Consequentially, CRISPR-Cas9 mediated knock-down of TMPRSS2 and TRMPSS4 in duodenal enterocytes results in a reduced viral infection in-vitro.40 Interestingly, ACE2 can mainly be found on the luminal side of enterocytes,42 which in our eyes argues in favor of an oral route of infection and against a basolateral uptake of the virus via a hematologic circulation of SARS-CoV-2. This evidence concerns the gene TMPRSS2 and viral infectious disease.