ACE2 and infection: While a study of the brain of fatal human COVID-19 cases showed ACE2 expression in cortical neurons and found evidence that ACE2 is required for infection of human brain organoids [26], neuroinvasion and spread in the K18-hACE2 mice is apparently not directly dependent upon ACE2 expression because the virus does not infect all ACE2-expressing cells and does infect cells without apparent ACE2 expression [42].