2.12 What Are Monoclonal Antibodies?
Because sexual reproduction through the fertilization of an egg by sperm involves
recombination of the father and mother’s chromosomes, the resulting second
generation possesses mixed traits from both parents and is identical to neither of
them. Asexual reproduction, in contrast, involves replication of the same chromosomes, which are distributed equally to two cells that are genetically identical. In
other words, a single cell divides repeatedly to form a group of completely identical
cells. The cells or individuals created from a single cell or individual through this
form of asexual reproduction are known as clones, and their creation is referred to
as cloning. An additional form of cloning in genetic engineering involves the
isolation of two identical genes. The first experiments with animal cloning used frog
eggs. Removal of the eggs’ nucleus and insertion of a nucleus from the small
intestine of a tadpole resulted in clones of completely identical frogs. Later
experiments involved the cloning of mice. While human clones may appear in
comics, this is actually a matter of semantics; not only is such a thing unnecessary,
but no actual experiments to create it have ever been performed (Khazaeli et al.
1994; Groth and Scheidegger 1980).
The benefit of monoclonal cells is that creating them allows for research under
the same conditions anywhere and at any time. For instance, the human cell as
“HeLa” was extracted in 1951 from the U.S. uterine cancer patient Henrietta Lacke
and bred into clones at cancer institutes all over the world. Cloning of a cell thus
allows for mass production of identical materials in any location. Another example
of this is the monoclonal antibody. Antibodies perform the role of bonding with and
eliminating antigens, or foreign material such as bacteria or virus that enter an
animal’s body. The antibody is a protein known as immunoglobulin, which is
produced by specialized plasma cells in lymphocytes (B lymphocytes, to be
specific). Clones exist for the million or so varieties of lymphocytes in the human
body, but each lymphocyte clone reacts only to one form of antigen. When an
antigen invades, a lymphocyte clone carrying a corresponding antibody on its
surface reproduces and specializes into plasma cells, which produce large volumes
of antibodies. Because there are already many clones producing different antibodies
within the body, many different varieties are already included in examples obtained
from the blood. These are known as polyclonal antibodies. In this case, the term
monoclonal antibody refers to a single kind of antibody produced by a single
lymphocyte clone (or, to be more precise, the antibody that reactions only with a
single antigenic determinant). In 1975, C. Milstein and G. Köhler developed a
method for producing monoclonal antibodies. As shown in Fig. 2.22, a mouse was
first given immunity with antigens. The mouse was then made to produce large
volumes of antibodies for two antigens, after which the spleen (which contains the
lymphocytes) was extracted. The lymphocytes from the spleen were subsequently
fused with cancerous myeloma cells from the bone marrow. Two methods are used
for fusing two types of cells, one in which polyethylene glycol is used to destroy
part of the membrane and one in which electrical stimulation is applied.
50
2 Introduction to Molecular Biology
Because sexual reproduction through the fertilization of an egg by sperm involves
recombination of the father and mother’s chromosomes, the resulting second
generation possesses mixed traits from both parents and is identical to neither of
them. Asexual reproduction, in contrast, involves replication of the same chromosomes, which are distributed equally to two cells that are genetically identical. In
other words, a single cell divides repeatedly to form a group of completely identical
cells. The cells or individuals created from a single cell or individual through this
form of asexual reproduction are known as clones, and their creation is referred to
as cloning. An additional form of cloning in genetic engineering involves the
isolation of two identical genes. The first experiments with animal cloning used frog
eggs. Removal of the eggs’ nucleus and insertion of a nucleus from the small
intestine of a tadpole resulted in clones of completely identical frogs. Later
experiments involved the cloning of mice. While human clones may appear in
comics, this is actually a matter of semantics; not only is such a thing unnecessary,
but no actual experiments to create it have ever been performed (Khazaeli et al.
1994; Groth and Scheidegger 1980).
The benefit of monoclonal cells is that creating them allows for research under
the same conditions anywhere and at any time. For instance, the human cell as
“HeLa” was extracted in 1951 from the U.S. uterine cancer patient Henrietta Lacke
and bred into clones at cancer institutes all over the world. Cloning of a cell thus
allows for mass production of identical materials in any location. Another example
of this is the monoclonal antibody. Antibodies perform the role of bonding with and
eliminating antigens, or foreign material such as bacteria or virus that enter an
animal’s body. The antibody is a protein known as immunoglobulin, which is
produced by specialized plasma cells in lymphocytes (B lymphocytes, to be
specific). Clones exist for the million or so varieties of lymphocytes in the human
body, but each lymphocyte clone reacts only to one form of antigen. When an
antigen invades, a lymphocyte clone carrying a corresponding antibody on its
surface reproduces and specializes into plasma cells, which produce large volumes
of antibodies. Because there are already many clones producing different antibodies
within the body, many different varieties are already included in examples obtained
from the blood. These are known as polyclonal antibodies. In this case, the term
monoclonal antibody refers to a single kind of antibody produced by a single
lymphocyte clone (or, to be more precise, the antibody that reactions only with a
single antigenic determinant). In 1975, C. Milstein and G. Köhler developed a
method for producing monoclonal antibodies. As shown in Fig. 2.22, a mouse was
first given immunity with antigens. The mouse was then made to produce large
volumes of antibodies for two antigens, after which the spleen (which contains the
lymphocytes) was extracted. The lymphocytes from the spleen were subsequently
fused with cancerous myeloma cells from the bone marrow. Two methods are used
for fusing two types of cells, one in which polyethylene glycol is used to destroy
part of the membrane and one in which electrical stimulation is applied.
50
2 Introduction to Molecular Biology