To develop its drugs quickly and at a relatively low cost, Regeneron uses a proprietary process in which they insert human DNA into mice, according to Forbes.
Regeneron has produced six different drugs with this process, including its biggest moneymaker, vision loss treatment Eylea. The company sold $4.6 billion worth of that drug in 2019 alone, Forbes reported.
But before Eylea was released in 2011, a string of Regeneron drugs failed, leading some critics to say that the firm was doomed, CNN reported.
"We were never in this for the quick fix," Schleifer told CNN Business' Matt Egan in 2014. "This isn't the software business where you could write a program, everybody loves it and before you know it, you're on top of the world ... We're doing something that is pretty darn difficult."
Regeneron has also worked on treatments for Ebola and MERS, endeavors that helped prepare the company for its work on the coronavirus, Business Insider's Andrew Dunn reported.