Are there really Vaccines for Addiction?

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It sounds like science fiction: give someone a shot and cure him of his addiction. But that’s the hope that vaccines to abused substances present us with. Unfortunately, the reality is a bit less magical, even if there is still promise.

The Promising Part

Our immune systems protect us by reacting to foreign invaders, usually viruses or bacteria. To keep it as simple as possible, the outline is that after an exposure, antibodies are formed which recognize the foreign substance, bind to it and keep it from having the effect it otherwise would in the body.

When a vaccine is given, such as the polio vaccine, we develop an immune response with subsequent exposures to the same thing. It doesn’t even have to be the entire polio virus, as long as our immune system has “seen” enough of the proteins that make up the virus coat, the antibodies will attach to it, and the virus won’t be able to cause disease.

So far, so good, and scientists have been pursuing this goal for some time. (One of many papers outlining the scheme in more technical terms.) A clear advantage is that an antibody response is already present, before someone comes across the next exposure. For drug vaccines, this is great. It puts a kind of supervisor right in their body; always watching, always “on.”

You could vaccinate someone ahead of time to give him protection and prevent getting addicted in the first place, or you could give someone a vaccine while he was in treatment and keep him from relapsing after release.

The Challenges

Physiology - the immune response is messy. It has to be because flexibility is part of its strength. We are not pre-programmed with an antibody response to every possible combination of proteins in nature; the body has to “learn” the response. But this complexity makes it harder to create a successful vaccine. Unlike computer programming where a certain input gives a predictable response, our immune systems are variable, both between different people and in the same person at different ages. This is why vaccines are often given more than once and why some viruses (like HIV) have no useful vaccine at all.

The Drugs - our immune system is geared to react to globs of protein, the kind of stuff virus coatings or bacterial cell walls are made of. But chemicals we abuse are much, much smaller than this. This is one reason why drugs of abuse can slip into our brains without being blocked by physical defenses. Their small size makes them invisible to some of our protective mechanisms. The challenge is then how to get our immune system to “see” these tiny entities in the first place.

One trick is to bind the drug chemically to something larger (like a piece of a pathogen) and use that for training purposes. An immune response to this larger package can then induce a similar response when the drug shows up by itself. A story in the Wall Street Journal shows how this strategy has been used by linking cocaine to a piece of the cholera bacterium.

The Addicts - addicts want to get high. That’s a plain fact. Whether it is to stave off cravings or to escape their own lives, the human element works against vaccination as a cure all. There are two ways the addict themselves ruins the treatment. The first is when they refuse to follow through with a booster vaccine (and vaccines tested so far only last a few weeks) because they want to return to getting high. The second problem is that an addict may increase their dose enough to overwhelm whatever the vaccine is blocking – even when there is a risk for overdose. A third, but less common failure would be if the addict simply switches to another drug that the vaccine is not effective against.

Current Vaccines

The problem of limited immunity (immunity that requires a series of booster shots) or immunity that is limited by the patient’s own genetic profile, may be solved. New techniques insert genes to directly stimulate antibodies into liver (or other organ) cells, essentially reprogramming the genes in those cells. This has the advantage of a constant production and no need to “prime” patients. This technique is still under investigation.

The New York Times reported the most promising vaccine research so far is with nicotine, although no products are on the market yet. Vaccine work has also been encouraging for cocaine and heroin, with mouse studies showing a strong effect with the heroin. But human studies have been less exciting.

However, scientists are realizing that a full immune response may not be necessary. Blunting the immediate effects of the drugs can still offer some help to addicts. Since antibodies are already present in the blood stream, not only is there an initial blunting of the “rush” from an illegal drug, but even the drug that gets into the brain (where antibodies cannot follow) can be captured as the drug moves back and forth across the blood-brain barrier. The antibodies bind up any drug that flows out of the brain and prevents it from cycling back in – one of the key ways a high is sustained.

This same capturing mechanism can be used to treat drug overdose, even if the patient hasn’t been previously vaccinated. This would also represent a step forward.

In the end, vaccines against drugs are not miracle cures, at least not yet and probably not for the foreseeable future. But they offer another way to attack our drug abuse problem and can be added to existing treatments.

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