Structural and immunological identification and antiviral infection experiment of the dominant cytotoxic T lymphocyte epitopes of the oncogenic Marek's disease virus

Mareks disease (MD) is a serious cancer caused by MDV in chickens, and it is also the first tumor disease that could be controlled by an attenuated vaccine in the world. However, the attenuated vaccine is able to inhibit only the formation of tumors but cannot prevent the infection of oncogenic viruses; instead, it leads to mutations and the emergence of a number of virulent strains. In this paper, the crystal structures of chicken MHC class I (pBF2*1501) molecules bound with 8-mer and 9-mer MDV peptides were solved. The results showed that the conformations of the 8-mer and 9-mer peptides in the antigen-binding groove (ABG) of pBF2*1501 are different; the ABG-8-mer is flat, and the ABG-9-mer has the "featured" M-type epitope morphology. Based on these results, multiple MDV epitopes were confirmed using the tetramer technique, and the immunoprotective effect of dominant epitope was confirmed using the protein adjuvant HSP108-N333 in BF2*1501-expressing chickens. The results showed that the two epitopes have obvious protective effects after a standard immunization program. After challenge, the mortality rate was only 20%, and the protective index (PI) reached 33% in the epitope group. The results verified that a single epitope could induce extremely strong specific antitumor T lymphocyte immunity. The results show that three key factors are crucial to obtain the best antitumor effect: accurate identification of dominant cytotoxic T lymphocyte (CTL) epitopes, efficient protein adjuvant and MHC matching. Meanwhile, the results also provided obvious advantages for the development of multiple epitope vaccines for tumor diseases. ImportanceMareks disease (MD) is the first tumor disease that can be controlled by an attenuated vaccine. However, the attenuated vaccine cannot prevent the infection of the oncogenic virus and instead leads to the emergence of a number of mutated virulent strains. First, the mechanism of the chicken BF2*1501 preferentially presents 9-mer peptide was clarified. Based on this result, multiple MDV epitopes were confirmed, and the dominant epitopes were identified. Subsequently, two epitope groups showed obvious protective effects after a standard immunization program, and the protective index (PI) of one of the epitope groups reached over 30%. The results showed that a single epitope could induce strong and efficient antitumor CTL immunity. Overall, three key factors are crucial to obtain the best antitumor effect: accurate identification of dominant epitopes, efficient protein adjuvant and MHC matching. Our results provide an obvious strategy for the development of multiple epitope vaccines in tumor diseases.