Human bone marrow stromal cells hamper specific interactions of CD4 and CD8 T lymphocytes with antigen-presenting cells

Short-term assays for mesenchymal stromal cell immunosuppression of T-lymphocytes

Introduction

Trauma patients are susceptible to coagulopathy and dysfunctional immune responses. Mesenchymal stromal cells (MSCs) are at the forefront of the cellular therapy revolution with profound immunomodulatory, regenerative, and therapeutic potential. Routine assays to assess immunomodulation activity examine MSC effects on proliferation of peripheral blood mononuclear cells (PBMCs) and take 3-7 days. Assays that could be done in a shorter period of time would be beneficial to allow more rapid comparison of different MSC donors. The studies presented here focused on assays for MSC suppression of mitogen-stimulated PBMC activation in time frames of 24 h or less.

Methods

Three potential assays were examined-assays of apoptosis focusing on caspase activation, assays of phosphatidyl serine externalization (PS+) on PBMCs, and measurement of tumor necrosis factor alpha (TNFα) levels using rapid ELISA methods. All assays used the same initial experimental conditions: cryopreserved PBMCs from 8 to 10 pooled donors, co-culture with and without MSCs in 96-well plates, and PBMC stimulation with mitogen for 2-72 h.

Results

Suppression of caspase activity in activated PBMCs by incubation with MSCs was not robust and was only significant at times after 24 h. Monitoring PS+ of live CD3+ or live CD4+/CD3+ mitogen-activated PBMCs was dose dependent, reproducible, robust, and evident at the earliest time point taken, 2 h, although no increase in the percentage of PS+ cells was seen with time. The ability of MSC in co-culture to suppress PBMC PS+ externalization compared favorably to two concomitant assays for MSC co-culture suppression of PBMC proliferation, at 72 h by ATP assay, or at 96 h by fluorescently labeled protein signal dilution. TNFα release by mitogen-activated PBMCs was dose dependent, reproducible, robust, and evident at the earliest time point taken, with accumulating signal over time. However, suppression levels with MSC co-culture was reliably seen only after 24 h.

Discussion

Takeaways from these studies are as follows: (1) while early measures of PBMC activation is evident at 2-6 h, immunosuppression was only reliably detected at 24 h; (2) PS externalization at 24 h is a surrogate assay for MSC immunomodulation; and (3) rapid ELISA assay detection of TNFα release by PBMCs is a robust and sensitive assay for MSC immunomodulation at 24 h.

Inhibition of Allogeneic and Autologous T Cell Proliferation by Adipose-Derived Mesenchymal Stem Cells of Ankylosing Spondylitis Patients

Background

In ankylosing spondylitis (AS), accompanied by chronic inflammation, T cell expansion plays a pathogenic role; the immunoregulatory properties of bone marrow-derived mesenchymal stem cells (BM-MSCs) are impaired, while functional characteristics of their adipose tissue-derived counterparts are (ASCs) unknown.

Methods

We evaluated the antiproliferative activity of AS/ASCs, obtained from 20 patients, towards allogeneic and autologous T lymphocytes, using ASCs from healthy donors (HD/ASCs) as the reference cell lines. The PHA-activated peripheral blood mononuclear cells (PBMCs) were cocultured in cell-cell contact and transwell conditions with untreated or TNF + IFNγ- (TI-) licensed ASCs, then analyzed by flow cytometry to identify proliferating and nonproliferating CD4⁺ and CD8⁺ T cells. The concentrations of kynurenines, prostaglandin E₂ (PGE₂), and IL-10 were measured in culture supernatants.

Results

In an allogeneic system, HD/ASCs and AS/ASCs similarly decreased the proliferation of CD4⁺ and CD8⁺ T cells and acted mainly via soluble factors. The concentrations of kynurenines and PGE₂ inversely correlated with T cell proliferation, and selective inhibitors of these factors synthesis significantly restored T cell response. AS/ASCs exerted a similar antiproliferative impact also on autologous T cells.

Conclusion

We report for the first time that despite chronic in vivo exposure to inflammatory conditions, AS/ASCs retain the normal capability to restrain expansion of allogeneic and autologous CD4⁺ and CD8⁺ T cells, act primarily via kynurenines and PGE₂, and thus may have potential therapeutic value. Some distinctions between the antiproliferative effects of AS/ASCs and HD/ASCs suggest in vivo licensing of AS/ASCs.

Inflammation, mesenchymal stem cells and bone regeneration

Achieving satisfactory reconstruction of bone remains an important goal in orthopedic and dental conditions such as bone trauma, osteoporosis, arthritis, osteonecrosis, and periodontitis. Appropriate temporal and spatial differentiation of mesenchymal stem cells (MSCs) is essential for postnatal bone regeneration. Additionally, an acute inflammatory response is crucial at the onset of bone repair, while an adaptive immune response has important implications during late bone remodeling. Various reports have indicated bidirectional interactions between MSCs and inflammatory cells or molecules. For example, inflammatory cells can recruit MSCs, direct their migration and differentiation, so as to exert anabolic effects on bone repair. Furthermore, both pro-inflammatory and anti-inflammatory cytokines can regulate MSCs properties and subsequent bone regeneration. MSCs have demonstrated highly immunosuppressive functions, such as inhibiting the differentiation of monocytes/hematopoietic precursors and suppressing the secretion of pro-inflammatory cytokines. This review emphasizes the important interactions between inflammatory stimuli, MSCs, and bone regeneration as well as the underlying regulatory mechanisms. Better understanding of these principles will provide new opportunities for promoting bone regeneration and the treatment of bone loss associated with immunological diseases.

Interaction of multipotent mesenchymal stromal and immune cells: Bidirectional effects

Adult multipotent mesenchymal stromal cells (MSCs) are considered one of the key players in physiological remodeling and tissue reparation. Elucidation of MSC functions is one of the most intriguing issues in modern cell physiology. In the present review, the interaction of MSCs and immune cells is discussed in terms of reciprocal effects, which modifies the properties of "partner" cells with special focus on the contribution of direct cell-to-cell contacts, soluble mediators and local microenvironmental factors, the most important of which is oxygen tension. The immunosuppressive phenomenon of MSCs is considered as the integral part of the response-to-injury mechanism.

MM-BMSCs induce naïve CD4+ T lymphocytes dysfunction through fibroblast activation protein α

Background

The tumor microenvironment plays a major role in multiple myelomas (MM). MM-BMSCs (bone marrow mesenchymal stromal cells) can support tumor growth and immune surveillance escape. On the other hand, fibroblast activation protein α, expressed by cancer stroma cells including BMSCs, has been shown to potentiate epithelial cancers growth and immune suppression.

Results

MM-BMSC inhibited proliferation of T cells (P = 0.0138), promoted senescence of T cells (P < 0.001), consistent with decreased CD28 and hTERT expression (P < 0.001), Treg/Th17 was down-regulated by MM-BMSC (P = 0.031). After treatment with FAPα inhibitor PT-100, senescent rate was decreased (P = 0.001), Treg/Th17 was up-regulated (P = 0.024). FAPα was up-regulated by TCCM (P = 0.02). p-AKT was increased in MM-BMSC co-cultured T cells (P = 0.021) and decreased by PT-100 (P = 0.017). Higher level of TGF-β was observed in MM-BMSC co-cultured medium (P < 0.001), and down-regulated by PT-100 (P = 0.038). p-AKT was upregulated as compared to T-cells without MM-BMSCs (P = 0.021). The abnormal p-AKT level was distinctly decreased by PT-100 (P = 0.017).

Materials and Methods

The expression of FAPα was analyzed by western blot and RT-PCR. The proliferation and senescence of CD4+ T cells was examined by cck-8 and β-gal staining, and Treg/Th17, CD28 expression was analyzed by FCM. The FAPα and PI3K pathway was analyzed by western blot and their relationship with T cell function was detected by FCM and RT-PCR. The level of IL-10, IL-17 and TGF-β was detected by ELISA.

Conclusions

MM-BMSCs inhibit T-cell proliferation and drive Th17 differentiation through FAPα/TGF-β axis, leading to the progression of myeloma. FAPα-induced T-cell senescence is mediated by the PI3K signaling pathway.

Interactions between MSCs and immune cells: implications for bone healing

It is estimated that, of the 7.9 million fractures sustained in the United States each year, 5% to 20% result in delayed or impaired healing requiring therapeutic intervention. Following fracture injury, there is an initial inflammatory response that plays a crucial role in bone healing; however, prolonged inflammation is inhibitory for fracture repair. The precise spatial and temporal impact of immune cells and their cytokines on fracture healing remains obscure. Some cytokines are reported to be proosteogenic while others inhibit bone healing. Cell-based therapy utilizing mesenchymal stromal cells (MSCs) is an attractive option for augmenting the fracture repair process. Osteoprogenitor MSCs not only differentiate into bone, but they also exert modulatory effects on immune cells via a variety of mechanisms. In this paper, we review the current literature on both in vitro and in vivo studies on the role of the immune system in fracture repair, the use of MSCs in the enhancement of fracture healing, and interactions between MSCs and immune cells. Insight into this paradigm can provide valuable clues in identifying cellular and noncellular targets that can potentially be modulated to enhance both natural bone healing and bone repair augmented by the exogenous addition of MSCs.

Human Amniotic Membrane-Derived Mesenchymal and Epithelial Cells Exert Different Effects on Monocyte-Derived Dendritic Cell Differentiation and Function

We previously demonstrated that mesenchymal cells from human amniotic membrane (hAMTCs) inhibit the generation and maturation of monocyte-derived dendritic cells (DCs) in vitro. Considering the crucial role of DCs in the immune response and that epithelial cells of the human amniotic membrane (hAECs) share some of the immunoregulatory properties of hAMTCs, we investigated whether hAECs also modulate monocyte-derived DCs. We compared hAECs with hAMTCs in a cell-to-cell contact setting and their secreted factors in modulating DC differentiation and function. First, we demonstrated that primary and expanded hAMTCs strongly inhibited the differentiation of DCs and induced a shift toward M2-like macrophages. This was observed when hAMTCs were cultured in contact (hAMTC-DC(cont)) or in Transwells (hAMTC-DC(tw)) with monocytes and even when medium conditioned by hAMTCs was used instead of hAMTCs. hAECs also prevented DC development, but to a lesser extent than hAMTCs. hAECs were more effective when cultured in contact with monocytes (hAEC-DC(cont)) rather than in Transwells (hAEC-DC(tw)). The modulatory capacity of hAECs changed during passaging unlike the hAMSCs. The ability to stimulate CD4(+) and CD8(+) T-cell proliferation was almost completely abolished by hAMTC-DC(cont), whereas hAMTC-DC(tw) and hAEC-DC(cont) displayed only a reduced ability to stimulate CD8(+) T cells. Furthermore, monocytes cocultured with hAMTCs and hAECs showed some similarities, but also differences in cytokine/chemokine secretion. Similarities were observed in the inhibition of IL-12p70 and TNF-α and the increase in IL-10 in supernatants taken from monocyte-DCs cocultured with hAMTCs and hAECs in contact and Transwell settings. The inflammatory factors IL-8, CXCL9, and MIP-1α were significantly lower in hAMTC-DC(cont), hAMTC-DC(tw), and hAEC-DC(cont) conditions. In contrast, only hAMTCs (in both contact and Transwell conditions) were able to significantly increase IL-1β and CCL2. Altogether, we demonstrated that hAMTCs and hAECs affect DC differentiation, but that hAMTCs exerted a stronger inhibitory effect, abolished T-cell proliferation, and also induced more changes in cytokine/chemokine production.

Characterization of the conditioned medium from amniotic membrane cells: prostaglandins as key effectors of its immunomodulatory activity

We previously demonstrated that cells isolated from the mesenchymal region of the human amniotic membrane (human amniotic mesenchymal tissue cells, hAMTC) possess immunoregulatory roles, such as inhibition of lymphocyte proliferation and cytokine production, and suppression of generation and maturation of monocyte-derived dendritic cells, as reported for MSC from other sources. The precise factors and mechanisms responsible for the immunoregulatory roles of hAMTC remain unknown. In this study, we aimed to identify the soluble factors released by hAMTC and responsible for the anti-proliferative effect on lymphocytes, and the mechanisms underlying their actions, in vitro. Conditioned medium (CM) was prepared under routine culture conditions from hAMTC (CM-hAMTC) and also from fragments of the whole human amniotic membrane (CM-hAM). We analyzed the thermostability, chemical nature, and the molecular weight of the factors likely responsible for the anti-proliferative effects. We also evaluated the participation of cytokines known to be involved in the immunomodulatory actions of MSC from other sources, and attempted to block different synthetic pathways. We demonstrate that the inhibitory factors are temperature-stable, have a small molecular weight, and are likely of a non-proteinaceous nature. Only inhibition of cyclooxygenase pathway partially reverted the anti-proliferative effect, suggesting prostaglandins as key effector molecules. Factors previously documented to take part in the inhibitory effects of MSCs from other sources (HGF, TGF-β, NO and IDO) were not involved. Furthermore, we prove for the first time that the anti-proliferative effect is intrinsic to the amniotic membrane and cells derived thereof, since it is manifested in the absence of stimulating culture conditions, as opposed to MSC derived from the bone marrow, which possess an anti-proliferative ability only when cultured in the presence of activating stimuli. Finally, we show that the amniotic membrane could be an interesting source of soluble factors, without referring to extensive cell preparation.

Adipose stem cells originate from perivascular cells

Recent research has shown that adipose tissues contain abundant MSCs (mesenchymal stem cells). The origin and location of the adipose stem cells, however, remain unknown, presenting an obstacle to the further purification and study of these cells. In the present study, we aimed at investigating the origins of adipose stem cells. α-SMA (α-smooth muscle actin) is one of the markers of pericytes. We harvested ASCs (adipose stromal cells) from α-SMA-GFP (green fluorescent protein) transgenic mice and sorted them into GFP-positive and GFP-negative cells by FACS. Multilineage differentiation tests were applied to examine the pluripotent ability of the α-SMA-GFP-positive and -negative cells. Immunofluorescent staining for α-SMA and PDGF-Rβ (platelet-derived growth factor receptor β) were applied to identify the α-SMA-GFP-positive cells. Then α-SMA-GFP-positive cells were loaded on a collagen-fibronectin gel with endothelial cells to test their vascularization ability both in vitro and in vivo. Results show that, in adipose tissue, all of the α-SMA-GFP-positive cells congregate around the blood vessels. Only the α-SMA-GFP-positive cells have multilineage differentiation ability, while the α-SMA-GFP-negative cells can only differentiate in an adipogenic direction. The α-SMA-GFP-positive cells maintained expression of α-SMA during multilineage differentiation. The α-SMA-GFP-positive cells can promote the vascularization of endothelial cells in three-dimensional culture both in vitro and in vivo. We conclude that the adipose stem cells originate from perivascular cells and congregate around blood vessels.

TSP-1 secreted by bone marrow stromal cells contributes to retinal ganglion cell neurite outgrowth and survival

Background

Bone marrow stromal cells (BMSCs) are pluripotent and thereby a potential candidate for cell replacement therapy for central nervous system degenerative disorders and traumatic injury. However, the mechanism of their differentiation and effect on neural tissues has not been fully elucidated. This study evaluates the effect of BMSCs on neural cell growth and survival in a retinal ganglion cell (RGCs) model by assessing the effect of changes in the expression of a BMSC-secreted protein, thrombospondin-1 (TSP-1), as a putative mechanistic agent acting on RGCs.

Methods and Findings

The effect of co-culturing BMSCs and RGCs in vitro was evaluated by measuring the following parameters: neurite outgrowth, RGC survival, BMSC neural-like differentiation, and the effect of TSP-1 on both cell lines under basal secretion conditions and when TSP-1 expression was inhibited. Our data show that BMSCs improved RGC survival and neurite outgrowth. Synaptophysin, MAP-2, and TGF-β expression are up-regulated in RGCs co-cultured with BMSCs. Interestingly, the BMSCs progressively displayed neural-like morphology over the seven-day study period. Restriction display polymerase chain reaction (RD-PCR) was performed to screen for differentially expressed genes in BMSCs cultured alone or co-cultured with RGCs. TSP-1, a multifactorial extracellular matrix protein, is critically important in the formation of neural connections during development, so its function in our co-culture model was investigated by small interfering RNA (siRNA) transfection. When TSP-1 expression was decreased with siRNA silencing, BMSCs had no impact on RGC survival, but reduced neurite outgrowth and decreased expression of synaptophysin, MAP-2 and TGF-β in RGCs. Furthermore, the number of BMSCs with neural-like characteristics was significantly decreased by more than two-fold using siRNA silencing.

Conclusions

Our data suggest that the TSP-1 signaling pathway might have an important role in neural-like differentiation in BMSCs and neurite outgrowth in RGCs. This study provides new insights into the potential reparative mechanisms of neural cell repair.