Fig. 3. Tethering of viral particles by bNAbs requires antibody bivalency.

a Primary CD4 T cells were infected with HIV-1 (strain CH058) for 48 h and then were cultivated for 24 h with monovalent Fab and bivalent F(ab’)₂ fragments of  the bNAb 10–1074. Binding of the antibody fragments (left), and fold-change in released p24 (middle) and cell-associated Gag (right) were measured. Each dot represents a donor of CD4 T cells (n = 8). **p = 0.0078, ns. not significant (two-tailed Wilcoxon test). Bars represent the mean. Antibodies were tested at a concentration of 100 nM, b Infected CD4 T cells (CH058) cultivated for 24 h with an isotype control (mGO53) or with a bNAb (10–1074) were stained with an anti-human IgG antibody coupled to colloidal gold beads and analyzed by transmission electron microscopy (TEM). Representative images are shown. Red arrowheads point colloidal gold beads, indicative of 10–1074. Yellow arrowheads indicate budding viral particles. Scale bar: 500 nm. One representative experiment (out of two) is shown. c Other examples of 10–1074-induced retention observed with TEM. The cell donor and the cell ID is indicated for each image. Scale bar: 200 or 500 nm. d Example of viral retention at budding site, including a bNAb immunogold staining in between a viral particle and a budding virion. One representative experiment (out of two) is shown. e Infected CD4 T cells (CH058) cultivated for 24 h with a bNAb (10–1074) were stained with an anti-human IgG antibody coupled to colloidal gold and analyzed by scanning electron microscopy. A representative image is shown. Bright white dots are the colloidal gold beads, indicative of 10–1074. A magnification on an area with strong colloidal gold staining is shown. Scale bar: 100 nm. One representative experiment (out of two) is shown. Source data are provided as a Source Data file.