MUCOSAL AND PARENTERAL VACCINATION AGAINST ACUTE AND LATENT MURINE CYTOMEGALOVIRUS (MCMV) INFECTION BY USING AN ATTENUATED MCMV MUTANT

We used a live attenuated murine cytomegalovirus (MCMV) mutant to anal yze mechanisms of vaccination against acute and latent CMV infection. We selected MCMV mutant RV7 as a vaccine candidate since this virus gr ows well in tissue culture but is profoundly attenuated for growth in normal and severe combined immunodeficient (SCID) mice (V.J. Cavanaugh et al., J. Virol. 70:1365-1374, 1996). BALB/c mice were immunized twi ce (0 and 14 days) subcutaneously (s.c.) with tissue culture-passaged RV7 and then challenged with salivary gland-passaged wild-type MCMV (s gMCMV) intraperitoneally (i.p.) on day 28. RV7 vaccination protected m ice against challenge with 10(5) PFU of sgMCMV, a dose that killed 100 % of mock-vaccinated mice. RV7 vaccination reduced MCMV replication 10 0- to 500-fold in the spleen between 1 and 8 days after challenge. We used the capacity to control replication of MCMV in the spleen 4 days after challenge as a surrogate for protection. Protection was antigen specific and required both live RV7 and antigen-specific lymphocytes. Interestingly, RV7 was effective when administered s.c., i.p., peroral ly, intranasally, and intragastrically, demonstrating that attenuated CMV applied to mucosal surfaces can elicit protection against parenter al virus challenge. B cells and immunoglobulin G mere not essential fo r RV7-induced immunity since B-cell-deficient mice were effectively va ccinated by RV7. CD8 T cells, but not CD4 T cells, were critical for R V7-induced protection. Depletion of CD8 T cells by passive transfer of monoclonal anti-CD8 (but not anti-CD4) antibody abrogated RV7-mediate d protection, and RV7 vaccination was less efficient in CD8 T-cell-def icient mice with a targeted mutation in the beta 2-microglobulin gene. Although gamma interferon is important for innate resistance to MCMV, it was not essential for RV7 vaccination since gamma interferon recep tor-deficient mice were protected by RV7 vaccination. Establishment of and/or reactivation from latency by sgMCMV was decreased by RV7 vacci nation, as measured by diminished reactivation of MCMV from splenic ex plants. We found no evidence for establishment of splenic latency by R V7 after s.c. vaccination. We conclude that RV7 administered through b oth systemic and mucosal routes is an effective vaccine against MCMV i nfection. It may be possible to design human CMV vaccines with similar properties.