ACE2 and infection: This genomic enrichment was unique to the differentially expressed retroelements induced by SARS-CoV-2 in Calu-3 cells and not in other viral infections or in the A549 or A549-ACE2 infections with SARS-CoV-2, which may be due to the differences in A549 permissibility to SARS-CoV-2 infection (17).