TIME100 Health: Nima Nassiri | TIME

It was literally a back-of-the-envelope idea. Dr. Nima Nassiri had pulled out an envelope to scribble notes on how a bladder transplant could be accomplished in a living person—a surgery that had yet to be performed successfully.

It was 2021, the COVID pandemic was raging, and Nassiri, then a medical resident, was brainstorming ideas with urologist Dr. Inderbir Gill in a school cafeteria.

About four years later, on May 4, 2025, Nassiri—now 37 and an assistant clinical professor of urology at the University of California, Los Angeles—and Gill performed a bladder transplant on a 41-year-old father of four. The procedure, a world first, was a tremendous success. The patient recovered well and has excellent bladder function, Nassiri says.