Human Umbilical Cord Blood Endothelial Progenitor Cell-Derived Extracellular Vesicles Control Important Endothelial Cell Functions

Circulating endothelial progenitor cells (EPCs) play a pivotal role in the repair of diseases in which angiogenesis is required. Although they are a potentially valuable cell therapy tool, their clinical use remains limited due to suboptimal storage conditions and, especially, long-term immune rejection. EPC-derived extracellular vesicles (EPC-EVs) may be an alternative to EPCs given their key role in cell-cell communication and expression of the same parental markers. Here, we investigated the regenerative effects of umbilical cord blood (CB) EPC-EVs on CB-EPCs in vitro. After amplification, EPCs were cultured in a medium containing an EVs-depleted serum (EV-free medium). Then, EVs were isolated from the conditioned medium with tangential flow filtration (TFF). The regenerative effects of EVs on cells were investigated by analyzing cell migration, wound healing, and tube formation. We also analyzed their effects on endothelial cell inflammation and Nitric Oxide (NO) production. We showed that adding different doses of EPC-EVs on EPCs does not alter the basal expression of the endothelial cell markers nor change their proliferative potential and NO production level. Furthermore, we demonstrated that EPC-EVs, when used at a higher dose than the physiological dose, create a mild inflammatory condition that activates EPCs and boosts their regenerative features. Our results reveal for the first time that EPC-EVs, when used at a high dose, enhance EPC regenerative functions without altering their endothelial identity.

Abstract 3665: Umbilical cord blood endothelial progenitor cell-derived extracellular vesicles control important endothelial cell functions

Background: Circulating endothelial progenitor cells (EPCs) play a pivotal role in vascular regeneration and the repair of diseases in which angiogenesis is required, including ischemia and tissue transplantation. Although they are a potentially valuable cell therapy tool, their clinical use remains limited due to suboptimal storage conditions and especially, immune rejection. Even if these cells have been shown to be tolerated by the immune system, their in vivo long-term effects still remain to be elucidated. EPC-derived extracellular vesicles (EPC-EVs) may be an attractive alternative to EPCs given their key role in cell-cell communication and expression of the same parental markers. In this study, we investigated the regenerative effects of umbilical cord blood EPC-EVs on EPCs in vitro.

Methods: EPCs were obtained from human umbilical cord blood (CB) and characterized by flow cytometry. After amplification, EPCs were cultured in a medium containing an EVs-depleted serum (EV-free medium). Then the conditioned medium was used to isolate the EVs with Tangential Flow Filtration (TFF). The EVs were characterized by a series of tests defining their size, number, and protein content. The regenerative effects of EPC-EVs on endothelial cells were investigated by analyzing cell migration, wound healing, and tube formation. We also analyzed the effect of EPC-EVs on endothelial cell inflammation and NO production.

Results: We showed that adding different doses of EPC-EVs on EPCs does not alter the basal expression of the endothelial cell markers CD31, CD144, and KDR, nor change their proliferative potential and NO production level. Furthermore, we demonstrated that EPC-EVs, when used at a higher than physiologic dose, create a mild inflammatory condition that activates EPCs and boosts their regenerative features like migration and tube formation functions.

Conclusions: Our results reveal for the first time that EPC-EVs, when used at a high dose, could enhance EPC regenerative functions without altering their endothelial identity.

Citation Format: Sawssen Ben Fraj, Sina Naserian, Bileyle Lorenzini, Sylvie Goulinet, Philippe Mauduit, Georges Uzan, Houda Haouas. Umbilical cord blood endothelial progenitor cell-derived extracellular vesicles control important endothelial cell functions. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3665.

Biallelic variants in NOS3 and GUCY1A3, the two major genes of the nitric oxide pathway, cause moyamoya cerebral angiopathy

BACKGROUND

Moyamoya angiopathy (MMA) is a rare cerebrovascular condition leading to stroke. Mutations in 15 genes have been identified in Mendelian forms of MMA, but they explain only a very small proportion of cases. Our aim was to investigate the genetic basis of MMA in consanguineous patients having unaffected parents in order to identify genes involved in autosomal recessive MMA.

METHODS

Exome sequencing (ES) was performed in 6 consecutive consanguineous probands having MMA of unknown etiology. Functional consequences of variants were assessed using western blot and protein 3D structure analyses.

RESULTS

Causative homozygous variants of NOS3, the gene encoding the endothelial nitric oxide synthase (eNOS), and GUCY1A3, the gene encoding the alpha1 subunit of the soluble guanylate cyclase (sGC) which is the major nitric oxide (NO) receptor in the vascular wall, were identified in 3 of the 6 probands. One NOS3 variant (c.1502 + 1G > C) involves a splice donor site causing a premature termination codon and leads to a total lack of eNOS in endothelial progenitor cells of the affected proband. The other NOS3 variant (c.1942 T > C) is a missense variant located into the flavodoxine reductase domain; it is predicted to be destabilizing and shown to be associated with a reduction of eNOS expression. The GUCY1A3 missense variant (c.1778G > A), located in the catalytic domain of the sGC, is predicted to disrupt the tridimensional structure of this domain and to lead to a loss of function of the enzyme. Both NOS3 mutated probands suffered from an infant-onset and severe MMA associated with posterior cerebral artery steno-occlusive lesions. The GUCY1A3 mutated proband presented an adult-onset MMA associated with an early-onset arterial hypertension and a stenosis of the superior mesenteric artery. None of the 3 probands had achalasia.

CONCLUSIONS

We show for the first time that biallelic loss of function variants in NOS3 is responsible for MMA and that mutations in NOS3 and GUCY1A3 are causing fifty per cent of MMA in consanguineous patients. These data pinpoint the essential role of the NO pathway in MMA pathophysiology.

Producing vesicle-free cell culture additive for human cells extracellular vesicles manufacturing

A new paradigm has emerged recently, which consists in shifting from cell therapy to a more flexible acellular "extracellular vesicle (EV) therapy" approach, thereby opening a new and promising field in nanomedicine. Important technical limitations have still to be addressed for the large-scale production of clinical-grade EV. Cells are cultured in media supplemented with human platelet lysate (hPL) (xenogenic-free) or GMP-grade fetal calf serum (FCS). However, these additives contain high amounts of EV that cannot be separated from cell-secreted -EV. Therefore, cells are generally maintained in additive-free medium during the EV secretion phase, however this can substantially limit their survival. In the present work, we developed a method to prepare vesicle-free hPL (EV-free hPL) or vesicle-free FCS (EV-free FCS) using tangential flow filtration (TFF). We show a very efficient EV depletion (>98%) for both pure hPL and FCS, with a highly conserved protein content. Culture medium containing our EV-free additives supported the survival of human bone marrow MSC (BM-MSC). MSC could survive at least 216 h, their conditioned medium being collected and changed every 72 h. Both the cell survival and the cumulative EV production were substantially higher than in the starving conditions classically used for EV production. In EV-free hPL containing medium, we show that purified EV kept their morphologic and molecular characteristics throughout the production. Finally, we tested our additives with 3 other cell types, human primary Endothelial Colony Forming Cells (ECFC) and two non-adherent human cell lines, Jurkat and THP-1. We confirmed that both EV-free hPL and FCS were able to maintain cell survival and EV production for at least 216 h. Our method provides therefore a new option to help producing large amounts of EV from virtually any mammalian cells, particularly those that do not tolerate starvation. This method can apply to any animal serum for research and development purpose. Moreover, EV-free hPL is clinical-grade compatible and allows preparing xenobiotic-free media for massive therapeutic EV production in both 2D (cell plates) and 3D (bioreactor) setting.

Research and Therapeutic Approaches in Stem Cell Genome Editing by CRISPR Toolkit

The most widely used genome editing toolkit is CRISPR (clustered regularly interspaced short palindromic repeats). It provides the possibility of replacing and modifying DNA and RNA nucleotides. Furthermore, with advancements in biological technology, inhibition and activation of the transcription of specific gene(s) has become possible. Bioinformatics tools that target the evolution of CRISPR-associated protein 9 (Cas9) turn this protein into a vehicle that is specific for a DNA or RNA region with single guide RNA (sgRNA). This toolkit could be used by researchers to investigate the function of stem cell gene(s). Here, in this review article, we cover recent developments and applications of this technique in stem cells for research and clinical purposes and discuss different CRISPR/Cas technologies for knock-out, knock-in, activation, or inhibition of gene expression. Additionally, a comparison of several deliveries and off-target detecting strategies is discussed.

An Evaluation of Different Types of Peptone as Partial Substitutes for Animal-derived Serum in Vero Cell Culture

Vero cells are one of the most frequently used cell types in virology. They can be used not only as a vehicle for the replication of viruses, but also as a model for investigating viral infectivity, cytopathology and vaccine production. There is increasing awareness of the need to limit the use of animal-derived components in cell culture media for a number of reasons, which include reducing the risk of contamination and decreasing costs related to the downstream processing of commercial products obtained via cell culture. The current study evaluates the use of protein hydrolysates (PHLs), also known as peptones, as partial substitutes for fetal bovine serum (FBS) in Vero cell culture. Eleven plant-based, two yeast-based, and three casein-based peptones were assessed, with different batches evaluated in the study. We tested the effects of three concentration ratios of FBS and peptone on Vero cell proliferation, four days after the initial cell seeding. Some of the tested peptones, when in combination with a minimal 1% level of FBS, supported cell proliferation rates equivalent to those achieved with 10% FBS. Collectively, our findings showed that plant-based peptones could represent promising options for the successful formulation of serum-reduced cell culture media for vaccine production. This is especially relevant in the context of the current COVID-19 pandemic, in view of the urgent need for SARS-CoV-2 virus production for certain types of vaccine. The current study contributes to the Three Rs principle of reduction, as well as addressing animal ethics concerns associated with FBS, by repurposing PHLs for use in cell culture.

Endothelial and hematopoietic hPSCs differentiation via a hematoendothelial progenitor

Background

hPSC-derived endothelial and hematopoietic cells (ECs and HCs) are an interesting source of cells for tissue engineering. Despite their close spatial and temporal embryonic development, current hPSC differentiation protocols are specialized in only one of these lineages. In this study, we generated a hematoendothelial population that could be further differentiated in vitro to both lineages.

Methods

Two hESCs and one hiPSC lines were differentiated into a hematoendothelial population, hPSC-ECs and blast colonies (hPSC-BCs) via CD144⁺-embryoid bodies (hPSC-EBs). hPSC-ECs were characterized by endothelial colony-forming assay, LDL uptake assay, endothelial activation by TNF-α, nitric oxide detection and Matrigel-based tube formation. Hematopoietic colony-forming cell assay was performed from hPSC-BCs. Interestingly, we identified a hPSC-BC population characterized by the expression of both CD144 and CD45. hPSC-ECs and hPSC-BCs were analyzed by flow cytometry and RT-qPCR; in vivo experiments have been realized by ischemic tissue injury model on a mouse dorsal skinfold chamber and hematopoietic reconstitution in irradiated immunosuppressed mouse from hPSC-ECs and hPSC-EB-CD144⁺, respectively. Transcriptomic analyses were performed to confirm the endothelial and hematopoietic identity of hESC-derived cell populations by comparing them against undifferentiated hESC, among each other’s (e.g. hPSC-ECs vs. hPSC-EB-CD144⁺) and against human embryonic liver (EL) endothelial, hematoendothelial and hematopoietic cell subpopulations.

Results

A hematoendothelial population was obtained after 84 h of hPSC-EBs formation under serum-free conditions and isolated based on CD144 expression. Intrafemorally injection of hPSC-EB-CD144⁺ contributed to the generation of CD45⁺ human cells in immunodeficient mice suggesting the existence of hemogenic ECs within hPSC-EB-CD144⁺. Endothelial differentiation of hPSC-EB-CD144⁺ yields a population of > 95% functional ECs in vitro. hPSC-ECs derived through this protocol participated at the formation of new vessels in vivo in a mouse ischemia model. In vitro, hematopoietic differentiation of hPSC-EB-CD144⁺ generated an intermediate population of > 90% CD43⁺ hPSC-BCs capable to generate myeloid and erythroid colonies. Finally, the transcriptomic analyses confirmed the hematoendothelial, endothelial and hematopoietic identity of hPSC-EB-CD144⁺, hPSC-ECs and hPSC-BCs, respectively, and the similarities between hPSC-BC-CD144⁺CD45⁺, a subpopulation of hPSC-BCs, and human EL hematopoietic stem cells/hematopoietic progenitors.

Conclusion

The present work reports a hPSC differentiation protocol into functional hematopoietic and endothelial cells through a hematoendothelial population. Both lineages were proven to display characteristics of physiological human cells, and therefore, they represent an interesting rapid source of cells for future cell therapy and tissue engineering.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02925-w.

Principles and Applications of CRISPR Toolkit in Virus Manipulation, Diagnosis, and Virus-Host Interactions

Viruses are one of the most important concerns for human health, and overcoming viral infections is a worldwide challenge. However, researchers have been trying to manipulate viral genomes to overcome various disorders, including cancer, for vaccine development purposes. CRISPR (clustered regularly interspaced short palindromic repeats) is becoming one of the most functional and widely used tools for RNA and DNA manipulation in multiple organisms. This approach has provided an unprecedented opportunity for creating simple, inexpensive, specific, targeted, accurate, and practical manipulations of viruses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), human immunodeficiency virus-1 (HIV-1), and vaccinia virus. Furthermore, this method can be used to make an effective and precise diagnosis of viral infections. Nevertheless, a valid and scientifically designed CRISPR system is critical to make more effective and accurate changes in viruses. In this review, we have focused on the best and the most effective ways to design sgRNA, gene knock-in(s), and gene knock-out(s) for virus-targeted manipulation. Furthermore, we have emphasized the application of CRISPR technology in virus diagnosis and in finding significant genes involved in virus-host interactions.

A compact integrated microfluidic oxygenator with high gas exchange efficiency and compatibility for long-lasting endothelialization

We have developed and tested a novel microfluidic device for blood oxygenation, which exhibits a large surface area of gas exchange and can support long-term sustainable endothelialization of blood microcapillaries, enhancing its hemocompatibility for clinical applications. The architecture of the parallel stacking of the trilayers is based on a central injection for blood and a lateral injection/output for gas which allows significant reduction in shear stress, promoting sustainable endothelialization since cells can be maintained viable for up to 2 weeks after initial seeding in the blood microchannel network. The circular design of curved blood capillaries allows covering a maximal surface area at 4 inch wafer scale, producing high oxygen uptake and carbon dioxide release in each single unit. Since the conventional bonding process based on oxygen plasma cannot be used for surface areas larger than several cm², a new "wet bonding" process based on soft microprinting has been developed and patented. Using this new protocol, each 4 inch trilayer unit can be sealed without a collapsed membrane even at reduced 15 μm thickness and can support a high blood flow rate. The height of the blood channels has been optimized to reduce pressure drop and enhance gas exchange at a high volumetric blood flow rate up to 15 ml min^-1. The simplicity of connecting different units in the stacked architecture is demonstrated for 3- or 5-unit stacked devices that exhibit remarkable performance with low primary volume, high oxygen uptake and carbon dioxide release and high flow rate of up to 80 ml min^-1.

Differences and similarities between mesenchymal stem cell and endothelial progenitor cell immunoregulatory properties against T cells

Bone-marrow-derived mesenchymal stem cells and endothelial progenitor cells have some interesting biological properties that make them unique for cell therapy of degenerative and cardiovascular disorders. Although both cell populations have been already studied and used for their regenerative potentials, recently their special immunoregulatory features have brought much more attention. Mesenchymal stem cells and endothelial progenitor cells have both proangiogenic functions and have been shown to suppress the immune response, particularly T cell proliferation, activation, and cytokine production. This makes them suitable choices for allogeneic stem cell transplantation. Nevertheless, these two cells do not have equal immunoregulatory activities. Many elements including their extraction sources, age/passage, expression of different markers, secretion of bioactive mediators, and some others could change the efficiency of their immunosuppressive function. However, to our knowledge, no publication has yet compared mesenchymal stem cells and endothelial progenitor cells for their immunological interaction with T cells. This review aims to specifically compare the immunoregulatory effect of these two populations including their T cell suppression, deactivation, cytokine production, and regulatory T cells induction capacities. Moreover, it evaluates the implications of the tumor necrosis factor alpha-tumor necrosis factor receptor 2 axis as an emerging immune checkpoint signaling pathway controlling most of their immunological properties.

Post-decellularization techniques ameliorate cartilage decellularization process for tissue engineering applications

Due to the current lack of innovative and effective therapeutic approaches, tissue engineering (TE) has attracted much attention during the last decades providing new hopes for the treatment of several degenerative disorders. Tissue engineering is a complex procedure, which includes processes of decellularization and recellularization of biological tissues or functionalization of artificial scaffolds by active cells. In this review, we have first discussed those conventional steps, which have led to great advancements during the last several years. Moreover, we have paid special attention to the new methods of post-decellularization that can significantly ameliorate the efficiency of decellularized cartilage extracellular matrix (ECM) for the treatment of osteoarthritis (OA). We propose a series of post-decellularization procedures to overcome the current shortcomings such as low mechanical strength and poor bioactivity to improve decellularized ECM scaffold towards much more efficient and higher integration.

Single-cell transcriptomic profiling and characterization of endothelial progenitor cells: new approach for finding novel markers

Background

Endothelial progenitor cells (EPCs) are promising candidates for the cellular therapy of peripheral arterial and cardiovascular diseases. However, hitherto there is no specific marker(s) defining precisely EPCs. Herein, we are proposing a new in silico approach for finding novel EPC markers.

Methods

We assembled five groups of chosen EPC-related genes/factors using PubMed literature and Gene Ontology databases. This shortened database of EPC factors was fed into publically published transcriptome matrix to compare their expression between endothelial colony-forming cells (ECFCs), HUVECs, and two adult endothelial cell types (ECs) from the skin and adipose tissue. Further, the database was used for functional enrichment on Mouse Phenotype database and protein-protein interaction network analyses. Moreover, we built a digital matrix of healthy donors’ PBMCs (33 thousand single-cell transcriptomes) and analyzed the expression of these EPC factors.

Results

Transcriptome analyses showed that BMP2, 4, and ephrinB2 were exclusively highly expressed in EPCs; the expression of neuropilin-1 and VEGF-C were significantly higher in EPCs and HUVECs compared with other ECs; Notch 1 was highly expressed in EPCs and skin-ECs; MIR21 was highly expressed in skin-ECs; PECAM-1 was significantly higher in EPCs and adipose ECs. Moreover, functional enrichment of EPC-related genes on Mouse Phenotype and STRING protein database has revealed significant relations between chosen EPC factors and endothelial and vascular functions, development, and morphogenesis, where ephrinB2, BMP2, and BMP4 were highly expressed in EPCs and were connected to abnormal vascular functions. Single-cell RNA-sequencing analyses have revealed that among the EPC-regulated markers in transcriptome analyses, (i) ICAM1 and Endoglin were weekly expressed in the monocyte compartment of the peripheral blood; (ii) CD163 and CD36 were highly expressed in the CD14+ monocyte compartment whereas CSF1R was highly expressed in the CD16+ monocyte compartment, (iii) L-selectin and IL6R were globally expressed in the lymphoid/myeloid compartments, and (iv) interestingly, PLAUR/UPAR and NOTCH2 were highly expressed in both CD14+ and CD16+ monocytic compartments.

Conclusions

The current study has identified novel EPC markers that could be used for better characterization of EPC subpopulation in adult peripheral blood and subsequent usage of EPCs for various cell therapy and regenerative medicine applications.

Human fetal liver MSCs are more effective than adult bone marrow MSCs for their immunosuppressive, immunomodulatory, and Foxp3+ T reg induction capacity

BACKGROUND

Mesenchymal stem cells (MSCs) exhibit active abilities to suppress or modulate deleterious immune responses by various molecular mechanisms. These cells are the subject of major translational efforts as cellular therapies for immune-related diseases and transplantations. Plenty of preclinical studies and clinical trials employing MSCs have shown promising safety and efficacy outcomes and also shed light on the modifications in the frequency and function of regulatory T cells (T regs). Nevertheless, the mechanisms underlying these observations are not well known. Direct cell contact, soluble factor production, and turning antigen-presenting cells into tolerogenic phenotypes, have been proposed to be among possible mechanisms by which MSCs produce an immunomodulatory environment for T reg expansion and activity. We and others demonstrated that adult bone marrow (BM)-MSCs suppress adaptive immune responses directly by inhibiting the proliferation of CD4+ helper and CD8+ cytotoxic T cells but also indirectly through the induction of T regs. In parallel, we demonstrated that fetal liver (FL)-MSCs demonstrates much longer-lasting immunomodulatory properties compared to BM-MSCs, by inhibiting directly the proliferation and activation of CD4+ and CD8+ T cells. Therefore, we investigated if FL-MSCs exert their strong immunosuppressive effect also indirectly through induction of T regs.

METHODS

MSCs were obtained from FL and adult BM and characterized according to their surface antigen expression, their multilineage differentiation, and their proliferation potential. Using different in vitro combinations, we performed co-cultures of FL- or BM-MSCs and murine CD3+CD25-T cells to investigate immunosuppressive effects of MSCs on T cells and to quantify their capacity to induce functional T regs.

RESULTS

We demonstrated that although both types of MSC display similar cell surface phenotypic profile and differentiation capacity, FL-MSCs have significantly higher proliferative capacity and ability to suppress both CD4+ and CD8+ murine T cell proliferation and to modulate them towards less active phenotypes than adult BM-MSCs. Moreover, their substantial suppressive effect was associated with an outstanding increase of functional CD4+CD25+Foxp3+ T regs compared to BM-MSCs.

CONCLUSIONS

These results highlight the immunosuppressive activity of FL-MSCs on T cells and show for the first time that one of the main immunoregulatory mechanisms of FL-MSCs passes through active and functional T reg induction.

TNFα priming through its interaction with TNFR2 enhances endothelial progenitor cell immunosuppressive effect: new hope for their widespread clinical application

Background

Bone marrow derived endothelial progenitor cells (EPCs) are immature endothelial cells (ECs) involved in neo-angiogenesis and endothelial homeostasis and are considered as a circulating reservoir for endothelial repair. Many studies showed that EPCs from patients with cardiovascular pathologies are impaired and insufficient; hence, allogenic sources of EPCs from adult or cord blood are considered as good choices for cell therapy applications. However, allogenic condition increases the chance of immune rejection, especially by T cells, before exerting the desired regenerative functions. TNFα is one of the main mediators of EPC activation that recognizes two distinct receptors, TNFR1 and TNFR2. We have recently reported that human EPCs are immunosuppressive and this effect was TNFα-TNFR2 dependent. Here, we aimed to investigate if an adequate TNFα pre-conditioning could increase TNFR2 expression and prime EPCs towards more immunoregulatory functions.

Methods

EPCs were pre-treated with several doses of TNFα to find the proper dose to up-regulate TNFR2 while keeping the TNFR1 expression stable. Then, co-cultures of human EPCs and human T cells were performed to assess whether TNFα priming would increase EPC immunosuppressive and immunomodulatory effect.

Results

Treating EPCs with 1 ng/ml TNFα significantly up-regulated TNFR2 expression without unrestrained increase of TNFR1 and other endothelial injury markers. Moreover, TNFα priming through its interaction with TNFR2 remarkably enhanced EPC immunosuppressive and anti-inflammatory effects. Conversely, blocking TNFR2 using anti-TNFR2 mAb followed by 1 ng/ml of TNFα treatment led to the TNFα-TNFR1 interaction and polarized EPCs towards pro-inflammatory and immunogenic functions.

Conclusions

We report for the first time the crucial impact of inflammation notably the TNFα-TNFR signaling pathway on EPC immunological function. Our work unveils the pro-inflammatory role of the TNFα-TNFR1 axis and, inversely the anti-inflammatory implication of the TNFα-TNFR2 axis in EPC immunoregulatory functions. Priming EPCs with 1 ng/ml of TNFα prior to their administration could boost them toward a more immunosuppressive phenotype. This could potentially lead to EPCs’ longer presence in vivo after their allogenic administration resulting in their better contribution to angiogenesis and vascular regeneration.

Current Preventions and Treatments of aGVHD: From Pharmacological Prophylaxis to Innovative Therapies

Graft versus host disease (GVHD) is one of the main causes of mortality and the reason for up to 50% of morbidity after hematopoietic stem cell transplantations (HSCT) which is the treatment of choice for many blood malignancies. Thanks to years of research and exploration, we have acquired a profound understanding of the pathophysiology and immunopathology of these disorders. This led to the proposition and development of many therapeutic approaches during the last decades, some of them with very promising results. In this review, we have focused on the recent GVHD treatments from classical chemical and pharmacological prophylaxis to more innovative treatments including gene therapy and cell therapy, most commonly based on the application of a variety of immunomodulatory cells. Furthermore, we have discussed the advantages and potentials of cell-free therapy as a newly emerging approach to treat GVHD. Among them, we have particularly focused on the implication of the TNFα-TNFR2 axis as a new immune checkpoint signaling pathway controlling different aspects of many immunoregulatory cells.

Regulatory T cell induction by mesenchymal stem cells depends on the expression of TNFR2 by T cells

Mesenchymal stem/stromal cells can modulate the effector immune cells especially T lymphocytes. Due to this important feature, they can regulate the development of a variety of disorders including inflammatory and autoimmune disorders, cancers, and transplantation outcomes. One of the most important MSC immunoregulatory functions is their capacity to convert conventional T cells into regulatory T cells. Several mechanisms, mostly related to MSCs but not T cells, have been shown essential for this aspect. The inflammatory microenvironment majorly caused by pro-inflammatory cytokines has been demonstrated to govern the direction of the immune response. In this respect, we have recently revealed that the TNFα-TNFR2 signaling controls several aspects of MSC immunomodulatory properties including their ability to suppress T cells and their conversion towards Foxp3-expressing Tregs. Here in this work, we have looked from another angle by investigating the impact of TNFR2 expression by T cells on their ability to be converted to suppressive Tregs by MSCs. We showed that unlike WT-T cells, their TNFR2 KO counterparts are remarkably less able to convert into Foxp3+ and Foxp3- Tregs. Furthermore, TNFR2 blockade diminished the anti-inflammatory cytokine secretion by iTregs and consequently resulted in less T cell immunosuppression. This work is the first evidence of the crucial association of TNFR2 expression by T cells with their iTreg conversion capacity by MSCs. It strengthens once more the potential of anti-TNFR2 administration for a strong and effective interference with the immunosuppression exerted by TNFR2-expressing cells.

TNFR2 Is a Crucial Hub Controlling Mesenchymal Stem Cell Biological and Functional Properties

Mesenchymal stem cells (MSCs) have drawn lots of attention as gold standard stem cells in fundamental and clinical researches during the last 20 years. Due to their tissue and vascular repair capacities, MSCs have been used to treat a variety of degenerative disorders. Moreover, MSCs are able to modulate immune cells’ functions, particularly T cells while inducing regulatory T cells (iTregs). MSCs are very sensitive to inflammatory signals. Their biological functions could remarkably vary after exposure to different pro-inflammatory cytokines, notably TNFα. In this article, we have explored the importance of TNFR2 expression in a series of MSCs’ biological and functional properties. Thus, MSCs from wild-type (WT) and TNFR2 knockout (TNFR2 KO) mice were isolated and underwent several ex vivo experiments to investigate the biological significance of TNFR2 molecule in MSC main functions. Hampering in TNFR2 signaling resulted in reduced MSC colony-forming units and proliferation rate and diminished the expression of all MSC characteristic markers such as stem cell antigen-1 (Sca1), CD90, CD105, CD44, and CD73. TNFR2 KO-MSCs produced more pro-inflammatory cytokines like TNFα, IFNγ, and IL-6 and less anti-inflammatory mediators such as IL-10, TGFβ, and NO and induced Tregs with less suppressive effect. Furthermore, the TNFR2 blockade remarkably decreased MSC regenerative functions such as wound healing, complex tube formation, and endothelial pro-angiogenic support. Therefore, our results reveal the TNFα–TNFR2 axis as a crucial regulator of MSC immunological and regenerative functions.

Physical plasma therapy accelerates wound re-epithelialisation and enhances extracellular matrix formation in cutaneous skin grafts

Skin grafting is a surgical method of cutaneous reconstruction, which provides volumetric replacement in wounds unable to heal by primary intention. Clinically, full-thickness skin grafts (FTSGs) are placed in aesthetically sensitive and mechanically demanding areas such as the hands, face, and neck. Complete or partial graft failure is the primary complication associated with this surgical procedure. Strategies aimed at improving the rate of skin graft integration will reduce the incidence of graft failure. Cold atmospheric plasma (CAP) is an emerging technology offering innovative clinical applications. The aim of this study was to test the therapeutic potential of CAP to improve wound healing and skin graft integration into the recipient site. In vitro models that mimic wound healing were used to investigate the ability of CAP to enhance cellular migration, a key factor in cutaneous tissue repair. We demonstrated that CAP enhanced the migration of epidermal keratinocytes and dermal fibroblasts. This increased cellular migration was possibly induced by the low dose of reactive oxygen and nitrogen species produced by CAP. Using a mouse model of burn wound reconstructed with a full-thickness skin graft, we showed that wounds treated with CAP healed faster than did control wounds. Immunohistochemical wound analysis showed that CAP treatment enhanced the expression of the dermal-epidermal junction components, which are vital for successful skin graft integration. CAP treatment was characterised by increased levels of Tgfbr1 mRNA and collagen I protein in vivo, suggesting enhanced wound maturity and extracellular matrix deposition. Mechanistically, we show that CAP induced the activation of the canonical SMAD-dependent TGF-β1 pathway in primary human dermal fibroblasts, which may explain the increased collagen I synthesis in vitro. These studies revealed that CAP improved wound repair and skin graft integration via mechanisms involving extracellular matrix formation. CAP offers a novel approach for treating cutaneous wounds and skin grafts. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

TNFα/TNFR2 signaling pathway: an active immune checkpoint for mesenchymal stem cell immunoregulatory function

BACKGROUND

In addition to their multilineage potential, mesenchymal stem cells (MSCs) have a broad range of functions from tissue regeneration to immunomodulation. MSCs have the ability to modulate the immune response and change the progression of different inflammatory and autoimmune disorders. However, there are still many challenges to overcome before their widespread clinical administration including the mechanisms behind their immunoregulatory function. MSCs inhibit effector T cells and other immune cells, while inducing regulatory T cells (T regs), thus, reducing directly and indirectly the production of pro-inflammatory cytokines. TNF/TNFR signaling plays a dual role: while the interaction of TNFα with TNFR1 mediates pro-inflammatory effects and cell death, its interaction with TNFR2 mediates anti-inflammatory effects and cell survival. Many immunosuppressive cells like T regs, regulatory B cells (B regs), endothelial progenitor cells (EPCs), and myeloid-derived suppressor cells (MDSCs) express TNFR2, and this is directly related to their immunosuppression efficiency. In this article, we investigated the role of the TNFα/TNFR2 immune checkpoint signaling pathway in the immunomodulatory capacities of MSCs.

METHODS

Co-cultures of MSCs from wild-type (WT) and TNFR2 knocked-out (TNFR2 KO) mice with T cells (WT and TNFα KO) were performed under various experimental conditions.

RESULTS

We demonstrate that TNFR2 is a key regulatory molecule which is strongly involved in the immunomodulatory properties of MSCs. This includes their ability to suppress T cell proliferation, activation, and pro-inflammatory cytokine production, in addition to their capacity to induce active T regs.

CONCLUSIONS

Our results reveal for the first time the importance of the TNFα/TNFR2 axis as an active immune checkpoint regulating MSC immunological functions.

The TNF/TNFR2 signaling pathway is a key regulatory factor in endothelial progenitor cell immunosuppressive effect

Background

Endothelial progenitor cells (EPCs) are non-differentiated endothelial cells (ECs) present in blood circulation that are involved in neo-vascularization and correction of damaged endothelial sites. Since EPCs from patients with vascular disorders are impaired and inefficient, allogenic sources from adult or cord blood are considered as good alternatives. However, due to the reaction of immune system against allogenic cells which usually lead to their elimination, we focused on the exact role of EPCs on immune cells, particularly, T cells which are the most important cells applied in immune rejection. TNFα is one of the main activators of EPCs that recognizes two distinct receptors. TNFR1 is expressed ubiquitously and its interaction with TNFα leads to differentiation and apoptosis, whereas, TNFR2 is expressed predominantly on ECs, immune cells and neural cells and is involved in cell survival and proliferation. Interestingly, it has been shown that different immunosuppressive cells express TNFR2 and this is directly related to their immunosuppressive efficiency. However, little is known about immunological profile and function of TNFR2 in EPCs.

Methods

Using different in-vitro combinations, we performed co-cultures of ECs and T cells to investigate the immunological effect of EPCs on T cells. We interrupted in the TNFα/TNFR2 axis either by blocking the receptor using TNFR2 antagonist or blocking the ligand using T cells derived from TNFα KO mice.

Results

We demonstrated that EPCs are able to suppress T cell proliferation and modulate them towards less pro-inflammatory and active phenotypes. Moreover, we showed that TNFα/TNFR2 immune-checkpoint pathway is critical in EPC immunomodulatory effect.

Conclusions

Our results reveal for the first time a mechanism that EPCs use to suppress immune cells, therefore, enabling them to form new immunosuppressive vessels. Furthermore, we have shown the importance of TNFα/TNFR2 axis in EPCs as an immune checkpoint pathway. We believe that targeting TNFR2 is especially crucial in cancer immune therapy since it controls two crucial aspects of tumor microenvironment: 1) Immunosuppression and 2) Angiogenesis.

Video Abstract. (MP4 46355 kb)

Cord blood-endothelial colony forming cells are immunotolerated and participate at post-ischemic angiogenesis in an original dorsal chamber immunocompetent mouse model

BACKGROUND

Cardiovascular diseases are the main cause of morbidity and mortality worldwide. Restoring blood supply to ischemic tissues is an essential goal for the successful treatment of these diseases. Growth factor or gene therapy efficacy remains controversial, but stem cell transplantation is emerging as an interesting approach to stimulate angiogenesis. Among the different stem cell populations, cord blood-endothelial progenitor cells (CB-EPCs) and more particularly cord blood-endothelial progenitor cell-derived endothelial colony forming cells (CB-ECFCs) have a great proliferative potential without exhibiting signs of senescence. Even if it was already described that CB-ECFCs were able to restore blood perfusion in hind-limb ischemia in an immunodeficient mouse model, until now, the immunogenic potential of allogenic CB-ECFCs remains controversial. Therefore, our objectives were to evaluate the immune tolerance potency of CB-ECFCs and their capacity to restore a functional vascular network under ischemic condition in immunocompetent mice.

METHODS

In vitro, the expression and secretion of immunoregulatory markers (HLA-G, IL-10, and TGF-β1) were evaluated on CB-ECFCs. Moreover, CB-ECFCs were co-cultured with activated peripheral blood mononuclear cells (PBMCs) for 6 days. PBMC proliferation was evaluated by [3H]-thymidine incorporation on the last 18 h. In vivo, CB-ECFCs were administered in the spleen and muscle of immunocompetent mice. Tissues were collected at day 14 after surgery. Finally, CB-ECFCs were injected intradermally in C57BL/6JRj mice close to ischemic macrovessel induced by thermal cauterization. Mice recovered until day 5 and were imaged, twice a week until day 30.

RESULTS

Firstly, we demonstrated that CB-ECFCs expressed HLA-G, IL-10, and TGF-β1 and secreted IL-10 and TGF-β1 and that they could display immunosuppressive properties in vitro. Secondly, we showed that CB-ECFCs could be tolerated until 14 days in immunocompetent mice. Thirdly, we revealed in an original ischemic model of dorsal chamber that CB-ECFCs were integrated in a new functional vascular network.

CONCLUSION

These results open up new perspectives about using CB-ECFCs as an allogeneic cell therapy product and gives new impulse to the treatment of cardiovascular diseases.

Different approaches for transformation of mesenchymal stem cells into hepatocyte-like cells

Due to the prominent role of the liver in the body and detoxification, its functionality can be affected in an irreversible manner by diseases. This phenomenon renders the liver to stop working, leading to morbidity and mortality. Therefore, liver transplantation is the only way to tackle this issue.In order to compensate for the lack of adequate healthy liver tissue for transplantation, therapeutic approaches such as hepatocyte transplantation have been proposed as an alternative. Recognizing the fact that mesenchymal stem cells are adult stem cells with the capacity to differentiate into several cell types, different methods have been invented to produce hepatocyte-like cells from mesenchymal stem cells. They can be divided into three main categories, such as addition of cytokines and growth factors, genetic modifications, and adjustment of microenvironment as well as physical parameters.In this review, we attempted to introduce diverse efficient methods for differentiating mesenchymal stem cells and their capability for transformation into hepatocyte-like cells.

GDF15 secreted by senescent endothelial cells improves vascular progenitor cell functions

Endothelial dysfunction (ED) is part of the first steps in the development of cardiovascular diseases (CVD). Growth Differentiation Factor 15 (GDF15) is a cytokine belonging to the Transforming Growth Factor β superfamily and its expression is increased both during ED and in CVD. Because high blood levels of GDF15 have been reported during ED, we hypothesized that GDF15 could be produced by endothelial cells in response to a vascular stress, possibly to attenuate endothelial function loss. Since senescence is mainly involved in both vascular stress and endothelial function loss, we used Endothelial Colony Forming Cells generated from adult blood (AB-ECFCs) as a model of endothelial cells to investigate GDF15 expression during cellular senescence. Then, we analyzed the potential role of GDF15 in AB-ECFC functions and senescence. When AB-ECFCs become senescent, they secrete increased levels of GDF15. We investigated GDF15 paracrine effects on non-senescent AB-ECFCs and showed that GDF15 enhanced proliferation, migration, NO production and activated several signaling pathways including AKT, ERK1/2 and SMAD2 without triggering any oxidative stress. Taken together, our results suggest that GDF15 production by senescent AB-ECFCs could act in a paracrine manner on non-senescent AB-ECFCs, and that this interaction could be beneficial to its model cells. Therefore, GDF15 could play a beneficial role in a dysfunctional vascular system as previously reported in patients with CVD, by limiting ED related to vascular stress occurring in these diseases.

Autologous endothelial progenitor cell therapy improves right ventricular function in a model of chronic thromboembolic pulmonary hypertension

BACKGROUND

Right ventricular (RV) failure is the main prognostic factor in pulmonary hypertension, and ventricular capillary density (CD) has been reported to be a marker of RV maladaptive remodeling and failure. Our aim was to determine whether right intracoronary endothelial progenitor cell (EPC) infusion can improve RV function and CD in a piglet model of chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

We compared 3 groups: sham (n = 5), CTEPH (n = 6), and CTEPH with EPC infusion (CTEPH+EPC; n = 5). After EPC isolation from CTEPH+EPC piglet peripheral blood samples at 3 weeks, the CTEPH and sham groups underwent right intracoronary infusion of saline, and the CTEPH+EPC group received EPCs at 6 weeks. RV function, pulmonary hemodynamics, and myocardial morphometry were investigated in the animals at 10 weeks.

RESULTS

After EPC administration, the RV fractional area change increased from 32.75% (interquartile range [IQR], 29.5%-36.5%) to 39% (IQR, 37.25%-46.50%; P = .030). The CTEPH+EPC piglets had reduced cardiomyocyte surface areas (from 298.3 μm² [IQR, 277.4-335.3 μm²] to 234.6 μm² (IQR, 211.1-264.7 μm²; P = .017), and increased CD31 expression (from 3.12 [IQR, 1.27-5.09] to 7.14 [IQR, 5.56-8.41; P = .017). EPCs were found in the RV free wall at 4 and 24 hours after injection but not 4 weeks later.

CONCLUSIONS

Intracoronary infusion of EPC improved RV function and CD in a piglet model of CTEPH. This novel cell-based therapy might represent a promising RV-targeted treatment in patients with pulmonary hypertension.

Celastrol reverses palmitic acid (PA)-caused TLR4-MD2 activation-dependent insulin resistance via disrupting MD2-related cellular binding to PA

Elevated plasma statured fatty acids (FFAs) cause TLR4/MD2 activation-dependent inflammation and insulin tolerance, which account for the occurrence and development of obesity. It has been confirmed that statured palmitic acid (PA) (the most abundant FFA) could bind MD2 to cause cellular inflammation. The natural compound celastrol could improve obesity, which is suggested via inhibiting inflammation, yet the detailed mechanism for celastrol is still unclear. As celastrol is reported to directly target MD2, we thought disrupting the binding between FFAs and MD2 might be one of the ways for celastrol to inhibit FFAs-caused inflammation and insulin resistance. In this study, we found evidence to support our hypothesis: celastrol could reverse PA-caused TLR4/MD2 activation-dependent insulin resistance, as determined by glucose-lowering ability, cellular glucose uptake, insulin action-related proteins and TLR4/MD2/NF-κB activation. Bioinformatics and cellular experiments showed that both celastrol and PA could bind MD2, and that celastrol could expel PA from cells. Finally, celastrol could reverse high fat diet caused hyperglycemia and obesity, and liver NF-kB activations. Taking together, we proved that celastrol could reverses PA-caused TLR4-MD2 activation-dependent insulin resistance via disrupting PA binding to MD2.

Stem cell therapy targeting the right ventricle in pulmonary arterial hypertension: is it a potential avenue of therapy?

Pulmonary arterial hypertension (PAH) is an incurable disease characterized by an increase in pulmonary arterial pressure due to pathological changes to the pulmonary vascular bed. As a result, the right ventricle (RV) is subject to an increased afterload and undergoes multiple changes, including a decrease in capillary density. All of these dysfunctions lead to RV failure. A number of studies have shown that RV function is one of the main prognostic factors for PAH patients. Many stem cell therapies targeting the left ventricle are currently undergoing development. The promising results observed in animal models have led to clinical trials that have shown an improvement of cardiac function. In contrast to left heart disease, stem cell therapy applied to the RV has remained poorly studied, even though it too may provide a therapeutic benefit. In this review, we discuss stem cell therapy as a treatment for RV failure in PAH. We provide an overview of the results of preclinical and clinical studies for RV cell therapies. Although a large number of studies have targeted the pulmonary circulation rather than the RV directly, there are nonetheless encouraging results in the literature that indicate that cell therapies may have a direct beneficial effect on RV function. This cell therapy strategy may therefore hold great promise and warrants further studies in PAH patients.

Expression of Coagulation Factor IX in a Haematopoietic Cell Line

We have developed a gene therapy project for haemophilia B which aims to express factor IX (FIX) in haematopoietic lineage. Haematopoietic stem cells and subsequent megakaryocyte-derived cells represent the target cells of this approach. Our speculation is that platelets can deliver the coagulation factor at the site of injury, and subsequently correct the haemostasis defect. In order to direct FIX expression in cells from the megakaryocytic lineage, we designed a FIX cassette where the FIX cDNA was placed under the control of the tissue-specific glycoprotein IIb (GPIIb) promoter. In stably transfected HEL cells, FIX production was higher when driven by the GPIIb promoter compared to the CMV promoter. Using a cassette containing both the GPIIb promoter and a truncated FIX intron 1, FIX synthesis was dramatically increased in HEL cells. Northern blot analysis demonstrated an increase in FIX mRNA amounts, which paralleled with an increase of FIX antigen in the culture supernatants. Using a one-stage clotting assay and an activation by FXIa and FVIIa/TF, the HEL-derived recombinant FIX was shown to be a biologically active protein. This recombinant protein exhibited a 60-kDa molecular mass and was more heterogeneous than plasma immunopurified FIX (Mononine®). The molecular mass difference could be partly explained by a different glycosylation pattern. The GPIIb promoter appears therefore to be a very attractive sequence to specifically direct FIX production in the megakaryocytic compartment of hematopoietic cells. These data also demonstrate that hematopoietic cells may represent potential target cells in an approach to gene therapy of haemophilia B.

Insights in the molecular mechanisms of the anti-angiogenic effect of an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase

3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) reduce the risk of coronary event by cholesterol-lowering dependent and independent mechanisms. We have already described that the inhibitory effect of cerivastatin on angiogenesis contribute to the cholesterol-independent beneficial effect and was due to the inhibition of the cell signaling cascade RhoA/FAK/Akt. In this study, new insights in the molecular mechanism of action were provided. It indicates an inhibition of exposure of alpha V beta 3 integrin on cell membrane and a modification of gene expression. The inhibition of angiogenesis could be related to 1) an increase in genes involved in the inhibition of cell proliferation (p19INK4, p21Waf/Cip1, Wnt-5a), the inhi bition of cell migration (Rho-GDI 1, α E-catenin) and 2) a downregulation of genes involved in angiogenesis (PAI-1, Vitronectin, HoxD3, Notch4) or in cell invasion (Semaphorin E). In addition, DNA repair protein genes (MLH1, XRCC1) were increased.

This study may indicate new biological interest of genes involved in angiogenesis control.

A fibrin antibody binding to fibronectin induces potent inhibition of angiogenesis

Antiserum from rabbits immunised with pure human fibrinogen was affinity purified on immobilised fibrin fragment E (FFE). This FFE antibody (Ab) induced significant growth inhibition of a human cancer xenograft in mice and suppression of tumour angiogenesis, leaving no formed vessels and only CD31-staining endothelial fragments in place. Tubule formation of HUVEC on MatrigelTM was also significantly inhibited by FFE Ab. Since MatrigelTM is fibrin-free, this effect implicated a different FFE Ab binding site than FFE. Flow cytometry of HUVEC showed that FFE Ab bound to HUVEC, but with a broad range of 55–98 %. Immunofluorescent staining of HUVEC explained this range, since FFE Ab was seen not to bind to human umbilical vein endothelial cells (HUVEC) directly but instead to a matrix protein variably adherent to HUVEC. This protein was identified as fibronectin (FN) by appearance, staining with FN Ab, and by a FN knockdown study. Neither HUVEC nor matrix reacted with fibrin D-dimer (DD) Ab. Immunofluorescent stains of HUVEC matrix with FFE and FN Ab’s showed that these Ab’s bound to the same epitopes on FN, as also seen on Western blots of purified FN. These findings indicate the presence of an antigenic determinant in fibrinogen/FFE that is homologous with an epitope(s) in FN recognised by FFE Ab, and critical for angiogenesis in this xenograft. The FN epitope(s) remains to be identified, but the present findings can be used for the selection of the appropriate clones from mice immunised with fibrinogen which can facilitate this identification, and which may also be of clinical use.

Circulating endothelial progenitors in vascular repair

Endothelial Colony Forming Cells (ECFCs) are obtained in culture from Circulating Endothelial Progenitor Cells. They display all characteristics of endothelial cells and they display stem cells features. Cord blood-derived ECFCs (CB-ECFCs) have a high clonogenic and proliferative potentials, and exhibit vascular repair capabilities useful for the treatment of ischemic diseases. However, the link between immaturity and functional properties of CB-ECFCs is still poorly defined. We showed that these cells have a high clonogenic potential and are capable to be efficiently reprogrammed into induced pluripotent stem cells. Moreover, we analyzed the expression of a broad panel of genes involved in embryonic stem cell properties. We define a novel stem cell transcriptional signature for CB-ECFCs fora better characterization and stratification according to their stem cell profile. We then improved the yield of CB-ECFC production for obtaining cells more functional in fewer passages. We used Glycosaminoglycans (GAG), components from the extracellular matrix which potentiate heparin binding growth factor activities. GAG mimetics were designed, having the capacity to increase the yield of ECFC during the isolation process, to increase the number of colonies, improve adhesion, proliferation, migration and self-renewal. GAG mimetics have thus great interest for vascular regeneration in combination with ECFC. Our results show that CB-ECFC are immature cells harboring specific functions such as formation of colonies, proliferation and formation of vascular structures in vitro and in vivo.

Initial clonogenic potential of human endothelial progenitor cells is predictive of their further properties and establishes a functional hierarchy related to immaturity

Endothelial progenitor cells (EPCs) generate in vitro Endothelial Colony Forming Cells (ECFCs) combining features of endothelial and stem/progenitor cells. Their angiogenic properties confer them a therapeutic potential for treating ischemic lesions. They may be isolated from umbilical cord blood (CB-ECFCs) or peripheral adult blood (AB-ECFCs). It is generally accepted that CB-ECFCs are more clonogenic, proliferative and angiogenic than AB-ECFCs. Nevertheless, only a few studies have focused on the functional heterogeneity of CB-ECFCs from different individuals. Moreover, AB-ECFC loss of function is yet to be precisely described. We have focused on these two issues that are critical for clinical perspectives. The detailed clonogenic profile of CB-ECFCs and AB-ECFCs was obtained and revealed a high inter individual heterogeneity and the absence of correlation with age. Most CB-ECFCs yielded initial colonies and had functional properties similar to those of AB-ECFCs. Conversely, a high clonogenicity was associated with an enhanced proliferative and angiogenic potential and stemness gene overexpression, confirming that immaturity, lost by AB-ECFCs, was a prerequisite to functionality. We thus demonstrated the importance of selecting CB-ECFCs according to specific criteria, and we propose using the initial clonogenicity as a relevant marker of their potential efficacy on vascular repair.

Detection and Characterization of Circulating Tumor Associated Cells in Metastatic Breast Cancer

The availability of blood-based diagnostic testing using a non-invasive technique holds promise for real-time monitoring of disease progression and treatment selection. Circulating tumor cells (CTCs) have been used as a prognostic biomarker for the metastatic breast cancer (MBC). The molecular characterization of CTCs is fundamental to the phenotypic identification of malignant cells and description of the relevant genetic alterations that may change according to disease progression and therapy resistance. However, the molecular characterization of CTCs remains a challenge because of the rarity and heterogeneity of CTCs and technological difficulties in the enrichment, isolation and molecular characterization of CTCs. In this pilot study, we evaluated circulating tumor associated cells in one blood draw by size exclusion technology and cytological analysis. Among 30 prospectively enrolled MBC patients, CTCs, circulating tumor cell clusters (CTC clusters), CTCs of epithelial-mesenchymal transition (EMT) and cancer associated macrophage-like cells (CAMLs) were detected and analyzed. For molecular characterization of CTCs, size-exclusion method for CTC enrichment was tested in combination with DEPArray™ technology, which allows the recovery of single CTCs or pools of CTCs as a pure CTC sample for mutation analysis. Genomic mutations of TP53 and ESR1 were analyzed by targeted sequencing on isolated 7 CTCs from a patient with MBC. The results of genomic analysis showed heterozygous TP53 R248W mutation from one single CTC and pools of three CTCs, and homozygous TP53 R248W mutation from one single CTC and pools of two CTCs. Wild-type ESR1 was detected in the same isolated CTCs. The results of this study reveal that size-exclusion method can be used to enrich and identify circulating tumor associated cells, and enriched CTCs were characterized for genetic alterations in MBC patients, respectively.

Celastrol targets IRAKs to block Toll-like receptor 4-mediated nuclear factor-κB activation

OBJECTIVE

Celastrol has been established as a nuclear factor-κB (NF-κB) activation inhibitor; however, the exact mechanism behind this action is still unknown. Using text-mining technology, the authors predicted that interleukin-1 receptor-associated kinases (IRAKs) are potential celastrol targets, and hypothesized that targeting IRAKs might be one way that celastrol inhibits NF-κB. This is because IRAKs are key molecules for some crucial pathways to activate NF-κB (e.g., the interleukin-1 receptor (IL-1R)/Toll-like receptor (TLR) superfamily).

METHODS

The human hepatocellular cell line (HepG2) treated with palmitic acid (PA) was used as a model for stimulating TLR4/NF-κB activation, in order to observe the potential effects of celastrol in IRAK regulation and NF-κB inhibition. The transfection of small interfering RNA was used for down-regulating TLR4, IRAK1 and IRAK4, and the Western blot method was used to detect changes in the protein expressions.

RESULTS

The results showed that celastrol could effectively inhibit PA-caused TLR4-dependent NF-κB activation in the HepG2 cells; PA also activated IRAKs, which were inhibited by celastrol. Knocking down IRAKs abolished PA-caused NF-κB activation.

CONCLUSION

The results for the first time show that targeting IRAKs is one way in which celastrol inhibits NF-κB activation.

A Novel Molecular and Functional Stemness Signature Assessing Human Cord Blood-Derived Endothelial Progenitor Cell Immaturity

Endothelial Colony Forming Cells (ECFCs), a distinct population of Endothelial Progenitor Cells (EPCs) progeny, display phenotypic and functional characteristics of endothelial cells while retaining features of stem/progenitor cells. Cord blood-derived ECFCs (CB-ECFCs) have a high clonogenic and proliferative potentials and they can acquire different endothelial phenotypes, this requiring some plasticity. These properties provide angiogenic and vascular repair capabilities to CB-ECFCs for ischemic cell therapies. However, the degree of immaturity retained by EPCs is still confused and poorly defined. Consequently, to better characterize CB-ECFC stemness, we quantified their clonogenic potential and demonstrated that they were reprogrammed into induced pluripotent stem cells (iPSCs) more efficiently and rapidly than adult endothelial cells. Moreover, we analyzed the transcriptional profile of a broad gene panel known to be related to stem cells. We showed that, unlike mature endothelial cells, CB-ECFCs expressed genes involved in the maintenance of embryonic stem cell properties such as DNMT3B, GDF3 or SOX2. Thus, these results provide further evidence and tools to appreciate EPC-derived cell stemness. Moreover this novel stem cell transcriptional signature of ECFCs could help better characterizing and ranging EPCs according to their immaturity profile.

Abstract P2-02-14: Detection and characterization of CTCs isolated by ScreenCell®-Filtration in metastatic breast cancer

Background: Circulating Tumor cells (CTCs) detection has prognostic and predictive implications in patients with metastatic breast cancer (MBC). Genomic and phenotypic analysis of CTCs hold enormous promise as blood-based molecular characterization and monitoring disease progression and treatment benefit with a strong potential to be translated into more individualized targeted treatments. FDA-approved CellSearch™ detection allows only enumeration of CTCs expressing EpCAM without molecular characterization. CTCs represent very heterogeneous populations of tumorigenic cancer cells and some subpopulations have undergone epithelial-Mesenchymal transition (EMT), which is associated metastasis process and an unfavourable outcome. EpCAM-based enrichment technique has failed to detect EMT subpopulations due to the decreased expression or loss of epithelial markers. Non-EpCAM-based approaches are needed for identifying EMT CTCs. The ScreenCell® devices are single-use and low-cost innovative devices that use a filter for enrichment-free isolation of CTCs by a two-steps combining size-based separation and staining using different markers. The DEPArray™ system is the ideal downstream isolation system to collect single or pooled CTCs for molecular and genetic analysis. In this study, we evaluated the feasibility of achieving CTCs detection/enumeration using ScreenCell® filtration followed by single cell isolation with the DEPArray™ in MBC patients.

Methods: The first part of the study consisted in evaluating CTCs detection/enumeration in 30 patients with stage III and stage IV breast cancer. 3 mL of whole blood in an EDTA or Transfix tubes was collected and processed on the ScreenCell® Cyto device following the instructions of the supplier. CTCs were stained with cytokeratin (CK-8, 18, and 19), leukocyte antigen (CD45), and a nuclear dye (DAPI) and counted under fluorescence microscope. CTCs were identified as positive staining for CK and DAPI and negative staining for CD45 (CK+/DAPI+CD45-). In the second part, After enrichment, CTCs were stained with CK, CD45, and DAPI and sorted with DEPArray™ Platform (Silicon Biosystems, Inc). Single CTCs were collected and the DNA of each single CTCs was amplified with Ampli1™ WGA kit, and the genome integrity index (GII) was assessed by Ampli1™ QC kit (Silicon Biosystems, Inc). Library was constructed and whole exome sequencing (WES) of DNA mutations was conducted.

Results: Twenty patient samples had CTCs detected (66.7%), the number of CTCs was 1 to 347 per 3.0 ml of whole blood. CTC-clusters were detected in 7 patient samples (23.3%). Single CTCs were collected on DEPArray™ platform after enrichment with ScreenCell filtration. GII was confirmed with the presence of short, medium, and long DNA fragments (3 to 4 PCR bands) in the WGA library by PCR-based assay. All collected CTCs showed high GII as measured by Ampli1™ QC kit (GII ≥ 3) for WES of DNA mutations. The data analysis of WES results is under processing.

Conclusions: ScreenCell® filtration is simple and effective devices to isolate CTCs and identify CTC-clusters. Isolation of single cells for molecular analysis using the combination of ScreenCell® filtration and DEPArray™ Platform is feasible for genetic characterization of CTCs.

Citation Format: Mu Z, Benali-Furet N, Uzan G, Ye Z, Austin L, Wang C, Nguyen1 T, Avery T, Jaslow R, Yang H, Cristofanilli M. Detection and characterization of CTCs isolated by ScreenCell®-Filtration in metastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-02-14.

Tripterine treatment improves endothelial progenitor cell function via integrin-linked kinase

BACKGROUND/AIMS

Atherosclerosis is associated with dysfunction of endothelial progenitor cells (EPCs). Tripterine, a chemical compound derived from the Chinese medicinal plant Tripterygium wilfordii Hook, displays anti-inflammatory properties in several animal models. We hypothesized that tripterine can improve EPC function and thus the efficiency of EPC transplantation.

METHODS AND RESULTS

Tripterine preconditioning (2.5 μM, 4 h) improved EPC proliferation, tube formation, migration, and adhesion, and reduced apoptosis in cells cultured in ox-LDL (200 µg/ml). Tripterine restored integrin-linked kinase (ILK) levels downregulated by ox-LDL in EPCs, suggesting the involvement of the ILK/Akt pathway. Small interfering RNA-mediated depletion of ILK and dominant-negative ILK transduction inhibited the phosphorylation of the ILK downstream signaling targets protein kinase B/Akt and glycogen synthase kinase 3-beta (GSK-3β), and reduced β-catenin and cyclin D1 expression. In atherosclerotic mice injected with green fluorescent protein-labeled EPCs to evaluate EPC function, tripterine decreased aortic lesions and plaque deposition, and injection of tripterine-treated EPCs restored ILK levels.

CONCLUSION

The present results suggest that tripterine improves vascular function in atherosclerosis by enhancing EPC function through a mechanism involving the ILK signaling pathway.

A fine structural modification of glycosaminoglycans is correlated with the progression of muscle regeneration after ischaemia: towards a matrix-based therapy?

Critical limb ischaemia often leads to amputation of the limb and potential mortality. Moreover, there are still significant problems with current therapeutic treatments, according to poor revascularisation of degenerated tissue probably due to modifications within the microenvironment. This study is focused on the changes of structure and bioactivity of glycosaminoglycans (GAGs), especially heparan sulphate (HS) and chondroitin sulphate (CS) in rat Extensor Digitorum Longus (EDL) muscle after ischaemia. Male Wistar rats were subjected to ischaemic-injury by ligation of the neurovascular trunk accompanying EDL-tendon. After 4, 8, 15, 21, 60 and 90 d, the rats were sacrificed and the muscles were collected and submitted to histological, biochemical and gene expression assays. We demonstrated that ischaemia induced modification of expression of enzymes involved in GAG biosynthesis which correlated with significant changes in HS and CS structural features such as size and sulphation pattern. These major structural changes are associated to modifications of GAG abilities to bind growth factors and to modulate cell activity. Moreover, a CS hallmark of injury is maintained as well after the regeneration process. Finally, we showed the relevance of the role of this glycanic matrix remodelling, since a GAG mimetic treatment accelerated muscle repair after ischaemia.

Celastrol Ameliorates EAE Induction by Suppressing Pathogenic T Cell Responses in the Peripheral and Central Nervous Systems

Multiple sclerosis (MS) is the prototypical inflammatory demyelinating disease of the central nervous system (CNS), and MS results in physical and cognitive impairments, such as fatigue, pain, depression and bladder dysfunction. Though many therapies for MS have been developed, the safety profile and effectiveness of these therapies still need to be defined. Thus, new therapies for MS must be explored. Celastrol, a quinonemethide triterpene, is a pharmacologically active compound present in Thunder God Vine root extracts used to treat inflammatory and autoimmune diseases. Molecular studies have identified several molecular targets, which are mostly centered on the inhibition of IKK-NF-κB signaling. The animal model of experimental autoimmune encephalomyelitis (EAE) has been widely used in MS studies; thus, we tried to explore the role of celastrol in EAE development in this study. We demonstrated that the intraperitoneal injection of celastrol significantly attenuated EAE disease. Th17 cell responses in the peripheral lymph nodes in EAE mice were also inhibited by celastrol. We determined that celastroldownregulated cytokine production in bone-marrow derived dendritic cells (BMDCs). Accordingly, T cells that were co-cultured with either BMDCs pre-treated with celastrolor splenic DCs and then collected on day 7 after EAE immunizationshowed that Th17 cell polarization is suppressed in the above two situations. Moreover, celastrol was required for tissue-infiltrating DCs to sustain Th17 responses in the central nervous system (CNS). Taken together, the results of our study demonstrate that celastrol ameliorates EAE development by suppressing pathogenic Th17 responses; this finding offers a better understanding of the role of celastrol in EAE development as well as new proposals for clinical interventions.

Heterogeneous functions of perinatal mesenchymal stromal cells require a preselection before their banking for clinical use

Perinatal sources of mesenchymal stromal cells (MSCs) have raised growing interest because they are readily and widely available with minimal ethical/legal issues and can easily be stored for allogeneic settings. In addition, perinatal tissues are known to be important in mediating the fetomaternal tolerance of pregnancy, which confer upon perinatal-MSCs (P-MSCs) a particular interest in immunomodulation. It has been recently shown that it is possible to deeply modify the secreted factor profiles of MSCs with different cytokine stimuli such as interferon gamma or tumor necrosis factor alpha to license MSCs for a better immunosuppresive potential. Therefore, we aimed to compare adult bone marrow-MSCs with MSCs from perinatal tissues (cord blood, umbilical cord, amnion, and chorion) on their in vitro immunological and stromacytic efficiencies under different priming conditions. Our results showed that P-MSCs had a potential to modulate the in vitro immune response and be useful for hematopoietic progenitor cell ex vivo expansion. However, we showed contrasted effects of cytokine priming embedded in an important between-donor variability. In conclusion, our study highlights the importance to elaborate predicitive in vitro tests to screen between-donor variability of perinatal tissues for banking allogeneic standardized MSCs.

Endoderm generates endothelial cells during liver development

Organogenesis requires expansion of the embryonic vascular plexus that migrates into developing organs through a process called angiogenesis. Mesodermal progenitors are thought to derive endothelial cells (ECs) that contribute to both embryonic vasculogenesis and the subsequent organ angiogenesis. Here, we demonstrate that during development of the liver, which is an endoderm derivative, a subset of ECs is generated from FOXA2+ endoderm-derived fetal hepatoblast progenitor cells expressing KDR (VEGFR2/FLK-1). Using human and mouse embryonic stem cell models, we demonstrate that KDR+FOXA2+ endoderm cells developing in hepatic differentiation cultures generate functional ECs. This introduces the concept that ECs originate not exclusively from mesoderm but also from endoderm, supported in Foxa2 lineage-tracing mouse embryos by the identification of FOXA2+ cell-derived CD31+ ECs that integrate the vascular network of developing fetal livers.

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Functional ECs are generated from human ESC-derived KDR+ endoderm cells

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Functional ECs are generated from mouse ESC-derived KDR+FOXA2+ endoderm cells

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FOXA2+ endoderm cells contribute in vivo to a subset of ECs in the mouse fetal liver

Celastrol inhibits lung infiltration in differential syndrome animal models by reducing TNF-α and ICAM-1 levels while preserving differentiation in ATRA-induced acute promyelocytic leukemia cells

All-trans retinoic acid (ATRA) is a revolutionary agent for acute promyelocytic leukemia (APL) treatment via differentiation induction. However, ATRA treatment also increases cytokine, chemokine, and adhesive molecule (mainly ICAM-1) expression, which can cause clinical complications, including a severe situation known as differentiation syndrome (DS) which can cause death. Therefore, it is of clinical significance to find a strategy to specifically blunt inflammatory effects while preserving differentiation. Here we report that the natural compound, celastrol, could effectively block lung infiltrations in DS animal models created by loading ATRA-induced APL cell line NB4. In ATRA-treated NB4 cells, celastrol could potently inhibit ICAM-1 elevation and partially reduce TNF-α and IL-1β secretion, though treatment showed no effects on IL-8 and MCP-1 levels. Celastrol’s effect on ICAM-1 in ATRA-treated NB4 was related to reducing MEK1/ERK1 activation. Strikingly and encouragingly, celastrol showed no obvious effects on ATRA-induced NB4 differentiation, as determined by morphology, enzymes, and surface markers. Our results show that celastrol is a promising and unique agent for managing the side effects of ATRA application on APL, and suggest that hyper-inflammatory ability is accompanied by, but not necessary for, APL differentiation. Thus we offered an encouraging novel strategy to further improve differentiation therapy.