Although the gold standard therapy for HBV-related end-stage liver disease is liver transplant, there are discrepancies between liver supply and liver demand. Stem cell therapy is an alternative approach to lever transplantation for HBV-related liver failure and liver cirrhosis. Previous research from our department shows that allogeneic bone marrow-derived MSCs are safe and effective for patients with HBV-related acute-on-chronic liver failure (ACLF)(8, 9). However, ethical issues, uncertainty about malignant differentiation and culture in vivo limit its wider uptake and clinical significance. Umbilical cord mesenchymal stem cells (UCMSCs) have shown great potential in regenerative medicine due to their extensive sources, multilineage differentiation potential, low immunogenicity and self-renewal ability(15). In the CCl4-induced acute liver injury model, significant hepatoprotective effects of UCMSCs with decreased levels of hepatocellular necrosis and lobular neutrophilic infiltration were found(16). A recent study (17) found that UCMSC treatment can disrupt the development of the inflammatory cascade by inhibiting monocyte activation, and peripheral infusion of human UCMSCs rescues acute liver failure lethality in monkeys. In this study, UCMSCs were used to treat patients with HBV-related liver failure. We found that the levels of ALT, AST, TBIL, and the MELD score gradually decreased and the value of PTA gradually increased after UCMSC treatments. This finding is consistent with previous reports showing that UCMSC transfusions significantly increased the survival rates in patients with ACLF; reduced the model for end-stage liver disease scores; increased serum albumin, cholinesterase, and prothrombin activity; and increased platelet counts(7). Yan et al.’s study(18) demonstrated that UCMSCs could deliver GPX1 to exert its hepatocyte protective effects by detoxifying CCl4 and H2O2 and reducing oxidative stress and apoptosis of hepatocytes. miR-455-3p-enriched exosomes derived from UCMSCs could attenuate macrophage infiltration and local liver damage and reduce the serum levels of inflammatory factors, thereby improving liver histology and systemic disorders(19). Certainly, when MSCs are used to treat liver disease, the trans differentiation of MSCs into hepatocytes was determined, and MSCs also secrete various bioactive molecules to promote liver regeneration(20). Therefore, it was not unexpected that UCMSCs would have such a good therapeutic effect on liver failure in this study.
The characteristics of MSCs are continuous self-renewal, proliferation, multipotent differentiation, and immunomodulatory activities. UCMSCs possess not only the common characteristics of MSCs but also more stable biological characteristics, relatively easy accessibility, abundant source, and no ethical issues, making UCMSCs a good choice for the treatment of liver fibrosis(21). In this study, the therapeutic effect of UCMSCs on liver cirrhosis was also investigated. Our results reveal that the treatment of MSCs significantly improves liver function in patients with liver cirrhosis as evidenced by the levels of ALT, AST, and total bilirubin. However, it has no beneficial effects in terms of PTA and the MELD score. This finding is consistent with previous reports of systematic reviews and meta-analyses of the therapeutic efficacy of MSCs against liver disease(22). In addition, ascites in patients with decompensated liver cirrhosis could be improved by UCMSCs(6). In a CCl4-induced rat liver fibrosis model(23), UCMSCs could differentiate into functional hepatocytes that improved both biochemical and histopathologic changes. In addition, secretomes from UCMSCs also reduced the liver expression of multiple fibrotic factors, collagens, metalloproteinases, TGFβ, and smad proteins in the TGFβ signaling pathways(24). Furthermore, UCMSCs also have a significant immune modulatory effect on immune cells(25). Therefore, UCMSCs can be a simple and effective treatment for the management of fibrotic liver diseases.
The dosage and duration of MSCs are two important issues. Using too many intraportal or intrahepatic BM-MNCs is counterproductive, and it seems more beneficial when they are enriched to reduce the cell number(11). In this study, we mainly focused on whether prolonging the treatment course can improve the curative effect of UCMSCs. Before 4 weeks of UCMSC treatment, the median decline and cumulative decline in TBIL were not significantly different between patients with prolonged treatment and patients with a standard 4-week treatment course. Moreover, the median decline and cumulative decline in TBIL of liver patients with a standard 4-week treatment course were higher than those of liver patients with prolonged treatment. Surprisingly, the data indicate that the median decline and cumulative decline in TBIL of prolonged treatment patients caught up or even surpassed the decline levels of patients with a standard 4-week treatment course after prolonging the treatment course of UCMSCs. Our results show that extending the treatment course can be an option to improve the efficacy of UCMSCs. At present, there are few clinical trials that have investigated the relationship between efficacy and MSC number. A recent meta-analysis(26) finding suggested that the number of cells injected was an important factor influencing the efficacy of autologous MSC therapies, and BMSCs > 4 × 108 were more beneficial to patients. However, some clinical trials with controls using adult stem cells show that cell number might play a role in the result and that too many cells might be deleterious(11). Our results show that increasing the dosage of MSCs by extending the course of treatment may be one of the most appropriate methods of using UCMSCs to treat liver disease. In the future, large-scale and prospective studies are required to identify prolonged strategies for patients receiving UCMSC therapies.
The last issue we are concerned about is which UCMSCs are more suitable for liver failure or liver cirrhosis? The results of this study showed that only the median TBIL decline of patients with liver failure was greater than that of patients with liver cirrhosis after 4 weeks of UCMSC treatment; no statistically significant differences in the levels of ALT, AST, and the PTA value or the MELD score were found between patients with liver failure and patients with liver cirrhosis at all observation weeks. However, the median decline and cumulative decline in the TBIL level of patients with liver failure with a standard 4-week treatment course were higher than those of patients with liver cirrhosis. Pseudolobule formation and destruction of the liver parenchyma may limit the trans differentiation of UCMSCs into hepatocytes. Apart from this, liver sinusoidal endothelial cells (LSECs) may play an important role in this difference. LSECs are the first cells affected by liver injury or chest rating the liver response to damage. LSECs govern regenerative process initiation, and aberrant LSEC activation in chronic liver injury induces fibrosis. Sustaining hepatic injury can lead to the loss of the LSEC phenotype and protective properties, promote angiogenesis and vasoconstriction and contribute to inflammation and fibrosis(27). Shubham et al. (28) found that cellular and functional loss of liver endothelial cells correlates with poor hepatocyte regeneration in acute-on-chronic liver failure. Therefore, standard 4-week UCMSC treatment for liver cirrhosis failed to achieve the same satisfactory effect as treatment for liver failure; the prolonging strategies for patients with liver cirrhosis may be a choice after weighing the advantages and disadvantages.
There were some limitations to this study. First, this study was a retrospective study. Second, this study was based on data from only one health center, yielding a rather small cohort and possible examiner bias. Third, the study period was only 24 weeks; a longer time could provide additional insights. In addition, the number of patients evaluated for treatment efficacy was relatively small. In the future, large-scale and prospective studies are required to identify the therapeutic effect of UCMSCs in HBV-related end-stage liver disease.
In conclusion, peripheral infusion of UCMSCs showed good therapeutic effect for HBV-related liver failure and liver cirrhosis; prolonging the treatment course can increase the curative effect of UCMSCs for end-stage liver disease, especially for patients with cirrhosis. The long-term efficacy should be further assessed in a randomized, large-scale, double-blind and well-controlled trial.