Inhibition of viral replication by monoclonal antibodies directed against human immunodeficiency virus gp120

Monoclonal antibodies (MAbs) were raised against the glycoprotein gp 120 of human immunodeficiency virus type 1 (strain HTLV-1IIB). The reactivity of five selected MAbs was characterized in several tests: ELISA, immunostaining of Western blots, immunofluorescence, immunoprecipitation, immunoelectron microscopy, alkaline phosphatase-anti-alkaline phosphatase assay and neutralization. The binding region was delimited by sequential overlapping Escherichia coli fusion proteins of the gpl20 sequence between amino acids (aa) 49 and 280. In the ELISA, when using sequential overlapping 15 aa peptides, the binding epitopes were localized between aa 64 and 78 for three MAbs and between aa 114 and 123 for the fourth Mab. The fifth Mab showed multiple reactions with different peptides possibly indicating a reaction with a discontinuous epitope. In virus growth inhibition assays, all five MAbs inhibited the spread of HIV-1 infection in cell cultures after a single or repeated treatment at a concentration of 63 ~tg/ml of the purified MAbs. All MAbs showed low but significant neutralizing activity at concentrations of 100 pg/ml.