Scientists are said to be just two years away from bringing the woolly mammoth back from extinction.
The giant prehistoric creatures could roam the Earth for the first time in 4,500 years after researchers successfully merged genes from the long dead mammals with that of elephants.
So far, they have successfully switched 45 sections of DNA since the project began in 2015.
And Harvard scientists claim they are now within two years of creating a hybrid embryo that will have all the characteristics of the shaggy beasts.
It would have genes for mammoth features such as long hair, thick layers of fat, and cold-resistant blood.
Experts then intend to grow the hybrid creature using an artificial womb.
Originally, they planned to use a female elephant as a surrogate mother – but there are concerns as the species is under threat.
The Harvard team said this could delay the “de-extinction” of mammoths for a few more years.
They are using a gene-editing technique called CRISPR to bring the giants back to life.
It allows scientists to precisely “cut and paste” DNA taken from frozen mammoth specimens into elephant stem cells.
Professor George Church, who heads the Harvard team, presented the latest stage of the project at the world’s largest gathering of scientists.
Speaking at the American Association for the Advancement of Science (AAAS) annual meeting in Boston, Prof Church said: “Our aim is to produce a hybrid elephant/mammoth embryo.
“We’re not there yet, but it could happen in a couple of years.”
His team have already identified areas of DNA affecting ear size, fat levels, hair and blood – and have edited them into elephant cells.
The nucleus of an Asian elephant egg cell will be removed and replaced with the nucleus of engineered mammoth cells.
Cloning techniques will be used to develop the egg in the lab.
Prof Church added: “We’re working on ways to evaluate the impact of all these edits and basically trying to establish embryogenesis [developing an embryo] in the lab.
“The list of edits affects things that contribute to the success of elephants in cold environments.”
Gene editing and its ethical implications have become hot topics in recent months,
But Prof Church said it is “just another technology”.
He said: “I don’t think it’s the cat’s meow. To say it’s changed everything is like saying the Beatles invented the ‘60s.”
Prof Church said the mammoth project could help save endangered elephants by allowing them to live in less populated areas.
It also combat global warming.
Reintroducing woolly mammoths to frozen parts of the planet would help stop ice from melting and prevent the release of greenhouse gas into the atmosphere.
Prof Church said: “They keep the tundra from thawing by punching through snow and allowing cold air to come in.”
Experts predict that reintroducing mammoths in Siberia could cause local temperatures to drop by up to 20C.