The diversity of development tools, an abundance of manufacturing options, and standardization of many unit operations has ushered in a golden age for monoclonal antibodies (mAbs). mAb process development and GMP manufacturing increasingly rely on platform processes involving streamlined production (usually a two to three week fed-batch cell culture), protein A capture, ion-exchange intermediate and polishing columns, and standard filtration steps.
Because of these developments, both innovator companies and contract manufacturers have achieved a high degree of familiarity with mAb manufacture, process development, and clinical development.
Platform manufacturing and quality initiatives are mutually supportive and enabling. As manufacturing platforms become more widely adopted, developers of mAbs have a somewhat easier time implementing quality by design and process analytics, which further aid in establishing standardized unit operations and support CMC regulatory submissions.
While platform processes have become common both upstream and downstream during mAb manufacturing, purification remains something of a bottleneck and an increasing cost contributor, particularly in chromatography-intensive processes. Rising titers are an often-cited contributor to upstream-downstream mismatches, while finding replacements for protein A has met with spotty success.
And while platforming is desirable in the manufacture of conventional mAbs, all bets are off for nonstandard antibody-like molecules, particularly antibody fragments, due to higher variation in titers and the need to alter purification from standard mAb operations. “Antibody fragments can also vary in terms of stability and solubility, presenting significant challenges to formulation scientists,” notes Gregory Zarbis-Papastoitsis, Ph.D., senior director for protein production at Eleven Biotherapeutics. Eleven develops antibodies, antibody fragments, and nonantibody proteins to treat eye diseases.
Chinese hamster ovary (CHO) cells remain the most popular mAb-producing cells due to regulatory familiarity and the large number of successful clinical- and commercial-stage products expressed in these cells. “However, as second-generation expression systems enter clinical trials and commercialization, CHO may experience a significant drop in popularity,” says Richard Hetrick, director of business development at Cytovance Biologics.
Single-use bioreactors are now mainstream and capable of handling clinical and even production-scale batches for many mAbs. The high doses at which antibodies are administered guarantees, however, that large stainless steel bioreactors will not disappear.
Despite vendors regularly breaking the size barrier for bioreactor bags, the point will eventually be reached where the bags become too large to handle. Disposal issues may also be problematic for very large bags. Regardless, upper size limits become moot as cellular and culture productivity continues to rise.
“With increase in yields it is debatable whether there will be much demand for 10,000-liter bioreactors in the future, as was projected a number of years ago,” Hetrick observes.
Improvements in volumetric productivity for mAb processes do not appear to be slowing down. To this point most were a result of media and feed strategies, but high-expressing cell lines and transfection strategies have played a role as well.
In June, ProBioGen announced a modification that improves volumetric yield in certain cells up to 2.5-fold for certain products produced in CHO cells. The technique involves co-expressing an enzyme along with the therapeutic mAb. The enzyme, according to ProBioGen, acts “on several cellular pathways and results in substantially enhanced volumetric productivities of protein drugs.”