Pathogenicity and immunogenicity of temperature-sensitive mutants of murine cytomegalovirus.

Two temperature-sensitive (ts) mutants (ts 21 and ts 24), which could complement each other, were isolated from cell culture-passaged murine cytomegalovirus (CC-MCMV). Characterization in vivo revealed that ts 21 lacked pathogenicity for suckling mice, neurovirulence for weanling mice and productive chronic infection in the salivary gland, whereas ts 24 was positive only for the first two parameters; both mutants retained immunogenicity comparable to that of the wild-type CC-MCMV. The immunogenicity of ts 21 and ts 24 was assessed by mortality of the immunized mice after challenge with virulent, salivary gland-passaged MCMV (SG-MCMV) and by replication of the challenge virus in the immunized hosts. The protective immunity conferred by ts 21 was maintained over a period of 3 months without production of infectious viruses in the salivary gland.