Recombinant measles viruses expressing altered hemagglutinin (H) genes: functional separation of mutations determining H antibody escape from neurovirulence.

Measles virus (MV) strain CAM/RB, which was adapted to growth in the brain of newborn rodents, is highly neurovirulent. It has been reported earlier that experimentally selected virus variants escaping from the monoclonal antibodies (MAbs) Nc32 and L77 to hemagglutinin (H) preserved their neurovirulence, whereas mutants escaping MAbs K71 and K29 were found to be strongly attenuated (U. G. Liebert et al., J. Virol. 68:1486-1493, 1994). To investigate the molecular basis of these findings, we have generated a panel of recombinant MVs expressing the H protein from CAM/RB and introduced the amino acid substitutions thought to be responsible for antibody escape and/or neurovirulence. Using these recombinant viruses, we identified the amino acid changes conferring escape from the MAbs L77 (377R-->Q and 378M-->K), Nc32 (388G-->S), K71 (492E-->K and 550S-->P), and K29 (535E-->G). When the corresponding recombinant viruses were tested in brains of newborn rodents, we found that the mutations mediating antibody escape did not confer differential neurovirulence. In contrast, however, replacement of two different amino acids, at positions 195G-->R and 200S-->N, which had been described for the escape mutant set, caused the change in neurovirulence. Thus, antibody escape and neurovirulence appear not to be associated with the same structural alterations of the MV H protein.