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For all the political, scientific, and ethical hand-wringing that accompanied the 21 infamous embryonic stem cell lines approved in 2001 for use in federally funded research by then-President George W. Bush, the fact remains that those cells were available to the scientific community. Researchers can thank a half-dozen facilities scattered across the United States, Israel, Sweden, and Singapore for initially keeping and distributing these cells, and then—starting in 2005—the National Institutes of Health (NIH)–funded National Stem Cell Bank (NCSB).

Like their financial counterparts, cell banks are repositories, centralized facilities that, in this case, accept, validate, store, expand, and distribute scientifically useful cell lines to the larger research community. Some are public, others are private; some serve local interests, while others support the broader community. All wrestle with fundamental issues of logistics, infrastructure, and workflow.

But stem cell banks must clear additional hurdles, too, especially if they deal in human embryonic stem cells (hESCs).

“We are not talking about blood or hair,” says Rosario Isasi, an attorney and research associate at McGill University in Montreal, of hESCs; “we are talking about something all humans find a morally sensitive area.” Isasi has studied stem cell governance for six years and recently coauthored a review on the subject (1). She says the most pressing ethical concern is “provenance:” ESC donors must be able to ensure that the cells they bank, like biological “blood diamonds,” were not unethically obtained.

On the technical side, hESCs are perhaps the trickiest and most temperamental cells biologists will ever grow, the cellular embodiment of the phrase “more art than science.” “It's almost [as if]… it's dependent on the phase of the moon when you start the cells as to whether they are going to grow well or not,” says Glyn Stacey, director of the UK Stem Cell Bank. Genetically unstable and prone to differentiate, hESCs must be maintained manually (i.e., without automation), and it can take months of hands-on experience before researchers become adept at working with them.

Testing, testing, testing

The list of tests to which stem cell banks subject their hESC lines can be exhaustive. In 2009, the International Stem Cell Banking Initiative produced a “consensus guidance” document including “a recommended minimum set of criteria for release of hESC cell banks.” (2) The recommendations included 10 different assays, from ensuring that the line matches its parental line, to tests for pluripotency, cell antigen expression, and genetic stability.

At the Wisconsin International Stem Cell (WISC) Bank, which took on the NSCB's duties when the national bank 's federal funding ended in February 2010, the testing regimen includes 27 separate assays including post-thaw viability, mycoplasma testing, gene expression profiling on NimbleGen microarrays, karyotyping, comparative genome hybridization, and flow cytometry, to name a few. The cells are also screened for human and animal pathogens such as HIV, bovine viral diarrhea virus, and porcine adeno-virus.

“This testing is extensive—almost too extensive,” says Erik Forsberg, executive director of the WiCell Research Institute, which oversees the WISC Bank. Forsberg estimates that each of the NSCB lines costs nearly $60,000 to test. WISC Bank hESCs that are not part of the NSCB are tested less exhaustively, as are iPS cells, according to Forsberg: for instance, these lines are not assayed for bovine, porcine, and murine viruses. Nevertheless, these lines still cost about $3000 each to test.

Single cardiomyocyte derived from human iPS cells and labeled with antibodies showing the organization of the contractile proteins. (Click to enlarge)

Timothy Kamp says iPS cells can differ in their ability to form heart cells. (Click to enlarge)

Compare this to the treatment traditional cell lines receive. At the American Type Culture Collection (ATCC), cell lines such as NIH 3T3 are tested for viability, contamination, morphology, and species identification: intraspecies identification of human lines using short tandem repeat analysis, and interspecies identification using amplification of the cytochrome C oxidase I gene. Some cells (including the ATCC's few stem cell lines) receive extra testing, too; PC-12 cells, for instance, are tested for their ability to form neurites in response to growth factor, whereas 3T3-L1 cells are tested for their ability to form adipocytes.