A Replication-Competent, Neuronal Spread-Defective, Live Attenuated Herpes Simplex Virus Type 1 Vaccine

Abstract

Herpes simplex virus type 1 (HSV-1) produces oral lesions, encephalitis, keratitis, and severe infections in the immunocompromised host. HSV-1 is almost as common as HSV-2 in causing first episodes of genital herpes, a disease that is associated with an increased risk of human immunodeficiency virus acquisition and transmission. No approved vaccines are currently available to protect against HSV-1 or HSV-2 infection. We developed a novel HSV vaccine strategy that uses a replication-competent strain of HSV-1, NS-gEnull, which has a defect in anterograde and retrograde directional spread and cell-to-cell spread. Following scratch inoculation on the mouse flank, NS-gEnull replicated at the site of inoculation without causing disease. Importantly, the vaccine strain was not isolated from dorsal root ganglia (DRG). We used the flank model to challenge vaccinated mice and demonstrated that NS-gEnull was highly protective against wild-type HSV-1. The challenge virus replicated to low titers at the site of inoculation; therefore, the vaccine strain did not provide sterilizing immunity. Nevertheless, challenge by HSV-1 or HSV-2 resulted in less-severe disease at the inoculation site, and vaccinated mice were totally protected against zosteriform disease and death. After HSV-1 challenge, latent virus was recovered by DRG explant cocultures from <10% of vaccinated mice compared with 100% of mock-vaccinated mice. The vaccine provided protection against disease and death after intravaginal challenge and markedly lowered the titers of the challenge virus in the vagina. Therefore, the HSV-1 gEnull strain is an excellent candidate for further vaccine development.Herpes simplex virus type 1 (HSV-1) and HSV-2 are closely related alphaherpesviruses that cause lifelong infections for which there is no cure. HSV-1 generally causes oral lesions, while HSV-2 remains the most common cause of genital ulcers; however, the epidemiology of genital herpes is changing in that 35% to 50% of new cases are now caused by HSV-1 (40). The life cycles of HSV-1 and HSV-2 are similar. After replication in epithelial cells, HSV enters local sensory nerve endings of the peripheral nervous system and spreads in a retrograde direction to neuronal cell bodies. HSV then spreads to adjacent neurons in ganglia, where a lifelong latent infection is established (43). During recurrences, HSV travels in the anterograde direction along axon fibers from infected neuronal cell bodies to skin or mucosal surfaces, resulting in asymptomatic virus shedding or symptomatic vesicles and ulcers.More than 70% of people in the United States are seropositive for HSV-1 or HSV-2 by age 49, with HSV-1 being more prevalent (44). Worldwide, the prevalence of infection is generally higher than in the United States (34). Complications of HSV infection include meningitis, encephalitis, esophagitis, disseminated disease in neonates and immunocompromised individuals, and herpes stromal keratitis, which can lead to blindness. Additionally, HSV-2 infection increases human immunodeficienc...

Herpes Simplex Virus Type 1 Glycoprotein E Mediates Retrograde Spread from Epithelial Cells to Neurites

“…In the murine flank model, wild-type (WT) virus replicates in the skin and then infects sensory neurons and spreads in a retrograde direction to the dorsal root ganglia (DRG). In this model, gE-deleted HSV-1 replicates in the skin but is not detected in the DRG (9,44). This phenotype differs from gE-deleted PRV, which is able to reach the DRG at WT levels (8).…”

“…Additionally, gE/gI promotes spread between epithelial cells. Viruses lacking either gE or gI form characteristically small plaques in cell culture and small inoculation site lesions in mice (4,9,18,40,58). In animal models, gE and gI also mediate viral spread in both anterograde and retrograde directions (4,19,44,56).…”

“…In all cases, the gE-deleted virus showed a pronounced defect in spread from the inoculation site to the cell bodies of innervating neurons. In the murine flank model, NS-gEnull was inoculated onto the skin, and no virus was detected in the DRG by titering or quantitative PCR (9,44). In the murine retina model, NS-gEnull was injected into the vitreous body of the eye, and no viral antigens were detected at brain sites reached by retrograde spread from the eye (56).…”

“…In vivo spread of gE-deleted HSV-1 to secondary tissues is influenced by reduced epithelial cell-to-cell spread at the inoculation site, resulting in lower titers available to infect neurons (4,9,18). Therefore, we used a compartmentalized neuron culture system to directly study retrograde spread of HSV-1.…”

“…However, these three proteins are dispensable for retrograde spread (3,8,11,12,31,46). In contrast, numerous animal models of infection have shown that HSV-1 gE is required for retrograde spread from the inoculation site to the cell bodies of innervating neurons (4,9,44,56). In the murine flank model, wild-type (WT) virus replicates in the skin and then infects sensory neurons and spreads in a retrograde direction to the dorsal root ganglia (DRG).…”