Optimizing Plasma Processes requires the correct matching of Innovations to Applications

Blood plasma is the liquid component of whole blood and contains a large variety of proteins with clinical uses. Albumin can be used to maintain blood volume after traumatic injuries and during surgery. Intravenously administered immunoglobulins (IVIGs) derived from plasma are the standard replacement therapy for treating immune deficiency disorders. They are also widely used for treating autoimmune and inflammatory disorders because of their immunomodulatory effects.

Plasma manufacturing is well established globally. Both albumin and immunoglobulin products are readily available at a commercial scale. The manufacturing processes for these products have evolved over many decades. Manufacturers typically use The Cohn fractionation process or the Kistler-Nitschmann method purify to Albumin from plasma (Figure 1). They can extract antibodies from the precipitates produced during the fractionation process. The subsequent production process for antibodies utilizes chromatography, virus filtration and inactivation technology. The last step in the process is usually a concentration and formulation procedure.

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Figure 1: Cold ethanol plasma fractionation according to the Kistler-Nitschmann process

Although plasma-processing companies must embrace process improvements to stay ahead of the competition they are often faced with the dilemma of “constantly innovating” and “never changing a winning team”. The conflict between introducing product lifecycle-extending process innovations without comprising regulatory compliance must be resolved in order for manufacturers to adopt product and method upgrades. Knowledge transfer between well-trained personnel at different sites can facilitate continual process optimization, reduce production downtime and increase yields. Process changes, however, typically require revalidation and mandatory approval from regulatory authorities. Revalidation procedures must demonstrate the modified process delivers equivalent reproducibility and performance to that of the original process.

Attempts to improve the performance of Albumin and IVIG manufacturing processes are focussing on ultrafiltration and diafiltration (UF/DF) steps within downstream processes. Ultrafilters constitute a significant proportion of the consumable costs associated with albumin production. Changes to UF/DF steps are not constrained by the same regulatory challenges that need to be overcome in order to change virus reduction filtration steps. Because IVIG production processes often contain multiple UF/DF steps, any performance improvements will have a significant improvement in the performance of the overall process.

To date, most plasma processes have used polyethersulfone (PESU) membranes in UF/DF steps. The membranes are re-used multiple times in dedicated ultrafiltration systems. UF/DF steps reduce the quantity of process impurities to an acceptable level and fulfil a role in concentrating the product at the end of the process. To ensure that membranes can be re-used as many times as possible manufacturers dedicate time to optimizing the design of their cleaning-in-place (CIP) procedures. Chemical resistance has previously been the limiting factor that has determined the number of times that firms can re-use PESU membranes. This is especially limiting in blood fractionation applications because of the protracted CIP procedures that are required for UF/DF membranes.

The plasma processing industry can achieve considerable process improvements by adopting new technologies that can overcome these limitations. To take advantage of membrane advances in this field it is important to select the appropriate technology for the application. Consideration must be given to the effort and therefore cost of making a process change in the context of the overall process economics. This article focusses on implementing membrane and filter technology innovations can maximize performance and minimize production downtime.

Optimization of Final Ultrafiltration Steps during Albumin Production

An important step in the manufacture of human albumin is the final ultrafiltration step. UF membranes installed for this purpose retain the albumin product while allowing process impurities to pass through the filter and enter the filtrate stream. Typically, manufacturers perform an initial concentration operation in order to reduce process volumes and facilitate fluid handing (1). A subsequent diafiltration operation removes ethanol from the product stream. Optimization of this diafiltration phase can lead to a significant increase in process performance. The final phase of the step concentrates the product for a second time and is used to reach the target concentration of the final albumin product. This process is illustrated in Figure 2.

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Fig. 2: Generic Process Steps for Albumin Final Concentration and Diafiltration

A choice of production-scale UF membranes are available that can retain albumin. The cassette geometry containing PESU membranes have become the predominant filter design. A new ultrafiltration crossflow cassette has been specifically designed for use in existing albumin ultrafiltration applications. By using the same format and membrane materials the costs associated with replacing existing ultrafiltration devices are minimized. This is especially important when seeking to improve the manufacture of albumin because the value of the final product does not support the costs incurred by making significant process changes within a conservative regulatory environment.

The design of the new PESUmax cassette incorporates an albumin-retentive membrane along with a novel flow-geometry configuration which can be used with existing hardware. It has a rejection efficiency for albumin greater than 99.9% and provides higher flux rates than has traditionally observed in albumin processing applications. The filtrate flow performance of the PESUmax is extremely good especially during the diafiltration phase that removes ethanol from the process stream (Table 1). The increase in processing performance allows for a reduction in both the total processing time and membrane area requirement.

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Table 1: PESUmax delivers 25% higher performance than other membranes.

The greatest potential for reducing costs by implementing the PESUmax ultrafilter, however, comes from reducing the downtime for cleaning between batches. The improved chemical resistance and flow configuration of PESUmax cassettes allows them to withstand more aggressive chemical cleaning treatments and storage procedures than competitor PESU cassettes (2) (see Figure 3).

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Figure 3: Comparison of caustic stability of PESUmax cassettes with competitor products

By allowing manufacturers to use more aggressive cleaning regimes, use of the PESUmax cassettes reduce downtime, allow batches to be run more frequently and increase facility throughput. Higher cleaning efficiencies also allow long filter lifetimes, less frequent filter changes and lower operating costs

Improvement in Yield Increases and Reduction in Downtime for Intravenous Immunoglobulin (IVIG) Processing

IVIG products are typically more valuable than albumin products. The process for manufacturing IVIG products may contain multiple UF/DF steps for removing impurities and decreasing process volumes. Improvements in UF/DF technology can, therefore, have a significant impact on the overall process economics and productivity.

PESU polymers used in plasma processing have a tendency to develop a thick gel-layer of protein on the upstream surface of the membrane. They require robust CIP conditions characterised by high temperatures, high concentrations of caustic solutions and long CIP run times to regenerate them effectively. The chemicals added to inactivate viruses can further reduce the useful life of PESU ultrafiltration membranes. To prevent low yields of high-value IVIG products it is important that cassettes have tight retention specifications which do not deteriorate with repeated use. The need for aggressive cleaning conditions coupled with the more limited chemical compatibility of PESU materials has made the re-use of membranes challenging in applications where the retention specification of the material is critical. For these reasons, Hydrosart® ultrafilters with a molecular weight cut-off of 30 kD are recommended for commercial-scale IVIG manufacture. These filters contain a hydrophilic, chemically resistant, cross-linked cellulose membrane polymer which is resistant to fouling and which has a high resistance to aggressive chemicals, excellent cleanability and low-binding properties (3). Figure 4a shows how effectively the Hydrosart® flux rates recover following CIP treatment. This cleanability property allows CIP run times to be limited in duration to 30 minutes to minimise process downtime (4).

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Fig. 4a: Fouling and Cleanability of Hydrosart® and competitor membranes
Clean Water flux virgin membrane (100%)
NaCL_post glob: flux without cleaning after globulin concentration
NaCL_final: flux after caustic cleaning (1N NaOH)

Figure 4b illustrates the benefit of the Hydrosart® filters relative to a competitor PESU and a competitor regenerated cellulose cassette. The three different types of unused cassettes were stored for 100 days in either 0.1N or 0.5N sodium hydroxide. Following this treatment the flux rates obtained through the competitor products increased while the retention of B12 diminished. In contrast, the Hydrosart® cassettes showed no increase in flux values or decrease in rejection performance. This illustrates that Hydrosart® cassettes are highly resistant to cleaning chemicals. Prolonged exposure to cleaning reagents will not lead to a reduction in yields of IVIG.

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Fig. 4b: Head-to-head Comparison of the Hydrosart® Ultrafilter Membrane and Selected Competitor Membranes
´Caustic Stability: 100 days of Storage in 0.1n or 0.5n NaOH
=> Flux and B12 Rejection

The results of an experiment that further demonstrates the resistance of Hydrosart® cassettes to aggressive cleaning regimes are shown in Figure 5. Flux rates and Cytochrome C rejection were determined from cassettes with two different membrane lots that were stored for over 300 hours in 1n sodium hydroxide at 50°C. Both the obtained flux rates and the rejection efficiency of Cytochrome C were stable and within specification over the duration of the experiment despite the aggressive treatment of the membranes.

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Fig. 5: The Caustic Stability of Hydrosart® Membranes Measure through Flux Rates and Cytochrome C Rejection

Caustic Stability: Stored for up to 300 h in 1n NaOH at 50°C (two membrane lots)
=> Flux and Cytochrome C Rejection

Finally, Figure 6 shows the results of stress tests performed with three different Hydrosart® cassette lots. Exposing the cassettes to 1n sodium hydroxide for 500 hours at 500C had little impact on either flux or rejection efficiency. It was possible to detect a decrease in mechanical stress test performance after 500 hours but this treatment far exceeds what cassettes would experience in a typical IVIG application. We have shown that no deleterious effects on stress test performance occur after exposure to a hot caustic cleaning solution of up to 200 hours. This duration limit exceeds the maximum requirement of the cassette in a IVIG UF/DF application.

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Fig. 6: Caustic resistance Hydrosart Cassettes under Stress Test Conditions
Stress Test: 500h in 1n NaOH @ 50°C (3 Cassette Lots: #73, #74, #75)
=> Flux, Cytochrome C Rejection, Peel-off Pressure

Conclusions

Cost-pressures in plasma processing mean manufacturers are looking for innovations that will increase productivity. Careful consideration must be given to the introduction of new technologies into a plasma production process because they are highly regulated.

PESUmax cassettes have been specifically designed for the concentration and diafiltration of albumin. The replacement of existing cassettes in albumin processes with PESUmax cassettes is possible as it requires no changes to the membrane material but dramatically improves permeate flow performance. Global industrial experience obtained in albumin production processes after introducing PESUmax cassettes has shown that use of PESUmax cassettes considerably enhances UF/DF unit operations. These cassettes permit final Albumin concentrations of 25% final and higher to be processed. In several projects in which Albumin manufacturers have replaced existing cassettes with the PESUmax cassettes they have installed them into available existing Crossflow Systems and achieved complete process and cleaning validation of the equipment. Within three consecutive validation runs, PESUmax cassettes consistently delivered stable yields and save considerable amount of time.

During IVIG/SCIG processing, 30kD Ultrafilter Hydrosart® cassettes are revolutionary alternatives for use in UF/DF unit operations. These ultrafilters substantially optimize IVIG/SCIG processes as they reduce cleaning downtime, provide significantly higher chemical and caustic resistance in CIP steps and have a positive impact on yield. Moreover, the crossflow cassettes feature an extended lifecycle, which provides robust batch-to-batch consistency. Long multiple-use conditions prevent the interruptions in production runs required for filter replacement and reduce overall downtime. The harmonized cassette design allows the direct implementation of the ultrafilter into existing Crossflow systems.

Despite the maturity of the plasma processing industry manufacturing improvements can still be made. Innovative new technologies have been developed that can increase productivity, yields and facility throughput. To take advantage of these developments, those working in the plasma processing industry must understand in which applications these different technologies are best suited.

References

(1) BioProcess International MARCH 2007 / Downstream Ultrafiltration for Human Serum Albumin. Purification by Crossflow Concentration of Human Serum Albumin with Ultrafiltration Membranes. Frank Meyeroltmanns and Matthias Grabosch

(2) “Ultrafiltration for Plasma Fractionation”
Karen Todd Helix UK; March 2001

(3) Sartorius-Stedim Application Note IGG Process

(4)Product Data Sheet on Hydrosart® printed by Sartorius Stedim Biotech
www.sartorius-stedim.com



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