I last wrote an update on stem cell research in December. On that occasion I explained that the National Institutes of Health (NIH) had announced the approval of thirteen new lines of human embryonic stem cells for use in NIH-funded research under the new NIH Guidelines for Human Stem Cell Research published in July of 2009.
What has been happening in stem cell science over the past six months to a year?
For the better part of the past two years, scientific attention has focused on comparing the traits and capabilities of induced pluripotent stem cells (iPSCs) with the putative "gold standard" human embryonic stem cells (hESCs). Unlike hESCs, which are obtained by destroying live embryos, iPSCs are made directly from adult cells -- such as skin cells -- by adding a small number of factors to these cells in the laboratory. These factors remodel the mature cells and convert them into stem cells that are functionally identical to stem cells obtained from embryos. No human eggs are required and no human embryos are generated or destroyed in the process.
Several recent side-by-side comparison studies of both hES cells and iPS cells have been conducted to evaluate which types of stem cells might be best suited to which tissue-generating tasks. The most recent research has brought to light two potential hurdles for the use of iPS cells. On the one hand, because iPS cells are derived from adult -- which is to say, fully determined -- cells, they often "remember" their cell-type of origin and revert back to it. Another recent study suggested that iPS cells may actually have an entire series of genetic switches turned "off" and that this might explain why they sometimes fail to robustly generate more specific types of tissues.
Since 2007, there has been steady progress in using iPS cells as models for the study of diseases. iPS cells derived from both animals and human adults have been isolated which bear the phenotypes (structural characteristics) found in several diseases including Alzheimers, Parkinson's, Huntington's, Multiple Sclerosis, Type 1 Diabetes and Sickle Cell Anemia. Because these lines of cells exhibit disease-specific phenotypes, researchers are able to study disease mechanisms, and use them for drug screening.
Another important inroad in iPS research has been continued confirmation by independent teams of scientists that the reprogramming of adult cells can be accomplished without having recourse to viruses as vehicles for transporting the reprogramming agents into the cells. Rather than having to manipulate the genome itself by inserting viruses into the cells to be reprogrammed -- hazardous to humans -- researchers have identified ways to turn on the pluripotency genes in those cells simply by manipulating the chemical environment of the culture surrounding the cells. In 2009, researchers were also able to reduce the number of reprogramming factors necessary for accomplishing the task down to only one from the original four used by Dr. Yamanaka in 2007.
Yet, the biggest stem cell news seems to be that stem cells have largely disappeared from the news. Two factors have contributed to the dearth of headline grabbing stem cell news of late. Despite advances summarized above, the most recent progress is cloaked in such technical complexity that, understandably, journalists have been unusually challenged to make the news accessible to the average reader.
The second factor, more notably, is that stem cell fervor has waned and public frustration over the lack of tangible progress in stem cell science is growing.
To be sure, criticism of the lack of progress in the translation of stem cell research to therapies has arisen from surprising sources. In March of 2009 Dr. Bernadine Healy, director of the National Institutes of Health under the first Bush adminstration, wrote in her U.S. News & World Report column that "embryonic stem cells, once thought to hold the cure for Alzheimer's, Parkinson's and diabetes, are obsolete." An editorial last January in Investor's Business Daily angrily criticized California's Proposition 71. This was the 2004 State law which allotted $6 billion of California taxpayer money to primarily embryo-destructive stem cell research over the next decade, an initiative that rode a tremendous wave of hyped advocacy for embryonic stem cell research. "Five years after a budget-busting $3 billion was allocated to embryonic stem cell research," wrote the editors, "there have been no cures, no therapies and little progress." Writing earlier this month in the Los Angeles Times, one science reporter felt it was time to offer her own mea culpa: don't blame the scientists for hyping the potential of hESC research; blame us, the reporters.