Discovery and characterization of CHO host cell protease-induced fragmentation of a recombinant monoclonal antibody during production process development

Monoclonal antibody (mAb) fragmentation is a widespread issue of protein stability that needs to be carefully monitored for critical mAb quality control during the production process development. This study describes here the discovery and characterization of CHO host cell protease-induced fragmentation of a therapeutic mAb-X in the formulation samples from an early production process. The fragmentation was observed in the sodium dodecyl sulfate capillary electrophoresis (CE-SDS) analysis of mAb-X formulation samples incubated at elevated temperature. Size exclusion liquid chromatography (SEC-HPLC) was used to analyze and collect these cleaved fragments derived from mAb-X. Reversed phase liquid chromatography mass spectrometry (RP-LC-MS) and tandem mass (MS/MS) analysis demonstrated that the fragment was generated mainly due to the hinge region cleavage of mAb-X. The fragmentation rate was characterized in the mAb-X formulation samples at pH from 4.0 to 6.0 using CE-SDS and SDS-PAGE analysis. The percentage of the main fragment increased dramatically from 2.8% to 31.2% as pH decreased from 6.0 to 4.0 at 40 °C for 28 days, which indicated the fragmentation was highly pH-dependent. The SDS-PAGE analysis further verified the pH-dependent property of the framentation of mAb-X. Moreover, the fragmentation was characterized in the presence and absence of pepstatin A, an inhibitor of acidic proteases. Significant inhibition of mAb-X fragmentation was observed with the addition of pepstatin A to mAb-X formulation samples. These results suggested residual acidic host cell protease(s) in the formulation samples from an early production process caused the fragmentation of mAb-X. To prove evidence, we developed an optimized protein A chromatography to enhance the residual host cell protease(s) removal capability of mAb-X purification process and consequently eliminate the above described cleaved fragment of mAb-X, which further supported the hypothesis that the fragmentation of mAb-X was catalyzed by the residual host cell protease(s) in the formulation samples from the early production process. This case study reiterated that residual host cell protease is a critical quality attribute (CQA) that should be carefully controlled and evaluated to guarantee successful manufacture processes for mAb products.