Stem-cell culture moves to the third dimension

Abstract

Stem-cell researcher Toshiro Sato places a culture dish under the microscope in his laboratory at Keio University School of Medicine in Tokyo. What he sees is not a sheet of cells, but something more complex — delicate spheres of tissue that are barely visible to the naked eye. These are organoids, 3D structures that develop when stem cells are given the proper environmental conditions to differentiate and arrange themselves into forms with properties similar to those of particular tissues or organs. Organoids can be derived from pluripotent stem cells, which have the potential to form any body tissue type — be it muscle, skin, gut or brain. When they are grown in the appropriate conditions, for example with specific growth factors, the stem cells self-organize into structures in which the different cell types are arranged similarly to the in vivo tissue. By contrast, organs-on-chips (OOCs) are generally made by arranging stem cells and cells that have already differentiated into the required cell types on a microfabricated device in positions and structures appropriate for the planned experiments. The difference between organoids and OOCs, says developmental biologist Madeline Lancaster at the MRC Laboratory of Molecular Biology in Cambridge, UK, “is self-organization versus construction” (see ‘Models in a nutshell’ box). Named ‘Method of the Year’ by Nature Methods last year, organoids are increasingly being used to study both normal development and the progression of diseases. Sato’s group, for instance, uses them to study the early stages of tumour formation. His team uses the CRISPR gene-editing technique to change the sequence of the DNA in the stem cells, and then see how that affects the development of the organoid. “It’s a way to see causality,” Sato says, “by testing if specific mutations recapitulate cancer development.” Both organoids and OOCs also have potential in assessing the efficacy and safety of drugs, chemicals and cosmetics, with possible applications in regenerative medicine. For instance, a challenge in randomized clinical trials is how to compare the effect of treatments because the genetics and life history of the participants can affect how they react, notes Donald Ingber, founding director of the Wyss Institute for Biologically Inspired Engineering at Harvard University in Cambridge, Massachusetts. OOCs and organoids derived from patients’ cells can eliminate these confounding effects by creating intervention and control populations that have identical genetics and clinical history. However, the technologies are not without their challenges, such as how to scale up production to meet growing basic and applied research demand while maintaining the reproducibility and fidelity of the structure to the in vivo organs they represent. Organs in a dish The pluripotent stem cells that researchers use to create organoids and OOCs include both naturally occurring embryonic stem (ES) cells and cells that are derived from differentiated cells such as fibroblasts and manipulated to revive their pluripotency, known as induced pluripotent stem cells (iPS cells). Lancaster, who uses organoids to study basic brain development and identify factors contributing to complex conditions such as autism and schizophrenia, says she uses ES cells for developing and testing protocols and new models. Models in a nutshell Organoids and organs-on-chips (OOCs) have applications in drug development, cosmetics testing, toxicology and personalized medicine. Here are some of their strengths and weaknesses. Organoids Origin: Generated from self-organizing embryonic stem cells (ES cells), induced pluripotent stem cells (iPS cells) or adult stem cells. Key strengths: Studies of developmental processes as single cells give rise to organs, including in disease. Key challenges: Increasing the reproducibility for applications that need a consistent outcome, such as drug testing, and finding ways to introduce or mimic vascularity. Learn more: Cell Press webinar ‘Organoids and beyond — 3D tissue in a dish’ (see go.nature.com/2jiumvb) OOCs Tissue origin: Typically, cell lines or differentiated cells isolated from a person, but can also be derived from stem cells. Key strengths: Reproducibility and consistency. Can incorporate biomechanical features. Key challenges: Using iPS cells and stem cells from patients rather than cell lines, to increase applicability to personalized medicine. Learn more: National Academies of Sciences, Engineering, and Medicine webinar ‘The NIH Microphysiological Systems Program’ (see go.nature.com/2hm3bch)