Antibody Molecules, Genetic Engineering of
331
variable domains of heavy and light chains (V
L
and V
H
) joined by a synthetic flexible
linker peptide. Thus, the scFv provides a fully functional antigen binding domain that
is encoded in a single gene and expressed as a single polypeptide.
Hybridoma
Cell derived by a fusion between a normal cell, usually a lymphocyte, and a tumor cell,
usually a myeloma cell.
Variable Region
Variable portion of the antibody molecule that is responsible for antigen binding.
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Antibodies have long been appreciated for their exquisite speci±city. With the
development of the hybridoma technology, it was possible to produce rodent
(mouse or rat) monoclonal antibodies that are the product of a single clone of
antibody-producing cells and have only one antigen-binding speci±city. Advances
in genetic engineering and expression systems have been applied to overcome
problems of immunogenicity of rodent-produced antibodies and to improve their
ability to trigger human immune effector mechanisms. The production of chimeric,
humanized, and totally human antibodies aswellasantibodieswithnovelstructures
and functional properties has resulted in improved monoclonal antibodies. As a
consequence, recombinant antibody-based therapies are now used to treat a variety
of diverse conditions that include infectious diseases, inflammatory disorders, and
cancer. This article summarizes and compares different strategies for developing
recombinant antibodies and their derivatives.
1
Antibody Structure and Engineering
1.1
The Basic Structure of Antibodies
Antibodies are molecules with multiple
properties
that
make
them
a
critical
component of the immune system. These
properties include the ability to recognize
a vast array of different molecules known
as
antigens
and to interact with and activate
the host effector systems.
The basic structure of all antibodies,
also known as
immunoglobulins
(Igs), is
a unit consisting of two identical light
polypeptide chains and two identical heavy
polypeptide
chains
linked
together
by
disul±de bonds (Fig. 1). Heavy and light
chains are encoded by separate genes
and are organized into discrete globular
domains separated by short peptide seg-
ments. The amino-terminus end of both
heavy and light chains is the antigen
binding site and consists of one domain
characterized by sequence variability (vari-
able region or V) in both the heavy and
light chains, called the V
H
and V
L
regions
respectively. The rest of the molecule has a
relatively constant (C) structure. The con-
stant region of the light chain is termed
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