Provided herein is a non-natural isolated chicken fibroblast cell that has the characteristics of immortalized growth and supporting replication of Marek's Disease Virus (MDV), wherein number of MDV produced by the cell is at least 1.5-fold greater than the number of the same MDV produced by a DF-1 cell under the same conditions. Also provided herein are methods including producing virus using the cell, determining the number of virus in a sample using the cell, and using the cell to produce protein.