Science: Instead, these so-called chimera studies will undergo an extra layer of ethical review but may ultimately be allowed to proceed. By Jocelyn Kaiser
'Although scientists who support such research welcomed the move, some were left trying to parse exactly what the draft policy will mean. It is “a step in the right direction,” says Sean Wu, a stem cell researcher at Stanford University in Palo Alto, California, who co-authored a letter to Science last year opposing the moratorium. But "we still don’t know what the outcome will be case by case,” he adds. However, some see the proposal as opening up research in some areas that had been potentially off-limits.
'At issue are experiments in which scientists introduce human pluripotent stem cells—cells that can potentially turn into any kind of tissue—into very early embryos of mice and other animals and then let the animals develop. Such experiments can be used to study human development, generate disease models, and potentially grow human organs for transplantation. But the idea of such human-animal chimeras has drawn public concern, and some scientists and ethicists worry that the experiments could produce, say, a supersmart mouse.'