FIG 6.

The D614G mutation preferentially increases the infectivity of P681H/R-carrying pseudoviruses. The infectivity of GFP lentivector pseudotyped with the different spikes was analyzed in HEK-ACE2 cells that were induced for TMPRSS2 expression or uninduced. (A) Representative infection experiment in HEK-ACE2 cells. Cells were inoculated with 0.25 μg of p24 equivalent. The infectivity of PV is measured by the percentage of GFP⁺ cells, reported in the top right corner of each plot. (B and C) Quantitation of PV infectivity at the intermediate PV dose corresponding to 0.125 μg of p24 equivalent. The percentage of GFP⁺ cells obtained in HEK-ACE2 cells (B) and HEK-ACE2-TMPRSS2 cells (C) normalized to the WT value is reported. Statistics were measured by one-way ANOVA, with the Holm-Šidák correction for multiple comparisons. D614 backbone mutants were compared to the WT D614 spike, while G614 backbone mutants were compared to the WT G614 spike. Means and SD are shown for ≥3 independent experiments. (D and E) Ratio of PV infectivity in HEK-ACE2 (D) and in HEK-ACE2-TMPRSS2 (E) for spikes in the G614 backbone to that for spikes in the D614 backbone. The ratio was computed for increasing doses of PV ranging from 0.0625 to 0.5 μg pf p24 equivalent. The preferential effect of the D614G mutation on the infectivity of PV carrying the P681H/R mutation is evidenced by ratios above 2 (red line, ratio = 2; gray line, ratio = 1). Means and SD are shown for ≥3 independent experiments, except for the T716I mutant at the highest dose, where n = 2. Statistics evaluating whether each ratio was different from 1 were measured by one-sample t tests. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.