Stem cells are the roots from which different cell lineages arise, and they exist in multiple forms. Embryonic stem cells (ESCs) are pluripotent, meaning they can differentiate into every cell type in the body. Adult stem cells are more restricted; they can differentiate only into specific lineages, such as neurons or blood cells. Inducible pluripotent stem cells (iPSCs) are ESC-like cells that are created from somatic (differentiated) cells using specific transcription factors or chemicals. Researchers studying stem cells have a range of tools to aid their work, including dedicated culture reagents, reprogramming kits, and characterization systems.
Culture Reagents:
Like all eukaryotic cells, stem cells require special nutrients – media and growth factors -- to thrive in culture. But stem cells present unique challenges. Some cells require non-standard cell culture reagents, such as feeder cell layers, conditioned media, or growth matrices. Sometimes, researchers want the cells to remain in a stem-like state, and other times they want them to differentiate. Different media and sera formulations are available for all these different types of culture, and for different classes of stem cell (that is, neural stem cell medium is not the same as ESC medium).
Those with an eye towards translational applications may want products that are free of animal-derived proteins (often called “xeno(biotic)-free”), or that are fully “defined” (meaning they contain no variable “black box” ingredients, such as serum). In particular, ESCs traditionally are cultured on mouse embryonic fibroblasts (MEF), and those planning to move their research to the clinic may be interested in feeder-free culture systems that are more likely to pass regulatory muster.
Characterization:
Once stem cells have been created or isolated, researchers can assess their “stemness” using differentiation assays, monitoring gene expression, or protein staining (eg, in flow cytometry or immunohistochemistry assays). An old-school approach to monitoring pluripotent stem cell plasticity (e.g. ESCs and iPSCs) is the teratoma assay, in which cells are injected into an animal to form a tumor, which should contain cells from all three germ layers.
iPSC Reprogramming:
iPSCs are created by reprogramming somatic cells via the expression of (usually four) transcription factors, and companies have developed multiple approaches to deliver them, including plasmid, viral, and mRNA-based expression systems. Alternatively, researchers can achieve the same effect using specific chemicals (though in general, at least one protein factor is required).