A recombinant baculovirus expressing multi-epitopes elicits protective immunity against ALV-J infection in chickens

Avian leukosis virus subgroup J (ALV-J) remains a persistent threat to the poultry industry owing to its oncogenic and immunosuppressive properties. We have previously established the pivotal role of CD8⁺ T cells in clearing ALV-J and identified several immunodominant CD8⁺ T cell epitopes. Building on this, we constructed a multi-epitope recombinant baculovirus vaccine (BV-GPGP) that incorporated the newly defined CD8⁺ T-cell epitopes with reported B-cell epitopes to induce both cellular and humoral immunity. Following a prime-boost immunization regimen with BV-GPGP, all vaccinated chickens produced ALV-J-specific antibodies, and the neutralizing antibody titer reached 1:8. Compared to the BV-WT group, the BV-GPGP group exhibited significantly higher IgM and IgY titres and increased proportions of B cells and CD8⁺ T cells. Furthermore, BV-GPGP vaccination significantly upregulated the expression of immune-related genes, including IL-13, IFN-γ, NK lysin, perforin, and IL-2. ELISPOT assays further confirmed enhanced IFN-γ secretion in response to the conserved ALV-J peptides Gag_374-382 and Gag₄₀₃-₄₁₁ in BV-GPGP group. After ALV-J challenge, BV-GPGP markedly reduced viremia at 7 days post-infection (DPI) (33.3%, 3/9) compared with BV-WT and PBS controls (88.9%, 8/9), and viremia was undetectable by 21 DPI in the BV-GPGP group whereas it persisted in the PBS group. These findings demonstrate that BV-GPGP effectively elicits both humoral and cellular immune responses and provides measurable protection against ALV-J.