Fig. 2: In vitro characterization of MV-014-212.

a Syncytia formed by MV-014-212 and MVK-014-212. Micrographs were taken at a total amplification of 100× under phase contrast or using tetramethylrhodamine filter. Yellow arrows point to syncytia. Scale bars are 100 µm. b Western blot showing full-length purified SARS-CoV-2 spike protein lacking the furin cleavage site (lane 1), MVK-014-212 (lane 2), MV-014-212 (lane 3), mock-infected Vero cell lysate (lane 4), blank (lane 5). The molecular weight markers correspond to the migration of the BIO-RAD Precision Plus Protein Dual Color Standards. The blue arrows indicate the expected size of the full-length spike and the cleaved protein (S1 + S2). The blots were derived from the same experiment and processed in parallel. c Multicycle replication kinetics of MV-014-212 compared to respiratory syncytial virus (RSV) A2 in serum-free Vero cells. Cells were infected at an MOI of 0.01 and incubated at 32 °C. Cells and supernatants were collected at 0, 12, 24, 48, 72, 96, and 120 h post infection. Titers of the samples were determined by plaque assay in Vero cells. Data points represent the means of two replicate wells and error bars represent the standard deviation. d Multicycle replication kinetics of MV-014-212 compared with MVK-014-212 in serum-free Vero cells. Cells were infected at an MOI of 0.01 and incubated at 32 °C. Cells and supernatants were collected at 0, 3, 24, and 72 h post infection. Titers of the samples were determined by plaque assay in Vero cells. Data points represent the means of three replicate wells and error bars represent the standard deviation. e Short-term thermal stability assay. Virus stocks of MV-014-212 prepared in Williams E medium supplemented with sucrose phosphate glutamate (SPG) buffer or prepared in SPG alone were incubated for 6 h at −80 °C, −20 °C, 4 °C, and room temperature and the titer determined by plaque assay. The bars show the mean of 2 technical replicates of 3 different samples, and the error bars denote SD. f Two-week thermal stability assay. Virus stocks of MV-014-212 in Williams E medium supplemented with SPG buffer were incubated for 14 days at 4 °C and room temperature (18 °C to 22 °C ± 2 °C) and the titer determined by plaque assay. The bars show the mean of 2 technical replicates of 3 different samples, and the error bars denote SD.