Biological assays are typically done on cell lines. However, many of the cell lines are so different from the cell systems that are encountered in real life, or in vivo that the results can often be flawed. To be perfectly physiological, scientists use primary human cells harvested from patients are cadavers. These are great systems but very hard to procure in large amounts and also very expensive.
Human iPSC cells make modern assays possible. They are differentiated cells from patients that have been reprogrammed to become undifferentiated through the use of Yamanaka factors, OCT4, SOX2, KLF4, and MYC. These cells are representative of primary cells, can divide for a short time in culture and most importantly differentiate into any other cell in that lineage. iPSC cells from vendors like ATCC are generally have a stable karyotype, express pluripotent markers (SSEA4, Tra-1-60, Tra 1-81 and Nanog) and have differentiation potential for three germ layers – ectoderm, endoderm and mesoderm.
Few things to note:
- The iPSC cells generally have a tendency to differentiate and therefore must be maintained in specific growth conditions for them to grow and then changed to specific conditions if made to differentiate.
- Undifferentiated cells are usually maintained with a feeder layer of mitotically/growth defective mouse embryonic fibroblasts or human foreskin fibroblasts but specially adapted cells are available which can be grown by themselves. This requires the presence of a specific matrix but for imaging and other biological assays, the feeder-free cells are generally more acceptable.
ATCC supplies many cell lines, for e.g. ACS-1014 is a ATCC-DYP0530 human iPSC that are useful for the study of Parkinsons disease, asthma or depression.
iPSC cells generally grow as colonies and can be characterized microscopically with high nucleus to cytoplasmic ratio with prominent nucleoli. As they grow, it requires diligence to maintain and remove the differentiated cells that grow from that colony.
The methods to grow them are relatively standardized and scientists are using them very often in Drug Discovery.