Biomedical Engineering Reference
In-Depth Information
Table 13.8
Some vaccine preparations that consist not of intact attenuated/
inactivated pathogen, but of surface antigens derived from such pathogens
Vacci ne
Sp e ci fi c antigen used
Anthrax vaccines
Antigen found in the sterile fi ltrate of
B. anthracis
H. infl uenzae
vaccines
Purifi ed capsular polysaccharide of
H. infl uenzae
type B
Hepatitis B vaccines
Hepatitis B surface antigen (HBsAg) purifi ed
from plasma of hepatitis B carriers
Meningococcal vaccines
Purifi ed (surface) polysaccharides from
N. meningitidis
(groups A or C)
Pneumococcal vaccine
Purifi ed polysaccharide capsular antigen from up
to 23 serotypes of
S. pneumoniae
The toxoid is then prepared by treating the active toxin produced with formaldehyde. The product
is normally sold as a sterile aqueous preparation. Tetanus vaccine production follows a similar ap-
proach.
Clostridium tetani
is cultured in appropriate media. The toxin is recovered and inactivated
by formaldehyde treatment. Again, it is usually marketed as a sterile aqueous-based product.
Traditional antigen-based vaccine preparations consist of appropriate antigenic portions of the
pathogen (usually surface-derived antigens; Table 13.8). In most cases, the antigenic substances
are surface polysaccharides. Many carbohydrate-based substances are inherently less immuno-
genic than protein-based material. Poor immunological responses are thus often associated with
administration of carbohydrate polymers to humans, particularly to infants. The antigenicity
of these substances can be improved by chemically coupling (conjugating) them to a protein-
based antigen. Several conjugated
H. infl uenzae
vaccine variants are available. In these cases, the
Haemophilus
capsular polysaccharide is conjugated variously to diphtheria toxoid, tetanus toxoid
or an outer membrane protein of
Neisseria meningitidis
(group B).
13.4.2 The impact of genetic engineering on vaccine technology
The advent of recombinant DNA technology has rendered possible the large-scale production of
polypeptides normally present on the surface of virtually any pathogen. These polypeptides, when
purifi ed from the producer organism (e.g.
E. coli, Saccharomyces cerevisiae
) can then be used as
'subunit' vaccines. This method of vaccine production exhibits several advantages over conven-
tional vaccine production methodologies. These include:
•
Production of a clinically safe product; the pathogen-derived polypeptide now being expressed
in a non-pathogenic recombinant host. This all but precludes the possibility that the fi nal prod-
uct could harbour undetected pathogen.
•
Production of subunit vaccine in an unlimited supply. Previously, production of some vaccines
was limited by supply of raw material (e.g. hepatitis B surface antigen; see below).
•
Consistent production of a defi ned product that would thus be less likely to cause unexpected
side effects.
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