Submitted to: Avian Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2003
Publication Date: 8/15/2003
Citation: Gimeno, I.M., Witter, R.L., Hunt, H.D., Reddy, S.M., Reed, W.M. 2003. Biocharacteristics shared by highly protective vaccines against Marek's disease. Avian Pathology. 33(1):59-68. Interpretive Summary: Marek's disease (MD), a virus-induced cancer-like disease of chickens, is considered as a major disease problem in commercial poultry. Vaccination has dramatically reduced the incidence of the disease, but very little is known about how vaccines work. The objective of this research was to establish an easy method for determining which characteristics of the vaccines are related with higher level of protection. We have determined that strong in vivo replication and early activation of the immune system are the two viral characteristics more related with strong protection. This important information about MD vaccines will help scientists in academia and industry understand how MD vaccine works and eventually lead to better control of the disease.
Technical Abstract: Attenuated serotype 1 Marek's disease virus strains vary widely in their protection properties. This study was conducted to elucidate which biological or immunological features of serotype 1 MDV strains are related with protection. Three pairs of vaccines, each one including a higher protective (HP) vaccine and a lower protective (LP) vaccine originating from the same MDV strain, were studied. Two other highly protective vaccines (RM1 and CVI988/BP5) were also included in the study. Comparison within pairs of vaccines showed that marked differences existed between the HP and the LP vaccines. Compared to LP vaccines, HP vaccines replicated better in vivo. Also, they induced an expansion of all T cell lineages (CD45+CD3+, CD4+CD8-, CD4-CD8+, CD4+CD8+) as well as a marked increase in the expression of the antigens of Mhc-I and Mhc-II in T cells. Thus, our results show that in vivo replication and early stimulation of the T cell lineage are two characteristics shared by HP vaccines. However, comparison among the four HP vaccines that provided protection equal to that of CVI988 (RM1, CVI988/BP5, CVI988 and 648A80) revealed variability, especially regarding in vivo replication. Strains RM1 and CVI988/BP5 showed much stronger replication in vivo than the other two vaccine strains (CVI988 and 648A80). Thus, no single set of characteristics could be used to identify the most protective MD vaccines implying, perhaps, that multiple mechanisms may be involved.