The two conceived of “prime editing” as a genetic search-and-replace function, aiming to improve on the first generation of CRISPR editing by more precisely making changes to DNA without cutting through the double-stranded helix. They described the scientific basis of their approach, and initial signs of it working to edit human cells, in a paper published in Nature in December 2019.

Prime editing uses some of the same cellular building blocks as CRISPR-cas9 editing, which scientists laid out as a method for altering human DNA a decade ago. The prime editor combines a modified cas9 enzyme with another that can generate new genetic code. They’re shepherded to the target DNA by an RNA guide and, once there, are designed to permanently edit a mutation or other genetic defect.

“The process is incredibly precise; it only edits that one spot,” said Keith Gottesdiener, Prime’s CEO. “It only makes the correction you’re aiming to make, and it doesn’t make corrections elsewhere in the genome.”

Prime raised its first $115 million from a Series A round led by Arch, F-Prime, GV and Newpath Partners. Just nine months later — a notably fast turnaround — Prime secured another $200 million in Series B funding from those same investors, as well as a slate of new venture capital firms and other backers.

“We’ve really felt this relentless pressure from the beginning,” said Gottesdiener, who joined the company in July 2020. “Series B just gave us a few more tools to really make it happen.”

Another advantage to prime editing suggested by the company’s preclinical work, according to Gottesdiener, is that the tool works to correct a wide range of disease-causing mutations. Prime editing could address more than 90% of known disease-causing mutations, he claimed, and has worked in every type of cell it’s been aimed at to date.

That versatility is a major selling point for the technology, particularly as companies like CRISPR Therapeutics, Intellia Therapeutics and Editas are making progress translating earlier-generation CRISPR editing tools into experimental medicines.

“It’s going to have a huge impact, and probably the most important reason is because you can use it almost anywhere,” Gottesdiener said.

Prime is working on multiple drug discovery programs targeted at diseases affecting the liver and eye as well conditions that can be treated through outside-the-body editing of stem cells. All are areas other gene editing companies are pursuing. More challenging, however, is Prime’s intent to target neuromuscular diseases as well.

Prime has not shared specific details on either the diseases or genes it’s focusing on first.

The startup benefits from a partnership with Beam, which also emerged out of Liu’s laboratory. Beam and Prime agreed to collaborate in late 2019, with the former company temporarily providing leadership and resources to explore what was then a very nascent technology. While Prime now stands on its own, the two companies will continue to “share research, expertise, and intellectual property” in certain areas like testing assays and manufacturing.

Prime plans to employ more than 100 people full-time by the end of 2021, the majority of whom will be scientists. Gottesdiener anticipates that the company is at least two years away from beginning clinical testing.

“I certainly would love to become the next Vertex or Biogen,” Gottesdiener said. “We have a lot to do. And we’re gonna need a lot of people to do it.”

Before joining Prime leadership last summer, Gottesdiener, a biotech veteran, helmed Rhythm Pharmaceuticals for nine years. He also worked in various roles across Merck & Co.