Virus Removal by Filtration: Points to Consider

Oct 01, 2006
Volume 19, Issue 10


Virus safety of biotech- and plasma-derived therapeutics is ensured through complementary manufacturing and quality control measures that include the control and monitoring of raw materials, the validation and implementation of effective virus clearance technology, and the monitoring of final filled product for the presence of virus. Virus filtration, which is considered a robust and effective virus clearance technology, is a common unit operation in the manufacture of biologicals. In this article, we review the points that need to be considered when selecting a virus retentive filter. The areas covered include regulatory considerations; selecting, optimizing, and validating a virus filtration step; and process scale implementation—areas that are of critical importance to users of virus filters.

Some biological therapeutic products are produced using mammalian cell lines or human plasma. The risk of contamination with either known or unknown viruses in these products has been demonstrated; hence, regulatory agencies have mandated that manufacturers evaluate the risks of virus contamination and take necessary measures to mitigate these risks. In addition to ensuring the purity of source materials, manufacturers are encouraged to institute steps in the purification process that will clear endogenous and adventitious viruses. Filtration has been successfully used in numerous processes as a robust step for virus clearance.

To implement virus retentive filtration successfully within a process, several points should be considered. These can be broadly categorized as follows:
  • Regulatory considerations
  • Process considerations
  • Virus filter-related considerations

This article reviews each of these categories and suggests factors to consider when selecting and implementing a virus filter.


To ensure the virological safety of biological therapeutics, regulatory guidance advocates virus control at various stages of the drug manufacturing process. Specifically, manufacturers should (a) select and test source materials for the absence of viruses; (b) test the capacity of the production process to remove or inactivate viruses; and (c) test the product at appropriate stages of production for freedom from detectable viruses.1

Regulators require that an overall safety margin, such as <1 virus particle per 106 doses, be used to demonstrate the virus safety of the manufacturing process. The drug manufacturer is required to quantify the virus "load" in the process. For biotech products derived from murine cell lines such as Chinese hamster ovaries (CHO) and nonsense oligonucleotide (NSO), this typically translates to ~12–18 log10 clearance for endogenous retroviruses and ~6 log10 removal for adventitious viruses. The following is a composite summary of regulatory guidance on virus clearance, with an emphasis on how the guidance relates to virus filtration. 2–5

  • The US Food and Drug Administration (FDA) requires that manufacturers of biotech products that use murine cell lines are to demonstrate the clearance capability of their manufacturing processes with one relevant retrovirus (murine retrovirus) before starting Phase I studies.
  • Regulatory agencies in Germany and France require that manufacturing processes be evaluated to clear non-enveloped parvoviruses in addition to retroviruses.
  • Before marketing authorization, manufacturers are required to assess clearance of multiple model and relevant viruses in their manufacturing processes.

Depending on regulatory requirements, one needs to consider if the process requires retrovirus clearance, or retrovirus and parvovirus removal. Virus clearance filters are broadly classified into two categories:

  • Filters that provide >4 or >6 log10 removal of large viruses, typically 80–100 nm endogenous retroviruses.
  • Filters that provide >4 log10 removal of small and large viruses (larger than 18–24 nm parvoviruses).

Table 1. Commercially available virus filtration products
Commercially available virus filters are listed in Table 1.

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