It is reported in this week’s Nature that scientists have successfully grown miniature stomachs in the lab from human stem cells, guiding them through the stages of development seen in an embryo. The lumps of living tissue, which are no bigger than a sesame seed, have a gland structure that is similar to human stomachs and can even harbour gut bacteria.

The study offers a window to how cells in human embryos morph into organs. Scientists say that these ‘gastric organoids’ could also be used to understand diseases such as cancer, and to test the stomach’s response to drugs.

In this study, the key to turning pluripotent stem cells into stomach cells was a pathway of interactions that acts as a switch between growing tissues in the intestine and in the antrum, a part of the stomach near its outlet to the small intestine.

When the stem cells were around three days old, researchers added a cocktail of proteins including Noggin, which suppresses that pathway, and timed doses of retinoic acid, a compound in vitamin A. After nine days, the cells were left to grow in a protein bath.

At 34 days though the resulting organoids were only a few millimetres in diameter and had no blood cells, immune cells, nor the ability to process food or secrete bile, they are remarkably similar to an actual stomach.

The researchers say that they can grow the stomach organoids from both embryonic stem cells and skin cells induced to pluripotency. Jason Mills, a gastrointestinal pathologist at Washington University School of Medicine in St. Louis, envisions growing thousands of such organoids, each from a different person’s cells, and infecting them with a pathogen to study the role of individual genetics.