As an undergraduate studying biomedical engineering, Bassil Dahiyat planned a career building medical devices. Pursuing a PhD at Caltech, however, he found himself working on much smaller structures; proteins. Indeed, Dahiyat designed the first completely artificial protein- a very simple one- by devising powerful algorithms that combine standard descriptions of the physical properties of protein molecules in novel ways. He then constructed the protein by chemically linking its amino acid building blocks. After graduating in 1997, Dahiyat founded Xencor and put his technology to work creating protein drugs. The Monrovia, CA, company has raised $65 million and plans next year to begin human trials of its first drug, an anti-inflammatory for treatment of rheumatoid arthritis, psoriasis, and Crohn’s disease. Today Xencor designs its drug candidates by “tweaking natural proteins,” says CEO Dahiyat, but he looks forward to computer models robust enough that he can design complex molecules from scratch, fulfilling his vision of completely artificial protein therapies. “The dream is to mimic how nature uses proteins- to essentially do any task you can imagine,” he says. “There’s this palette that we haven’t even started to paint with.”