Immune Control and Vaccination against the Epstein-Barr Virus in Humanized Mice

Urgency and necessity of Epstein-Barr virus prophylactic vaccines

Epstein-Barr virus (EBV), a γ-herpesvirus, is the first identified oncogenic virus, which establishes permanent infection in humans. EBV causes infectious mononucleosis and is also tightly linked to many malignant diseases. Various vaccine formulations underwent testing in different animals or in humans. However, none of them was able to prevent EBV infection and no vaccine has been approved to date. Current efforts focus on antigen selection, combination, and design to improve the efficacy of vaccines. EBV glycoproteins such as gH/gL, gp42, and gB show excellent immunogenicity in preclinical studies compared to the previously favored gp350 antigen. Combinations of multiple EBV proteins in various vaccine designs become more attractive approaches considering the complex life cycle and complicated infection mechanisms of EBV. Besides, rationally designed vaccines such as virus-like particles (VLPs) and protein scaffold-based vaccines elicited more potent immune responses than soluble antigens. In addition, humanized mice, rabbits, as well as nonhuman primates that can be infected by EBV significantly aid vaccine development. Innovative vaccine design approaches, including polymer-based nanoparticles, the development of effective adjuvants, and antibody-guided vaccine design, will further enhance the immunogenicity of vaccine candidates. In this review, we will summarize (i) the disease burden caused by EBV and the necessity of developing an EBV vaccine; (ii) previous EBV vaccine studies and available animal models; (iii) future trends of EBV vaccines, including activation of cellular immune responses, novel immunogen design, heterologous prime-boost approach, induction of mucosal immunity, application of nanoparticle delivery system, and modern adjuvant development.

A bivalent Epstein-Barr virus vaccine induces neutralizing antibodies that block infection and confer immunity in humanized mice

Epstein-Barr virus (EBV) is the major cause of infectious mononucleosis and is associated with several human cancers and, more recently, multiple sclerosis. Despite its prevalence and health impact, there are currently no vaccines or treatments. Four viral glycoproteins (gp), gp350 and gH/gL/gp42, mediate entry into the major sites of viral replication, B cells, and epithelial cells. Here, we designed a nanoparticle vaccine displaying these proteins and showed that it elicits potent neutralizing antibodies that protect against infection in vivo. We designed single-chain gH/gL and gH/gL/gp42 proteins that were each fused to bacterial ferritin to form a self-assembling nanoparticle. Structural analysis revealed that single-chain gH/gL and gH/gL/gp42 adopted a similar conformation to the wild-type proteins, and the protein spikes were observed by electron microscopy. Single-chain gH/gL or gH/gL/gp42 nanoparticle vaccines were constructed to ensure product homogeneity needed for clinical development. These vaccines elicited neutralizing antibodies in mice, ferrets, and nonhuman primates that inhibited EBV entry into both B cells and epithelial cells. When mixed with a previously reported gp350 nanoparticle vaccine, gp350D₁₂₃, no immune competition was observed. To confirm its efficacy in vivo, humanized mice were challenged with EBV after passive transfer of IgG from mice vaccinated with control, gH/gL/gp42+gp350D₁₂₃, or gH/gL+gp350D₁₂₃ nanoparticles. Although all control animals were infected, only one mouse in each vaccine group that received immune IgG had detectable transient viremia. Furthermore, no EBV lymphomas were detected in immune animals. This bivalent EBV nanoparticle vaccine represents a promising candidate to prevent EBV infection and EBV-related malignancies in humans.

Dose-Dependent Outcome of EBV Infection of Humanized Mice Based on Green Raji Unit (GRU) Doses

Humanized mouse models are used as comprehensive small-animal models of EBV infection. Previously, infectious doses of EBV used in vivo have been determined mainly on the basis of TD₅₀ (50% transforming dose), which is a time-consuming process. Here, we determined infectious doses of Akata-EBV-GFP using green Raji units (GRUs), and characterized dose-dependent effects in humanized mice. We defined two outcomes in vivo, including an infection model and a lymphoma model, following inoculation with low or high doses of Akata-EBV-GFP, respectively. Inoculation with a low dose induced primary B cells to become lymphoblastoid cell lines in vitro, and caused latent infection in humanized mice. In contrast, a high dose of Akata-EBV-GFP resulted in primary B cells death in vitro, and fatal B cell lymphomas in vivo. Following infection with high doses, the frequency of CD19⁺ B cells decreased, whereas the percentage of CD8⁺ T cells increased in peripheral blood and the spleen. At such doses, a small part of activated CD8⁺ T cells was EBV-specific CD8⁺ T cells. Thus, GRUs quantitation of Akata-EBV-GFP is an effective way to quantify infectious doses to study pathologies, immune response, and to assess (in vivo) the neutralizing activity of antibodies raised by immunization against EBV.

Nanotechnology Frontiers in γ-Herpesviruses Treatments

Epstein–Barr Virus (EBV) and Kaposi’s sarcoma associated-herpesvirus (KSHV) are γ-herpesviruses that belong to the Herpesviridae family. EBV infections are linked to the onset and progression of several diseases, such as Burkitt lymphoma (BL), nasopharyngeal carcinoma (NPC), and lymphoproliferative malignancies arising in post-transplanted patients (PTDLs). KSHV, an etiologic agent of Kaposi’s sarcoma (KS), displays primary effusion lymphoma (PEL) and multicentric Castleman disease (MCD). Many therapeutics, such as bortezomib, CHOP cocktail medications, and natural compounds (e.g., quercetin or curcumin), are administrated to patients affected by γ-herpesvirus infections. These drugs induce apoptosis and autophagy, inhibiting the proliferative and cell cycle progression in these malignancies. In the last decade, many studies conducted by scientists and clinicians have indicated that nanotechnology and nanomedicine could improve the outcome of several treatments in γ-herpesvirus-associated diseases. Some drugs are entrapped in nanoparticles (NPs) expressed on the surface area of polyethylene glycol (PEG). These NPs move to specific tissues and exert their properties, releasing therapeutics in the cell target. To treat EBV- and KSHV-associated diseases, many studies have been performed in vivo and in vitro using virus-like particles (VPLs) engineered to maximize antigen and epitope presentations during immune response. NPs are designed to improve therapeutic delivery, avoiding dissolving the drugs in toxic solvents. They reduce the dose-limiting toxicity and reach specific tissue areas. Several attempts are ongoing to synthesize and produce EBV vaccines using nanosystems.

Therapeutic vaccines for aggressive B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common aggressive B-cell lymphoma and highly heterogeneous disease. With the standard immunochemotherapy, anti-CD20 antibody rituximab (R-) plus CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy, 30-40% of DLBCLs are refractory to initial immunochemotherapy or experience relapse post-therapy with poor clinical outcomes despite salvage therapies. Mechanisms underlying chemoresistance and relapse are heterogeneous across DLBCL and within individual patients, representing hurdles for targeted therapies targeting a specific oncogenic signaling pathway. In recent years, paradigm-shifting immunotherapies have shown impressive efficacy in various cancer types regardless of underlying oncogenic mechanisms. Vaccines are being developed for DLBCL to build protective immunity against relapse after first complete remission and to promote antitumor immune responses synergizing with immune checkpoint inhibitors to treat refractory/relapsed patients. This article provides a brief review of current progress in vaccine development in DLBCL and discussion on immunologic mechanisms underlying the therapeutic effectiveness and resistance.