Human cytomegalovirus (HCMV) infection causes severe illness in newborns and immunocompromised patients. Since treatment options are limited there is an unmet need for new therapeutic approaches. Defensins are cationic peptides, produced by various human tissues, which serve as antimicrobial effectors of the immune system. Furthermore, some defensins are proteolytically cleaved, resulting in the generation of smaller fragments with increased activity. Together, this led us to hypothesize that defensin-derived peptides are natural human inhibitors of virus infection with low toxicity.We screened several human defensin HNP4-and HD5-derived peptides and found HD5(1-9) to be antiviral without toxicity at high concentrations. HD5(1-9) inhibited HCMV cellular attachment and thereby entry and was active against primary as well as a multiresistant HCMV isolate. Moreover, cysteine and arginine residues were identified to mediate the antiviral activity of HD5(1-9). Altogether, defensin-derived peptides, in particular HD5(1-9), qualify as promising candidates for further development as a novel class of HCMV entry inhibitors..

AUTHOR SUMMARY 49Defensins are peptides produced by various human organs which take part in the 50 natural defense against pathogens. Recently, it has been shown that defensins are 51 further cleaved to smaller peptides that have high intrinsic anti-microbial activity. We 52 here challenged the hypothesis that these peptides might have antiviral activity, and due 53 to their presumably natural occurrence, low toxicity. Indeed, we found one peptide 54 fragment that turned out to block the attachment of the human cytomegalovirus (HCMV) 55 to cells. Furthermore, this peptide did not show toxicity in various cellular assays or 56 impede the embryonic development of zebrafish at the concentrations used to block 57 HCMV. This is important, since HCMV is one of the most important viral congenital 58 infections. Altogether, our results hold promise for the development of a new class of 59 antivirals against HCMV.