Viral fitness dictates virulence and capacity to evade host immune defenses. Understanding the biological underpinnings of such features is essential for rational vaccine development. We have previously shown that the live-attenuated herpes simplex virus 1 (HSV-1) mutant lacking the nuclear localization signal (NLS) on the ICP0 gene (0ΔNLS) is sensitive to inhibition by interferon beta (IFN-) in vitro and functions as a highly efficacious experimental vaccine. Here, we characterize the host immune response and in vivo pathogenesis of HSV-1 0ΔNLS relative to its fully virulent parental strain in C57BL/6 mice. Additionally, we explore the role of type 1 interferon (IFN-␣/) signaling on virulence and immunogenicity of HSV-1 0ΔNLS and uncover a probable sex bias in the induction of IFN-␣/ in the cornea during HSV-1 infection. Our data show that HSV-1 0ΔNLS lacks neurovirulence even in highly immunocompromised mice lacking the IFN-␣/ receptor. These studies support the translational viability of the HSV-1 0ΔNLS vaccine strain by demonstrating that, while it is comparable to a virulent parental strain in terms of immunogenicity, HSV-1 0ΔNLS does not induce significant tissue pathology.IMPORTANCE HSV-1 is a common human pathogen associated with a variety of clinical presentations ranging in severity from periodic "cold sores" to lethal encephalitis. Despite the consistent failures of HSV subunit vaccines in clinical trials spanning the past 28 years, opposition to live-attenuated HSV vaccines predicated on unfounded safety concerns currently limits their widespread acceptance. Here, we demonstrate that a live-attenuated HSV-1 vaccine has great translational potential.KEYWORDS HSV-1, T cells, antibody, cornea, mouse, neovascularization S trategies for vaccine development have transitioned largely from empirical to so-called "next-generation" or rational approaches during the past 2 decades, a shift largely driven by technological advances and a better understanding of how innate immunity influences the generation of adaptive protection (1, 2). Despite these breakthroughs, the average person still acquires multiple herpesvirus infections during childhood (3). A licensed vaccine, however, exists only for varicella-zoster virus (VZV) (4). The live-attenuated Oka vaccine for VZV is generally well tolerated and has significantly reduced the incidence of VZV infection, morbidity, and mortality in the United States (5, 6). Furthermore, epidemiologic studies indicate that acquisition of herpes simplex virus 1 (HSV-1) has shifted toward early to late adolescence in recent decades within the United States, potentially creating an opportunity to introduce an effective prophylactic HSV-1 vaccine into the childhood vaccine regimen (7). HSV vaccines have been tested in multiple clinical trials, but these studies have focused on protein subunit vaccines