In my last blog post, I talked about Frances Arnold’s work on the directed evolution of enzymes, which won her half of the Nobel Prize in Chemistry, 2018.
The other half of the prize went to George Smith and Sir Gregory Winter for the phage display of peptides and antibodies.
A phage (abbreviation of bacteriophage) is a virus which infects bacteria. By nature, they are very simple things, just a small piece of genetic material in a capsule made of protective proteins. They reproduce by injecting their genetic material into bacteria and ‘hijacking’ their metabolism, so the bacteria produce new copies of the phage’s genetic material! Phage display, developed by George Smith around 1985, is where bacteriophages are used to create new proteins. Adding a gene into the phage DNA could lead to the new protein it coded for being produced on the phage surface and then identified. Essentially, the phage infects the bacteria, which then produces new proteins!
This makes it sound rather straightforward – but of course, it wasn’t.
In the early 1980s, the human genome hadn’t been sequenced. We knew it contained all the genes required to produce all the proteins in the human body – those that we’re made of, and those that are necessary for bodily processes and functions – but we couldn’t identify the specific gene for a particular protein. Smith started using bacteriophages in the hope that they might be able to be used to clone genes.
Smith’s plan was to use the idea that although we didn’t know what a lot of the genes did, we did know a lot of the different proteins. He realised that if he put a gene fragment into the genetic material which coded for the protein capsule of the bacteriophage, the new phages produced would have the protein corresponding to that unknown gene fragment in their protein capsule. Antibodies could then be used to ‘fish’ phages containing particular protein fragments out of the mix. Antibodies are highly selective, and so could find and bind to a single protein among thousands with an enormous degree of precision.
The gene (red, A) for a particular protein is inserted into the DNA coding for the protein capsule (blue) of the phage (B). The new phages produced have the protein (red) in the protein capsule (C).
A known antibody would bind to a known protein. From that known protein, you could identify the previously unknown gene fragment.
This was the foundation of phage display.
A Y-shaped antibody (yellow) with binding sites (orange) at the ends of the ‘arms’.
Gregory Winter combined Smith’s phage display with Arnold’s directed evolution to develop new antibodies which could be used to treat diseases in the body.
Antibodies are sort of Y-shaped molecules, and the far end of each ‘arm’ binds to foreign substances in the body. The human body is capable of producing hundreds of thousands of different antibodies, so there is always one which can attach to a bacteria or virus that enters the body. Cleverly though, they don’t attach to any of the body’s own molecules.
Winter joined the antibody binding site to the phage protein coat – at the genetic code level – so that the antibody’s binding site ended up on the surface of the phage. He built up a whole ‘library’ of phages with different varieties of antibodies on their surfaces, literally millions of different phage-antibody variants! From this ‘library’ he could fish out those antibodies which bound to a particular protein. Using Frances Arnold’s directed evolution approach, he could then generate antibodies with even stronger attachments to that protein. To combat problems with the human body viewing these antibodies as foreign – and attacking them – Winter based his antibodies on human antibodies.
The antibodies are inserted into the phage protein coat, as described above. Those which bind to the target are selected from the first generation (green ticks), while the rest are discarded (red crosses). Those selected phages undergo directed evolution to give a second generation, some of which will bind more strongly to the target than the first generation. After another round (or several) of directed evolution, you can evolve antibodies which bind much more strongly to the target than the original antibodies.
By 1994, antibodies which could attach to cancer cells with a high level of specificity had been developed. One of these can even trigger the release of the body’s natural killer cells so they attack tumour cells and slow their growth. In some cases, patients with metastatic cancer (cancer which has spread from its original site to other parts of the body) have been cured! Obviously, this is a huge breakthrough in cancer care.
In fact, the world’s top-selling prescription medicine, a treatment for rheumatoid arthritis (among other auto-immune diseases), was produced using this method! It works by neutralising the protein which drives the inflammation found in a lot of these diseases, reducing the problems it can cause.
These antibodies can be really powerful – as well as providing new routes into the treatment of cancers and autoimmune diseases, there are also:
- Antibodies which can neutralise the bacterial toxin which causes anthrax.
- Antibodies which slow the autoimmune disease lupus.
- Antibodies in the trials stage which could combat Alzheimer’s disease.
- Many others, also currently in trial stages.
Frances Arnold started out to find new fuels for an environmentally-friendly transport sector.
George Smith started out to try and make clones of genes as part of the project to sequence the human genome.
Without either of their work, Gregory Winter could not have done what he did – and that has lead to a drug which is helping to cure some forms of cancer.
No Scientist is an island – they all work with other people, building on the work that went before them.
As George Smith put it: “Very few research breakthroughs are novel. Virtually all of them build on what went on before. It’s happenstance. Mine was an idea in a line of research that built very naturally on the lines of research that went before.”
Congratulations to these three brilliant Scientists for their Nobel Prize in Chemistry. Between them, they have changed the face of both Chemistry and Medicine for decades to come.