The first hESC was isolated in 1998, and researchers are still working to find the strengths and nuances of each type of stem cell. "All of them are interesting; all of them are important," Collins said about the three types of stem cells. The science is still too new to know for sure which types of stem cells will be best suited to which kinds of research and treatments. "Shouldn't we be pursuing the most exciting options in parallel?" he asked.
A growing body of research is pointing to crucial differences in how each of these cell types behave. "Despite our best efforts" to make iPS cells behave like hES cells, "there are still some differences," Daley said. Recent findings have shown that iPSCs tend to retain a cellular memory of the type of cell from which they have been derived. Such a recollection can be an advantage if scientists are looking to turn a reprogrammed skin cell back into skin cells, he noted. But "the fact that that memory exists, that might actually thwart your research" if it treats iPSCs as purely pluripotent as hESCs.
Collins and others argue not just for a permanent removal of the injunction to resume research with confidence, but also for an extension of the number of embryonic stem cell lines available to federally funded researchers. He noted that even the Obama administration's 75 approved stem cell lines (increased from the Bush administration's 21) are not enough for robust research in the field. In order to thoroughly investigate cures for a diverse population, cell lines from a large sampling of individuals are needed. And to study many developmental disorders, such as fragile X syndrome, researchers would be well served to be able to study a stem cell line that contained the relevant mutations. "We're just scratching the surface of the potential," Collins said of embryonic stem cells.