1). R788 clinical trial As reported previously after transplantation of embryonic (ED28) porcine liver fragments,[7] the engrafted cell clusters formed chimeric vascular connections and exhibited

marked proliferation for 2 months in a setting where host liver cells were not induced to divide. Fluorescence-activated cell sorting analysis revealed that approximately 4% of the cells stained for both AFP and albumin, whereas approximately 33% developed a more mature phenotype, staining for albumin only. AFP and albumin were undetectable in 65% of cells, but whether these cells represented iPSCs that failed to differentiate or were HUVECs or stromal cells was not defined. The engrafted cell clusters secreted human albumin and alpha-1-antitrypsin in the peripheral blood at levels of 1-2 μg/mL, exhibited human CYP activity, and improved the survival of mice in a toxic hepatic injury model. The level of human albumin in the blood of transplanted animals was consistent and 5- to 10-fold greater than that described in all but one previously published study.[8] Though dissociation of single hepatocytes from the extracellular matrix can lead to loss of function and reduced AZD0530 survival, the investigators, by generating cell clusters incorporating endothelial and mesenchymal cells, induced the iPS-derived cells to mature toward a hepatocyte

phenotype and to engraft, expand, and function in vivo after transplantation aminophylline at extrahepatic sites. Although the findings are encouraging, it is perhaps premature to characterize

the engrafted clusters as liver organoids. First, the studies of gene expression and hepatic function, although extensive, did not unequivocally demonstrate that the human iPSC-derived hepatocytes were differentiated any further toward mature hepatocytes than what has been previously published. Second, because the engrafted cell clusters did not develop cholangiocytes or biliary structures (Fig. 2), they did not truly generate authentic liver tissue, as do embryonic porcine implants, which initially contain no biliary structures, but develop mature biliary cells after transplantation in immune-deficient mice.[9] Because embryonic porcine liver organogenesis is critically dependent on gestational age at the time of transplantation in immune-deficient mice, it is possible that the iPSC-derived hepatic endoderm or the supporting endothelial and mesenchymal cells were insufficiently capable of providing the signals necessary for complete liver development. It is known that extensive development of embryonic tissue is possible after transplantation, in some circumstances, because peritoneal implantation of embryonic kidney tissue results in the formation of functioning nephrons as well as a collecting system that can prolong the survival of anephric rats.