Scientists digging into the makeup of lab-grown kidney models turned up a surprising finding: The organoids also contained heart and muscle cells. Here’s what study author Dr. Ben Humphreys of Washington University in St. Louis told me about the finding, published in Cell Stem Cell.

A CLOSE-UP LOOK AT A KIDNEY ORGANOID. (HUMPHREYS LAB)

What did you set out to study?

We have been differentiating pluripotent stem cells into kidney organoids for several years. We wanted to see what kinds of cells are actually there. We turned to a powerful technique that allowed us to take inventory of all the cells in the kidney organoid. We found that while there are 12 or more kidney cell types, they’re more immature and similar to a developing fetal kidney. We also saw there were non-kidney cells lurking, hidden in the organoids.

What’s the takeaway from that finding?

It’s not a big setback for the field, it just shows we have work to do. We need to really carefully characterize all the cells that are present in organoids.