Primary isolate neutralization by HIV type 1-infected patient sera in the era of highly active antiretroviral therapy

Sera from highly selected HIV-1-positive patients are known to have the abi lity to neutralize a diverse array of primary isolates of HIV-1, The human osteosarcoma cell line that expresses CD4 and chemokine receptors (GHOST ce lls) was adapted to study HIV-1 neutralization in 37 HIV-1-infected individ uals who were selected because of slow disease progression or nonprogressio n. Many of these individuals were receiving combination drug therapy. Molec ularly cloned HIV-1 JR-FL and NL4-3 viruses were used as prototypes to defi ne assay conditions. Sera were then tested at a 1:40 dilution against six a dditional primary isolates, three of which utilized CCR5 and three of which used both CCR5 and CXCR4, The assay was highly reproducible and independen t of viral input titer, with a readout at 48 hr equivalent to that at later time points. As previously reported, neutralization sensitivity was entire ly independent of coreceptor usage. Only a few sera from slow progressors w ere able to neutralize a broad array of primary isolates at a 1:40 dilution , and the best clinical predictor of broadly neutralizing antibody for prim ary isolates was the present use of antiretroviral agents. In further studi es it was found that purified antibody accounted for the majority of the me asured neutralization. However, experiments with exogenous addition of anti viral agents showed that the use of nucleosides also greatly contributed to the measured neutralization in some patients. Measurement of neutralizatio n of HIV-1 primary isolates by sera from patients receiving antiretroviral therapy must be carried out with some caution.