Phenotypic changes of human cells in human-rat liver during partial hepatectomy-induced regeneration.

AIM: To examine the human hepatic parenchymal and stromal components in rat liver and the phenotypic changes of human cells in liver of human-rat chimera (HRC) generated by in utero transplantation of human cells during partial hepatectomy (PHx)-induced liver regeneration. METHODS: Human hepatic parenchymal and stromal components and phenotypic changes of human cells during liver regeneration were examined by flow cytometry, in situ hybridization and immunohistochemistry. RESULTS: ISH analysis demonstrated human Alu-positive cells in hepatic parenchyma and stroma of recipient liver. Functional human hepatocytes generated in this model potentially constituted human hepatic functional units with the presence of donor-derived human endothelial and biliary duct cells in host liver. Alpha fetoprotein (AFP)(+), CD34(+) and CD45(+) cells were observed in the chimeric liver on day 10 after PHx-induced liver regeneration and then disappeared in PHx group, but not in non-PHx group, suggesting that dynamic phenotypic changes of human cells expressing AFP, CD34 and CD45 cells may occur during the chimeric liver regeneration. Additionally, immunostaining for human proliferating cell nuclear antigen (PCNA) showed that the number of PCNA-positive cells in the chimeric liver of PHx group was markedly increased, as compared to that of control group, indicating that donor-derived human cells are actively proliferated during PHx-induced regeneration of HRC liver. CONCLUSION: HRC liver provides a tool for investigating human liver regeneration in a humanized animal model.

[Establishment of a tight tetracycline-controlled HCV-C double transgenic mouse model].

OBJECTIVE: To develop a tight tetracycline-controlled HCV-C double transgenic mouse model. METHODS: By crossbreeding of ApoE-rtTA-tTS transgenic mice with TRE-HCV-C transgenic mice, the double transgenic mice were produced in the F1 generation. The presence of HCV-C and tTS gene in the F1 generation was confirmed by PCR, followed by further identification and quantification of the transgene using Southern blot hybridization. The expression of HCV-C in the liver of the mouse model was detected immunohistochemically. RESULTS AND CONCLUSION: Two transgenic mice were obtained, which contained ApoE-rtTA-tTS and TRE-HCV-C genes in the genome. Five founders contained HCV-C gene as confirmed by PCR and Southern blot hybridization. The tight tetracycline-controlled system may facilitate further study of HCV-C gene expression and gene therapy of hepatic cellular carcinoma.

Generation of human/rat xenograft animal model for the study of human donor stem cell behaviors in vivo.

AIM: To accurately and realistically elucidate human stem cell behaviors in vivo and the fundamental mechanisms controlling human stem cell fates in vivo, which is urgently required in regenerative medicine and treatments for some human diseases, a surrogate human-rat chimera model was developed. METHODS: Human-rat chimeras were achieved by in utero transplanting low-density mononuclear cells from human umbilical cord blood into the fetal rats at 9-11 d of gestation, and subsequently, a variety of methods, including flow cytometry, PCR as well as immunohistochemical assay, were used to test the human donor contribution in the recipients. RESULTS: Of 29 live-born recipients, 19 had the presence of human CD45(+) cells in peripheral blood (PB) detected by flow cytometry, while PCR analysis on genomic DNA from 11 different adult tissues showed that 14 selected from flow cytometry-positive 19 animals possessed of donor-derived human cell engraftment in multiple tissues (i.e. liver, spleen, thymus, heart, kidney, blood, lung, muscle, gut and skin) examined at the time of tissue collection, as confirmed by detecting human beta2-microglobulin expression using immunohistochemistry. In this xenogeneic system, the engrafted donor-derived human cells persisted in multiple tissues for at least 6 mo after birth. Moreover, transplanted human donor cells underwent site-specific differentiation into CK18-positive human cells in chimeric liver and CD45-positive human cells in chimeric spleen and thymus of recipients. CONCLUSION: Taken together, these findings suggest that we successfully developed human-rat chimeras, in which xenogeneic human cells exist up to 6 mo later. This humanized small animal model, which offers an in vivo environment more closely resembling to the situations in human, provides an invaluable and effective approach for in vivo investigating human stem cell behaviors, and further in vivo examining fundamental mechanisms controlling human stem cell fates in the future. The potential for new advances in our better understanding the living biological systems in human provided by investigators in humanized animals will remain promising.

Formation of human hepatocyte-like cells with different cellular phenotypes by human umbilical cord blood-derived cells in the human-rat chimeras.

We took advantage of the proliferative and permissive environment of the developing pre-immune fetus to develop a noninjury human-rat xenograft small animal model, in which the in utero transplantation of low-density mononuclear cells (MNCs) from human umbilical cord blood (hUCB) into fetal rats at 9-11 days of gestation led to the formation of human hepatocyte-like cells (hHLCs) with different cellular phenotypes, as revealed by positive immunostaining for human-specific alpha-fetoprotein (AFP), cytokeratin 19 (CK19), cytokeratin 8 (CK8), cytokeratin 18 (CK18), and albumin (Alb), and with some animals exhibiting levels as high as 10.7% of donor-derived human cells in the recipient liver. More interestingly, donor-derived human cells stained positively for CD34 and CD45 in the liver of 2-month-old rat. Human hepatic differentiation appeared to partially follow the process of hepatic ontogeny, as evidenced by the expression of AFP gene at an early stage and albumin gene at a later stage. Human hepatocytes generated in this model retained functional properties of normal hepatocytes. In this xenogeneic system, the engrafted donor-derived human cells persisted in the recipient liver for at least 6 months after birth. Taken together, these findings suggest that the donor-derived human cells with different cellular phenotypes are found in the recipient liver and hHLCs hold biological activity. This humanized small animal model, which offers an in vivo environment more closely resembling the situations in human, provides an invaluable approach for in vivo investigating human stem cell behaviors, and further in vivo examining fundamental mechanisms controlling human stem cell fates in the future.