Biomedical Engineering Reference
In-Depth Information
by the HGPRT enzyme contributed by fused splenic B cells. Thus, only
fused cells, called hybridomas, survive! The resulting hybridomas can be
screened for the production of antibodies of the desired specificity. These
can then be cloned to ensure that they are monoclonal and perpetuated
indefinitely. A typical hybridoma produces one to several thousand anti-
body molecules per cell per second (!) and therefore can produce about
antibody molecules per day, which is about 25 picograms (pg; a pg
is of antibody. Using typical culture conditions, about 1 to
of antibody can be collected per ml of tissue culture medium, although
systems have been developed that greatly improve the yield.
One other modification has been made to myeloma cells for the use
in producing monoclonal antibodies. Myelomas are themselves malig-
nantly transformed plasma cells and thus normally produce their own
antibody molecules (usually of unknown specificity). Because the heavy
and light chains of the myeloma antibodies can combine with the light
and heavy chains of the antibodies contributed by the fused B cell, the
original hybridomas produced “mixed antibodies” in addition to the an-
tibodies of interest. Myelomas used today as fusion partners are those
that have lost the ability to produce their own antibody molecules, al-
though they retain the ability to secrete antibodies at high rates. The
most widely used fusion partner is a myeloma referred to as SP2/0-
Ag14, a myeloma derived from a tumor of a mouse.
Stable somatic fusions between cells can only be carried out using
cells within a species or closely related species. Because the majority
of myelomas that can be successfully adapted to tissue culture and be
modified for use in producing hybridomas have come from mice, most
moAb are derived from immunized rodents (mice, rats, and hamsters),
although rabbit monoclonal antibodies have also been reported.
Humanized monoclonal antibodies
Antibodies from one species are themselves antigenic when injected
into an unrelated species. Therefore, murine monoclonal antibodies that
could otherwise be used for diagnostic purposes, or to attach a human
tumor, cannot be safely administered more that once into humans with-
out the potential for causing serious complications, including death. In
fact, the danger in injecting antibodies from other species into humans
was recognized in the first half of the century, when the only treat-
ment for tetanus infections (sometimes referred to as “lockjaw”) was the
administration of an anti-tetanus toxin to a patient produced in animals
(usually horses). Tetanus is caused by bacterium Clostridium tetani,
which releases a toxin that acts on nerves to cause muscle contractions
that do not abate, and is often fatal. The administration of an anti-toxin
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