DPP4 and COVID-19: Interestingly, peptides taken from milk proteins and endowed with ACE inhibitory activity have also been investigated recently, via in silico studies, for their ability to prevent interaction among the COVID-19 spike glycoproteins and the host cell dipeptidyl peptidase-4 (DPP-4, [34]); however, these promising results are still lacking validation by in vitro or in vivo studies.