Several protocols have been developed for generating kidney organoids from pluripotent stem cells (PSCs). Now, Nuria Montserrat and colleagues describe a protocol for the production of kidney organoids that transcriptomically resemble second trimester human fetal kidneys. They also show that use of a soft hydrogel promotes the differentiation of kidney organoid compartments. “One of our main goals has been to gain fundamental knowledge about the generation of renal-derived cells from human PSCs,” says Montserrat. “In order to better mimic the environment of differentiating nephron progenitor cells in vivo, we lengthened the time human PSCs were exposed to a 3D microenvironment, thereby forcing cell-to-cell and cell-to-extracellular matrix contact.” This approach, combined with the administration of inductive cues, led to the derivation of kidney organoids with multiple nephron-like structures. A comparison of the transcriptional profile of day 16 organoids indicated they matched that of human fetal kidneys at 22 weeks gestation.

To improve the vascularization of the kidney organoids, the researchers implanted organoids into chick chorioallantoic membranes (CAMs). “Previous studies have reported vascularization of kidney organoids following transplantation under the kidney capsule of immunodeficient mice,” says Montserrat. “CAMs are a highly vascularized tissue that represents a naturally inmmunodeficient environment. After transplantation, the induced glomerular-like structures became vascularized and acquired morphological features, such as slit diaphragm-like structures and secondary foot processes, indicating further differentiation.” Montserrat and colleagues then fabricated polyacrylamide hydrogels that mimicked the biophysical properties of the CAM. “Using soft hydrogels during the first steps of PSC differentiation generated a higher number of nephron progenitors and nephrons than conventional approaches,” she explains. “These hydrogels represent an affordable approach to further advance the field of organoid engineering.”