Various number of expression and host systems are used in biologics manufacturing. The most commonly preferred systems are based on bacteria, yeast, mammalian cells, insect cells, and transgenic animals. A wide range of molecules including insulin, mAbs, vaccines and recombinant proteins are produced by using different kind of host systems. Because of several reasons impacting the product quality and yield, mammalian cells are utilized. Moreover, mammalian cells are generally used in virus based vaccine manufacturing. Chinese Hamster Ovary (CHO) is the most widely used cell line for high yield stable recombinant protein production, while Human Embronic Kidney (HEK) is favoured for transient transfection low yield protein manufacturing, viral based vaccine and gene and cell therapy related vector production. Other mammalian cell lines such as NSO, Sp2.0, Vero, MRC-5 and PerC.6 are also used in both recombinant protein and virus productions. Multiple modifications are carried out on industrial cell lines in order to make them more suitable both for high yield and high quality protein production. Thanks to all of these alterations, high productivity and quality levels are achieved in biotechnology industry.