A novel strategy for longer term differentiation of human embryonic tissues from pluripotent stem cells and simulations of teratoma formation in vitro

Understanding the mechanisms that occur during human tissue development is a major challenge in the fields of developmental biology, stem cell biology and regenerative medicine. Currently, various methods have been employed to study this process; however, each of them has its unique advantages and limitations. Working with human embryos represents a more physiologically option; nevertheless, ethical concerns arise due to its nature. Animal models are a popular method to elucidate signalling pathways and processes. However, animal studies are not always representative of human events. In vitro models employing human pluripotent stem cells have become an important surrogate for studying human embryogenesis and tissue differentiation. Nevertheless, these cell culture systems do not always provide the appropriate microenvironmental cues in a spatiotemporal manner to enable hPSCs to differentiate into complex 3D tissue structures. Having a better understanding of this topic will allow for the development of more robust differentiation protocols, the creation of cell therapies to treat diseases, and the study and characterisation of human pluripotent stem cells. In this project, a two-step culture method which combines hPSC-derived embryoid bodies (EBs) with porous scaffold was established to enhance their viability and extend their differentiation. This approach enabled the formation of tissue-like structures of increasing complexity over time. Furthermore, manipulating their differentiation through physical and chemical cues towards specific germ layers was possible and successful. The introduction of co-culture and dynamic systems impacted importantly the differentiation and morphology of the tissue structures formed. Human EB derived tissues were highly reminiscent of xenograft teratoma samples from the same human pluripotent stem cell population. This confirms the similarity and complexity of the in vitro tissue-like structures to the in vivo samples. The novel in vitro model developed in this study offers a controllable and reproducible method to form complex tissue structures in vitro for studying human tissue development, as well an animal-free alternative to the teratoma assay.