Abstract: BACKGROUND: Stem cells play an important role in liver regeneration and self-repair ability, which is of great significance for clinical diagnosis and treatment of liver diseases.  
OBJECTIVE: To summarize the current clinical trials and basic research in this field in and outside China, review the types of stem cells used to treat liver diseases in the past, and the treatment programs of various types of stem cells for various types of liver diseases, outline the clinical application prospects of various types of stem cells in the future application of liver diseases, and provide a research basis for the treatment of clinical liver diseases.
METHODS: Using “stem cells, mesenchymal stem cells, hepatic stem cell, embryonic stem cell, induced pluripotent stem cell, hematopoietic stem cell, hepatopathy, non-alcoholic fatty liver disease, liver cirrhosis, liver failure, autoimmune hepatitis, hepatocellular carcinoma” as search words, the relevant articles in PubMed, Web of Science and Wiley e-journal databases were searched, and 71 articles were selected for review according to the inclusion criteria.  
RESULTS AND CONCLUSION: (1) Mesenchymal stem cells, liver stem cells, embryonic stem cells, induced pluripotent stem cells and hematopoietic stem cells are the main stem cells for the treatment of liver diseases. The characteristics, expression period and application of these stem cells in differentiation after liver injury are summarized in this paper. (2) In general, mesenchymal stem cells can repair liver through exosomes, matrix metalloproteinase and anti-inflammatory response. Liver stem cells can differentiate liver oval cells and small hepatocellular progenitor cells to form mature liver cells and promote liver injury repair.  Induced pluripotent stem cells, embryonic stem cells and hematopoietic stem cells can transform into mature hepatocytes through rapid proliferation and differentiation. (3) The treatment of various liver diseases by stem cells is mainly achieved by inducing endogenous cell proliferation, immune regulation, inhibiting inflammation, promoting liver cell regeneration and repairing damaged tissues. (4) On the whole, at present, mesenchymal stem cells are relatively easy to obtain, have the broadest application prospects, and do not involve ethical issues. They are transforming from preclinical research to clinical research. Because mesenchymal stem cells can differentiate into various adult stem cells, they have the advantages of low immunogenicity, strong self-proliferation and differentiation ability. Especially for the treatment of immune hepatitis, liver cirrhosis and hepatocellular carcinoma and other liver diseases, mesenchymal stem cells have the most ideal effect. (5) Induced pluripotent stem cells are more effective in the treatment of end-stage liver disease because they can differentiate into specific somatic cells and hepatocytes without immune rejection. (6) However, stem cell transplantation can induce acute rejection, such as diarrhea, jaundice, and skin rashes. Poor histocompatibility between donors and recipients can easily lead to adverse reactions such as graft-versus-host reactions. After stem cell transplantation, the use of stem cells and its clinical safety assessment still need the support of more clinical trials and evidence-based medicine data.

Key words: stem cell, mesenchymal stem cell, induced pluripotent stem cell, liver disease, liver cirrhosis, hepatocellular carcinoma, clinical treatment, review