Methods for Viral Inactivation and Clearance
The robust and reliable capability to eliminate viruses must be demonstrated by a risk-based approach.10 Today's requirements demand a statistically independent combination of methods (orthogonal technologies) for removing enveloped
and nonenveloped viruses based on the different physical principles of removal and inactivation, and yet are complementary
to each other.11–12
Several methods can be used for virus clearance in bioprocessing. These include inactivation methods such as solvent and detergent
(SD) or chemical treatments, low pH, microwave heating, adsorption by chromatography, and removal by mechanical or molecular
sieving using normal and tangential-flow filtration methods. The first three of these, treatments with solvents and detergents,
low pH, or microwave heating, all have significant limitations in their ability to inactivate small nonenveloped viruses.
SD treatments were commonly used for plasma proteins and were considered the gold standard for inactivating enveloped viruses.13
It has been shown that SD treatments of a recombinant protein can completely and rapidly inactivate enveloped viruses like
PI-3, XMuLV, IBR, and MCF.14 However, small nonenveloped viruses are not being eliminated substantially by this virus-clearance technology. Low pH inactivation
of murine retroviruses is reported to be highly dependent on time, temperature, pH, and relatively independent of the recombinant
protein type or conductivity conditions outlined.15 Heating is not considered one of the most reliable methods for virus inactivation because of the variation in stability
of each viral genome to heat or temperature.
Viral Clearance Capabilities of Membrane Chromatography
Chromatography and filtration, on the other hand, are widely accepted methods for virus adsorption and removal respectively
and act as orthogonal techniques in the viral-clearance platform. Membrane chromatography, a relatively newer technique gaining
prominence in biomanufacturing, has proven to be efficient in removing small nonenveloped viruses.16 Ion-exchange membrane adsorbers, with ligand–virus-binding properties similar to those of anion-exchange (AEX) chromatography,
have the disposable option as an added advantage. This not only reduces capital costs but also eliminates post-use cleaning,
sterilization, validation, and risk of carry-over contamination, thereby simplifying adsorptive virus clearance.17,18
Table1
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Efficient clearance data between 4.41 log10 and 6.67 log10 for MVM has been determined for membrane chromatography.19 Additional studies have demonstrated that membrane chromatography meets and exceeds viral-clearance performance of Q resin
chromatography.20 Clearance capabilities of Sartobind Q for nonenveloped viruses have been shown to be between 3.56 log10 for MVM and more
than 6.92 log10 for PPV.21 It has been demonstrated that the platform tested membrane chromatography, has a process capacity greater than 3,000 g MAb/m2 or 10.7 kg MAb/L with a LRV >5 for four model viruses.17 Mass balance in viral-clearance study is another important parameter to demonstrate efficient virus removal by membrane
adsorbers. A 100% recovery was demonstrated for PRV, Reo-3, and MVM, when the membrane was stripped with 1-M NaCl, illustrating
efficient charge capture for the three model viruses while high salt treatment of the membrane showed 70% recovery for MuLV.16 The virus-clearance capability of such technology has been presented in Tables 1a and 1b.
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