Biomedical Engineering Reference
In-Depth Information
TABL E 8.3. Properties of Some Model Viruses
Diameter
(nm)
Physicochemical
Resistance
Description
a
Virus
Shape
Parvoviruses
b
SS DNA, nonenveloped
18-24
Icosahedral
Very high
Reovirus
DS RNA, nonenveloped
60-80
Spherical
Medium
Hepatitis A
SS RNA, nonenveloped
22-30
Icosahedral
High
XMuLV, MuLV
SS RNA, enveloped
80-110
Spherical
Low
Pseudorabies
DS DNA, enveloped
120-200
Spherical
Medium
a
SS, single-stranded; DS, double-stranded.
b
Mouse minute virus (MMV), porcine parvovirus (PPV), canine parvovirus (CPV), and bovine parvovirus (BPV)
interpretation of viral inactivation studies. Among these variables are protein concen-
tration, presence of product stabilizers, temperature (e.g., during pH inactivation), and
exposure time. Finally, variability in the purity, viability, and titers of stock virus
preparations can contribute to variation in virus clearance results. On a positive note,
the industry is moving cooperatively toward a better understanding of the impact of virus
spikes on clearance studies [15].
In biopharmaceutical manufacturing, virus removal is typically accom-
plished by virus filters and/or chromatography.
Removal.
C
HROMATOGRAPHY
. Regulators have expressed concern that virus LRV provided by a
chromatography column might deteriorate with repeated use of the column, necessitat-
ing resin lifetime studies for viral clearance. A study carried out at U.S. Food and Drug
Administration specifically addressed consistency of retrovirus removal during repeated
use of Protein A resins [16]. The authors used a PCR assay for reverse transcriptase
(TM-PERT) as a surrogate for actual infectivity assays to evaluate retrovirus clearance.
This study demonstrated that protein A column performance, measured by antibody step
yield and breakthrough, deteriorated prior to noticeable reduction of retrovirus LRV.
Similarly, a study on Q Sepharose
Fast Flow operated in flow-through mode demon-
strated that band spreading, reduced DNA clearance, and increased column backpressure
occur prior to LRV loss for the nonenveloped SV40 and enveloped X-MuLV [17]. This
study also demonstrated the importance of resin cleaning. Both the use of cleaning
solutions that degrade the resin and not cleaning the resin decreased the ability of the
column to remove SV40, MMV, and X-MuLV.
Generic and matrix approaches for viral clearance by chromatography were
described many years ago [18]. In another publication [19], robust viral clearance
(
4 log
10
) by anion exchange chromatography was reported for both SV40 and X-MuLV
over defined conditions that include the following:
>
.
pH range: 7.0-8.0
.
Conductivity: 4.6-12mS/cm
.
Resin capacity:
<
200 g/L
