Biomedical Engineering Reference
In-Depth Information
endogenous viruses from cell banks or adventitious viruses from personnel
can have serious clinical implications. According to the European Medicines
Agency (EMEA), potential contaminants may have the following charac-
teristics: enveloped or nonenveloped, small or large, deoxyribonucleic acid
(DNA) or ribonucleic acid (RNA), and unstable or resistant viruses. Viral
safety of licensed biological products must be assured by three complemen-
tary approaches:
• Thorough testing of the cell line and all raw materials for viral
contaminants
• Assessing the capacity of downstream processing to clear infec-
tious viruses
• Testing the product at appropriate steps for contaminating viruses
A combination of methods—inactivation, adsorption, and size exclusion—is
available. The FDA requires demonstration of virus clearance by two meth-
ods. Examples of inactivation procedures are solvent and detergent, chemi-
cal treatments, low pH, or microwave heating. Methods of adsorption utilize
chromatography, and removal by mechanical or molecular size exclusion
uses normal (forward) and tangential flow filtration methods. The treatments
with solvents/detergent, low pH, or microwave heating all have significant
limitations in their ability to inactivate small nonenveloped viruses. Low pH
inactivation of murine retroviruses is reported to be highly dependent on
time, temperature, and pH, and relatively independent of the recombinant
protein type or conductivity conditions outlined. Heating is considered one
of the most reliable methods for virus inactivation because of the variation
in stability of each virus genome to heat or temperature.
Ion exchange and Protein A chromatography are widely used to remove
viruses, and several key studies have been conducted in collaboration with
the FDA, yet the responsibility of proving suitability of any method remains
the responsibility of the developer.
Viral inactivation such as by ultraviolet exposure is also available, where
the virus particles are physically or chemically altered.
Despite the clear demand for downstream processing steps that can pro-
vide high levels of viral reduction, few new techniques have surfaced to
complement or replace those approaches common in today's biotechnology
manufacturing processes. This is particularly true for smaller viruses, such
as the parvovirus, which often exhibit resistance to many inactivation strate-
gies such as detergent and heat treatments.
Unfortunately, the risk of failing viral contamination is severe;
Table 8.1
shows the action plan in various situations.
Implementing ultraviolet bactericidal (UVC) treatment as one of the
orthogonal technologies for virus clearance both for animal cell culture
media- and animal cell culture-derived biologicals is recommended. Virus
