The Impacts of Contamination
Historically, on a number of occasions, viral contamination has been detected in products. Perhaps the most well-known case
was the vesivirus 2117 contamination discovered in Genzyme's manufacturing facility in Allston, Boston in 2009. As a result,
the manufacturing facility was closed for months, causing a supply shortage of the drugs, Cerezyme (used to treat Gaucher's
disease) and Fabrazyme (for the treatment Fabry's disease). The incident caused significant problems for patients who needed
It was not the first time Genzyme had detected vesivirus in its manufacturing plants. Contamination had also been found at
its site in Geel, Belgium. Such incidents highlight the importance of detecting and removing viral contamination at the outset
for patient safety. Although patient safety is the greatest concern, these events can also have an effect on business. For
example, Genzyme's share prices fell following news of the contamination events, which then became the major factor driving
Sanofi-Aventis' acquisition of Genzyme in 2011 (1).
Testing for Viruses
Failing to screen for contamination when working with mammalian starting materials is unacceptable. Viral contamination events
can be managed by a number of different approaches, but the first step should always be testing. In general, high-risk materials
of biological origin undergo viral clearance, also known as inactivation techniques, to ensure safety. This step is designed
to reduce the potential for viral contamination to be introduced into the process from materials in the early stages.
There are regulations regarding testing procedures that must be complied with for biological materials, such as cell stocks
and raw materials, used in biopharmaceutical manufacturing. The characterization of master and working cell banks may typically
take approximately three months. These tests are completed under strictly regulated guidelines. Testing of cell substrates
include identity tests (phenotypic or genotypic characterization), purity tests (free from adventitious microbial agents and
cellular contaminants, bacteria, fungi, mycoplasma, and virus), cell-line stability testing and karyology, as well as tumorigenicity.
In-vitro testing is carried out using cell-based assays to screen for potential viral contamination. It is generally done on multiple
cell lines that are known to be susceptible to a wide range of human and animal viruses. Three or four different cell lines
are typically used, including the species of origin (e.g., CHO) and one susceptible to human viruses. Ultimately, the choice
of cell lines will be determined by the viruses likely to be present, whether as an endogenous contamination or as a result
of handling of the cells.
In-vivo testing is used to assess for potential viral contamination with those viruses that are unable to grow in in-vitro cell-culture methods. The animal species selected for these studies is defined by the nature and source of the cell substrate
being used for the production process. The use of in-vivo studies is carefully controlled, from both regulatory and ethical standpoints.
In addition, other tests that can be used include checking for the presence of retrovirus using electron microscopy or molecular
biology techniques such as reverse transcriptase assays. Antibody-production tests are also used to determine if species-specific
viruses are present when rodent cell lines are used.
For blood and plasma-derived blood products, the process is slightly different as manufacturers have to rely on donor-screening
programs. Various control elements are in place; for example, plasma from donors cannot be fractionated and used in therapeutic
products, such as those used to treat hemophiliacs, because of the concerns that remain around bovine spongiform encephalitis
The preferred approach with respect to animal-derived materials is to remove these components from the production process
where possible. Significant progress has been made in the replacement of animal-derived materials with recombinant products
and plant-derived material. However, even plant-derived raw materials are not without risk.
A new technique called massively parallel sequencing is a powerful tool for detailed, molecular characterization of raw materials.
The technology, also known as next-generation sequencing, captures the sequences of millions of nucleic-acid strands in a
sample, whether expected or contaminant. While it is not typically used as a routine quality-control (QC) test, it does facilitate
an understanding of the universe of potential contaminants. With this additional insight, specific polymerase chain reaction
(PCR) based assays can be used as routine QC tests to control the quality of the raw material.