Pre-clinical study of hepatocyte transplantation using human embryonic stem cell-derived hepatocytes

在英国，肝病是第五大最常见的死亡原因，而且还在急剧上升。全肝移植的实用性有限，不能满足临床需要。其他选择包括向肝病患者输注肝细胞悬浮液，但这又一次受到肝脏缺乏的限制。因此，显然有必要扩大功能性肝细胞以用于临床应用，如肝细胞移植。在与Geron的合作下，我们已经开发出高效的方法来引导人类胚胎干细胞沿着肝细胞谱系下行，从而获得90%的纯度。在这些细胞可以用于临床之前，有两个主要的问题需要克服。(1)这些细胞在肝脏内的输送需要改进，因为目前我们只能输送少量细胞。(2)有人担心胚胎干细胞在移植后会形成肿瘤，我们会找出控制输入的肝细胞进入肝脏的分子，并增强其活性，从而增加进入肝脏的细胞数目。首先，我们将在一个复杂的多细胞培养模型中对肝细胞进行这一操作，该模型模拟了活器官中发生的事情。在确定了在组织培养中哪些分子在改善肝细胞的植入方面最重要之后，我们将继续进行小鼠模型，在那里我们可以测试刺激这些分子在活体中的效果。值得注意的是，我们将使用一只患有代谢性肝脏疾病的小鼠，这意味着除了能够量化移植到小鼠肝脏内的人类肝细胞的数量外，我们还可以看到它们对代谢缺陷的影响。这是及时的，因为这种细胞的第一次临床研究很可能发生在代谢性肝病患者身上。通过净化我们输注的肝细胞群体以及限制给药途径，我们打算证明我们可以完全消除肿瘤发展的风险。然而，有一个理论上的风险，即将人类胚胎干细胞移植到小鼠体内不能充分评估肿瘤发展的风险。因此，作为一种安全措施，我们还将进行将小鼠胚胎干细胞注入小鼠体内的实验，以排除这种可能性。

In the UK liver disease is the fifth most common cause of death, and it is rising dramatically. Whole organ liver transplantation is limited in its availability, it is not capable of meeting the clinical need. Other options include infusing suspensions of liver cells into patients with liver disease, but this is again limited by a lack of livers. Thus, there is a clear need to expand functional liver cells for clinical applications such as liver cell transplantation. In collaboration with Geron, we have generated highly efficient methods to direct human embryonic stem cells down the liver cell lineage resulting in 90% purity. There are two main issues to be overcome before these cells can be used clinically. (1) The delivery of these cells within the liver needs to be improved as at present we can only deliver small numbers of cells. (2) There are concerns that cells derived from embryonic stem cells can form tumours after transplantation.We will identify the molecules which control the entry of infused liver cells into the liver, and augment their activity, thus improving the number of cells entering. Initially we will do this with liver cells in a complex multi-cellular culture model which mimics what happens in a living organ. Having identified which molecules are most important in improving the engraftment of liver cells in tissue culture we will then proceed to a mouse model where we can test the effects of stimulating these molecules in a living organism. Of note we will use a mouse which has a metabolic liver disorder, which means that as well as being able to quantify the number of human liver cells which have engrafted within the mouse liver we can also see what impact they have had on the metabolic defect. This is timely, as it is likely that the first clinical studies with such cells will occur in patients with metabolic liver disease.By purifying the population of liver cells we infuse as well as limiting the route of administration we intend to demonstrate that we can completely abrogate the risk of tumour development. There is however a theoretical risk that transplanting human embryonic stem liver cells into a mouse will not adequately assess the risk of tumour development. As a fail-safe therefore we will also perform experiments in which we infuse mouse embryonic stem liver cells into the mouse to exclude this possibility.