Fei Ann Ran was born in Szechuan, China, and moved with her family to Pasadena, California, when she was ten years old. She traveled to the East Coast for college and enrolled for her PhD at Boston Children’s Hospital. But more than halfway through, Ran suffered a devastating setback: her supervisor, geneticist Laurie Jackson-Grusby, ran out of funding and closed her lab. “She left,” Ran told me in a cafe on Longwood Avenue, the central artery of the Harvard Medical School campus. “She decided not to publish any of our work. I was in my fifth year of grad school. It was a pretty terrifying time.”20
A member of Ran’s PhD committee, Harvard chemistry professor Greg Verdine, suggested she contact Zhang, whom Verdine remembered as a star student. Ran didn’t know much about genome editing or Zhang. A friend told her Zhang was famous for his work on TALENs. But she didn’t know what TALENs were, either—she misheard this as “Talent.” Luckily, she fit the bill. One of Zhang’s postdocs, Neville Sanjana, was developing a method to treat an inherited brain disorder called Angelman syndromeV by building a TALEN activator to switch on a silent gene. Ran made one TALEN but soon switched to working on the easier CRISPR system.
In July, Zhang gave a public lecture at the Broad Institute on “Engineering the Brain” in which he discussed the potential of genome editing to understand the brain and potentially treat incurable brain disorders. There was still no mention of CRISPR. Meanwhile, Ran was devouring the CRISPR literature and most of all hoping to salvage her PhD. “I was so single-minded on getting this to work in mammalian cells,” she said. “Feng and Le had been doing a lot of work in mammalian cells. There was no question it couldn’t work but how could it work robustly?” Le Cong and Ran were keen to try the new sgRNA approach, but it didn’t perform as well as adding the crRNA and tracrRNA separately. By incrementally extending the tail of the tracrRNA, they were able to boost the gene-editing efficiency.
Ran found the atmosphere in the lab exhilarating despite the long hours, the group working around the clock almost in shifts. Le Cong still technically belonged to Church, but had a special bond with Zhang, “almost a father-son relationship.” The group would eat an early dinner and a late-night supper, frequently Chinese takeout, in the kitchen adjacent to Zhang’s laboratory. From the Broad’s tenth floor, Ran could gaze across the Charles River and admire the Boston skyline—the twin peaks of the Hancock Building and the Prudential Center, the sparkling floodlights of Fenway Park. But the only nightlife that mattered was in the lab. “I was the later crew, but Feng was the omni crew,” she said. “He’d show up before everybody and leave after everybody.” His wife, Yufen Shi, whom Zhang met at Stanford and married in 2011, would often wait patiently for him in his office.
Occasionally there was time to relax outside the lab. Shortly after her arrival, Ran accompanied her colleagues on a summer camping trip to nearby Harbor Island. Most of the group slept in a twenty-person tent. In a lab photo from one of those group activities, Zhang’s youthful appearance blends in with his students and postdocs. Anyone not knowing him would be hard pressed to pick out the professor. Zhang displayed a childlike excitability, desperate to see everyone’s latest results. “It was like taking a kid to a candy store,” Ran said. She kept improving the gene-editing efficiency and showed they could edit more than one gene at a time. The experiments worked routinely, unlike the frustrations with TALENs.
The final question was could they get CRISPR-Cas9 to edit genes inside human cells? Ran and Le Cong took Cas9, made a new guide RNA, and put everything into human cells growing in a petri dish. “And then we waited… and then we waited,” she recalled.21 A few days later, they sequenced the genome of those cells. “We could see the scars of DNA damage and repair—in other words, mutations—exactly where we thought they’d be. This was really exciting!”22 Zhang was excited, too. “I want to see!” he said. He told her: “Isn’t this cool that you’re one of the only people in the world to see this?”
As noted earlier, many groups were desperately interested in applying CRISPR to genome editing, not least members of the Church lab. Before Zhang left, Prashant Mali had been working on TALENs and dabbling with other gene-editing technologies. “CRISPR was just on our list of nucleases,” Church told me. “But we were always looking for precision editing. And we wanted to do it in human cells.”23 Kevin Esvelt had joined the Church lab after a successful PhD with Harvard chemist David Liu. He’d got a rudimentary version of CRISPR working in the lab, which he was using like antivirus software to prevent infections from stray viruses. Intrigued by Esvelt’s experience working with Cas9 in bacteria, Mali asked for his help getting CRISPR to work in mammalian cells. Esvelt had his doubts, assuming Doudna had an insurmountable lead. But Mali persisted. “This is going to be so big that if we discover one tiny little piece that the other groups miss, it will be worth it.”24
As it turned out, that “one tiny piece” was demonstrating the need for the whole sgRNA—truncating it reduced activity. With help from another talented grad student named Luhan Yang, Church submitted their paper to Science in late October. It not only demonstrated “facile, robust, and multiplexable human genome engineering” but also predicted that more than 40 percent of human gene sequences were amenable to genome editing using CRISPR. As a courtesy, he emailed Doudna to let her know his group had extended her results to editing in normal human cells. As far as he knew, that was a first.
Of course, it wasn’t. Three weeks earlier, Zhang had submitted his group’s manuscript to the same journal. Le Cong and Ran were credited as co–first authors, and Marraffini and his student Wenyan Jiang were also included. Barrangou was one of the referees helping Science judge the merits of those and similar results from other teams. Barrangou judged that the reports from Church and Zhang demonstrating CRISPR editing in human cells were the most significant of the bunch. Of the two, Feng’s paper was perhaps the better but “they’ve got to take both, back to back. The single-guide RNA technology is the tipping point. The real credit should go to George and Feng to show genome editing in human cells.”25
Science published Zhang’s article alongside Church’s paper on January 3, 2013.26, 27, Jin-Soo Kim’s demonstration of CRISPR gene editing in human cells came out four weeks later, in Nature Biotechnology.28 Jínek and Doudna presented their human cell success in eLife. There were also reports from Keith Joung (Massachusetts General Hospital) working on zebrafish29 and Marraffini, squeezed out by Science, who published his studies on bacteria in March.30
Ran was on vacation when she got the news of her first major publication, which more or less secured her PhD. Six months of hard work at the cutting edge of science had made up for five years of fruitless labor and frustration. Her reaction was more relief than jubilation. She remained in the lab for another year before writing up her thesis. “I have this great suggestion,” Zhang told her at one point. “Download Arno Pro. It’s a great font!” Ran still has it on her computer. “That’s how I got my PhD, with the help of Feng’s font,” she laughs. She didn’t see much of him as she finished in the lab, and learned about the birth of his first child from an unusual source. While receiving the referee reports for a subsequent paper, the journal editor’s email said, “Congratulations on Ingrid.” Ran smiles: “We learned about it from a journal editor!”