The Durability of Vaccine Efficacy against Ocular HSV-1 Infection Using ICP0 Mutants 0∆NLS and 0∆RING Is Lost over Time

Immune Response of the Host and Vaccine Development

Vaccines are one of the greatest achievements of modern medicine, offering an effective way to fight and control infectious diseases [...].

HSV-1 0∆NLS vaccine elicits a robust B lymphocyte response and preserves vision without HSV-1 glycoprotein M or thymidine kinase recognition

Effective experimental prophylactic vaccines against viral pathogens such as herpes simplex virus type 1 (HSV-1) have been shown to protect the host through T and/or B lymphocyte-driven responses. Previously, we found a live-attenuated HSV-1 mutant, 0ΔNLS used as a prophylactic vaccine, provided significant protection against subsequent ocular HSV-1 challenge aligned with a robust neutralizing antibody response. Yet, how the virus mutant elicited the humoral immune response relative to parental virus was unknown. Herein, we present the characterization of B cell subsets in vaccinated mice at times after primary vaccination and following boost compared to the parental virus, termed GFP105. We found that 0∆NLS-vaccinated mice possessed more CD4⁺ follicular helper T (T_FH) cells, germinal B cells and class-switched B cells within the first 7 days post-vaccination. Moreover, 0∆NLS vaccination resulted in an increase in plasmablasts and plasma cells expressing amino-acid transporter CD98 along with an elevated titer of HSV-1-specific antibody compared to GFP105-vaccinated animals. Furthermore, O∆NLS-vaccine-induced CD4⁺ (T_FH) cells produced significantly more IL-21 compared to mice immunized with the parental HSV-1 strain. In contrast, there were no differences in the number of regulatory B cells comparing the two groups of immunized mice. In comparing sera recognition of HSV-1-encoded proteins, it was noted antiserum from GFP105-vaccinated mice immunoprecipitated HSV-1 thymidine kinase (TK) and glycoprotein M (gM) whereas sera from 0∆NLS-immunized mice did not even though both groups of vaccinated mice displayed similar neutralizing antibody titers to HSV-1 and were highly resistant to ocular HSV-1 challenge. Collectively, the results suggest (1) the live-attenuated HSV-1 mutant 0∆NLS elicits a robust B cell response that drives select B cell responses greater than the parental HSV-1 and (2) HSV-1 TK and gM are likely expendable components in efficacy of a humoral response to ocular HSV-1 infection.

Noncognate Signals Drive Enhanced Effector CD8+ T Cell Responses through an IFNAR1-Dependent Pathway after Infection with the Prototypic Vaccine, 0ΔNLS, against Herpes Simplex Virus 1

Previous studies by our group identified a highly efficacious vaccine 0ΔNLS (deficient in the nuclear localization signal of infected cell protein 0) against HSV-1 in an experimental ocular mouse model. However, details regarding fundamental differences in the initial innate and adaptive host immune response were not explored. Here, we present a side-by-side analysis of the primary infection characterizing differences of the host immune response in mice infected with 0ΔNLS versus the parental, GFP105. The results show that local viral infection and replication are controlled more efficiently in mice exposed to 0ΔNLS versus GFP105 but clearance of infectious virus is equivalent comparing the two groups. Moreover, the 0ΔNLS-infected mice displayed enhanced effector CD8⁺ but not CD4⁺ T cell responses from the draining lymph nodes at day 7 post infection measured by IFN-γ and TNF-α production along with changes in cell metabolism. The increased effector function of CD8⁺ T cells from 0ΔNLS-infected mice was not driven by changes in antigen presentation but lost in the absence of a functional type I IFN pathway. These results are further supported by enhanced local expression of type I IFN and IFN-inducible genes along with increased IL-12 production by CD8α⁺DCs in the draining lymph nodes of 0ΔNLS-infected mice compared to the GFP105-infected animals. It was also noted the recall to HSV-1 antigen by CD8⁺ T cells was elevated in mice infected with HSV-1 0ΔNLS compared to GFP105. Collectively, the results underscore the favorable qualities of HSV-1 0ΔNLS as a candidate vaccine against HSV-1 infection. IMPORTANCE Cytotoxic T lymphocytes (CTLs) play a critical role in the clearance for many viral pathogens including herpes simplex virus 1 (HSV-1). Here, we compared the cellular innate and adaptive immune response in mice infected with an attenuated HSV-1 (0ΔNLS) found to be a highly successful experimental prophylactic vaccine to parental HSV-1 virus. We found that CD8⁺ T cell effector function is elevated in 0ΔNLS-infected mice through noncognate signals including IL-12 and type I interferon (IFN) pathways along with changes in CD8⁺ T cell metabolism whereas other factors including cell proliferation, co-stimulatory molecule expression and antigen presentation were dispensable. Thus, an increase in CTL activity established by exposure to HSV-1 0ΔNLS in comparison to parental HSV-1 likely contributes to the efficacy of the vaccine and underscores the nature of the attenuated virus as a vaccine candidate for HSV-1 infection.