Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2011
Publication Date: 6/30/2011
Citation: Hunt, H.D., Dunn, J.R. 2011. Serial transfer of a transplantable tumor: implications for Marek's vaccine mechanisms. Avian Diseases. 55(2):293-301. Interpretive Summary: Marek’s Disease Virus (MDV) is a widespread pathogen of chickens that causes cancer-like disease consisting primarily of T cell tumors. How chickens defend against T cell tumors after virus infection is unknown. This report provides evidence that the chickens immune sytem can recognize MDV induced tumors and protect the chicken from disease however this immune balance is fragile with any number of environmental influences causing immune depression and the develoment of overwhelming disease. This information is essential for any program to control the disease.
Technical Abstract: The mechanism of Marek’s disease (MD) vaccination to prevent the lymphoproliferative disease in chickens is not well understood. It is generally recognized that vaccination prevents disease, including the induction of T cell tumors, but does not prevent the pathogenic virus from infecting and replicating in the vaccinated host nor does vaccination prevent bird to bird spread of the oncogenic virus. At what stage the vaccinated immune system intervenes in the process from infection to the induction of tumors remains obscure. Using a transplantable tumor induced by the Md5 strain of MDV we show that CVI988 vaccination does not prevent the induction transplantable tumors in the 15 X 7 chicken line. T cell receptor spectratyping was used to follow the transplantable tumor in serial passages in-vivo. This transplantable tumor could be passed in vaccinated birds. The length of time between vaccination and challenge (5 to 12 days) had little or no influence on the ability to transfer the tumor. There was variability in the manifestation of the disease produced by the transplanted tumor. Some chickens presented as normal but were still capable of transmitting the transplanted tumor to newly vaccinated recipients via their blood. This indicates that some chickens can control, but not eliminate, the tumor. The variables inducing health or disease in the challenged chickens remain obsure but likely environmental or other factors depress the immune system allowing the tumor to overwhelm the immune system.