FIG. 3.

Plasmid DNA immunization of BALB/c mice with pcDNA3-based vectors used alone or in combination and the reductions in spleen titers following increasing sublethal challenge doses of virulent MCMV. BALB/c mice were i.d. immunized three times over 2 weeks with 40 μg of DNA consisting of either pcDNA3 or a cocktail of 10 μg of each antigen-expressing plasmid to be tested and the balance of 40 μg consisting of pcDNA3. Two weeks after the last immunization, mice were i.p. challenged with either 20 × 10³, 40 × 10³, 80 × 10³, or 120 × 10³ PFU, and spleens were harvested 6 days postchallenge for MCMV titer determination. Spleen titer values presented are the means of the log₁₀ PFU per spleen for four mice with the standard error (SE) of the mean indicated by error bars. (A) Spleen titers of mice immunized with either pcDNA3, pcDNA3-pp89, pcDNA3-M84, or Gp. I. (B) Spleen titers from the same pcDNA3- or pcDNA3-pp89-immunized mice as in panel A as well as the Gp. II-immunized mice. (C) Spleen titers from an independent experiment in which mice were immunized with 30 μg of pcDNA3, 10 μg of pcDNA3-pp89 plus 20 μg of pcDNA3 to normalize masses), or 30 μg of Gp. III (10 μg of each plasmid shown).