A Live-Attenuated HSV-2 ICP0− Virus Elicits 10 to 100 Times Greater Protection against Genital Herpes than a Glycoprotein D Subunit Vaccine
(A) Mean ± sem neutralizing antibody titer of Day 60 serum samples (n = 20 per group). The titer of each serum sample was considered to be the reciprocal of the largest serum dilution that reduced HSV-2's cytopathic effect in Vero cell monolayers by at least 50%. (B) Representative immunofluorescent labeling of fixed HSV-2 plaques with a 1∶5,000 dilution of Day 60 serum from each immunization group. (C) Flow cytometric measurement of pan-HSV-2-specific IgG levels in Day 60 sera, as determined by IgG binding to fixed HSV-2-infected cells versus uninfected Vero cells (n = 8 per group). In panels A and C, a double asterisk (**) denotes p<0.001 that neutralizing antibody titers or pan-HSV-2 IgG levels were equivalent to naïve mice, as determined by one-way ANOVA and Tukey's post hoc t-test. The difference in pan HSV-2 IgG levels between 0ΔNLS- and gD-2-immunized mice was significant (p<0.0001; two-sided, paired t-test). (D) Regression analysis of the logarithm of pan-HSV-2 IgG levels (x-variable, as measured on Day 60) in n = 25 mice versus the logarithmic reduction in vaginal HSV-2 MS shedding (y-variable, as measured on Day 81) observed in the same n = 25 mice at 24 hours post-vaginal challenge. The x-variable data is based on a subset of the data summarized in Figure 5C, and likewise the y-variable data is based on a subset of the data summarized in Figure 4C. The individual datum points are derived from n = 5 mice per group that were immunized with medium (naïve), GFP, gD-2, HSV-2 0ΔNLS, or HSV-2 MS (ACV-restrained infection), as indicated in the legend in Panel D. The quantity on the y-axis, Δlog (pfu/vagina), represents the logarithmic decrease of HSV-2 MS shed from an individual mouse vagina at 24 hours post-challenge relative to 5.20 logs, which was the average titer of HSV-2 MS shed by naïve mice at 24 hours post-challenge. The goodness-of-fit of the correlation between log (pan-HSV-2 IgG) and Δlog (pfu/vagina) was r2 = 0.83 and the slope of the correlation was 1.38±0.13 (p<10−9).