Roku and Hex, the chimeric Rhesus Macaques. Source: OHSU News

Roku and Hex, the chimeric Rhesus Macaques. Source: OHSU News

In January 2012, the first chimera monkeys were born in an Oregon laboratory.

The word “chimera” may evoke images of the fearsome mythological beast that is part lion, part serpent, and part goat. But in the field of science, a chimera is defined as an animal produced in a lab by combining DNA from two or more organisms. An adult chimera contains cells composed of different sets of genomes. This was first done with mice in the 1960s, and since then, chimeras of rats, rabbits and various livestock have also been created. But it wasn’t until last year that this experiment was performed on primates.

To do this, researchers at the Oregon National Primate Research Center combined cells from early embryos of rhesus macaque monkeys in vitro. At this early stage, the cells in the embryo were totipotent—unspecialized, with the ability to differentiate into any of the cells needed by the organism. The cells did not fuse, but stayed together to cooperatively form tissues and organ systems. They were then implanted into female rhesus monkeys, where the embryos continued to develop. Three healthy males were born: Chimero and a pair of twins named Roku and Hex. They all have cells of up to six different genomes (in fact, Roku carries both male and female cells) and have shown no birth defects.

Interestingly, the surrogate mothers rejected the infants after birth, possibly because they were delivered by C-section rather than through natural birth.

The method used to create these chimera monkeys was different from ones used to create chimeric animals in the past. With mice, cultured stem cells injected into a young embryo integrated themselves into tissues of the adult animal, giving rise to a chimera. But when this was attempted in primates, the primate embryos did not integrate the cultured stem cells into tissues. This may be due to the fact that when stem cells are grown in culture, they lose some of their potency. Researchers have only been able to produce chimera monkeys by combining young embryos, whose stem cells are more potent.

In recent years, innovations in stem cell therapy have been used to treat diseases such as leukemia and AIDS, and there are more potential uses for stem cells in other areas of medicine. Research with chimeric animals helps scientists understand the complex process of embryonic development: how cells differentiate and become specialized for specific functions in the body as the embryo develops into an adult. Studies of how stem cells behave in primate embryos are important steps to understand how they function in humans.

1. Byrner, J., Pappas, S., January 5, 2012, Baby Monkeys With 6 Genomes Are Scientific First,, (January 19, 2013)

2. January 5, 2012, Chimera Monkeys Born in US, The Telegraph, (January 19, 2013)

3. Sample, I., January 5, 2012, Chimera Monkeys Created in Lab by Combining Several Embryos into One, The Guardian, (January 19, 2013)