Scientists have long complained that the Bush administration's stem cell funding policy restricted their research to only a handful of human embryonic stem cell lines. A study published Friday in Nature Biotechnology confirms that the majority of lab experiments over the last decade has indeed focused on two or three cell lines -- the result of choices made by both President George W. Bush and the scientists themselves.
Researchers from Stanford University, the Mayo Clinic and the University of Michigan analyzed all 1,217 requests for stem cell lines that were made to the National Stem Cell Bank between 1999 and 2008. What they found was "far less diversity of materials than most believe," they wrote.
Though the Bush administration said the bank maintained 21 cell lines eligible for funding from the National Institutes of Health, three of those lines have never been available to researchers, and a fourth line just became usable this year, the researchers said.
Of the remaining 17 cell lines, more than three-quarters of all requests from scientists involved just two. The H1 line accounted for 39% of the orders, and the H9 line made up an additional 38%, according to records from the stem cell bank. The only other line that has been requested more than 100 times is H7. Nine of the lines haven't even made it into the double digits. It's not clear if only those three lines were easy to work with, or if they were favored for other reasons.
The researchers also examined requests for human embryonic stem cell lines developed and maintained by the Harvard Stem Cell Institute. Harvard offers 28 cell lines, though the researchers focused on the 17 that have been available since 2004. (The others were too new to have been requested very often, they reasoned.) None of the Harvard lines could be used in NIH-funded experiments until the Obama administration's more expansive funding policy took effect last month.
There was considerably more diversity in Harvard's 946 shipments, according to the study. The two most popular cell lines accounted for only 25% of requests.
The researchers also scanned 534 stem cell studies published in peer-reviewed journals between 1999 and 2008. The H9 cell line appeared in 83% of studies, while the H1 line was in 61% and H7 was in 24%. Less than 36% of the publications included any of the other NIH lines.
The Harvard lines showed up in fewer than 3% of the studies, according to the analysis.
The researchers speculated that scientists using federal funds might have been more conservative about their experiments and thus tended to cluster around the most popular NIH-approved lines. The pattern might also reflect a "first-mover advantage," because laboratories seeking to replicate previous experiments would strive to use the same materials.
"The lasting legacy of Bush-era policies," the researchers concluded, is a human embryonic stem cell field "that relies very heavily on a small number of well-used but less than ideal cell lines."