vessel jacket A temperature control method consisting of a double wall outside the main vessel wall. Liquid or steam flows through the
jacket to heat (or cool) the fluid in the vessel. Because biopharmaceutical products are so sensitive and vessel jackets can
cause uneven heating (hot or cold spots), shell-and-tube or plate-and-frame heat exchangers are more common in biopharmaceutical
viability The extent to which cells and tissues are living. Cells can be metabolically viable, but not reproductively viable.
viral clearance step Process step which separates a given class of virus, if any are present, from the desired product. A clearance factor may
be estimated by performing scaled-down experiments using a model virus, to determine process capability.
viral inactivation step Process step, which inactivates the activity of a given class of virus, in order to provide assurance of safety. An inactivation
factor may be estimated by performing scaled-down experiments using a model virus, to determine process capability.
virus The simplest form of life: RNA or DNA wrapped in a shell of protein, sometimes with a means of injecting that genetic material
into a host organism (infection). Viruses cannot reproduce on their own, but require the aid of a host (bacteria, plant, or
animal). The host cell's synthesis is often inhibited by the infecting virus, which may or may not result in disease (more
than 200 viruses are known to produce human disease). An individual virus particle is called a virion, and virions vary in structure, complexity, and size (ranging from 20–25 nm or less to 2,000 nm or more). Six classes of
virus are defined by whether they are single or double stranded, DNA or RNA, or positive or negative.
virus-like particles Also RVLP (retrovirus-like particles); particles that resemble retroviruses, yet lack infectivity, and usually are found in established
lines of mammalian cells. Cell bank characterization seeks to determine whether viral activity is present, as a means of assessing
risk. Not present in non-mammalian cells or cell lines.
viscosity Thickness of a liquid; determines its internal resistance to shear forces.
warning letter The most serious FDA postaudit (after inspection) letter, notifying a manufacturer of adverse inspection findings and giving
it 15 days to reply with a concrete plan for remediation. May or may not be associated with other actions, such as injunction,
consent decree, or product seizure.
washing (of a column) Flushing a column with a large volume of a solvent or buffering agent prior to selective elution of the desired
well-characterized A chemical entity whose identity, purity, impurities, potency, and quantity can be determined and controlled; most well-characterized
biologics are recombinant DNA-derived proteins or monoclonal antibodies.
western blot An immunochemical method for identifying proteins in a complex mixture, proteins separated by electrophoresis are transferred
(blotted) from the gel medium to a protein-binding nitrocellulose or polymeric membrane; the transferred proteins are then
detected by their relative binding to labeled antibodies
Water for injection; very pure water that meets specifications defined by the USP or other compendia; suitable for parenteral uses.
withdrawal Product withdrawal; a recall of a lot of product that is done voluntarily by a firm, when there is concern about product
quality that is not proven. A recall may be mandated by FDA or regulatory bodies. See also recall.
WHO The World Health Organization, a United Nations organization.
working cell bank A cell bank that is usually made from a single vial of the master cell bank, in which each vial has comparable contents and
is expected to perform consistently when introduced into a process or assay. Both master and working cell banks are extensively
tested and characterized before use. Manu-facturing usually starts when a vial of working cell bank is thawed and added to
a reactor. (See master cell bank).