Specifically, ACE2, TMPRSS2, CLEC4M, DPP4 and TMPRSS11D expression levels in normal tissues were derived from the GENT2 database (http://gent2.appex.kr/gent2), containing data from about 28 000 controls and cancer subjects (angiotensin converting enzyme 2; for further details on tissues and numerosity, see Table S1). Here, DPP4 is linked to cancer.