An Introduction to Monoclonal Antibodies.

Monoclonal antibodies, the demonstration of the ability to make which won Jerne, Kohler and Milstein the Nobel Prize in Physiology, are extremely versatile tools in medicine & biological research. Before moving on, it is important to familiarise oneself with some terminology.

Antibodies are molecules that can bind to antigens, and are made by cells called B-lymphocytes in animals. They are made up of two heavy chains and two light chains, and have constant regions and variable regions. Heavy chains are just longer than light chains, and constant regions are identical in all antibodies from a species, while variable regions are, um, variable.

Structure of IgG, A typical antibody, schematic representation.

If you took the serum of an animal species, you would find that the mixture of antibodies contained therein would be polyclonal by nature, i.e, they would contain antibodies and antibody producing cells that are capable of reacting to a wide variety of antigens, even if each antibody would be specific to its own antigen.

Sometimes this is ok, as in the case of antivenom, but in some other cases, especially for antibody therapy in humans and for use in diagnostics, better quality is desirable. This is where monoclonality becomes important, a mixture of monoclonal antibodies would only react with ONE specific antigen, with the implication being that all the antibodies in the mixture belong to a single clone of antibody-producing cells (that is what monoclonal means, simple Latin & English)

A Graphical Summary of how monoclonal antibodies are produced.

Monoclonal antibodies are produced using a technology that relies on isolating a B-cell that produces a specific antibody and fusing it with cells that come from a cancerous mouse cell, with the cancer being known as multiple myeloma. To produce a monoclonal antibody of our choice, the following procedure is adopted…

[1] Inject the antigen that we need antibodies against into mice.

[2] Harvest the spleen from the mouse after a few days, which should be around two weeks if one were to assume that the time for the primary humoural response to build was the same as that in humans.

[3] Isolate multiple myeloma cells that do not produce antibodies and cannot produce HGPRT (That is a substance required for growth in a HAT medium) , media are concoctions that serve as food for growing cells.

[4] Fuse with B-Lymphocytes obtained from step [2], then put into HAT medium for culture. The clever part of this step is that only successfully fused cells can grow in HAT medium. These fused cells are called Hybridomas.

[5] Select B-Lymphocytes that produce the required antibody, start to culture them, and ta-da, you have a source of monoclonal antibodies. Lovely, innit?

So now we have a source of high quality monoclonal antibodies, but it doesn’t end here, remember that I said that constant regions are only constant in all antibodies from a particular species? This means that the constant regions of rat antibodies are different from those of human antibodies, and this can trigger an immune reaction if rat/mouse antibodies are put into humans (for purposes of therapy) , as a result, a process called humanization is carried out.

Here, genetic engineering is used to modify the amino acid sequence of antibodies such that it is identical to naturally occurring human antibodies insofar antigenicity is concerned. One way of doing this is to modify human B-lymphocytes so that they produce the antibody with the variable regions we want and then create hybridomas, and proceed with the workflow presented above.

Another approach involves the use of chimerisation, while these antibodies are just semi-humanized, they are better than completely unmodified animal-derived monoclonal antibodies, here, the antigen binding fragments of mouse antibodies are fused with the constant region peptides of human antibodies, resulting in a mouse-human hybrid antibody.

Various degrees of humanization, a graphical summary.

In my last post, which was on Gleevec, I focussed on a small-molecule drug, monoclonal antibodies belong to a different class of drug, called biologics, which are molecules of biological origin. Monoclonal antibodies can be used not only to bind to and block things like target receptors but also to provoke an immune response against those targets. This can be beneficial and not so beneficial, since there are constraints imposed by the immunogenecity of the targets we are looking at.

List of FDA-Approved Monoclonal Antibodies for Therapeutic Use.

List of FDA-Approved Monoclonal Antibodies for Therapeutic Use. Courtesy Wikipedia.

This table was obtained from the relevant article on Wikipedia , please click on the thumbnail for a larger, clearer view.

So, please do dig around on the internet to learn more about Monoclonal antibodies, they are sure to stay because of specificity, amenability to engineering, ease of large scale production and ease of use. They are also used in things like antibody based diagnostic kits regularly.

That’s it from me, for the moment, on this topic. In the meantime, you may want to consult Basic Biotechnology, 3rd Edition, Ratledge and Kristiansen, Cambridge University Press as a reference, there is a dedicated chapter on this subject.

You may also want to hear the scientists who developed this technology explain their work at the Nobel Prize Ceremony in 1984, Dr.Jerne’s Nobel lecture is here , Dr.Kohler’s Nobel lecture is here and Dr.Milstein’s lecture is here

Enjoy 🙂

– Ankur

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3 responses to “An Introduction to Monoclonal Antibodies.

  1. Shishir K Chakravarthy

    Wow,thats cool…The antibody IgG goes through the placenta too doesn’t it?…I mean isn’t it transfered from mother the offspring?

    • Yes it does because of its small size; it is invariably present as a monomer whereas the other subtypes may take up multimeric forms, including dimers for IgA and pentamers for IgM, IgD and IgE can be trimeric at times.

  2. Pingback: The immune system – a brief overview | Exploreable

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