DPP4 and severe acute respiratory syndrome: We selected the genes ACE2, TMPRSS2, CTSL, DPP4, PAICS, and DAAM1 for further investigations using scRNA-seq transcriptome data from cells of the syncytiotrophoblast (n = 1,144), villous cytotrophoblast (n = 8,244), and extravillous trophoblast (n = 2,170) of non-disease human placental tissues, considering the potential relevance of these genes for SARS-CoV infection and replication in the organ (Figure 1D).