Monoclonal antibody-selected variants of MHV-4 contain substitutions and deletions in the E2 spike glycoprotein.

Selection and analysis of MHV-4 (strain JHM) variants resistant to E2-specific neutralizing MAbs was performed. Two types of variation in the E2 spike glycoprotein were found. From minimally passaged stocks of MHV-4, putative point mutants were obtained. These mutants were resistant only to the MAb used to select them. In contrast, multiply passaged stocks were found to harbor variants uniformly resistant to two selecting MAbs. Northern and Western blot analysis of the viral RNAs and proteins synthesized by these doubly-resistant variants showed that they contained large deletions in both mRNA 3 and its E2 translation product, localized to a 15 kilodalton region within the amino terminal 90B post-translational fragment. The selective advantage of this second class of variants lacking sequences within E2 90B was a result of their reduced cytopathology, thereby allowing cultures to support virus production for prolonged periods.