Organoid

An organoid is a miniature, simplified version of an organ grown in the laboratory. It starts from stem cells, either pluripotent stem cells (embryonic or induced pluripotent) or adult stem cells taken from a tissue, which are set in a gel that stands in for the extracellular matrix and fed with growth factors. Given the right signals, the cells multiply, specialize and arrange themselves into a three-dimensional structure, usually no more than a few millimeters across, that holds several of the organ's cell types in their natural layout.

The modern field took off in 2009, when Hans Clevers's group grew self-renewing mini-guts from single intestinal stem cells of mice. Since then, organoids resembling the stomach, liver, pancreas, kidney, lung, retina and brain have been made. Because they can be built from human cells, they model human disease more closely than flat cell cultures or laboratory animals: brain organoids helped show how Zika virus harms the developing brain, and organoids grown from a patient's tumor can be used to test which drugs might work for that person.

Organoids still have limits. Most lack blood vessels, nerves and immune cells, and many stay immature, resembling fetal rather than adult tissue. Researchers are combining them with organ-on-a-chip devices and bioengineered scaffolds to close these gaps.