Comprehensive Virus Clearance Evaluation Using Microscale Membrane Adsorbers

Membrane adsorbers can be a simple and effective choice for anion-exchange (AEX) purification of biopharmaceuticals. However, as Sherri Dolan (global technology consultant for virus clearance at Sartorius) explained during a May 2022 presentation, biomanufacturers generally do not leverage their membranes’ full loading capacities. Doing so could improve process economics and decrease costs for several downstream applications.

Dolan’s Presentation
Membrane adsorbers are ideal for flow-through AEX applications (e.g., secondary purification and polishing) because they can be used at high flow rates and loaded to high capacities (in flow-through mode). Biomanufacturers often apply adsorbers only for small-scale activities, the rationale being that scale-up necessitates development of a costly membrane configuration. However, membrane adsorbers often are not loaded to their full capacities. Doing so could improve process economics and enable application of this technology at larger scales.

Dolan described her company’s work with a customer that was exploring membrane-adsorber options in case of supply-chain disruptions. The customer wanted to determine the maximum amount of product that could be loaded while maintaining acceptable virus retention, so a suitable small-scale device was required. Because such studies involve duplicate screening of four model-virus panels, they can require significant amounts of product and incur high costs, especially when loading membranes to high levels. Thus, low-volume scale-down models that can be loaded to high capacities are highly beneficial.

Sartorius offers two such options. The Sartobind Q Nano device is a 1-mL spiral-wound membrane. The Sartobind Q Pico device is a 0.08-mL flat-sheet disc. The picoscale device appealed to the customer because it requires 1.6 g of sample per run. Thus, operators could use 12.5× less material than what would be needed for a nanoscale device during a typical viral clearance validation study.

Sartorius performed three sets of experiments for the customer. Initial studies focused on scalability across the Sartobind Q pico- and nanoscale devices. Scientists ran two nanoscale and one picoscale system, all loaded with 5 kg of a bispecific antibody (bsAb) product per liter of membrane. The samples were spiked with known concentrations of murine minute virus (MMV). Log reduction values (LRVs) were comparable across all three runs.

The second set of studies evaluated picoscale-device loading capacity across four products: a monoclonal antibody (MAb), a dual–variable-domain immunoglobulin (DVD-Ig), and two bsAbs. Samples were loaded on the membrane to a capacity of 20 kg/L.

The MAb and first bsAb showed no virus breakthrough when loaded up to 20 kg/L, whereas the DVD-Ig and second bsAb had breakthrough at
5 kg/L. Based on previous analytics, the team knew that the problematic bsAb contained aggregates that might compete with MMV for binding space. Low LRVs were more difficult to explain for the DVD-Ig because its impurity profile did not show risks for binding of nonviral impurities. Thus, analysts cannot rely on impurity profiles and product attributes alone to identify maximum loading capacities. Dolan recommended performing a virus retention study to determine maximum product-loading capacity while maintaining virus retention.

Dolan emphasized the importance of such studies by describing financial impacts from underloading a membrane adsorber during purification of material from a 10,000-L reactor with an output of 5 g/L. Loading 2 kg/L would require 24.8 L of membrane volume, she explained. Increasing loads to 5 kg/L could reduce needs for both membrane volume and process buffer by 60%. Loading 20 kg/L could increase such savings to 90%.

In a third set of studies, Sartorius compared MMV retention by the customer’s membrane adsorber with that of the Sartobind Q Pico device using the same molecules as in the loading-capacity studies. The Sartobind Q Pico device achieved higher MMV clearance for all materials, with LRVs ranging from 4.4 to 5.6.

Questions and Answers
How can high pressure be prevented during picoscale device operation? Placement of an in-line prefilter helps to prevent membrane clogging and associated pressure problems.

Should preuse integrity tests be performed on Sartobind Q devices? Sartorius recommends pre- and postuse diffusion testing, especially for the picoscale device, which can be sensitive to pressure pulses >80 psi.

Can Sartobind Q Pico devices be used in bind–elute mode? Sartorius recommends the nanoscale device for bind–elute applications.

Find the full webinar online at www.bioprocessintl.com/category/webinars.