Efficacy and safety of cell associated vaccines against Marek's disease virus grown in a continuous cell line from chickens.

The Marek's disease virus (MDV) vaccine strains CVI 988 and herpes virus of turkeys (HVT) strain FC126, usually are grown in primary chicken embryo fibroblasts (CEF). We found that the strains could be grown also in the so-called JBJ-1 cell line to titres in the same range as when chicken embryo fibroblasts were used. The JBJ-1 cell line is a fibroblast-like continuous chicken cell line, which can be grown in flat bottom tissue culture flasks, roller bottles and on micro carriers. We investigated the efficacy of experimental CVI 988 vaccines grown in JBJ-1 cells and the efficacy of combinations of CVI 988 grown in JBJ-1 cells with HVT FC 126 also grown in JBJ-1 cells. The study was performed in accordance with European Pharmacopoeia monograph 0589 for live MDV disease vaccines. Groups of 1-day-old SPF chicks were vaccinated subcutaneously or intramuscularly, with 10(2.5) TCID50 per dose of CVI 988 alone or in combination with 500PFU per dose of HVT. As a control a group vaccinated with CVI 988 grown in CEF was included. One group was not vaccinated. Five days after vaccination all chickens were challenged with the very virulent MDV strain RB1B. After challenge the chickens were observed for a period of 70 days for signs of Marek's disease (MD). The protection induced by CVI 988 grown in JBJ-1 cells and the combination of CVI 988 and HVT-FC126 both grown in JBJ-1 cells, amply complied with the requirements of the European Pharmacopoeia which prescribes that the protection index should be at least 80%. The safety of the vaccines grown in JBJ-1 cells was tested in a field study in commercial layer chickens. No signs of MD were noticed during the study and no other signs attributable to the vaccine. It is concluded that the JBJ-1 cell line is a suitable substrate for the current vaccines against MD.