New antibody formats for therapy

When medical design

surpasses evolution

The research team in the Immunotherapy and Cell Engineering Laboratory is exploring a new generation of biological medicines based on engineered antibodies.

A new generation of biological medicines is on the way: Recombinantly engineered antibodies that are much more efficient and versatile than those produced by the body. They are also far better than conventional recombinant antibodies, which mimic the natural ones – and it will be possible to produce them much more cheaply.

It’s a bit like breeding a hunting dog with a super-sensitive nose and extremely strong muscles – and then teaching it to shoot.

Only this hunting dog is microscopic and, instead of hunting hares or pheasants, it preys on a wide range of viruses, bacteria, parasites or cancer cells in our bodies.

Oh, and it hasn’t been bred, but was designed in a laboratory at Aarhus University. Moreover, its future siblings will probably be produced in yeast tanks.

Antibodies with six arms
The super hunting dog is a multivalent antibody.

Antibodies play an important role in our immune system: they identify potentially undesirable elements (termed antigens) in the body and bind to them so that other immune cells can neutralise them – just like when a hunting dog has tracked down a prey and immobilises it until the hunter arrives.

Natural antibodies are bivalent, i.e. they have two points of interaction with the antigen. An antibody molecule is shaped like a Y in which two identical binding sites are located in the two upper ‘arms’ while the lower arm interacts with the immune system.

By recombining the genes in strands of DNA (hence the term recombinant), scientists have so far managed to create multivalent antibody molecules with up to six binding sites. Instead of a Y, they will thus look like a Ж.

A better grip
The extra antibody binding sites provide a great advantage because each one creates only a weak binding to the ‘prey’, making it difficult in many cases to create sufficiently strong interactions by means of conventional antibodies.

“An antibody with six ‘arms’ is more efficient than one with two arms because the cumulative binding is stronger, and because it provides a better bridge between the targeted antigen and the immune system. This is of particular importance for the prevention of tumours which can be quite resistant to ordinary antibodies,” explains Associate Professor Luis Álvarez-Vallina.

Adjustable functionalities
Not only do the new antibodies have several arms for gripping, they can also be made smaller than normal, making them more effective, particularly against cancer cells. In addition, they are much more versatile than the conventional recombinant antibodies presently used in healthcare.

Since the first usable copy of an antibody molecule was produced in 1975, 39 different monoclonal antibodies have made it into clinical use.

They are called monoclonal antibodies because they are produced by cells that are all clones of a single cell from a mammal – typically a mouse – immunised with a human molecule or cell that its antibody is supposed to react with.

The monoclonal antibodies are typically engineered to resemble human antibodies so that the patient’s own immune system does not attack them. However, each one of them is still ‘programmed’ to bind to one specific target – namely that which was injected into the mouse.

“We now have the technology to adapt the recombinant antibodies to many different tasks. For example, we can adjust their penetration ability and their ability to inhibit growth factors (in conditions such as arthritis and other autoimmune diseases). Within the same molecule, we can also combine an antibody and a toxin, which can be aimed directly at tumour cells. It’s like having a very versatile tracker dog with a rifle,” says Associate Professor Álvarez-Vallina.

Expensive but good
The artificial antibodies are gaining importance in research as well as in the diagnosis and treatment of diseases. Scientists and doctors use them not only to detect bacteria, viruses or metastases, but also to treat them.

In principle, the monoclonal antibodies can be produced in unlimited quantities. By artificially fusing the plasma cell that produces the desired antibody with a specific myeloma cell, it is possible to create a hybrid that divides into millions of cells, all of which are genetically identical to the first one. The technique is called hybridoma and it is expensive.

However, Associate Professor Álvarez-Vallina and his colleagues have caused yeast cells to produce fragments of antibodies with three binding sites. The yeast Pichia pastoris is often used to express the genetic information in DNA into proteins, and it does so very efficiently and cheaply.

In this case, the yield was approximately 20 times higher than with human cells.

“This way we can produce more and better antibodies more efficiently and cheaply. In a few years, the method will be ready for industrial use,” predicts Associate Professor Álvarez-Vallina.