Potency Analysis of Mesenchymal Stromal Cells Using a Phospho-STAT Matrix Loop Analytical Approach

The Potential Use of THP-1, a Monocytic Leukemia Cell Line, to Predict Immune-Suppressive Potency of Human Bone-Marrow Stromal Cells (BMSCs) In Vitro: A Pilot Study

Adoptive transfer of cultured BMSCs was shown to be immune-suppressive in various inflammatory settings. Many factors play a role in the process, but no master regulator of BMSC-driven immunomodulation was identified. Consequently, an assay that might predict BMSC product efficacy is still unavailable. Below, we show that BMSC donor variability can be monitored by IL-10 production of monocytes/macrophages using THP-1 cells (immortalized monocytic leukemia cells) co-cultured with BMSCs. Using a mixed lymphocyte reaction (MLR) assay, we also compared the ability of the different donor BMSCs to suppress T-cell proliferation, another measure of their immune-suppressive ability. We found that the BMSCs from a donor that induced the most IL-10 production were also the most efficient in suppressing T-cell proliferation. Transcriptome studies showed that the most potent BMSC batch also had higher expression of several known key immunomodulatory molecules such as hepatocyte growth factor (HGF), PDL1, and numerous members of the PGE2 pathway, including PTGS1 and TLR4. Multiplex ELISA experiments revealed higher expression of HGF and IL6 by the most potent BMSC donor. Based on these findings, we propose that THP-1 cells may be used to assess BMSC immunosuppressive activity as a product characterization assay.

Effects of Atrazine exposure on human bone marrow-derived mesenchymal stromal cells assessed by combinatorial assay matrix

Introduction

Mesenchymal Stromal/Stem cells (MSCs) are an essential component of the regenerative and immunoregulatory stem cell compartment of the human body and thus of major importance in human physiology. The MSCs elicit their beneficial properties through a multitude of complementary mechanisms, which makes it challenging to assess their phenotype and function in environmental toxicity screening. We here employed the novel combinatorial assays matrix approach/technology to profile the MSC response to the herbicide Atrazine, which is a common environmental xenobiotic, that is in widespread agricultural use in the US and other countries, but banned in the EU. Our here presented approach is representative for screening the impact of environmental xenobiotics and toxins on MSCs as an essential representative component of human physiology and well-being.

Methods

We here employed the combinatorial assay matrix approach, including a panel of well standardized assays, such as flow cytometry, multiplex secretome analysis, and metabolic assays, to define the phenotype and functionality of human-donor-derived primary MSCs exposed to the representative xenobiotic Atrazine. This assay matrix approach is now also endorsed for characterization of cell therapies by leading regulatory agencies, such as FDA and EMA.

Results

Our results show that the exposure to Atrazine modulates the metabolic activity, size, and granularity of MSCs in a dose and time dependent manner. Intriguingly, Atrazine exposure leads to a broad modulation of the MSCs secretome (both upregulation and downmodulation of certain factors) with the identification of Interleukin-8 as the topmost upregulated representative secretory molecule. Interestingly, Atrazine attenuates IFNγ-induced upregulation of MHC-class-II, but not MHC-class-I, and early phosphorylation signals on MSCs. Furthermore, Atrazine exposure attenuates IFNγ responsive secretome of MSCs. Mechanistic knockdown analysis identified that the Atrazine-induced effector molecule Interleukin-8 affects only certain but not all the related angiogenic secretome of MSCs.

Discussion

The here described Combinatorial Assay Matrix Technology identified that Atrazine affects both the innate/resting and cytokine-induced/stimulated assay matrix functionality of human MSCs, as identified through the modulation of selective, but not all effector molecules, thus vouching for the great usefulness of this approach to study the impact of xenobiotics on this important human cellular subset involved in the regenerative healing responses in humans.

IL4I1-catalyzed tryptophan metabolites mediate the anti-inflammatory function of cytokine-primed human muscle stem cells

Muscle stem cells (MuSCs) have been demonstrated to exert impressive therapeutic efficacy in disease settings through orchestrating inflammatory microenvironments. Nevertheless, the mechanisms underlying the immunoregulatory property of MuSCs remain largely uncharacterized. Here, we showed that interleukin-4-induced-1 (IL4I1), an essential enzyme that catalyzes indole metabolism in humans, was highly expressed in human MuSCs exposed to IFN-γ and TNF-α. Functionally, the MuSCs were found to inhibit the infiltration of neutrophils into sites of inflammation in a IL4I1-dependent manner and thus ameliorate acute lung injury in mice. Mechanistically, the indole metabolites, including indole-3-pyruvic acid (I3P) and indole-3-aldehyde (I3A), produced by IL4I1, acted as ligands to activate aryl hydrocarbon receptor (AHR), leading to augmented expression of TNF-stimulated gene 6 (TSG-6) in inflammatory cytokine-primed MuSCs. Furthermore, I3P administration alone suppressed neutrophil infiltration into damaged lungs. I3P could also reduce the level of reactive oxygen species in neutrophils. Therefore, our study has uncovered a novel mechanism by which MuSCs acquire their immunoregulatory property and may help to develop or optimize MuSC-based therapies for inflammatory diseases.

Potency Assays for Mesenchymal Stromal Cell Secretome-Based Products for Tissue Regeneration

Adult stem cells maintaining tissue homeostasis and regeneration are tightly regulated by their specific microenvironments or stem cell niches. The dysfunction of niche components may alter the activity of stem cells and ultimately lead to intractable chronic or acute disorders. To overcome this dysfunction, niche-targeting regenerative medicine treatments such as gene, cell, and tissue therapy are actively investigated. Here, multipotent mesenchymal stromal cells (MSCs), and particularly their secretomes, are of high interest due to their potency to recover and reactivate damaged or lost stem cell niches. However, a workflow for the development of MSC secretome-based products is not fully covered by regulatory authorities, and and this issue significantly complicates their clinical translation and has possibly been expressed in a huge number of failed clinical trials. One of the most critical issues in this regard relates to the development of potency assays. In this review, guidelines for biologicals and cell therapies are considered to be applied for the development of potency assays for the MSC secretome-based products that aim for tissue regeneration. Specific attention is paid to their possible effects on stem cell niches and to a spermatogonial stem cell niche in particular.

Advanced Technologies for Potency Assay Measurement

Crucial for their application, cell products need to be well-characterized in the cell manufacturing facilities and conform to regulatory approval criteria before infusion into the patients. Mesenchymal Stromal Cells (MSCs) are the leading cell therapy candidate in clinical trials worldwide. Early phase clinical trials have demonstrated that MSCs display an excellent safety profile and are well tolerated. However, MSCs have also exhibited contradictory efficacy in later-phase clinical trials with reasons for this discrepancy including poorly understood mechanism of MSC therapeutic action. With likelihood that a number of attributes are involved in MSC derived clinical benefit, an assay that measures a single quality of may not adequately reflect potency, thus a combination of bioassays and analytical methods, collectively called "assay matrix" are favoured for defining the potency of MSC more adequately. This chapter highlights advanced technologies and targets that can achieve quantitative measurement for a range of MSC attributes, including immunological, genomic, secretome, phosphorylation, morphological, biomaterial, angiogenic and metabolic assays.

Conglomeration of T- and B-Cell Matrix Responses Determines the Potency of Human Bone Marrow Mesenchymal Stromal Cells

Cell manufacturing facilities need to define the potency of mesenchymal stromal cells (MSCs) as cellular therapeutics in advanced clinical trials or marketing approval. Since MSCs' mechanism of action in humans is not well defined, more than a single functional property of MSCs needs to be captured as a surrogate measure of potency utilizing assay matrix technologies. However, the current limitation is the sole investigation of MSC-mediated T-cell suppression as a surrogate measure of potency. We investigated the effect of MSCs on B-cell matrix responses to be incorporated into the assay matrix potency analytical system. Our results demonstrate that MSCs inhibit B-cell differentiation and block pan-antibody secretion upon activation of B cells in the PBMCs. In contrast, MSCs are inferior in blocking B-cell matrix responses when purified B cells are used. Mechanistic analysis has demonstrated that MSC-mediated inhibition of B-cell matrix responses is non-contact dependent and Tryptophan metabolic pathway plays a major role, akin to the mechanism of MSC-mediated T-cell suppression. MSCs also inhibit both T-cell and B-cell responses when both of these lymphoid populations are concurrently activated in the PBMCs. Secretome analysis of MSC and T/B cell-activated PBMC cocultures identified direct and inverse correlative matrix signatures between humoral antibody isotypes and secretory molecules. The current analysis of the combined and concomitant investigation of T-cell and B-cell matrix responses fulfills the potency assay matrix strategy by incorporating MSCs' interaction with more than a single inflammatory immune responder.

Putative critical quality attribute matrix identifies mesenchymal stromal cells with potent immunomodulatory and angiogenic "fitness" ranges in response to culture process parameters

Adipose-derived mesenchymal stromal cells (MSC(AT)) display immunomodulatory and angiogenic properties, but an improved understanding of quantitative critical quality attributes (CQAs) that inform basal MSC(AT) fitness ranges for immunomodulatory and/or angiogenic applications is urgently needed for effective clinical translation. We constructed an in vitro matrix of multivariate readouts to identify putative CQAs that were sensitive enough to discriminate between specific critical processing parameters (CPPs) chosen for their ability to enhance MSC immunomodulatory and angiogenic potencies, with consideration for donor heterogeneity. We compared 3D aggregate culture conditions (3D normoxic, 3D-N) and 2D hypoxic (2D-H) culture as non-genetic CPP conditions that augment immunomodulatory and angiogenic fitness of MSC(AT). We measured multivariate panels of curated genes, soluble factors, and morphometric features for MSC(AT) cultured under varying CPP and licensing conditions, and we benchmarked these against two functional and therapeutically relevant anchor assays - in vitro monocyte/macrophage (MΦ) polarization and in vitro angiogenesis. Our results showed that varying CPP conditions was the primary driver of MSC(AT) immunomodulatory fitness; 3D-N conditions induced greater MSC(AT)-mediated MΦ polarization toward inflammation-resolving subtypes. In contrast, donor heterogeneity was the primary driver of MSC(AT) angiogenic fitness. Our analysis further revealed panels of putative CQAs with minimum and maximum values that consisted of twenty MSC(AT) characteristics that informed immunomodulatory fitness ranges, and ten MSC(AT) characteristics that informed angiogenic fitness ranges. Interestingly, many of the putative CQAs consisted of angiogenic genes or soluble factors that were inversely correlated with immunomodulatory functions (THBS1, CCN2, EDN1, PDGFA, VEGFA, EDIL3, ANGPT1, and ANG genes), and positively correlated to angiogenic functions (VEGF protein), respectively. We applied desirability analysis to empirically rank the putative CQAs for MSC(AT) under varying CPP conditions and donors to numerically identify the desirable CPP conditions or donors with maximal MSC(AT) immunomodulatory and/or angiogenic fitness. Taken together, our approach enabled combinatorial analysis of the matrix of multivariate readouts to provide putative quantitative CQAs that were sensitive to variations in select CPPs that enhance MSC immunomodulatory/angiogenic potency, and donor heterogeneity. These putative CQAs may be used to prospectively screen potent MSC(AT) donors or cell culture conditions to optimize for desired basal MSC(AT) immunomodulatory or angiogenic fitness.

Integrated analysis of the tumor microenvironment using a reconfigurable microfluidic cell culture platform

The tumor microenvironment (TME) is a complex network of non-malignant cells and stroma that perform a wide array of vital roles in tumor growth, immune evasion, metastasis, and therapeutic resistance. These highly diverse roles have been shown to be critically important to the progression of cancers and have already shown potential as therapeutic targets. Therefore, there has been a tremendous push to elucidate the pathways that underlie these roles and to develop new TME-directed therapies for cancer treatment. Unfortunately, TME-focused research has been limited by a lack of translational in vitro culture platforms that can model this highly complex niche and can support the integrated analysis of cell biology and function. In the current study, we investigate whether an independently developed reconfigurable microfluidic platform, known as Stacks, can address the critical need for translational multi-cellular tumor models and integrated analytics in TME research. We present data on multi-cellular culture of primary human cells in Stacks as well as the orthogonal analysis of cellular polarization, differentiation, migration, and cytotoxicity in this reconfigurable system. These expanded capabilities of Stacks are highly relevant to the cancer research community with the potential to enhance clinical translation of pre-clinical TME studies and to yield novel biological insight into TME crosstalk, metastasis, and responses to novel drug combinations or immune therapies.

A STAT5-Smad3 dyad regulates adipogenic plasticity of visceral adipose mesenchymal stromal cells during chronic inflammation

Adipogenic differentiation of visceral adipose tissue-resident multipotent mesenchymal stromal cells (VA-MSC) into adipocytes is metabolically protective. Under chronic inflammatory stress, this neoadipogenesis process is suppressed by various pro-inflammatory cytokines and growth factors. However, the underlying mechanism(s) regulating VA-MSC plasticity remains largely unexplored. Using an adipogenic differentiation screen, we identified IFNγ and TGFβ as key inhibitors of primary human VA-MSC differentiation. Further studies using human and mouse VA-MSCs and a chronic high-fat diet-fed murine model revealed that IFNγ/JAK2-activated STAT5 transcription factor is a central regulator of VA-MSC differentiation under chronic inflammatory conditions. Furthermore, our results indicate that under such conditions, IFNγ-activated STAT5 and TGFβ-activated Smad3 physically interact via Smad4. This STAT5-Smad4-Smad3 complex plays a crucial role in preventing the early adipogenic commitment of VA-MSCs by suppressing key pro-adipogenic transcription factors, including CEBPδ, CEBPα, and PPARγ. Genetic or pharmacological disruption of IFNγ-TGFβ synergy by inhibiting either STAT5 or Smad3 rescued adipogenesis under chronic inflammatory stress. Overall, our study delineates a central mechanism of MSC plasticity regulation by the convergence of multiple inflammatory signaling pathways.

Chemokine Assay Matrix Defines the Potency of Human Bone Marrow Mesenchymal Stromal Cells

Potency analysis of mesenchymal stromal cells (MSCs) is required for their use in advanced clinical trials. Assay matrix strategy evaluating more than a single property of MSCs is an emerging strategy in potency analysis. Here we developed an assay matrix approach focusing on the secretory chemokine responses of MSCs using multiplex analytical method. MSCs’ innate fitness in secreting matrix of chemokines is correlated with their metabolic fitness in differential degrees. In addition, innately secreting chemokines are correlated among themselves in a unique pattern. MSC’s matrix chemokine responses to exogenous stimulation of IFNγ and/or TNFα are distinct. However, the combination of IFNγ and TNFα is superior than individual stimulations in eliciting robust and broad matrix chemokine responses of MSCs. Correlation matrix analysis has identified that chemokine responses to IFNγ and/or TNFα display unique correlative secretion patterns. MSC and peripheral blood mononuclear cells coculture analysis has identified the correlation matrix responses of chemokines that predicted immune suppression. In addition, MSC-mediated blocking of T-cell proliferation predominantly correlates with chemokines in an inverse manner. Knockdown of chemokines has demonstrated that MSC-sourced inherent chemokines do not actively play a role in T-cell suppression and thus are the bystander predictors of T-cell suppression. The present analysis of MSC’s matrix chemokine responses can be deployed in the advanced potency analysis of MSCs.

Potential mechanisms and therapeutic targets of mesenchymal stem cell transplantation for ischemic stroke

Ischemic stroke is one of the major causes of death and disability in the world. Currently, most patients cannot choose intravenous thrombolysis or intravascular mechanical thrombectomy because of narrow therapeutic windows and severe complications. Stem cell transplantation is an emerging treatment and has been studied in various central nervous system diseases. Animal and clinical studies showed that transplantation of mesenchymal stem cells (MSCs) could alleviate neurological deficits and bring hope for ischemic stroke treatment. This article reviewed biological characteristics, safety, feasibility and efficacy of MSCs therapy, potential therapeutic targets of MSCs, and production process of Good Manufacturing Practices-grade MSCs, to explore the potential therapeutic targets of MSCs in the process of production and use and provide new therapeutic directions for ischemic stroke.

Advancing Treatment of Bone Metastases through Novel Translational Approaches Targeting the Bone Microenvironment

Bone metastases represent a lethal condition that frequently occurs in solid tumors such as prostate, breast, lung, and renal cell carcinomas, and increase the risk of skeletal-related events (SREs) including pain, pathologic fractures, and spinal cord compression. This unique metastatic niche consists of a multicellular complex that cancer cells co-opt to engender bone remodeling, immune suppression, and stromal-mediated therapeutic resistance. This review comprehensively discusses clinical challenges of bone metastases, novel preclinical models of the bone and bone marrow microenviroment, and crucial signaling pathways active in bone homeostasis and metastatic niche. These studies establish the context to summarize the current state of investigational agents targeting BM, and approaches to improve BM-targeting therapies. Finally, we discuss opportunities to advance research in bone and bone marrow microenvironments by increasing complexity of humanized preclinical models and fostering interdisciplinary collaborations to translational research in this challenging metastatic niche.

IFN-γ and PPARδ influence the efficacy and retention of multipotent adult progenitor cells in graft vs host disease

Cell‐based therapy for the treatment of inflammatory disorders has focused on the application of mesenchymal stromal cells (MSCs) and multipotent adult progenitor cells (MAPCs). Despite the recent positive findings in industry‐sponsored clinical trials of MSCs and MAPCs for graft vs host disease (GvHD), cell therapy is efficacious in some but not all patients, highlighting the need to identify strategies to enhance cell‐based therapeutic efficacy. Here, we demonstrate the capacity for interferon (IFN)‐γ licensing to enhance human MAPC efficacy and retention following early administration in a humanized mouse model of acute GvHD (aGvHD). Activation of the nuclear receptor peroxisome proliferator‐activated receptor delta (PPARδ) negatively influenced the retention and efficacy of human MAPCs as well as IFN‐γ‐licensed MAPCs in the aGvHD model. PPARδ antagonism significantly enhanced the efficacy of human MAPCs when administered early in the humanized aGvHD model. COX‐2 expression in human MAPC was significantly decreased in IFN‐γ licensed MAPCs exposed to a PPARδ agonist. Importantly, MAPC exposure to the PPARδ antagonist in the presence of a COX‐2 inhibitor indomethacin before administration significantly reduced the efficacy of PPARδ antagonized MAPCs in the aGvHD humanized mouse model. This is the first study to demonstrate the importance of PPARδ in human MAPC efficacy in vivo and highlights the importance of understanding the disease microenvironment in which cell‐based therapies are to be administered. In particular, the presence of PPARδ ligands may negatively influence MAPC or MSC therapeutic efficacy.

Preclinical Evaluation of the Safety and Efficacy of Cryopreserved Bone Marrow Mesenchymal Stromal Cells for Corneal Repair

Purpose

Mesenchymal stromal cells (MSCs) have been shown to enhance tissue repair as a cell-based therapy. In preparation for a phase I clinical study, we evaluated the safety, dosing, and efficacy of bone marrow–derived MSCs after subconjunctival injection in preclinical animal models of mice, rats, and rabbits.

Methods

Human bone marrow–derived MSCs were expanded to passage 4 and cryopreserved. Viability of MSCs after thawing and injection through small-gauge needles was evaluated by vital dye staining. The in vivo safety of human and rabbit MSCs was studied by subconjunctivally injecting MSCs in rabbits with follow-up to 90 days. The potency of MSCs on accelerating wound healing was evaluated in vitro using a scratch assay and in vivo using 2-mm corneal epithelial debridement wounds in mice. Human MSCs were tracked after subconjunctival injection in rat and rabbit eyes.

Results

The viability of MSCs after thawing and immediate injection through 27- and 30-gauge needles was 93.1% ± 2.1% and 94.9% ± 1.3%, respectively. Rabbit eyes demonstrated mild self-limiting conjunctival inflammation at the site of injection with human but not rabbit MSCs. In scratch assay, the mean wound healing area was 93.5% ± 12.1% in epithelial cells co-cultured with MSCs compared with 40.8% ± 23.1% in controls. At 24 hours after wounding, all MSC-injected murine eyes had 100% corneal wound closure compared with 79.9% ± 5.5% in controls. Human MSCs were detectable in the subconjunctival area and peripheral cornea at 14 days after injection.

Conclusions

Subconjunctival administration of MSCs is safe and effective in promoting corneal epithelial wound healing in animal models.

Translational Relevance

These results provide preclinical data to support a phase I clinical study.

Wnt Signaling Regulates the Lymphatic Endothelial Transdifferentiation of Adipose-Derived Stromal Cells In Vitro

Lymphedema is a chronic, progressive disease that causes pain as well as heavy economic burdens to patients. Reconstruction of the impaired lymphatic system is the key to treat lymphedema. Currently, there is no cure, but mesenchymal stromal cells show promising potential for lymphatic endothelial regeneration. Adipose-derived stromal cells (ADSCs) have been proved to support lymphangiogenesis both in vivo and in vitro. However, the mechanism in vascular endothelial growth factor C-induced (VEGF-C-induced) lymphatic endothelial transdifferentiation of ADSCs remains unknown. In this study, we show a novel link between the Wingless and int-1 (Wnt) pathway and the lymphatic endothelial differentiation process. We used LiCl to activate Wnt and DKK-1 to inhibit Wnt. Compared with the Wnt inhibition group and the control groups, the Wnt activation group produced more lymphatic endothelial cell (LEC)-related mRNA and proteins. Besides, Wnt-activated ADSCs formed longer tubes in two-dimensional culture and promoted the growth of lymphatic vessels in a three-dimensional transwell ADSC-LEC co-culture system. Our results demonstrated that activation of Wnt during the lymphatic endothelial transdifferentiation of ADSCs would enhance the efficacy of VEGF-C treatment. We anticipate our assay to expand our knowledge of Wnt in cell transdifferentiation and lay a foundation for future efforts to explore a novel and effective ADSC-based therapy for lymphedema.

Ruxolitinib Inhibits IFNγ Licensing of Human Bone Marrow Derived Mesenchymal Stromal Cells

Ruxolitinib is a JAK2/JAK1 inhibitor that blocks the inflammatory JAK-STAT signaling pathway. Ruxolitinib has been demonstrated to be effective in the treatment of steroid-resistant acute graft-versus-host disease (GVHD). Ruxolitinib's effect on inflammatory cells of hematopoietic origin is known. However, its effect on nonhematopoietic cell types with immune-modulating and antigen-presenting cell competency plausibly involved in pathogenesis of GVHD has not been explored. Mesenchymal stromal cells (MSCs) are CD45^- nonhematopoietic cells of the bone marrow with immune modulatory functions in vivo. MSCs' immunobiology largely depends on their responsiveness to IFNγ. We aimed to define the effect of ruxolitinib on the immunobiology of MSCs that are modulated by IFNγ. Human bone marrow derived MSCs, peripheral blood mononuclear cells (PBMCs), and primary bone marrow aspirates were analyzed for their sensitivity to ruxolitinib-mediated blocking of IFNγ-induced STAT-1 phosphorylation and downstream effector molecules, utilizing Western blot, flow cytometry, secretome analysis, and phosflow techniques. IFNγ-induced cytostatic effects on MSCs are reversed by ruxolitinib. Ruxolitinib inhibits IFNγ and secretome of activated peripheral PBMC-induced STAT-1 phosphorylation on human bone marrow derived MSCs. In addition, ruxolitinib inhibits IFNγ-induced pro-GVHD pathways on MSCs, which includes HLAABC(MHCI), HLADR(MHCII), CX3CL1, and CCL2. IFNγ-induced immunosuppressive molecules IDO and PDL-1 were also inhibited by ruxolitinib on MSCs. Comparative analysis with PBMCs has demonstrated that MSCs are as equal as to HLADR⁺ PBMC populations in responding to ruxolitinib-mediated inhibition of IFNγ-induced STAT-1 phosphorylation. Ex vivo analysis of human marrow aspirates has demonstrated that ruxolitinib blocks IFNγ-induced STAT-1 phosphorylation in CD45^+/-HLADR^+/- populations at different levels, which is depending on their sensitivity to IFNγ responsiveness. These results inform the hypothesis that ruxolitinib's immune-modulatory effects in vivo may pharmacologically involve marrow and tissue-resident MSCs. Ruxolitinib affects the immunobiology of MSCs equivalent to professional HLADR⁺ antigen presenting cells, which collectively mitigate GVHD.

Sub-nanoliter metabolomics via mass spectrometry to characterize volume-limited samples

The human metabolome provides a window into the mechanisms and biomarkers of various diseases. However, because of limited availability, many sample types are still difficult to study by metabolomic analyses. Here, we present a mass spectrometry (MS)-based metabolomics strategy that only consumes sub-nanoliter sample volumes. The approach consists of combining a customized metabolomics workflow with a pulsed MS ion generation method, known as triboelectric nanogenerator inductive nanoelectrospray ionization (TENGi nanoESI) MS. Samples tested with this approach include exhaled breath condensate collected from cystic fibrosis patients as well as in vitro-cultured human mesenchymal stromal cells. Both test samples are only available in minimum amounts. Experiments show that picoliter-volume spray pulses suffice to generate high-quality spectral fingerprints, which increase the information density produced per unit sample volume. This TENGi nanoESI strategy has the potential to fill in the gap in metabolomics where liquid chromatography-MS-based analyses cannot be applied. Our method opens up avenues for future investigations into understanding metabolic changes caused by diseases or external stimuli.

Mesenchymal Stromal Cells' Therapy for Polyglutamine Disorders: Where Do We Stand and Where Should We Go?

Polyglutamine (polyQ) diseases are a group of inherited neurodegenerative disorders caused by the expansion of the cytosine-adenine-guanine (CAG) repeat. This mutation encodes extended glutamine (Q) tract in the disease protein, resulting in the alteration of its conformation/physiological role and in the formation of toxic fragments/aggregates of the protein. This group of heterogeneous disorders shares common molecular mechanisms, which opens the possibility to develop a pan therapeutic approach. Vast efforts have been made to develop strategies to alleviate disease symptoms. Nonetheless, there is still no therapy that can cure or effectively delay disease progression of any of these disorders. Mesenchymal stromal cells (MSC) are promising tools for the treatment of polyQ disorders, promoting protection, tissue regeneration, and/or modulation of the immune system in animal models. Accordingly, data collected from clinical trials have so far demonstrated that transplantation of MSC is safe and delays the progression of some polyQ disorders for some time. However, to achieve sustained phenotypic amelioration in clinics, several treatments may be necessary. Therefore, efforts to develop new strategies to improve MSC's therapeutic outcomes have been emerging. In this review article, we discuss the current treatments and strategies used to reduce polyQ symptoms and major pre-clinical and clinical achievements obtained with MSC transplantation as well as remaining flaws that need to be overcome. The requirement to cross the blood-brain-barrier (BBB), together with a short rate of cell engraftment in the lesioned area and low survival of MSC in a pathophysiological context upon transplantation may contribute to the transient therapeutic effects. We also review methods like pre-conditioning or genetic engineering of MSC that can be used to increase MSC survival in vivo, cellular-free approaches-i.e., MSC-conditioned medium (CM) or MSC-derived extracellular vesicles (EVs) as a way of possibly replacing the use of MSC and methods required to standardize the potential of MSC/MSC-derived products. These are fundamental questions that need to be addressed to obtain maximum MSC performance in polyQ diseases and therefore increase clinical benefits.

Use of MSCs and MSC-educated macrophages to mitigate hematopoietic acute radiation syndrome

Purpose of Review

Innovative and minimally toxic treatment approaches are sorely needed for the prevention and treatment of hematopoietic acute radiation syndrome (H-ARS). Cell therapies have been increasingly studied for their potential use as countermeasures for accidental and intentional ionizing radiation exposures which can lead to fatal ARS. Mesenchymal stem/stromal cells (MSCs) are a cell therapy that have shown promising results in preclinical studies of ARS, and are being developed in clinical trials specifically for H-ARS. MSCs, MSC-educated macrophages (MEMs) and MSC-exosome educated macrophages (EEMs) all have the potential to be used as adoptive cell therapies for H-ARS. Here we review how MSCs have been reported to mitigate inflammation from radiation injury while also stimulating hematopoiesis during ARS.

Recent findings

We discuss emerging work with immune cell subsets educated by MSCs, including MEMs and EEMs, in promoting hematopoiesis in xenogeneic models of ARS. We also discuss the first placental-derived MSC product to enter phase I trials, PLX-R18, and the challenges faced by bringing MSC and other cell therapies into the clinic for treating ARS.

Summary

Although MSCs, MEMs and EEMs are potential cell therapy candidates in promoting hematopoietic HRS, challenges persist in translational clinical development of these products to the clinic. Whether any of these cellular therapies will be sufficient as stand-alone therapies to mitigate H-ARS or if they will be a bridging therapy that insures survival until a curative allogeneic hematopoietic stem cell transplant can be performed are the key questions that will have to be answered.

MCP-1 Priming Enhanced the Therapeutic Effects of Human Mesenchymal Stromal Cells on Contact Hypersensitivity Mice by Activating the COX2-PGE2/STAT3 Pathway

Mesenchymal stromal cells (MSCs) have become a promising treatment for inflammation-related diseases, and their therapeutic efficacy mainly depends on crosstalk between MSCs and inflammation. However, methods to improve the immunosuppressive efficiency of MSCs in different diseases still need to be developed. In this study, we investigated whether preconditioning MSCs with a disease-related inflammatory cytokine could increase their immunosuppressive properties and improve therapeutic efficacy. In a contact hypersensitivity (CHS) mouse model, inflammatory profile screening revealed that among all tested cytokines, monocyte chemotactic protein-1 (MCP-1) exhibited the most significantly increased level in the local microenvironment. As expected, MSCs preconditioned with MCP-1 (P-MSCs) exhibited an enhanced ability to downregulate proinflammatory cytokine secretion, induce regulatory T cells, inhibit T cell proliferation, and polarize M2-type macrophages. In vivo experiments showed that P-MSCs alleviated ear swelling and local proinflammatory cytokine production more effectively than control MSCs. Mechanistically, MCP-1 could significantly activate the signal transducer and activator of transcription 3 (STAT3) signaling pathway and induce the expression of cyclooxygenase-2 (COX2) and prostaglandin E2 (PGE2) in MSCs. STAT3 inhibitor reversed the MCP-1-mediated enhancing of their immunosuppressive ability. Collectively, our findings demonstrate that CHS-related MCP-1 preconditioning enhanced the immunomodulatory effects of MSCs and improved their therapeutic efficacy in CHS. Enhancing the immunosuppressive efficacy of MSCs by preconditioning with certain disease-related inflammatory cytokines may provide a new strategy for MSC-based therapies for inflammatory diseases.

Recent advances in understanding mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are among of the most studied cell type for cellular therapy thanks to the ease of isolation, cultivation, and the high ex vivo expansion potential. In 2018, the European Medicines Agency finally granted the first marketing authorization for an MSC product. Despite the numerous promising results in preclinical studies, translation into routine practice still lags behind: therapeutic benefits of MSCs are not as satisfactory in clinical trial settings as they appear to be in preclinical models. The bench-to-bedside-and-back approach and careful evaluation of discrepancies between preclinical and clinical results have provided valuable insights into critical components of MSC manufacturing, their mechanisms of action, and how to evaluate and quality-control them. We sum up these past developments in the introductory section (“Mesenchymal stromal cells: name follows function”). From the huge amount of information, we then selected a few examples to illustrate challenges and opportunities to improve MSCs for clinical purposes. These include tissue origin of MSCs, MSC culture conditions, immune compatibility, and route of application and dosing. Finally, we add some information on MSC mechanisms of action and translation into potency assays and give an outlook on future perspectives raising the question of whether the future clinical product may be cell-based or cell-derived.