Search

BACKGROUND: Human embryonic kidney-293 (HEK-293) cells are commonly used as a transient expression host but their application in stable therapeutic protein production is limited. This is presumably due to the absence of a suitable amplifiable expression system and hence limited protein output compared with other mammalian cells such as Chinese hamster ovary cells. This paper describes a rapid clonal selection method for isolating HEK293 cell lines with high specific productivity, for a non-amplifiable expression system, to achieve high-level, scalable expression of recombinant antibodies. RESULTS: Flow cytometry utilizing cold capture of secreted protein on the cell surface was applied to isolate high expressing clones from a stable antibiotic resistant pool. The top three isolated clones showed a five- to seven-fold improvement in volumetric outputs compared with the initial resistant pool (∼20 mg L−1) under batch conditions. In fed-batch conditions using commercially available hydrolysate supplements, the final titre was further increased to 500–600 mg L−1 in shaker flasks. One clone was scaled up to 25 L bag production using a similar hydrolysate feeding regime. The antibody titre reached 655 mg L−1, and 12 g of antibody was recovered after purification, demonstrating scalability of the process. The process of clonal selection through to fed-batch production of gram quantities was completed within 4 months. CONCLUSION: HEK-293 cells can be used as a stable host for the production of biopharmaceuticals, producing gram quantities of recombinant proteins for preclinical development. Copyright © 2011 Society of Chemical Industry

The ligand-binding region of the low-density lipoprotein (LDL) receptor is formed by seven N-terminal, imperfect, cysteine-rich (LB) modules. This segment is followed by an epidermal growth factor precursor homology domain with two N-terminal, tandem, EGF-like modules that are thought to participate in LDL binding and recycling of the endocytosed receptor to the cell surface. EGF-A and the concatemer, EGF-AB, of these modules were expressed in Escherichia coli. Correct protein folding of EGF-A and the concatemer EGF-AB was achieved in the presence or absence of calcium ions, in contrast to the LB modules, which require them for correct folding. Homonuclear and heteronuclear 1H-15N NMR spectroscopy at 17.6 T was used to determine the three-dimensional structure of the concatemer. Both modules are formed by two pairs of short, anti-parallel beta-strands. In the concatemer, these modules have a fixed relative orientation, stabilized by calcium ion-binding and hydrophobic interactions at the interface. 15N longitudinal and transverse relaxation rates, and [1H]-15N heteronuclear NOEs were used to derive a model-free description of the backbone dynamics of the molecule. The concatemer appears relatively rigid, particularly near the calcium ion-binding site at the module interface, with an average generalized order parameter of 0.85+/-0.11. Some mutations causing familial hypercholesterolemia may now be rationalized. Mutations of D41, D43 and E44 in the EGF-B calcium ion-binding region may affect the stability of the linker and thus the orientation of the tandem modules. The diminutive core also provides little structural stabilization, necessitating the presence of disulfide bonds. The structure and dynamics of EGF-AB contrast with the N-terminal LB modules, which require calcium ions both for folding to form the correct disulfide connectivities and for maintenance of the folded structure, and are connected by highly mobile linking peptides.