Biomedical Engineering Reference
In-Depth Information
The use of viral vectors may ultimately prove more effective, as a T-cell response appears to be
central to the immunological destruction of cancer cells.
The latter approach has been adopted in experimental studies involving malignant melanoma.
These transformed cells express signifi cantly elevated levels of a surface glycoprotein, p97. p97
is also expressed (but at far lower levels) on the surface of many normal cell types. Initial animal
studies have indicated that administration of a recombinant vaccinia vector expressing p97 has a
protective effect against challenge with melanoma cells. However, protracted safety studies would
be required in this, or similar, instances to prove that such vaccines would not, for example, in-
duce an autoimmune response if the antigen was not wholly tumour specifi c. The development
of truly effective cancer vaccines probably requires a more comprehensive understanding of the
transformed phenotype and how these cells normally evade immune surveillance in the fi rst place.
Not withstanding this, limited clinical studies in this fi eld have already begun.
13.4.9 Recombinant veterinary vaccines
Amongst the limited number of biopharmaceuticals approved for animal use, recombinant vac-
cines represent the single largest subgroup. Several such products target pigs, including 'Porcilis
pesti' and 'Bayovac CSF E2'. Porcilis pesti, for example, contains a recombinant form of the
classical swine fever virus E2 antigen, the immunodominant surface antigen associated with this
viral pathogen. It is used to immunize young pigs. An overview of its manufacture is presented
in Figure 13.14. The process is initiated by growth of Spodoptera frugiperda cells, typically in a
500 l fermenter. The cells are then infected with the recombinant baculovirus vector, resulting in
high-level expression of the recombinant E2 antigen. The antigen is harvested from the production
medium by low-speed centrifugation and membrane fi ltration steps, which serve to remove intact
Infection with recombinant
Baculovirus vector
Fermentation of Spodoptera
frugiperda cells
Centrifugation and
filtration
β-propiolactone treatment
Formulation as an oil-in-
water emulsion
Figure 13.14
Overview of the manufacture of the veterinary vaccine 'Porcilis pesti'. Refer to text for specifi c
details
 
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