Attenuation of a highly virulent oncogenic herpesvirus by computer-aided virus reengineering

• Applicant: Professor Dr. Nikolaus Osterrieder
• Subject Area: Veterinary Medical Science ; Virology
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 240384313

Vaccines are the most valuable and cost-effective tools to fight infectious diseases, particularly virus infections. The ´death by thousand cut´ is a new and revolutionary strategy that has enabled attenuation of viruses to a desired level, in a controlled manner, and with unprecedented efficiency and speed. This strategy, also known as synthetic attenuated virus engineering (SAVE), is based on introduction of several hundred nucleotide mutations into coding sequences without changing the amino acid composition of encoded proteins. Thus, the mutated virus, a modified live viral vaccine (MLV), is antigenically identical with the parental pathogenic virus, but its replication and pathogenic capacity is impaired. The actual encoding of amino acid in open reading frames (ORFs) is biased and some synonymous codons are used more often than others (codon bias). Consequently, utilization of rare codons results in suboptimal translation. Similarly, but independently of codon bias, codon pair combinations in ORFs are also not random. Some synonymous codon pairs are found in ORFs significantly more or less frequently than it would be expected based on the overall frequencies of two codons that form a codon pair (codon pair bias). Codon pair usage affects translational efficiency more than codon bias, and thus, unfavorable codon pairs are normally rarely used. Utilization of naturally underrepresented codon pairs creates unfavorable conditions for efficient protein translation, and this causes attenuation of a virus. The SAVE strategy has been successfully used in attenuation of two unrelated RNA viruses (poliovirus and influenza virus) and a pathogenic bacterium (Streptococcus pneumoniae), but it has not been tested on large double-stranded DNA viruses, such as asfarviruses, poxviruses or herpesviruses. Before this technology can be applied for production of viral vaccines, it must be comprehensively studied and tested.The proposed project will explore promising applications this technology for the first time on a large DNA virus. The overall goal of the proposed project is to determine how a herpesvirus can be attenuated most efficiently by the SAVE technology. To address this objective we will use a unique small animal model, which involves the highly virulent and oncogenic Marek´s disease herpesvirus (MDV), and the chicken. The central hypothesis for this project is that codon pair deoptimization of MDV genes will result in fully attenuated herpesviruses and that the attenuated viruses will be highly efficacious MLV vaccines. The mutant viruses will be first constructed and tested in vitro, and then evaluated for their ability to induce vaccinal protection without being virulent themselves by in vivo experiments.We expect that the proposed will have significant and positive impact on virology and vaccinology and that comprehensive understanding of the SAVE technology will ultimately lead the development of superior animal and human vaccines.

• DFG Programme: Research Grants