**5. Cell based manufacturing of therapeutic proteins**

Therapeutic proteins production using human cell lines has greatly influenced different medical areas including biopharmaceutical research and vaccine production. Mammalian cell lines prove futile in protein production due to their likelihood of possessing post-translational modifications (PTMs) achieved from recombinant proteins that are in accordance with the endogenous human proteins. These cell lines show exquisite specificity to produce similar proteins to those in humans naturally synthesized, an advantage over mammalian expression systems [99]. One of the most routinely and high yields of proteins production is performed by using cell-based expression systems such as Chinese hamster ovary (CHO) a cell line that constitutes major advances such as accomplishment of gene amplification, specific productivity, better selection strategies, and devising greater expression units and advanced hosts. CHO cells have established their safety profile for 20 years from the production of its first recombinant biotherapeutic protein in 1986 [100]. Other human cell lines such as BHK-21 cells are used for the generation of few coagulation factors such as factor VIII [101]. There are two vital human cell lines namely, HEK293 and HT-1080 that are used to manufacture licensed products of human PTMs. The advancement in protein-based drug development and technologies has driven more towards the therapeutic proteins market that comprises of sales of these therapeutic proteins. The methods that are involved in the production of these proteins are pegylation, glycoengineering, albumin fusion, Fc-fusion, product purity, targeting, and functionality of therapeutic protein drugs. Few examples of therapeutic protein drugs which has been produced using protein engineering technologies and approved by the Food and Drug Administration (FDA) from the past five years are imiglucerase, Belimumab, alfa, coagulation factor IX recombinant human and albiglutide [102]. A French pharmaceutical company named Sanofi accomplished a great achievement of strengthening its R&D strategy with the best proprietary therapeutic proteins production pharmaceutical company, Ablynx, for a nanobody technology platform.
