Probiotics have been getting quite a bit of attention of late. By definition, they are "live microorganisms which when administered in adequate amounts confer a health beneﬁt on the host." This rather vague definition has led to a host of potential benefits ranging from better digestion to improved weight management and even better mental health. But until recently, no one has mentioned vaccines. Yet, a probiotic oral vaccine may one day be our route to protection against infection.
The best candidate for an oral vaccine is known as Lactobacillus acidophilus. It was discovered almost a century ago and has been thoroughly examined in the lab. You can usually find this bacterium in fermented milk products but it can be found in a variety of other places, including the human body. It can live on our teeth, in our guts, and for women, in the vagina.
Because L. acidophilus is tolerated by our bodies, researchers have believed it communicates with the immune system in a friendly manner to prevent any defensive attacks. When this was tested in 1997, the bacterium definitely had an effect in humans. But surprisingly, instead of keeping the immune system calm, the cells involved in immunity became more active; just not against the bacteria.
Improving (or if you will, boosting) immunity might seem like a great selling point but for the researchers, this meant the bacterium could have a much greater role in another area of health: vaccines. Instead of using chemicals to improve the immune response, one would simply ingest acidophilus bacteria. In 2008 this was tested in pigs using an oral rotavirus vaccine. Sure enough, once the bacteria were ingested, the immune response was enhanced and led to even protection against the viral pathogen.
But this wasn't the end of the story. In 2011, the involvement of probiotics in vaccines took another leap. This time, instead of adding bacteria to a vaccine, the acidophilus would actually be the vaccine.
Here's how it works. Physical pieces of a particular pathogen are first integrated into L. acidophilus. This new hybrid is then mass produced in the lab. When the bacteria are ready, instead of an injection, they are ingested. If all works out well, the person will be safe from future infection.
The theory may seem sound but until last year, it had not been tested. In this study, a Chinese team of researchers attempted to use a probiotic vaccine to protect mice against the gastrointestinal pathogen, Helicobacter pylori. The results were incredibly positive and opened the door to other possible probiotic vaccines against other intestinal enemies as well as a virus not normally associated with the gut.
In 2012, a group of American researchers decided to make an attempt at another pathogen: HIV. Though known as a bloodborne virus, the authors believed an oral vaccine might be able to boost the immune response sufficiently to prevent infection. They tested the new concept in mice and were happy to find an increase in immunity, specifically against HIV. To the authors, this meant the start of a journey towards a novel approach to a seemingly undefeatable enemy.
But there was one slight problem. In 2014, one particular issue was raised in the development of HIV vaccines. Because the virus happens to target the immune system, vaccination may simply not work and could make the situation worse. In order to make a viable oral vaccine, the immune activation would have to be done in a way that evades HIV attack.
That obstacle may now be overcome. Last week, the same American researchers developed a possible route forward. Using L. acidophilus, they were able to figure out how to enhance the immune system without allowing HIV to take advantage.
The process was rather simple in design. Instead of allowing the pieces of HIV to sit on the cell itself, the team put it inside a part of the bacterium known as the S layer protein A. This protein coats the cell in a protective layer to keep it from harm. It's also known to be involved in triggering enhancement of the immune system in a way that evades HIV infection. For the authors, this was the best place to put the vaccine candidate.
Using mice once again, the group examined the effect of vaccination. As expected, the animals developed immunity to HIV. But the type of response was different. This time, HIV would not have an opportunity to take advantage. It would be unable to evade the oncoming assault and in theory, be killed.
The trial offered more evidence to support probiotic vaccines. But this wasn't what made the authors happy. Their success came from knowing they could modify the type of immune response triggered through oral vaccination. To them, this power could push HIV vaccination forward as well as open the door for other possible infections for which vaccination may not be possible.
Admittedly, this study is just the beginning of the probiotic vaccine era. Much more work in the lab and with animals needs to be done before we'll see any human clinical trials. But considering the need for proper vaccination against a variety of pathogens, this approach may take us to a new type of medicine where a pill represents not only a cure, but ultimate protection.
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