2 PBMC-BASED NEUTRALIZATION ASSAYS DEPICT LOW REACTIVITY OF BOTH ANTI-V3 MONOCLONAL-ANTIBODIES AND IMMUNE SERA AGAINST HIV-1 PRIMARY ISOLATES

The neutralizing activity of anti-V3 monoclonal antibodies (MAbs) and anti-HIV-1 immune sera was tested against HIV-1 laboratory strains and African primary isolates. Neutralization was investigated in Phytohae magglutinin (PHA)-stimulated peripheral blood mononuclear cell (PBMC) cultures by means of two distinct viral titer reduction assays. In the se assays, virus was detected by means of either p24 antigen measureme nt using ELISA or HIV provirus synthesis using PCR, respectively. Anti -V3 MAbs and anti-HIV-1 immune sera neutralized efficiently the homolo gous laboratory HIV-1 strains used for eliciting immune response but s howed no neutralizing activity against most primary isolates. The two neutralization assays used provided similar results. However, a PCR-ba sed assay circumvented the limitations due to low levels of virus repl ication. The mechanism of resistance of the primary isolates to neutra lizing antibodies was complex and was not simply predicted by partial sequence determination of the epitopes. This points out the need for r eliable neutralization assays of HIV-1 primary isolates in order to ev aluate the role of humoral immunity during HIV-1 infection and for fut ure vaccine strategies. Copyright (C) 1997 Elsevier Science B.V.