Posted by jlwile on May 20, 2010
The smartest person with whom I have ever worked sent me a very interesting article from Science Daily. She and I wrote several articles related to the science behind vaccination years ago, and this article is relevant to that issue. It reports on a study published in BMC Immunology, an open-access journal. The results of the study are worth noting.
The researchers studied peripheral blood mononuclear cells (PBMCs) and how susceptible they were to infection by HIV, the virus that causes AIDS. PBMC is the name given to any blood cell that has a round nucleus. Since red blood cells don’t have a nucleus, what this means is that the researchers were looking at certain white blood cells, which are a part of the body’s immune system. Obviously, the susceptibility of white blood cells to HIV is an important issue in the study of AIDS.
Here is the key: they looked at the PBMCs from 10 volunteers who had never been vaccinated against smallpox as well as the PBMCs from 10 volunteers who had been vaccinated against smallpox with a Vaccinia-based vaccine 3 to 6 months prior to the study. Vaccinia is a virus in the poxvirus family that is typically used to produce the immune response to protect against smallpox. Guess what they found.
They found that the PBMCs from people who had recently been given the Vaccinia-based vaccine were significantly less prone to infection than those from the people who had never been given the vaccine. In other words, the white blood cells from people who were recently vaccinated against smallpox were more resistant to HIV infection than those who had never been given the vaccine!
Now why in the world would a vaccination against smallpox make white blood cells more resistant to HIV? Well, according to the authors, it has been previously shown that when a person is infected with the virus that causes measles, for example, his or her white blood cells are also resistant to HIV infection. They think this occurs because the other virus is more easily detected by the immune system, and that “primes” the immune system to start dealing with infections. As a result, a virus that is not easily detected by the body (like HIV) gets attacked because the immune system has already been kicked into high gear by the other virus.
Of course, the article in Science Daily and the research article say that these results might explain the sudden explosion of AIDS cases that started in Africa in the mid-to-late 1950s. As the Science Daily article quotes an author of the study:
There have been several proposed explanations for the rapid spread of HIV in Africa…Our finding that prior immunization with vaccinia virus may provide an individual with some degree of protection to subsequent HIV infection suggests that the withdrawal of such vaccination may be a partial explanation.
So in other words, once smallpox was eradicated, routine vaccination went away. As a result, people’s immune systems weren’t being “primed” by the Vaccinia virus that is a part of the smallpox vaccine, and this led to a significant rise in AIDS cases. It is an interesting conclusion, and I think the study provides evidence for it.
However, I have a word of caution: Don’t think that we can start vaccinating people against smallpox and that will somehow reduce the spread of AIDS. First, what happens in a Petri dish is not always indicative of what happens in the body. Thus, just because some cells taken from people were resistant to HIV in a controlled laboratory setting doesn’t mean they will behave the same inside a person.
Second, there are risks associated with smallpox vaccination, as there are with any medical treatment. In order for the risks to be worth taking, the benefits have to be significant. When smallpox is a viable threat, the benefits of smallpox vaccination far exceed the risks, so getting the smallpox vaccine is clearly the best course of action. However, this study has no way of measuring the actual amount of protection the smallpox vaccine might provide against AIDS. Thus, the benefits are completely unknown. Until we can quantify exactly what level of protection is given (if any) by the smallpox vaccine, there is just no medically justifiable reason to start vaccinating against smallpox when smallpox itself isn’t a danger.
So while this study offers no immediate help in the fight against AIDS, it gives us some interesting new avenues to pursue. After all, if the measles virus and the Vaccinia virus really do give some level of protection against AIDS, we should be able to find the commonalities between those viruses (as well as other viruses that do the same). Those commonalities might help us produce an effective vaccination that specifically protects against HIV.