Mesenchymal stromal cells derived from various tissues: Biological, clinical and cryopreservation aspects: Update from 2015 review.

Mesenchymal stromal cells (MSCs) have become one of the most investigated and applied cells for cellular therapy and regenerative medicine. In this update of our review published in 2015, we show that studies continue to abound regarding the characterization of MSCs to distinguish them from other similar cell types, the discovery of new tissue sources of MSCs, and the confirmation of their properties and functions that render them suitable as a therapeutic. Because cryopreservation is widely recognized as the only technology that would enable the on-demand availability of MSCs, here we show that although the traditional method of cryopreserving cells by slow cooling in the presence of 10% dimethyl sulfoxide (Me2SO) continues to be used by many, several novel MSC cryopreservation approaches have emerged. As in our previous review, we conclude from these recent reports that viable and functional MSCs from diverse tissues can be recovered after cryopreservation using a variety of cryoprotectants, freezing protocols, storage temperatures, and periods of storage. We also show that for logistical reasons there are now more studies devoted to the cryopreservation of tissues from which MSCs are derived. A new topic included in this review covers the application in COVID-19 of MSCs arising from their immunomodulatory and antiviral properties. Due to the inherent heterogeneity in MSC populations from different sources there is still no standardized procedure for their isolation, identification, functional characterization, cryopreservation, and route of administration, and not likely to be a "one-size-fits-all" approach in their applications in cell-based therapy and regenerative medicine.

Cryopreservation-induced delayed injury and cell-type-specific responses during the cryopreservation of endothelial cell monolayers.

The cryopreservation of endothelial cell monolayers is an important step that bridges the cryopreservation of cells in suspension to that of tissues. Previous studies have identified clear distinctions in freezing mechanisms between cells in suspension and in monolayers, as well as developed novel protocols for monolayer cryopreservation. Recently, our group has shown that human umbilical vein endothelial cell (HUVEC) and porcine corneal endothelial cell (PCEC) monolayers grown on Rinzl plastic substrate can be cryopreserved in 5% dimethyl sulfoxide, 6% hydroxyethyl starch, and 2% chondroitin sulfate, following a slow-cooling protocol (-1 °C/min) with rapid plunge into liquid nitrogen from -40 °C. However, membrane integrity assessments were done immediately post thaw, which may result in an overestimation of cell viability due to possible delayed injury responses. Here, we show that for the optimal protocol condition of plunge at the -40 °C interrupt temperature, HUVEC and PCEC monolayers exhibited no significant immediate post-thaw injuries nor delayed injury responses during the 24-h post-thaw overnight culture period. HUVEC monolayers experienced no significant impact to their natural growth rate during the post-thaw culture, while PCEC monolayers experienced significantly higher growth than the unfrozen controls. The difference in the low-temperature responses between HUVEC and PCEC monolayers was further shown under high temperature plunge conditions. At these suboptimal plunge temperatures, HUVEC monolayers exhibited moderate immediate membrane injury but a pronounced delayed injury response during the 24-h post-thaw culture, while PCEC monolayers showed significant immediate membrane injury but no additional delayed injury response during the same period. Therefore, we provide further validation of our group's previously designed endothelial monolayer cryopreservation protocol for HUVEC and PCEC monolayers, and we identify several cell-type-specific responses to the freezing process.

Temperature Dependence of Membrane Permeability Parameters for Five Cell Types Using Nonideal Thermodynamic Assumptions to Mathematically Model Cryopreservation Protocols.

Cryopreservation is the process of preserving biological matter at subzero temperatures for long-term storage. During cryopreservation, cells are susceptible to various injuries that can be mitigated by controlling the cooling and warming profiles and cryoprotective agent (CPA) addition and removal procedures. Mathematical modeling of the changing cell volume at different temperatures can greatly reduce the experiments needed to optimize cryopreservation protocols. Such mathematical modeling requires as inputs the cell membrane permeabilities to water and CPA and the osmotically inactive fraction of the cell. Since the intra- and extracellular solutions are generally thermodynamically nonideal, our group has been incorporating the osmotic virial equation to model the solution thermodynamics that underlie the cell volume change equations, adding the second and third osmotic virial coefficients of the grouped intracellular solute to the cell osmotic parameters that must be measured. In our previous work, we reported methods to obtain cell osmotic parameters at room temperature by fitting experimental cell volume kinetic data with equations that incorporated nonideal solution thermodynamics assumptions. Since the relevant cell volume excursions occur at different temperatures, the temperature dependence of the osmotic parameters plays an important role. In this work, we present a new two-part fitting method to obtain five cell-type-specific parameters (water permeability, dimethyl sulfoxide permeability, osmotically inactive fraction, and the second and third osmotic virial coefficients of the intracellular solution) from experimental measurements of equilibrium cell volume and cell volume as a function of time at room temperature and 0 °C for five cell types, namely, human umbilical vein endothelial cells (HUVECs), H9c2 rat myoblasts, porcine corneal endothelial cells (PCECs), the Jurkat T-lymphocyte cell line, and human cerebral microvascular endothelial cells (hCMECs/D3 cell line). The fitting method in this work is based on both equilibrium and kinetic cell volume data, enabling us to solve some technical challenges and expand our previously reported measurement technique to 0 °C. Finally, we use the measured parameters to model the cell volume changes for a HUVEC cryopreservation protocol to demonstrate the impact of the nonideal thermodynamic assumptions on predicting the changing cell volume during freezing and thawing.

Permeation kinetics of dimethyl sulfoxide in porcine corneoscleral discs.

The cornea is the transparent tissue in front of the eye that bends light to help the eye focus. More than five million people's vision can be restored by a corneal transplant (keratoplasty), but there is a scarcity of suitable donor tissue. Cryopreservation could potentially increase the on-demand availability of corneas by reducing expiration and contamination during hypothermic storage, and allow equitable distribution. Understanding the transport of water and cryoprotectants across the tissue is important in developing effective cryopreservation protocols. Here, we first measured the shrinking and swelling kinetics at 22 °C and 0 °C of porcine corneoscleral discs when exposed to phosphate-buffered saline and to a cryoprotectant vehicle solution containing 2.5% chondroitin sulfate and 1% dextran. Other valuable measurements were made including the density and osmolality of the vehicle solution at 0 °C, and the water fraction of porcine cornea and sclera. Using the knowledge gained from this first part to minimize background swelling, we then examined permeation kinetics of dimethyl sulfoxide (Me2SO) in porcine corneoscleral discs at 0 °C, the temperature at which cryoprotectant loading typically occurs. The concentration data obtained as a function of time were fitted to a Fick's law model of one-dimensional diffusion to measure an effective diffusion coefficient of Me2SO, which was found to be 5.306×10-11 m2/s. We further quantified permeation kinetics of Me2SO in sclera alone at 0 °C to support our hypothesis that our measurements for corneoscleral discs will not be affected by the presence of the sclera. The obtained effective diffusion coefficient can be used in modelling aimed at developing cryopreservation protocols that minimize the exposure time of the corneas during the cryoprotectant loading step.

Cryopreservation of human cerebral microvascular endothelial cells with glycerol.

The cryopreservation of human cerebral microvascular endothelial cells (hCMEC) has facilitated their commercial availability for research studying the blood-brain barrier. The currently employed cryopreservation protocol uses 10% dimethyl sulfoxide (Me2SO) in cell medium, or 5% Me2SO in 95% fetal bovine serum (FBS) as cryoprotective agents (CPAs). However, Me2SO is toxic to cells and FBS is animal-derived and not chemically defined, so reducing the concentrations of these components is desirable. Recently, we showed that cryopreserving hCMEC in cell medium with 5% Me2SO and 6% hydroxyethyl starch (HES) results in over 90% post-thaw cell viability. This previous work was performed using an interrupted slow cooling (graded freezing) approach followed by SYTO13/GelRed staining to assay for membrane integrity. In this paper, we repeated graded freezing of hCMEC in cell medium containing 5% Me2SO and 6% HES, but this time using Calcein AM/propidium iodide staining to ensure that the stain is an equivalent alternative to SYTO13/GelRed for assessment of cell viability, and that results are comparable to those previously published. Next, using graded freezing experiments and Calcein AM/propidium iodide staining, we examined the effectiveness of non-toxic glycerol as a CPA at different concentrations, loading times, and cooling rates. The cryobiological response of hCMEC was used to develop a protocol that optimizes both the permeating and non-permeating capabilities of glycerol. HCMEC in cell medium loaded with 10% glycerol for 1 h at room temperature, ice nucleated at -5 °C and held for 3 min, and then cooled at -1 °C/min to -30 °C before plunging into liquid nitrogen had post-thaw viability of 87.7% ± 1.8%. Matrigel tube formation assay and immunocytochemical staining of junction protein ZO-1 were carried out on post-thaw hCMEC to ensure that the cryopreserved cells were viable and functional, in addition to being membrane-intact.

Cryopreservation and post-thaw characterization of dissociated human islet cells.

The objective of this study is to optimize the cryopreservation of dissociated islet cells and obtain functional cells that can be used in single-cell transcriptome studies on the pathology and treatment of diabetes. Using an iterative graded freezing approach we obtained viable cells after cooling in 10% dimethyl sulfoxide and 6% hydroxyethyl starch at 1°C/min to -40°C, storage in liquid nitrogen, rapid thaw, and removal of cryoprotectants by serial dilution. The expression of epithelial cell adhesion molecule declined immediately after thaw, but recovered after overnight incubation, while that of an endocrine cell marker (HPi2) remained high after cryopreservation. Patch-clamp electrophysiology revealed differences in channel activities and exocytosis of various islet cell types; however, exocytotic responses, and the biophysical properties of voltage-gated Na+ and Ca2+ channels, are sustained after cryopreservation. Single-cell RNA sequencing indicates that overall transcriptome and crucial exocytosis genes are comparable between fresh and cryopreserved dispersed human islet cells. Thus, we report an optimized procedure for cryopreserving dispersed islet cells that maintained their membrane integrity, along with their molecular and functional phenotypes. Our findings will not only provide a ready source of cells for investigating cellular mechanisms in diabetes but also for bio-engineering pseudo-islets and islet sheets for modeling studies and potential transplant applications.

Cryopreservation of human cerebral microvascular endothelial cells and astrocytes in suspension and monolayers.

The blood-brain barrier (BBB) keeps pathogens and toxins out of the brain but also impedes the entry of pharmaceuticals. Human cerebral microvascular endothelial cells (hCMECs) and astrocytes are the main functional cell components of the BBB. Although available commercially as cryopreserved cells in suspension, improvements in their cryopreservation and distribution as cryopreserved monolayers could enhance BBB in vitro studies. Here, we examined the response to slow cooling and storage in liquid nitrogen of immortalized hCMEC/D3 cells and human primary astrocytes in suspension and in monolayers. HCMEC/D3 cells in suspension cryopreserved in 5% dimethyl sulfoxide (DMSO) and 95% fetal bovine serum or in 5% DMSO and 6% hydroxyethyl starch (HES) showed post-thaw membrane integrities above 90%, similar to unfrozen control. Cryopreservation did not affect the time-dependent ability of hCMEC/D3 cells to form tubes on Matrigel. Primary astrocytes in suspension cryopreserved in the presence of 5% DMSO and 6% HES had improved viability over those cryopreserved in 10% DMSO. Monolayers of single cultures or co-cultures of hCMEC/D3 cells and astrocytes on fibronectin-coated Rinzl coverslips retained membrane integrities and metabolic function, after freezing in 5% DMSO, 6% HES, and 2% chondroitin sulfate, that were comparable to those of unfrozen controls even after overnight incubation. Rinzl is better than glass or Thermanox as an underlying solid substrate for cryopreserving hCMEC/D3 monolayers. Cryopreserved hCMEC/D3 monolayers expressed the junction proteins ZO-1 and claudin-5 similar to their unfrozen counterparts. Hence, we describe improved cryopreservation protocols for hCMEC/D3 cells and astrocytes in suspension, and a novel protocol for the cryopreservation of monolayers of hCMEC/D3 cells and astrocytes as single cultures or co-cultures that could expand their distribution for research on disease modeling, drug screening, and targeted therapy pertaining to the BBB.

Protocol for Cryopreservation of Endothelial Monolayers.

One of the major challenges in the preservation of complex tissues is the cryosensitivity of the endothelium, the single layer of cells lining blood vessels, corneas, and other tissues. The increasing importance of endothelial monolayers in tissue-engineered constructs for transplantation and research warrants the need to develop protocols for the successful cryopreservation of cells in monolayers. In this chapter, we describe a recently published cryopreservation protocol that we developed based on examination of various factors that influence the post-thaw recovery of endothelial monolayers. To efficiently investigate cryopreservation protocol parameters, we employed an interrupted slow-cooling procedure (graded freezing) that allows dissecting loss of cell viability into contributions from slow-cooling injury and rapid-cooling injury. Our optimized protocol involves culturing cells on Rinzl plastic coverslips, using a combination of a penetrating cryoprotectant (5% dimethyl sulfoxide) and a non-penetrating cryoprotectant (6% hydroxyethyl starch), addition of 2% chondroitin sulfate, controlled cooling at 0.2 °C/min or 1 °C/min, and removal of cryoprotectant immediately after thaw. The protocol has been validated for human umbilical vein and porcine corneal endothelial cell monolayers.

Cryopreservation of swine colostrum-derived cells.

Mesenchymal stromal cells (MSCs) have been demonstrated to possess anti-inflammatory and antimicrobial properties and are of interest in biotechnologies that will require cryopreservation. Recently, MSC-like cells were isolated from colostrum and milk. We used an interrupted slow freezing procedure to examine cryoinjury incurred during slow cooling and rapid cooling of MSC-like cells from swine colostrum. Cells were loaded with either dimethyl sulfoxide (Me2SO) or glycerol, cooled to a nucleation temperature, ice-nucleated, and further cooled at 1 °C/min. At several temperatures along the cooling path, cells were either thawed directly, or plunged into liquid nitrogen for storage and later thawed. The pattern of direct-thaw and plunge-thaw responses was used to guide optimization of cryopreservation protocol parameters. We found that both 5% Me2SO (0.65 M, loaded for 15 min on ice) or 5% glycerol (0.55 M, loaded for 1 h at room temperature) yielded cells with high post-thaw membrane integrity when cells were cooled to at least -30 °C before being plunged into, and stored in, liquid nitrogen. Cells cultured post-thaw exhibited osteogenic differentiation similar to fresh unfrozen control. Fresh and cryopreserved MSC-like cells demonstrated antimicrobial activity against S. aureus. Also, the antimicrobial activity of cell-conditioned media was higher when both fresh and cryopreserved MSC-like cells were pre-exposed to S. aureus. Thus, we were able to demonstrate cryopreservation of colostrum-derived MSC-like cells using Me2SO or glycerol, and show that both cryoprotectants yield highly viable cells with osteogenic potential, but that cells cryopreserved with glycerol retain higher antimicrobial activity post-thaw.

Cryopreservation of human umbilical vein and porcine corneal endothelial cell monolayers.

Cryopreservation of endothelium is one of the major challenges in the cryopreservation of complex tissues. Human umbilical vein endothelial cells (HUVECs) in suspension are available commercially and recently their post-thaw cell membrane integrity was significantly improved by cryopreservation in 5% dimethyl sulfoxide (Me2SO) and 6% hydroxyethyl starch (HES). However, cryopreservation of cells in monolayers has been elusive. The exact mechanisms of damage during cell monolayer cryopreservation are still under investigation. Here, we show that a combination of different factors contribute to significant progress in cryopreservation of endothelial monolayers. The addition of 2% chondroitin sulfate to 5% Me2SO and 6% HES and cooling at 0.2 or 1 °C/min led to high membrane integrity (97.3 ±â€¯3.2%) immediately after thaw when HUVECs were cultured on a substrate with a coefficient of thermal expansion similar to that of ice. The optimized cryopreservation protocol was applied to monolayers of primary porcine corneal endothelial cells, and resulted in high post-thaw viability (95.9 ±â€¯3.7% membrane integrity) with metabolic activity 12 h post-thaw comparable to unfrozen control.

Expansion and cryopreservation of porcine and human corneal endothelial cells.

Impairment of the corneal endothelium causes blindness that afflicts millions worldwide and constitutes the most often cited indication for corneal transplants. The scarcity of donor corneas has prompted the alternative use of tissue-engineered grafts which requires the ex vivo expansion and cryopreservation of corneal endothelial cells. The aims of this study are to culture and identify the conditions that will yield viable and functional corneal endothelial cells after cryopreservation. Previously, using human umbilical vein endothelial cells (HUVECs), we employed a systematic approach to optimize the post-thaw recovery of cells with high membrane integrity and functionality. Here, we investigated whether improved protocols for HUVECs translate to the cryopreservation of corneal endothelial cells, despite the differences in function and embryonic origin of these cell types. First, we isolated endothelial cells from pig corneas and then applied an interrupted slow cooling protocol in the presence of dimethyl sulfoxide (Me2SO), with or without hydroxyethyl starch (HES). Next, we isolated and expanded endothelial cells from human corneas and applied the best protocol verified using porcine cells. We found that slow cooling at 1 °C/min in the presence of 5% Me2SO and 6% HES, followed by rapid thawing after liquid nitrogen storage, yields membrane-intact cells that could form monolayers expressing the tight junction marker ZO-1 and cytoskeleton F-actin, and could form tubes in reconstituted basement membrane matrix. Thus, we show that a cryopreservation protocol optimized for HUVECs can be applied successfully to corneal endothelial cells, and this could provide a means to address the need for off-the-shelf cryopreserved cells for corneal tissue engineering and regenerative medicine.

Improved Cryopreservation of Human Umbilical Vein Endothelial Cells: A Systematic Approach.

Cryopreservation of human umbilical vein endothelial cells (HUVECs) facilitated their commercial availability for use in vascular biology, tissue engineering and drug delivery research; however, the key variables in HUVEC cryopreservation have not been comprehensively studied. HUVECs are typically cryopreserved by cooling at 1 °C/min in the presence of 10% dimethyl sulfoxide (DMSO). We applied interrupted slow cooling (graded freezing) and interrupted rapid cooling with a hold time (two-step freezing) to identify where in the cooling process cryoinjury to HUVECs occurs. We found that linear cooling at 1 °C/min resulted in higher membrane integrities than linear cooling at 0.2 °C/min or nonlinear two-step freezing. DMSO addition procedures and compositions were also investigated. By combining hydroxyethyl starch with DMSO, HUVEC viability after cryopreservation was improved compared to measured viabilities of commercially available cryopreserved HUVECs and viabilities for HUVEC cryopreservation studies reported in the literature. Furthermore, HUVECs cryopreserved using our improved procedure showed high tube forming capability in a post-thaw angiogenesis assay, a standard indicator of endothelial cell function. As well as presenting superior cryopreservation procedures for HUVECs, the methods developed here can serve as a model to optimize the cryopreservation of other cells.

Beyond membrane integrity: Assessing the functionality of human umbilical vein endothelial cells after cryopreservation.

Assessment of cell membrane integrity is one of the most widely used methods to measure post-cryopreservation viability of cells such as human umbilical vein endothelial cells (HUVECs). However, an evaluation of cell function provides a better measure of cell quality following cryopreservation. The tube formation assay mimics angiogenesis in vitro and can be used to quantitate the ability of endothelial cells to form capillary-like tubular structures when cultured on reconstituted basement membrane (Matrigel). We compared the membrane integrity (measured by flow cytometry) and tube forming ability of HUVEC suspensions exposed to 10% dimethyl sulfoxide (Me2SO), cooled at 1 °C/min to various sub-zero temperatures, plunged directly into liquid nitrogen, stored for an hour, and thawed rapidly. We found that as membrane integrity increased so did the various parameters associated with the extent of in vitro angiogenesis; however, in comparison to fresh cells with a similar percentage of membrane-intact cells, the extent of tube formation, expressed as total tube length, is significantly lower in previously frozen cells for the lower range of post-thaw membrane integrities. Our findings underscore the value of an assay that quantifies a specific function that a cell is known to perform in vivo to measure the success of cryopreservation protocols.

Mesenchymal stromal cells derived from various tissues: Biological, clinical and cryopreservation aspects.

Originally isolated from bone marrow, mesenchymal stromal cells (MSCs) have since been obtained from various fetal and post-natal tissues and are the focus of an increasing number of clinical trials. Because of their tremendous potential for cellular therapy, regenerative medicine and tissue engineering, it is desirable to cryopreserve and bank MSCs to increase their access and availability. A remarkable amount of research and resources have been expended towards optimizing the protocols, freezing media composition, cooling devices and storage containers, as well as developing good manufacturing practices in order to ensure that MSCs retain their therapeutic characteristics following cryopreservation and that they are safe for clinical use. Here, we first present an overview of the identification of MSCs, their tissue sources and the properties that render them suitable as a cellular therapeutic. Next, we discuss the responses of cells during freezing and focus on the traditional and novel approaches used to cryopreserve MSCs. We conclude that viable MSCs from diverse tissues can be recovered after cryopreservation using a variety of freezing protocols, cryoprotectants, storage periods and temperatures. However, alterations in certain functions of MSCs following cryopreservation warrant future investigations on the recovery of cells post-thaw followed by expansion of functional cells in order to achieve their full therapeutic potential.

Effect of supercooling and cell volume on intracellular ice formation.

Intracellular ice formation (IIF) has been linked to death of cells cryopreserved in suspension. It has been assumed that cells can be supercooled by 2 to 10°C before IIF occurs, but measurements of the degree of supercooling that cells can tolerate are often confounded by changing extracellular temperature and solutions of different osmolality (which affect the cell volume). The purpose of this study was to examine how the incidence of IIF in the absence of cryoprotectants is affected by the degree of supercooling and cell volume. Human umbilical vein endothelial cells were suspended in isotonic (300 mOsm) and hypertonic (∼600 to 700 mOsm) solutions and exposed to supercooling ranging from 2 to 10°C before extracellular ice was nucleated. The number of cells undergoing IIF was examined in a cryostage (based on the darkening of cells upon intracellular freezing ("flashing")) as a function of the degree of supercooling, and cell survival post-thaw was assessed using a membrane integrity assay. We found that while the incidence of IIF increased with supercooling in both isotonic and hypertonic solutions, it was higher in the isotonic solution at any given degree of supercooling. Since cells in hypertonic solution were shrunken due to water efflux, we hypothesized that the difference in IIF behavior could be attributed to the decreased volume of cells in the hypertonic solution. Our results confirm that cells with a smaller diameter before extracellular ice nucleation have a decreased probability of IIF and suggest that cell volume could play a more significant role in the incidence of IIF than the extracellular ice nucleation temperature.

Polymeric nanoparticle-mediated silencing of CD44 receptor in CD34+ acute myeloid leukemia cells.

The adhesion receptor CD44 plays an important role in the survival and retention of leukemic stem/progenitor cells (LSPC) within the bone marrow (BM) niche, as well as in the high relapse rates of acute myeloid leukemia (AML). Down-regulating CD44 could be clinically relevant not only for suppression of the deregulated function of LSPC but also in LSPC response to chemotherapeutic agents. Small interfering RNA (siRNA) delivery is a promising approach for AML treatment, and we recently reported effective siRNA delivery into difficult-to-transfect AML cell lines using lipid-substituted polyethylenimine/siRNA complexes (polymeric nanoparticles). In this study, we investigated polymeric nanoparticle-mediated silencing of CD44 in CD34+ LSPC cell models (leukemic KG-1 and KG-1a cell lines) as well as primary AML cells. Polymeric nanoparticle-mediated silencing decreased surface CD44 levels in KG-1, KG-1a and primary AML cells by up to 27%, 30% and 20% at day 3, respectively. Moreover, CD44 silencing resulted in induction of apoptosis in KG-1 cells, reduced adhesion of KG-1 and KG-1a cells to hyaluronic acid-coated cell culture plates and BM-MSC, and decreased adhesion of primary AML cells to BM-MSC. Our results suggest that polymeric nanoparticle-mediated silencing of CD44 might be a useful technique for inhibiting LSPC interactions with their microenvironment, thereby prohibiting leukemia progression or sensitizing LSPC to chemotherapy.

Migration, proliferation, and differentiation of cord blood mesenchymal stromal cells treated with histone deacetylase inhibitor valproic Acid.

Mesenchymal stromal cells (MSC) have great potential for cellular therapies as they can be directed to differentiate into certain lineages or to exert paracrine effects at sites of injury. The interactions between stromal cell-derived factor (SDF)-1 and its receptors CXCR4 and CXCR7 play pivotal roles in the migration of MSC to injured tissues. We evaluated whether a histone deacetylase inhibitor valproic acid (VPA) modulates the migration of cord blood (CB-) derived MSC towards SDF-1 and their proliferation and differentiation. We found that in MSC, VPA increased (i) the gene and total protein expression of CXCR4 and CXCR7 and primed migration towards a low gradient of SDF-1, (ii) the gene expression of MMP-2 and secretion and activation of proMMP-2, (iii) the proliferation and gene expression of pluripotency markers SOX2 and Oct-4, and exposure to lower concentrations of VPA (≤5 mM) had no effect on their differentiation to osteocytes and chondrocytes. Thus, our study indicates that VPA enhances the migration of CB MSC towards SDF-1 by increasing the expression of CXCR4, CXCR7, and MMP-2. VPA at low concentrations may be used for ex vivo treatment of MSC to increase their recruitment to sites of injury without compromising their ability to proliferate or differentiate.

CXCR4 transfection of cord blood mesenchymal stromal cells with the use of cationic liposome enhances their migration toward stromal cell-derived factor-1.

BACKGROUND AIMS: The interaction between stromal cell-derived factor (SDF)-1 and its receptor CXCR4 is one of the mechanisms by which mesenchymal stromal cells (MSCs) are recruited to sites of injury. SDF-1 is upregulated in damaged tissues, but because the surface expression of CXCR4 on cultured MSCs is low, we investigated whether the delivery of CXCR4 into MSCs with the use of the cationic liposomal reagent IBAfect would increase their migration toward SDF-1. METHODS: We examined (i) the effect of MSC confluency, passage number, duration of transfection and amount of IBAfect and plasmid on transfection efficiency as determined by flow cytometric analysis of CXCR4 and (ii) whether IBAfect-mediated CXCR4 transfection affected the viability, proliferation and differentiation of MSCs as well as their response toward an SDF-1 gradient in a trans-Matrigel migration assay. RESULTS: We found that transfection efficiency of up to 40% was achieved after 24-h transfection of 50% confluent MSCs (at passage 4) with an IBAfect:plasmid ratio of 3.6 µL:0.6 µg, and CXCR4 transcript expression in transfected MSCs was 10(5)-fold higher than in non-transfected cells. Transfected MSCs retained their ability to differentiate to osteocytes and chondrocytes but had lower proliferation. Importantly, overexpression of surface CXCR4 with the use of IBAfect significantly increased (>3-fold) the number of cells migrating toward an SDF-1 gradient relative to cells migrating to media alone, compared with non-transfected cells (1.3-fold). CONCLUSIONS: Our results suggest that IBAfect-mediated delivery of CXCR4 into MSCs is a highly efficient technique that may be useful for enhancing the recruitment of systemically infused MSCs for tissue repair.

Enhancing the migration ability of mesenchymal stromal cells by targeting the SDF-1/CXCR4 axis.

Mesenchymal stromal cells (MSCs) are currently being investigated in numerous clinical trials of tissue repair and various immunological disorders based on their ability to secrete trophic factors and to modulate inflammatory responses. MSCs have been shown to migrate to sites of injury and inflammation in response to soluble mediators including the chemokine stromal cell-derived factor-(SDF-)1, but during in vitro culture expansion MSCs lose surface expression of key homing receptors particularly of the SDF-1 receptor, CXCR4. Here we review studies on enhancement of SDF-1-directed migration of MSCs with the premise that their improved recruitment could translate to therapeutic benefits. We describe our studies on approaches to increase the CXCR4 expression in in vitro-expanded cord blood-derived MSCs, namely, transfection, using the commercial liposomal reagent IBAfect, chemical treatment with the histone deacetylase inhibitor valproic acid, and exposure to recombinant complement component C1q. These methodologies will be presented in the context of other cell targeting and delivery strategies that exploit pathways involved in MSC migration. Taken together, these findings indicate that MSCs can be manipulated in vitro to enhance their in vivo recruitment and efficacy for tissue repair.