Neutralisation of cell-cell spread between autologous primary T cells. Antibodies targeting the CD4 binding site, the MPER and gp120 glycans were serially diluted and incubated with HIV-1 (NL4.3) infected primary CD4+ T cells for 1 h at 37°C exactly as in Figure 1. Dye-labeled uninfected autologous primary target T cells were added and cells incubated for 48 h to allow for cell-cell spread of HIV-1. T cells were then fixed and stained for intracellular HIV-1 Gag and analysed by flow cytometry. (A) Representative dot plots showing the percentage of Gag + target cells in the absence of antibody (untreated) or in the presence of 5 μg/ml J3, J3-Fc or VRC01. 4E10 did not inhibit cell-cell transfer (50 μg/ml). NI target = uninfected target cells only. (B) The percentage of Gag+, dye-labeled target T cells relative to untreated controls was quantified and IC50 values (μg/ml) were calculated. A representative from experiments performed with two independent donors is shown.