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Encyclopedia of Physical Science and Technology EN007K-319 July 2, 2001 17:53

428 Hybridomas, Genetic Engineering of

monoclonal antibody. The hybridoma is created from
the fusion of an antibody-secreting B-lymphocyte and
a transformed myeloma. The term was first used in the
1970s following the breakthrough work of Kohler and
Milstein.
Immunoglobulin Proteins found in the blood that show
antibody activity.
Monoclonal antibody An antibody that is specific to a
single antigen. A monoclonal antibody is synthesized
from a homogeneous population of hybridoma cells.
Polyethylene glycol This is a commonly used fusogen
for the fusion of two cells.
Quadroma A cell formed by the fusion of two hybrido- FIGURE 1 Structures of immunoglobulin isotypes.
mas. The immunoglobulin product of a quadroma will
contain a mixture of heavy and light chain structures vasive molecule. Normally the binding is to only part of
derived from each parental line. a large molecule (the epitope) and so there may be many
Variable region The region of an immunoglobulin in different antibodies for a particular compound. Antibod-
which the amino acid sequence changes so that the ies have become essential tools for biological research be-
molecule can bind to a specific antigen. cause of their very specific recognition and affinity for one
compound (the antigen). This has not only led to the use
of antibodies in the recognition of specific cellular com-
HYBRIDOMAS are hybrid cells capable of the continu- ponents but also to the development of routine diagnostic
ous production of monoclonal antibodies. They combine medical tests. More recently antibodies have been used as
the key properties of the two parental cells: a myeloma therapeutic agents for the treatment of human disease.
with an infinite life span and a B-lymphocyte capable of Each B-lymphocyte is capable of producing one type
synthesizing a single antibody. The technology for pro- of antibody in response to a particular antigen which in-
ducing hybridomas was developed by Kohler and Milstein teracts with a cell surface receptor. Stimulation by an anti-
who gained the Nobel Prize in 1984. Hybridomas can be gen causes growth and an expansion of the cell population
growninsuspensioninlargebioreactorsfortheproduction capable of producing the corresponding antibody. The va-
of kilogram quantities of monoclonal antibodies. The an- riety of antibodies present in any animal reflects the pop-
tibodies have a range of applications because of their high ulation of B-lymphocytes which have been stimulated by
specificity in recognizing selected proteins. This enables previous exposure to a range of antigens.
them to be used for diagnosis and testing in applications Antibodies are found in a specific protein fraction of
such as blood typing, the detection of virus, pregnancy blood called the gamma-globulin or the immunoglobulin
testing or for the detection of contaminants in food. The fraction. They are synthesized by a subset of white blood
application of monoclonal antibodies as human therapeu- cells—the B-lymphocytes. The molecular structures of the
ticagentsinthetreatmentofdiseasehasbeensuggestedfor five major classes (isotypes) of immunoglobulins (IgM,
a number of years. However, there have been difficulties IgD, IgG, IgE, and IgA) are shown in Fig. 1. The basic
in the production of antibodies that are not immunogenic structural arrangement of two heavy associated with two
to humans. In the late 1990s a range of human or “hu- light chains is similar for all the isotypes. However, each
manized” antibodies have been produced specifically for isotype is distinguished by different heavy chain structures
the treatment of cancer. The number of such therapeutic which are of varying length, number of domains, and gly-
monoclonal antibodies is likely to increase in the future as can structures. The glycans are indicated by the fork struc-

a result of the numerous clinical trials that are now taking tures ( ). It is also to be noted that the IgM configuration
place. consists of five basic structures linked as a pentamer.
I. INTRODUCTION: THE NATURE II. THE MOLECULAR STRUCTURE
OF ANTIBODIES OF ANTIBODIES

Antibodies are glycoproteins found in body fluids includ- A structural representation of an antibody (immunoglobu-
ing blood, milk, and mucous secretions and serve an es- lin, IgG) which has an overall molecular mass of 150 kD is
sential role in the immune system that protects animals shown in Fig. 2. This is the major class of immunoglobulin
from infection or the cytotoxic effects of foreign com- found in blood serum. The molecular structure consists
pounds. Antibodies will bind with high affinity to an in- of two light and two heavy chains bound by disulfide