Tissue Engineering 3D iPSC-derived human hepatic organoids

Liver cells maintained on conventional flat plastic dishes (in 2D) rapidly lose their function. This is as a result of taking the liver cells out of their normal 3D environment, which is optimal for their function. In addition due to limited availability of healthy human liver tissue, which is earmarked for transplantation, current cell models used for drug development / toxicity testing include rodent hepatocytes or human cancer cell lines grown on 2D flat plastic dishes. These models do not reflect the functions of a normal liver and this is one reason why many drugs fail at the clinical trial stage. Therefore we need alternative approaches. The emerging field of micro-scale tissue engineering investigates incorporating precise control over the cells environment (3D). We have now produced a proof of concept for 3D liver like tissue, which exhibits enhanced levels of function as compared to the above cell models. In addition we have overcome a major hurdle of supply by using human pluripotent stem cells that provide a limitless supply of material and can be effectively coaxed into livers cells by exposure to a cocktail of chemicals. To generate 3D liver like tissue we have developed hydrogels which are water based gels, to which we add cells to make a "bioink". This bioink provides the necessary 3D support, which can be moulded into different shapes or printed using a 3D bioprinter. This provides the 3D microenvironment for the cells to self assemble into a liver like conformation. In addition we have added additional cell types, the reasoning for this is that the liver in the human body is made of many different cell types, which are required for its function and support. By adding additional cell types we have demonstrated enhanced function when compared to conventional flat 2D cell cultures. We have now improved the current state of the art by refining this approach to generate liver tissue that closely resemble human liver.

Current cell culture models used to interrogate disease and toxicology etc., rely on conventional 2D static culture systems. In many cases immortalized or tumor derived cell lines are used, these have lost many of the characteristics of the cell type the y are meant to model due to extensive time in culture, which leads to particular homogeneous populations of cells being selected. A more relevant model system is based on primary cells, which have not been exposed to the selective pressures of convention al cell systems of above. But these systems have their innate inadequacies, for example freshly isolated 2D primary hepatocyte monocultures on plastic or collagen rapidly lose polarity and differentiated function. This is a consequence of lose their surr ounding 3D micro-environment, which comprises the extracellular matrix (ECM) and interactions with other crucial non-parenchymal cell types. This phenomenon is not unique to hepatocytes, it has been observed in a number of other primary culture systems in cluding cardiac and kidney. Therefore using advanced tissue engineering (TE) enabling technologies we will arrange stem cell derived progeny in 3-dimensional space to closely resemble, in physiology and composition, for example a functional liver sinusoid . The creation of this, 3D liver organoid, will be developed as to be amenable for high throughput studies on liver function. The physiologically relevant, 3D human organotypic models; offer a considerable advance in medical research and an important alte rnative to animal studies. Additionally by developing in vitro relevant 3D tissue models that recapitulate their native counterparts, could then be translated to either the clinical setting and/ or towards the pharmaceutical arena with 3D organotypic live r models to interrogate disease such as metabolic disorders and infectious agents such as hepatitis. These platforms could be utilised to investigate toxicology and help reduce drug attrition rates.