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Purpose: A clinical vaccine that protects from ocular herpes simplex virus type 1 (HSV-1) infection and disease still is lacking. In the present study, preclinical vaccine trials of nine asymptomatic (ASYMP) peptides, selected from HSV-1 glycoproteins B (gB), and tegument proteins VP11/12 and VP13/14, were performed in the "humanized" HLA-transgenic rabbit (HLA-Tg rabbit) model of ocular herpes. We recently reported that these peptides are highly recognized by CD8+ T cells from "naturally" protected HSV-1-seropositive healthy ASYMP individuals (who have never had clinical herpes disease)., Methods: Mixtures of three ASYMP CD8+ T-cell peptides derived from either HSV-1 gB, VP11/12, or VP13/14 were delivered subcutaneously to different groups of HLA-Tg rabbits (n = 10) in incomplete Freund's adjuvant, twice at 15-day intervals. The frequency and function of HSV-1 epitope-specific CD8+ T cells induced by these peptides and their protective efficacy, in terms of survival, virus replication in the eye, and ocular herpetic disease were assessed after an ocular challenge with HSV-1 (strain McKrae)., Results: All mixtures elicited strong and polyfunctional IFN-γ- and TNF-α-producing CD107+CD8+ cytotoxic T cells, associated with a significant reduction in death, ocular herpes infection, and disease (P < 0.015)., Conclusions: The results of this preclinical trial support the screening strategy used to select the HSV-1 ASYMP CD8+ T-cell epitopes, emphasize their valuable immunogenic and protective efficacy against ocular herpes, and provide a prototype vaccine formulation that may be highly efficacious for preventing ocular herpes in humans.

Purpose: The authors recently reported that a recombinant HSV-1 expressing two extra copies of glycoprotein K (gK) exacerbated corneal scarring (CS) in mice. The authors also identified a peptide, STVVLITAYGLVLVW, within the signal sequence of gK as an immunodominant gK T-cell-stimulatory region both in vitro and in vivo and identified a highly conserved potential CD8(+) T-cell epitope (ITAYGLVL) within the peptide. In this study, the effect of giving this octamer (8mer) as an eye drop 1 hour before ocular infection with HSV-1 was investigated., Methods: Naive mice and rabbits received the gK 8mer or control peptides as eye drops and were then ocularly infected with HSV-1. Virus replication in the eye and trigeminal ganglia (TG), survival, CS, and relative amounts of gB, gK, CD4, CD8, IFN-gamma, and granzyme A/B transcripts were determined in the cornea and TG of infected animals at various times after infection. The effect of the gK 8mer was also analyzed in immunized HLA transgenic mice., Results: The gK 8mer resulted in a short-term significant increase in virus replication in the eyes of BALB/c mice, C57BL/6 mice, and NZW rabbits. gK 8mer treatment also increased viral neurovirulence and viral induced CS in ocularly infected mice. Moreover, in HSV-infected humanized HLA-A*0201 transgenic mice, the gK 8mer epitope induced strong IFN-gamma-producing cytotoxic CD8(+) T-cell responses, as assessed by CD107a/b expression and IFN-gamma ELISAs., Conclusions: gK 8mer induced CD8(+) T-cell responses were unlikely to occur soon enough to account for increased virus replication on day 1 after infection. In contrast, the data are consistent with CD8(+) T cells being involved in the appearance of CS at late times after infection. In addition, the gK peptide may affect viral replication and innate immune responses through other undefined mechanisms.

Purpose: An important phase in the development of an ocular herpes simplex virus type 1 (HSV-1) subunit vaccine is the identification of an efficient, safe, and adjuvant-free antigen delivery system capable of inducing and sustaining long-term memory T-cell protective immunity. This study was conducted to test the hypothesis that immunization with self-adjuvanting lipopeptide bearing HSV-1 glycoprotein D (gD) T-cell epitopes would elicit long-term HSV-specific T cells and decrease infection, disease, or both in a ocular herpes mouse model., Methods: Five immunodominant CD4(+) T-cell peptide epitopes (gD(1-29), gD(49-82), gD(146-179), gD(228-257), and gD(332-358)), recently identified from HSV-1 gD, were covalently linked to a palmitic acid moiety (lipopeptides) and delivered subcutaneously in adjuvant-free saline. The primary and memory T cells induced by these molecularly defined lipopeptides and their protective efficacy were assessed, in terms of virus replication in the eye, ocular disease, and survival., Results: Three gD lipopeptides, that drive dendritic cell maturation in vitro, induced long-term, virus-specific, IFN-gamma-producing CD4(+) Th(1) responses, associated with a reduction in ocular herpes infection and disease. Immunization with a cocktail of these three highly immunogenic Th(1) lipopeptides increased survival, lowered the peak of ocular virus titer, and cleared the ocular disease., Conclusions: Vaccination with a mixture self-adjuvanting lipopeptides containing novel HSV-1 immunodominant gD T-cell epitopes protected mice from ocular herpes infection and disease. The strength of protective immunity induced by these lipopeptides together with their safety provide a molecularly defined vaccine formulation that could combat ocular herpes infection and disease in humans.

Purpose: To investigate the therapeutic efficacy of periocular vaccination with herpes simplex virus (HSV) recombinant glycoprotein D from HSV-1 (gD1) or HSV-2 (gD2) in decreasing HSV-induced recurrent dendritic keratitis and HSV-induced recurrent ocular shedding in rabbits latently infected with HSV-1., Methods: Rabbits latently infected with HSV-1 were vaccinated periocularly (by subconjunctival injection) with gD1 and adjuvant, gD2 and adjuvant, or adjuvant alone. Eyes were examined daily for 49 days for recurrent herpetic keratitis and for recurrent infectious HSV-1 shedding., Results: In both vaccinated groups, a significantly decreased number of eyes exhibited recurrences of herpetic keratitis compared with recurrences in adjuvant-treated control eyes (gD1 group, 27/1372, [2%]; gD2 group, 24/1274, [2%]; and control, 54/1274 [4%]; P < 0.005). Eyes in the gD1-vaccinated group (44/1308 [3.4%]; P = 0.01), but not those in the gD2-vaccinated group (71/1274 [5.6%]; P = 0.93), had significantly decreased viral shedding (positive cultures compared with total cultures) compared with eyes in the adjuvant-treated control group (69 of 1275 [5.4%])., Conclusions: Recurrent HSV-1 corneal disease was significantly reduced by therapeutic local periocular vaccination. The vaccine may be more efficacious against HSV-1-induced recurrent corneal disease than against recurrent HSV-1 ocular shedding. Its efficacy against corneal disease appeared to be longer lasting than its efficacy against recurrent spontaneous shedding. The heterotypic gD2 vaccine was as efficacious as the homotypic gD1 vaccine against recurrent corneal disease, whereas the homotypic vaccine was much more efficacious than the heterotypic vaccine against recurrent HSV-1 shedding. This is the first report in any animal model of a successful therapeutic vaccine against recurrent HSV-1-induced corneal disease. These results support the concept that development of a therapeutic vaccine for ocular HSV-1 recurrence in humans may be possible.

Purpose: To determine whether the exacerbation of herpes simplex virus type-1 (HSV-1) induced corneal scarring that the authors reported previously in HSV-1 glycoprotein K (gK) vaccinated BALB/c mice challenged with HSV-1 strain McKrae was a general phenomenon independent of virus and mouse strains. To determine the gK-induced immune response leading to exacerbation of HSV-1-induced corneal scarring., Methods: BALB/c or C57BL/6 mice were vaccinated with gK, ocularly challenged with HSV-1 strain KOS or McKrae, and the relative amount of corneal scarring determined 28 days after challenge. The T cells, total serum, or purified immunoglobulin G (IgG) isolated from gK-vaccinated mice was transferred individually to naive mice, and the affects on corneal scarring after HSV-1 challenge were determined., Results: The KOS challenge of gK-vaccinated BALB/c mice resulted in significant corneal scarring (P = 0.0003), despite the fact that KOS normally produces no corneal scarring. McKrae challenge of gK-vaccinated C57BL/6 mice resulted in significant corneal scarring (P < 0.0001), despite the fact that C57BL/6 mice are normally refractory to HSV-1-induced corneal scarring. Passive transfer of total anti-gK mouse sera or purified anti-gK mouse IgG, but not adoptive transfer of total anti-gK T-cells to naive mice, resulted in exacerbation of corneal scarring after HSV-1 challenge (P < 0.0001). Mice defective for T-cell-dependent antibody production were not susceptible to exacerbation of HSV-1-induced corneal scarring by gK vaccination (P < 0.0001)., Conclusions: The ability of gK vaccination to exacerbate HSV-1-induced corneal scarring was not mouse strain or HSV-1 strain specific. The gK-induced exacerbation of corneal scarring was related to anti-gK IgG. How anti-gK IgG exacerbated HSV-1 induced corneal scarring remains to be determined.

Purpose: To compare the efficacy of each of seven expressed herpes simplex virus 1 (HSV-1) glycoproteins as vaccines to protect against ocular disease after primary ocular HSV-1 infection., Methods: Mice were vaccinated three times with equal amounts of each of seven individually expressed HSV-1 glycoproteins (gB, gC, gD, gE, gG, gH, and gI) and then ocularly challenged with McKrae, a corneal disease-producing strain of HSV-1. Viral clearance from the eye, blepharitis, keratitis, and neovascularization were determined at various times after infection., Results: Mice vaccinated with gD or gB had the best protection against eye disease. Vaccination with gI, gC, or gE produced moderate protection against eye disease. Vaccination with gG produced less protection, and vaccination with gH produced no apparent protection against eye disease., Conclusions: These results suggest that when used as vaccines, different HSV-1 glycoproteins provide different levels of protection against HSV-1-induced eye disease. Based on comparison with the authors' previously published results, the ability of each glycoprotein to protect against eye disease correlated with the ability of the glycoprotein to induce high serum neutralizing antibody titers and killer cell activity. Results suggest that the effectiveness of these seven glycoproteins in protecting against eye disease can be ranked as follows: gD > gB > gI > (gC = gE) > gG > gH.

Purpose: To address the possibility of neuronal-like herpes simplex virus type 1 (HSV-1) latency in the cornea by determining if regulation of the HSV-1 LAT promoter in stromal keratocytes is similar to LAT promoter regulation in neurons., Methods: Transient chloramphenicol acetyltransferase (CAT) assays were used to measure the relative promoter activity of various HSV-1 LAT promoter fragments in primary human corneal cells versus neuronal and nonneuronal cells., Results: The authors found that the LAT promoter, whose location they previously mapped in neurons using transient CAT assays, functioned in stromal keratocytes using the same assay system and that two regions between -283 and -1932 nucleotides relative (upstream) to the start of LAT transcription slightly increased the LAT promoter activity in stromal keratocytes. They previously showed a similar increase in neuronal cells, and a large decrease in nonneuronal cells. In addition, they found that a neuronal specific enhancer region they previously defined between -162 and -283 nucleotides upstream of the start of LAT transcription also enhanced promoter activity in stromal keratocytes. Using gel-shift assays, they detected a nuclear factor specific to neurons and stromal keratocytes that binds to the LAT promoter and that may be a LAT regulatory factor., Conclusions: Recently, it has been suggested that the cornea might serve as an alternative site of latent herpes simplex virus type 1 (HSV-1) infection. However, this remains controversial. The authors' findings suggest that corneal and neuronal cells regulate the LAT promoter similarly and that this regulation differs from that seen in nonneuronal cells. Thus, the possibility of neuronal-like latency in the cornea remains plausible.

One potential complication of systemic herpes simplex virus (HSV) vaccination is that subsequent ocular infection may lead to increased immunogenic corneal scarring. Therefore, V52, a genetically engineered vaccinia virus that expresses the HSV-1 glycoprotein gD, was tested for ocular safety and for protection against ocular challenge with a stromal-disease-producing strain (McKrae) of HSV-1. To maximize immune response, rabbits were vaccinated by a series of inoculations. V52-vaccinated rabbits developed significant HSV-1 neutralizing antibody titers; however, they were not as high as those induced by vaccination with live HSV-1 McKrae. One month after the final vaccination, all rabbits were challenged ocularly. Eyes were monitored for 35 days for epithelial keratitis, stromal keratitis, and iritis. In no case was epithelial keratitis, stromal keratitis, or iritis significantly exacerbated by vaccination. The gD V52 recombinant vaccine provided protection against HSV-1 induced epithelial keratitis (P = 0.02) and long-term stromal scarring (P = 0.04). There was no significant reduction in the incidence of trigeminal ganglionic latency in the vaccinated rabbits (P greater than 0.05). Thus, our results indicate that V52, a gD recombinant vaccine probably is safe with regard to corneal scarring, and may provide a small amount of protection against ocular HSV-1 infection. The amount of protection provided was less than that reported in mice and guinea pigs. This suggests that to provide high levels of ocular protection in rabbits (and probably in humans), HSV-1 vaccines may have to elicit a more vigorous immune response than that produced by normal HSV-1 infection.