Site Meter

Saturday, February 26, 2005

Hepatitis potato not ready for prime time

I have some thoughts which belong at this 20 hits a day blog (maybe) but not a the 800 hits a day fistfulofeuros where I am guest blogging.

First the issue is edible vaccines. There is some hope that eating proteins which are found on viruses will give some immunity to the viruses. Since plants can be engineered to produce the desired proteins, it would be possible to make self reproducing edible vaccines.

A hint of the potential of this approach is provided by the hepatitis potato. A potato which produces a hepatitis B surface antigen. Some of the people who ate this potato showed some increase in immunity to hepatitis B.

Now this is one case of the general problem that we digest proteins. Lots of otherwise wonderful proteins are of limited medical use because they have to be injected. I have some vague and unreliable recollections of special mechanisms used so that proteins in mother's milk are absorbed before they are digested.

My current understanding is that the protein in question is IgG, an antibody. It is useful because mom loans her immunity to the kid. Sad to say, I don't know if this works with humans. I know it works with rats. I will now attempt a major contribution to rat health which might or might not be relevant to human health.

This mechanism is active in the very young breast feeding pup (or maybe infant). This means that it is likely to be useful mostly for vaccines. Now a serious problem is that the body does not make an immune reaction to an antigen that already has IgG stuck to it. This is a fact and it makes sense, since it would normally imply that the immune system is already fighting away.

So it would be nice to make a plant that produces an antigen and produces a IgG antibody which sticks to that antigen such that the IgG falls off once the complex is absorbed. I just thought of a way to do that.

The idea is to make a hybrid protein which consists of the target antigen fused with a normal human protein -- say albumin (incidentally there is also an mechanism to bring albumin from the gut to the blood stream so maybe this is enough right there). Then (maybe) make the plant make IgG which sticks to albumin. The hope is that pulling in this antibody, the system will pull in the attached antigen albumin hybrid. Then in the blood there is lots of human albumin which will compete with the antigen albumin hybrid for the antibody causing the antibody to fall off. Then the antigen albumin hybrid will be recognised as a foreign protein which is unknown to the immune system -- that is as a vaccine.

No comments: