Downstream Processing

To assess current trends in separation and purification, BioPharm International turned to Yujing Yang, director, purification technology, Sartorius Stedim Biotech North America and Mark A. Snyder, manager, process R&D applications group, Bio-Rad Laboratories.

Q: What are the two biggest challenges in downstream processing today?
Yang: For monoclonal antibodies (MAbs), high titer (5–10g/L) and cost ($/g MAb produced) are probably the two major challenges now. For other biologics, vaccines, and recombinant proteins, time to
develop a production-scale process (speed to market) and cost may be on top of other challenges.
Snyder: Probably the biggest challenge is to make facilities as multifunctional as possible, with the minimum amount of equipment. The second biggest challenge is the amount and number of buffers required for any purification step; this, in turn, puts more pressure on process development to come up with a robust process, which ultimately leads to increased reliance on design space as a tool for process understanding.

Q: Many biopharmaceutical companies are considering alternatives to Protein A today. Do you see any particular alternative gaining traction? Do you think the industry will move completely away from Protein A in the next decade?
Yang: Though precipitation and ion exchange chromatography for MAb capture have been considered and tried with some acceptable results, Protein A would still be the work horse for its ease of use and consistency in performance. The major complaint for Protein A resin is its cost, and with the patent expiring soon, varieties of Protein A media and suppliers may be seen, which can certainly change the situation and bring the price down.
Snyder: Some pharmaceutical companies are already using high-capacity ion exchangers as a platform alternative to Protein A and I expect this trend to grow. The industry is highly unlikely to move completely away from Protein A in the next 10 years owing to legacy processes and the fear of change.

Q: What are some of the alternative technologies being developed to improve downstream processing operations?
Yang: One new technology would be membrane chromatography, which has much higher throughput (50–100x faster than traditional resin columns) and is great for polishing and contaminate removal. Crossflow filter membrane chemistry also has been improved from PES to regenerated cellulose. The membrane chemistry has low protein binding, consistent and high sample flux, and can be cleaned by NaOH.
Snyder: Substitution of membranes for resin-based steps; increased capacity resins; new, orthogonal resin chemistries; use of multiple viral inactivation steps in a single process; and single-use technology.

Q: MAbs still dominate the biopharmaceutical market but we are seeing a growing interest in MAb fusion molecules and MAb fragments. How much of a challenge do these present to traditional downstream platforms? Yang: MAb fusion and MAb fragments purification will not be too bad if they can still be captured by Protein A. Otherwise, the current MAb downstream purification platform needs to be redeveloped, which would be a big challenge.
Snyder: Probably the greatest challenge will be in the initial capture step because Protein A will not work with these molecules. The challenge will be to get the target molecule to a relatively high level of purity; after this point, traditional methods of chromatography can continue to function as they always have.

Q: Is the growth of vaccines affecting the growth of certain types of downstream technologies over others?
Yang: Many vaccines are based on viruses. Some are polysaccharide based, some are protein conjugates, and some are DNA based. Current resin-based purification technologies do not do well with most of the giant molecules. Traditional resins with diffusive pores show very low binding capacity and are slow in process. To deal with these new challenges, new technologies, such as membrane chromatography and monolith columns, will be more competitive against the resin columns.
Snyder: To some extent. The ability to include traditional viral inactivation steps in vaccine manufacture can be limited for a number of different vaccine classes. In addition, certain specific resins are known to preferentially interact with viruses and virus-like particles, which will give them continually increased visibility in this market segment.