Sensitivity of HIV transmission by cell-free virus or by transmission in co-cultures to neutralizing antibodies.

<p>(<b>A</b>) A barrier was placed into the cell-free path of HIV at the extracellular step using neutralizing antibodies. (<b>B</b>) The infectivity of cell-free HIV_NL4-3-GLuc on MT4 cells was measured in the absence and presence of increasing amounts of neutralizing antibodies (NAb) 4E10, 2G12, and 2F5 (µg/ml). Infectivity was normalized to 1 using mock-treated control. (<b>C</b>) Scheme depicts the experimental approach to test the sensitivity of HIV spreading in co-cultures to neutralizing antibodies. At 6 h post-transfection, donor and target cells were co-cultured and cell-cell contacts were allowed to form for 2 h. Transmission events occurring during these 2 h were measured by terminating transmission with saquinavir (SQV) and allowing all previous infection events to proceed for 36 h and result in luciferase expression. These base level infections were set to 1. In parallel, the ability of neutralizing antibodies (NAb) to interfere with the spreading of infection to indicated cell types during a window of 4 h was determined. At the end of the 4 h incubation transmissions were terminated using SQV and the produced luciferase was determined 32 h later. (<b>D–F</b>) Dose response for indicated neutralizing antibodies 4E10, 2G12, 2F5 in co-cultures of HEK293 HIV-producer cells with the indicated target cell lines as described in (C). (<b>G</b>) The data point at 2.5 µg/ml from figures D–F. Infectivity is normalized to the baseline infection levels measured during the first 2 h of co-culture. Error bars represent the standard error of the mean from 3 experiments.