When the antibody locks on to the invader it tries to get rid of it in a variety of ways. With the common cold, it will orchestrate responses that include a runny nose and cough, designed to flush the bugs out of the body. Inflammation and swelling are other weapons in its armoury of the killer cells But sometimes the immune system does not work properly. It may not recognise an invader as a dangerous alien, or the antibody response it mounts may be too weak so the defences are easily overcome, as in some cancers.

On other occasions it can overreact, as with rheumatoid arthritis where healthy tissue is destroyed.The philosophy behind the CAT approach is that there is an antibody to just about everything, and that if it isn’t present it can be added in the form of a drug. Just as every action has a reaction, so each disease-causing molecule has an antibody, and the secret of success for CAT is to mix and match antibodies with diseases.The jewel in the CAT crown is the huge collection of antibodies its researchers have cloned over the past decade. It has amassed a biological library of 100 billion individual antibodies, by far the biggest collection in the world and 10 times as many as the average human has.But although big in numbers, the library is small on volume. At the company’s high- tech factory in Melbourn, near Cambridge, there are no overloaded benches with foaming test tubes and gantries of bubbling beakers. All the antibodies are neatly stored in freezers.The simple but remarkable fact of molecular life is that a single copy of all 100 billion antibodies can be contained in one teardrop of colourless, odourless liquid. Inside each teardrop is a micro-version of the human immune system and somewhere among the 100 billion antibodies are treatments for nearly all the diseases known to man and probably quite a few still waiting to be discovered.The key to a successful antibody library is its size and diversity.

The larger thelibrary, the more chance it has of containing high-quality antibodies that will bind to any given target. A second key factor, and another area where CAT is a world leader, is speed of production of antibodies, by growing them in fast-replicating bacteria. No other antibody isolation technology can match the speed and capacity of CAT. As a bonus, it works with human antibodies rather than animal-based products, thus minimising the risks of side-effects.CAT tests its arsenal of antibodies against molecules implicated in disease. The routine is to expose the target molecule to a test-tube of antibodies and stand back and see which of them stick to it. It’s an ingenious approach which many believe will revolutionise medicine and the pharmaceutical industry over 20 years. Some believe one in three drugs will eventually be antibody-based, perhaps more.”The library sits in tubes in the freeze,” says Dr Chiswell.

“When you decide on your target, you essentially coat it on the sides of a tube, and then you pour the library into the tube. You let it sit there for a bit.” When the library is drained out of the tube, the antibodies which recognised that particular molecule as an enemy will be left sticking to it.These antibodies are recovered and their genetic code added to the DNA of bacteria. As the cells of bacteria grow and multiply, each additional cell grows a cloned antibody. The bacteria works like a super- efficient biological factory giving birth to a huge number of antibodies.

After further tests, these antibodies, the natural enemies of the bug, may form the basis of a new drug treatment for that disease.Dr Chiswell says proving the technology in the early days wasn’t difficult. “It took off on a technical basis almost immediately, Greg had already shown in his lab how we could make large lines of antibodies. Probably the first experiment John did formed the basis of how we could get the antibodies out of those long lines What we developed was a new way of making antibodies. It means we can isolate them very quickly, literally within a day or two and faster than anyone else.”But it was three years after the start of the CAT, in 1993, before this became routine in the lab That year was a turning point for the fledgling company. Its researchers published their isolation technology successes in Nature, and the next round of funding was raised. A year later, a deal with BSF Pharma, part of Knol Pharmaceuticals, was struck, and in 1996, Genentech, one of the first and most successful American biotechs came on board.Three years ago, the company raised £10m to grow the operation to flotation and was listed on the London Stock Exchange with a share price of £5 and capitalisation of £100m At the time there was no product in the pipeline. Now there are four products in clinical development, with many more waiting in the wings.Pride of place as lead product and the drug likely to be the first to come to market is D2E7, an antibody to rheumatoid arthritis.