Viral growth kinetics of G-mutant vaccines in vitro and in BALB/c mice. A, Vero cells and (B) NHBE cells differentiated at ALI were infected with A2-line19F, A2-line19F-G155 (deleted mucin domains), A2-line19F-G155S (deleted mucin and transmembrane domains), or A2 (NHBE cells only). Data represent the geometric mean of 2 or 3 experimental replicates (± geometric SD), expressed as FFU/mL. Vaccine attenuation was measured in BALB/c mice infected intranasally on day 4 postinfection by (C) live-virus FFU assay or by (D) RT-PCR. C, Data represent the geometric mean titer (± geometric SD) viral lung titer in log10(FFU/g lung). D, Data represent the mean (± SD) delta-delta cycle threshold (ΔΔCt) value between GAPDH and RSV M gene, normalized to A2-line19F. Statistical comparisons were made using 1-way analysis of variance of log-transformed titers with Tukey post hoc comparisons test. ** P ≤ .01, *** P ≤ .005, and **** P ≤ .001. Abbreviations: ALI, air-liquid interface; FFU, fluorescent focus units; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; NHBE, normal human bronchial epithelial; RSV, respiratory syncytial virus; RT-PCR, real-time polymerase chain reaction. The dashed lines represent the lower limits of detection of the assays.
