“Pig hearts to be tested in humans” read a headline in the Financial Times in September 1995. The article quoted confident predictions that porcine hearts, genetically engineered to avoid rejection, would be transplanted into patients the following year — helping to ease the worldwide shortage of human organs.

More than 25 years passed before that forecast finally came true. Last month surgeons at the University of Maryland School of Medicine in Baltimore successfully replaced the failing heart of a 57-year-old man with a fresh one from a pig with 10 gene edits. Four weeks later the patient, David Bennett, continues to recover with no signs of rejection.

Xenotransplantation — replacing human organs with those from other species, typically referred to as “xeno” by scientists — has followed cycles of hope and disappointment dating back at least to 1984 when surgeons in California gave Baby Fae, born with a lethal cardiac defect, a baboon’s heart which failed after three weeks.