Although the gold standard therapy for HBV-related end-stage liver disease is liver transplantation, there are discrepancies between liver supply and liver demand. Stem cell therapy is an alternative approach to liver 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 ACLF(8, 9). However, ethical issues, uncertainty about malignant differentiation in vivo and the need for culture limit its application and clinical significance. UCMSCs have shown great potential in regenerative medicine due to their abundant sources, multilineage differentiation potential, low immunogenicity and self-renewal ability(15). In the CCl4-induced acute liver injury model, significant hepatoprotective effects of UCMSCs were observed, with decreased levels of hepatocellular necrosis and lobular neutrophilic infiltration(16). A recent study (17) found that UCMSC treatment can disrupt 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, and TBIL and MELD scores gradually decreased and that PTA values gradually increased after UCMSC treatment. This finding is consistent with previous reports showing that UCMSC transfusions significantly increased survival rates in patients with ACLF, reduced MELD 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 hepatocyte protective effects by detoxifying CCl4 and H2O2 and reducing oxidative stress and apoptosis in 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). When MSCs were used to treat liver disease, the trans differentiation of MSCs into hepatocytes was observed, and MSCs also secreted 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 include 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, an 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 treatment with 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 values and MELD scores. This finding is consistent with previous 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 pathway(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 MSC treatment 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 decrease and cumulative decrease in TBIL were not significantly different between patients with prolonged treatment and patients with a standard 4-week treatment course. Moreover, the median decrease and cumulative decrease in TBIL of liver patients with a standard 4-week treatment course were larger than those of liver patients with prolonged treatment. Surprisingly, the data indicate that the median decrease and cumulative decrease in TBIL of patients with prolonged treatment were equivalent to or even surpassed the decreases of patients with a standard 4-week treatment course. Our results show that extending the treatment course may be an option to improve the efficacy of UCMSCs. At present, few clinical trials have investigated the relationship between efficacy and MSC number. A recent meta-analysis(26) suggested that the number of cells injected was an important factor influencing the efficacy of autologous MSC therapy, and a dose of > 4 × 108 BMSCs was more beneficial for patients. However, some clinical trials with controls using adult stem cells showed 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 whether UCMSCs are more suitable for liver failure or liver cirrhosis. The results of this study showed that only the median TBIL decrease of patients with liver failure was larger than that of patients with liver cirrhosis after 4 weeks of UCMSC treatment; no statistically significant differences in the levels of ALT or AST, the PTA values or the MELD scores were found between patients with liver failure and patients with liver cirrhosis at all observation weeks. However, the median decrease and cumulative decrease in the TBIL level of patients with liver failure who received a standard 4-week treatment course were larger than those of patients with liver cirrhosis. Pseudo lobule formation and destruction of the liver parenchyma may limit the trans differentiation of UCMSCs into hepatocytes. In addition, liver sinusoidal endothelial cells (LSECs) may play an important role in this difference. LSECs are the first cells affected by liver or chest injury and are involved in the response of the liver to damage. LSECs govern initiation of the regenerative process initiation, and aberrant LSEC activation in chronic liver injury induces fibrosis. Sustaining hepatic injury can lead to 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 ACLF. Therefore, a standard 4-week UCMSC treatment for liver cirrhosis failed to achieve the same satisfactory effect as treatment for liver failure; strategies for prolonging treatment for patients with liver cirrhosis may be an option after weighing the advantages and disadvantages.
There were some limitations of 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 study period 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 confirm the therapeutic effect of UCMSCs in HBV-related end-stage liver disease.
In conclusion, peripheral infusion of UCMSCs showed good therapeutic effects 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 of this approach should be further assessed in a randomized, large-scale, double-blind and well-controlled trial.