In a world first, Chinese scientists say they cloned two monkeys by transplanting donor cells into eggs, a feat that could lead to genetically engineered primates for drug testing, gene editing and brain research.

The cloned macaque monkeys are the latest application of a test-tube technique called somatic cell nuclear transfer pioneered 20 years ago with the creation of the cloned sheep named Dolly. It has been used to clone 23 species from rodeo bulls to polo ponies and pet cats. But the ability to clone primates eluded scientists until the project made public Wednesday in the journal Cell.

“For the cloning of a primate species, including humans, the technical barrier is now broken,” said senior author Qiang Sun, director of the Nonhuman Primate Research Facility at the Chinese Academy of Sciences Institute of Neuroscience in Shanghai, in an interview. “In principle it could be used in humans, but there is no intention for us to apply this method to humans.”

The Chinese bioengineers made the two female monkeys by surgically replacing the nucleus of an egg with fetal donor tissue and then using special chemicals designed to trigger genes required for embryo development. The monkeys appear to be healthy and developing normally, the scientists said.

Two others, made at the same time using adult donor cells instead of fetal tissue, died within hours of birth, said the scientists, who couldn’t explain why. The failure is significant because adult cells are easier to obtain for cloning than cells from aborted monkey fetuses.