Compared with other systems, the greatest advantage of mammalian cell expression systems is that they can guide the correct folding of proteins and provide a variety of post-translational processing functions such as complex N-type glycosylation and accurate O-type glycosylation. In some cases, the activity of its expression products is much better than that of prokaryotic expression systems and eukaryotic expression systems such as yeast and insect cells. The host cells used most frequently in routine experiments are HEK 293 cells and CHO cells. The former is generally used for instantaneous expression of recombinant proteins and for obtaining a small amount of bioactive recombinant proteins in a short time. The latter is generally used for stable expression of recombinant proteins. CHO cells play an important role in industrial production and medical treatment due to their stable genetic traits, fast growth rate, ability to withstand certain shear force and osmotic pressure, and similar glycosylation modification to humans. The company provides cell transient protein expression services and cell stable strain construction services, and has a mainstream industrial CHO GS expression system (i.e., "glutamine synthetase screening system"), through which the CHO antibody stable cell line constructed can reach an expression level of 3g/L.