A therapeutic protein or monoclonal antibody (mAb) can be turned into an effective therapy and a revenue-generating product only if it can be efficiently filtered from the process stream. If a product is inefficiently filtered, the overall process slows, just as surely as it may slow due to upstream bottlenecks. Yet upstream limitations, not filtration problems, sometimes seem more amenable to technological fixes, if not more urgent. For example, upstream limitations have prompted improvements in bioreactor technologies that have allowed manufacturers to grow cell cultures at higher densities.

In recent years, however, efficiency-enhancing development has become less upstream-centric. Drug manufacturers have started to recognize that if they are to benefit fully from upstream improvements, they need to improve downstream operations, too.

In general, drug manufacturers are looking for increased filtration capacity. Besides working to meet this demand, filtration technology developers helping biomanufacturers handle higher product concentrations, reduce wastage of costly inputs and valuable outputs, simplify workflows, and overcome the special processing challenges posed by gene therapies and cell-based therapies.

Raising concentrations

The drug industry’s focus on higher dosage biopharmaceuticals is influencing filtration technology design. “Concurrent with the trend toward the development of drug product for subcutaneous delivery, we are seeing requests for sterilizing-grade filters that perform reliably with concentrated drug product and drug substance,” observes Oliver Triebsch, senior director, marketing, Pall Biotech. He adds that sterilizing-grade filter membranes which can sustain stable flow rates are particularly sought after.

Demand for enhanced filtration membranes has also been recognized by GE Healthcare Life Sciences. “We have started seeing more interest and potential in modified membranes to fit its purpose better, such as charged depth filters for clarification, but also new applications where a membrane technology is used in new situations,” comments Fredrik Lundström, the company’s product manager.

“One of the most interesting areas,” he continues, “is using membrane structures for chromatography in bind-elute mode.” In chromatography, flow-through mode is when the column is being flushed with solvent. In contrast, bind-elute mode is when elements in the process stream are being separated by binding to the column.

“Flow-through membrane chromatography has been around for some time, but the novel fiber-based technology, FibroSelect, significantly increases productivity,” Lundström asserts. “Other advantages of the FibroSelect technology are possibilities to closed processing and completely disposable devices.”

Christine Gebski, vice president of product management and field applications at Repligen, has also noted the drive toward higher concentration products. “Developers of mAbs,” she says, “are striving to formulate bulk drug substances to higher protein concentrations, with concentration targets rising from less than 100 mg/mL to now as high as to 200 mg/mL.”

Gebski notes that the trend has been factored into Repligen’s technology development efforts. “Protein formulation is achieved with tangential flow filtration (TFF) using flat-sheet cassettes in classic ultrafiltration and or diafiltration operations,” she details. “With TangenXTM SIUSTM and Pro TFF, we have demonstrated the ability to achieve these higher concentrations, with either single-use or reusable product options.”

Reducing costs

Cost efficiency is another driver, one that is becoming more important as biopharmaceutical active ingredients become more valuable. Also, these ingredients are being used to create increasingly valuable products.

“Subcutaneous treatments, which require high-concentration formulations, pose extra challenges in terms of concentration and buffer exchange steps, as well as in subsequent fluid handling, sterile filtration, and filling steps,” Triebsch elaborates. “These challenges include extensive processing times, yield loss in holdup, and additional cumulative sheer damage to the molecules.”

“Higher concentration means higher value of product per unit volume,” he adds. “End users are particularly interested in devices that can allow them maximize the recovery of these feeds post-filtration, particularly during process development when fluid is scarce.”

Increasing cost pressure is changing bioprocessing in other ways, according to Lundström. “Connecting process steps to avoid downtime is becoming more relevant,” he tells GEN. “For filtration, users have started to use approaches such as single-pass TFF to quickly concentrate the product a few times.”

He points out that GE Healthcare is responding to a trend toward more concentrated protein solutions, where holdup volumes are becoming critical. “The recently launched GE Healthcare ÄKTATM readyflux,” he asserts, “provides high-quality holdup volume at the capacity provided.”

Eliminating bottlenecks

Balancing downstream filtration capacity with higher upstream productivity is another very important innovation driver in the filtration sector, says Tony Hunt, president and CEO, Repligen. “Biopharma companies and contract manufacturers want flexible filtration solutions that improve yield, simplify workflows, eliminate other unit operations, and streamline the manufacturing process,” he tells GEN.

Upstream bioprocessing may be simplified and intensified, Repligen asserts, if the bioreactor is attached to a cell retention device. For example, Repligen says that its ATF System is capable of 100% cell retention and 80% faster implementation in perfusion operations. Available in single-use or stainless-steel formats, the ATF is based on alternating tangential flow technology, that is, the action of a diaphragm moving upward and downward within a pump head.

Repligen entered the filtration technology market in 2014 with the acquisition of the ATF platform from Refine Technology. In 2017, Repligen further expanded its offering by buying Spectrum, which brought Repligen membrane separation and hollow fiber filtration technology.

While incorporating new technologies, Repligen has maintained its position as a major supplier of Protein A, which is still the most widely used material in chromatography resin production. By spanning that which is enduring and that which is emergent, the company, Hunt suggests, has gained unique insight into the filtration sector.

“Repligen has really diversified and expanded over the past five years,” he declares. “Today, Protein A ligands represent less than 20% of the revenue of the company. We have transformed from being an OEM provider to being a direct-to-customer bioprocess provider.

“We have innovated and brought high-impact products to market like XCell ATF perfusion systems, OPUS prepacked chromatography columns, and both hollow-fiber and flat-sheet TFF systems. Also, we are addressing major pain points in the biologics manufacturing workflow. Consequently, we are now considered one of the leaders in the field of filtration and chromatography.”

It’s a mAb, mAb, mAb, mAb world

At the molecular level, modern mAb-based drugs and therapeutic proteins differ significantly from older products, both in terms of how they are designed and how they interact with therapeutic targets. However, from a filtration standpoint, little has changed in how these molecules are recovered from the process stream, notes Triebsch.

He allows that current mAbs are very similar to the older mAbs, both in terms of concentration and molecular behavior. Nonetheless, he insists that “some newly engineered mAb variants—such as bispecific antibodies (bsAbs), antibody fragments, pro-antibodies, fusion proteins, to name a few—can pose additional filtration challenges.”

The drug industry already knows how to filter mAbs, says Lundström, who tells GEN that, for the most part, current technologies are sufficient: “The mAb process has been more or less a platform for many years, and there has been a true revolution in terms of titer development due to better cell line development and media optimization. Traditional therapeutic proteins in CHO cells do not come close in terms of mass of product produced per liter.”

“Filtration technology has not changed as such,” he continues, “but we see some challenges in harvest in single-use operations, and ion-exchange membranes are sometimes seen in some early clinical trials.”

Gebski also says the evolution of biopharmaceuticals has had less of an impact on the development of filtration technologies than other factors: “Irrespective of the scientific evolution in antibody development, filtration technologies have been fairly conserved.”

“For instance, with TFF operations, the choice of filter molecular weight cut-off to be used is driven by the size of the molecule, which remains the same for a given type of therapeutic protein,” she details. “Also, some advances in the flat-sheet cassette screen construction have enabled high-protein concentrations to be attained.”

Future demand

The drug industry’s interest in cell and gene therapies is often cited as a driver of processing technology innovation, including innovation in the filtration systems sector. “In the gene and cell therapy markets adjacent to the classic mAb, recombinant protein space,” Triebsch tells GEN, “there will be demand linked to the sterile filtration of viruses and other gene-delivery vehicles such as liposomes and exosomes.”

Triebsch predicts that the when the technology sector develops filtration products, it will consider biopharma’s interest in single-use, disposable systems: “We will see an ongoing trend toward more presterilized devices, which embody ready-to-process functionality and are integratable into single-use assemblies. We will also see improvements in devices such as transfer tubing, especially for high-concentration formulations.”

The growing influence of the cell and gene therapy sectors is also being factored into GE Healthcare’s development of all processing technologies, including its filtration systems, says Lundström. “The number of cell and gene therapy indications has increased tremendously the last couple of years,” he tells GEN, adding that this is a particularly attractive opportunity for filtration technology developers.

“Typically, the production of viral vectors is not as standardized as that of mAbs, and it includes more filtration and fewer chromatography steps,” he continues. “However, it is more important to have closed processing. In multiproduct production, utilizing disposable technology is a necessity.”

To cater for this demand, GE Healthcare has developed a range of hollow-fiber technologies that enable closed and sterile operations during TFF. “Our novel
FibroSelect technology is anticipated to be a great leap forward in terms of chromatography operations,” asserts Lundström. “All wetted parts are disposable and support completely closed assembly.”

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