The bovine respiratory disease complex (BRDC) remains a major problem for both beef and dairy cattle industries worldwide. BRDC frequently involves an initial viral respiratory infection resulting in immunosuppression, which creates a favorable condition for fatal secondary bacterial infection. Current polyvalent modified live vaccines against bovine herpesvirus type 1(BoHV-1) and bovine viral diarrhea virus (BVDV) have limitations concerning their safety and efficacy. To address these shortcomings and safety issues, we have constructed a quadruple gene mutated BoHV-1 vaccine vector (BoHV-1 QMV), which expresses BVDV type 2, chimeric E2 and Flag-tagged Erns-fused with bovine granulocyte monocyte colony-stimulating factor (GM-CSF) designated here as QMV-BVD2*. Here we compared the safety, immunogenicity, and protective efficacy of QMV-BVD2* vaccination in calves against BVDV-2 with Zoetis Bovi-shield Gold 3 trivalent (BoHV-1, BVDV types 1 and 2) vaccine. The QMV-BVD2* prototype subunit vaccine induced the BoHV-1 and BVDV-2 neutralizing antibody responses along with BVDV-1 and -2 cross-reactive cellular immune responses. Moreover, after a virulent BVDV-2 challenge, the QMV-BVD2* prototype subunit vaccine conferred a more rapid recall BVDV-2-specific neutralizing antibody response and considerably better recall BVDV types 1 and 2-cross protective cellular immune responses than that of the Zoetis Bovi-shield Gold 3.

Studies of immune responses elicited by bovine viral diarrhea virus (BVDV) vaccines have primarily focused on the characterization of neutralizing B cell and CD4⁺ T cell epitopes. Despite the availability of commercial vaccines for decades, BVDV prevalence in cattle has remained largely unaffected. There is limited knowledge regarding the role of BVDV-specific CD8⁺ T cells in immune protection, and indirect evidence suggests that they play a crucial role during BVDV infection. In this study, the presence of BVDV-specific CD8⁺ T cells that are highly cross-reactive in cattle was demonstrated. Most importantly, novel potent IFN-γ–inducing CD8⁺ T cell epitopes were identified from different regions of BVDV polyprotein. Eight CD8⁺ T cell epitopes were identified from the following structural BVDV Ags: E^rns, E1, and E2 glycoproteins. In addition, from nonstructural BVDV Ags N^pro, NS2-3, NS4A-B, and NS5A-B, 20 CD8⁺ T cell epitopes were identified. The majority of these IFN-γ–inducing CD8⁺ T cell epitopes were found to be highly conserved among more than 200 strains from BVDV-1 and -2 genotypes. These conserved epitopes were also validated as cross-reactive because they induced high recall IFN-γ⁺CD8⁺ T cell responses ex vivo in purified bovine CD8⁺ T cells isolated from BVDV-1– and -2–immunized cattle. Altogether, 28 bovine MHC class I–binding epitopes were identified from key BVDV Ags that can elicit broadly reactive CD8⁺ T cells against diverse BVDV strains. The data presented in this study will lay the groundwork for the development of a contemporary CD8⁺ T cell–based BVDV vaccine capable of addressing BVDV heterogeneity more effectively than current vaccines. Key Points BVDV-1– and -2–immunized cattle developed cross-reactive CD8⁺ T cells. IFN-γ–inducing CD8⁺ T cell epitopes were identified from various BVDV Ags. CD8⁺ T cell epitopes are highly conserved across >200 BVDV-1 and -2 strains.