What Miniature Lab-Grown Brains Reveal About the Effects of Covid-19

Organoids are helping scientists study the coronavirus

Emily Mullin
Published in
8 min readJul 13, 2020


Close up of purple gloved fingers holding up a small test tube of clear liquid of brain organoids.
A test tube containing brain organoids. Photo: Center for Alternatives to Animal Testing, Johns Hopkins University

The tiny blobs of brain tissue that Thomas Hartung grows in his lab at Johns Hopkins University aren’t much to look at. Just barely visible, they are little more than squishy white specks.

Known as “mini brains,” or organoids, these minuscule structures made from stem cells contain neurons that spontaneously emit electrical activity as a real brain would. The ones Hartung grows resemble the brain of a human fetus at five months of development.

Hartung and his team are using the brain organoids to better understand SARS-CoV-2, the virus that causes Covid-19. What they’ve found so far about the brain’s susceptibility to the virus is concerning: “It’s bad news adding to a pile of bad news,” Hartung tells OneZero.

Scientists have been growing organoids for over a decade, but the current pandemic has led to a flurry of interest in using them to study the new coronavirus. Researchers are now conducting similar tests with miniature lungs, guts, and livers, as well as rubbery “organs-on-chips.”

There’s a lot scientists still don’t know about the virus, and lab animals can only tell us so much. Since many animals don’t get Covid-19 like people do, human mini organs offer a way to learn which cells the virus can infect and how infection damages the body. Plus, organoids are a faster and cheaper option than using research animals because they can be mass-produced by the hundreds or thousands in the lab. Scientists are also using mini organs as stand-ins for real ones to test potential drugs to treat Covid-19.

Before Covid-19, brain organoids helped unravel another viral mystery: why some pregnant women who got infected with the Zika virus gave birth to babies with smaller brains and heads. When scientists exposed mini brains to Zika, they found that still-developing neurons were especially susceptible to the virus.

After Hartung and his colleagues read reports of some Covid-19 patients experiencing neurological symptoms in addition to respiratory ones, they wanted to know whether SARS-CoV-2 could infect brain cells, too.



Emily Mullin

Former staff writer at Medium, where I covered biotech, genetics, and Covid-19 for OneZero, Future Human, Elemental, and the Coronavirus Blog.

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