US researchers said they have created the world’s first mixed-embryo monkeys by merging cells from up to six different embryos, in what could be a big advance for medical research.
Until now, rodents have been the primary creatures used to make chimeras, a lab animal produced by combining two or more fertilised eggs or early embryos together.
Scientists have long been able to create “knock-out” mice with certain genes deleted in order to study a host of ailments and remedies, including obesity, heart disease, anxiety, diabetes and Parkinson’s disease.
Attempts to create melded primates have failed in the past, but scientists in the western state of Oregon succeeded by altering the method used to make mice.
The breakthrough came when they mixed cells together from very early stage rhesus monkey embryos when they are able to give rise to a whole animal as well as the placenta and other life-sustaining tissues.
“Knock-out” mice are typically made by introducing embryonic stem cells that have been cultured in a lab dish into a mouse embryo, but that method failed in monkeys.
Primate embryos do not allow cultured embryonic stem cells to become integrated, as mice do.
Combining primate cells apparently requires more potent, early stage cells from a living embryo, said lead researcher Shoukhrat Mitalipov of the Oregon National Primate Research Centre at Oregon Health and Science University.
The experiment produced three healthy male rhesus monkeys they named Roku, Hex and Chimero, with gene traits from all of the separate embryos used to meld them.
“The cells never fuse, but they stay together and work together to form tissues and organs,” said Dr Mitalipov. “The possibilities for science are enormous.”
But the British Union for the Abolition of Vivisection (BUAV) called the research “deeply disturbing”.
Jarrod Bailey, the organisation’s scientific consultant, said: “Using such highly sentient animals in this research raises enormous ethical concerns and imposes a heavy welfare burden, resulting in severe suffering to many animals.
“As few genetically modified animals show the ‘desired’ characteristics, many will be killed even before any research can take place, while others will die of severe and unrelated malformations caused by the genetic modifications.
“The monkeys who do exhibit characteristics of ‘interest’ are destined to suffer greatly by their very nature, and via the experiments to which they will be subjected.”
The research is published online ahead of the release of the January 20 issue of the journal Cell.
Scientists use rhesus monkeys to study HIV/AIDS drugs, research vaccines for rabies, smallpox and polio, and to study potential uses for embryonic stem cells. They have also been launched into space on test missions by the US and Russia.
“We cannot model everything in the mouse,” Dr Mitalipov said. “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.”
Researchers at the same Oregon facility in 2000 created the first genetically modified monkey, ANDi, who was carrying an extra bit of DNA that was inserted while he was an unfertilised egg.
That experiment was described in Science in 2001.