Patient-ready iPS cells?

For the first time, human skin cells have been reprogrammed without using DNA, according to a linkurl:study;http://www.cell.com/cell-stem-cell/fulltext/S1934-5909(09)00214-8 published online today (May 28) in __Cell Stem Cell__. Although further optimization is still required, this new technique, which involves only four genetically engineered proteins, could yield the first clinic-ready human induced pluripotent stem (iPS) cells.

Human iPS cells generated
by direct protein delivery
Image: Kwang-Soo Kim

"This is the first safe method for generating patient-specific stem cells," linkurl:Robert Lanza,;http://www.robertlanza.com/ chief scientific officer of Advanced Cell Technology (ACT), who coauthored the study, told __The Scientist__. "We now have a way to actually go into a patient without the problem of immune rejection." linkurl:Last month,;http://www.the-scientist.com/blog/display/55657/ a team led by the Scripps Research Institute's linkurl:Sheng Ding;http://www.scripps.edu/chem/ding/ reported the first DNA-free method for obtaining iPS cells, although his team only published experiments using mouse cells. Ding and his colleagues started with the four most commonly used reprogramming factors -- the same ones used by Kyoto University's linkurl:Shinya Yamanaka;http://www.med.kyoto-u.ac.jp/E/grad_school/introduction/1517/ to create the world's first iPS cells in 2006. The researchers then tacked on poly-arginine "tails" onto each of the proteins to help them penetrate the cell, purified the proteins from __E. coli__, and reprogrammed mouse fibroblasts with the four recombinant proteins in combination with a small molecule called linkurl:valproic acid;http://en.wikipedia.org/wiki/Valproic_acid (VPA). Now, linkurl:Kwang-Soo Kim,;http://www.mclean.harvard.edu/about/bios/detail.php?username=kskim a stem cell researcher at Harvard Medical School and Korea's CHA University, in collaboration with Lanza, demonstrate that a very similar -- but, they argue, safer -- approach also works in human cells. Their technique doesn't require any chemical additives, which the researchers say could have mutagenic side-effects. Ding, however, called this claim "scientifically ignorant," noting that VPA, a histone deacetylase inhibitor, is commonly used clinically to treat a range of neurological disorders, and all epigenetic modifiers -- regardless of whether they're proteins or small molecules -- pose similar risks. Kim's team independently came up with the idea to fuse arginine repeats onto the same four reprogramming factors, but instead of producing the proteins in bacteria, the researchers cultured four human cell lines to express each of the recombinant proteins. They then repeatedly bathed human skin cells with combined total extracts from the cell lines and over the course of eight weeks obtained fully reprogrammed stem cells without the addition of any other chemicals. The iPS cells passed the standard barrage of tests for pluripotency, and microarray analyses demonstrated that these cells exhibited similar gene expression profiles to embryonic stem cells. The new study "validated this protein-based approach for reprogramming," Ding told __The Scientist__. "Now people will be more convinced that this [technique] is the way to go," and it should stimulate biochemists and protein specialists to improve the methodology, he added. But he said that using whole cell extracts instead of purified proteins is "somewhat going backwards." Kim admitted that the method, which was about 10 times less efficient than virus-based reprogramming, still requires some optimization, but by omitting any foreign chemicals, his approach is simpler and potentially more efficient, he argued. The new technique didn't require any additional chemical tinkering because mammalian-cultured proteins are in a "biologically much more active form" than proteins derived from __E. coli__, Kim said. Once all the kinks are worked out and "once we have the purified proteins, we have a perfectly controllable and inducible system," he added. Unlike previous approaches to reprogramming human cells, which either permanently or temporarily modified the cells' DNA, this new protein-based method never fiddles with the genome, so it should be near-ready for clinical applications, said Lanza, adding that the researchers hope to file at least one investigational new drug application with the US Food and Drug Administration by mid- to late-2010. Stem Cell & Regenerative Medicine International, a joint venture linkurl:launched last December;http://www.advancedcell.com/press-release/joint-venture-between-cha-biotech-and-advanced-cell-technology-to-be-called-stem-cell--regenerative-medicine-international between Worcester, Mass.-based ACT and Soeul-based CHA Biotech, plans to turn the iPS cells into blood cells to treat hematopoietic and vascular diseases. ACT, meanwhile, has its sights on treating degenerative retinal disorders using the technology, he said. They might be jumping the gun, however. "This [protein-based] method is certainly much safer, but we still don't know if this iPS reprogramming process will cause subtle epigenetic as well as genetic abnormalities," Ding said.
**__Related stories:__***linkurl:Purely protein pluripotency;http://www.the-scientist.com/blog/display/55657/
[23rd April 2009]*linkurl:Pluripotency via plasmids;http://www.the-scientist.com/blog/display/55548/
[26th March 2009]*linkurl:Piggybacking to pluripotency;http://www.the-scientist.com/blog/display/55486/
[1st March 2009]