Why Do We Need Chimeric Monkeys?

Their birth shows that much more needs to be done before results on stem cells from mice can be applied to humans

Homer wrote that a chimera is ‘a thing of immortal make, not human, lion-fronted and snake behind, a goat in the middle, and snorting out the breath of the terrible flame of bright fire.’ In genetics the term is used more prosaically but still refers to an object of wonder, a creature formed from the fusion of two or more embryos that develop into a healthy organism. A chimera such as this, then, has cells from at least four parents. Sometimes the process can occur naturally when two embryos in a single womb fuse together early on, and the phenomenon has even been reported in humans. 

Which is why, when the news that scientists had produced the world’s first chimeric monkeys with cells from six parents made headlines earlier this week, it was not because the phenomenon was unknown or because scientists were involved in some experiments that subscribe to Hollywood stereotypes, but because the chimeras so produced will help us get a clearer understanding of how cells develop and differentiate.  Homer wrote that a chimera is ‘a thing of immortal make, not human, lion-fronted and snake behind, a goat in the middle, and snorting out the breath of the terrible flame of bright fire.’ In genetics the term is used more prosaically but still refers to an object of wonder, a creature formed from the fusion of two or more embryos that develop into a healthy organism. A chimera such as this, then, has cells from at least four parents. Sometimes the process can occur naturally when two embryos in a single womb fuse together early on, and the phenomenon has even been reported in humans. 

Which is why, when the news that scientists had produced the world’s first chimeric monkeys with cells from six parents made headlines earlier this week, it was not because the phenomenon was unknown or because scientists were involved in some experiments that subscribe to Hollywood stereotypes, but because the chimeras so produced will help us get a clearer understanding of how cells develop and differentiate.  Scientists have for several decades been able to produce chimeric mice, but it had been difficult so far to produce chimeric primates, animals which resemble us far more than mice do. To produce such monkeys, Shoukhrat Mitalipov of the Oregon National Primate Research Center extracted individual cells from up to six very early embryos, each containing just four cells, and then mixed these together in a single, new embryo. While chimeric mice could be produced using embryonic stem cells (from a later stage of embryonic development), the same process does not seem to work with monkeys. The failure suggests that what is possible using these cells in mice may not extend to primates and hence humans. 

“We cannot model everything in the mouse,” Mitalipov declared. “If we want to move stem cell therapies from the lab to clinics and from the mouse to humans, we need to understand what these primate cells can and can’t do. We need to study them in humans, including human embryos.” He emphasised, however, that there is no practical need for (or intention by) anyone to produce human chimeras. To produce such monkeys, Shoukhrat Mitalipov of the Oregon National Primate Research Center extracted individual cells from up to six very early embryos, each containing just four cells, and then mixed these together in a single, new embryo. While chimeric mice could be produced using embryonic stem cells (from a later stage of embryonic development), the same process does not seem to work with monkeys. The failure suggests that what is possible using these cells in mice may not extend to primates and hence humans. 

“We cannot model everything in the mouse,” Mitalipov declared. “If we want to move stem cell therapies from the lab to clinics and from the mouse to humans, we need to understand what these primate cells can and can’t do. We need to study them in humans, including human embryos.” He emphasised, however, that there is no practical need for (or intention by) anyone to produce human chimeras.

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