Human T-lymphotropic virus 1 (HTLV-1) is associated with the development of several pathologies and chronic infection in humans. The inefficiency of the available treatments and the challenge in developing a protective vaccine highlight the need to produce effective immunotherapeutic tools. The HTLV-1 basic leucine zipper (bZIP) factor (HBZ) plays an important role in the HTLV-1 persistence, conferring a survival advantage to infected cells by reducing the HTLV-1 proteins expression, allowing infected cells to evade immune surveillance, and enhancing cell proliferation leading to increased proviral load. We have generated a recombinant Modified Virus Vaccinia Ankara (MVA-HBZ) and a plasmid DNA (pcDNA3.1(+)-HBZ) expressing a multiepitope protein based on peptides of HBZ to study the immunogenic potential of this viral-derived protein in BALB/c mice model. Mice were immunized in a prime-boost heterologous protocol and their splenocytes (T CD4⁺ and T CD8⁺) were immunophenotyped by flow cytometry and the humoral response was evaluated by ELISA using HBZ protein produced in prokaryotic vector as antigen. T CD4⁺ and T CD8⁺ lymphocytes cells stimulated by HBZ-peptides (HBZ_42–50 and HBZ_157–176) showed polyfunctional double positive responses for TNF-α/IFN-γ, and TNF-α/IL-2. Moreover, T CD8⁺ cells presented a tendency in the activation of effector memory cells producing granzyme B (CD44^+High/CD62L^−Low), and the activation of Cytotoxic T Lymphocytes (CTLs) and cytotoxic responses in immunized mice were inferred through the production of granzyme B by effector memory T cells and the expression of CD107a by CD8⁺ T cells. The overall data is consistent with a directive and effector recall response, which may be able to operate actively in the elimination of HTLV-1-infected cells and, consequently, in the reduction of the proviral load. Sera from immunized mice, differently from those of control animals, showed IgG-anti-HBZ production by ELISA. Our results highlight the potential of the HBZ multiepitope protein expressed from plasmid DNA and a poxviral vector as candidates for therapeutic vaccine.

Background/Objectives: Varicellovirus bovinealpha1 and Varicellovirus bovinealpha5 (BoAHV-1 and BoAHV-5), respectively, are widely distributed pathogens that cause distinct clinical conditions in cattle including infectious bovine rhinotracheitis, infectious pustular vulvovaginitis/balanoposthitis, and meningoencephalitis. Due to the establishment of viral latency, controlling these infections is challenging, and vaccination remains the most effective strategy. In this study, vaccine candidates targeting both BoAHV-1 and BoAHV-5 were developed. Methods: A synthetic gene encoding immunodominant epitopes from the gB and gD proteins and tegument phosphoprotein of BoAHV-1 and BoAHV-5 was designed to produce a multi-epitope recombinant antigen, expressed both in a prokaryotic system (RecBoAHV) and by a modified vaccinia Ankara (MVA-BoAHV) viral vector. The binding affinity of MHC-I to bovine leukocyte antigens (BoLA) was predicted using the NetMHCpan tool (version 4.1). The immunogenicity of the vaccine candidates was evaluated in rabbit and mouse models, using prime-boost immunization protocols. Sera from bovines naturally infected with BoAHV-1 and/or BoAHV-5 were used to evaluate the chimeric protein antigenicity. Immune responses were assessed by indirect ELISA and Western blot. Results: The recombinant multi-epitope protein was effectively recognized by IgG and IgM antibodies in sera from cattle naturally infected with BoAHV-1 or BoAHV-5, confirming the antigenic specificity. Both RecBoAHV and MVA-RecBoAHV induced strong and specific humoral immune responses in rabbits following a homologous prime-boost regimen. In mice, both homologous and heterologous prime-boost protocols revealed robust immunogenicity, particularly after the second booster dose. Conclusions: These findings highlight the immunogenic potential of the RecBoAHV multi-epitope vaccine candidates for controlling BoAHV-1 and BoAHV-5 infections. Further characterization of these vaccine formulations is currently underway in bovine, the target specie.

Bovine herpesviruses comprise a diverse group of pathogens with distinct tissue tropisms, epidemiological patterns, and clinical relevance. Bovine alphaherpesviruses 1 and 5 (BoAHV-1, BoAHV-5) are the best characterized, given their association with respiratory, reproductive, and neurological disease, whereas less is known about BoAHV-2 and the gammaherpesviruses BoGHV-4 and BoGHV-6. A central challenge for control is the capacity of these viruses to establish lifelong latent or persistent infection, evade host immunity, and reactivate under physiological or stress-related conditions. This review critically examines bovine herpesvirus pathogenesis and host immune responses, emphasizing viral tropism, latency, reactivation, innate and adaptive immune responses, and immune-evasion mechanisms. We evaluate current vaccination strategies, including modified-live, inactivated, intranasal, and gene-deleted marker vaccines, highlighting their capacity to reduce clinical disease and shedding alongside their limited ability to prevent infection, latency, or reactivation, with attention to cross-protection between BoAHV-1 and BoAHV-5 and regional differences in vaccine availability. Emerging platforms, including attenuated gene-deleted viruses and subunit, multi-epitope, DNA, and vectored vaccines, are assessed according to experimental evidence. Although several candidates improve humoral, cellular, or mucosal immunity, none has consistently achieved sterilizing immunity together with prevention of latency and transmission, reinforcing the need to integrate improved vaccination with DIVA-compatible surveillance, biosecurity, and long-term control strategies.