Deciphering the role of telomeric repeats encoded by Marek’s disease virus-vaccines in latency, integration and protection against disease

• Applicant: Professor Benedikt Bertold Kaufer, Ph.D.
• Subject Area: Veterinary Medical Science
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525166869

Marek’s disease virus (MDV) is a highly oncogenic alphaherpesvirus that causes immunosuppression, neurological symptoms and T cell lymphomas in chickens. Vaccines are crucial to protect billions of chickens against this deadly virus every year. Three different live vaccine viruses, herpesvirus of turkey (HVT), gallid herpesvirus 3 (GaHV-3, aka. SB-1) and the attenuated MDV strain CVI988, are used to protect against MDV and also serve as vaccine vectors against other pathogens; however, hardly anything is known about the biology of these viruses. Our preliminary data revealed that theses vaccine viruses integrate into the ends of host chromosomes containing the host telomeres in latently infected cells. Intriguingly, these MDV vaccine viruses harbor telomeric repeat arrays (TMRs) identical to the host telomeres at both ends of their genomes, which could facilitate integration. We therefore hypothesize that the TMRs facilitate integration of the vaccine viruses into host telomeres, and thereby contribute to vaccine latency and vaccine protection due to prolonged exposure with the virus. We will address this hypothesis with three specific aims. Specifically, we will 1) determine the role of the TMRs in vaccine replication and integration in vitro, 2) elucidate the role of the TMRs in the establishment of vaccine latency and reactivation in the host and 3) investigate if integration and persistence of the vaccine viruses contribute to the protection against MDV. To achieve aim 1, we will generate recombinant vaccine viruses (HVT, SB-1 and CVI988) lacking TMRs (∆TMR) to assess the role of these viral telomere sequences in virus replication and integration using our recently established in vitro integration assay. Further, we will investigate the integration sites of wild type and ∆TMR vaccine viruses using our novel Bionano imaging approach. To address aim 2, we will infect chickens with wild type and ∆TMR vaccines (HVT-∆TMR already available) and monitor virus replication, dissemination and shedding into the environment over time. Beyond that, we will investigate latency and reactivation in the presence and absence of the TMRs in the lymphoid organs. In aim 3, we will vaccinate chickens with wild type and ∆TMR vaccines (HVT-∆TMR already available) and challenge them with a very virulent MDV strain. We will assess the efficacy of these vaccines in suppressing MDV replication and shedding, and determine if prolonged persistence facilitated by vaccine virus integration contributes to vaccine-protection against MDV. Taken together, this project will provide crucial insights into the biology of these important veterinary vaccine viruses including the roles of the TMRs in vaccine integration, latency and vaccine protection against this deadly pathogen.

• DFG Programme: Research Grants