ACE2 and COVID-19: The biological plausibility for the androgen theory on COVID-19 is corroborated by the fact that SARS-CoV-2 cell entry largely depends on an endogenous transmembrane protease, serine 2 (TMPRSS2), that primes the virus, a critical step for its entrance through the coupling to the angiotensin-converting enzyme 2 (ACE2) receptors [18], and the inhibition of TMPRSS2 would reduce SARS-CoV-2 infectivity.