A groundbreaking cell-transplant surgery has let a paralyzed man walk again. Darek Fidyka, 40, was paralyzed in 2010 after being stabbed multiple times in the spine. In collaboration with London scientists, surgeons in Poland transplanted cells from Fidyka’s nasal cavity into his spinal cord. Scientists hoped that the cells would help fibers above and below his injury to reconnect, and they used nerve grafts to fill in the gap in his spinal cord. Two years after the surgery, Fidyka’s regained his ability to walk. It’s “more impressive than man walking on the moon,” said Prof. Geoff Raisman, who led the U.K. research team behind the surgery.