Although the title given to this article is a bit frivolous, the research in this field certainly is not.
This type of vaccine delivery aims to deliver vaccines into the body via the GI tract, the major problem of course being the degradation of antigens by HCl in the stomach.

A bit of history first...

The concept of edible vaccines is nowhere as recent as you would expect it to be. The idea was first put forth by Dr. Charles Arntzen (then a Professor at University of Texas A&M) 10 years ago as an inexpensive and painless way to deliver vaccines which would be especially useful in developing countries like India. Prototype vaccines were developed even at that early stage, however with relatively poor understanding of the bacterial/viral genomes back then, the success rate was limited.

Image : The Lord and Master of Edible vaccine research, Dr. Charles Arntzen.

Around 1995-1996, tests using edible vaccines in mice began to become impressively successful. The mice, which were fed potatoes which contained antigens, showed a good systemic and mucosal response (more about mucosal immunity later...) to these antigens. The first diseases that the mice were immunized against included cholera, ETEC and hepatitis B.

Human trials were first conducted at around 1996-1997. Only a few trials have been conducted to date , and an edible vaccine is a long way off. But judging from the results of the trials, the "edible vaccine" or "Biotech Bannana" is anything but impossible...

Had enough of TP?? ok...:) sorry... lets see how you can: 

Make your own Biotech banana :

In short the process is this : You mess around with the genetic code of the plant (more on how to do this later..) and introduce a gene which codes for a particular protein antigen (bacterial/viral)  into its genome. (Producing what is called a transgenic organism, or an organism which contains genes belonging to one or more organisms e.g. transgenic pigs which have human organs)

Image:  production of transgenic DNA. Please click on the image to have a look at the larger picture before you read further.... :)

Now as this genetically modified plant grows, it synthesizes the protein antigen along with the normal plant proteins.
When someone eats this plant or its fruit, along with the other plant proteins, he also ingests the antigen. This antigen then induces an immune response in the person who swallowed the fruit.

Simple isn't it... well actually not quite... Introducing the bacterial/viral gene can be a messy process. Since the discussion about that subject is a bit technical, I have placed it at the very end of this article.

Current research on the subject:

Whoa! Now that all the technical stuff is behind us, we can take a look at what exactly this new approach to vaccination has achieved so far...

1) Animal Trials : 

Animal trials (usually with mice) , as I have already mentioned, have been going on for a long, long time. Mice have been immunized against Rabies, Hepatitis B, ETEC, cholera , Helicobacter Pylori with varying (but gradually increasing) success.

Image : A mouse contemplating some nice looking potatoes while sitting over some tomatoes...lol..just kidding...had to write something....

2) Human Trials :

The first ever trial of an edible vaccine was in 1998 at the University of Maryland, USA.The goal of the study was to demonstrate that an edible vaccine could stimulate an immune response in humans. Volunteers ate bite-sized pieces of raw potato that had been genetically engineered to produce part of the toxin secreted by the Escherichia coli bacterium.
Ten of the 11 volunteers (91 percent) who ingested the transgenic potatoes had fourfold rises in serum antibodies.

A recent study conducted by Arntzen involved the Norwalk Virus (which causes diarrhea). In this study, 19 out of 20 persons showed increases in the serum antibody levels.

Image : Computer reconstruction of the Norwalk virus.

Similarly, after Hilary Krapowski of Thomas Jefferson University fed transgenic lettuce carrying a hepatitis B antigen to three volunteers, two of the subjects displayed a good systemic response.

Scientists are even toying around with the idea of introducing some HIV genes into plants thus developing an edible HIV vaccine!]

Advantages/Disadvantages of the biotech banana/ other edible vaccines :

Advantages:

1) Although the technology at first seems like something done for convenience rather than being something of significant utility, the fact is that poorly developed nations like India which have a relatively poor vaccination program are most likely to benefit from such a vaccine.
This is also the reason why many of the projects mentioned here (including Arntzen's early work) have been funded by the WHO.

Image : No caption required I think...

2) Mucosal immunity : The vaccines which are given parenterally (e.g. Intramuscularly) induce a systemic response but little or no local immune response in the GI tract. This so called "mucosal immunity " is increasingly being considered very important for defense against GI pathogens. ( Remember OPV..)

3) And of course, it's painless and convenient

Disadvantages:

1) The vaccine dose would be inadequate if the patient eats only one banana/potato instead of the recommended two. Furthermore, there might be difficulties in judging the dose itself since the amount of antigen in each fruit cannot be accurately measured.

2) The risk of introducing a new gene into the Plant DNA population is not known. The gene may jump species and propagate into other plants (or wild varieties of the same plants). 
This may cause unpredictable results including a decrease in the number or even extinction of a particular plant species due to growth stunting caused by the viral/bacterial gene. (This has been known to occur in research studies, including Arntzen's)

3)"Oral Tolerance":  In another concern, scientists need to be sure that vaccines meant to enhance immune responses do not backfire and suppress immunity instead. Research into a phenomenon called oral tolerance has shown that ingesting certain proteins can at times cause the body to shut down its responses to those proteins.
This may cause the body to become more susceptible to a particular disease agent rather than become immunized against it.

According to Dr. Cummins of the "Organics Consumer union" (US) :
"Scientists who are not beholden to the biotech industry would agree that edible vaccines are too dangerous to pursue"
And furthermore : "The whole idea is crazy."

- Oncogen
Comments? Corrections? Additions? Please email oncogen@kemates.com 

Additional Notes :

Ahh.. lets get down to some nitty gritty shall we?

Why bananas?

The major problem with edible vaccines is the possible degradation of the antigen (in other words denaturation of the antigenic protein). The problem of degradation by gastric HCl has been solved somewhat by increasing the amount of antigen that is ingested.
However, denaturation of the antigen can also occur during the cooking process. As a result of this the edible vaccines would have to be eaten raw. (imagine eating raw potatoes...)
Most of the research has so far concentrated on potatoes (since they are easier to grow) but a lot of research has also been put in adapting the technology to more palatable alternatives like bananas, tomatoes and lettuce.

Unexpected benefits:

Remember the "oral tolerance" thing I mentioned earlier? Well it can be put to constructive use in autoimmunity:

In the past 15 years, investigators have identified several beta cell proteins that can elicit autoimmunity in people predisposed to type I diabetes. The main culprits, however, are insulin and a protein called GAD (glutamic acid decarboxylase). Scientists have developed plant-based diabetes vaccines, such as potatoes containing insulin or GAD. Feeding of the vaccines to a mouse strain that becomes diabetic helped to suppress the immune attack and to prevent or delay the onset of high blood sugar.

HEY! You still haven't mentioned how you can get the viral/Bacterial gene inside the plant DNA!!!

Still interested? Click on the link below for an explanation (I'll let you in on a secret.. this is THE most interesting part of the article):

How to get a viral/Bacterial gene inside Plant DNA