TMPRSS2 and viral infectious disease: TMPRSS2 is more largely expressed in human tissue than ACE2, whereas single-cell RNA sequencing (scRNAseq) in human respiratory tissue has shown a co-expression of ACE2 and TMPRSS2 in lungs, heart, and kidneys, which would indicate that these cells are strongly susceptible to viral infection (Ding et al., 2004).