The birth of three monkeys from a stem cell research program is being hailed as a major breakthrough in genetic engineering. It appears that the mouse stem cells widely used in studies, follow a different developmental process, that was previously thought to be identical to primate and human.

Scientists have opened a window to a new strategy, and one which has seemed out of reach for more than ten years. Now it is possible for cloning primate and even human stem cells, into living breathing organisms.

The monkeys were all male and appear to be healthy. The work, by developmental biologist Masahito Tachibana of the Oregon National Primate Research Center, was reported in the journal ‘Cell’.

Instead of using embryonic stem cells cultured from lines of cells grown in petri dishes, the researchers used early-stage stem cells taken directly from monkey four-cell embryos to create 10 chimeric, or genetically mixed, embryos. The cells were combined from the early stage embryos, so the DNA was mixed, and the fetuses were incubated in female monkeys.

Three out of the four survived full term and are currently between four and six months old. They carry mixed DNA from six different genetic lineages. Genetically, it’s as if they had as many as six parents, an impossibility naturally.

More interestingly, although they have both male and female DNA, they are all developing as males, because masculine genes have dominated the monkeys development.

The three rhesus monkeys, named Chimero, Roku and Hex, are said to be normal and healthy.

The researchers were able to make monkey chimeras only when they mixed cells from very early stage embryos, in which each individual embryonic cell was “totipotent”. That means the cells are capable of growing into a whole animal as well as the placenta and other life-sustaining tissues.

It seems that scientists made a mistake by assuming that mimouse development would mirror human or primate development. The study also suggests that cultured primate and human embryonic stem cells, some of which have been frozen in labs for as long as two decades, may not be as potent as those found inside a living embryo.

Dr. Mitalipov one of the team members said :

“We cannot model everything in the mouse … 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.

The work with stem cells is one of the holy grails of genetic engineering because it holds the possibility to grow new body parts, including replacement organs, and initially new nerve fibres for those who have suffered paralysis. It also bodes well for curing Parkinson’s disease.

Written by Rupert Shepherd