Targeted coronavirus infection of human cancer cells. Cells were inoculated (MOI of 5) with preincubated mixtures of FIPV or fMHV (control: no virus) and the bispecific adapter protein scFv 23F-425. The cells were stained for coronavirus proteins 24 h after inoculation. All cell lines tested showed susceptibility to EGFR-targeted FIPV or fMHV. Values in parentheses indicate the relative EGFR expression (relative geometric mean fluorescence (GMF)) as determined for each cell line by FACS analysis and expressed as the ratio of the GMF values obtained in the presence and absence of the anti-EGFR antibody.