The biotechnology company Revivicor has become embroiled in a scandal over the death of a transplant patient after he received a gene-edited pig heart that turned out to be infected with a pig virus.

The transplant, the first of a pig organ into a living human being, took place back in January of this year when surgeons from the University of Maryland Medical Center transplanted the genetically engineered pig heart, provided by Revivicor, into a 57-year-old man with end-stage cardiac disease. The controversial operation was hailed as a milestone in xenotransplantation, the process of moving tissues between species, but the patient died just two months later and now it seems a pig virus may have contributed to his death.

Arthur Caplan, a bioethicist at New York University, told MIT Technology Review, “It’s a big red flag”. “Such experiments are tough to justify,” he says, if doctors can’t prevent or control infection.