(571e) Development of Novel Process for Purifying Misfolding-Prone Fusion Protein While Enhancing Desired Glycoform

The purification process for a fusion protein containing the Fc region of IgG1 was developed. Less than 20% of the protein was initially expressed as the correctly folded product of interest (POI), with the remainder misfolded. This presented significant challenges for the downstream purification efforts. Additionally, the terminal monosaccharide of its N-linked complex glycans was typically occupied by sialic acid. Presence of this sialic acid affects absorption, serum half-life, and clearance from the serum, as well as the physical, chemical and immunogenic properties of the drug. Insufficient or inconsistent sialylation was also a major obstacle in achieving process consistency. Several methods were employed to overcome these challenges. A novel pH shift refolding strategy was incorporated into the harvest step to improve productivity, and a high throughput method was used to rapidly optimize the affinity protein A chromatography step, thereby upgrading the purity of the POI to >80% after the primary capture step. Integration of these steps with two newly developed polishing chromatography steps further increased the purity to > 90%, with concomitant control of the total sialic acid content of the final drug substance. This presentation will discuss the strategies for the design and optimization of the downstream process modules; specific function for each unit operation and performance thereof, will be highlighted.