The effects of cell type and culture condition on the procoagulant activity of human mesenchymal stromal cell-derived extracellular vesicles.

BACKGROUND: Mesenchymal stromal cell (MSC)-derived extracellular vesicles (EVs) have great potential as a cell-free therapy in wound healing applications. Because EV populations are not equivalent, rigorous characterization is needed before clinical use. Although there has been much focus on their RNA composition and regenerative capabilities, relatively less is known regarding the effects of MSC cell type (adipose tissue [Ad-MSCs] or bone marrow [BM-MSCs]) and culture condition (monolayer or spheroid) on MSC-EV performance, including characteristics related to their ability to promote coagulation, which could determine EV safety if administered intravenously. METHODS: The successful isolation of EVs derived from Ad-MSCs or BM-MSCs cultured in either monolayer or spheroid cultures was confirmed by NanoSight (particle size distribution) and Western blot (surface marker expression). Extracellular vesicle surface expression of procoagulant molecules (tissue factor and phosphatidylserine) was evaluated by flow cytometry. Extracellular vesicle thrombogenicity was tested using calibrated thrombogram, and clotting parameters were assessed using thromboelastography and a flow-based adhesion model simulating blood flow over a collagen-expressing surface. RESULTS: The MSC cell type and culture condition did not impact EV size distribution. Extracellular vesicles from all groups expressed phosphatidylserine and tissue factor on their surfaces were functionally thrombogenic and tended to increase clotting rates compared to the negative control of serum-free media without EVs. On average, EVs did not form significantly larger or stronger clots than the negative control, regardless of cell source or culture condition. Additionally, EVs interfered with platelet adhesion in an in vitro flow-based assay. CONCLUSION: Adipose-derived EVs were more thrombogenic and expressed higher amounts of phosphatidylserine. Our findings suggest that, like intact MSCs, source variability among EVs is an important factor when considering EVs for potential therapeutic purposes. LEVEL OF EVIDENCE: Therapeutic care management, level II.

Mesenchymal Stem Cells Reconditioned in Their Own Serum Exhibit Augmented Therapeutic Properties in the Setting of Acute Respiratory Distress Syndrome.

Mesenchymal stem cells (MSCs) are a promising form of therapy for acute respiratory distress syndrome (ARDS). The objective of this study was twofold: (a) to characterize cytokine expression in serum from ARDS subjects receiving MSCs and (b) to determine MSC function following "preconditioning" with ARDS serum. In phase I, serum from three cohorts of animals (uninjured [no ARDS, n = 4], injured untreated [n = 5], and injured treated with approximately 6 million per kilogram MSCs [n = 7]) was analyzed for expression of inflammatory mediators. In phase II, the functional properties of bone marrow porcine MSCs were assessed following "preconditioning" with serum from the three cohorts. In phase III, the findings from the previous phases were validated using human bone marrow MSCs (hBM-MSCs) and lipopolysaccharide (LPS). Serum from injured treated animals had significantly lower levels of interferon-γ and significantly higher levels of interleukin (IL)-1 receptor antagonist (IL-1RA) and IL-6. Similarly, upon exposure to the injured treated serum ex vivo, the MSCs secreted higher levels of IL-1RA and IL-10, dampened the secretion of proinflammatory cytokines, exhibited upregulation of toll-like receptor 4 (TLR-4) and vascular endothelial growth factor (VEGF) genes, and triggered a strong immunomodulatory response via prostaglandin E2 (PGE2 ). hBM-MSCs demonstrated a similar augmented therapeutic function following reconditioning in a LPS milieu. Administration of MSCs modulated the inflammatory milieu following ARDS. Exposure to ARDS serum ex vivo paralleled the trends seen in vivo, which appear to be mediated, in part, through TLR-4 and VEGF and PGE2 . Reconditioning MSCs in their own serum potentiates their immunotherapeutic function, a technique that can be used in clinical applications. Stem Cells Translational Medicine 2019;8:1092-1106.

Preconditioning in an Inflammatory Milieu Augments the Immunotherapeutic Function of Mesenchymal Stromal Cells.

Multipotent mesenchymal stromal cells (MSCs) have emerged as potent therapeutic agents for multiple indications. However, recent evidence indicates that MSC function is compromised in the physiological post-injury milieu. In this study, bone marrow (BM)- and adipose-derived (AD)-MSCs were preconditioned in hypoxia with or without inflammatory mediators to potentiate their immunotherapeutic function in preparation for in vivo delivery. Human MSCs were cultured for 48 hours in either normoxia (21% O2) or hypoxia (2% O2) with or without the addition of Cytomix, thus creating 4 groups: 1) normoxia (21%); 2) Cytomix-normoxia (+21%); 3) hypoxia (2%); and 4) Cytomix-hypoxia (+2%). The 4 MSC groups were subjected to comprehensive evaluation of their characteristics and function. Preconditioning did not alter common MSC surface markers; nonetheless, Cytomix treatment triggered an increase in tissue factor (TF) expression. Moreover, the BM-MSCs and AD-MSCs from the +2% group were not able to differentiate to chondrocytes and osteoblasts, respectively. Following Cytomix preconditioning, the metabolism of MSCs was significantly increased while viability was decreased in AD-MSCs, but not in BM-MSCs. MSCs from both tissues showed a significant upregulation of key anti-inflammatory genes, increased secretion of IL-1 receptor antagonist (RA), and enhanced suppression of T-cell proliferation following the Cytomix treatment. Similarly, following a lipopolysaccharide challenge, the Cytomix-treated MSCs suppressed TNF-α secretion, while promoting the production of IL-10 and IL-1RA. These preconditioning approaches facilitate the production of MSCs with robust anti-inflammatory properties. AD-MSCs preconditioned with Cytomix under normoxia appear to be the most promising therapeutic candidates; however, safety concerns, such as thrombogenic disposition of cells due to TF expression, should be carefully considered prior to clinical translation.

An in vitro pilot study of apheresis platelets collected on Trima Accel system and stored in T-PAS+ solution at refrigeration temperature (1-6°C).

BACKGROUND: Using platelet additive solution (PAS) to dilute fibrinogen during long-term cold storage of platelets (PLTs) decreases PLT activation and increases functional PLT shelf life. We performed a randomized, paired study to assess the in vitro quality of PLTs stored in the cold in T-PAS+ for up to 18 days evaluated against PLTs stored under currently allowable conditions (5-day room temperature-stored PLTs [RTP] and 3-day cold-stored PLTs [CSP]). STUDY DESIGN AND METHODS: PLTs were collected from healthy volunteers (n = 10) and diluted to 65% T-PAS+/35% plasma before cold storage. Double-dose apheresis PLTs (in 100% plasma) were collected from the same donors and split into two bags (one bag RTP, one bag CSP). All bags were sampled on the day of collection (Day 0). CSP and RTP bags were sampled on Days 3 and 5, respectively. T-PAS+ samples were assessed on Days 3, 5, 14, 16, and 18 of storage for metabolism, hemostatic function, and activation. RESULTS: After 18 days of storage in T-PAS+, pH was 6.71 ± 0.04, PLT count was comparable to Day 3 CSP, PLT function (aggregation and clot strength) was comparable to Day 5 RTP, and PLT activation was significantly increased. CONCLUSION: Refrigerated PLTs stored in T-PAS+ for 18 days met FDA pH standards. Functional metrics suggest activity of T-PAS+-stored PLTs and the potential to contribute to hemostasis throughout 18 days of storage. Extending the shelf life of PLTs would increase access to hemostatic resuscitation for bleeding patients in military and civilian settings.

Short-term physiological hypoxia potentiates the therapeutic function of mesenchymal stem cells.

BACKGROUND: In the bone marrow, MSCs reside in a hypoxic milieu (1-5% O2) that is thought to preserve their multipotent state. Typically, in vitro expansion of MSCs is performed under normoxia (~ 21% O2), a process that has been shown to impair their function. Here, we evaluated the characteristics and function of MSCs cultured under hypoxia and hypothesized that, when compared to normoxia, dedicated hypoxia will augment the functional characteristics of MSCs. METHODS: Human and porcine bone marrow MSCs were obtained from fresh mononuclear cells. The first study evaluated MSC function following both long-term (10 days) and short-term (48 h) hypoxia (1% O2) culture. In our second study, we evaluated the functional characteristics of MSC cultured under short-term 2% and 5% hypoxia. MSCs were evaluated for their metabolic activity, proliferation, viability, clonogenicity, gene expression, and secretory capacity. RESULTS: In long-term culture, common MSC surface marker expression (CD44 and CD105) dropped under hypoxia. Additionally, in long-term culture, MSCs proliferated significantly slower and provided lower yields under hypoxia. Conversely, in short-term culture, MSCs proliferated significantly faster under hypoxia. In both long-term and short-term cultures, MSC metabolic activity was significantly higher under hypoxia. Furthermore, MSCs cultured under hypoxia had upregulated expression of VEGF with concomitant downregulation of HMGB1 and the apoptotic genes BCL-2 and CASP3. Finally, in both hypoxia cultures, the pro-inflammatory cytokine, IL-8, was suppressed, while levels of the anti-inflammatories, IL-1ra and GM-CSF, were elevated in short-term hypoxia only. CONCLUSIONS: In this study, we demonstrate that hypoxia augments the therapeutic characteristics of both porcine and human MSCs. Yet, short-term 2% hypoxia offers the greatest benefit overall, exemplified by the increase in proliferation, self-renewing capacity, and modulation of key genes and the inflammatory milieu as compared to normoxia. These data are important for generating robust MSCs with augmented function for clinical applications.