Dose-specific Efficacy of Adipose-derived Mesenchymal Stem Cells in Septic Mice

Mesenchymal stem cells (MSCs) therapy for sepsis has been extensively studied in the past decade, however, the treatment regimen and mechanism of action of MSCs remain elusive. Here, we attempted to understand the efficacy and mechanism of action of MSCs on rescuing mice with sepsis. A mouse model of sepsis was produced by cecal ligation and puncture (CLP). Allogeneic adipose-derived MSCs (ADSCs) were administered by intravenous infusion at 6 h after CLP, and dose-related effects of ADSCs on these mice were determined by survival rate, histopathological changes, biochemical and coagulation parameters, bacterial load, and plasma levels of endotoxin and inflammatory cytokines. The tissue distribution of intravenously infused ADSCs in septic mice was investigated by pre-labeling ADSCs with the lipophilic membrane dye PKH26. RNA sequencing analysis was performed to assess the transcriptional changes in peripheral blood mononuclear cells (PBMCs) and the liver. A significant therapeutic effect of ADSCs at a dose of 2×107 cells/kg in septic mice was evidenced by a remarkable reduction in mortality (36% vs 9% survival rate), blood bacterial burden, systemic inflammation, and multiple organ damage. In contrast, ADSCs at a lower dose (1×107 cells/kg) failed to achieve any beneficial outcomes, while ADSCs at a higher dose (4×107 cells/kg) caused more early death within 24 hours after CLP, retaining a steady survival rate of 21% thereafter. PKH26-labeled ADSCs were predominantly localized in the lungs of septic mice after intravenous infusion, with only a smaller proportion of PKH26-positive signals appearing in the liver and spleen. RNA-sequencing analysis identified that insufficient phagocytic activity of PBMCs in addition to a hyperactivation of the hepatic immune response was responsible for the ineffectiveness of low-dose ADSCs therapy, and acute death caused by high-dose ADSCs infusion was associated with impaired coagulation signaling in PBMCs and exacerbated hepatic hypoxic injury. Our findings demonstrate a dose-specific effect of ADSCs on the treatment of sepsis due to dose-related interactions between exogenous stem cells and the host’s microenvironment. Therefore, a precise dosing regimen is a prerequisite for ADSCs therapy for sepsis. Different doses of ADSCs (1×107, 2×107 or 4×107 cells/kg, resuspended in 0.2 mL of 1% albumin solution) or vehicle (1% albumin) were administered intravenously at 6 h after CLP surgery via the tail vein. To determine the dose-related mechanisms of action of ADSCs, RNA-sequencing analysis was performed in PBMCs and liver in CLP mice at 6 h after vehicle or different doses of ADSCs treatment.