Patent Publication Number: US-2021189347-A1

Title: Method for producing liver stem cells or liver progenitor cells by direct reprogramming

Description:
TECHNICAL FIELD 
     The present invention relates to a method for producing hepatic stem cells or hepatic progenitor cells by introducing given reprogramming factors into vascular endothelial cells, etc. 
     BACKGROUND ART 
     Techniques have already been known to prepare hepatocytes by introducing a certain set of genes into human fibroblasts, as exemplified by a method for preparing induced hepatocytes from non-hepatic cells, in which CEBPA, HNF4A, FOXA3, GATA4, HNF1A and so on are used as reprogramming factors (Patent Document 1: JP 2015-527084 A). 
     Moreover, it has been known that once mouse embryonic fibroblasts have been transfected with Hnf1β and Foxa3, they will be reprogrammed into hepatic stem cells (Non-patent Document 1), and other methods have also been known, e.g., a method for reprogramming human fibroblasts into mature hepatocytes upon expression of FOXA3, HNF1A and HNF4A (Non-patent Document 2), a method for preparing human induced hepatocytes upon overexpression of HNF1A, HNF4A and HNF6 together with maturation factors ATFS, PROX1 and CEBPA (Non-patent Document 3), etc. 
     However, hepatocytes induced by these conventional methods are poor in proliferation potency and also cannot differentiate into cholangiocytes. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         
           
             Patent Document 1: JP 2015-527084 A 
           
         
       
    
     Non-Patent Documents 
     
         
         
           
             Non-patent Document 1: Bing Yu et al., Cell Stem Cell 13, 1-13, Sep. 5, 2013 
             Non-patent Document 2: Pengyu Huang et al., Cell Stem Cell 14, 1-15, Mar. 6, 2014 
             Non-patent Document 3: Yuanyuan Du et al., Cell Stem Cell 14, 1-10, Mar. 6, 2014 
           
         
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     Once it has been possible to obtain hepatic stem cells or hepatic progenitor cells (hereinafter referred to as hepatic stem/hepatic progenitor cells) which have proliferation potency and are capable of differentiating into cholangiocytes, these cells when cultured will allow the supply of desired hepatocytes or cholangiocytes in an amount enough for the intended purpose. For this reason, there has been a demand for the development of a method for producing hepatic stem/hepatic progenitor cells. 
     As a result of extensive and intensive efforts made to solve the problem stated above, the inventors of the present invention have succeeded in obtaining hepatic stem/hepatic progenitor cells upon combination of given genes, which in turn led to the completion of the present invention. 
     Means to Solve the Problem 
     Namely, the present invention is as follows. 
     (1) A method for inducing conversion from non-hepatic stem cells or non-hepatic progenitor cells into hepatic stem cells or hepatic progenitor cells, which comprises introducing any of the following combinations into the non-hepatic stem cells or non-hepatic progenitor cells:
 
(a) a combination of HNF1, HNF6 and FOXA;
         (b) a combination of HNF1 gene, HNF6 gene and FOXA gene;   (c) a combination of HNF1, MYC and FOXA; or   (d) a combination of HNF1 gene, MYC gene and FOXA gene.
 
(2) A method for producing hepatic stem cells or hepatic progenitor cells, which comprises the step of inducing hepatic stem cells or hepatic progenitor cells by the method according to (1) above.
 
(3) The method according to (1) or (2) above, wherein HNF1 is HNF1A.
 
(4) The method according to any one of (1) to (3) above, wherein FOXA is FOXA3.
 
(5) The method according to any one of (1) to (4) above, wherein the combination is (a) or (b), and MYC or MYC gene is further introduced.
 
(6) The method according to any one of (1) to (5) above, wherein MYC is L-MYC.
 
(7) The method according to any one of (1) to (6) above, wherein the non-hepatic stem cells or non-hepatic progenitor cells are vascular endothelial cells or blood-derived cells.
 
(8) The method according to (7) above, wherein the vascular endothelial cells are derived from umbilical veins, peripheral blood or umbilical cord blood.
 
(9) The method according to (7) above, wherein the blood-derived cells are peripheral blood T cells or umbilical cord blood T cells.
 
(10) Hepatic stem cells or hepatic progenitor cells produced by the method according to any one of (2) to (9) above.
 
(11) A method for producing hepatocytes or cholangiocytes, which comprises the steps of:
   (a) inducing hepatic stem cells or hepatic progenitor cells by the method according to (1) above; and   (b) allowing the induced hepatic stem cells or hepatic progenitor cells to differentiate into hepatocytes or cholangiocytes.       

     Effects of the Invention 
     The present invention provides a method for inducing conversion from any cells other than hepatic stem cells and hepatic progenitor cells, i.e., non-hepatic stem cells or non-hepatic progenitor cells (hereinafter referred to as “non-hepatic stem/non-hepatic progenitor cells”) into hepatic stem/hepatic progenitor cells (reprogramming method), and a method for producing hepatic stem/hepatic progenitor cells. The present invention allows direct conversion from non-hepatic stem/non-hepatic progenitor cells (e.g., vascular endothelial cells) into hepatic stem/hepatic progenitor cells. The thus induced hepatic stem/hepatic progenitor cells have long-term proliferation potency and are capable of differentiating into hepatocytes or cholangiocytes. In addition, not only embryonic vascular endothelial cells, but also vascular endothelial cells in adult peripheral blood can be induced into hepatic stem/hepatic progenitor cells. Thus, the present invention also allows liver function test and drug screening with the use of hepatic stem/hepatic progenitor cells derived from peripheral blood. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows identification of specific factors responsible for inducing human induced hepatic progenitor cells (hiHepPCs). 
         FIG. 2  shows differentiation from hiHepPCs into hepatocyte-like cells. 
         FIG. 3  shows the results of functional analysis and gene expression analysis on hepatocyte-like cells differentiated from hiHepPCs. 
         FIG. 4  shows liver tissue reconstruction by hiHepPC transplantation. 
         FIG. 5  shows differentiation from hiHepPCs into cholangiocyte-like cells. 
         FIG. 6  shows the results obtained when HUVEC-derived hiHepPCs were analyzed for their proliferation potency and differentiation potency by clone analysis. 
         FIG. 7  shows that the time required for hiHepPC induction is reduced upon addition of L-MYC. 
         FIG. 8  shows hiHepPC induction from human peripheral blood-derived vascular endothelial cells (HPBECs). 
         FIG. 9  shows the results obtained when HPBEC-derived 4F-hiHepPCs were analyzed for their proliferation potency and differentiation potency by clone analysis. 
         FIG. 10  shows the analysis results obtained when FOXA3, which is one of the hiHepPC-inducing factors, was replaced with FOXA1 and FOXA2. 
         FIG. 11  shows hiHepPC induction from human peripheral blood-derived T cells (HPBTCs). 
         FIG. 12  shows an overview of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present invention relates to a method for inducing conversion from non-hepatic stem/non-hepatic progenitor cells into hepatic stem/hepatic progenitor cells, which comprises introducing a combination of reprogramming factors HNF1A, HNF6 and FOXA, a combination of genes encoding these factors, a combination of reprogramming factors HNF1A, MYC and FOXA or a combination of genes encoding these factors into the non-hepatic stem/non-hepatic progenitor cells. The present invention is not intended to induce cells which have already differentiated, but is characterized by inducing hepatic stem/hepatic progenitor cells, which serve as their origin, from non-hepatic stem/non-hepatic progenitor cells, and is configured to use a combination of reprogramming factors as mentioned above. 
     1. Non-Hepatic Stem/Non-Hepatic Progenitor Cells 
     In the present invention, the non-hepatic stem/non-hepatic progenitor cells to be used are intended to mean any cells other than desired hepatic stem/hepatic progenitor cells. Examples of non-hepatic stem/non-hepatic progenitor cells include fibroblasts, endothelial cells, blood cells, umbilical cord blood cells, bone marrow cells, keratinocytes, hepatocytes, cholangiocytes, myofibroblasts, neuronal lineage cells, epithelial lineage cells and so on. In the present invention, vascular endothelial cells or blood-derived cells can be used, by way of example. Examples of vascular endothelial cells include those derived from umbilical veins, peripheral blood or umbilical cord blood, while examples of blood-derived cells include peripheral blood cells or umbilical cord blood cells (e.g., peripheral blood T cells or umbilical cord blood T cells). The non-hepatic stem/non-hepatic progenitor cells to be used in the present invention may be of mammalian origin (e.g., mouse, rat, rabbit, cat, dog, monkey, human). In one embodiment of the present invention, the non-hepatic stem/non-hepatic progenitor cells to be used are those of human origin. 
     2. Reprogramming Factors 
     The term “reprogramming” refers to a process that changes the differentiation status of cells to their another differentiation status or their undifferentiated status. In the present invention, the above non-hepatic stem/non-hepatic progenitor cells are induced into hepatic stem/hepatic progenitor cells. In the present invention, non-hepatic stem/non-hepatic progenitor cells can be induced into hepatic stem/hepatic progenitor cells without being converted into pluripotent stem cells. Factors for use in such reprogramming (reprogramming factors) are as shown below:
         (a) a combination of HNF1, HNF6 and FOXA;   (b) a combination of HNF1 gene, HNF6 gene and FOXA gene;   (c) a combination of HNF1, MYC and FOXA; or   (d) a combination of HNF1 gene, MYC gene and FOXA gene.       

     HNF1 (Hepatocyte Nuclear Factor 1) is a protein having a homeodomain, and there are two isoforms HNF1A and HNF1B. 
     HNF6 (Hepatocyte Nuclear Factor 6) is a homeodomain-type transcription factor involved in human tissue development, and is responsible for controlling the development of various tissues including pancreas and liver and is also responsible for controlling the expression of various hepatic genes. 
     FOXA is a hepatocyte nuclear factor (transcription factor) required during the earliest process of liver tissue formation, and includes FOXA1, FOXA2 and FOXA3. These FOXA transcription factors share 90% or more homology at the amino acid level in their common forkhead/wingedhelix domain, and are therefore deemed to have functional complementarity to each other. 
     Moreover, in the present invention, if the above combination of reprogramming factors is (a) or (b), L-MYC may further be combined. 
     MYC family genes are known as transcription factors which work upon binding to nuclear DNA, and there are c-MYC, L-MYC and N-MYC in humans. In the present invention, all of these factors can be used. 
     Table 1 shows the amino acid sequences of the above reprogramming factors, and the nucleotide sequences of genes encoding these factors. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Reprogramming factor  
                 Nucleotide sequence  
                 Amino acid sequence 
               
               
                   
               
             
            
               
                 HNF1A NM_000545  
                 SEQ ID NO: 1  
                 SEQ ID NO: 2  
               
               
                 HNF6 NM_004498  
                 SEQ ID NO: 3  
                 SEQ ID NO: 4  
               
               
                 FOXA1 NM_004496  
                 SEQ ID NO: 5  
                 SEQ ID NO: 6  
               
               
                 FOXA2 NM_021784  
                 SEQ ID NO: 7  
                 SEQ ID NO: 8  
               
               
                 FOXA3 NM_004497  
                 SEQ ID NO: 9  
                 SEQ ID NO: 10  
               
               
                 L-MYC GenBank: M19720.1  
                 SEQ ID NO: 11  
                 SEQ ID NO: 12 
               
               
                   
               
            
           
         
       
     
     Some of the genes encoding these factors can be cloned by reference to “Molecular Cloning, A Laboratory Manual (4th edition)” (Cold Spring Harbor Laboratory Press (2012)), etc., or may also be available from addgene, etc. 
     A gene encoding HNF1A is herein referred to as “HNF1A gene” while a gene encoding HNF6 is herein referred to as “HNF6 gene.” Genes encoding the other factors are also referred to in the same manner as above. 
     In one embodiment of the present invention, it is possible to use, for example, the following combination of reprogramming factors or a set of genes encoding these factors:
         NF1A, HNF6 and FOXA3;   NF1A, L-MYC and FOXA3; or   NF1A, HNF6, FOXA3 and L-MYC.       

     The reprogramming factors (genes or proteins) used in the present invention are not limited to the nucleotide sequences and amino acid sequences represented by the SEQ ID NOs shown in Table 1, and may also include the mutants shown below as long as they have the functions as reprogramming factors intended in the present invention:
         (a) proteins which consist of amino acid sequences with deletion, substitution or addition of one or several (e.g., 10 or less, 5 or less, 4 or less, 3 or less, or 2) amino acids in the amino acid sequences shown in Table 1 and which have the functions as reprogramming factors intended in the present invention possessed by the respective reprogramming factors;   (b) proteins which consist of amino acid sequences sharing a homology of 80% or more, 85% or more, 90% or more, 95% or more, 98% or more, or 99% or more with the amino acid sequences shown in Table 1 and which have the functions as reprogramming factors intended in the present invention possessed by the respective reprogramming factors;   (c) nucleic acids encoding the proteins shown in (a) above;   (d) nucleic acids encoding the proteins shown in (b) above; and   (e) nucleic acids which are hybridizable under stringent conditions with nucleic acids consisting of nucleotide sequences complementary to the nucleotide sequences shown in Table 1 and which encode proteins having the functions as reprogramming factors intended in the present invention possessed by the respective reprogramming factors.       

     In the present invention, the term “stringent conditions” refers to, for example, conditions of 5×SSC, 5×Denhardt&#39;s solution, 0.5% SDS, 50% formamide and 50° C. Under these conditions, it can be expected that DNA and/or RNA having a higher homology is more efficiently obtained at a higher temperature. However, the stringency of hybridization would be affected by a plurality of factors, including temperature, DNA and/or RNA concentration, DNA and/or RNA length, ionic strength, reaction time, salt concentration and so on. Those skilled in the art would be able to achieve the same stringency by selecting these factors as appropriate. 
     3. Introduction of Reprogramming Factors into Cells 
     To introduce the reprogramming factors into non-hepatic stem/non-hepatic progenitor cells serving as host cells, a recombinant vector(s) may be constructed to carry genes encoding the reprogramming factors in the same vector or separate vectors. In the present invention, the vector(s) may be constructed by using a replicon which may be inserted to cause the replication of an insert segment. The vector(s) may be constructed as an expression vector(s) in which one or more expression regulatory sequences are operably linked, and may be constructed to comprise DNA(s) for controlling the transcription and/or translation of an additional DNA sequence(s) other than the reprogramming factors. Examples of expression regulatory sequences include a promoter, an enhancer, a transcription terminator and so on. 
     In the present invention, the genes encoding the reprogramming factors may be inserted as follows: a set of genes to be introduced may all be linked to a single vector or these individual genes may be linked to separate vectors. Alternatively, some of the genes may be linked to a single vector, and the other genes may be linked to other vector(s). 
     Examples of expression vectors available for use in the present invention include plasmids, bacteriophages, as well as virus vectors derived from retrovirus, vaccinia virus, adenovirus, lentivirus, adeno-associated virus, Sendai virus and other viruses. Such an expression vector may be introduced into non-hepatic stem/non-hepatic progenitor cells in any manner, for example, by infecting the cells with an expression vector(s) comprising genes encoding the respective reprogramming factors. In addition to this, lipofection, electroporation, calcium phosphate transfection or the like may be used for this purpose, by way of example. The dose of the virus vector(s) when infected into the cells may be adjusted as appropriate. 
     The method of the present invention for inducing conversion from non-hepatic stem/non-hepatic progenitor cells into hepatic stem/hepatic progenitor cells may be carried out either in vitro or in vivo. If the method is carried out in vitro, the expression vector(s) may be introduced into non-hepatic stem/non-hepatic progenitor cells to obtain transformants, which may then be cultured for a given period of time. Culture may be accomplished by using a medium for use in animal cell culture, and subculture may then be repeated as needed to thereby cause reprogramming into hepatic stem/hepatic progenitor cells. 
     If the method is carried out in vivo, the expression vector(s) may be introduced by any known introduction techniques into non-hepatic stem/non-hepatic progenitor cells in an animal, e.g., through its dermal tissue or via the intravascular or intraperitoneal route to thereby obtain transformants. Then, cells reprogrammed into hepatic stem/hepatic progenitor cells can be confirmed in the animal&#39;s tissue or in cells collected from the animal&#39;s tissue. 
     Whether or not the resulting cells were reprogrammed into hepatic stem/hepatic progenitor cells can be confirmed by markers which are expressed in these cells. Examples of such markers include albumin, α-fetoprotein, E-cadherin and so on. 
     Alternatively, in the present invention, polypeptides of the following factors may also be directly introduced into cells:
         HNF1A, HNF6 and FOXA3;   HNF1A, L-MYC and FOXA3; or   HNF1A, HNF6, FOXA3 and L-MYC.       

     The above factors may be prepared in a genetic engineering manner (see, e.g., “Molecular Cloning, A Laboratory Manual (4th edition)” (Cold Spring Harbor Laboratory Press (2012)) and the resulting polypeptides may be introduced into cells, for example, by being linked to membrane-permeable peptides, etc., or by means of cationic lipids. Moreover, transfection reagents are also commercially available (e.g., PULSin (PPU), Prote-IN (HYG), BioPORTER Protein Delivery Reagent (GTS)). 
     EXAMPLES 
     The present invention will be further described in more detail by way of the following illustrative examples, although the scope of the present invention is not limited by these examples. 
     Example 1 
     (1) Identification of Specific Factors Responsible for Inducing Human Induced Hepatic Progenitor Cells (hiHepPCs) 
       FIG. 1A  schematically shows the hiHepPC induction experiment. 
     Commercially available human umbilical vein endothelial cells (HUVECs) were transfected with a retrovirus vector (gene expression vector) through retrovirus infection. During transfection, HUVECs were cultured in a medium (HUVEC medium) composed of a 1:1 mixture of Medium 200 and Fibrolife serum-free cell culture medium. After virus infection, the cells were cultured for 2 days in a medium (Hepato-medium (plus)) composed of Hepato-medium (i.e., a 1:1 mixed medium of DMEM and F12 supplemented with 4% fetal bovine serum, 1 μg/ml insulin, 10 −7  M dexamethasone, 10 mM nicotinamide, 2 mM L-glutamine, 50 μM β-mercaptoethanol, and penicillin/streptomycin) supplemented with 20% Fibrolife serum-free cell culture medium, 20 ng/ml HGF, 1 μM A83-01, 2 μM SB43852 and 5 μM Y27632, followed by analysis at any time while subculturing the cells in Hepato-medium (plus). 
     HUVECs were transfected with an empty vector (mock), a combination of HNF4A and FOXA3 (H4A/F3), a combination of HNF4A, FOXA3, HNF1A and HNF6 (H4A/F3/H1A/H6), a combination of HNF4A, FOXA3 and HNF1A (H4A/F3/H1A), a combination of HNF4A, FOXA3 and HNF6 (H4A/F3/H6), a combination of HNF4A, HNF1A and HNF6 (H4A/H1A/H6), a combination of HNF4A, HNF1A, HNF6, ATFS, PROX1 and CEBPA (H4A/H1A/H6+APC) or a combination of FOXA3, HNF1A and HNF6 (F3/H1A/H6), followed by immunostaining for ALBUMIN (ALB) and counting of ALB-positive cells at each passage (P) from 1 to 6. Moreover, immunostaining for E-CADHERIN (E-CAD) was also conducted at P6. 
     The results obtained are shown in  FIG. 1B . 
     ALB is a marker expressed in hepatic progenitor cells and hepatocytes, while E-CAD is a marker for epithelial cells. As can be seen from immunostaining for ALB and E-CAD, the phase contrast photographs (Phase) of the cells, as well as the graphs showing the ratio of ALB-positive cells, it is indicated that hepatic progenitor-like cells having proliferation potency are induced upon introduction of F3/H1A/H6. 
     In  FIG. 1B , PH and PN in each graph represent parental HUVEC and passage number, respectively. Two independent experiments were conducted and the respective results are shown in blue and red lines on each graph. DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     In addition, three independent experiments were conducted to introduce the gene set F3/H1A/H6 into HUVECs to thereby induce hiHepPCs. 
     The results obtained are shown in  FIG. 1C . This figure shows the number of cells proliferated during 16 passages of subculture of hiHepPCs obtained in the respective experiments (hiHepPC-1, hiHepPC-2, hiHepPC-3). hiHepPCs continue to proliferate, whereas HUVECs stop their proliferation in mid-course of their subculture. 
     Further, the results of chromosomal analysis on hiHepPCs at the 12th passage of subculture are shown in  FIG. 1D . When 20 cells were analyzed, the number of chromosomes was normal in all of them. 
     (2) Differentiation from hiHepPCs into Hepatocyte-Like Cells 
     HUVEC-derived hiHepPCs were co-immunostained for ALB and α-fetoprotein (AFP) at each passage (P) from 1 to 6 to thereby calculate the AFP-positive rate among ALB-positive cells. 
     The results obtained are shown in  FIG. 2 . 
     In panel A, during earlier processes of hiHepPC induction, cells positive for both ALB and AFP characteristic of hepatic progenitor cells account for a higher proportion, whereas the proportion of cells positive for ALB alone characteristic of hepatocytes is increased with the number of passages. This result suggests that HUVECs will first be converted into hiHepPCs and hepatocyte-like cells will then be differentiated from hiHepPCs. The graph shows the mean±standard deviation (n=3) of data obtained by analysis on hiHepPCs prepared in three independent experiments. DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     Likewise, as to panel B, hepatocyte-like cells differentiated from HUVEC-derived hiHepPCs express not only ALB, but also hepatocyte markers AAT, ASGPR1 and CYP3A4. On the other hand, HUVECs express a vascular endothelial cell marker, CD31, but are negative for expression of all the hepatocyte markers. DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     (3) Functional Analysis and Gene Expression Analysis on Hepatocyte-Like Cells Differentiated from hiHepPCs 
       FIG. 3  shows the results of functional analysis and gene expression analysis on hepatocyte-like cells differentiated from hiHepPCs. 
     Panel A indicates that hepatocyte-like cells differentiated from HUVEC-derived hiHepPCs allow glycogen accumulation, lipid synthesis, and uptake and release of indocyanine green (ICG), as in the case of hepatocytes. Scale bar: 50 μm. 
     Panel B indicates that hepatocyte-like cells differentiated from HUVEC-derived hiHepPCs have the ability to cause albumin secretion, urea synthesis and cytochrome P450 activation. hiHepPCs prepared in three independent experiments (hiHepPC-1, hiHepPC-2, hiHepPC-3) were used in the analysis. A human liver cancer-derived cell line, HepG2, was used as a positive control. Each graph shows the mean±standard deviation (n=3). 
     Panel C indicates that hepatocyte-like cells differentiated from HUVEC-derived hiHepPCs react with hepatotoxic drugs (acetaminofen, amiodarone, dicrofenac) to cause cell death. hiHepPCs prepared in three independent experiments (hiHepPC-1, hiHepPC-2, hiHepPC-3) were used in the analysis. The graph shows the mean±standard deviation (n=3). *P&lt;0.05, **P&lt;0.01 
     Panel D shows the results obtained when three HUVECs (HUVEC-1, HUVEC-2, HUVEC-3) and three hiHepPCs (hiHepPC-1, hiHepPC-2, hiHepPC-3) were analyzed for their gene expression by mRNA-seq. The gene expression profile of human hepatocytes was obtained from public data, and this profile was analyzed together with the data of HUVECs and hiHepPCs. The upper heat map shows the results of clustering analysis, indicating that hiHepPCs resemble the gene expression pattern of human hepatocytes but greatly differ from HUVECs. On the other hand, the lower heat maps show the expression patterns of genes involved in fatty acid metabolism, cholesterol metabolism, glucose metabolism and drug or xenobiotic metabolism, indicating that hepatocyte-like cells differentiated from hiHepPCs express various hepatic function genes. 
     (4) Liver Tissue Reconstruction by hiHepPC Transplantation 
     First, immunodeficient mice (NSG mice) at 3 weeks of age were administered with retrorsine once a week until 7 weeks of age, i.e., five times in total. Subsequently, 1 week after the last retrorsine administration, these mice were administered once with carbon tetrachloride (CC14) to induce hepatopathy. Then, on the following day, 1×10 7  HUVEC-derived hiHepPCs were transplanted into the liver of each mouse through the portal vein from the spleen. After 2 months had passed since the transplantation, the liver and serum of each mouse were analyzed. 
     The results obtained are shown in  FIG. 4 . 
     Panel A schematically shows the hiHepPC transplantation experiment. 
     Panel B shows the concentration of human albumin present in mouse serum after hiHepPC transplantation. This panel shows the analysis results obtained for 5 mice transplanted with hiHepPCs. As negative controls, the analysis results obtained for non-transplanted NSG mouse serum and HUVEC-transplanted NSG mouse serum are shown. TP represents transplantation. The graph shows the mean±standard deviation (n=2). 
     Panel C shows the results obtained when HUVEC- or hiHepPC-transplanted mouse liver tissue was immunostained with anti-human AAT antibody. Liver tissue reconstruction by hiHepPC-derived hepatocyte-like cells is observed in the hiHepPC-transplanted mouse liver. TP represents transplantation. DNA in the cells was stained with DAPI (blue). Scale bar: 100 μm. 
     (5) Differentiation from hiHepPCs into Cholangiocyte-Like Cells 
       FIG. 5  shows differentiation from hiHepPCs into cholangiocyte-like cells. 
     Panel A indicates that when HUVECs and HUVEC-derived hiHepPCs are three-dimensionally cultured in Matri gel for 1 week, only hiHepPCs form spherical tissue (spheroid) having an epithelial luminal structure. These spheroids can be subcultured for passages (P). Scale bar: 100 μm. 
     Panel B indicates that a spheroid formed from HUVEC-derived hiHepPCs has polarity (local expression patterns of E-CAD, EZRIN, ZO-1 and Phalloidin) and is formed by epithelial cells expressing cholangiocyte markers (CK19, SOX9, HNF1B, CFTR, EpCAM, α-TUBULIN). DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     Panel C indicates that a spheroid formed from HUVEC-derived hiHepPCs also takes up a fluorescent dye (rhodamine), as in the case of the bile duct. The uptake is inhibited upon Verapamil addition, thus indicating that this uptake is mediated by a transporter. Scale bar: 50 μm. 
     Panel D shows electron microscope photographs of a spheroid formed from HUVEC-derived hiHepPCs. The spheroid has microvilli on the luminal side and its cells are joined by tight junction (indicated with arrows in the figure). Scale bar: 10 μm (left figure), 500 nm (right figure). 
     (6) Analysis of HUVEC-derived hiHepPCs for their proliferation potency and differentiation potency by clone analysis hiHepPCs prepared in three independent experiments (hiHepPC-1, hiHepPC-2, hiHepPC-3) were each subjected to clone sorting by flow cytometry (FACS) and seeded at one cell per well in a 96-well culture plate, followed by single cell culture. Then, cells expanded from one cell (hiHepPC clone) were analyzed. 
     This analysis procedure is shown in  FIG. 6A  and the analysis results obtained are shown in  FIGS. 6B to 6D . 
     In panel B, the graphs in the left and right figures show the ratio of colonies formed as a result of single cell culture (per 570 wells) and the ratio of clones still expanding (per 570 wells), respectively, obtained for each of hiHepPC-1, hiHepPC-2 and hiHepPC-3. 
     Panel C shows a phase contrast image (Phase) and an ALB and E-CAD co-immunostaining image obtained for expanded hiHepPC clones. DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. Panel D indicates that when three-dimensionally cultured in Matri gel, expanded hiHepPC clones differentiate into cholangiocyte-like cells to thereby form spheroids having an epithelial luminal structure. Scale bar: 50 μm. 
     (7) Reduction of the Time Required for hiHepPC Induction Upon Addition of L-MYC 
     In addition to FOXA3, HNF1A and HNF6, L-MYC was also simultaneously introduced into HUVECs, followed by analysis. 
     The results obtained are shown in  FIG. 7 . 
     In panel A, HUVECs were immunostained for ALB at each passage (P) from 1 to 6, and immunostaining for E-CAD and a phase contrast photograph (Phase) were also obtained at P6. DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     Panel B shows the results obtained when HUVECs were transfected with a combination of F3/H1A/H6+L-MYC, followed by counting of ALB-positive cells at each passage from 1 to 6 to give the ratio of ALB-positive cells in graphical form. PH and PN in the graph represent parental HUVEC and passage number, respectively. Two independent experiments were conducted and the respective results are shown in blue and red lines on the graph. The combination of F3/H1A/H6+L-MYC was found to more quickly induce ALB-positive cells than a combination of F3/H1A/H6 (see  FIG. 1B ). 
     (8) hiHepPC Induction from Human Peripheral Blood-Derived Vascular Endothelial Cells (HPBECs) 
       FIG. 8A  schematically shows the induction experiment of hiHepPCs from HPBECs. First, mononuclear cells were separated from peripheral blood collected from normal volunteers, and were then cultured in HPBEC medium (EGM™-2MV BulletKit™ Medium supplemented with 20% fetal bovine serum) to obtain HPBECs. Then, HPBECs were transfected with a combination of F3/H1A/H6 (3F) or a combination of F3/H1A/H6+L-MYC (4F) through retrovirus infection. After virus infection, the cells were cultured for 2 days in a 1:1 mixed medium of HPBEC medium and Hepato-medium (plus). Subsequently, the cells were further cultured for 43 days in Hepato-medium (plus), followed by analysis at any time while subculturing the cells. 
     The results obtained are shown in  FIGS. 8B to 8E . 
     Panel B shows phase contrast images (Phase) and ALB immunostaining images of HPBECs not receiving virus infection and HPBECs transfected with 3F or 4F (at 45 days after virus infection) (note: these photographs are not of the same field of view). A group of cells encircled with a dotted line represents induced hiHepPCs (hiHepPCs induced with 3F or 4F are expressed as 3F-hiHepPCs or 4F-hiHepPCs, respectively). The graph on the right side shows the ratio of ALB-positive cells observed among HPBECs not receiving virus infection and HPBECs transfected with 3F or 4F (at 45 days after virus infection and at the third passage (P)). Using peripheral blood collected from two normal subjects, independent experiments were conducted and the respective results are shown in blue and red bars on the graph. Scale bar: 100 μm. 
     Panel C indicates that 3F-hiHepPCs and 4F-hiHepPCs induced from HPBECs are both partially AFP-positive, whereas hepatocyte-like cells differentiated from 3F-hiHepPCs and 4F-hiHepPCs express not only ALB, but also hepatocyte markers AAT, ASGPR1 and CYP3A4. Moreover, hepatocyte-like cells differentiated from 3F-hiHepPCs and 4F-hiHepPCs allow glycogen accumulation, lipid synthesis, and uptake and release of indocyanine green (ICG), as in the case of hepatocytes. Furthermore, when three-dimensionally cultured in Matri gel, 3F-hiHepPCs and 4F-hiHepPCs differentiate into cholangiocyte-like cells to thereby form spheroids having an epithelial luminal structure. DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     Panel D indicates that hepatocyte-like cells differentiated from 3F-hiHepPCs and 4F-hiHepPCs have the ability to cause albumin secretion, urea synthesis and cytochrome P450 activation. 3F-hiHepPCs (3F-hiHepPC-1, 3F-hiHepPC-2) and 4F-hiHepPCs (4F-hiHepPC-1, 4F-hiHepPC-2) prepared using peripheral blood from two normal subjects were used in the analysis. A human liver cancer-derived cell line, HepG2, was used as a positive control. Each graph shows the mean±standard deviation (n=3). 
     Panel E indicates that hepatocyte-like cells differentiated from 3F-hiHepPCs and 4F-hiHepPCs react with hepatotoxic drugs (acetaminofen, amiodarone, dicrofenac) to cause cell death. 3F-hiHepPCs (3F-hiHepPC-1, 3F-hiHepPC-2) and 4F-hiHepPCs (4F-hiHepPC-1, 4F-hiHepPC-2) prepared using peripheral blood from two normal subjects were used in the analysis. The graph shows the mean±standard deviation (n=3). *P&lt;0.05, **P&lt;0.01 
     (9) Analysis of HPBEC-Derived 4F-hiHepPCs for their Proliferation Potency and Differentiation Potency by Clone Analysis 
     Procedures for clone analysis of the cells and the results obtained are shown in  FIG. 9 . 
     In panel A, a colony of HPBEC-derived 4F-hiHepPCs encircled with a dotted line was picked up, and the cells were dissociated and then seeded at one cell per well in a 96-well culture plate, followed by single cell culture. Then, cells expanded from one cell (4F-hiHepPC clone) were analyzed. Scale bar: 100 μm. 
     Panel B shows, from the left side, a phase contrast image (Phase) of one cell (4F-hiHepPC clone) seeded in one well of the 96-well culture plate, a phase contrast image (Phase) of cells expanded from one cell, an ALB and E-CAD co-immunostaining image of the expanded cells, and a spheroid having an epithelial luminal structure, which was formed upon three-dimensional culture of cholangiocyte-like cells differentiated from the expanded cells. DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     (10) Experiments with FOXA1 and FOXA2 
       FIG. 10  indicates that FOXA3, which is one of the hiHepPC-inducing factors, can be replaced with FOXA1 or FOXA2. 
     Panel A indicates that hiHepPCs (FOXA1) induced from HUVECs with a combination of FOXA1, HNF1A and HNF6 as well as hiHepPCs (FOXA2) induced from HUVECs with a combination of FOXA2, HNF1A and HNF6 both have epithelial cell morphology, do not express a vascular endothelial cell marker, CD31, and are partially AFP-positive, as in the case of hiHepPCs induced with a combination of FOXA3, HNF1A and HNF6. On the other hand, hepatocyte-like cells differentiated from hiHepPCs (FOXA1) and hiHepPCs (FOXA2) express not only ALB, but also hepatocyte markers AAT, ASGPR1 and CYP3A4. DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     Panel B indicates that hepatocyte-like cells differentiated from HUVEC-derived hiHepPCs (FOXA1) and hiHepPCs (FOXA2) allow glycogen accumulation, lipid synthesis, and uptake and release of indocyanine green (ICG), as in the case of hepatocytes. Furthermore, when three-dimensionally cultured in Matri gel, hiHepPCs (FOXA1) and hiHepPCs (FOXA2) differentiate into cholangiocyte-like cells to thereby form spheroids having an epithelial luminal structure. Scale bar: 50 μm. 
     (11) hiHepPC Induction from Human Peripheral Blood-Derived T Cells (HPBTCs) 
     Mononuclear cells were separated from human peripheral blood and then cultured in T cell medium (a 1:1 mixed medium of HPBEC medium and Fibrolife serum-free cell culture medium supplemented with 10 ng/ml rIL-2 and 0.05 pl/cell Dynabeads HumanT-Activator CD3/CD28) to facilitate T cell expansion. 
     The results obtained are shown in  FIG. 11 . 
     The photograph in panel A shows a phase contrast image (Phase) of HPBTCs before hiHepPC induction. Scale bar: 50 μm. 
     Panel B shows phase contrast images (Phase) and ALB and E-CAD co-immunostaining images of 3F-hiHepPCs and 4F-hiHepPCs prepared from HPBTCs by transfection with a combination of F3/H1A/H6 (3F) or a combination of F3/H1A/H6+L-MYC (4F). DNA in the cells was stained with DAPI (blue). Scale bar: 50 μm. 
     The foregoing experiments indicate that when introduced into HUVECs, HPBECs or HPBTCs, a combination of FOXA3, HNF1A and HNF6 (optionally together with L-MYC) allows induction (direct reprogramming) of hiHepPCs which have proliferation potency and are capable of differentiating into hepatocyte-like cells and cholangiocyte-like cells. A summary of these experiments is shown in  FIG. 12 . 
     Using the same procedure, the inventors of the present invention have also succeeded in allowing human fibroblasts to differentiate into hepatocyte-like cells and cholangiocyte-like cells. Moreover, using the same procedure, the inventors of the present invention have also succeeded in allowing human umbilical cord blood T cells to differentiate into hepatocyte-like cells and cholangiocyte-like cells. 
     Furthermore, the inventors of the present invention have also succeeded in allowing human umbilical cord blood T cells to differentiate into hepatocyte-like cells and cholangiocyte-like cells by introducing a combination of FOXA3, HNF1A and L-MYC into the human umbilical cord blood T cells. 
     Sequence Listing Free Text 
     SEQ ID NO: 12: Xaa represents Ser or Thr (Location: 362).