Biological therapeutics are increasingly being formulated to high protein concentrations to decrease drug substance storage space and increase the flexibility of administration to patients. With the higher protein concentration targets comes added challenges to the downstream purification manufacturing process. Tangential flow filtration (TFF) operations are typically performed to reach target protein concentration. TFF operations for a given drug substance may include an Ultrafiltration and Diafiltration (UFDF) step, or a UFDF step followed by a single pass tangential flow filtration (SPTFF) step. Whether a TFF step achieves a target protein concentration is determined by at‐line protein concentration measurements performed at the completion of a process step. If the measured protein concentration is outside the specified range, the unit operation may need to be restarted, reprocessing may need to be performed, or a batch may need to be terminated. Out of specification protein concentration measurements may be a result of the TFF operation or sample measurement. Increased viscosities associated with high concentration TFF operations pose added challenges to the TFF process and sample measurement. Implementation of an inline process analytical technology (PAT) to monitor real‐time protein concentration during TFF operations has the potential to improve the accuracy of the operations in achieving target protein concentrations. This will result in improved process consistency and efficiency, increased operator confidence and decreased likelihood of batch failures. This paper studies the performance of a K‐Patents PR‐23 refractometer (Vaisala) as a PAT to monitor and control the UFDF and SPTFF unit operations of a commercial scale monoclonal antibody purification process.

Ultrafiltration/diafiltration (UF/DF) has been the hallmark for concentrating and buffer exchange of protein and peptide‐based therapeutics for years. Here we examine the capabilities and limitations of UF/DF membranes to process oligonucleotides using antisense oligonucleotides (ASOs) as a model. Using a 3 kDa UF/DF membrane, oligonucleotides as small as 6 kDa are shown to have low sieving coefficients (<0.008) and thus can be concentrated to high concentrations (≤200 mg/mL) with high yield (≥95%) and low viscosity (<15 centipoise), provided the oligonucleotide is designed not to undergo self‐hybridization. In general, the oligonucleotide should be at least twice the reported membrane molecular weight cutoff for robust retention. Regarding diafiltration, results show that a small amount of salt is necessary to maintain adequate flux at concentrations exceeding about 40 mg/mL. Removal of salts along with residual solvents and small molecule process‐related impurities can be robust provided they are not positively charged as the interaction with the oligonucleotide can prevent passage through the membrane, even for common divalent cations such as calcium or magnesium. Overall, UF/DF is a valuable tool to utilize in oligonucleotide processing, especially as a final drug substance formulation step that enables a liquid active pharmaceutical ingredient.

Direct depth filtration is an established technology for single‐use harvest operation. Advantages of direct depth filtration include familiarity with depth filtration in downstream processes and simplicity of the operation. Drawbacks include low capacity, large footprint, labor‐intensive set‐up, high water use, and high waste in the form of discarded filters. Single‐use centrifugation is emerging as an alternative to depth filtration for the single‐use harvest step. Within the single‐use centrifugation space, disc stack centrifugation represents the newest entrant. In this study, we evaluated the performance of the GEA kytero single‐use disc stack centrifuge to clarify two monoclonal antibody‐producing cell culture fluids. The separation performance of the GEA kytero centrifuge varied between the two cell culture fluids, with differences in centrate turbidity and centrate filterability measured. A comparison was then performed to determine resource savings, compared to direct two‐stage depth filtration, when using a GEA kytero centrifuge to harvest a 1000 L bioreactor. The analysis concluded that replacement of the first stage of depth filters with a GEA kytero centrifuge has the potential to decrease the required second stage depth filtration area by up to 80%. The decrease in depth filter area resulting from the use of the GEA kytero would result in a decrease in the harvest step footprint, a decrease in buffer volume required to prime and rinse depth filters, and a decrease in the volume of plastic waste. An economic comparison of the GEA kytero single‐use centrifuge against a direct depth filtration step found that for a 1000 L harvest step, the GEA kytero centrifuge may reduce costs by up to 20% compared with two‐stage direct depth filtration.

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