Mesenchymal stem cells (MSCs) are currently studied and used in numerous clinical trials. Nevertheless, some concerns have been raised regarding the safety of these infusions and the thrombogenic risk they induce. MSCs express procoagulant activity (PCA) linked to the expression of tissue factor (TF) that, when in contact with blood, initiates coagulation. Some even describe a dual activation of both the coagulation and the complement pathway, called Instant Blood-Mediated Inflammatory Reaction (IBMIR), explaining the disappointing results and low engraftment rates in clinical trials. However, nowadays, different approaches to modulate the PCA of MSCs and thus control the thrombogenic risk after cell infusion are being studied. This review summarizes both in vitro and in vivo studies on the PCA of MSC of various origins. It further emphasizes the crucial role of TF linked to the PCA of MSCs. Furthermore, optimization of MSC therapy protocols using different methods to control the PCA of MSCs are described.

The efficacy of mesenchymal stem cell infusion is currently tested in numerous clinical trials. However, therapy-induced thrombotic consequences have been reported in several patients. The aim of this study was to optimize protocols for heterologous human adult liver-derived progenitor cell (HHALPC) infusion, in order to eliminate acute thrombogenesis in liver-based metabolic or acute decompensated cirrhotic (ADC) patients. In rats, thrombotic effects were absent when HHALPCs were infused at low cell dose (5 × 106 cells/kg), or at high cell dose (5 × 107 cells/kg) when combined with anticoagulants. When HHALPCs were exposed to human blood in a whole blood perfusion assay, blocking of the tissue factor (TF) coagulation pathway suppressed fibrin generation and platelet activation. In a Chandler tubing loop model, HHALPCs induced less explosive activation of coagulation with blood from ADC patients, when compared to blood from healthy controls, without alterations in coagulation factor levels other than fibrinogen. These studies confirm a link between TF and thrombogenesis, when TF-expressing cells are exposed to human blood. This phenomenon however, could be controlled using either a low, or a high cell dose combined with anticoagulants. In clinical practice, this points to the suitability of a low HHALPC dose infusion to cirrhotic patients, provided that platelet and fibrinogen levels are monitored.

Background: Mesenchymal stem cell (MSC) transplantation is a fast-developing therapy in regenerative medicine. However, some concerns have been raised regarding their safety and the infusion-related pro-coagulant activity. The aim of this study is to analyze the induced thrombogenic risk and the safety of adding anticoagulants during intraportal infusions of liver-derived MSCs (HepaStem), in patients with Crigler-Najjar (CN) and urea cycle disorders (UCD). Methods: Eleven patients (6 CN and 5 UCD patients) were included in this partially randomized phase 1/2 study. Three cell doses of HepaStem were investigated: low (12.5 × 10 6 cells/kg), intermediate (50 × 10 6 cells/kg), and high doses (200 × 10 6 cells/kg). A combination of anticoagulants, heparin (10 I.U./5 × 10 6 cells), and bivalirudin (1.75 mg/ kg/h) were added during cell infusions. The infusion-related thrombogenic risk and anticoagulation were evaluated by clinical monitoring, blood sampling (platelet and D-dimer levels, activated clotting time, etc.) and liver Doppler ultrasound. Mixed effects linear regression models were used to assess statistically significant differences. Results:One patient presented a thrombogenic event such as a partial portal vein thrombus after 6 infusions. Minor adverse effects such as petechiae, epistaxis, and cutaneous hemorrhage at the site of catheter placement were observed in four patients. A significant decrease in platelet and increase in D-dimer levels were observed at the end of the infusion cycle, normalizing spontaneously after 7 days. No significant and clinically relevant increase in portal vein pressure could be observed once the infusion cycle was completed. Conclusions: The safety-and the infusion-related pro-coagulant activity remains a concern in MSC transplantation. In our study, a combination of heparin and bivalirudin was added to prevent the thrombogenic risk induced by HepaStem infusions in 11 patients. A significant decrease in platelet and increase in D-dimer levels were observed, suggesting the activation of coagulation in these patients; however, this was spontaneously reversible in time. We can conclude that adding this combination of anticoagulants is safe and limits infusion-related thrombogenesis to subclinical signs in most of the patients. Trial registration: ClinicalTrials.gov identifier:

The liver has an important function in the human body and plays a crucial role in its metabolism. Orthotopic liver transplantation (OLT) is the gold standard treatment for patients presenting liver failure or end stage liver diseases, and is also applied for liver based intractable metabolic disorders. Due to organ shortage, invasive surgery and persistent mortality/morbidity, other treatments have to be explored. Amongst these, hepatocyte transplantation is an attractive alternative and has shown promising results in the treatment of miscellaneous metabolic disorders.