A Live-Attenuated HSV-2 ICP0− Virus Elicits 10 to 100 Times Greater Protection against Genital Herpes than a Glycoprotein D Subunit Vaccine
(A) Design of vaccine-challenge experiments. Protein-immunized mice were injected in their right, rear footpads on Day 0 with 10 µg monophosphoryl lipid A, 2.5 µg gD-2 or GFP, and alum (n = 40 per group). On Day 30, mice received an equivalent immunization in their left, rear footpads. Virus-immunized mice received injections on Days 0 and 30 of culture medium (mock), 1×106 pfu of HSV-2 0ΔNLS, or 1×106 pfu of HSV-2 MS (n = 40 per group). Mice immunized with HSV-2 MS received 1 mg/ml acyclovir in drinking water from Days −1 to +20 p.i. On Day 60, blood was harvested from all mice, and on Days 80, 90, or 100, mice were challenged with wild-type HSV-2 MS. (B) HSV-2 replication in mouse footpads. In a parallel experiment, mice were footpad-injected with 1×106 pfu of HSV-2 MS in the presence or absence of oral acyclovir (ACV) or 1×106 pfu of HSV-2 0ΔNLS. On Days 1, 2, and 3 p.i., footpad titers of infectious HSV-2 were determined in n = 8 mice per group; on days 5 and 7 p.i., footpad titers were determined in n = 4 mice per group. All datum points represent mean ± sem pfu per footpad. A double asterisk (**) denotes p<0.001 that viral titers per footpad were the same as HSV-2 MS-inoculated mice not treated with acyclovir. (C) Mean ± sem relative abundance of gD-2 specific IgG antibody in mouse serum on Day 60 p.i., as determined by ELISA on 1∶100 dilutions of mouse serum (n = 30 per group). Relative units of IgG abundance are expressed as “fold-increase above background,” as determined relative to a 0.33-log dilution series of high titer anti-HSV-2 antiserum that provided the standard curve that defined the quantitative relationship between anti-gD-2 IgG antibody abundance and colorimetric development. A double asterisk (**) denotes p<0.001 that gD-2-antibody levels were equivalent to naïve (medium-treated) mice, as determined by one-way ANOVA and Tukey's post hoc t-test.