Functional human gastrointestinal organoids can be engineered from three primary germ layers derived separately from pluripotent stem cells.

Human organoid model systems lack important cell types that, in the embryo, are incorporated into organ tissues during development. We developed an organoid assembly approach starting with cells from the three primary germ layers-enteric neuroglial, mesenchymal, and epithelial precursors-that were derived separately from human pluripotent stem cells (PSCs). From these three cell types, we generated human antral and fundic gastric tissue containing differentiated glands surrounded by layers of smooth muscle containing functional enteric neurons that controlled contractions of the engineered antral tissue. Using this experimental system, we show that human enteric neural crest cells (ENCCs) promote mesenchyme development and glandular morphogenesis of antral stomach organoids. Moreover, ENCCs can act directly on the foregut to promote a posterior fate, resulting in organoids with a Brunner's gland phenotype. Thus, germ layer components that are derived separately from PSCs can be used for tissue engineering to generate complex human organoids.

Translating Developmental Principles to Generate Human Gastric Organoids.

Gastric diseases, including peptic ulcer disease and gastric cancer, are highly prevalent in human beings. Despite this, the cellular biology of the stomach remains poorly understood relative to other gastrointestinal organs such as the liver, intestine, and colon. In particular, little is known about the molecular basis of stomach development and the differentiation of gastric lineages. Although animal models are useful for studying gastric development, function, and disease, there are major structural and physiological differences in human stomachs that render these models insufficient. To look at gastric development, function, and disease in a human context, a model system of the human stomach is imperative. This review details how this was achieved through the directed differentiation of human pluripotent stem cells in a 3-dimensional environment into human gastric organoids (HGOs). Similar to previous work that has generated human intestine, colon, and lung tissue in vitro, HGOs were generated in vitro through a step-wise differentiation designed to mimic the temporal-spatial signaling dynamics that control stomach development in vivo. HGOs can be used for a variety of purposes, including genetic modeling, drug screening, and potentially even in future patient transplantation. Moreover, HGOs are well suited to study the development and interactions of nonepithelial cell types, such as endothelial, neuronal, and mesenchymal, which remain almost completely unstudied. This review discusses the basics of stomach morphology, function, and developmental pathways involved in generating HGOs. We also highlight important gaps in our understanding of how epithelial and mesenchymal interactions are essential for the development and overall function of the human stomach.