Submitted to: Avian Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2016
Publication Date: 6/6/2016
Citation: Mays, J.K., Black Pyrkosz, A.A., Spatz, S.J., Fadly, A.M., Dunn, J.R. 2016. Protective efficacy of a recombinant bacterial artificial chromosome clone of a very virulent Marek’s disease virus containing a reticuloendotheliosis virus long terminal repeat. Avian Pathology. 45(6):1-31. doi:10.1080/03079457.2016.1197376.
Interpretive Summary: Marek’s disease virus (MDV) causes Marek’s disease (MD), a cancer-like disease in poultry. Vaccination is used worldwide to control MD, but increasingly virulent field strains can overcome this protection, driving a need to create new vaccines. The use of recombinant DNA technology has greatly increased the ability to generate new vaccine candidates. We recently developed a recombinant candidate vaccine by inserting the long terminal repeat (LTR) region of a reticuloendotheliosis virus (REV) into a very virulent MDV strain. This recombinant did not cause disease in susceptible chickens. In the current study, we analyzed the ability of the recombinant vaccine candidate to protect against challenge with a very virulent plus MDV strain (vv+MDV). The recombinant vaccine candidate did not demonstrate the same level of protection against MD lesions as the most effective commercially available MD vaccine. If combined with other MD vaccines, however, the easy manipulation of this recombinant virus could potentially make it an excellent platform as a vectored vaccine (with genes from other poultry pathogens inserted).
Technical Abstract: Marek’s disease virus (MDV), an alphaherpesvirus, causes Marek’s disease (MD), a lymphoproliferative disease in poultry characterized by T-cell lymphomas, nerve lesions and mortality. Vaccination is used worldwide to control MD, but increasingly virulent field strains can overcome this protection, driving a need to create new vaccines. Previous studies revealed that insertion of reticuloendotheliosis virus (REV) long-terminal repeat (LTR) into a bacterial artificial chromosome (BAC) clone of a very virulent strain of MDV, Md5 rendered the resultant recombinant virus, rMd5 REV-LTR BAC, fully attenuated in maternal antibody positive (Mab+) chickens at passage 40. In the current study, the protective efficacy of rMd5 REV-LTR BAC was evaluated. First, passage 70 was identified as being fully attenuated in Mab- chickens and chosen as the optimal passage level for use in protective efficacy studies. Second, three protective efficacy trials were conducted comparing the rMd5 REV-LTR p70 BAC to the CVI988/Rispens vaccine. Groups of Mab+ and Mab- 15I5×71 chickens were vaccinated in ovo at 18 days of embryonation or intra-abdominally at day of hatch, and challenged at 5 days post-hatch with the vv+MDV strain 686. Vaccination at day of hatch and in ovo with rMd5 REV-LTR p70 BAC protected chickens against MDV-induced bursa and thymic atrophy, but did not provide the same level of protection against MD tumors as that afforded by the commercial vaccine, CVI988/Rispens.