Polymerase chain reaction-based assay for antibody-mediated neutralizationof HIV-1 reveals a population of nonneutralized virus undetected by conventional p24 assay

To be successful with strategies involving passive immunization or the gene ration of neutralizing antibodies against HIV, it is crucial that we improv e our understanding of the process of antibody-mediated HIV neutralization. We have used a neutralization assay based on polymerase chain reaction (PC R) that is more rapid and sensitive than the conventional p24 neutralizatio n assay based on enzyme-linked immunosorbent assay (ELISA). PCR assays perm it measurement of the number of infectious events and can detect small amou nts of HIV-1 only a few days postinfection. in these studies, the human ant i-V3 monoclonal antibody 694/98-D was used to neutralize the infectivity of the laboratory isolate HIVIIIB for CEM-SS cells. 8E5/LAV cells, which cont ain a single integrated copy of proviral DNA per cell, served as a standard to determine the amount of HIV-1 copies in infected CEM-SS cells. Evaluati on of antibody-mediated neutralization was possible at 2 to 3 days postinfe ction, at a time when p24 readouts were not conclusive. We achieved >95% ne utralization of HIVIIIB, and of its molecular clone HXB2, using the monoclo nal antibody 694/98-D. This degree of neutralization is probably highly sig nificant in vivo. Nevertheless, a small amount of both HIVIIIB and HXB2 (si milar to 5%) escapes neutralization and can consistently be detected after a few days by this sensitive assay. Experiments with different anti-HIV mon oclonal antibodies and viruses showed that the assay could be applied to an ti-V3 as well as anti-CD4 binding domain antibodies as well as HIV laborato ry strains or primary isolates.