Anti-donor immune responses elicited by allogeneic mesenchymal stem cells: what have we learned so far?

Intralymphatic Administration of Adipose Mesenchymal Stem Cells Reduces the Severity of Collagen-Induced Experimental Arthritis

Mesenchymal stem cells (MSCs) are multipotent stromal cells with immunomodulatory properties. They have emerged as a very promising treatment for autoimmunity and inflammatory diseases such as rheumatoid arthritis. Previous studies have demonstrated that MSCs, administered systemically, migrate to lymphoid tissues associated with the inflammatory site where functional MSC-induced immune cells with a regulatory phenotype were increased mediating the immunomodulatory effects of MSCs. These results suggest that homing of MSCs to the lymphatic system plays an important role in the mechanism of action of MSCs in vivo. Thus, we hypothesized that direct intralymphatic (IL) (also referred as intranodal) administration of MSCs could be an alternative and effective route of administration for MSC-based therapy. Here, we report the feasibility and efficacy of the IL administration of human expanded adipose mesenchymal stem cells (eASCs) in a mouse model of collagen-induced arthritis (CIA). IL administration of eASCs attenuated the severity and progression of arthritis, reduced bone destruction and increased the levels of regulatory T cells (CD25⁺Foxp3⁺CD4⁺ cells) and Tr1 cells (IL10⁺CD4⁺), in spleen and draining lymph nodes. Taken together, these results indicate that IL administration of eASCs is very effective in modulating established CIA and may represent an alternative treatment modality for cell therapy with eASCs.

New Delivery Systems of Stem Cells for Vascular Regeneration in Ischemia

The finances of patients and countries are increasingly overwhelmed with the plague of cardiovascular diseases as a result of having to chronically manage the associated complications of ischemia such as heart failures, neurological deficits, chronic limb ulcers, gangrenes, and amputations. Hence, scientific research has sought for alternate therapies since pharmacological and surgical treatments have fallen below expectations in providing the desired quality of life. The advent of stem cells research has raised expectations with respect to vascular regeneration and tissue remodeling, hence assuring the patients of the possibility of an improved quality of life. However, these supposed encouraging results have been short-lived as the retention, survival, and engraftment rates of these cells appear to be inadequate; hence, the long-term beneficial effects of these cells cannot be ascertained. These drawbacks have led to the relentless research into better ways to deliver stem cells or angiogenic factors (which mobilize stem cells) to the regions of interest to facilitate increased retention, survival, engraftment, and regeneration. This review considered methods, such as the use of scaffolds, retrograde coronary delivery, improved combinations, stem cell pretreatment, preconditioning, stem cell exosomes, mannitol, magnet, and ultrasound-enhanced delivery, homing techniques, and stem cell modulation. Furthermore, the study appraised the possibility of a combination therapy of stem cells and macrophages, considering the enormous role macrophages play in repair, remodeling, and angiogenesis.

Transcriptome Profiling of IL-17A Preactivated Mesenchymal Stem Cells: A Comparative Study to Unmodified and IFN-γ Modified Mesenchymal Stem Cells

Human mesenchymal stem cells pretreatment with IL-17A (MSC-17) potently enhances T cell immunosuppression but not their immunogenicity, in addition to avidly promoting the induction of suppressive regulatory T cells. The aim of this study was to identify potential mechanisms by which human MSC-17 mediate their superior immunomodulatory function. Untreated-MSC (UT-MSC), IFN-γ treated MSC (MSC-γ), and MSC-17 were assessed for their gene expression profile by microarray. Significantly regulated genes were identified for their biological functions (Database for Annotation, Visualisation and Integrated Discovery, DAVID). Microarray analyses identified 1278 differentially regulated genes between MSC-γ and UT-MSC and 67 genes between MSC-17 and UT-MSC. MSC-γ were enriched for genes involved in immune response, antigen processing and presentation, humoral response, and complement activation, consistent with increased MSC-γ immunogenicity. MSC-17 genes were associated with chemotaxis response, which may be involved in T cell recruitment for MSC-17 immunosuppression. MMP1, MMP13, and CXCL6 were highly and specifically expressed in MSC-17, which was further validated by real-time PCR. Thus, MMPs and chemokines may play a key role in mediating MSC-17 superior immunomodulatory function. MSC-17 represent a potential cellular therapy to suppress immunological T cell responses mediated by expression of an array of immunoregulatory molecules.

Ultrasound-Mediated Mesenchymal Stem Cells Transfection as a Targeted Cancer Therapy Platform

Mesenchymal stem cells (MSCs) hold tremendous potential as a targeted cell-based delivery platform for inflammatory and cancer therapy. Genetic manipulation of MSCs, however, is challenging, and therefore, most studies using MSCs as therapeutic cell carriers have utilized viral vectors to transduce the cells. Here, we demonstrate, for the first time, an alternative approach for the efficient transfection of MSCs; therapeutic ultrasound (TUS). Using TUS with low intensities and moderate frequencies, MSCs were transfected with a pDNA encoding for PEX, a protein that inhibits tumor angiogenesis, and studied as a cell vehicle for in vivo tumor therapy. TUS application did not alter the MSCs' stemness or their homing capabilities, and the transfected MSCs transcribed biologically active PEX. Additionally, in a mouse model, 70% inhibition of prostate tumor growth was achieved following a single I.V. administration of MSCs that were TUS-transfected with pPEX. Further, the repeated I.V. administration of TUS-pPEX transfected-MSCs enhanced tumor inhibition up to 84%. Altogether, these results provide a proof of concept that TUS-transfected MSCs can be effectively used as a cell-based delivery approach for the prospective treatment of cancer.

Detection of Stem Cell Transplant Rejection with Ferumoxytol MR Imaging: Correlation of MR Imaging Findings with Those at Intravital Microscopy

Purpose To determine whether endogenous labeling of macrophages with clinically applicable nanoparticles enables noninvasive detection of innate immune responses to stem cell transplants with magnetic resonance (MR) imaging. Materials and Methods Work with human stem cells was approved by the institutional review board and the stem cell research oversight committee, and animal experiments were approved by the administrative panel on laboratory animal care. Nine immunocompetent Sprague-Dawley rats received intravenous injection of ferumoxytol, and 18 Jax C57BL/6-Tg (Csf1r-EGFP-NGFR/FKBP1A/TNFRSF6) 2Bck/J mice received rhodamine-conjugated ferumoxytol. Then, 48 hours later, immune-matched or mismatched stem cells were implanted into osteochondral defects of the knee joints of experimental rats and calvarial defects of Jax mice. All animals underwent serial MR imaging and intravital microscopy (IVM) up to 4 weeks after surgery. Macrophages of Jax C57BL/6-Tg (Csf1r-EGFP-NGFR/FKBP1A/TNFRSF6) 2Bck/J mice express enhanced green fluorescent protein (GFP), which enables in vivo correlation of ferumoxytol enhancement at MR imaging with macrophage quantities at IVM. All quantitative data were compared between experimental groups by using a mixed linear model and t tests. Results Immune-mismatched stem cell implants demonstrated stronger ferumoxytol enhancement than did matched stem cell implants. At 4 weeks, T2 values of mismatched implants were significantly lower than those of matched implants in osteochondral defects of female rats (mean, 10.72 msec for human stem cells and 11.55 msec for male rat stem cells vs 15.45 msec for sex-matched rat stem cells; P = .02 and P = .04, respectively) and calvarial defects of recipient mice (mean, 21.7 msec vs 27.1 msec, respectively; P = .0444). This corresponded to increased recruitment of enhanced GFP- and rhodamine-ferumoxytol-positive macrophages into stem cell transplants, as visualized with IVM and histopathologic examination. Conclusion Endogenous labeling of macrophages with ferumoxytol enables noninvasive detection of innate immune responses to stem cell transplants with MR imaging. ^© RSNA, 2017 Online supplemental material is available for this article.

Biodistribution and Immunogenicity of Allogeneic Mesenchymal Stem Cells in a Rat Model of Intraarticular Chondrocyte Xenotransplantation

Xenogeneic chondrocytes and allogeneic mesenchymal stem cells (MSC) are considered a potential source of cells for articular cartilage repair. We here assessed the immune response triggered by xenogeneic chondrocytes when injected intraarticularly, as well as the immunoregulatory effect of allogeneic bone marrow-derived MSC after systemic administration. To this end, a discordant xenotransplantation model was established by injecting three million porcine articular chondrocytes (PAC) into the femorotibial joint of Lewis rats and monitoring the immune response. First, the fate of MSC injected using various routes was monitored in an in vivo imaging system. The biodistribution revealed a dependency on the injection route with MSC injected intravenously (i.v.) succumbing early after 24 h and MSC injected intraperitoneally (i.p.) lasting locally for at least 5 days. Importantly, no migration of MSC to the joint was detected in rats previously injected with PAC. MSC were then administered either i.v. 1 week before PAC injection or i.p. 3 weeks after to assess their immunomodulatory function on humoral and adaptive immune parameters. Anti-PAC IgM and IgG responses were detected in all PAC-injected rats with a peak at week 2 postinjection and reactivity remaining above baseline levels by week 18. IgG2a and IgG2b were the predominant and long-lasting IgG subtypes. By contrast, no anti-MSC antibody response was detected in the cohort injected with MSC only, but infusion of MSC before PAC injection temporarily augmented the anti-PAC antibody response. Consistent with a cellular immune response to PAC in PAC-injected rats, cytokine/chemokine profiling in serum by antibody array revealed a distinct pattern relative to controls characterized by elevation of multiple markers at week 2, as well as increases in proliferation in draining lymph nodes. Notably, systemic administration of allogeneic MSC under the described conditions did not diminish the immune response. IL-2 measurements in cocultures of rat peripheral blood lymphocytes with PAC indicated that PAC injection induced some T-cell hyporesponsiveness that was not enhanced in the cohorts additionally receiving MSC. Thus, PAC injected intraarticularly in Lewis rats induced a cellular and humoral immune response that was not counteracted by the systemic administration of allogeneic MSC under the described conditions.

Improved osteogenesis and upregulated immunogenicity in human placenta-derived mesenchymal stem cells primed with osteogenic induction medium

BACKGROUND

Mesenchymal stem cells (MSCs) are widely used in cell-based therapy owing to their multilineage potential and low immunogenicity. However, low differentiation efficiency and unpredictable immunogenicity of allogeneic MSCs in vivo limit their success in therapeutic treatment. Herein, we evaluated the differentiation potential and immunogenicity of human placenta-derived MSCs manipulated with osteogenic priming and dedifferentiation process.

METHODS

MSCs from human placentas were subjected to osteogenic induction and then cultivated in osteogenic factor-free media; the obtained cell population was termed dedifferentiated mesenchymal stem cells (De-MSCs). De-MSCs were induced into osteo-, chondro- and adipo-differentiation in vitro. Cell proliferation was quantified by a Cell-Counting Kit-8 or tritiated thymidine ([(3)H]-TdR) incorporation. Meanwhile, the osteogenesis of De-MSCs in vivo was assayed by real-time PCR and histological staining. The expressions of stem cell markers and co-stimulatory molecules on De-MSCs and lymphocytes from primed BALB/c mouse with De-MSCs were determined by flow cytometry.

RESULTS

De-MSCs exhibited some properties similar to MSCs including multiple differentiation potential and hypoimmunogenicity. Upon re-osteogenic induction, De-MSCs exhibited higher differentiation capability than MSCs both in vitro and in vivo. Of note, De-MSCs had upregulated immunogenicity in association with their osteogenesis, reflected by the alternated expressions of co-stimulatory molecules on the surface and decreased suppression on T cell activation. Functionally, De-MSC-derived osteoblasts could prime lymphocytes of peripheral blood and spleen in BALB/c mice in vivo.

CONCLUSIONS

These data are of great significance for the potential application of De-MSCs as an alternative resource for regenerative medicine and tissue engineering. In order to avoid being rejected by the host during allogeneic De-MSC therapy, we suggest that immune intervention should be considered to boost the immune acceptance and integration because of the upregulated immunogenicity of De-MSCs with redifferentiation in clinical applications.

Response to Intravenous Allogeneic Equine Cord Blood-Derived Mesenchymal Stromal Cells Administered from Chilled or Frozen State in Serum and Protein-Free Media

Equine mesenchymal stromal cells (MSC) are commonly transported, chilled or frozen, to veterinary clinics. These MSC must remain viable and minimally affected by culture, transport, or injection processes. The safety of two carrier solutions developed for optimal viability and excipient use were evaluated in ponies, with and without allogeneic cord blood-derived (CB) MSC. We hypothesized that neither the carrier solutions nor CB-MSC would elicit measurable changes in clinical, hematological, or biochemical parameters. In nine ponies (study 1), a bolus of HypoThermosol^® FRS (HTS-FRS), CryoStor^® CS10 (CS10), or saline was injected IV (n = 3/treatment). Study 2, following a 1-week washout period, 5 × 10⁷ pooled allogeneic CB-MSCs were administered IV in HTS-FRS following 24 h simulated chilled transport. Study 3, following another 1-week washout period 5 × 10⁷ pooled allogeneic CB-MSCs were administered IV in CS10 immediately after thawing. Nine ponies received CB-MSCs in study 2 and 3, and three ponies received the cell carrier media without cells. CB-MSCs were pooled in equal numbers from five unrelated donors. In all studies, ponies were monitored with physical examination, and blood collection for 7 days following injection. CD4 and CD8 lymphocyte populations were also evaluated in each blood sample. In all three studies, physical exam, complete blood cell count, serum biochemistry, and coagulation panel did not deviate from established normal ranges. Proportions of CD4⁺ and CD8⁺ lymphocytes increased at 168 h postinjection in CB-MSC treatment groups regardless of the carrier solution. Decreases in CD4^+/CD8⁺ double positive populations were observed at 24 and 72 h in CB-MSC-treated animals. There was no difference in viability between CB-MSCs suspended in HTS-FRS and CS10. HTS-FRS and CS10 used for low volume excipient injection of MSC suspensions were not associated with short-term adverse reactions. HTS-FRS and CS10 both adequately maintain CB-MSC viability following hypothermic or frozen simulated transport, respectively. CB-MSCs do not elicit clinical abnormalities, but allogeneic stimulation of CD4⁺ and CD8⁺ lymphocyte populations may occur. Future studies should include in vitro or in vivo evaluation of cell-mediated or adaptive immunity to autologous, identical allogeneic, or MSC originating from additional unrelated individuals in order to better characterize this response.

Transcriptional profiling reveals intrinsic mRNA alterations in multipotent mesenchymal stromal cells isolated from bone marrow of newly-diagnosed type 1 diabetes patients

Background

Bone marrow multipotent mesenchymal stromal cells (MSCs) are a diverse subset of precursors that contribute to the homeostasis of the hematopoietic niche. MSCs can be isolated and expanded in vitro and have unique immunomodulatory and regenerative properties that make them attractive for the treatment of autoimmune diseases, including type 1 diabetes (T1D). Whether autologous or allogeneic MSCs are more suitable for therapeutic purposes has not yet been established. While autologous MSCs may present abnormal function, allogeneic cells may be recognized and rejected by the host immune system. Thus, studies that investigate biological characteristics of MSCs isolated from T1D patients are essential to guide future clinical applications.

Methods

Bone marrow-derived MSCs from recently diagnosed type 1 diabetes patients (T1D-MSCs) were compared with those from healthy individuals (C-MSCs) for morphological and immunophenotypic characteristics and for differentiation potential. Bioinformatics approaches allowed us to match absolute and differential gene expression of several adhesion molecules, immune mediators, growth factors, and their receptors involved with hematopoietic support and immunomodulatory properties of MSCs. Finally, the differentially expressed genes were collated for functional pathway enrichment analysis.

Results

T1D-MSCs and C-MSCs were similar for morphology, immunophenotype, and differentiation potential. Our absolute gene expression results supported previous literature reports, while also detecting new potential molecules related to bone marrow-derived MSC functions. T1D-MSCs showed intrinsic abnormalities in mRNA expression, including the immunomodulatory molecules VCAM-1, CXCL12, HGF, and CCL2. Pathway analyses revealed activation of sympathetic nervous system and JAK STAT signaling in T1D-MSCs.

Conclusions

Collectively, our results indicate that MSCs isolated from T1D patients present intrinsic transcriptional alterations that may affect their therapeutic potential. However, the implications of these abnormalities in T1D development as well as in the therapeutic efficacy of autologous MSCs require further investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0351-y) contains supplementary material, which is available to authorized users.

Mesenchymal stem cells to treat diabetic neuropathy: a long and strenuous way from bench to the clinic

As one of the most common complications of diabetes, diabetic neuropathy often causes foot ulcers and even limb amputations. Inspite of continuous development in antidiabetic drugs, there is still no efficient therapy to cure diabetic neuropathy. Diabetic neuropathy shows declined vascularity in peripheral nerves and lack of angiogenic and neurotrophic factors. Mesenchymal stem cells (MSCs) have been indicated as a novel emerging regenerative therapy for diabetic neuropathy because of their multipotency. We will briefly review the pathogenesis of diabetic neuropathy, characteristic of MSCs, effects of MSC therapies for diabetic neuropathy and its related mechanisms. In order to treat diabetic neuropathy, neurotrophic or angiogenic factors in the form of protein or gene therapy are delivered to diabetic neuropathy, but therapeutic efficiencies are very modest if not ineffective. MSC treatment reverses manifestations of diabetic neuropathy. MSCs have an important role to repair tissue and to lower blood glucose level. MSCs even paracrinely secrete neurotrophic factors, angiogenic factors, cytokines, and immunomodulatory substances to ameliorate diabetic neuropathy. There are still several challenges in the clinical translation of MSC therapy, such as safety, optimal dose of administration, optimal mode of cell delivery, issues of MSC heterogeneity, clinically meaningful engraftment, autologous or allogeneic approach, challenges with cell manufacture, and further mechanisms.

Mesenchymal Stem Cells Modulate the Functional Properties of Microglia via TGF-β Secretion

: The regulation of microglial cell phenotype is a potential therapeutic intervention in neurodegenerative disease. Previously, we reported that transforming growth factor-β (TGF-β) levels in mesenchymal stromal cells (MSCs) could be used as potential biological markers to predict the effectiveness of autologous MSC therapy in patients with amyotrophic lateral sclerosis. However, the underlying mechanism of TGF-β in MSCs was not fully elucidated in determining the functional properties of microglia. In this study, we aimed to clarify the role of TGF-β that is involved in MSC effectiveness, especially focusing on microglia functional properties that play a pivotal role in neuroinflammation. We found that MSC-conditioned media (MSC-CM) inhibited proinflammatory cytokine expression, restored alternative activated microglia phenotype markers (fractalkine receptor, mannose receptor, CD200 receptor), and enhanced phagocytosis in lipopolysaccharide (LPS)-stimulated microglia. In addition, TGF-β in MSC-CM played a major role in these effects by inhibiting the nuclear factor-κB pathway and restoring the TGF-β pathway in LPS-stimulated microglia. Recombinant TGF-β also induced similar effects to MSC-CM in LPS-stimulated microglia. Therefore, we propose that MSCs can modulate the functional properties of microglia via TGF-β secretion, switching them from a classically activated phenotype to an inflammation-resolving phenotype. The latter role may be associated with the inhibition of neuroinflammatory processes in neurodegenerative disorders.

SIGNIFICANCE

The results of this study showed that microglia functional properties may be modulated depending on the composition and quantity of mesenchymal stromal cell (MSC)-secreting factors. Transforming growth factor (TGF)-β is proposed as a modulator of microglia functional properties among MSC-secreting factors, and this study aligns with a previous clinical study by these same authors. TGF-β releasing capacity could be an important factor enhancing the therapeutic efficacy of MSCs in clinical trials.

Mesenchymal Stromal Cells Prevent Allostimulation In Vivo and Control Checkpoints of Th1 Priming: Migration of Human DC to Lymph Nodes and NK Cell Activation

Although the immunomodulatory potency of mesenchymal stromal cells (MSC) is well established, the mechanisms behind are still not clear. The crosstalk between myeloid dendritic cells (mDC) and natural killer (NK) cells and especially NK cell-derived interferon-gamma (IFN-γ) play a pivotal role in the development of type 1 helper (Th1) cell immune responses. While many studies explored the isolated impact of MSC on either in vitro generated DC, NK, or T cells, there are only few data available on the complex interplay between these cells. Here, we investigated the impact of MSC on the functionality of human mDC and the consequences for NK cell and Th1 priming in vitro and in vivo. In critical limb ischemia patients, who have been treated with allogeneic placenta-derived mesenchymal-like stromal cells (PLX-PAD), no in vivo priming of Th1 responses toward the major histocompatibility complex (MHC) mismatches could be detected. Further in vitro studies revealed that mDC reprogramming could play a central role for these effects. Following crosstalk with MSC, activated mDC acquired a tolerogenic phenotype characterized by reduced migration toward CCR7 ligand and impaired ability to stimulate NK cell-derived IFN-γ production. These effects, which were strongly related to an altered interleukin (IL)-12/IL-10 production by mDC, were accompanied by an effective prevention of Th1 priming in vivo. Our findings provide novel evidence for the regulation of Th1 priming by MSC via modulation of mDC and NK cell crosstalk and show that off-the-shelf produced MHC-mismatched PLX-PAD can be used in patients without any sign of immunogenicity.

Preclinical Studies of Mesenchymal Stem Cell (MSC) Administration in Chronic Obstructive Pulmonary Disease (COPD): A Systematic Review and Meta-Analysis

BACKGROUND

In the last two decades, mesenchymal stem cells (MSCs) have been pre-clinically utilized in the treatment of a variety of kinds of diseases including chronic obstructive pulmonary disease (COPD). The aim of the current study was to systematically review and conduct a meta-analysis on the published pre-clinical studies of MSC administration in the treatment of COPD in animal models.

METHODS AND RESULTS

A systematic search of electronic databases was performed. Statistical analysis was performed using the Comprehensive Meta-Analysis software (Version 3). The pooled Hedges's g with 95% confidence intervals (95% CIs) was adopted to assess the effect size. Random effect model was used due to the heterogeneity between the studies. A total of 20 eligible studies were included in the current systematic review. The overall meta-analysis showed that MSC administration was significantly in favor of attenuating acute lung injury (Hedges's g = -2.325 ± 0.145 with 95% CI: -2.609 ~ -2.040, P < 0.001 for mean linear intercept, MLI; Hedges's g = -3.488 ± 0.504 with 95% CI: -4.476 ~ -2.501, P < 0.001 for TUNEL staining), stimulating lung tissue repair (Hedges's g = 3.249 ± 0.586 with 95% CI: 2.103~ 4.394, P < 0.001) and improving lung function (Hedges's g = 2.053 ± 0.408 with 95% CI: 1.253 ~ 2.854, P< 0.001). The mechanism of MSC therapy in COPD is through ameliorating airway inflammation (Hedges's g = -2.956 ± 0.371 with 95% CI: -3.683 ~ -2.229, P< 0.001) and stimulating cytokine synthesis that involves lung tissue repair (Hedges's g = 3.103 ± 0.734 with 95% CI: 1.664 ~ 4.541, P< 0.001).

CONCLUSION

This systematic review and meta-analysis suggest a promising role for MSCs in COPD treatment. Although the COPD models may not truly mimic COPD patients, these pre-clinical studies demonstrate that MSC hold promise in the treatment of chronic lung diseases including COPD. The mechanisms of MSCs role in preclinical COPD treatment may be associated with attenuating airway inflammation as well as stimulating lung tissue repair.

Intravenous administration of expanded allogeneic adipose-derived mesenchymal stem cells in refractory rheumatoid arthritis (Cx611): results of a multicentre, dose escalation, randomised, single-blind, placebo-controlled phase Ib/IIa clinical trial

OBJECTIVES

To evaluate the safety and tolerability of the intravenous administration of Cx611, a preparation of allogeneic expanded adipose-derived stem cells (eASCs), in patients with refractory rheumatoid arthritis (RA), as well as to obtain preliminary clinical efficacy data in this population.

METHODS

It is a multicentre, dose escalation, randomised, single-blind (double-blind for efficacy), placebo-controlled, phase Ib/IIa clinical trial. Patients with active refractory RA (failure to at least two biologicals) were randomised to receive three intravenous infusions of Cx611: 1 million/kg (cohort A), 2 million/kg (cohort B), 4 million/kg (cohort C) or placebo, on days 1, 8 and 15, and they were followed for therapy assessment for 24 weeks.

RESULTS

Fifty-three patients were treated (20 in cohort A, 20 in cohort B, 6 in cohort C and 7 in placebo group). A total of 141 adverse events (AEs) were reported. Seventeen patients from the group A (85%), 15 from the group B (75%), 6 from the group C (100%) and 4 from the placebo group (57%) experienced at least one AE.Eight AEs from 6 patients were grade 3 in intensity (severe), 5 in cohort A (lacunar infarction, diarrhoea, tendon rupture, rheumatoid nodule and arthritis), 2 in cohort B (sciatica and RA) and 1 in the placebo group (asthenia). Only one of the grade 3 AEs was serious (the lacunar infarction). American College of Rheumatology 20 responses for cohorts A, B, C and placebo were 45%, 20%, 33% and 29%, respectively, at month 1, and 25%, 15%, 17% and 0%, respectively, at month 3.

CONCLUSIONS

The intravenous infusion of Cx611 was in general well tolerated, without evidence of dose-related toxicity at the dose range and time period studied. In addition, a trend for clinical efficacy was observed. These data, in our opinion, justify further investigation of this innovative therapy in patients with RA.

TRIAL REGISTRATION NUMBERS

EudraCT: 2010-021602-37; NCT01663116; Results.

Culture expanded primary chondrocytes have potent immunomodulatory properties and do not induce an allogeneic immune response

OBJECTIVE

Allogeneic cell therapies, such as mesenchymal stromal cells (MSC), which have potent regenerative and anti-inflammatory potential are being investigated as a therapy for osteoarthritis (OA) and cartilage injury. Here we describe another potential source of regenerative and anti-inflammatory allogeneic cells, culture expanded primary chondrocytes (CEPC). In direct comparison to allogeneic MSC, we extensively assess the immunological interactions of CEPC in an allogeneic setting.

METHODS

Chondrocytes were isolated from rat articular cartilage and cultured in normoxic or hypoxic conditions. In vitro co-culture assays with allogeneic lymphocytes and macrophages were used to assess the immunomodulatory capacities of the chondrocytes, followed by immune response analysis by flow cytometry, ELISA and qPCR.

RESULTS

CEPC showed reduced induction of proliferation, activation and cytotoxic granzyme B expression in allogeneic T cells. Importantly, exposure to pro-inflammatory cytokines did not increase CEPC immunogenicity despite increases in MHC-I. Furthermore, CEPC had a potent ability to suppress allogeneic T cell proliferation, which was dependent on nitric oxide production. This suppression was contact independent in hypoxia cultured CEPC. Finally, chondrocytes were shown to have the capacity to modulate pro-inflammatory macrophage activity by reducing MHC-II expression and TNF-α secretion.

CONCLUSION

These data indicate the potential use of allogeneic chondrocytes in OA and cartilage defects. The lack of evident immunogenicity, despite exposure to a pro-inflammatory environment, coupled with the immunomodulatory ability indicates that these cells have the potential to evade the host immune system and suppress inflammation, thus potentially facilitating the resolution of OA induced inflammation and cartilage regeneration.

Immunogenicity of allogeneic mesenchymal stromal cells: what has been seen in vitro and in vivo?

Mesenchymal stromal cells (MSC) are promising candidates for supporting regeneration and suppressing undesired immune reactivity. Although autologous MSC have been most commonly used for clinical trials, data on application of allogeneic MHC-unmatched MSC were reported. The usage of MSC as an 'off-the-shelf' product would have several advantages; however, it is an immunological challenge. The preclinical studies on the (non)immunogenicity of MSC are contradictory and, unfortunately, solid data from clinical trials are missing. Induction of an alloresponse would be a major limitation for the application of allogeneic MSC. Here we discuss the key elements for the induction of an alloresponse and targets of immunomodulation by MSC as well as preclinical and clinical hints on allo(non)response to MSC.

MSC surface markers (CD44, CD73, and CD90) can identify human MSC-derived extracellular vesicles by conventional flow cytometry

BACKGROUND

Human mesenchymal stromal cells (hMSC) are multipotent cells with both regenerative and immunomodulatory activities making them an attractive tool for cellular therapy. In the last few years it has been shown that the beneficial effects of hMSC may be due to paracrine effects and, at least in part, mediated by extracellular vesicles (EV). EV have emerged as important mediators of cell-to-cell communication. Flow cytometry (FCM) is a routine technology used in most clinical laboratories and could be used as a methodology for hMSC-EV characterization. Although several reports have characterized EV by FCM, a specific panel and protocol for hMSC-derived EV is lacking. The main objective of our study was the characterization of hMSC-EV using a standard flow cytometer.

METHODS

Human MSC from bone marrow of healthy donors, mesenchymal cell lines (HS-5 and hTERT) and a leukemic cell line (K562 cells) were used to obtain EV for FCM characterization. EV released from the different cell lines were isolated by ultracentrifugation and were characterized, using a multi-parametric analysis, in a conventional flow cytometer. EV characterization by transmission electron microscopy (TEM), western blot (WB) and Nano-particle tracking analysis (NTA) was also performed.

RESULTS

EV membranes are constituted by the combination of specific cell surface molecules depending on their cell of origin, together with specific proteins like tetraspanins (e.g. CD63). We have characterized by FCM the EV released from BM-hMSC, that were defined as particles less than 0.9 μm, positive for the hMSC markers (CD90, CD44 and CD73) and negative for CD34 and CD45 (hematopoietic markers). In addition, hMSC-derived EV were also positive for CD63 and CD81, the two characteristic markers of EV. To validate our characterization strategy, EV from mesenchymal cell lines (hTERT/HS-5) were also studied, using the leukemia cell line (K562) as a negative control. EV released from mesenchymal cell lines displayed the same immunophenotypic profile as the EV from primary BM-hMSC, while the EV derived from K562 cells did not show hMSC markers. We further validated the panel using EV from hMSC transduced with GFP. Finally, EV derived from the different sources (hMSC, hTERT/HS-5 and K562) were also characterized by WB, TEM and NTA, demonstrating the expression by WB of the exosomal markers CD63 and CD81, as well as CD73 in those from MSC origin. EV morphology and size/concentration was confirmed by TEM and NTA, respectively.

CONCLUSION

We described a strategy that allows the identification and characterization by flow cytometry of hMSC-derived EV that can be routinely used in most laboratories with a standard flow cytometry facility.

Neural and mesenchymal stem cells in animal models of Huntington's disease: past experiences and future challenges

Huntington's disease (HD) is an inherited disease that causes progressive nerve cell degeneration. It is triggered by a mutation in the HTT gene that strongly influences functional abilities and usually results in movement, cognitive and psychiatric disorders. HD is incurable, although treatments are available to help manage symptoms and to delay the physical, mental and behavioral declines associated with the condition. Stem cells are the essential building blocks of life, and play a crucial role in the genesis and development of all higher organisms. Ablative surgical procedures and fetal tissue cell transplantation, which are still experimental, demonstrate low rates of recovery in HD patients. Due to neuronal cell death caused by accumulation of the mutated huntingtin (mHTT) protein, it is unlikely that such brain damage can be treated solely by drug-based therapies. Stem cell-based therapies are important in order to reconstruct damaged brain areas in HD patients. These therapies have a dual role: stem cell paracrine action, stimulating local cell survival, and brain tissue regeneration through the production of new neurons from the intrinsic and likely from donor stem cells. This review summarizes current knowledge on neural stem/progenitor cell and mesenchymal stem cell transplantation, which has been carried out in several animal models of HD, discussing cell distribution, survival and differentiation after transplantation, as well as functional recovery and anatomic improvements associated with these approaches. We also discuss the usefulness of this information for future preclinical and clinical studies in HD.

The challenges and promises of allogeneic mesenchymal stem cells for use as a cell-based therapy

Mesenchymal stem cells (MSCs) are ideal for cell-based therapy in various inflammatory diseases because of their immunosuppressive and tissue repair properties. Moreover, their immunosuppressive properties and low immunogenicity contribute to a reduced or weakened immune response elicited by the implantation of allogeneic MSCs compared with other cell types. Therefore, implantation of allogeneic MSCs may be a promising cell-based therapy. In this review, we first summarize the unique advantages of allogeneic MSCs for therapeutic applications. Second, we critically analyze the factors influencing their therapeutic effects, including administration routes, detection time-points, disease models, differentiation of MSCs in vivo, and timing and dosage of MSC administration. Finally, current approaches to allogeneic MSC application are discussed. In conclusion, allogeneic MSCs are a promising option because of their low immunogenicity and immunosuppressive and tissue repair capabilities. Further investigations are needed to enhance the consistency and efficacy of MSCs when used as a cell-based therapy in inflammatory diseases as well as for tissue repair.

The current landscape of the mesenchymal stromal cell secretome: A new paradigm for cell-free regeneration

The unique properties of mesenchymal stromal/stem cells (MSCs) to self-renew and their multipotentiality have rendered them attractive to researchers and clinicians. In addition to the differentiation potential, the broad repertoire of secreted trophic factors (cytokines) exhibiting diverse functions such as immunomodulation, anti-inflammatory activity, angiogenesis and anti-apoptotic, commonly referred to as the MSC secretome, has gained immense attention in the past few years. There is enough evidence to show that the one important pathway by which MSCs participate in tissue repair and regeneration is through its secretome. Concurrently, a large body of MSC research has focused on characterization of the MSC secretome; this includes both soluble factors and factors released in extracellular vesicles, for example, exosomes and microvesicles. This review provides an overview of our current understanding of the MSC secretome with respect to their potential clinical applications.

Safety of allogeneic bone marrow derived mesenchymal stromal cell therapy in renal transplant recipients: the neptune study

Background

Mesenchymal stromal cells (MSC) may serve as an attractive therapy in renal transplantation due to their immunosuppressive and reparative properties. While most studies have used autologous MSCs, allogeneic MSCs offer the advantage of immediate availability for clinical use. This is of major importance for indications where instant treatment is needed, for example allograft rejection or calcineurin inhibitor toxicity. Clinical studies using allogeneic MSCs are limited in number. Although these studies showed no adverse reactions, allogeneic MSCs could possibly elicit an anti-donor immune response, which may increase the incidence of rejection and impact the allograft survival in the long term. These safety issues should be addressed before further studies are planned with allogeneic MSCs in the solid organ transplant setting.

Methods/design

10 renal allograft recipients, 18–75 years old, will be included in this clinical phase Ib, open label, single center study. Patients will receive two doses of 1.5 × 10⁶ per/kg body weight allogeneic bone marrow derived MSCs intravenously, at 25 and 26 weeks after transplantation, when immune suppression levels are reduced. The primary end point of this study is safety by assessing biopsy proven acute rejection (BPAR)/graft loss after MSC treatment. Secondary end points, all measured before and after MSC infusions, include: comparison of fibrosis in renal biopsy by quantitative Sirius Red scoring; de novo HLA antibody development and extensive immune monitoring; renal function measured by cGFR and iohexol clearance; CMV and BK infection and other opportunistic infections.

Discussion

This study will provide information on the safety of allogeneic MSC infusion and its effect on the incidence of BPAR/graft loss.

Trial registration: NCT02387151

Cell therapy for full-thickness wounds: are fetal dermal cells a potential source?

The application of autologous dermal fibroblasts has been shown to improve burn wound healing. However, a major hurdle is the availability of sufficient healthy skin as a cell source. We investigated fetal dermal cells as an alternative source for cell-based therapy for skin regeneration. Human (hFF), porcine fetal (pFF) or autologous dermal fibroblasts (AF) were seeded in a collagen–elastin substitute (Novomaix, NVM), which was applied in combination with an autologous split thickness skin graft (STSG) to evaluate the effects of these cells on wound healing in a porcine excisional wound model. Transplantation of wounds with NVM+hFF showed an increased influx of inflammatory cells (e.g., neutrophils, macrophages, CD4⁺ and CD8⁺ lymphocytes) compared to STSG, acellular NVM (Acell-NVM) and NVM+AF at post-surgery days 7 and/or 14. Wounds treated with NVM+pFF presented only an increase in CD8⁺ lymphocyte influx. Furthermore, reduced alpha-smooth muscle actin (αSMA) expression in wound areas and reduced contraction of the wounds was observed with NVM+AF compared to Acell-NVM. Xenogeneic transplantation of NVM+hFF increased αSMA expression in wounds compared to NVM+AF. An improved scar quality was observed for wounds treated with NVM+AF compared to Acell-NVM, NVM+hFF and NVM+pFF at day 56. In conclusion, application of autologous fibroblasts improved the overall outcome of wound healing in comparison to fetal dermal cells and Acell-NVM, whereas application of fetal dermal fibroblasts in NVM did not improve wound healing of full-thickness wounds in a porcine model. Although human fetal dermal cells demonstrated an increased immune response, this did not seem to affect scar quality.

The role of adult tissue-derived stem cells in chronic leg ulcers: a systematic review focused on tissue regeneration medicine

Wound healing is an articulated process that can be impaired in different steps in chronic wounds. Chronic leg ulcers are a special type of non-healing wounds that represent an important cause of morbidity and public cost in western countries. Because of their common recurrence after conventional managements and increasing prevalence due to an ageing population, newer approaches are needed. Over the last decade, the research has been focused on innovative treatment strategies, including stem-cell-based therapies. After the initial interest in embryonic pluripotent cells, several different types of adult stem cells have been studied because of ethical issues. Specific types of adult stem cells have shown a high potentiality in tissue healing, in both in vitro and in vivo studies. Aim of this review is to clearly report the newest insights on tissue regeneration medicine, with particular regard for chronic leg ulcers.

GDF-15 secreted from human umbilical cord blood mesenchymal stem cells delivered through the cerebrospinal fluid promotes hippocampal neurogenesis and synaptic activity in an Alzheimer's disease model

Our previous studies demonstrated that transplantation of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) into the hippocampus of a transgenic mouse model of Alzheimer's disease (AD) reduced amyloid-β (Aβ) plaques and enhanced cognitive function through paracrine action. Due to the limited life span of hUCB-MSCs after their transplantation, the extension of hUCB-MSC efficacy was essential for AD treatment. In this study, we show that repeated cisterna magna injections of hUCB-MSCs activated endogenous hippocampal neurogenesis and significantly reduced Aβ42 levels. To identify the paracrine factors released from the hUCB-MSCs that stimulated endogenous hippocampal neurogenesis in the dentate gyrus, we cocultured adult mouse neural stem cells (NSCs) with hUCB-MSCs and analyzed the cocultured media with cytokine arrays. Growth differentiation factor-15 (GDF-15) levels were significantly increased in the media. GDF-15 suppression in hUCB-MSCs with GDF-15 small interfering RNA reduced the proliferation of NSCs in cocultures. Conversely, recombinant GDF-15 treatment in both in vitro and in vivo enhanced hippocampal NSC proliferation and neuronal differentiation. Repeated administration of hUBC-MSCs markedly promoted the expression of synaptic vesicle markers, including synaptophysin, which are downregulated in patients with AD. In addition, in vitro synaptic activity through GDF-15 was promoted. Taken together, these results indicated that repeated cisterna magna administration of hUCB-MSCs enhanced endogenous adult hippocampal neurogenesis and synaptic activity through a paracrine factor of GDF-15, suggesting a possible role of hUCB-MSCs in future treatment strategies for AD.

Therapeutic Potential of Multipotent Mesenchymal Stromal Cells and Their Extracellular Vesicles

The therapeutic potential of mesenchymal stromal cells (MSCs) is evident by the number of new and ongoing trials targeting an impressive variety of conditions. In bone and cartilage repair, MSCs are expected to replace the damaged tissue, while in other therapies they modulate a therapeutic response by the secretion of bioactive molecules. MSCs possess a phenotypic plasticity and harbor an arsenal of bioactive molecules that can be released upon sensing signals in the local milieu either directly or packaged in extracellular vesicles (EVs). The reported paracrine effects comprise many of the important functions of MSCs, including supporting hematopoietic stem cells in the bone marrow, promoting angiogenesis, and modulating the immune system. The major drawback in MSC therapy is the incomplete understanding of cell fate following systemic administration as well as the mechanisms by which these cells correct disease. In this review we discuss what is known about MSC engraftment, hemocompatibility, and immunomodulation, as well as the potential of bringing the MSC-EV field toward a clinical translation.

Allogeneic Adipose-Derived Stem Cells Protect Fat Grafts at the Early Stage and Improve Long-Term Retention in Immunocompetent Rats

BACKGROUND

Syngeneic adipose-derived stem cells (ASCs) promote the survival of fat grafts. But it is unclear whether allogeneic ASCs have a similar protective effect. In this study, we investigated the protective effect of allogeneic ASCs in a fat graft model of immunocompetent rats.

METHODS

Syngeneic and allogeneic ASCs were derived from Lewis (LEW) and Norway-Brown rats, respectively. Fifty-four LEW rats were divided into three groups. Each LEW rat was injected subcutaneously at two paravertebral spots with adipose granules premixed with DMEM (AFT group), syngeneic ASCs (SYNG group), or allogeneic ASCs (ALLG group). Fat grafts were harvested at 7 and 14 days to examine apoptosis rates and immunochemistry staining was performed for Perilipin A and CD34. At 3 months, fat graft volume retentions were measured. The proportion of regulatory T (Treg) cells and the ratio of CD4/CD8 cells in blood were analyzed at 7 days.

RESULTS

Expression of Perilipin A and CD34 was higher in the ALLG group than the AFT group at 14 days (P < 0.05). The apoptosis rate in the ALLG group decreased in comparison with the AFT group at 7 and 14 days (P < 0.05). At 3 months, allogeneic ASCs increased fat graft volume retentions (P < 0.05). No difference was found in the proportion of Treg cells and CD4/CD8 cells ratio between groups. There were no statistically significant difference between ALLG and SYNG groups at all time points (P > 0.05).

CONCLUSIONS

Allogeneic ASCs protected fat grafts at the early stage and improved long-term volume retention in the fat graft model of immunocompetent rats with no or little obvious immune rejection.

Extracellular vesicles in lung microenvironment and pathogenesis

Increasing attention is being paid to the role of extracellular vesicles (EVs) in various lung diseases. EVs are released by a variety of cells, including respiratory cells and immune cells, and they encapsulate various molecules, such as proteins and microRNAs, as modulators of intercellular communication. Cancer cell-derived EVs play crucial roles in promoting tumor progression and modifying their microenvironment. By contrast, noncancerous cell-derived EVs demonstrate protective functions against injury, such as tissue recovery and repair, to maintain physiological homeostasis. Airway cells in contact with harmful substances may alter their EV composition and modify the balanced reciprocal interactions with surrounding mesenchymal cells. We summarize the novel findings of EV function in various lung diseases, primarily chronic obstructive pulmonary disease (COPD) and lung cancer.

Analysis of multipotent mesenchymal stromal cells used for acute graft-versus-host disease prophylaxis

BACKGROUND

Multipotent mesenchymal stromal cells (MSCs) are used for prophylaxis of acute graft-versus-host disease (aGvHD) after allogeneic hematopoietic cell transplantation (allo-HCT). Not all samples of MSC are efficient for aGvHD prevention. The suitability of MSCs for aGvHD prophylaxis was studied.

METHODS

MSCs were derived from the bone marrow (BM) of HCT donor and cultivated for no more than three passages. The characteristics of donor BM samples including colony-forming unit fibroblast (CFU-F) concentration, growth parameters of MSCs, and the relative expression levels (REL) of different genes were analyzed. MSCs were injected intravenously precisely at the moment of blood cell reconstitution.

RESULTS

MSCs infusion induced a significant threefold decrease in aGvHD development and improved overall survival compared with the standard prophylaxis group. In ineffective MSC samples (9.4%), a significant decrease in total cell production and the REL of CSF1, FGFR1, and PDGFRB was observed. In all studied BM samples, the cumulative MSC production and CFU-F concentrations decreased with age. The expression levels of FGFR2, PPARG, and VEGF differed by age.

CONCLUSIONS

A universal single indicator for the prediction of MSC eligibility for aGvHD prophylaxis was not identified. A multiparameter mathematical model for selecting MSC samples effective for the prevention of aGvHD was proposed.

Safety and Efficacy Endpoints for Mesenchymal Stromal Cell Therapy in Renal Transplant Recipients

Despite excellent short-term graft survival after renal transplantation, the long-term graft outcome remains compromised. It has become evident that a combination of sustained alloreactivity and calcineurin-inhibitor- (CNI-) related nephrotoxicity results in fibrosis and consequently dysfunction of the graft. New immunosuppressive regimens that can minimize or eliminate side effects, while maintaining efficacy, are required to improve long-term graft survival. In this perspective mesenchymal stromal cells (MSCs) are an interesting candidate, since MSCs have immunosuppressive and regenerative properties. The first clinical trials with MSCs in renal transplantation showed safety and feasibility and displayed promising results. Recently, the first phase II studies have been started. One of the most difficult and challenging aspects in those early phase trials is to define accurate endpoints that can measure safety and efficacy of MSC treatment. Since both graft losses and acute rejection rates declined, alternative surrogate markers such as renal function, histological findings, and immunological markers are used to measure efficacy and to provide mechanistic insight. In this review, we will discuss the current status of MSCs in renal transplantation with a focus on the endpoints used in the different experimental and clinical studies.

Myocardial regeneration strategy using Wharton's jelly mesenchymal stem cells as an off-the-shelf 'unlimited' therapeutic agent: results from the Acute Myocardial Infarction First-in-Man Study

INTRODUCTION

In large-animal acute myocardial infarction (AMI) models, Wharton's jelly (umbilical cord matrix) mesenchymal stem cells (WJMSCs) effectively promote angiogenesis and drive functional myocardial regeneration. Human data are lacking.

AIM

To evaluate the feasibility and safety of a novel myocardial regeneration strategy using human WJMSCs as a unique, allogenic but immuno-privileged, off-the-shelf cellular therapeutic agent.

MATERIAL AND METHODS

The inclusion criterion was first, large (LVEF ≤ 45%, CK-MB > 100 U/l) AMI with successful infarct-related artery primary percutaneous coronary intervention reperfusion (TIMI ≥ 2). Ten consecutive patients (age 32-65 years, peak hs-troponin T 17.3 ±9.1 ng/ml and peak CK-MB 533 ±89 U/l, sustained echo LVEF reduction to 37.6 ±2.6%, cMRI LVEF 40.3 ±2.7% and infarct size 20.1 ±2.8%) were enrolled.

RESULTS

30 × 10(6) WJMSCs were administered (LAD/Cx/RCA in 6/3/1) per protocol at ≈ 5-7 days using a cell delivery-dedicated, coronary-non-occlusive method. No clinical symptoms or ECG signs of myocardial ischemia occurred. There was no epicardial flow or myocardial perfusion impairment (TIMI-3 in all; cTFC 45 ±8 vs. 44 ±9, p = 0.51), and no patient showed hs-troponin T elevation (0.92 ±0.29 ≤ 24 h before vs. 0.89 ±0.28 ≤ 24 h after; decrease, p = 0.04). One subject experienced, 2 days after cell transfer, a transient temperature rise (38.9°C); this was reactive to paracetamol with no sequel. No other adverse events and no significant arrhythmias (ECG Holter) occurred. Up to 12 months there was one new, non-index territory lethal AMI but no adverse events that might be attributable to WJMSC treatment.

CONCLUSIONS

This study demonstrated the feasibility and procedural safety of WJMSC use as off-the-shelf cellular therapy in human AMI and suggested further clinical safety of WJMSC cardiac transfer, providing a basis for randomized placebo-controlled endpoint-powered evaluation.

Peculiarities of Gene Transfer into Mesenchymal Stem Cells

Murine mesenchymal stem cells in long-term bone marrow culture were genetically labeled using lentiviral vector carrying enhanced green fluorescent protein (eGFP) reporter gene under SFFV promoter or without it. We studied the developmental fate of labeled mesenchymal stem cells in stromal cell layers of long-term bone marrow culture and in ectopic hemopoietic foci formed by these stromal layers under the renal capsule of syngeneic mice. The frequency of labeled polypotent stromal precursors (fibroblast CFU) was analyzed in adherent cell layers of long-term culture and ectopic foci formed from them. The proportion of labeled fibroblast CFU in ectopic foci increased by 10 times in case of implantation of adherent cell layers infected with lentivirus containing eGFP reporter gene without promoter. eGFP expression leads to rejection of labeled stromal cells. Labeling with eGFP-carrying vector without promoter makes possible long-term tracking of mesenchymal stromal cells.

Cell Injury-Induced Release of Fibroblast Growth Factor 2: Relevance to Intracerebral Mesenchymal Stromal Cell Transplantations

Beneficial effects of intracerebral transplantation of mesenchymal stromal cells (MSC) and their derivatives are believed to be mediated mostly by factors produced by engrafted cells. However, the mesenchymal cell engraftment rate is low, and the majority of grafted cells disappear within a short post-transplantation period. Here, we hypothesize that dying transplanted cells can affect surrounding tissues by releasing their active intracellular components. To elucidate the type, amounts, and potency of these putative intracellular factors, freeze/thaw extracts of MSC or their derivatives were tested in enzyme-linked immunosorbent assays and bioassays. We found that fibroblast growth factor (FGF)2 and FGF1, but not vascular endothelial growth factor and monocyte chemoattractant protein 1 levels were high in extracts despite being low in conditioned media. Extracts induced concentration-dependent proliferation of rat cortical neural progenitor cells and human umbilical vein endothelial cells; these proliferative responses were specifically blocked by FGF2-neutralizing antibody. In the neuropoiesis assay with rat cortical cells, both MSC extracts and killed cells induced expression of nestin, but not astrocyte differentiation. However, suspensions of killed cells strongly potentiated the astrogenic effects of live MSC. In transplantation-relevant MSC injury models (peripheral blood cell-mediated cytotoxicity and high cell density plating), MSC death coincided with the release of intracellular FGF2. The data showed that MSC contain a major depot of active FGF2 that is released upon cell injury and is capable of acutely stimulating neuropoiesis and angiogenesis. We therefore propose that both dying and surviving grafted MSC contribute to tissue regeneration.

Equine allogeneic bone marrow-derived mesenchymal stromal cells elicit antibody responses in vivo

Introduction

This study tested the hypothesis that Major Histocompatibility Complex (MHC) incompatible equine mesenchymal stromal cells (MSCs) would induce cytotoxic antibodies to donor MHC antigens in recipient horses after intradermal injection. No studies to date have explored recipient antibody responses to allogeneic donor MSC transplantation in the horse. This information is critical because the horse is a valuable species for assessing the safety and efficacy of MSC treatment prior to human clinical application.

Methods

Six MHC heterozygote horses were identified as non-ELA-A2 haplotype by microsatellite typing and used as allogeneic MHC-mismatched MSC recipients. MHC homozygote horses of known ELA-A2 haplotype were used as MSC and peripheral blood leukocyte (PBL) donors. One MHC homozygote horse of the ELA-A2 haplotype was the recipient of ELA-A2 donor MSCs as an MHC-matched control. Donor MSCs, which were previously isolated and immunophenotyped, were thawed and culture expanded to achieve between 30x10⁶ and 50x10⁶ cells for intradermal injection into the recipient’s neck. Recipient serum was collected and tested for the presence of anti-donor antibodies prior to MSC injection and every 7 days after MSC injection for the duration of the 8-week study using the standard two-stage lymphocyte microcytotoxicity dye-exclusion test. In addition to anti-ELA-A2 antibodies, recipient serum was examined for the presence of cross-reactive antibodies including anti-ELA-A3 and anti-RBC antibodies.

Results

All MHC-mismatched recipient horses produced anti-ELA-A2 antibodies following injection of ELA-A2 MSCs and developed a wheal at the injection site that persisted for the duration of the experiment. Anti-ELA-A2 antibody responses were varied both in terms of strength and timing. Four recipient horses had high-titered anti-ELA-A2 antibody responses resulting in greater than 80% donor PBL death in the microcytotoxicity assays and one of these horses also developed antibodies that cross-reacted when tested on lymphocyte targets from a horse with an unrelated MHC type.

Conclusions

Allogeneic MSCs are capable of eliciting antibody responses in vivo that can be strong and also cross-reactive with MHC types other than that of the donor. Such responses could limit the effectiveness of repeated allogeneic MSC use in a single horse, and could also result in untoward inflammatory responses in recipients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0053-x) contains supplementary material, which is available to authorized users.

Mesenchymal Stem Cell-derived Extracellular Vesicles: Toward Cell-free Therapeutic Applications

Mesenchymal stem (stromal) cells (MSCs) are multipotent cells with the ability to differentiate into several cell types, thus serving as a cell reservoir for regenerative medicine. Much of the current interest in therapeutic application of MSCs to various disease settings can be linked to their immunosuppressive and anti-inflammatory properties. One of the key mechanisms of MSC anti-inflammatory effects is the secretion of soluble factors with paracrine actions. Recently it has emerged that the paracrine functions of MSCs could, at least in part, be mediated by extracellular vesicles (EVs). EVs are predominantly released from the endosomal compartment and contain a cargo that includes miRNA, mRNA, and proteins from their cells of origin. Recent animal model-based studies suggest that EVs have significant potential as a novel alternative to whole cell therapies. Compared to their parent cells, EVs may have a superior safety profile and can be safely stored without losing function. In this article, we review current knowledge related to the potential use of MSC-derived EVs in various diseases and discuss the promising future for EVs as an alternative, cell-free therapy.

Analgesia for neuropathic pain by dorsal root ganglion transplantation of genetically engineered mesenchymal stem cells: initial results

Background

Cell-based therapy may hold promise for treatment of chronic pain. Mesenchymal stem cells (MSCs) are readily available and robust, and their secretion of therapeutic peptides can be enhanced by genetically engineering. We explored the analgesic potential of transplanting bone marrow-derived MSCs that have been transduced with lentivectors. To optimize efficacy and safety, primary sensory neurons were targeted by MSC injection into the dorsal root ganglia (DRGs).

Results

MSCs were transduced using lentivectors to express enhanced green fluorescent protein (EGFP) or to co-express the analgesic peptide glial cell line-derived neurotrophic factor (GDNF) and EGFP by a viral 2A bicistronic transgene cassette. Engineered MSCs were injected into the 4^th lumbar (L4) and L5 DRGs of adult allogeneic rats to evaluate survival in the DRGs. MSCs were detected by immunofluorescence staining up to 2–3 weeks after injection, distributed in the extracellular matrix space without disrupting satellite glial cell apposition to sensory neurons, suggesting well-tolerated integration of engrafted MSCs into DRG tissue. To examine their potential for inhibiting development of neuropathic pain, MSCs were injected into the L4 and L5 DRGs ipsilateral to a spinal nerve ligation injury. Animals injected with GDNF-engineered MSCs showed moderate but significant reduction in mechanical allodynia and hyperalgesia compared to controls implanted with MSCs expressing EGFP alone. We also observed diminished long-term survival of allografted MSCs at 3 weeks, and the development of a highly-proliferating population of MSCs in 12% of DRGs after transplantation.

Conclusions

These data indicate that genetically modified MSCs secreting analgesic peptides could potentially be developed as a novel DRG-targeted cell therapy for treating neuropathic pain. However, further work is needed to address the challenges of MSC survival and excess proliferation, possibly with trials of autologous MSCs, evaluation of clonally selected populations of MSCs, and investigation of regulation of MSC proliferation.

Enhanced medial collateral ligament healing using mesenchymal stem cells: dosage effects on cellular response and cytokine profile

Mesenchymal stem cells (MSCs) have potential therapeutic applications for musculoskeletal injuries due to their ability to differentiate into several tissue cell types and modulate immune and inflammatory responses. These immune-modulatory properties were examined in vivo during early stage rat medial collateral ligament healing. Two different cell doses (low dose 1 × 10(6) or high dose 4 × 10(6) MSCs) were administered at the time of injury and compared with normal ligament healing at days 5 and 14 post-injury. At both times, the high dose MSC group demonstrated a significant decrease in M2 macrophages compared to controls. At day 14, fewer M1 macrophages were detected in the low dose group compared to the high dose group. These results, along with significant changes in procollagen I, proliferating cells, and endothelialization suggest that MSCs can alter the cellular response during healing in a dose-dependent manner. The higher dose ligaments also had increased expression of several pro-inflammatory cytokines at day 5 (IL-1β, IFNγ, IL-2) and increased expression of IL-12 at day 14. Mechanical testing at day 14 revealed increased failure strength and stiffness in low dose ligaments compared to controls. Based on these improved mechanical properties, MSCs enhanced functional healing when applied at a lower dose. Different doses of MSCs uniquely affected the cellular response and cytokine expression in healing ligaments. Interestingly, the lower dose of cells proved to be most effective in improving functional properties.

Interferon-gamma modification of mesenchymal stem cells: implications of autologous and allogeneic mesenchymal stem cell therapy in allotransplantation

Bone marrow-derived mesenchymal stem cells (MSC) have unique immunomodulatory and reparative properties beneficial for allotransplantation cellular therapy. The clinical administration of autologous or allogeneic MSC with immunosuppressive drugs is able to prevent and treat allograft rejection in kidney transplant recipients, thus supporting the immunomodulatory role of MSC. Interferon-gamma (IFN-γ) is known to enhance the immunosuppressive properties of MSC. IFN-γ preactivated MSC (MSC-γ) directly or indirectly modulates T cell responses by enhancing or inducing MSC inhibitory factors. These factors are known to downregulate T cell activation, enhance T cell negative signalling, alter T cells from a proinflammatory to an anti-inflammatory phenotype, interact with antigen-presenting cells and increase or induce regulatory cells. Highly immunosuppressive MSC-γ with increased migratory and reparative capacities may aid tissue repair, prolong allograft survival and induce allotransplant tolerance in experimental models. Nevertheless, there are contradictory in vivo observations related to allogeneic MSC-γ therapy. Many studies report that allogeneic MSC are immunogenic due to their inherent expression of major histocompatibility (MHC) molecules. Enhanced expression of MHC in allogeneic MSC-γ may increase their immunogenicity and this can negatively impact allograft survival. Therefore, strategies to reduce MSC-γ immunogenicity would facilitate "off-the-shelf" MSC therapy to efficiently inhibit alloimmune rejection and promote tissue repair in allotransplantation. In this review, we examine the potential benefits of MSC therapy in the context of allotransplantation. We also discuss the use of autologous and allogeneic MSC and the issues associated with their immunogenicity in vivo, with particular focus on the use of enhanced MSC-γ cellular therapy.

Mesenchymal stem cell therapy promotes corneal allograft survival in rats by local and systemic immunomodulation

Mesenchymal stem cells (MSCs) are being investigated extensively due to their ability to dampen immune responses. Here, we tested the ability of MSCs from three distinct sources to prolong rat corneal allograft survival. A fully allogeneic rat cornea transplant model (DA to LEW) was used. Recipient rats received 1 × 10(6) MSCs (syn [LEW], allo [DA] or third-party [Wistar Furth]) intravenously 7 days before transplantation and again on the day of transplantation (day 0). A high percentage of untreated and syn-MSC treated allografts were rejected (80% and 100%, respectively). Preactivation of syn-MSCs with interferon gamma also failed to prolong allograft survival. Conversely, corneal allograft survival was significantly prolonged in allo-MSC treated (90%) and third-party MSC treated (80%) allograft recipients. Flow cytometric analysis revealed less infiltrating natural killer T cells in corneas of both allo- and third-party MSC treated animals, coupled with a higher proportion of splenic CD4+Foxp3+ regulatory T cells, compared to controls. In the case of allo- and third-party MSCs, results from a delayed-type hypersensitivity assay clearly showed that hypo-responsiveness was specific for corneal donor-associated allo-antigens. Thus, allo- and third-party MSC treatment prolongs corneal allograft survival by suppressing peripheral immune responses and promoting an intragraft immunoregulatory milieu.