On September 9, the reporter learned from the Fifth Medical Center of the PLA General Hospital that Wang Fusheng, an academician of the CAS Member and director of the infectious disease medical department of the center, systematically revealed the dose effect relationship and the immune regulation mechanism in human body of mesenchymal stromal cells in the treatment of decompensated cirrhosis. This research result was recently published in the international journal "Signal Transduction and Targeted Therapy", which is expected to bring new effective treatment approaches for patients with end-stage liver disease. It is understood that decompensated cirrhosis is a manifestation of chronic liver disease progressing to the end-stage, often accompanied by serious complications such as ascites and hepatic encephalopathy, with a high mortality rate. Liver transplantation is the only cure for this disease. In recent years, mesenchymal stromal cells have been regarded as an important new strategy for treating decompensated liver cirrhosis due to their immunomodulatory and tissue repair potential. However, due to limitations in dose selection, efficacy evaluation, and related mechanisms, the key bottleneck of their clinical translation has not yet been overcome. The research team conducted a systematic evaluation of 24 patients with moderate to severe decompensated cirrhosis through phase I clinical trials. Research has found that mesenchymal stromal cell therapy is safe and tolerable, and even with high doses and multiple infusions, patients have not experienced serious related adverse reactions. In terms of mechanism research, the research team has made three important discoveries. Firstly, it was identified for the first time in the human body that MX1+monocytes are a key subpopulation of cells mediating the immune regulatory effects of mesenchymal stromal cells. Mesenchymal stromal cells can reduce the proportion of MX1+monocytes and weaken their pro-inflammatory function in a dose-dependent manner, thereby achieving therapeutic effects. Meanwhile, MX1+monocytes can exert regulatory effects on other immune cells, thereby balancing anti-inflammatory and anti infective abilities. Secondly, the immune regulatory effect of mesenchymal stromal cells reaches its peak on the 7th day after infusion and weakens on the 14th day, providing a key theoretical basis for designing multiple dosing interval regimens. Thirdly, the change in the proportion of MX1+monocytes is correlated with clinical outcomes and has the potential to become a novel biomarker for predicting mesenchymal stromal cell therapy response, for future clinical treatment. This study fills the gap in the mechanism of action of mesenchymal stromal cells in the human body, and brings the possibility of clinical translation of mesenchymal stromal cells and personalized precision therapy. (New Society)