C-Terminal Cysteine PEGylation of Adalimumab Fab with an Engineered Interchain SS Bond

Analysis of thermostability for seven Phe to Ala and six Pro to Gly mutants in the Fab constant region of adalimumab

To identify amino acids that play important roles in the structural stability of Fab, seven phenylalanine residues in the Fab constant region of the therapeutic antibody adalimumab were subjected to alanine mutagenesis. Six Fab mutants, H:F130A, H:F154A, H:F174A, L:F118A, L:F139A and L:F209A, showed decreased thermostability compared with wild-type Fab. In contrast, the Tm for the L:F116A mutant was 1.7°C higher than that of wild-type Fab, indicating that the F116 residue was unfavorable for Fab thermostability. Six proline mutants, H:P131G, H:P155G, H:P175G, L:P119G, L:P120G and L:P141G, were also prepared to investigate the effect of proline residues adjacent to mutated phenylalanine residues. The thermostability of the H:P155G and L:P141G mutants in particular was significantly reduced, with decreases in Tm of 5.0 and 3.0°C, respectively, compared with wild-type Fab. The H:P155 and L:P141 residues have a cis conformation, whereas the other mutated proline residues have a trans conformation. H:P155 and L:P141 had stacking interactions with the H:F154 and L:Y140, respectively, at the interface between the variable and constant regions. It is suggested that the interactions of the aromatic ring with a cis-form proline at the interface between the variable and constant regions is important for stability of Fab.

A comparative analysis of recombinant Fab and full-length antibody production in Chinese hamster ovary cells

Monoclonal antibodies are the leading class of biopharmaceuticals in terms of numbers approved for therapeutic purposes. Antigen-binding fragments (Fab) are also used as biotherapeutics and used widely in research applications. The dominant expression systems for full-length antibodies are mammalian cell-based, whereas for Fab molecules the preference has been an expression in bacterial systems. However, advances in CHO and downstream technologies make mammalian systems an equally viable option for small- and large-scale Fab production. Using a panel of full-length IgG antibodies and their corresponding Fab pair with different antigen specificities, we investigated the impact of the IgG and Fab molecule format on production from Chinese hamster ovary (CHO) cells and assessed the cellular capability to process and produce these formats. The full-length antibody format resulted in the recovery of fewer mini-pools posttransfection when compared to the corresponding Fab fragment format that could be interpreted as indicative of a greater overall burden on cells. Antibody-producing cell pools that did recover were subsequently able to achieve higher volumetric protein yields (mg/L) and specific productivity than the corresponding Fab pools. Importantly, when the actual molecules produced per cell of a given format was considered (as opposed to mass), CHO cells produced a greater number of Fab molecules per cell than obtained with the corresponding IgG, suggesting that cells were more efficient at making the smaller Fab molecule. Analysis of cell pools showed that gene copy number was not correlated to the subsequent protein production. The amount of mRNA correlated with secreted Fab production but not IgG, whereby posttranscriptional processes act to limit antibody production. In summary, we provide the first comparative description of how full-length IgG and Fab antibody formats impact on the outcomes of a cell line construction process and identify potential limitations in their production that could be targeted for engineering increases in the efficiency in the manufacture of these recombinant antibody formats.

A comprehensive analysis of novel disulfide bond introduction site into the constant domain of human Fab

Generally, intermolecular disulfide bond contribute to the conformational protein stability. To identify sites where intermolecular disulfide bond can be introduced into the Fab’s constant domain of the therapeutic IgG, Fab mutants were predicted using the MOE software, a molecular simulator, and expressed in Pichia pastoris. SDS-PAGE analysis of the prepared Fab mutants from P. pastoris indicated that among the nine analyzed Fab mutants, the F130C(H):Q124C(L), F174C(H):S176C(L), V177C(H):Q160C(L), F174C(H):S162C(L), F130C(H):S121C(L), and A145C(H):F116C(L) mutants mostly formed intermolecular disulfide bond. All these mutants showed increased thermal stability compared to that of Fab without intermolecular disulfide bond. In the other mutants, the intermolecular disulfide bond could not be completely formed, and the L132C(H):F118C(L) mutant showed only a slight decrease in binding activity and β-helix content, owing to the exertion of adverse intermolecular disulfide bond effects. Thus, our comprehensive analysis reveals that the introduction of intermolecular disulfide bond in the Fab’s constant domain is possible at various locations. These findings provide important insights for accomplishing human Fab stabilization.