How to Tackle EBV and KSHV Infection: Treatments and Vaccines for Tumorigenic Human γ-Herpesviruses

Abstract

Epstein-Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV) are oncogenic γ-herpesviruses, responsible for around 2% of cancer cases worldwide. In addition to its transformation potential, EBV is involved in pathogenesis of autoimmune diseases, such as multiple sclerosis, as well as infectious mononucleosis. Despite EBV and KSHV association with several pathologies, currently there is no effective treatment to counteract their infection. In this thesis, we address two different treatment approaches: antiviral compounds and vaccines.

In the first study, we evaluated the antiviral capacity of entry inhibitors, primarily sulfated and sulfonated cyclodextrins, to inhibit KSHV and EBV infection. While only KSHV was susceptible to sulfated cyclodextrins in vitro, both EBV and KSHV were inhibited by the sulfonated cyclodextrins. We found that the two compounds exert antiviral effects through different mechanisms. Sulfated cyclodextrins obstructed binding of the virus to its cellular receptor but leave the viral particle intact (virustatic effect). In contrast, sulfonated cyclodextrins led to complete disruption of the viral particle (virucidal effect). In vivo, prophylaxis with sulfonated cyclodextrins reduced KSHV infection burden in a humanized mouse model, suggesting a potential role as KSHV antivirals.

The second project focused on the development of a live attenuated vaccine against EBV, which comprises a yellow fever virus 17D (YF17D) viral vector carrying the immunogenic C-terminus of the Epstein-Barr nuclear antigen 1 (EBNA1). The vector, denominated YF-E1, demonstrated in vitro immunogenic potential in activating CD8+ and CD4+ EBNA1-specific T cells. When evaluated as a prophylactic vaccine against EBV-associated tumors in a conventional humanized mouse model, YF-E1 showed promising capacity to reduce metastasis. However, immunogenicity and replication of the vaccine appeared to be suboptimal. Therefore, we tested YF-E1 in a second humanized mouse model, known to reproduce certain human-like YF17D immune responses, combined with temporary blocking of the mouse type I interferon receptor. This strategy was followed to enhance YF-E1 replication and immunogenicity. Indeed, we observed increased YF17D replication in this model. Moreover, induction of YF17D neutralizing antibodies as well as earlier and stronger T cell responses upon YF-E1 vaccination were observed. Assessment of protection against EBV remains to be elucidated.