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Monoclonal Antibodies

Humans (and all jawed vertebrates) have the ability to make antibodies able to Not only does this provide the basis for protection against disease organisms, but it makes antibodies attractive candidates to target other types of molecules found in the body, such as: Thus the remarkable specificity of antibodies makes them promising agents for human therapy. Imagine, for example, being able to

But there are problems to be solved before antibodies can be used in human therapy.

1. The response of the immune system to any antigen, even the simplest, is polyclonal. That is, the system manufactures antibodies of a great range of structures both in their binding regions as well as in their effector regions.

Link to a discussion of how antibody diversity is created.

2. Even if one were to isolate a single antibody-secreting cell, and place it in culture, it would die out after a few generations because of the limited growth potential of all normal somatic cells.

Links to

What is needed is a way to make "monoclonal antibodies":

This problem was solved for mice in 1975 with a technique devised by Köhler and Milstein (for which they shared a Nobel Prize in 1984).

An antibody-secreting B cell, like any other cell, can become cancerous. The unchecked proliferation of such a cell is called a myeloma.

Köhler and Milstein found a way to combine They did this by literally fusing myeloma cells with antibody-secreting cells from an immunized mouse. The technique is called somatic cell hybridization. The result is a hybridoma.

The procedure

Mix Use an agent to facilitate fusion of adjacent plasma membranes. Even so, the success rate is so low that there must be a way to select for the rare successful fusions. So,

use myeloma cells that have:

1. The first property is exploited by transferring the cell fusion mixture to a culture medium — called HAT medium because it contains: The logic:

2. Test the supernatants from each culture to find those producing the desired antibody.

3. Because the original cultures may have been started with more than one hybridoma cell, you must now isolate single cells from each antibody-positive culture and subculture them.

4. Again, test each supernatant for the desired antibodies. Each positive subculture — having been started from a single cell — represents a clone and its antibodies are monoclonal. That is, each culture secretes a single kind of antibody molecule directed against a single determinant on a preselected antigen.

5. Scale up the size of the cultures of the successful clones.

Hybridoma cultures can be maintained indefinitely:

Uses for monoclonal antibodies

Monoclonal antibodies are widely used as diagnostic and research reagents as well as in human therapy. (It is estimated that worldwide sales of monoclonal antibodies in 2009 exceeded 36 billion dollars.)

In some in vivo applications, the antibody itself is sufficient. Once bound to its target, it triggers the normal effector mechanisms of the body.

In other cases, the monoclonal antibody is coupled to another molecule, for example

Some monoclonal antibodies that have been introduced into human medicine

As of 2011, 35 monoclonal antibody preparations have been approved by the U.S. Food and Drug Administration for use in humans. Here is a selection.

To suppress the immune system

To kill or inhibit malignant cells

Angiogenesis Inhibitors

Other

Problems with monoclonal therapy

Mouse antibodies are "seen" by the human immune system as foreign, and the human patient mounts an immune response against them, producing HAMA ("human anti-mouse antibodies"). These not only cause the therapeutic antibodies to be quickly eliminated from the host, but also form immune complexes that cause damage to the kidneys.
Link to discussion of immune complex disorders.

(Monoclonal antibodies raised in humans would lessen the problem, but few people would want to be immunized in an attempt to make them, and most of the attempts that have been made have been unsuccessful.)

However, using genetic engineering it is possible to make mouse-human hybrid antibodies to reduce the problem of HAMA.

In both cases, the new gene is expressed in mammalian cells grown in tissue culture (E. coli cannot add the sugars that are a necessary part of these glycoproteins).

Looking ahead

Other ways of solving the problem of HAMA are being vigorously pursued.

Transgenic mice. One of these is to exploit transgenic technology to make transgenic mice that: The result is a mouse that

Phage display is another technique for making all-human monoclonal antibodies. Link to discussion.

Monoclonal T-cell Receptors (TCRs)

Antibodies can bind to molecules expressed at the surface of target cells (as well as to soluble molecules) but are not effective against the peptide fragments that antigen-presenting cells contain tucked within their histocompatibility molecules. T-cell receptors are the ligands needed for that job. [Discussion]

So monoclonal antibodies are not effective against intracellular antigens, e.g. virus-encoded proteins and tumor-specific antigens. But now progress is being made toward the development of monoclonal T-cell receptors (αβ TCRs).

Two ways in which these molecules could be helpful:

Look forward to clinical trials.

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23 February 2013