PROTECTION AGAINST HIV-1 INFECTION IN HU-PBL-SCID MICE BY PASSIVE-IMMUNIZATION WITH A NEUTRALIZING HUMAN MONOCLONAL-ANTIBODY AGAINST THE GP120 CD4-BINDING SITE

Objective: Mice with severe combined immunodeficiency (SCID) transplan ted with human peripheral blood lymphocytes (hu-PBL) have been shown t o be useful as an animal model for HIV-1 infection. This model was use d to assess the ability of a human anti-gp120 antibody to protect agai nst HIV-1 infection. Design and methods: hU-PBL-SCID mice were injecte d with an HIV-1 broadly neutralizing human monoclonal antibody against the gp120 CD4-binding site prior to challenge with HIV-1(SF2). The an tibody b12, employed for these studies, was isolated from an antibody phage-display library prepared from bone-marrow of a long-term asympto matic HIV-1-seropositive donor. Both Fab fragments and whole immunoglo bulin (Ig) G1 b12 antibody were assessed for protection. Results: Fab b12, tested at a dose approximate to 1.9mg/kg, was able to protect 25% of hu-PBL-SCID mice from HIV-1 infection. IgG1 b12, which displayed f avorable pharmacokinetic properties, showed a dose-dependent protectio n that was complete with a regimen of two injections of 100 mu g per m ouse. The in vivo protective dose of antibody at the time of virus cha llenge was estimated to be 4.5-7 mg/kg from antibody clearance data. C onclusions: This study demonstrates for the first time that complete p rotection against HIV-1 infection can be achieved in the hU-PBL-SCID m odel by passive immunization with physiologically relevant doses of a human gp120 CD4-binding site antibody derived from natural infection.