A Novel Sample Preparation for Shotgun Proteomics Characterization of HCPs in Antibodies.

Residual host cell proteins (HCPs) in biopharmaceuticals derived from recombinant DNA technology can present potential safety risks to patients or compromise product stability. Thus, the downstream purification process is designed to demonstrate robust removal of these impurities. ELISA using polyclonal anti-HCP antibodies as reagents for capture, detection, and quantitation purposes is most commonly used to monitor HCP removal during process development, but this technique has limitations. More recently, LC-MS for residual HCP characterization has emerged as a powerful tool to support purification process development. However, mass spectrometry needs to overcome the enormous dynamic range to detect low ppm levels of residual HCPs in biopharmaceutical samples. We describe a simple and powerful methodology to characterize residual HCPs in (monoclonal) antibodies by combining a novel sample preparation procedure using trypsin digestion and a shotgun proteomics approach. Differing from the traditional methodology, the sample preparation approach maintains nearly intact antibody while HCPs are digested. Thus, the dynamic range for HCP detection by MS is 1 to 2 orders of magnitude less than the traditional trypsin digestion sample preparation procedure. HCP spiking experiments demonstrated that our method could detect 0.5 ppm of HCP with molecular weight >60 kDa, such as rPLBL2. Application of our method to analyze a high-purity NIST monoclonal antibody standard RM 8670 derived from a murine cell line expression system resulted in detection of 60 mouse HCPs; twice as many as previously reported with 2D-UPLC/IM/MSE method. A control monoclonal antibody used for 70 analyses over 450 days demonstrated that our method is robust.

Alkaline cation-exchange chromatography for the reduction of aggregate and a mis-formed disulfide variant in a bispecific antibody purification process.

During the purification development of a bispecific antibody, cation-exchange chromatography was screened for its ability to separate a prominently expressed (>12%) mis-formed disulfide bond variant, termed MAb-diabody, and aggregate from the product of interest. The influence of pH, product load (g of product per liter of resin) and linear velocity on the separations were evaluated for the strong cation-exchange resins SP Sepharose HP and POROS(®) HS50. Cation-exchange chromatography is commonly operated distant to the isoelectric point of a molecule, generally leading to acidic conditions for antibody purification. However, the results herein demonstrated improved removal of MAb-diabody with increasing pH, resulting in reduction of MAb-diabody content greater than 12-fold when operating near the alkaline pI of the product. This approach was successful over a range of linear velocities and g/L of resin loading. Aggregate removal was less affected by pH and was effectively reduced from 10.9% to less than 3% for each condition. Furthermore, this method was successfully scaled to a 60 cm diameter column using SP Sepharose HP resin.