Surgeons at New York University Langone Health have announced the second ever successful transplantation of a genetically-modified pig kidney into a human recipient. The achievement comes three months after the first such procedure was performed, and could pave the way for the use of non-human organs in patients requiring life-saving transplants.

To be clear, both of the operations completed to date were experimental, involving people who are not expected to actually live with the porcine kidneys. The first was transplanted into a braindead woman whose family gave permission for doctors to perform the surgery shortly before her life-support was switched off. Now, the same team of surgeons has repeated the feat on a recently deceased individual who was maintained on a ventilator.

Known as xenotransplantation, animal-to-human transplants are seen by scientists as a potential solution to the current shortage of donor organs. Sadly, many people die while waiting for a transplant because there simply aren’t enough organs available, yet the prospect of using components from livestock rather than having to wait for a human donor to become available could save countless lives.

The challenge, however, lies in the fact that our immune systems are primed to recognize foreign material, which is why our bodies naturally reject organs from other species. For instance, most mammals other than humans produce a sugar called alpha-gal, and the insertion of this molecule into our bodies triggers an antibody response that is designed to destroy the invading material.

To prevent this from occurring, the surgeons used pig kidneys that had been genetically engineered to lack the gene responsible for the production of alpha-gal, thereby avoiding this immune response. In their latest experiment, the modified kidney was attached to blood vessels from the recipient’s upper leg and maintained outside of the abdomen for a period of 54 hours for study and observation.

As with their first attempt, the surgeons reported that not only was the organ not rejected by the recipient but that it also appeared to be functioning well. Waste products such as creatinine were filtered through the kidney at an appropriate rate, while urine production matched that of a normal human kidney.

“We have been able to replicate the results from the first transformative procedure to demonstrate the continued promise that these genetically engineered organs could be a renewable source of organs to the many people around the world awaiting a life-saving gift,” lead surgeon Dr Robert Montgomery said of the incredible achievement in a statement.

“There is much more work to do before we begin living human trials, but our preliminary findings give us hope.”