Figure 3. D614G substitution significantly enhances SARS-CoV-2 replication in primary human airway tissues.

(a) Experimental scheme. D614 and G614 viruses were inoculated onto the primary human airway tissues at an MOI of 5. After incubation for 2 h, the culture was washed with DPBS, then maintained at for 5 days. To harvest, DPBS was added and allowed to incubate at 37°C for 30 min to elute the virus. (b-d) Viral replication and genomic RNA/PFU ratios. The amounts of infectious virus (b) and genomic RNA (c) were quantified by plaque assay and real-time RT-qPCR, respectively. The genomic RNA/PFU ratio (d) was calculated to indicate virion infectivity. Symbols represent individual samples, bar heights represent means, and error bars represent standard deviations. P values were determined by two-tailed Mann–Whitney test (n=6, two independent experiments conducted in triplicate). The results of the Mann-Whitney test are reported for all instances of p<0.05. (e,f) Competition assay. A mixture of D614 and G614 viruses with initial ratios of 1:1 (e), 3:1(f), or 9:1(g) were inoculated onto the human airway tissues at a total MOI of 5. Ratios after competition were measure by Sanger sequencing. Circles represent individual samples (n=6, two independent experiments conducted in triplicate). The midline represents the sample mean, and the shaded region represents +/− one unit of standard error about the mean. The width of the catseye plot represents the distribution of the model-adjusted means, and the heights extend to span 99.8% of the distribution of the mean. The y-axis is displayed on the log₁₀ scale such that the null value is 1. P values are calculated for the group (strain) coefficient for each linear regression model, and are reported for all instances of p<0.05.