Insertion of the Marek’s Disease Virus Virokine vIL8 (aka vCXCL13) into a Vaccine Strain

• Stefanie Severin, Animal Science, University of Delaware

• Mark Parcells, Animal and Food Sciences, University of Delaware

Marek’s Disease (MD) is the most common cancer in the Animal Kingdom, caused by a highly contagious cell-associated alphaherpesvirus known as Marek’s Disease Virus (MDV). In chickens and turkeys, MD is characterized by paralysis, immune suppression, T-cell lymphomas, and death. This disease spreads through the inhalation of dander or litter contaminated with feather follicles shed from infected birds. MDV is composed of three viruses: Mardivirus-1 (MDV-1), Mardivirus-2 (MDV-2), and Herpesvirus of Turkeys (HVT). MDV-1 strains are responsible for causing cancer in infected birds. There are existing vaccines that prevent mortality and the development of tumors, the most common of which is derived from HVT. However, vaccinated birds can still become infected and shed the virus, which may be conducive to the evolution of more virulent strains. In 2001, it was discovered that MDV encoded what appeared like a viral version of the chicken interleukin-8 gene, and this this was named vIL-8 (Parcells and Kung). However, it has been revealed instead of portraying homology to IL-8, vIL-8 is more likely an orthologue to CXCL13, a chemokine in chickens. Unlike IL-8, CXCL13 recruits B cells rather than neutrophils. The deletion of vIL-8 from the MDV-1 genome significantly reduces the virus’ ability to infect B-cells early in infection (Haertle et. al, 2017). Thus, we hypothesize that adding this gene to the HVT vaccine strain will increase its replication by attracting more lymphocytes for infection. Upon insertion of vIL-8, we can perform a vaccine evaluation in live chickens. We will monitor the birds for any adverse outcomes including organ damage and tissue formation. Moreover, we will assess how the addition of vIL-8 affects replication in culture. As MDV can have devastating financial impacts on commercial flocks, a vaccine that induces a more robust immune response would be advantageous for poultry production.