Background & aims: The immunomodulatory characteristics of mesenchymal stem cells (MSCs) make them a promising therapeutic approach for liver fibrosis (LF). Here, we postulated that MSCs could potentially suppress the pro-fibrotic activity of intrahepatic B cells, thereby inhibiting LF progression. Approach & results: Administration of MSCs significantly ameliorated LF as indicated by reduced myofibroblast activation, collagen deposition, and inflammation. The treatment efficacy of MSCs can be attributed to decreased infiltration, activation, and pro-inflammatory cytokine production of intrahepatic B cells. Single-cell RNA sequencing revealed a distinct intrahepatic B cell atlas and a subtype of naive B cells (B-II) was identified, which were markedly abundant in fibrotic liver, displaying mature features with elevated expression of several proliferative and inflammatory genes. Transcriptional profiling of total B cells revealed that intrahepatic B cells displayed activation, proliferation, and pro-inflammatory gene profile during LF. Fibrosis was attenuated in mice ablated with B cells (μMT) or in vivo treatment with anti-CD20. Moreover, fibrosis was recapitulated in μMT after adoptive transfer of B cells, which in turn could be rescued by MSC injection, validating the pathogenic function of B cells and the efficacy of MSCs on B cell-promoted LF progression. Mechanistically, MSCs could inhibit the proliferation and cytokine production of intrahepatic B cells through exosomes, regulating the MAPK and NF-kappa B signaling pathways. Conclusions: Intrahepatic B-cell serve as a target of MSCs, play an important role in the process of MSC-induced amelioration of LF, and may provide new clues for revealing the novel mechanisms of MSC action. Export

Primary sclerosing cholangitis (PSC) is an autoimmune cholangiopathy characterized by chronic inflammation of the biliary epithelium and periductal fibrosis, with no curative treatment available, and liver transplantation is inevitable for end-stage patients. Human placental mesenchymal stem cell (hpMSC)-derived exosomes have demonstrated the ability to prevent fibrosis, inhibit collagen production and possess immunomodulatory properties in autoimmune liver disease. Here, we prepared hpMSC-derived exosomes (Exo^MSC) and further investigated the anti-fibrotic effects and detailed mechanism on PSC based on Mdr2^−/− mice and multicellular organoids established from PSC patients. The results showed that Exo^MSC ameliorated liver fibrosis in Mdr2^−/− mice with significant collagen reduction in the preductal area where Th17 differentiation was inhibited as demonstrated by RNAseq analysis, and the percentage of CD4⁺IL-17A⁺T cells was reduced both in Exo^MSC-treated Mdr2^−/− mice (Mdr2^−/−-Exo) in vivo and Exo^MSC-treated Th17 differentiation progressed in vitro. Furthermore, Exo^MSC improved the hypersecretory phenotype and intercellular interactions in the hepatic Th17 microenvironment by regulating PERK/CHOP signaling as supported by multicellular organoids. Thus, our data demonstrate the anti-fibrosis effect of Exo^MSC in PSC disease by inhibiting Th17 differentiation, and ameliorating the Th17-induced microenvironment, indicating the promising potential therapeutic role of Exo^MSC in liver fibrosis of PSC or Th17-related diseases.

The efficacy of mesenchymal stem cell (MSC)-based therapy for acute liver injury (ALI) involves coordination with the hepatic immune system, a complex and coordinated network of immune-cell interactions. However, studies of the immunomodulatory effects of MSCs have focused on a limited number of cell subsets rather than a systematic assessment. Carbon tetrachloride (CCl4) was used to induce ALI in mice. To determine the efficacy of MSCs, ALI mice were injected with MSCs via the tail vein, and histopathological changes, survival rate, and the serum levels of liver enzymes were determined. To assess the immune response induced by MSCs, a mass cytometry panel of 43 metal isotope-tagged antibodies was used to characterize the hepatic immune compartment at days 1, 2, 3, and 7 after administration of MSCs or PBS. MSC treatment significantly alleviated CCl4-induced ALI and improved the survival rate. MSC treatment also modulated the hepatic immune system in terms of the distribution of immune-cell subsets and the phenotype of single cells. During the injured phase, MSCs inhibited a systemic response by reducing the numbers of Ly6ClowCD8+ TRM cells, conventional NK cells, and IgM+IgD+ B cells; suppressing the activation of Ly6ChiCD8+ TRM cells; downregulating MHC II and IgM expression in IgM+IgD+ B cells; and increasing the number of immunosuppressive monocyte-derived macrophages. During the recovery phase, MSCs promoted the retention of Ly6ClowCD8+ TRM cells and maintained the immunosuppressive activity of monocyte-derived macrophages. The response to MSC treatment differed between the injured and recovery phases, emphasizing the benefit of dynamic assessment of the immunomodulatory effects of MSCs. We determined the immunomodulatory effects of MSC treatment on the subtype distribution and phenotypes of hepatic immune cells.

Background: Immune system disorders play important roles in acute lung injury (ALI), and mesenchymal stem cell (MSC) treatment can reduce inflammation during ALI. In this study, we compared the changes in lung B cells during MSC treatment.Methods: We investigated the effects of MSCs on lung B cells in a mouse model of lipopolysaccharide (LPS)-induced ALI. MSCs were administered intratracheally 4 h after LPS. As vehicle-treated controls, mice were treated with phosphate-buffered saline (PBS) containing 2% C57BL/6 (PBS group). Histopathological changes, survival rate, inflammatory factor levels, and the number of neutrophils in bronchoalveolar lavage fluid (BALF) were determined. Single-cell RNA sequencing (scRNA-Seq) analysis was performed to evaluate the transcriptional changes in lung B cells between the PBS, LPS, and LPS/MSC groups on days 3 and 7.Results: MSC treatment ameliorated LPS-induced ALI, as indicated by the reductions in mortality, the levels of chemokines and cytokines in BALF, and the severity of lung tissue histopathology in ALI mice. Lung B cells in the PBS group remained undifferentiated and had an inhibitory phenotype. Based on our scRNA-Seq results, the differentially expressed genes (DEGs) in lung B cells in both the PBS group and LPS group were involved in chemotaxis processes and some proinflammatory pathways. MSC treatment inhibited the expression of chemokine genes that were upregulated by LPS and were related to the recruitment of neutrophils into lung tissues. Immunoglobulin-related gene expression was decreased in lung B cells of mice treated with LPS/MSC for 7 days. The DEGs regulated by MSCs were enriched in biological processes, including humoral immune response and apoptotic signaling.Conclusions: Lung B cells played an important role in the effects of treatment of ALI with MSCs. These observations provide new insights into the mechanisms underlying the effects of MSC treatment for ALI.

Background. The mechanisms of mesenchymal stem cell (MSC) transplantation to protect against acute liver injury have been well studied within the liver. However, the associated changes in the intestinal microbiota during this process are poorly understood.Methods. In this study, compact bone-derived MSCs were injected into mice after carbon tetrachloride (CCl₄) administration. Potential curative effect of MSC was evaluated by survival rate and biochemical and pathological results. Overall structural changes of microbial communities and alterations in the intestinal microbiota were assessed by sequenced 16S rRNA amplicon libraries from the contents of the cecum and colon.Results. MSCs significantly reduced the serum levels of aspartate transaminase and alanine transaminase and improved the histopathology and survival rate. Lower expression and discontinuous staining of zonula occludens, as well as disrupted tight junctions, were observed in CCl₄-treated mice at 48 h compared with MSC-transplanted mice. Moreover, MSC transplantation to the liver leads to intestinal microbiota changes that were reflected in the decreased abundance of BacteroidetesS24-7andBacteroidaceaeand increased abundance of FirmicutesClostridiales,Ruminococcaceae, andLactobacillusat the initial time point compared with that in CCl₄-treated mice. In addition, phylogenetic investigation of communities by the reconstruction of unobserved states (PICRUSt) based on the Greengenes database revealed functional biomarkers of MSC-transplanted mice involved in cell motility, signal transduction, membrane transport, transcription, and metabolism of lipids, cofactors, vitamins, terpenoids, and polyketides, as well as xenobiotics.Conclusion. The initial alterations in the Firmicutes/Bacteroidetes ratio, which resulted from MSC infusion to the liver, maintain intestinal mucosal biology and homeostasis that may be beneficial to liver repair.