If stem cell researchers were oil prospectors, it could be said that they struck a gusher last week. But to realize the potential boundless riches they now must figure out how to build refineries, pipelines and gas stations.
Biologists were electrified last week when scientists in Japan and Wisconsin reported that they could turn human skin cells into cells that behave like embryonic stem cells, able to grow indefinitely and to potentially turn into any type of tissue in the body.
The discovery, if it holds up, would decisively solve the raw material problem. It should provide an unlimited supply of stem cells without the ethically controversial embryo destruction and the restrictions on federal financing that have impeded work on human embryonic cells.
But scientists still face the challenge of taking that abundant raw material and turning it into useful medical treatments, like replacement tissue for damaged hearts and brains. And that challenge will be roughly as daunting for the new cells as it has been for the embryonic stem cells.
“Even though we have this nice new sources of cells, it doesn’t solve all the downstream problems of getting them into the body in useful form,” said James A. Thomson of the University of Wisconsin, who led one of the teams that developed the stem cell substitutes. Thomson was also the first to isolate human embryonic stem cells, about a decade ago.
Still, the new discovery should accelerate progress — if only because with the ethical issues seemingly out of the way, more scientists and money will be drawn to the field.
There are two ways that stem cells can lead to treatments for diseases. Making replacement tissues for ailing organs is the direct way. But many scientists say the biggest impact of the new cells will be on the indirect way: using the cells to learn about diseases and then applying that knowledge to develop conventional drugs.
Using the new technique, scientists could take a skin cell from a person with a certain disease and generate stem cells. Those cells could then be turned into other cells, allowing the scientists to look at neurons from a person with Alzheimer’s disease, say, or heart cells from a person with heart failure. And a pharmaceutical company might get an early read on a new Alzheimer’s drug by trying it out on the newly created neurons.
“You cannot really go to a patient and say, ‘I want to study your brain,”‘ said Dr. Lorenz Studer, who works on neural stem cells at the Memorial Sloan-Kettering Cancer Center. “For the first time it gets us access to these cells.”
Some scientists have been trying to make disease-specific embryonic cells by creating a cloned embryo of a person with the disease. But that effort requires women to undergo sometimes risky treatments to donate their eggs.
Some diseased cells, like those from a tumor biopsy, are already available for study, but those are from a person already sick. The new approach would allow scientists to watch the disease as it developed and potentially design drugs not just to treat it but to prevent it.
“This is a whole new way of thinking about how we might investigate human disease,” said Kenneth S. Zaret, program leader for cell and developmental biology at the Fox Chase Cancer Center in Philadelphia.
Just this month, Israeli scientists reported in the journal Cell Stem Cell that they had created stem cell lines from embryos donated by families with a history of fragile X syndrome, a disease that leads to mental retardation and is caused by the silencing of a particular gene. Studying the stem cells, they got a better understanding of when and how this silencing occurred.
Still, it is not yet clear how useful this new approach will be. Will a neuron from an Alzheimer’s patient have to sit in a petri dish for 70 years before it becomes diseased? Or, as is the case with some diseases, will the neurons have to interact with other types of cells?
Moreover, scientists already have many tools to figure out causes of disease — imaging systems that can peer into cells, knockout mice, genome studies. But it is not always easy to translate knowledge about a disease into a treatment. And even if it were, it still takes years of testing in animals and people before a drug can reach the market.
The gene responsible for Huntington’s disease was discovered in 1993, but there is still no cure. And the decoding of the human genome, contrary to some early expectations, has not led to a burst of new drugs, at least not yet.
When it comes to the direct approach, creating replacement cells and tissues for transplants, there are many challenges for both cells. Scientists do not envision transplanting embryonic stem cells themselves, either the real ones or the new close imitations, because they could turn into tumors inside the body.