The Chimera of Greek mythology had the head of a lion, the body of a goat, and the tail of a snake. Nowadays, scientists create real chimeras by combining cells from different species to develop better laboratory models for studying diseases and to grow organs for transplants. In a recent study, published in Cell, scientists created a chimeric monkey composed of cells from two different types of monkeys. This result was achieved by injecting embryonic stem cells (ESCs) from one monkey’s embryo into another’s embryo. ESCs are the earliest stage of any cell before they develop into a specific type. The modified embryo was then transferred into a surrogate female monkey, resulting in the birth of a monkey with two sets of DNA. 

This work was the first successful report of generating chimeric monkeys using ESCs. The team carefully optimized the experimental conditions by adjusting nutrients in the liquid that helps ESCs grow. They tagged the ESCs with green fluorescents to distinguish which cells came from which monkey. As a result, they were able to integrate up to 20 fluorescent ESCs into the embryos.

Only one chimeric monkey was born and it had to be euthanized after 10 days because it was dying. Nonetheless, the post-mortem examination revealed that the donor ESCs significantly contributed (80-92%) to crucial organs such as the brain, lungs, heart, and adrenal gland, making the experiment a success.

These findings are crucial for genetic engineering in non-human primates, offering a path to greatly enhance animal models for biomedical research on disease. Similarly, this approach could pave the way for growing human organs in non-human primate hosts, saving countless human lives. However, this work also presents significant ethical questions that need to be addressed: to what extent is this acceptable? Should we consider developing a human lung or a human brain in a monkey? Would interspecies ancestry hurt chimeras?

This study was led by Jing Cao, a graduate student in the laboratory of Dr. Zhen Liu in the Institute of Neuroscience, Center for Excellence in Brain Science and Intelligence Technology at the Chinese Academy of Sciences in Shanghai, China.

Managing Correspondent: Marwa Osman

Press article: This hybrid baby monkey is made of cells from two embryos (News from Nature)

Original article: Live birth of chimeric monkey with high contribution from embryonic stem cells (Cell)

Image Credit: Image by Pavan Prasad from Pixabay