An effective immune-suppressing drug therapy has enabled the longest-to-date survival of a heart transplant from a pig to a baboon, reports a study in Nature Communications this week. The implanted pig organ did not replace the baboon’s heart, but was instead connected to the baboon’s circulatory system, which allowed it to beat for more than two years.

Xenotransplantation - organ transplant between different species - has the potential to overcome the limitation of organ shortage among human patients. The main obstacle to xenotransplantation has been the strong immune reaction of the organ recipient, which leads to organ rejection and failure. Scientists have been developing strategies to prevent organ rejection, such as tweaking the organ donors’ genes associated with immune response and developing immune-suppressing drugs for the organ recipients.

Muhammad Mohiuddin and colleagues used a previously established line of donor pigs with three genetic modifications that allowed for a degree of immune tolerance in recipient baboons, close relatives of humans. The authors fine-tuned a treatment based on antibodies and drugs in order to control the baboons’ immune system. In the study, five baboons received pig’s hearts and the implanted organs survived as long as the recipients were kept on the immune-suppressing therapy - up to 945 days (with a median of 298 days).

In future work, this so-called ‘immunomodulatory’ treatment remains to be tested in a situation in which a baboon’s heart is replaced with one from a genetically modified pig.