Science Interviews

Interview

Sun, 9th Jan 2005

An Anti-smoking And Anti-cocaine Vaccine

Dr. Campbell Bunce Campbell - We've come up with a novel way to help addicts kick both the smoking and cocaine habit: a kind of anti-addiction vaccine. Using the vaccine helps to prevent the high people get from t

Part of the show Addiction & Anti-Nicotine Vaccines

Chris - So how does the vaccine work?

Campbell - The basis behind the vaccine is that it stimulates the immune system to generate antibodies towards nicotine or cocaine. Antibodies are very large proteins and bond specifically to nicotine or cocaine. When the antibody meets nicotine, it binds to it and prevents the nicotine molecule from getting into the brain. Normally, nicotine and cocaine molecules are very small, but when they are bound to the very large antibodies, they can no longer cross the blood-brain barrier. The antibody complex acts like a sponge that maintains nicotine in the bloodstream and stops it getting to the brain and giving the addict a high. If people stop getting high, then hopefully it will break the habit.

Kat - How would this work in tandem with people trying to quit the physical habit? Many people say it has just become part of their behaviour.

Campbell - That's a difficult question to answer until we do some formal testing. However, there are two main aspects to quitting: firstly come withdrawal symptoms. These are often experienced soon after the addict decides to quit, and can take many forms. After that, those that give up are at risk of a relapse. This usually happens when people are in an environment in which they experience all the cues they associate with the drug-taking habit. This might be by going into a pub, having a drink in their hand and then wanting to reach for a cigarette. They re - experience the pleasure of their old habit and can slip back into regular use. If the person is vaccinated, it will prevent the hit from the moment of weakness and stop the reinforcement of the habit.

Chris - When you inject something into somebody, it produces an immune response and creates antibodies. Seeing as many people smoke cigarettes for years, how come they don't have antibodies for nicotine already?

Campbell - The immune system has evolved to spot the difference between itself and foreign proteins. However, very small molecules (such as nicotine and cocaine) can evade the immune system, as they are too small to be recognised. In designing the vaccine, we had to think of a way to allow the immune system to recognise the molecules. We found that it can recognise small molecules when they are attached to much larger immunogenic proteins. The vaccine is designed to physically attach small molecules to a very large protein. This fools the immune system into making antibodies against things it wouldn't see otherwise, and thus raises an immune response.

Kat - How long will the response last for?

Campbell - The most effective vaccines tend to be live forms of the infectious disease. As you go down the scale, you get protein vaccines, which are less able to get a strong and long lasting immune response. Our vaccine is even further down the scale as it looks at very small molecules. What we've found in the clinic so far is that we can raise a reasonably high antibody response towards nicotine and cocaine. The antibodies generally persist for about 6 months.

Chris - So the nicotine locks on and can't get through to the brain, but then what happens? Does the nicotine leach off or get burnt up somewhere?

Campbell - What the antibodies do is protect the drug from the normal metabolism that it is usually subjected to. Nicotine in a vaccinated subject should have its half life increased two-fold, meaning that it is burnt up faster. It should be a very dynamic interaction.

Chris - Will it be possible to vaccinate someone who has never smoked before?

Campbell - Yes, it would. Theory would suggest that they wouldn't get a high from smoking and therefore wouldn't become addicted.

Chris - If there is only so much nicotine the antibody can soak up, then surely if someone smoked lots and lots of cigarettes, they would still get a hit. Will this vaccine not encourage people to smoke more?

Campbell - That is one of the most asked questions. There is a concern that it is possible to overcome the antibodies, but we haven't seen anything like that happen in our trials so far.

Kat - Do people injected with the vaccine say they report less of a high?

Campbell - We have not accurately measured self-reported pleasure. When people have relapsed, we simply asked them whether they get more, less or the same amount of pleasure as they did before. From those we have asked, a high proportion report a reduction in pleasure. This should make people feel less inclined to continue.

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