Immunogenicity and protection mediated by next-generation EBV gH/gL vaccines in non-human primate and humanized mouse models of infection

Abstract

Epstein Barr Virus (EBV) is an orally transmitted, γ-herpesvirus infecting 90% of adults worldwide. Infection is associated with various cancers and development of multiple sclerosis. A vaccine that prevents infection and reduce the global burden of EBV-associated disease is an urgent, yet unmet need. EBV infects epithelial cells and B cells, therefore an effective vaccine would likely have to block infection of both these cell types. The viral gH/gL glycoprotein complex is essential for entry, making it an attractive vaccine target. Additionally, antibodies against gH/gL have been shown to be protective against infection in vitro and in vivo. In this work we evaluate two different next-generation vaccine platforms to immunize animals with EBV gH/gL. In one project we evaluated the immunogenicity of a multimeric gH/gL nanoparticle vaccine administered with two different adjuvants, Sigma Adjuvant System (SAS) and Saponin/MPLA nanoparticles (SMNP), in rhesus macaques. Formulation with SMNP elicited higher titers of binding and neutralizing antibodies, and higher frequency of vaccine-specific IFNɣ+IL2+ CD4+ T cells. After oral challenge with the EBV orthologue rhesus lymphocryptovirus (rhLCV), all macaques in the control and SAS groups became infected, while one of four animals in the SMNP group remained aviremic and were seronegative against non-vaccine antigens, indicating protection. Further study revealed considerable antigenic disparity between the rhLCV gH/gL and EBV gH/gL. We found that our protected animal displayed a broader pattern of epitope recognition, as visualized by electron microscopy polyclonal epitope mapping, which may be linked to protection. The observed prevention of rhLCV infection in one macaque, despite the substantial antigenic disparity between the vaccine and challenge strain, supports the further pursuit of gH/gL nanoparticle vaccines against EBV. In a second project, we have developed and optimized an alphavirus-derived self-amplifying mRNA vaccine platform (repRNA) to immunize mice with EBV gH/gL. The lead candidate tested was able to elicit a vaccine-specific CD8+ T cell response as well as high-titers of neutralizing antibodies that persisted for at least 8 months post immunization. Transfer of vaccine-elicited IgG protected humanized mice from EBV-driven tumor formation and death following high-dose viral challenge. These data demonstrate that repRNA-gH/gL formulated with a localizing cationic nanocarrier (LION) is a promising candidate vaccine for preventing EBV infection and/or related malignancies in humans and encourage clinical development of vaccines targeting EBV gH/gL. A third work-in-progress section describes a potential route of Fc-mediated EBV infection. In sum, this work describes the generation of immunogenic next-generation vaccines targeting EBV gH/gL and highlights some of the challenges and considerations of using the two most common animal models for EBV to evaluate vaccine-elicited protection.