Fig. 1.

A single-chain variable fragment (scFv) derived from mAb 77.4 inhibits MeV infection in vitro and in vivo. a Measles virus (MeV) fusion (F) protein in PyMOL (Schrödinger) using the crystal structure of MeV prefusion F ectodomain² (PDBID: 5YXW). b–c scFv inhibits MeV infection: Vero-SLAM cells treated with the indicated concentration of scFv (or not treated) were infected with MeV IC323-EGFP at a multiplicity of infection of 0.001. Images were obtained using epifluorescence microscopy 48 h after infection (scale bar = 200 µm). d scFv inhibits MeV H/F-mediated fusion: Fusion of MeV G954 or IC323 H/F-coexpressing cells with SLAM-bearing cells in the presence of the scFv at the indicated concentrations was quantified at 6 h. The results are presented as the percent reduction in luminescence (Y-axis) compared to no treatment. Each bar represents the mean (±standard error) of results from at least three separate experiments. e scFv blocks MeV in vivo: Cotton rats were infected intranasally with 10⁵ TCID₅₀/mL MeV WTFb. Animals received either the indicated amount of the mAb 77.4-derived scFv construct (n = 4) or vehicle (n = 8) 24 h and 12 h prior to infection. Animals were euthanized 5 days after infection. The results are presented as TCID₅₀/g of lung tissue. Statistical analyses were performed using the Mann–Whitney U test. f–g The mAb 77.4-derived scFv and HRC4 peptide inhibitor were synergistic in fusion assays. The effects of mAb 77.4-derived scFv and the HRC4 inhibitor on MeV H/F-mediated cell fusion were assessed and analyzed using Combenefit software. f Loewe synergy and antagonism response surface for scFv and HRC4 at the indicated concentrations. g Multicolor synergism response surface in comparison to the additive outcome. Data are from three independent experiments