Scientists Are Growing Human Organs In Animals—And It’s Working

By Darren Orf – Popular Mechanics

The word “chimera” usually evokes images of mythological, multi-headed beasts, but the term also comes with more modern, scientific connotations. For one, there have been around 100 or so documented cases of human chimeras—people with two distinct genetic cell lines (often the result of one fraternal twin absorbing the other in utero). In some extremely rare cases, unborn twins can become the genetic parent of a chimera’s offspring.

A more common form of chimerism is actually reflection of the concept’s mythical, animalic roots—interspecies chimerism. Famously, in 2017, scientists created the world’s first human-pig chimeras (in this case, a pig embryo with a tiny collection of human cells) in the hopes of growing human-compatible organs for transplantation. Fast forward eight years later, and the process still remains tricky, as a host organism’s cells—such as a mouse’s or a pig’s—have defenses known as “RNA innate immunity” that allow the host’s cells to outcompete human cells during the chimeric process.