Abstract Genital herpes affects 650 million people globally. Vaccines are urgently needed to prevent infection and treat individuals already infected. During the current funding cycle, we developed a candidate vaccine for preventing genital herpes that uses nucleoside-modified mRNA encapsulated within lipid nanoparticles (LNP) to express herpes simplex virus type 2 (HSV-2) glycoproteins C, D, and E (gC2, gD2, gE2). The vaccine targets an entry molecule, gD2, and two immune evasion molecules, gC2 and gE2. Our vaccine candidate will enter phase 1 human trials in December 2022. Our new goals are to define the immune correlates of protection for the trivalent vaccine using sera we collected from immunized mice and guinea pigs during this grant cycle, and to develop an mRNA-based vaccine as immunotherapy. In Aim 1, we will define the immune correlates of protection. Our hypothesis is that by defining immune correlates, we will better understand the mechanisms of vaccine protection and the immune responses required for success in human trials. We will use high throughput biosensor technology and our extensive panel of gC2, gD2, and gE2 monoclonal antibodies to determine whether the trivalent vaccine produces antibodies to crucial epitopes on gC2, gD2 and gE2. The epitopes of interest include those on gC2 that bind complement component C3b to inhibit complement activation, gE2 that bind the IgG Fc domain to block Fc-mediated activities including complement activation and antibody-dependent cellular cytotoxicity, and gD2 that bind to cell receptors for virus entry and mediate cell-to-cell spread. We will correlate antibody binding to these important epitopes with protection against clinical outcomes including genital lesions and latent infection. The epitope mapping studies will enable us to assess the contribution of each of the glycoprotein immunogens to protection. Aim 2 uses mRNA immunogens to develop a genital herpes therapeutic vaccine. We hypothesize that T cell responses will be particularly important for a successful therapeutic vaccine. In Preliminary studies, we infected guinea pigs intravaginally with HSV-2 and once recovered, we immunized with glycoproteins E and I (gE2/gI2) mRNA-LNP. gE2/gI2 mRNA-LNP reduced the number of days with recurrent genital lesions by 47%, an excellent start towards our primary endpoint of >70% reduction in recurrent genital lesions. To achieve our goal of >70%, we will incorporate other antigens, including additional glycoproteins, immediate early, capsid and tegument immunogens and assess CD4 and CD8 T cell responses in male and female mice. We will advance the best candidates for efficacy studies in guinea pigs. We will focus initially on glycoprotein immunogens because of the remarkable success of a therapeutic vaccine for a closely related virus, varicella zoster virus, that uses glycoprotein E as the antigen. We will include the trivalent gC2/gD2/gE2 vaccine in the therapeutic studies to determine whether one vaccine formulation will be effective for prevention and treatment. If successful, the studies in Aims 1 and 2 will have a positive impact on billions of people by preventing and treating genital herpes.

Project Narrative Vaccines are urgently needed to prevent genital herpes and treat people already infected. We developed an nucleoside-modified mRNA vaccine candidate to prevent genital herpes that will enter phase 1 human trials in December 2022. In this renewal application, we propose using serum samples from mice and guinea pigs collected during the prior grant cycle to define the immune correlates of protection for the prevention vaccine, and to immunize mice and guinea pigs with nucleoside-modified mRNA antigens to develop a vaccine for treating genital herpes.