CTSL and COVID-19: More comprehensive results from scRNA-seq in first trimester pregnant women with and without COVID-19 showed that villous trophoblast cells express low levels of ACE2 and TMPRSS2, but high levels of DDP4 (the MERS-CoV entry mediator) and CTSL, which, according to the authors (Constantino et al., 2021), could be non-canonical cell-entry mediators for SARS-CoV-2.