Blood drawn with a simple needle stick can be coaxed into producing stem cells that may have the ability to form any type of tissue in the body, three independent papers report in the July 2 Cell Stem Cell. The new technique will allow scientists to tap a large, readily available source of personalized stem cells.
Because taking blood is safe, fast and efficient compared to current stem cell harvesting methods, some of which include biopsies and pretreatments with drugs, researchers hope that blood-derived stem cells could one day be used to study and treat diseases — though major safety hurdles remain.
The findings “represent a huge and important progression in the field,” stem cell biologist Shinya Yamanaka of Kyoto University in Japan and the Gladstone Institute of Cardiovascular Disease in San Francisco, Calif., writes in a commentary appearing in the same issue of the journal.
Three research groups used similar methods to prod certain immune cells in human blood to become induced pluripotent stem cells. Because they are reprogrammed adult cells, these stem cells share many of the same regenerative abilities as true embryonic stem cells but may not have as much versatility in the kinds of mature cells they can become. But induced pluripotent cells are harvested from adults and so don’t face the same ethical mires posed by embryo-derived stem cells. And as techniques for manipulating induced pluripotent cells improve, some researchers think they may be just as useful.
The new studies accomplished the reprogramming feat by using viruses to deliver a four-gene cocktail that reverts the cells to a naïve state in which any developmental path is open. In theory at least, these induced pluripotent stem cells could go on to form neurons in the brain, muscle cells in the leg or beating heart cells.
Scientists’ manipulations turned the stem cells in the new studies into several types of mature blood cells, including infection-fighting T cells. What’s more, all the groups showed that a batch of the stem cells implanted into mice developed into the three main types of progenitor cells found in human embryos. In embryos, these progenitor cells give rise to different tissues.
More research is needed to determine whether these cells can be further coaxed to form fully functional tissue, says Rudolf Jaenisch of MIT and the Whitehead Institute for Biomedical Research in Cambridge, Mass., who led one of the studies. The concern is that if these cells retain traces of memory from their previous lives as blood cells, they may not be good at forming other tissue types.
Past studies have induced other kinds of mature cells to form stem cells. The most common source has been adult skin cells called fibroblasts, which have been manipulated into stem cells as well as directly into neurons (SN: 2/27/10, p. 5). But harvesting fibroblasts is harder than drawing blood, requiring surgery and sutures. What’s more, inducing fibroblasts to form stem cells can take about a month in the lab, during which mutations can accumulate. The new blood cell techniques can be completed in a few days.
Stanford University stem cell biologist Marius Wernig points out that the new method is still less efficient than the fibroblast technique. “But with improving technology, this cell type could very well replace the skin fibroblasts currently mostly used to generate induced pluripotent stem cells from patients,” Wernig says.
Researchers are still a long way off from transplanting such stem cells or their mature offspring into people safely. The viruses used to deliver genes into the cells may have unintended consequences, and the cells’ long-term behavior is still unknown.
But even if the cells won’t be put directly into patients, Jaenisch says that the new method “opens up access to enormous resources of collected cells from patients” that can be used to study diseases. For example, lab experiments with cells from these collections might be used to study why motor neurons from people with amyotrophic lateral sclerosis die, or how healthy liver cells respond to a promising but potentially toxic drug.