The key was figuring out how to deliver mRNA in stealth mode: enabling it to evade the body's surveillance system and be accepted as something natural. Moderna, Afeyan said, has figured that out.
"Initially, I did not believe the data," said Stéphane Bancel, now Moderna's CEO. "When he started to explain the technology, I said that's impossible; mRNA will never be a drug."
Bancel at the time was running bioMerieux, a French diagnostics company with 6,000 employees and a market value of more than $3 billion. A student of business history, Bancel said he saw the potential of mRNA following the same S-shaped curve that characterizes the path of any new breakthrough.
Read MoreBiotech's torrid run may not be over, analysts say
"I said, 'Wow, this is going to be like any new technology. We can get 100 times, 1,000 times improvement," Bancel said. "And if we can do that, then we can make drugs today that we cannot make with where the technology is."
It was a big bet, leaving a "nice, comfy job" to head a start-up in an area of medicine that's never worked before, Bancel said.
"One reason I took the plunge is, I said if this is going to work and it is going to end up being the next big thing, I'd hate myself every morning shaving in the mirror [if I'd passed it up]," he said.