A CMV DNA vaccine primes for memory immune responses to live-attenuated CMV (Towne strain)

CMV-seronegative subjects vaccinated intramuscularly or intradermally with a DNA vaccine encoding pp65, IE1, and gB were administered live-attenuated CMV (Towne) to characterize immune priming by the DNA vaccine. CMV-specific memory T-cells (detected by standard ELISPOT assay in only 20% of subjects) were detected by IFN-γ cultured ELISPOT assay in 60% of subjects primed intramuscularly and correlated with immune responses after Towne. The median time to first pp65 T-cell and gB antibody response after Towne was 14 days for DNA-primed subjects vs. 28 days for controls administered Towne only (p = 0.02 and 0.03, respectively). Furthermore, there was a trend toward more DNA-vaccinated subjects than controls developing a gB-specific IFN-γ T-cell response after Towne administration (47% vs. 0%, p = 0.06).