導入された間葉系幹細胞の運命と機能：現在の洞察と将来の方向性

The in vivo fate of mesenchymal stromal cells (MSCs), including their clearance, interaction with host tissues, and persistence, remains incompletely understood following systemic or local clinical administration to patients. Although immune-mediated clearance mechanisms, such as triggering of the instant blood-mediated inflammatory reaction, activation of coagulation and complement pathways, apoptosis and efferocytosis have been identified, their contributions to MSC function and efficacy are still under investigation. To address these knowledge gaps, an international panel of experts in MSC biology and clinical regenerative medicine convened to assess current evidence and define key unanswered questions. Discussions were structured around three thematic domains: (i) biodistribution and mechanisms of action following systemic delivery; (ii) biological implications of local or depot-based administration and (iii) the dynamics of MSC persistence and clearance in vivo. A major focus was on the role of MSC apoptosis and its immunological consequences, particularly interactions between apoptotic MSCs, phagocytes and endothelial barriers. This perspective highlights the most urgent research questions identified during the meeting and in follow-up discussions and proposes experimental strategies to move beyond traditional cell tracking toward interrogating functional persistence, immune modulation and delivery context. Addressing these gaps will deepen our understanding of MSC behavior in vivo and guide the development of safer, more predictable and more effective MSC-based interventions.