DeepIFC: Virtual fluorescent labeling of blood cells in imaging flow cytometry data with deep learning.

Imaging flow cytometry (IFC) combines flow cytometry with microscopy, allowing rapid characterization of cellular and molecular properties via high-throughput single-cell fluorescent imaging. However, fluorescent labeling is costly and time-consuming. We present a computational method called DeepIFC based on the Inception U-Net neural network architecture, able to generate fluorescent marker images and learn morphological features from IFC brightfield and darkfield images. Furthermore, the DeepIFC workflow identifies cell types from the generated fluorescent images and visualizes the single-cell features generated in a 2D space. We demonstrate that rarer cell types are predicted well when a balanced data set is used to train the model, and the model is able to recognize red blood cells not seen during model training as a distinct entity. In summary, DeepIFC allows accurate cell reconstruction, typing and recognition of unseen cell types from brightfield and darkfield images via virtual fluorescent labeling.

A management model in blood, tissue and cell establishments to ensure rapid and sustainable patient access to advanced therapy medicinal products in Europe.

Blood, tissue and cell establishments (BTCs) stand out in the management of donor selection, procurement and processing of all types of substances of human origin (SoHO). In the last decades, the framework created around BTCs, including hospitals and national health system networks, and their links to research, development and innovation organizations and agencies have spurred their involvement in the study of groundbreaking advanced therapy medicinal products (ATMP). To further improve strategic synergies in the development of ATMPs, it will be required to promote intra- and inter-European collaborations by creating an international network involving BTCs and major stakeholders (i.e., research organizations, hospitals, universities, patient associations, public agencies). This vision is already shared with the European Blood Alliance, the association of non-profit blood establishments, with 26 member states throughout the European Union and European Free Trade Association states. Herein we present and analyze the "BTC for ATMP Development And Manufacture" (BADAM) model, an ethically responsible business model based on the values and missions of BTCs and their commitment to health equity, patient access and education (based on voluntary donation of SoHO to address unmet clinical needs, while contributing to training professionals and scientific literacy of our Society).

Immunomodulatory Properties of Packed Red Blood Cells during Storage.

Introduction: Red blood cell (RBC) transfusion may affect the recipient immune system. During RBC storage in an unphysiological environment, RBC quality and function are impaired, the cells bleb extracellular vesicles (EVs), and other bioactive substances accumulate in the storage medium. EVs can carry reactive biomolecules and mediate cell-cell interactions. Thus, EVs could explain RBC transfusion related immunomodulation, particularly after prolonged storage. Methods: We exposed peripheral blood mononuclear cells (PBMCs) to allogeneic RBC supernatant (SN) and EVs from fresh and longer-stored RBC units, diluted plasma, and storage solution SAGM, and studied activation and proliferation of T-cells by flow cytometry, and cytokine secretion of LPS-stimulated PBMCs by enzyme-linked immunosorbent assay (ELISA). Results: Both fresh and longer-stored RBC SN but not EVs induced immunomodulation in recipient cells. RBC SN and diluted plasma augmented the proliferation of particularly CD8+ T-cells in a 4-day proliferation assay. T-cell activation by SN was evident already after 5 h as shown by upregulation of CD69. SN suppressed monocyte TNF-α and increased IL-10 secretion while diluted plasma increased secretion of both cytokines. Conclusion: This in vitro study demonstrates that stored RBC SN will have mixed immunomodulatory effects depending on responder cells and conditions, independent of RBC storage age. Fresh RBCs containing relatively few EVs can induce immune responses. Residual plasma in the products may contribute to these effects.

Exploring Transcriptomic Landscapes in Red Blood Cells, in Their Extracellular Vesicles and on a Single-Cell Level.

Being enucleated, RBCs lack typical transcriptomes, but are known to contain small amounts of diverse long transcripts and microRNAs. However, the exact role and importance of these RNAs are lacking. Shedding of extracellular vesicles (EVs) from the plasma membrane constitutes an integral mechanism of RBC homeostasis, by which RBCs remove unnecessary cytoplasmic content and cell membrane. To study this further, we explored the transcriptomes of RBCs and extracellular vesicles (EVs) of RBCs using next-generation sequencing. Furthermore, we performed single-cell RNA sequencing on RBCs, which revealed that approximately 10% of the cells contained detectable levels of mRNA and cells formed three subpopulations based on their transcriptomes. A decrease in the mRNA quantity was observed across the populations. Qualitative changes included the differences in the globin transcripts and changes in the expression of ribosomal genes. A specific splice form of a long non-coding RNA, Metastasis Associated Lung Adenocarcinoma Transcript 1 (MALAT1), was the most enriched marker in one subpopulation of RBCs, co-expressing with ribosomal structural transcripts. MALAT1 expression was confirmed by qPCR in CD71-enriched reticulocytes, which were also characterized with imaging flow cytometry at the single cell level. Analysis of the RBC transcriptome shows enrichment of pathways and functional categories required for the maturation of reticulocytes and erythrocyte functions. The RBC transcriptome was detected in their EVs, making these transcripts available for intercellular communication in blood.

Phospholipid composition of packed red blood cells and that of extracellular vesicles show a high resemblance and stability during storage.

Red blood cells (RBCs) are stored up to 35-42days at 2-6°C in blood banks. During storage, the RBC membrane is challenged by energy depletion, decreasing pH, altered cation homeostasis, and oxidative stress, leading to several biochemical and morphological changes in RBCs and to shedding of extracellular vesicles (EVs) into the storage medium. These changes are collectively known as RBC storage lesions. EVs accumulate in stored RBC concentrates and are, thus, transfused into patients. The potency of EVs as bioactive effectors is largely acknowledged, and EVs in RBC concentrates are suspected to mediate some adverse effects of transfusion. Several studies have shown accumulation of lipid raft-associated proteins in RBC EVs during storage, whereas a comprehensive phospholipidomic study on RBCs and corresponding EVs during the clinical storage period is lacking. Our mass spectrometric and chromatographic study shows that RBCs maintain their major phospholipid (PL) content well during storage despite abundant vesiculation. The phospholipidomes were largely similar between RBCs and EVs. No accumulation of raft lipids in EVs was seen, suggesting that the primary mechanism of RBC vesiculation during storage might not be raft -based. Nonetheless, a slight tendency of EV PLs for shorter acyl chains was observed.

Reply: Adenosine Producing Mesenchymal Stromal Cells.

Adenosine signaling has been described as one of the many immunosuppressive mechanisms of mesenchymal stromal cells (MSCs). Central players in adenosine signaling are the ectonucleotidases CD39 and CD73, which convert ADP/ATP to AMP and AMP to adenosine, respectively. CD73 is one of the three phenotypic markers of MSCs and thus, highly expressed on MSCs. Instead, there has been conflicting results whether MSCs intrinsically express CD39 or not. Stem Cells 2017;35:1649-1650.

Adenosinergic Immunosuppression by Human Mesenchymal Stromal Cells Requires Co-Operation with T cells.

Mesenchymal stem/stromal cells (MSCs) have the capacity to counteract excessive inflammatory responses. MSCs possess a range of immunomodulatory mechanisms, which can be deployed in response to signals in a particular environment and in concert with other immune cells. One immunosuppressive mechanism, not so well-known in MSCs, is mediated via adenosinergic pathway by ectonucleotidases CD73 and CD39. In this study, we demonstrate that adenosine is actively produced from adenosine 5'-monophosphate (AMP) by CD73 on MSCs and MSC-derived extracellular vesicles (EVs). Our results indicate that although MSCs express CD39 at low level and it colocalizes with CD73 in bulge areas of membranes, the most efficient adenosine production from adenosine 5'-triphosphate (ATP) requires co-operation of MSCs and activated T cells. Highly CD39 expressing activated T cells produce AMP from ATP and MSCs produce adenosine from AMP via CD73 activity. Furthermore, adenosinergic signaling plays a role in suppression of T cell proliferation in vitro. In conclusion, this study shows that adenosinergic signaling is an important immunoregulatory mechanism of MSCs, especially in situations where ATP is present in the extracellular environment, like in tissue injury. An efficient production of immunosuppressive adenosine is dependent on the concerted action of CD39-positive immune cells with CD73-positive cells such as MSCs or their EVs.

Real-Time Label-Free Monitoring of Nanoparticle Cell Uptake.

The surface plasmon resonance technique in combination with whole cell sensing is used for the first time for real-time label-free monitoring of nanoparticle cell uptake. The uptake kinetics of several types of nanoparticles relevant to drug delivery applications into HeLa cells is determined. The cell uptake of the nanoparticles is confirmed by confocal microscopy. The cell uptake of silica nanoparticles and polyethylenimine-plasmid DNA polyplexes is studied as a function of temperature, and the uptake energies are determined by Arrhenius plots. The phase transition temperature of the HeLa cell membrane is detected when monitoring cell uptake of silica nanoparticles at different temperatures. The HeLa cell uptake of the mesoporous silica nanoparticles is energy-independent at temperatures slightly higher than the phase transition temperature of the HeLa cell membrane, while the uptake of polyethylenimine-DNA polyplexes is energy-dependent and linear as a function of temperature with an activation energy of Ea = 62 ± 7 kJ mol-1 = 15 ± 2 kcal mol-1 . The HeLa cell uptake of red blood cell derived extracellular vesicles is also studied as a function of the extracellular vesicle concentration. The results show a concentration dependent behavior reaching a saturation level of the extracellular vesicle uptake by HeLa cells.

The effects of culture conditions on the functionality of efficiently obtained mesenchymal stromal cells from human cord blood.

BACKGROUND AIMS: Cord blood (CB) is an attractive source of mesenchymal stromal cells (MSCs) because of its abundant availability and ease of collection. However, the success rate of generating CB-MSCs is low. In this study, our aim was to demonstrate the efficiency of our previously described method to obtain MSCs from CB and further characterize them and to study the effects of different culture conditions on MSCs. METHODS: CB-MSC cultures were established in low oxygen (3%) conditions on fibronectin in 10% fetal bovine serum containing culture medium supplemented with combinations of growth factors. Cells were characterized for their adipogenic, osteogenic and chondrogenic differentiation capacity; phenotype; and HOX gene expression profile. The functionality of the cells cultured in different media was tested in vitro with angiogenesis and T-cell proliferation assays. RESULTS: We demonstrate 87% efficacy in generating MSCs from CB. The established cells had typical MSC characteristics with reduced adipogenic differentiation potential and a unique HOX gene fingerprint. Growth factor-rich medium and a 3% oxygen condition enhanced cell proliferation; however, the growth factor-rich medium had a negative effect on the expression of CD90. Dexamethasone-containing medium improved the capacity of the cells to suppress T-cell proliferation, whereas the cells grown without dexamethasone were more able to support angiogenesis. CONCLUSIONS: Our results demonstrate that the composition of expansion medium is critical for the functionality of MSCs and should always be appropriately defined for each purpose.

Safety and biodistribution study of bone marrow-derived mesenchymal stromal cells and mononuclear cells and the impact of the administration route in an intact porcine model.

BACKGROUND AIMS: Bone marrow mononuclear cells (BM-MNCs) and bone marrow-derived mesenchymal stem stromal cells (BM-MSCs) could have therapeutic potential for numerous conditions, including ischemia-related injury. Cells transplanted intravascularly may become entrapped in the lungs, which potentially decreases their therapeutic effect and increases the risk for embolism. METHODS: Twelve pigs were divided into groups of 3 and received (99m)Tc- hydroxymethyl-propylene-amine-oxime-labeled autologous BM-MNCs or allogeneic BM-MSCs by either intravenous (IV) or intra-arterial (IA) transplantation. A whole body scan and single photon emission computed tomography/computed tomography (SPECT/CT) were performed 8 h later, and tissue biopsies were collected for gamma counting. A helical CT scan was also performed on 4 pigs to detect possible pulmonary embolism, 2 after IV BM-MSC injection and 2 after saline injection. RESULTS: The transplantation route had a greater impact on the biodistribution of the BM-MSCs than the BM-MNCs. The BM-MNCs accumulated in the spleen and bones, irrespective of the administration route. The BM-MSCs had relatively higher uptake in the kidneys. The IA transplantation decreased the deposition of BM-MSCs in the lungs and increased uptake in other organs, especially in the liver. Lung atelectases were frequent due to mechanical ventilation and attracted transplanted cells. CT did not reveal any pulmonary embolism. CONCLUSIONS: Both administration routes were found to be safe, but iatrogenic atelectasis might be an issue when cells accumulate in the lungs. The IA administration is effective in avoiding pulmonary entrapment of BM-MSCs. The cell type and administration method both have a major impact on the acute homing.

OxLDL sensitizes platelets for increased formation of extracellular vesicles capable of finetuning macrophage gene expression.

Platelet extracellular vesicles (PEVs) generated upon platelet activation may play a role in inflammatory pathologies such as atherosclerosis. Oxidized low-density lipoprotein (oxLDL), a well-known contributor to atherogenesis, activates platelets and presensitizes them for activation by other agonists. We studied the effect of oxLDL on the secretion, composition, and inflammatory functions of PEVs using contemporary EV analytics. Platelets were activated by co-stimulation with thrombin (T) and collagen (C) ± oxLDL and characterized by high-resolution flow cytometry, nanoparticle tracking analysis, proximity extension assay, western blot, and electron microscopy. The effect of PEVs on macrophage differentiation and functionality was examined by analyzing macrophage surface markers, cytokine secretion, and transcriptome. OxLDL upregulated TC-induced formation of CD61+, P-selectin+ and phosphatidylserine+ PEVs. Blocking the scavenger receptor CD36 significantly suppressed the oxLDL+TC-induced PEV formation, and HDL caused a slight but detectable suppression. The inflammatory protein cargo differed between the PEVs from stimulated and unstimulated platelets. Both oxLDL+TC- and TC-induced PEVs enhanced macrophage HLA-DR and CD86 expression and decreased CD11c expression as well as secretion of several cytokines. Pathways related to cell cycle and regulation of gene expression, and immune system signaling were overrepresented in the differentially expressed genes between TC PEV -treated vs. control macrophages and oxLDL+TC PEV -treated vs. control macrophages, respectively. In conclusion, we speculate that oxLDL and activated platelets contribute to proatherogenic processes by increasing the number of PEVs that provide an adhesive and procoagulant surface, contain inflammatory mediators, and subtly finetune the macrophage gene expression.

ATMP-classified, scalable, autologous cell spray for the treatment of skin wounds and assessment of its effects on wound healing clinically and on a molecular level.

BACKGROUND: Autologous split-thickness skin grafts (STSGs) are the standard of care for closure of deep and large burns. However, perforation and extensive fishnet-like expansion of the grafts to achieve greater area wound coverage can lead to treatment failures or esthetically poor healing outcomes and scarring. The purpose of this study was to validate an autologous advanced therapy medicinal product (ATMP)-compliant skin cell suspension and evaluate its efficacy to promote epithelialization. METHODS: Cells isolated from a piece of STSG according to ATMP classification requirements were sprayed onto 20 patients during a single operation in a validation study. Comparative evaluation of treatment efficacy was carried out using side-by-side skin graft donor site wounds that were standardized in depth. Firstly, we characterized wound healing transcriptomes at 14 and 21 days from serial wound biopsies in seven patients. Then, side-by-side wounds in four patients were treated with or without the skin cells. The wounds were photographed, clinical outcomes assessed, and the treatment and control wound transcriptomes at 14 days were compared to the untreated wounds' healing transcriptomes. RESULTS: The average cell yield after isolation from the STSG was 2.4 × 106 cells/cm2 with 96 % viability. The product contained mainly keratinocytes and their precursors but also other skin cells such as fibroblasts were present. As compared to vehicle-treated donor site wounds, the wounds treated with cells demonstrated improved epithelialization by both direct comparison and machine learning analysis of the transcriptomes. CONCLUSIONS: We showed that rapid and scalable ATMP-classified processing of skin cells is feasible, and application of the skin cells effectively promotes healing and epithelization of donor site wounds.

Spatial and temporal expression pattern of germ layer markers during human embryonic stem cell differentiation in embryoid bodies.

Human embryonic stem cell (hESC) differentiation in embryoid bodies (EBs) provides a valuable tool to study the interplay of different germ layers and their influence on cell differentiation. The gene expression of the developing EBs has been shown in many studies, but the protein expression and the spatial composition of different germ layers in human EBs have not been systematically studied. The aim of the present work was to study the temporal and spatial organisation of germ layers based on the expression of mesoderm (Brachyury T), endoderm (AFP) and ectoderm (SOX1) markers during the early stages of differentiation in eight hESC lines. Tissue multi-array technology was applied to study the protein expression of a large number of EBs. According to our results, EB formation and the organisation of germ layers occurred in a similar manner in all the lines. During 12 days of differentiation, all the germ layer markers were present, but no obvious distinct trajectories were formed. However, older EBs were highly organised in structure. Pluripotency marker OCT3/4 expression persisted unexpectedly long in the differentiating EBs. Cavity formation was observed in the immunocytological sections, and caspase-3 expression was high, suggesting a role of apoptosis in hESC differentiation and/or EB formation. The expression of Brachyury T was notably low in all the lines, also those with the best cardiac differentiation capacity, while the expression of SOX1 was higher in some lines, suggesting that the neural differentiation propensity may be detectable already in the early stages of EB differentiation.

Human Mesenchymal Stromal Cell Secretome Promotes the Immunoregulatory Phenotype and Phagocytosis Activity in Human Macrophages.

Human mesenchymal stromal/stem cells (hMSCs) show great promise in cell therapy due to their immunomodulatory properties. The overall immunomodulatory response of hMSCs resembles the resolution of inflammation, in which lipid mediators and regulatory macrophages (Mregs) play key roles. We investigated the effect of hMSC cell-cell contact and secretome on macrophages polarized and activated toward Mreg phenotype. Moreover, we studied the effect of supplemented polyunsaturated fatty acids (PUFAs): docosahexaenoic acid (DHA) and arachidonic acid, the precursors of lipid mediators, on hMSC immunomodulation. Our results show that unlike hMSC cell-cell contact, the hMSC secretome markedly increased the CD206 expression in both Mreg-polarized and Mreg-activated macrophages. Moreover, the secretome enhanced the expression of programmed death-ligand 1 on Mreg-polarized macrophages and Mer receptor tyrosine kinase on Mreg-activated macrophages. Remarkably, these changes were translated into improved Candida albicans phagocytosis activity of macrophages. Taken together, these results demonstrate that the hMSC secretome promotes the immunoregulatory and proresolving phenotype of Mregs. Intriguingly, DHA supplementation to hMSCs resulted in a more potentiated immunomodulation with increased CD163 expression and decreased gene expression of matrix metalloproteinase 2 in Mreg-polarized macrophages. These findings highlight the potential of PUFA supplementations as an easy and safe method to improve the hMSC therapeutic potential.

Label-free characterization and real-time monitoring of cell uptake of extracellular vesicles.

Extracellular vesicles (EVs) have the ability to function as molecular vehicles and could therefore be harnessed to deliver drugs to target cells in diseases such as cancer. The composition of EVs determines their function as well as their interactions with cells, which consequently affects the cell uptake efficacy of EVs. In this study, we present two novel label-free approaches for studying EVs; characterization of EV composition by time-gated surface-enhanced Raman spectroscopy (TG-SERS) and monitoring the kinetics and amount of cellular uptake of EVs by surface plasmon resonance (SPR) in real-time. Using these methods, we characterized the most abundant EVs of human blood, red blood cell (RBC)- and platelet (PLT)-derived EVs and studied their interactions with prostate cancer cells. Complementary studies were performed with nanoparticle tracking analysis for concentration and size determinations of EVs, zeta potential measurements for surface charge analysis, and fluorophore-based confocal imaging and flow cytometry to confirm EV uptake. Our results revealed distinct biochemical features between the studied EVs and demonstrated that PLT-derived EVs were more efficiently internalized by PC-3 cells than RBC-derived EVs. The two novel label-free techniques introduced in this study were found to efficiently complement conventional techniques and paves the way for further use of TG-SERS and SPR in EV studies.

Polyunsaturated fatty acids modify the extracellular vesicle membranes and increase the production of proresolving lipid mediators of human mesenchymal stromal cells.

Human mesenchymal stromal/stem cells (hMSCs) are used in experimental cell therapy to treat various immunological disorders, and the extracellular vesicles (hMSC-EVs) they produce have emerged as an option for cell-free therapeutics. The immunomodulatory function of hMSCs resembles the resolution of inflammation, in which proresolving lipid mediators (LMs) play key roles. Multiple mechanisms underlying the hMSC immunosuppressive effect has been elucidated; however, the impact of LMs and EVs in the resolution is poorly understood. In this study, we supplemented hMSCs with polyunsaturated fatty acids (PUFAs); arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, which serve as precursors for multiple LMs. We then determined the consequent compositional modifications in the fatty acid, phospholipid, and LM profiles. Mass spectrometric analyses revealed that the supplemented PUFAs were incorporated into the main membrane phospholipid classes with different dynamics, with phosphatidylcholine serving as the first acceptor. Most importantly, the PUFA modifications were transferred into hMSC-EVs, which are known to mediate hMSC immunomodulation. Furthermore, the membrane-incorporated PUFAs influenced the LM profile by increasing the production of downstream prostaglandin E2 and proresolving LMs, including Resolvin E2 and Resolvin D6. The production of LMs was further enhanced by a highly proinflammatory stimulus, which resulted in an increase in a number of mediators, most notably prostaglandins, while other stimulatory conditions had less a pronounced impact after a 48-h incubation. The current findings suggest that PUFA manipulations of hMSCs exert significant immunomodulatory effects via EVs and proresolving LMs, the composition of which can be modified to potentiate the therapeutic impact of hMSCs.

Mesenchymal Stromal Cells and Their Extracellular Vesicles Enhance the Anti-Inflammatory Phenotype of Regulatory Macrophages by Downregulating the Production of Interleukin (IL)-23 and IL-22.

Resolution-phase macrophage population orchestrates active dampening of the inflammation by secreting anti-inflammatory and proresolving products including interleukin (IL)-10 and lipid mediators (LMs). We investigated the effects of both human bone marrow-derived mesenchymal stromal cells (MSCs) and MSC-derived extracellular vesicles (MSC-EVs) on mature human regulatory macrophages (Mregs). The cytokines and LMs were determined from cell culture media of Mregs cultivated with MSCs and MSC-EVs. In addition, the alterations in the expression of cell surface markers and the phagocytic ability of Mregs were investigated. Our novel findings indicate that both MSC coculture and MSC-EVs downregulated the production of IL-23 and IL-22 enhancing the anti-inflammatory phenotype of Mregs and amplifying proresolving properties. The levels of prostaglandin E2 (PGE2) were substantially upregulated in MSC coculture media, which may endorse proresolving LM class switching. In addition, our results manifest, for the first time, that MSC-EVs mediate the Mreg phenotype change via PGE2. These data suggest that both human MSC and MSC-EVs may potentiate tolerance-promoting proresolving phenotype of human Mregs.

Unexpected complication in a rat stroke model: exacerbation of secondary pathology in the thalamus by subacute intraarterial administration of human bone marrow-derived mesenchymal stem cells.

This study examined whether human bone marrow mesenchymal stromal/stem cells (BMMSCs) could alleviate the secondary pathology in the thalamus after middle cerebral artery occlusion (MCAO) in rats. Atypical accumulation of both amyloid-ß (Aß) and calcium in the thalamus was significantly higher in rats receiving the BMMSCs infusion 48 hours after MCAO as compared with the vehicle MCAO group. The elevated Aß/calcium accumulation correlated with the level of impaired sensorimotor function. Although secondary pathology in the thalamus seems to be rodent specific, it needs to be taken into account because it may impair long-term behavioral recovery and negate therapeutic treatment effects.

Differential Clearance of Rat and Human Bone Marrow-Derived Mesenchymal Stem Cells From the Brain After Intra-arterial Infusion in Rats.

Intra-arterial (IA) delivery of bone marrow-derived mesenchymal stem cells (BM-MSCs) has shown potential as a minimally invasive therapeutic approach for stroke. The aim of the present study was to determine the whole-body biodistribution and clearance of technetium-99m ((99m)Tc)-labeled rat and human BM-MSCs after IA delivery in a rat model of transient middle cerebral artery occlusion (MCAO) using single-photon emission computed tomography (SPECT). Our hypothesis was that xenotransplantation has a major impact on the behavior of cells. Male RccHan:Wistar rats were subjected to sham operation or MCAO. Twenty-four hours after surgery, BM-MSCs (2 × 10(6) cells/animal) labeled with (99m)Tc were infused into the external carotid artery. Whole-body SPECT images were acquired 20 min, 3 h, and 6 h postinjection, after which rats were sacrificed, and organs were collected and weighed for measurement of radioactivity. The results showed that the majority of the cells were located in the brain and especially in the ipsilateral hemisphere immediately after cell infusion both in sham-operated and MCAO rats. This was followed by fast disappearance, particularly in the case of human cells. At the same time, the radioactivity signal increased in the spleen, kidney, and liver, the organs responsible for destroying cells. Further studies are needed to demonstrate whether differential cell behavior has any functional impact.

The cerebral embolism evoked by intra-arterial delivery of allogeneic bone marrow mesenchymal stem cells in rats is related to cell dose and infusion velocity.

INTRODUCTION: Intra-arterial cell infusion is an efficient delivery route with which to target organs such as the ischemic brain. However, adverse events including microembolisms and decreased cerebral blood flow were recently reported after intra-arterial cell delivery in rodent models, raising safety concerns. We tested the hypothesis that cell dose, infusion volume, and velocity would be related to the severity of complications after intra-arterial cell delivery. METHODS: In this study, 38 rats were subjected to a sham middle cerebral artery occlusion (sham-MCAO) procedure before being infused with allogeneic bone-marrow mesenchymal stem cells at different cell doses (0 to 1.0 × 10(6)), infusion volumes (0.5 to 1.0 ml), and infusion times (3 to 6 minutes). An additional group (n = 4) was infused with 1.0 × 10(6) cells labeled with iron oxide for in vivo tracking of cells. Cells were infused through the external carotid artery under laser Doppler flowmetry monitoring 48 hours after sham-MCAO. Magnetic resonance imaging (MRI) was performed 24 hours after cell infusion to reveal cerebral embolisms or hemorrhage. Limb placing, cylinder, and open field tests were conducted to assess sensorimotor functions before the rats were perfused for histology. RESULTS: A cell dose-related reduction in cerebral blood flow was noted, as well as an increase in embolic events and concomitant lesion size, and sensorimotor impairment. In addition, a low infusion velocity (0.5 ml/6 minutes) was associated with high rate of complications. Lesions on MRI were confirmed with histology and corresponded to necrotic cell loss and blood-brain barrier leakage. CONCLUSIONS: Particularly cell dose but also infusion velocity contribute to complications encountered after intra-arterial cell transplantation. This should be considered before planning efficacy studies in rats and, potentially, in patients with stroke.