metalloproteinases production, and on primary tumour growth of MCa mammary carcinoma, the effect of human serum albumin on their cytotoxicity. There are differences between ruthenium and osmium. The Os complex is up to 6× more potent than RM175 towards highly-invasive breast MDA-MB-231, human breast MCF-7 and human epithelial HBL-100 cancer cells, but whereas RM175 was active against MCa mammary carcinoma in vivo and caused metastasis reduction, AFAP51 was not. Intriguingly the presence of human serum albumin in the growth medium enhanced the cytotoxicity of both compounds. RM175 increased the resistance of MDA-MB-231 cells to detachment from substrates and both compounds inhibited the production of MMP-2. These data confirm the key role of ruthenium itself in anti-metastatic activity. It will be interesting to explore the activity of osmium arene complexes in other tumour models and the possibility of changing the non-arene ligands to tune the anticancer activity of osmium in vivo.     

Co-transplantation of olfactory ensheathing glia and mesenchymal stromal cells does not have synergistic effects after spinal cord injury in the rat

Background aimsOlfactory ensheathing glia (OEG) and mesenchymal stromal cells (MSC) are suitable candidates for transplantation therapy of spinal cord injury (SCI). Both facilitate functional improvement after SCI by producing trophic factors and cytokines. In this study, the co-transplantation of both types of cells was studied to clarify their additive and/ or synergistic effects on SCI.MethodsA balloon-induced compression lesion was used to produce SCI in rats. OEG, MSC or both OEG and MSC (3 × 10⁵ cells of each cell type) were implanted by intraspinal injection 1 week after SCI. The effect of transplantation was assessed using behavioral, electrophysiologic and histologic methods.ResultsHindlimb function was examined with Basso, Beattie and Bresnahan (BBB) and Plantar tests. Improvement was found in all three groups of transplanted rats with different time–courses, but there was no significant difference among the groups at the end of the experiment. Motor-evoked potentials after SCI decreased in amplitude from 7 mV to 10 µV. Linear regression analysis showed a modest recovery in amplitude following transplantation, but no change in the control rats. Histologic findings showed that the white and gray matter were significantly spared by transplantation after SCI.ConclusionsFunctional improvement was achieved with transplantation of OEG and/or MSC, but the co-transplantation of OEG and MSC did not show synergistic effects. The poor migration of OEG and MSC might prevent their concerted action. Pre-treatment with a Rho antagonist and a combination of intraspinal and intravenous injection of the cells might be beneficial for SCI therapy.     

Improving mesenchymal stem/stromal cell potency and survival: Proceedings from the International Society of Cell Therapy (ISCT) MSC preconference held in May 2018, Palais des Congrès de Montréal,Organized by the ISCT MSC Scientific Committee

As part of the International Society of Cell Therapy (ISCT) 2018 Annual Meeting, the Mesenchymal Stem/Stromal Cell (MSC) committee organized a pre-conference, which covered methods of improving MSC engraftment and potency in vivo and clinical efficacy using MSC potency assays. The speakers examined methods to improve clinical efficacy using MSC potency assays and methods to improve MSC engraftment/homing/potency in vivo. Discussion of patient “responders” versus “non-responders” in clinical trials and working toward ways to identify them were also included.     

GMP-manufactured density gradient media for optimized mesenchymal stromal/stem cell isolation and expansion

Background aimsBone marrow (BM) mesenchymal stromal/stem cells (MSC) are therapeutic tools in regenerative medicine and oncology. MSC isolation is often performed starting from a separation step based on research-grade 1.077 g/mL density gradient media (DGM). However, MSC clinical application should require the introduction of good manufacturing practice (GMP) reagents. We took advantage of two novel GMP DGM with densities of 1.077 and 1.073 g/mL (Ficoll-Paque? PREMIUM and Ficoll-Paque PREMIUM 1.073, respectively) to test whether these reagents could isolate MSC efficiently while simultaneously comparing their performance.MethodsBM samples were processed using either 1.077 or 1.073 g/mL GMP DGM. BM mononucleated cell (MNC) fractions were analyzed for viability, immunophenotype, clonogenic potential, ex vivo expansion and differentiation potential.ResultsNo differences were noticed in cell recovery and viability between the groups. Fluorescence-activated cell-sorting (FACS) analyzes on freshly isolated cells indicated that the 1.073 g/mL GMP DGM more efficiently depleted the CD45⁺ fraction in comparison with 1.077 GMP DGM. Moreover, in the 1.073 group, fibroblastic colony-forming units (CFU-F) were 1.5 times higher and the final MSC yield 1.8 times increased after four passages. Both reagents isolated MSC with the expected phenotype; however, 1.073-isolated MSC showed a higher expression of CD90, CD146 and GD2. Additionally, MSC from both groups were capable of fully differentiating into bone, adipose cells and cartilage.ConclusionsBoth GMP DGM enriched MSC from BM samples, suggesting that these reagents would be suitable for clinical-grade expansions. In addition, the density of 1.073 g/mL provides a significant advantage over 1.077 g/mL GMP DGM, impacting the quantity of MSC obtained and reducing the ex vivo expansion time for optimized cell-based clinical applications.     

Mesenchymal stromal cells derived from umbilical cord blood migrate in response to complement C1q

Background aimsMesenchymal stromal cells (MSC) have great potential for tissue regeneration and cellular therapy. They migrate preferentially to sites of inflammation and tissue injury, but the molecular signals that guide them to their target tissue remain to be elucidated. We have shown that complement component 1 subcomponent q (C1q) enhances the homing-related response of hematopoietic stem/progenitor cells.MethodsIn this study, we investigated whether C1q elicits directional signals that could influence the migration of MSC to injured tissues/organs.ResultsWe found that C1q chemoattracted human umbilical cord blood-derived MSC in a dose-dependent manner and that the receptor for the global domains of Clq (gC1qR) is present on the surface of MSC. Specific gC1qR antibody blocked the chemotactic response of MSC to C1q, indicating that the C1q/gC1qR interaction may be responsible for the C1q-mediated migration of MSC. Further, we found that C1q enhanced/primed the migration of MSC across reconstituted basement membrane Matrigel towards a low gradient of the chemokine stromal cell-derived factor-1 (SDF-1), which is also present at sites of injury, partly as a result of an increase in surface expression of the SDF-1 receptor CXCR4. Moreover, C1q increased the secretion by MSC of matrix metalloproteinase (MMP)-2 and induced the phosphorylation of ERK1/2.ConclusionsThese results indicate that C1q mediates the migration of MSC in two ways: first, by acting as a chemoattractant, and second, by priming chemotactic responses to SDF-1. Our findings suggest new molecular mechanisms of MSC migration that may contribute to their clinical application in tissue repair.     

Effects of different detachment procedures on viability,nitroxide reduction kinetics and plasma membrane heterogeneity of V‐79 cells

Cell detachment procedures can cause severe damage to cells. Many studies require cells to be detached before measurements; therefore, research on cells that have been grown attached to the bottom of the culture dish and later detached represents a special problem with respect to the experimental results when the properties of cell membranes undergo small changes such as in spectroscopic studies of membrane permeability. We characterized the influence of three different detachment procedures: cell scraping by rubber policeman, trypsinization and a citrate buffer treatment on V‐79 cells in the plateau phase of growth (arrested in G₁). We have measured cell viability by a dye‐exclusion test; nitroxide reduction kinetics and membrane fluidity by EPR (electron paramagnetic resonance) method using the lipophilic spin‐probe MeFASL(10,3) (5‐doxylpalmitoyl‐methylester), which partitions mainly in cell membranes and the hydrophilic spin‐probe TEMPONE (4‐oxo‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl). The resulting cell damage due to the detachment process was observed with SEM (scanning electron microscopy). We found out that cell viability was 91% for trypsin treatment, 85% for citrate treatment and 70% for cell scraping. Though the plasma membrane was mechanically damaged by scraping, the membrane domain structure was not significantly altered compared with other detachment methods. On the other hand, the spin‐probe reduction rate, which depends both on the transport across plasma membrane as well as on metabolic properties of cells, was the highest for trypsin method, suggesting that metabolic rate was the least influenced. Only the reduction rate of trypsin‐treated cells stayed unchanged after 4 h of stirring in suspension. These results suggest that, compared with scraping cells or using citrate buffer, the most suitable detachment method for V‐79 cells is detachment by trypsin and keeping cells in the stirred cell suspension until measurement. This method provides the highest cell viability, less visible damage on SEM micrographs and leaves the metabolic rate of cells unchanged.     

Targeted gene addition to human mesenchymal stromal cells as a cell-based plasma-soluble protein delivery platform

Background aimsGene-modified mesenchymal stromal cells (MSC) provide a promising tool for cell and gene therapy-based applications by potentially acting as a cellular vehicle for protein-replacement therapy. However, to avoid the risk of insertional mutagenesis, targeted integration of a transgene into a ‘safe harbor’ locus is of great interest.MethodsWe sought to determine whether zinc finger nuclease (ZFN)-mediated targeted addition of the erythropoietin (Epo) gene into the chemokine [C-C motif] receptor 5 (CCR5) gene locus, a putative safe harbor locus, in MSC would result in stable transgene expression in vivo.ResultsWhether derived from bone marrow (BM), umbilical cord blood (UCB) or adipose tissue (AT), 30–40% of human MSC underwent ZFN-driven targeted gene addition, as determined by a combination of fluorescence-activated cell sorting (FACS)- and polymerase chain reaction (PCR)-based analyzes. An enzyme-linked immunosorbent assay (ELISA)-based analysis of gene-targeted MSC expressing Epo from the CCR5 locus showed that these modified MSC were found to secrete a significant level of Epo (c. 2 IU/10⁶cells/24 h). NOD/SCID/γC mice injected with ZFN-modified MSC expressing Epo exhibited significantly higher hematocrit and Epo plasma levels for several weeks post-injection, compared with mice receiving control MSC.ConclusionsThese data demonstrate that MSC modified by ZFN-driven targeted gene addition may represent a cellular vehicle for delivery of plasma-soluble therapeutic factors.     

Migration potential and gene expression profile of human mesenchymal stem cells induced by CCL25

Recruitment of mesenchymal stem cells (MSC) to tissue damages is a promising approach for in situ tissue regeneration. The physiological mechanisms and regulatory processes of MSC trafficking to injured tissue remain poorly understood. However, the pivotal role of chemokines in MSC recruitment has already been shown.The aim of this study was to determine the migratory potential and the gene expression profile of MSC stimulated with the CC chemokine CCL25 (TECK). Bone marrow derived human MSC were exposed to different doses of CCL25 in a standardized chemotaxis assay. Microarray gene expression profiling and pathway analysis were performed for CCL25 stimulated MSC.Maximum migration of MSC towards CCL25 was observed at 10³ nM. Microarray analysis revealed an induction of molecules directly involved in chemotaxis and homing of bone marrow cells (CXCL1-3, CXCL8, PDE4B), cytoskeletal and membrane reorganisation (CXCL8, PLD1, IGFBP1), cellular polarity (PLD1), and cell movement (CXCL1-3, CXCL6, CXCL8, PTGS2, PDE4B, TGM2). Respective chemokine secretion was confirmed by protein membrane-array analysis. The activation of CXCR2 ligands (CXCL1-3, CXCL5-6, CXCL8) and a LIF-receptor/gp130 ligand (LIF) indicated an involvement of the respective signaling pathways during initiation of chemotaxis and migration.These results suggest CCL25 as a new potential candidate for further in situ regeneration approaches.     

Mesenchymal stromal cells impair the differentiation of CD14(++) CD16(-) CD64(+) classical monocytes into CD14(++) CD16(+) CD64(++) activate monocytes

Background aimsMesenchymal stromal cells (MSC) possess immunomodulatory activity both in vitro and in vivo. However, little information is available regarding their function during the initiation of immunologic responses through their interactions with monocytes. While many studies have shown that MSC impair the differentiation of monocytes into dendritic cells and macrophages, there are few articles showing the interaction between MSC and monocytes and none of them has addressed the question of monocyte subset modulationMethodsTo understand better the mechanism behind the benefit of MSC infusion for graft-versus-host treatment through monocyte involvement, we performed mixed leucocyte reactions (MLR) in the presence and absence of MSC. After 3 and 7 days, cultures were analyzed by flow cytometry using different approachesResultsMSC induced changes in monocyte phenotype in an MLR. This alteration was accompanied by an increase in monocyte counting and CD14 expression. MSC induced monocyte alterations even without contact, although the parameters above were more pronounced with cell–cell contact. Moreover, the presence of MSC impaired major histocompatibility complex (MHC) I and II, CD11c and CCR5 expression and induced CD14 and CD64 expression on monocytes. These alterations were accompanied by a decrease in interleukin (IL)-1β and IL-6 production by these monocytes, but no change was observed taking into account the phagocytosis capacity of these monocytesConclusionsOur results suggest that MSC impair the differentiation of CD14⁺⁺ CD16^? CD64⁺ classical monocytes into CD14⁺⁺ CD16⁺ CD64⁺⁺ activated monocytes, having an even earlier role than the differentiation of monocytes into dendritic cells and macrophages.     

Labeling of mesenchymal stromal cells with iron oxide-poly(L-lactide) nanoparticles for magnetic resonance imaging: uptake, persistence, effects on cellular function and magnetic resonance imaging properties

Background aimsMesenchymal stromal cells (MSC) are the focus of research in regenerative medicine aiming at the regulatory approval of these cells for specific indications. To cope with the regulatory requirements for somatic cell therapy, novel approaches that do not interfere with the natural behavior of the cells are necessary. In this context in vivo magnetic resonance imaging (MRI) of labeled MSC could be an appropriate tool. Cell labeling for MRI with a variety of different iron oxide preparations is frequently published. However, most publications lack a comprehensive assessment of the non-interference of the contrast agent with the functionality of the labeled MSC, which is a prerequisite for the validity of cell-tracking via MRI.MethodsWe studied the effects of iron oxide–poly(l-lactide) nanoparticles in MSC with flow cytometry, transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), Prussian blue staining, CyQuant^® proliferation testing, colony-forming unit–fibroblast (CFU-F) assays, flow chamber adhesion testing, immunologic tests and differentiation tests. Furthermore iron-labeled MSC were studied by MRI in agarose phantoms and Wistar rats.ResultsIt could be demonstrated that MSC show rapid uptake of nanoparticles and long-lasting intracellular persistence in the endosomal compartment. Labeling of the MSC with these particles has no influence on viability, differentiation, clonogenicity, proliferation, adhesion, phenotype and immunosuppressive properties. They show excellent MRI properties in agarose phantoms and after subcutaneous implantation in rats over several weeks.ConclusionsThese particles qualify for studying MSC homing and trafficking via MRI.     

Non-multipotent stroma inhibit the proliferation and differentiation of mesenchymal stromal cells in vitro

Background aimsThe ability to expand and maintain bone marrow (BM)-derived mesenchymal stem cells (MSC) in vitro is an important aspect of their therapeutic potential. Despite this, the exact composition of stromal cell types within these cultures and the potential effects of non-stem cells on the maintenance of MSC are poorly understood.MethodsC57BL/6J BM stroma was investigated as a model to determine the relationship between MSC and non-multipotent cells in vitro. Whole BM and single-cell derived cultures were characterized using flow cytometry and cell sorting combined with multipotent differentiation. Proliferation of individual stromal populations was evaluated using BrdU.ResultsAt a single-cell level, MSC were distinguished from committed progenitors, and cells lacking differentiation ability, by the expression of CD105 (CD105⁺). A 3-fold reduction in the percentage of CD105⁺ cells was detected after prolonged culture and correlated with loss of MSC. Depletion of CD105⁺ cells coincided with a 10–20% increase in the frequency of proliferating CD105^? cells. Removal of CD105^? stroma caused increased proliferation in CD105⁺ cells, which could be diminished by conditioned media from parent cultures. Comparison of the multipotent differentiation potential in purified and non-purified CD105⁺ cells determined that MSC were detectable for at least 3 weeks longer when cultured in the absence of CD105^? cells.ConclusionsThis work identifies a simple model for characterizing the different cellular components present in BM stromal cultures and demonstrates that stromal cells lacking multipotent differentiating capacity greatly reduce the longevity of MSC.     

Platelet lysate from whole blood-derived pooled platelet concentrates and apheresis-derived platelet concentrates for the isolation and expansion of human bone marrow mesenchymal stromal cells: production process, content and identification of active components

Background aimsThe clinical use of human mesenchymal stromal cells (MSC) requires ex vivo expansion in media containing supplements such as fetal bovine serum or, alternatively, human platelet lysate (PL).MethodsPlatelet concentrates were frozen, quarantine stored, thawed and sterile filtered to obtain PL. PL content and its effect on fibroblast–colony-forming unit (CFU-F) formation, MSC proliferation and large-scale expansion were studied.ResultsPL contained high levels of basic fibroblast growth factor (bFGF), soluble CD40L (sCD40L), vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), platelet-derived growth factor AA (PDGF-AA), platelet-derived growth factor AB/BB (PDGF-AB/BB), chemokine (C-C) ligand 5 (CCL5; RANTES) transforming growth factor-β1 (TGF-β1) and chemokine (C-X-C) ligand 1/2/3 (GRO), with low batch-to-batch variability, and most were stable for up to 14 days. Inhibition of PDGF-BB and bFGF decreased MSC proliferation by about 20% and 50%, respectively. The strongest inhibition (about 75%) was observed with a combination of anti-bFGF + anti-PDGF-BB and anti-bFGF + anti-TGF-β1 + anti-PDGF-BB. Interestingly, various combinations of recombinant PDGF-BB, bFGF and TGF-β1 were not sufficient to promote cell proliferation. PL from whole blood-derived pooled platelet concentrates and apheresis platelet concentrates did not differ significantly in their growth-promoting activity on MSC.ConclusionsPL enhances MSC proliferation and can be regarded as a safe tool for MSC expansion for clinical purposes. \in particular, PDGF-BB and bFGF are essential components for the growth-promoting effect of PL, but are not sufficient for MSC proliferation.