Scientists have opened up the possibility of interspecies lung, kidney and other organ transplants after creating part-human, part-pig embryo.

A team led by the Salk Institute for Biological Studies have made advances in the ability to grow cells, tissues and organs of one species within an organism of a different species by generating human cells and tissues in an early-stage pig.

This represents the first time scientists have demonstrated that an interspecies organ transplant is possible and may lead to medical professionals one day being able to grow human tissue using chimera embryos in farm animals to make organs available for transplants.

The modified animals may also lead to new models for testing drugs and understanding early human development.

The team of researchers were led by developmental biologist Juan Carlos Izpisua Belmonte of the Salk Institute for Biological Studies, was able to generate human cells and tissues in early-stage pig and cattle embryos, the first step towards a generation of transplantable human organs using large animals whose organ size, physiology and anatomy are similar to humans.

“Our findings may offer hope for advancing science and medicine by providing an unprecedented ability to study early embryo development and organ formation, as well as a potential new avenue for medical therapies,” Izpisua Belmonte said in a statement. “We have shown that a precisely targeted technology can allow an organism from one species to produce a specific organ composed of cells from another species.

“This provides us with an important tool for studying species evolution, biology and disease, and may lead ultimately to the ability to grow human organs for transplant,” he added. 

The experiment included injecting human stem cells into the embryo of a pig and the researchers said the embryo at this point was “highly inefficient.”

The embryo is then implanted in the uterus of a sow and the scientists then allowed it to grow.

The stem cells developed into the precursors of several tissue types including heart live and neurons after four weeks with a small fraction of the developing pig being made up of human cells.

Scientists have long attempted to use stem cells to grow replacement organs for patients, but often came up short because of the complexity of recreating an animal’s physiology from scratch.

While the pig embryos came up inefficient, there is some hope that they can eventually be used for organ transplants because a pig’s organ sizes and developmental timescales are more comparable to humans.

“Of course, the ultimate goal of chimeric research is to learn whether we can use stem-cell and gene-editing technologies to generate genetically-matched human tissues and organs and we are very optimistic that continued work will lead to eventual success,” Izpisua Belmonte said. “But in the process we are gaining a better understanding of species evolution as well as human embryogenesis and disease that is difficult to get in other ways.”

The study was published in Cell.