Human SeruM Albumin Microspheres Approximate Initial Organ-Specific Biodistributions of Transplanted Hepatocytes and Are Effective Cell Surrogates for Safety Studies

Adult human liver mesenchymal stem/progenitor cells participate in mouse liver regeneration after hepatectomy

The advances in stem cell science have promoted research on their use in liver regenerative medicine. Beyond the demonstration of their ability to display metabolic functions in vitro, candidate cells should demonstrate achievable in situ differentiation and ability to participate to liver repopulation. In this work, we studied the in vivo behavior of adult liver mesenchymal stem/progenitor cells (ADHLSCs) after transplantation into immunodeficient mice. The kinetics of engraftment and in situ hepatogenic differentiation were analyzed. Response of transplanted ADHLSCs to regenerative stimulus was also evaluated. Nondifferentiated ADHLSCs were intrasplenically transplanted into SCID mice. Efficiency of transplantation was evaluated at the level of engraftment and in situ differentiation using immunohistochemistry, in situ hybridization, and RT-PCR. After bromodeoxyuridine (BrdU) implantation, proliferation of transplanted ADHLSCs in response to 20% hepatectomy was assessed using immunohistochemistry. We demonstrated that ADHLSC engraftment in the SCID mouse liver was low but remained stable up to 60 days posttransplantation, when albumin (ALB) immunopositive ADHLSCs were still detected and organized as clusters. Coexpression of ornithine transcarbamylase (OTC) demonstrated ADHLSC in situ differentiation mostly near the hepatic portal vein. After 20% hepatectomy on 1 month transplanted mice, the percentage of BrdU and human ALB immunopositive ADHLSCs increased from 3 to 28 days post-BrdU implantation to reach 31.3 ± 5.4% of the total analyzed human cells. In the current study, we demonstrate that transplanted ADHLSCs are able to differentiate in the non preconditioned SCID mouse liver mainly in the periportal area. In response to partial hepatectomy, integrated ADHLSCs proliferate and participate to recipient mouse liver regeneration.

Enzymatically labeled chromosomal probes for in situ identification of human cells in xenogeneic transplant models

Analysis of the viability, differentiation, clonogenicity and function of human stem/progenitor cells requires suitable xenograft models. However, the identification of transplanted cells has been generally difficult. Fluorescence in situ hybridization is a tedious method for analyzing tissues, and localization of transplanted cells with X or Y chromosome probes is limited by the sparse signals produced. Therefore, we examined the possibility of generating either pan-nuclear signals with a total human DNA probe or multiple nuclear signals with a pan-centromeric human DNA probe. The probes were labeled with digoxigenin to make reaction products visible by light microscopy and to allow the use of immunohistochemistry methods incorporating various color schemes to demonstrate specific properties of transplanted cells. The ability to localize all types of nucleated human cells with such probes will facilitate studies of stem cell biology and cell and gene therapy, as well as the development of new animal models.

Integration and proliferation of transplanted cells in hepatic parenchyma following D-galactosamine-induced acute injury in F344 rats

To determine whether liver repopulation with cell transplantation could be of therapeutic value in acute hepatic failure, it is necessary to establish the fate of transplanted hepatocytes. This study used dipeptidyl peptidase IV-deficient F344 rats as recipients to analyse the engraftment and proliferation of transplanted hepatocytes. Syngeneic hepatocytes were transplanted intrasplenically 24-30 h after induction of liver injury by D-galactosamine (GalN). Portosystemic shunting was analysed with 99m-Tc-labelled albumin microspheres. GalN-treated rats showed characteristic hepatic necrosis, inflammation, gamma-glutamyl transpeptidase activation, and regenerative activity, without increased portosystemic shunting (>99% 99m-Tc activity was in the liver in normal and GalN-treated rats). Transplanted cells entered hepatic sinusoids promptly and were observed in liver plates at 48 h. The number of transplanted cells increased in GalN-treated rats by approximately seven-fold (range two- to 12-fold), along with evidence for DNA synthesis between 3 and 14 days after cell transplantation and greater prevalence of larger transplanted cell clusters. These findings indicate that the liver can be safely repopulated in animals with acute liver failure, although the time required for regenesis of plasma membrane structures and proliferation in transplanted hepatocytes will need to be considered in developing therapeutic strategies.