Genetic Engineering & Biotechnology News

SEP15 2017

Genetic Engineering & Biotechnology News (GEN) is the world's most widely read biotech publication. It provides the R&D community with critical information on the tools, technologies, and trends that drive the biotech industry.

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24 | SEPTEMBER 15, 2017 | CO N T I N U O U S B I O P R O C E S S I N G Dana C. Pentia, Ph.D., and James R. Peyser Continuous bioprocessing is inevitably be- coming the future of biomanufacturing. To date, several steps within a biomanufactur- ing process can be operated continuously. Upstream bioreactor perfusion systems, like the Xcell™ ATF (Repligen), produce a clarified harvest of monoclonal antibody (mAb) products—or other biologics—at a continuous rate within a sterile, closed system. These product harvests are often directly suitable for downstream chroma- tography steps. Downstream, continuous chromatography—enabled by multicolumn chromatography systems with sterilized, in- tegrated flow paths—has made considerable advances. Systems suitable for GMP produc- tion are now available. However, to make a truly continuous process, from seed bioreac- tor to drug product, some missing links in the process still need to be developed and integrated. One of these links is connecting upstream bioreactors with a downstream capture step. A challenge in such an integrated, in- terconnected system is bioburden control. Again, the upstream half of the process is ahead of the downstream in this regard. Gamma-irradiated single-use bioreactors, and single-use gamma-irradiated filtration systems are already available. In down- stream, sterility is harder to control, primar- ily due to complexities of chromatography systems. Newer chromatography systems with single-use gamma-irradiated flow paths solve part of this problem. The other unsolved part to this challenge is the lack of chromatography columns that meet this same standard of bioburden con- trol. To date, the most common method in chromatography for bioburden control is chemical sanitization with sodium hydrox- ide. This is, however, not an ideal method for a continuous process that could run for weeks or months. The concentration and exposure time of sodium hydroxide required for complete inactivation of bacteria and spores is high, greater than 0.5 M sodium hydroxide with long exposure time of hours or even days. This approach is not viable within a continuous manufacturing strat- egy, due to time and stability constrains for even the most stable Protein A resins on the market. For that reason, a different biobur- den control method is needed. The most accepted and reliable method is gamma irra- diation. Solving the challenges of bioburden control in downstream column chromatog- raphy opens the door to having a completely closed system encompassing both upstream cell culture and downstream purification op- erations that can be operated continuously with low risk of bacterial contamination. A solution for downstream continuous capture is to utilize prepacked Protein A columns that can be gamma irradiated. Data are presented showing that gamma-irradiat- ed prepacked columns are structurally sta- ble, maintain functional performance, and can be operated in a closed system without bacterial contamination. A way to preserve functionality of Protein A from damaging ef- fects of gamma irradiation is also presented. Compatibility of Opus Columns Hardware with Gamma Irradiation Opus ® prepacked column components are made of medical-grade polypropylene and medical-grade silicone. Several tests were conducted to determine if column hardware could withstand sterilizing doses of gamma radiation while maintaining claimed pressure ratings. Irradiating empty columns with 25–30 kGy of gamma radia- tion didn't change the tensile strength or elasticity of the polypropylene components, or of the silicone O-rings. The assembled column was pressure-tested, meeting the claim of ≥4 bar for an extended period of time. To evaluate if a packed bed will still be integral in performance following gamma exposure, a 20 cm i.d. by 20 cm bed height Opus column prepacked with agarose resin was gamma irradiated to 30 kGy. The packed bed performance measure by HETP, asymmetry, and pressure drop was main- tained (Table 1 and Figure 1). Maintenance of Sterility over the Duration of Continuous Bioproduction The ultimate goal of gamma-irradiating purification columns is to control bioburden in a continuous, interconnected, lengthy bioproduction process. To test the effective- ness of gamma irradiation in eliminating Bioburden Control in Continuous Capture of Monoclonal Antibodies Methods to Simultaneously Reduce Bioburden and Maintain Column Integrity, Explained ➜

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