Mesenchymal Stromal Cells at the Interface of Hemostasis and Immunothrombosis

Mesenchymal stromal cells are increasingly used for their immunomodulatory and regenerative properties, yet their interaction with the hemostatic system remains incompletely understood. This review examines the mechanisms through which these cells influence coagulation within the broader framework of immunothrombosis. Evidence from in vitro studies, animal models, and early clinical observations indicates that mesenchymal stromal cells can promote thrombin generation through tissue factor expression and phosphatidylserine exposure, while also engaging complement pathways, platelets, and innate immune responses. Counter-regulatory mechanisms, including adenosine-mediated platelet inhibition and immune reprogramming after cellular clearance, contribute to a context-dependent biological effect. Functional assays, rather than tissue factor expression alone, appear necessary to estimate the effective procoagulant potential of these products. Clinical data suggest that major thrombotic events remain uncommon, although subclinical activation of coagulation pathways may occur. The hemostatic impact of mesenchymal stromal cells depends on multiple variables, including cell source, dose, route of administration, and host inflammatory status. The available evidence supports a working model in which early coagulation and complement activation may be followed by immune modulation, supporting integrated strategies to optimise both safety and therapeutic efficacy. A central conclusion is that tissue factor, although mechanistically necessary for MSC-associated procoagulant activity, is not by itself an independent predictor of clinical thrombotic risk; the effective coagulation response also depends on phosphatidylserine exposure, membrane context, and host inflammatory conditions.