Two CD4 oligopeptides, corresponding to residues (37–53) and (37–55) of the V1 domain of CD4, which recent structural studies propose as the most likely binding site of HIV-1 gp120, have been chemically synthesized by solid-phase techniques, modified by the addition of two side-chain protected cysteines at both termini and purified by HPLC. Their ability to inhibit the infectivity of human immunodeficiency virus type 1 (HIV-1) (HTLV-IIIB, RF and GB8 strains) in different cell lines was monitored by the production of progeny virus, p24 and reverse transcriptase activity in the culture supernatants and by electron microscopy. The results indicated that the peptides inhibited HIV-1 infectivity in a dose-dependent fashion without any detectable cytotoxicity
