The recombinant plasmid pcDNA-env was constructed by inserting the env gene of ALV-J into the vector pcDNA3.1.Chicken embryo fibroblast cell line DF-1 was transfected with the recombinant plasmid pcDNA-env by Lipofectin.Then the transfected DF-1 cells were analyzed for transient ALV-J env expression by indirect immunofluorescence assay(IFA) and were selected for resistant cells to Zeocin.The Zeocin-resistant cells were passaged for 30 generations and then frozen.After 13 months,these cells were refreshed an...