Mini-Brain (IMAGE) Johns Hopkins Medicine Caption 'Mini-brain' bioengineered from human stem cells. The ball is about one third of a millimeter and contains about 30,000 cells. The cell nuclei are blue. The SARS-CoV-2 virus is stained red, indicating that a small fraction of brain cells carries a large number of virus particles. This means that virus has multiplied in infected cells. Credit Center for Alternatives to Animal Testing (CAAT), Johns Hopkins Bloomberg School of Public Health Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.